Patent Publication Number: US-2023149693-A1

Title: Ventricular assist device

Description:
The invention relates to a ventricular assist device. In particular the invention lies in the field of medical devices, specifically in the field of ventricular assist systems and devices. 
     Heart failure, chronic ischemic heart disease, and acute myocardial infarction rank amongst the top causes of death in many countries, such as for example Germany. Specifically, all three of said causes of death are linked to an impairment of the pumping function of the human heart. However, drug-based therapeutic approaches often only show a limited effect, wherein up to 25% of all patients having received stationary drug-based treatments require re-admission within 30 days. Replacing the pumping function of the heart with a donor organ is often not possible due to a lack of available donor organs. Furthermore, the use of a donor organ may in the long term lead to further complications, such as organ rejection, transplant vasculopathy, and the development of malignant neoplasms caused by the suppression of the immune response. Replacing the pumping function of the heart with an artificial pumping device, such as a ventricular assist device (VAD), is currently only temporarily possible, as further complications such as infections and embolisms may persist. 
     Commercially available VADs may be implemented as axial and centrifugal pumps, which may be implanted intra-corporally or extra-corporally. However, it was found within the scope of this invention that the commercially available VADs suffer from several drawbacks. For example, some commercially available VADs rely on ball bearings, which were found within the scope of this invention to cause a significant internal heat build-up and internal wear-and-tear, which contributes to a reduced lifetime of the respective VAD. Furthermore, such commercially available VADs may also produce a significant noise during their operation, which can lead to additional psychological strains for the patient. 
     It is therefore an object of the present invention to provide a ventricular assist device having an improved operation and enhanced lifetime. 
     At least the above object is achieved by a ventricular assist device according to independent claim  1 . 
     One aspect of the disclosure relates to a ventricular assist device for implantation into a lumen of a blood vessel, comprising: an impeller fixed to a rotor shaft, wherein the impeller is configured to rotate around a longitudinal axis of the rotor shaft; a drive unit comprising a magnetic motor configured to cause rotation of the impeller around the longitudinal axis; a first active magnetic bearing configured to bear a first end section of the rotor shaft relative to the drive unit; a second active magnetic bearing configured to bear a second end section of the rotor shaft relative to the drive unit; and a control unit configured to control the magnetic motor, the first active magnetic bearing and the second active magnetic bearing. The blood vessel may be a vein or an artery of a user, preferentially a pulmonary artery or an aorta of the user. 
     The impeller is fixed to the rotor shaft, wherein the impeller is configured to rotate around a longitudinal axis of the rotor shaft. The impeller may be fixed to the rotor shaft by any means or method, such as for example by being integrally formed with the rotor shaft or by being fixed to the rotor shaft by, for example, friction fit and/or compression fit, chemical bonding, and/or using a fixing means, such as for example glues and/or corresponding engaging portions of the impeller and rotor shaft. Both impeller and rotor shaft are configured to rotate around a mutual axis, specifically the longitudinal axis of the rotor shaft. Furthermore, the ventricular assist device may be substantially cylindrically shaped and wherein the ventricular assist device may have a central axis, wherein, preferentially, the longitudinal axis of the rotor shaft may be substantially identical to the central axis of the cylindrically shaped ventricular assist device. In particular, such an impeller of a ventricular assist device of claim  1  allows for high rotational speeds, in particular in excess of 10000 rotations per minute. The impeller may further comprise at least one, preferentially six speed sensor magnets fixed to the impeller, wherein the drive unit may comprise a speed sensor, such as a speed Hall sensor, configured to detect a rotational motion of the at least one speed sensor magnets. The speed sensor may be configured to thereby determine a rotational speed of the impeller and provide said determined speed to the control unit and/or the magnetic motor. 
     Furthermore, the impeller may be configured to minimize turbulent flow in a fluid to be pumped by the ventricular assist device. The impeller may further be configured to reduce shear stress on the fluid to be pumped during an operation of the ventricular assist device. Furthermore, the impeller may be designed to have a high efficiency in order to minimize energy losses, which could contribute to a higher energy consumption of the ventricular assist device and/or a heating effect on the fluid to be pumped during the operation of the ventricular assist device. The impeller may be further configured to minimise damage to the fluid to be pumped, such as blood, during rotation of the impeller, wherein the impeller may in particular be configured to minimize any sharp edges of the impeller, minimize any dead water zones in a fluid field of a fluid to be pumped at and downstream of the impeller, and/or minimize zones of high shear strain in a fluid field of a fluid to be pumped at and downstream of the impeller. Furthermore, the impeller may be configured to produce a head of at least 20 mmHg, preferably at least 30 mmHg, further preferably at least 40 mmHg, and/or the impeller may be configured to produce a head of at most 150 mmHg, preferably at most 130 mmHg, further preferably at most 120 mmHg. Furthermore, the impeller may be configured to produce a volume flow of at least 1 l/min, preferably at least 2 l/min, further preferably at least 3 l/min, and/or the impeller may be configured to produce a volume flow of at most 10 l/min, preferably at most 8 l/min, further preferably at most 7 l/min. Furthermore, the impeller may comprise at least one impeller vane, wherein a number of impeller vanes of the impeller may be chosen according to specific operational requirements of the ventricular assist device. Furthermore, the impeller may comprise one or more hydraulic surfaces, wherein the hydraulic surfaces are surfaces of the impeller that may come into contact with the fluid to be pumped by the ventricular assist device during operation of the ventricular assist device. Preferentially, at least some, preferably all of the one or more hydraulic surfaces are finely polished. In other words, at least some, preferably all of the one or more hydraulic surfaces may be polished surfaces. Furthermore, the one or more hydraulic surfaces may comprise one or more surface coatings, such as one or more heparin coatings and/or one or more pyrocarbon coatings, wherein said one or more surface coatings may be configured to reduce a thrombogenicity of the one or more hydraulic surfaces. However, such surface coatings may not be restricted to hydraulic surfaces of the impeller. In particular, any surface of the ventricular assist device that may come into contact with the fluid to be pumped by the ventricular assist device during operation of the ventricular assist device may comprise one or more of the one or more surface coatings, as described above. 
     The drive unit comprises the magnetic motor, wherein the magnetic motor is configured to cause rotation of the impeller around the longitudinal axis. In other words, the magnetic motor is configured to generate a force on the impeller and/or the rotor shaft to cause rotation of the impeller around the longitudinal axis. In particular, the ventricular assist device may be configured such that when the ventricular assist device is placed in a fluid and the magnetic motor causes rotation of the impeller around the longitudinal axis, the rotating impeller causes a flow of the fluid relative to the ventricular assist device. Furthermore, the magnetic motor may be any kind of magnetic and/or electric motor capable of causing rotation of the impeller around the longitudinal axis. 
     The first active magnetic bearing is configured to bear a first end section of the rotor shaft relative to the drive unit. In particular, the adjective “active” is to be understood in this respect to indicate that the first active magnetic bearing may be actively controlled by the control unit in order to control a position of the first end section relative to the first active magnetic bearing and/or to the drive unit. The first active magnetic bearing may be further configured to control the position of the first end section relative to the first active magnetic bearing and/or to the drive unit by at least one of a permanent magnetic field and a temporary magnetic field. 
     The second active magnetic bearing is configured to bear a second end section of the rotor shaft relative to the drive unit. In particular, the adjective “active” is to be understood in this respect to indicate that the second active magnetic bearing may be actively controlled by the control unit in order to control a position of the second end section relative to the second active magnetic bearing and/or to the drive unit. The second active magnetic bearing may be further configured to control the position of the second end section relative to the second active magnetic bearing and/or to the drive unit by at least one of a permanent magnetic field and a temporary magnetic field. 
     The first end section and/or the second end section of the rotor shaft may be integrally formed with the rotor shaft. Alternatively, the first end section may comprise a first magnetisable element fixedly connected to the rotor shaft and the second end section may comprise a second magnetisable element fixedly connected to the rotor shaft, wherein the rotor shaft between the first magnetisable element and the second magnetisable element may be non-magnetisable. The first magnetisable element and/or the second magnetisable element may comprise at least one magnetisable material, e.g. magnetisable stainless steel 1.4016. The rotor shaft may further comprise a non-magnetisable section in between the first end section and the second end section, preferably in between the first magnetisable element and the second magnetisable element. 
     The control unit is configured to control the magnetic motor, the first active magnetic bearing and the second active magnetic bearing. The control unit may, for example, be implemented as a PID control unit configured to control the magnetic motor, the first active magnetic bearing and the second active magnetic bearing. The control unit may be implemented as a centralised unit configured to control each of the magnetic motor, the first active magnetic bearing and the second active magnetic bearing. Alternatively, the control unit may comprise one or more control sub-units, wherein each control sub-unit may be configured to control at least one of the magnetic motor, the first active magnetic bearing and the second active magnetic bearing. At least two of the one or more control sub-units may be connected to one another to transfer at least one of power and data between each other, wherein said at least two of the one or more control sub-units may be connected to one another wirelessly and/or via a physical connection, e.g. a wire connection. Alternatively or additionally, at least two of the one or more control sub-units may not be connected to one another to transfer at least one of power and data between each other, i.e. said at least two of the one or more control sub-units may be provided as separate control sub-units independent of one another. The control unit and/or the one or more control sub-units may be provided on one or more printed circuit boards (PCBs). The control unit may have one or more interfaces, such as a Bluetooth interface and/or an USB interface. Furthermore, the control unit may comprise one or more performance enhancers, such as H-bridges, for controlling magnetic bearing coils and magnetic drive coils of the ventricular assist device. 
     For example, the control unit may comprise at least one first control sub-unit configured to control the first active magnetic bearing, wherein the at least one first control sub-unit may be arranged proximal to, preferably on, the first active magnetic bearing. Furthermore, for example, the control unit may comprise at least one second control sub-unit configured to control the second active magnetic bearing, wherein the at least one second control sub-unit may be arranged proximal to, preferably on, the second active magnetic bearing. In particular, such an arrangement may allow for a modular design of the first and second active magnetic bearings, respectively, thereby, for example, allowing for a simplified assembly process and/or a simplified replacement of parts. 
     In particular, an operational state of the ventricular assist device may be a state in which the impeller is arranged relative to the drive unit such that the magnetic motor is able to cause the rotation of the impeller, in which the first end section is born by the first active magnetic bearing, and in which the second end section is born by the second active magnetic bearing. 
     Preferentially, the first active magnetic bearing is arranged on a first side of the drive unit, wherein the first active magnetic bearing may be fixed to the drive unit on the first side of the drive unit. Preferentially, the second active magnetic bearing is arranged on a second side of the drive unit, wherein the second active magnetic bearing may be fixed to the drive unit on the second side of the drive unit. In particular, the first side of the drive unit may be located approximately opposite to the second side of the drive unit, preferentially along a direction parallel to the central axis. 
     Preferentially, the control unit is configured to control the magnetic motor to adjustably generate a magnetic force on the rotor shaft to control a rotational speed of the impeller; control the first active magnetic bearing to adjustably generate a magnetic force on the first end section to control a first position of the first end section relative to the first active magnetic bearing; and control the second active magnetic bearing to adjustably generate a magnetic force on the second end section to control a second position of the second end section relative to the second active magnetic bearing. 
     In particular, the control unit may be configured to control the magnetic motor to adjustably generate the magnetic force on the rotor shaft to control the rotational speed of the impeller. For example, the control unit may be configured to control the magnetic motor to adjustably generate the magnetic force on the rotor shaft to increase and/or decrease the rotational speed of the impeller around the longitudinal axis. Furthermore, the control unit may be configured to control the magnetic motor to adjustably generate the magnetic force on the rotor shaft to change the direction of rotation of the impeller around the longitudinal axis. 
     In particular, the control unit may be configured to control the first active magnetic bearing to adjustably generate a magnetic force on the first end section, preferentially the first magnetisable element, to control a first position of the first end section relative to the first active magnetic bearing. For example, the first active magnetic bearing may comprise at least one coil, wherein the at least one coil may be adjustably supplied with a current to adjustably generate the magnetic field. Preferentially, the control unit may be configured to control the first active magnetic bearing to adjustably generate a magnetic force on the first end section, preferentially the first magnetisable element, to maintain the first position of the first end section at a first predetermined position relative to the first active magnetic bearing. The first predetermined position may in particular be a position along the central axis of the ventricular assist device. 
     In particular, the control unit may be configured to control the second active magnetic bearing to adjustably generate a magnetic force on the second end section, preferentially the second magnetisable element, to control a second position of the second end section relative to the second active magnetic bearing. For example, the second active magnetic bearing may comprise at least one coil, wherein the at least one coil may be adjustably supplied with a current to adjustably generate the magnetic field. Preferentially, the control unit may be configured to control the second active magnetic bearing to adjustably generate a magnetic force on the second end section, preferentially the second magnetisable element, to maintain the second position of the second end section at a second predetermined position relative to the second active magnetic bearing. The second predetermined position may in particular be a position along the central axis of the ventricular assist device. 
     In particular, the control unit may be configured to control the first active magnetic bearing to adjustably generate a magnetic force on the first end section and to control the second active magnetic bearing to adjustably generate a magnetic force on the second end section to maintain the longitudinal axis of the rotor shaft substantially along the central axis of the ventricular assist device in the operational state. 
     In particular, it may therefore be possible to significantly improve the operation of the ventricular assist device by ensuring an optimal position of the rotor shaft and impeller relative to other components of the ventricular assist device, such as the drive unit. Specifically, the flow field of the ventricular assist device during operation of said ventricular assist device can therefore be reliably maintained. 
     In particular, the first active magnetic bearing may comprise a first radial magnetic bearing configured to adjust a radial position of the first end section relative to the first radial magnetic bearing, and a first radial sensor unit configured to determine the radial position of the first end section, preferentially relative to the first radial magnetic bearing. Furthermore, the first radial magnetic bearing may be configured to adjustably generate a magnetic force on the first end section to control the radial position of the first end section relative to the first radial magnetic bearing. In particular, the first radial magnetic bearing may be configured to adjustably generate a magnetic force on the first end section along a substantially radial direction relative to the longitudinal axis of the rotor shaft and/or relative to the central axis, while, preferentially, generating substantially no magnetic force on the first end section substantially parallel to the longitudinal axis of the rotor shaft and/or to the central axis. The first radial sensor unit may in particular comprise any kind of sensor capable of determining the radial position of the first end section, preferentially relative to the first radial magnetic bearing. 
     In particular, the second active magnetic bearing may comprise a second radial magnetic bearing configured to adjust a radial position of the second end section relative to the second radial magnetic bearing, and a second radial sensor unit configured to determine the radial position of the second end section, preferentially relative to the second radial magnetic bearing. Furthermore, the second radial magnetic bearing may be configured to adjustably generate a magnetic force on the second end section to control the radial position of the second end section relative to the second radial magnetic bearing. In particular, the second radial magnetic bearing may be configured to adjustably generate a magnetic force on the second end section along a substantially radial direction relative to the longitudinal axis of the rotor shaft and/or relative to the central axis, while, preferentially, generating substantially no magnetic force on the second end section substantially parallel to the longitudinal axis of the rotor shaft and/or to the central axis. The second radial sensor unit may in particular comprise any kind of sensor capable of determining the radial position of the second end section, preferentially relative to the second radial magnetic bearing. 
     The first radial magnetic bearing may in particular comprise at least two first bearing segments, wherein said first bearing segments may be arranged circumferentially, preferentially equally spaced, around the central axis and/or the longitudinal axis of the rotor shaft in the operational state of the ventricular assist device. Each of the at least two first bearing segments may in particular be arranged substantially adjacent the rotor shaft and/or the first end section in the operational state of the ventricular assist device. Furthermore, the first radial magnetic bearing may in particular comprise at least three, preferentially at least four first bearing segments. 
     Furthermore, the first radial sensor unit may comprise a first radial sensor configured to measure and/or determine a capacitance between each of the first bearing segments and the first end section. In particular, the first radial sensor may be configured to measure an absolute value of the capacitance between each of the first bearing segments and the first end section and/or a change of capacitance between each of the first bearing segments and the first end section. Furthermore, the first radial sensor may be configured to determine the radial position of the first end section based on the measured capacitance between each of the first bearing segments and the first end section. The first radial sensor may comprise an operational amplifier. 
     In particular, the rotor shaft is not fixedly connected to the first radial magnetic bearing and can therefore move in relation to the first radial magnetic bearing during operation of the ventricular assist device. Specifically, such movement may cause the rotor shaft, in particular the first end section, to move closer to one or more first bearing segments of the at least two first bearing segments, while moving away from one or more other first bearing segments of the at least two first bearing segments. In particular, a change in the relative distances between the first end section and any of the first bearing segments causes a change in the capacitance between the first end section and the respective first bearing segment. Therefore, by measuring the capacitance, e.g. an absolute value of the capacitance and/or a change of capacitance, between each of the first bearing segments and the first end section, it may be possible to determine the distance and/or a change in distance between each of the first bearing segments and the first end section. Based on the determined distance and/or the determined change in distance between each of the first bearing segments and the first end section, it may therefore be possible to accurately derive the radial position of the first end section relative to the first radial magnetic bearing. Specifically, the first radial sensor may be configured to, in such a manner, determine the radial position of the first end section based on the measured capacitance between each of the first bearing segments and the first end section. 
     The second radial magnetic bearing may in particular comprise at least two second bearing segments, wherein said second bearing segments may be arranged circumferentially, preferentially equally spaced, around the central axis and/or the longitudinal axis of the rotor shaft in the operational state of the ventricular assist device. Each of the at least two second bearing segments may in particular be arranged substantially adjacent the rotor shaft and/or the second end section in the operational state of the ventricular assist device. Furthermore, the second radial magnetic bearing may in particular comprise at least three, preferentially at least four second bearing segments. 
     Furthermore, the second radial sensor unit may comprise a second radial sensor configured to measure and/or determine a capacitance between each of the second bearing segments and the second end section. In particular, the second radial sensor may be configured to measure an absolute value of the capacitance between each of the second bearing segments and the second end section and/or a change of capacitance between each of the second bearing segments and the second end section. Furthermore, the second radial sensor may be configured to determine the radial position of the second end section based on the measured capacitance between each of the second bearing segments and the second end section. The second radial sensor may comprise an operational amplifier. 
     In particular, the rotor shaft is not fixedly connected to the second radial magnetic bearing and can therefore move in relation to the second radial magnetic bearing during operation of the ventricular assist device. Specifically, such movement may cause the rotor shaft, in particular the second end section, to move closer to one or more second bearing segments of the at least two second bearing segments, while moving away from one or more other second bearing segments of the at least two second bearing segments. In particular, a change in the relative distances between the second end section and any of the second bearing segments causes a change in the capacitance between the second end section and the respective second bearing segment. Therefore, by measuring the capacitance, e.g. an absolute value of the capacitance and/or a change of capacitance, between each of the second bearing segments and the second end section, it may be possible to determine the distance and/or a change in distance between each of the second bearing segments and the second end section. Based on the determined distance and/or the determined change in distance between each of the second bearing segments and the second end section, it may therefore be possible to accurately derive the radial position of the second end section relative to the second radial magnetic bearing. Specifically, the second radial sensor may be configured to, in such a manner, determine the radial position of the second end section based on the measured capacitance between each of the second bearing segments and the second end section. 
     Preferentially, each of the first bearing segments comprises a magnetic yoke arranged adjacent the first end section. In particular, each of the first bearing segments may comprise at least one magnetic yoke arranged adjacent the first end section in the operational state of the ventricular assist device. The magnetic yoke may be at least partially formed from a magnetisable material, such as for example magnetisable stainless steel 1.4016. In particular, at least one, preferentially each, magnetic yoke may comprise two, preferentially equal, halves, wherein each of the halves may be formed from a magnetisable material. Furthermore, the at least one, preferentially each, magnetic yoke may further comprise an insulating plate arranged between the respective two halves, wherein the insulating plate may be configured to electrically and/or magnetically insulate the two halves from one another. In particular, a change in the relative distances between the first end section and a respective first bearing segment causes a change in the capacitance between the first end section and the respective first bearing segment, which results in a change in the capacitance between the two halves of a respective magnetic yoke. The first radial sensor may in particular be configured to measure the capacitance, e.g. an absolute value of the capacitance and/or a change of capacitance, between the two halves of the respective magnetic yoke of a first bearing segment in order to determine the distance and/or a change in distance between the respective first bearing segment and the first end section. Based on the determined distance and/or the determined change in distance between each of the first bearing segments and the first end section, it may therefore be possible to accurately derive the radial position of the first end section relative to the first radial magnetic bearing. Specifically, the first radial sensor may be configured to, in such a manner, determine the radial position of the first end section. 
     Preferentially, each of the first bearing segments comprises at least one first radial magnetic coil, wherein the first radial magnetic coil is wound around the magnetic yoke. In particular, the at least one first radial magnetic coil may be wound at least partially around each of the two halves of the respective magnetic yoke. Preferentially, the control unit is configured to control a current supplied to each of the first radial magnetic coils. In particular, the control unit may be configured to control a current supplied to each of the first radial magnetic coils to adjustably generate a magnetic force on the first end section to adjust the radial position of the first end section relative to the first radial magnetic bearing. 
     Preferentially, each of the second bearing segments comprises a magnetic yoke arranged adjacent the second end section. In particular, each of the second bearing segments may comprise at least one magnetic yoke arranged adjacent the second end section in the operational state of the ventricular assist device. The magnetic yoke may be at least partially formed from a magnetisable material, such as for example magnetisable stainless steel 1.4016. In particular, at least one, preferentially each, magnetic yoke may comprise two, preferentially equal, halves, wherein each of the halves may be formed from a magnetisable material. Furthermore, the at least one, preferentially each, magnetic yoke may further comprise an insulating plate arranged between the respective two halves, wherein the insulating plate may be configured to electrically and/or magnetically insulate the two halves from one another. In particular, a change in the relative distances between the second end section and a respective second bearing segment causes a change in the capacitance between the second end section and the respective second bearing segment, which results in a change in the capacitance between the two halves of a respective magnetic yoke. The second radial sensor may in particular be configured to measure the capacitance, e.g. an absolute value of the capacitance and/or a change of capacitance, between the two halves of the respective magnetic yoke of a second bearing segment in order to determine the distance and/or a change in distance between the respective second bearing segment and the second end section. Based on the determined distance and/or the determined change in distance between each of the second bearing segments and the second end section, it may therefore be possible to accurately derive the radial position of the second end section relative to the second radial magnetic bearing. Specifically, the second radial sensor may be configured to, in such a manner, determine the radial position of the second end section. 
     Preferentially, each of the second bearing segments comprises at least one second radial magnetic coil, wherein the second radial magnetic coil is wound around the magnetic yoke. In particular, the at least one second radial magnetic coil may be wound at least partially around each of the two halves of the respective magnetic yoke. Preferentially, the control unit is configured to control a current supplied to each of the second radial magnetic coils. In particular, the control unit may be configured to control a current supplied to each of the second radial magnetic coils to adjustably generate a magnetic force on the second end section to adjust the radial position of the second end section relative to the second radial magnetic bearing. 
     Preferentially, the at least two first bearing segments may be substantially identically constructed. Alternatively or additionally, the at least two second bearing segments may be substantially identically constructed. Alternatively or additionally, the at least two first bearing segments and the at least two second bearing segments may be substantially identically constructed. Thereby, an easy and efficient assembly and production of the ventricular assist device is made possible. 
     Preferentially, the at least two first bearing segments are substantially equally spaced in a circumferential direction around the longitudinal axis and/or the central axis. In particular, the at least two first bearing segments are preferentially substantially equally spaced in a circumferential direction around the longitudinal axis and/or the central axis in the operational state. Thereby, a facile and efficient magnetic bearing of the first end section may be provided. However, the disclosure is not limited to such a feature, wherein other spacings of the at least two first bearing segments are possible. 
     Preferentially, the at least two second bearing segments are substantially equally spaced in a circumferential direction around the longitudinal axis and/or the central axis. In particular, the at least two second bearing segments are preferentially substantially equally spaced in a circumferential direction around the longitudinal axis and/or the central axis in the operational state. Thereby, a facile and efficient magnetic bearing of the second end section may be provided. However, the disclosure is not limited to such a feature, wherein other spacings of the at least two second bearing segments are possible. 
     Furthermore, using the first radial sensor to determine the radial position of the first end section and/or the second radial sensor to determine the radial position of the second end section may further enhance the accuracy and efficiency of the ventricular assist device, and may further simplify the production process of the ventricular assist device. In particular, as the first radial sensor and the second radial sensor do not rely on the measurement of a magnetic field of a sensor magnet, the first radial sensor may be able to determine the radial position of the first end section and/or the second radial sensor may be able to determine the radial position of the second end section independently of a shape of the magnetic field of such a sensor magnet. Therefore, for example, effects of a non-homogeneous magnetic field of such a sensor magnet, which may cause errors in the determination of the radial positions of the first and second end sections, respectively, may be avoided and/or reduced. In particular, this may further improve the reliability and lifetime of the ventricular assist device, as the position of the rotor shaft in the ventricular assist device can be more accurately maintained. 
     Preferentially, the first radial sensor unit comprises a first radial Hall sensor arrangement configured to determine the radial position of the first end section. Preferentially, the first radial Hall sensor arrangement may be configured to continuously determine the radial position of the first end section or determine the radial position of the first end section at given measurement intervals. The measurement intervals may be predetermined and/or dynamically adjusted. For example, the measurement intervals may be based on a current rotational speed of the impeller, wherein a higher speed corresponds to a shorter measurement interval. 
     Preferentially, the second radial sensor unit comprises a second radial Hall sensor arrangement configured to determine the radial position of the second end section. Preferentially, the second radial Hall sensor arrangement may be configured to continuously determine the radial position of the second end section or determine the radial position of the second end section at given measurement intervals. The measurement intervals may be predetermined and/or dynamically adjusted. For example, the measurement intervals may be based on a current rotational speed of the impeller, wherein a higher speed corresponds to a shorter measurement interval. 
     The first radial Hall sensor arrangement may comprise a first permanent magnet fixed to the first end section, and at least one first radial Hall sensor arranged adjacent the first permanent magnet in a radial direction relative to the longitudinal axis, in particular relative to the longitudinal axis and/or the central axis in the operational state of the ventricular assist device. In particular, the first permanent magnet may be directly fixed to the first end section and/or rotor shaft. Alternatively the first end section may comprise a first non-magnetisable element fixedly connected to the rotor shaft and/or the first magnetisable element, wherein the first permanent magnet is fixedly connected to the first non-magnetisable element. The first radial Hall sensor arrangement may in particular comprise two or more first radial Hall sensors, wherein the two or more first radial Hall sensors are spaced, preferentially equally spaced, in a circumferential direction around the longitudinal axis, in particular around to the longitudinal axis and/or the central axis in the operational state of the ventricular assist device. 
     In particular, as the rotor shaft, and consequently the first permanent magnet, moves relative to the first active magnetic bearing, a distance between the first permanent magnet and one or more of the first radial Hall sensors may change, which may result in a shifted magnetic field of the first permanent magnet caused by the movement of the first permanent magnet. The one or more first radial Hall sensors may in particular be configured to measure said magnetic field and/or a change in said magnetic field. Based on said measured magnetic field and/or said measured change in the magnetic field, the one or more first radial Hall sensors and/or the first radial Hall sensor arrangement may be configured to determine a distance and/or change in distance between the first permanent magnet and each of the respective one or more first radial Hall sensors. Based on said determined distance and/or change in distance between the first permanent magnet and each of the respective one or more first radial Hall sensors, the first radial Hall sensor arrangement may in particular be configured to determine the radial position of the first end section. 
     Preferentially, the first permanent magnet may have a magnetic field that is substantially circular symmetric around the longitudinal axis of the rotor shaft. The first radial Hall sensor arrangement may further comprise a first calibration data unit, wherein the first calibration data unit may in particular comprise calibration data for the first radial Hall sensor arrangement. In particular, the calibration data may comprise a shape and/or strength of the magnetic field of the first permanent magnet, such as for example a vector field representation of the H-field of the first permanent magnet and/or a vector field representation of the B-field of the first permanent magnet. 
     In particular, the one or more first radial Hall sensors and/or the first radial Hall sensor arrangement may determine the distance and/or change in distance between the first permanent magnet and each of the respective one or more first radial Hall sensors based on the measured magnetic field and/or the measured change in the magnetic field and the calibration data. In particular, it may thereby be possible to compensate for effects of a non-circular symmetric magnetic field of the first permanent magnet on the determined position of the first end section. This may increase the reliability and the accuracy of the first radial Hall sensor arrangement, and/or allow the use of first permanent magnets, which have a magnetic field that deviates from a substantially circular symmetry around the longitudinal axis of the rotor shaft. 
     The second radial Hall sensor arrangement may comprise a second permanent magnet fixed to the second end section, and at least one second radial Hall sensor arranged adjacent the second permanent magnet in a radial direction relative to the longitudinal axis, in particular relative to the longitudinal axis and/or the central axis in the operational state of the ventricular assist device. In particular, the second permanent magnet may be directly fixed to the second end section and/or rotor shaft. Alternatively the second end section may comprise a second non-magnetisable element fixedly connected to the rotor shaft and/or the second magnetisable element, wherein the second permanent magnet is fixedly connected to the second non-magnetisable element. The second radial Hall sensor arrangement may in particular comprise two or more second radial Hall sensors, wherein the two or more second radial Hall sensors are spaced, preferentially equally spaced, in a circumferential direction around the longitudinal axis, in particular around to the longitudinal axis and/or the central axis in the operational state of the ventricular assist device. 
     In particular, as the rotor shaft, and consequently the second permanent magnet, moves relative to the second active magnetic bearing, a distance between the second permanent magnet and one or more of the second radial Hall sensors may change, which may result in a shifted magnetic field of the second permanent magnet caused by the movement of the second permanent magnet. The one or more second radial Hall sensors may in particular be configured to measure said magnetic field and/or a change in said magnetic field. Based on said measured magnetic field and/or said measured change in the magnetic field, the one or more second radial Hall sensors and/or the second radial Hall sensor arrangement may be configured to determine a distance and/or change in distance between the second permanent magnet and each of the respective one or more second radial Hall sensors. Based on said determined distance and/or change in distance between the second permanent magnet and each of the respective one or more second radial Hall sensors, the second radial Hall sensor arrangement may in particular be configured to determine the radial position of the second end section. 
     Preferentially, the second permanent magnet may have a magnetic field that is substantially circular symmetric around the longitudinal axis of the rotor shaft. The second radial Hall sensor arrangement may further comprise a second calibration data unit, wherein the second calibration data unit may in particular comprise calibration data for the second radial Hall sensor arrangement. In particular, the calibration data may comprise a shape and/or strength of the magnetic field of the second permanent magnet, such as for example a vector field representation of the H-field of the second permanent magnet and/or a vector field representation of the B-field of the second permanent magnet. 
     In particular, the one or more second radial Hall sensors and/or the second radial Hall sensor arrangement may determine the distance and/or change in distance between the second permanent magnet and each of the respective one or more second radial Hall sensors based on the measured magnetic field and/or the measured change in the magnetic field and the calibration data. In particular, it may thereby be possible to compensate for effects of a non-circular symmetric magnetic field of the second permanent magnet on the determined position of the second end section. This may increase the reliability and the accuracy of the second radial Hall sensor arrangement, and/or allow the use of second permanent magnets, which have a magnetic field that deviates from a substantially circular symmetry around the longitudinal axis of the rotor shaft. 
     The first radial sensor unit may be configured to provide the determined radial position of the first end section to the control unit, wherein the control unit may be configured to control the first radial magnetic bearing of the first active magnetic bearing to adjustably generate a magnetic force on the first end section on the basis of the determined radial position of the first end section. In particular, the first radial sensor unit may be configured to determine a first radial position of the first end section using the first radial sensor and to determine a second radial position of the first end section using the first radial Hall sensor arrangement. In particular, the first radial sensor unit may be configured to compare the first radial position and the second radial position of the first end section to determine the accuracy of the determined radial position of the first end section and/or to determine any error or malfunctions of the first radial sensor and the first radial Hall sensor arrangement, respectively. The first radial sensor unit may be configured to determine the radial position based on the first radial position of the first end section and/or the second radial position of the first end section. The first radial sensor unit may in particular be configured to determine the radial position of the first end section based on an arithmetic mean or a weighted average of the first radial position of the first end section and the second radial position of the first end section. 
     The second radial sensor unit may be configured to provide the determined radial position of the second end section to the control unit, wherein the control unit may be configured to control the second radial magnetic bearing of the second active magnetic bearing to adjustably generate a magnetic force on the second end section on the basis of the determined radial position of the second end section. In particular, the second radial sensor unit may be configured to determine a first radial position of the second end section using the second radial sensor and to determine a second radial position of the second end section using the second radial Hall sensor arrangement. In particular, the second radial sensor unit may be configured to compare the first radial position and the second radial position of the second end section to determine the accuracy of the determined radial position of the second end section and/or to determine any error or malfunctions of the second radial sensor and the second radial Hall sensor arrangement, respectively. The second radial sensor unit may be configured to determine the radial position based on the first radial position of the second end section and/or the second radial position of the second end section. The second radial sensor unit may in particular be configured to determine the radial position of the second end section based on an arithmetic mean or a weighted average of the first radial position of the second end section and the second radial position of the second end section. 
     Preferentially, the first radial magnetic bearing may be one of a homopolar magnetic bearing and a heteropolar magnetic bearing, and/or the second radial magnetic bearing may be one of a homopolar magnetic bearing and a heteropolar magnetic bearing. 
     Preferentially, the ventricular assist device may comprise an axial sensor arrangement configured to determine an axial position of the rotor shaft along the longitudinal axis and/or the central axis in the operational state. In particular, the axial sensor arrangement may comprise any type of sensor capable of detecting and/or measuring the axial position of the rotor shaft along the longitudinal axis and/or the central axis in the operational state relative to the drive unit and/or the first active magnetic bearing and/or the second active magnetic bearing. 
     Preferentially, the axial sensor arrangement may comprise a ring-shaped permanent magnet fixed to the rotor shaft in a circumferential direction around the rotor shaft. In particular, the ring-shaped permanent magnet may be formed from any possible magnetic material. The ring-shaped permanent magnet may be fixed to the rotor shaft between the first end section and the second end section, preferably between the first magnetisable element and the second magnetisable element. 
     The axial sensor arrangement may further comprise an axial Hall sensor arranged adjacent the ring-shaped permanent magnet in a direction parallel to the longitudinal axis, wherein the axial Hall sensor is configured to determine the axial position of the rotor shaft. In particular, the axial Hall sensor may be fixedly connected to the drive unit, wherein the ventricular assist device is configured such that during rotation of the impeller in the operational state the ring-shaped permanent magnet rotates adjacent to the axial Hall sensor. Therefore, an axial movement of the rotor shaft along the longitudinal axis and/or the central axis may cause a distance between the axial Hall sensor and the ring-shaped permanent magnet to change, which causes a change in the magnetic field measured by the axial Hall sensor. Based on such a measured changed magnetic field and/or change of the magnetic field, the axial Hall sensor may be configured to determine the axial position of the rotor shaft. While the axial sensor arrangement has been described using one axial Hall sensor above, the axial sensor arrangement is not restricted to this. Specifically, the axial Hall sensor arrangement may comprise one or more axial Hall sensors arranged adjacent the ring-shaped permanent magnet in a direction parallel to the longitudinal axis, wherein the one or more axial Hall sensors may further be equally spaced in a circumferential direction around the central axis. Preferentially, the axial sensor arrangement may be configured to provide the determined axial position of the rotor shaft to the control unit. 
     Preferentially, the first active magnetic bearing may comprise a first axial magnetic bearing configured to adjust the axial position of the rotor shaft along the longitudinal axis. In particular, the first axial magnetic bearing may be configured to adjustably generate a magnetic force on the rotor shaft to adjust the axial position of the rotor shaft along the longitudinal axis and/or the central axis. In particular, the control unit may be configured to control the first axial magnetic bearing to adjustably generate a magnetic force on the rotor shaft to adjust the axial position of the rotor shaft along the longitudinal axis and/or the central axis, preferentially based on the determined axial position of the rotor shaft. 
     In particular, the rotor shaft may comprise a first magnetisable disk, preferentially a first circular or ring-shaped planar magnetisable disk, fixed to the rotor shaft, preferably to the non-magnetisable section of the rotor shaft. The first magnetisable disk may be fixed to the rotor shaft such that the longitudinal axis is normal to the first magnetisable disk. The first magnetisable disk may in particular comprise at least one magnetisable material. In particular, the first axial magnetic bearing may be configured to adjustably generate a magnetic force on the first magnetisable disk to adjust the position of the rotor shaft along the longitudinal axis and/or the central axis. 
     The first axial magnetic bearing may further comprise a first axial magnetic coil. The first axial magnetic coil may be arranged adjacent the first magnetisable disk. The first axial magnetic coil may be wound around the longitudinal axis and/or the central axis in the operational state, wherein the first axial magnetic coil may be fixedly connected to the drive unit and/or the first active magnetic bearing. In particular, the first axial magnetic coil may be configured such that the rotor shaft is rotatable with respect to the first axial magnetic coil. The control unit may be configured to control a current to the first axial magnetic coil to adjustably generate a magnetic force on the rotor shaft to adjust the axial position of the rotor shaft along the longitudinal axis and/or the central axis, preferentially based on the determined axial position of the rotor shaft. 
     The first axial magnetic bearing may further comprise a first magnetic pot. The first magnetic pot may be formed from any magnetisable material. The first magnetic pot may further be configured to contain and/or surround the first axial magnetic coil, wherein the first magnetic pot may be configured to be open along a surface of the first axial magnetic coil adjacent the first magnetisable disk. In other words, the first axial magnetic coil may be arranged in the first magnetic pot, wherein the first magnetic pot may be configured to be open along a surface of the first axial magnetic coil adjacent the first magnetisable disk. In particular, it may therefore be possible to direct and/or orient a magnetic field generated by the first axial magnetic coil, thereby improving the performance of the first axial magnetic bearing. 
     Preferentially, the second active magnetic bearing may comprise a second axial magnetic bearing configured to adjust the axial position of the rotor shaft along the longitudinal axis. In particular, the second axial magnetic bearing may be configured to adjustably generate a magnetic force on the rotor shaft to adjust the axial position of the rotor shaft along the longitudinal axis and/or the central axis. In particular, the control unit may be configured to control the second axial magnetic bearing to adjustably generate a magnetic force on the rotor shaft to adjust the axial position of the rotor shaft along the longitudinal axis and/or the central axis, preferentially based on the determined axial position of the rotor shaft. 
     In particular, the rotor shaft may comprise a second magnetisable disk, preferentially a second circular or ring-shaped planar magnetisable disk, fixed to the rotor shaft, preferably to the non-magnetisable section of the rotor shaft. The second magnetisable disk may be fixed to the rotor shaft such that the longitudinal axis is normal to the second magnetisable disk. The second magnetisable disk may in particular comprise at least one magnetisable material. In particular, the second axial magnetic bearing may be configured to adjustably generate a magnetic force on the second magnetisable disk to adjust the position of the rotor shaft along the longitudinal axis and/or the central axis. 
     The second axial magnetic bearing may further comprise a second axial magnetic coil. The second axial magnetic coil may be arranged adjacent the second magnetisable disk. The second axial magnetic coil may be wound around the longitudinal axis and/or the central axis in the operational state, wherein the second axial magnetic coil may be fixedly connected to the drive unit and/or the second active magnetic bearing. In particular, the second axial magnetic coil may be configured such that the rotor shaft is rotatable with respect to the second axial magnetic coil. The control unit may be configured to control a current to the second axial magnetic coil to adjustably generate a magnetic force on the rotor shaft to adjust the axial position of the rotor shaft along the longitudinal axis and/or the central axis, preferentially based on the determined axial position of the rotor shaft. 
     The second axial magnetic bearing may further comprise a second magnetic pot. The second magnetic pot may be formed from any magnetisable material. The second magnetic pot may further be configured to contain and/or surround the second axial magnetic coil, wherein the second magnetic pot may be configured to be open along a surface of the second axial magnetic coil adjacent the second magnetisable disk. In other words, the second axial magnetic coil may be arranged in the second magnetic pot, wherein the second magnetic pot may be configured to be open along a surface of the second axial magnetic coil adjacent the second magnetisable disk. In particular, it may therefore be possible to direct and/or orient a magnetic field generated by the second axial magnetic coil, thereby improving the performance of the second axial magnetic bearing. 
     Furthermore, the rotor shaft may comprise a single magnetisable disk, preferentially a single circular or ring-shaped planar magnetisable disk, fixed to the rotor shaft, preferably to the non-magnetisable section of the rotor shaft. The single magnetisable disk may be fixed to the rotor shaft such that the longitudinal axis is normal to the single magnetisable disk. The single magnetisable disk may in particular comprise at least one magnetisable material. In particular, the first axial magnetic bearing may be configured to adjustably generate a magnetic force on the single magnetisable disk to adjust the position of the rotor shaft along the longitudinal axis and/or the central axis and the second axial magnetic bearing may be configured to adjustably generate a magnetic force on the single magnetisable disk to adjust the position of the rotor shaft along the longitudinal axis and/or the central axis. 
     Preferentially, the determined axial position is provided to the control unit. In other words, the axial sensor arrangement is configured to provide the determined axial position of the rotor shaft along the longitudinal axis and/or the central axis to the control unit. Furthermore, the control unit may be configured to control the first axial magnetic bearing of the first active magnetic bearing and/or the second axial magnetic bearing of the second active magnetic bearing to adjust the axial position of the rotor shaft on the basis of the determined axial position of the rotor shaft. For example, the control unit may control a current supplied to the first axial magnetic coil of the first axial magnetic bearing and/or to the second axial magnetic coil of the second axial magnetic bearing to adjust the axial position of the rotor shaft on the basis of the determined axial position of the rotor shaft. 
     Preferentially, the control unit may further comprise a transmitter configured to transmit data to a remote device, wherein the control unit is preferentially configured to detect a malfunction of the ventricular assist device and subsequently transmit an alert on the basis of the detected malfunction. For example, the control unit may be configured to detect when the ventricular assist device cannot set a rotational speed of the rotor shaft to a desired value, such as when a blockage is preventing sufficient rotation of the rotor shaft. The remote device may in particular be a handheld device, such as a smartphone. An app on said smartphone maybe configured to display the transmitted data, such as performance data of the ventricular assist device. Preferentially, the control unit may further comprise a receiver configured to receive data from a remote device. In particular, the received data may comprise for example operation instructions to the control unit, a data request to the control unit, and/or firmware updates. Preferentially, the control unit may further comprise a data storage device, wherein the data storage device may be configured to store, for example, historical operational data and/or parameters of the ventricular assist device. 
     Preferentially, a geometry of the ventricular assist device may be configured such that a flow field of a fluid pumped by the ventricular assist device through the ventricular assist device in the operational state does not comprise any dead water zones. In particular, a dead water zone is to be understood in this respect as a flow zone of the flow field having an average flow vector of zero. In other words, fluid located in a dead water zone of the flow field is not able to leave the dead water zone. In particular, this can cause severe problems for the operation of the ventricular assist device, as such dead water zones may significantly reduce the overall pumping performance of the ventricular assist device. Furthermore, when pumping a live fluid, such as blood, live particles of the fluid, such as blood cells, eventually consume all available nutrients and/or oxygen contained in the dead water zone, causing said live particles to eventually suffocate and/or starve. Said dead particles may then cause blood clots, which could lead to thrombosis. 
     Preferentially, the ventricular assist device may be configured to have a geometry such that the fluid pumped by the ventricular assist device does not flow over any sharp edges of the ventricular assist device. In other words, the ventricular assist device may be configured such that the flow field of the fluid pumped by the ventricular assist device through the ventricular assist device in the operational state has a smooth geometry. Specifically, it was found that sharp edges of the ventricular assist device may cause dead water zones, as discussed above. Furthermore, it was found that by implementing such a smooth geometry, a shear strain on the fluid to be pumped could significantly be reduced, thereby causing less potential damage to live particles in said fluid. In particular, the ventricular assist device may therefore be configured to have a geometry such that a shear strain load on the fluid to be pumped does not exceed a shear strain threshold of the fluid to be pumped during a pumping operation of the ventricular assist device and/or during rotation of the impeller. Specifically, possible geometries of the ventricular assist device may be designed and/or verified using numerical methods modelling, and/or verified using analysis of fluid pumped by the ventricular assist device, such as for example using blood damage analysis. In addition, such a geometry of the ventricular assist device may allow for a significantly improve energy conversion efficiency of up to 75%, and furthermore significantly reduces the resistance experienced by a passive flow of fluid, i.e. while the ventricular assist device is not pumping said fluid, through the ventricular assist device. An example of such a passive flow of fluid may be a flow of blood caused by the own pumping action of a heart of a user of the ventricular assist device. 
     Preferentially, the flow field of the fluid pumped by the ventricular assist device within the ventricular assist device in the operational state may have a variable diameter along the central axis. Specifically, the ventricular assist device may be configured such that the impeller is arranged in a portion of the flow field having the smallest diameter. 
     Preferentially, the ventricular assist device may further comprise a diffusor arranged adjacent the impeller. In particular, the ventricular assist device may further comprise a diffusor arranged adjacent the impeller in the operational state. The diffusor may in particular be configured to at least partially reduce and/or remove swirl produced in a fluid flow caused by the rotation of the impeller. The diffusor may further be configured to reduce and/or minimize turbulent flow in the fluid flow caused by the rotation of the impeller. In particular, such a minimized and/or reduced turbulent flow may reduce damage to a fluid to be pumped, such as blood. Furthermore, the diffusor may be configured to cause a lowest possible total pressure loss and/or a highest possible static pressure gain of a fluid pumped by the ventricular assist device. In particular, the diffusor may have a diffusor geometry, wherein the diffusor geometry may for example be determined using numerical modelling based on at least the viscosity of the fluid to be pumped and/or the outgoing flow of the impeller. Preferentially, the diffusor may comprise at least one stator vane, wherein a number of stator vanes of the diffusor may be chosen according to specific operational requirements of the ventricular assist device. Preferentially, the ventricular assist device may be configured such that the number of stator vanes of the diffusor is larger or smaller than the number of impeller vanes of the impeller. 
     Preferentially, the ventricular assist device may be configured to be fully implanted into the lumen of the blood vessel, such as a vein or artery, e.g. the aorta or the pulmonary artery. Fully implanted into the lumen of the blood vessel in this context is to be understood in particular as implanted into the lumen, such that after implantation the ventricular assist device is fully enclosed in said lumen. The ventricular assist device may comprise one or more attachment elements, such as one or more attachment grooves, on an outer surface of the ventricular assist device configured to fix the ventricular assist device to the blood vessel. In particular, the one or more attachment grooves may extend along a substantially circumferential direction around the central axis and/or the longitudinal axis, wherein at least one attachment groove may extend fully around the ventricular assist device and/or at least one attachment groove may extend only partially around the ventricular assist device. In particular, the one or more attachment elements may be configured to fix the ventricular assist device to a wall of the blood vessel and/or an inner surface of the wall of the blood vessel. Alternatively or additionally, the ventricular assist device may be configured to be fixable to the blood vessel, in particular to the wall of the blood vessel, by one or more fixing elements arranged outside the lumen of the blood vessel, preferentially outside the blood vessel. 
     For example, the one or more fixing elements may comprise one or more wires or ties configured to fix the ventricular assist device to the wall of the blood vessel and/or the inner surface of the wall of the blood vessel by at least one of friction fit and positive fit. Furthermore, the one or more wires or ties may be configured to reduce a surface pressure on the wall of the blood vessel, in order to reduce and/or avoid tissue damage, such as tissue necrosis, to said wall. In particular, said one or more wires or ties may be configured to at least partially compress the blood vessel, in particular the wall of the blood vessel between the ventricular assist device, preferentially the one or more attachment grooves of the ventricular assist device, and the respective one of the wires or ties. The number of wires or ties may be adjusted in accordance with a specific required holding force. Furthermore, the one or more wires or ties may be configured to be brought into a closed loop form by at least one of knotting, stapling, gluing, fusing, and/or the use of one or more clamps and/or brackets. The suitability of such a closed loop form has been verified by FEM (finite element method) calculations. The one or more wires or ties may be made from medical grade PTFE-tissue. 
     Furthermore, due to the compact design of the ventricular assist device and/or due to the ventricular assist device preferentially not comprising any physical connections, such as a wire connection, through the skin and/or the walls of the blood vessel, such as a vein or artery of a user, the ventricular assist device may be implanted in a minimally invasive procedure. In particular, such a minimally invasive procedure may not require the use of pulmonary support machines. Furthermore, the ventricular assist device may easily be further miniaturised. 
     Preferentially, the magnetic motor may be configured to cause rotation of the impeller, such that a pumping action of the ventricular assist device is synchronised or asynchronised with the pumping action of a user heart. 
     Preferentially, the magnetic motor is configured to cause rotation of the impeller in a pulsatile operation mode. During the pulsatile operation mode, the magnetic motor may be operated to cause rotation of the impeller at a first rotational speed during times when a heart of a user is working/pumping, and the magnetic motor may be operated to not cause rotation of the impeller during times when the heart is resting or to cause rotation of the impeller at a second rotational speed when the heart is resting, wherein the first rotational speed is preferentially higher than the second rotational speed. In particular, using such a pulsatile operation mode, the ventricular assist device may be able to assist the natural circulation caused by the heart. Furthermore, the user maintains having a pulse even during operation of the ventricular assist device. Furthermore, the pulsatile operation mode may prevent additional complications, such as aortic valve insufficiency, thrombus formation, and/or gastrointestinal arteriovenous malformations. 
     Preferentially, the magnetic motor is configured to cause rotation of the impeller in a counter-pulsatile operation mode. During the counter-pulsatile operation mode, the magnetic motor may be operated to cause rotation of the impeller at a third rotational speed during times when a heart of a user is resting, and the magnetic motor may be operated to not cause rotation of the impeller during times when the heart is working/pumping or to cause rotation of the impeller at a fourth rotational speed when the heart is working/pumping, wherein the third rotational speed is preferentially higher than the fourth rotational speed. In particular, using such a counter-pulsatile operation mode, the ventricular assist device may be able to assist the circulation caused by the heart, as well as reduce a mechanical load on the heart, specifically by providing relief for the ventricle. 
     Preferentially, the ventricular assist device may further comprise pulse detecting means configured to detect a pulse of a heart of a user of the ventricular assist device. The pulse detecting means may comprise remote devices configured to detect the pulse of the heart and to transmit information of the detected pulse to the ventricular assist device, and/or the pulse detecting means may comprise local devices configured to detect the pulse of the heart, such as for example pressure detecting means. In particular, the magnetic motor may be configured to cause rotation of the impeller in the pulsatile operation mode and/or the counter-pulsatile operation mode on the basis of the detected pulse of the heart of the user. 
     Preferentially, the magnetic motor is configured to cause rotation of the impeller in a continuous operation mode. During the continuous operation mode, the magnetic motor may be operated to cause rotation, preferentially at a constant rotational speed or at a variable rotational speed dependent for example on a current activity of the user, of the impeller during times when a heart of a user is resting and during times when the heart is working/pumping. In particular, using such a counter-pulsatile operation mode, the ventricular assist device may be able to assist the circulation caused by the heart, as well as reduce a mechanical load on the heart. 
     Preferentially, the magnetic motor may be configured to be switchable between the pulsatile operation mode, the counter-pulsatile operation mode, and/or the continuous operation mode. 
     Preferentially, the ventricular assist device comprises a power unit configured to provide power to the ventricular assist device, wherein the power unit may comprise a power reception unit configured to, preferentially wirelessly and transcutaneously, receive power. Wirelessly and transcutaneously is to be understood in this context such that the power reception unit may be configured to receive power over one or more wireless connections that do not require a physical connection, such as a wire connection, through the skin and/or the walls of the blood vessel, such as a vein or an artery of a user. However, alternatively or additionally, the power reception unit may comprise one or more physical connections, such as one or more wire connections, through the skin and/or the walls of the blood vessel, such as a vein or an artery of a user, wherein the power reception unit may be configured to receive power over the one or more physical connections. Furthermore, the power unit may comprise a power storage unit configured to store power. The power storage unit may comprise any means of storing power, such as one or more batteries and/or one or more electrostatic storage modules, such as a Goldcap capacitor. 
     Preferentially, the magnetic motor is a brushless DC-motor, and, optionally, wherein the brushless DC-motor has a large airgap. In particular, an imaginary plane may be perpendicular to the central axis of the ventricular assist device in the operational state, wherein all such imaginary planes intersect at least one component of the ventricular assist device. In such an imaginary plane, a total blocked area comprises all areas occupied by one or more components of the ventricular assist device in the respective imaginary plane. Furthermore, in such an imaginary plane, a total flow area comprises all areas, preferentially within the ventricular assist device, through which a fluid to be pumped can flow. Preferentially, the ventricular assist device may be configured such that the total flow area is at least 1.25 times, preferably at least 1.5 times as large as the total blocked area for any imaginary plane, as defined above. Preferentially, the ventricular assist device may be configured such that the total flow area is at least 1.25 times, preferably at least 1.5 times as large as the total blocked area for all of the imaginary planes, as defined above, that intersect at least one component of the impeller and/or the magnetic motor. 
     Preferentially, the brushless DC-motor has an inflow surface. Preferentially, the airgap of the brushless DC-motor has a size of at least 50%, preferably at least 60% of the inflow surface. Furthermore, the airgap of the brushless DC-motor may have a size of at least 50%, preferably at least 60% of the inflow surface in a section of the ventricular assist device, wherein said section comprises at least the magnetic motor and/or the impeller. 
     Preferentially, the first active magnetic bearing and the second active magnetic bearing are substantially identically constructed. In particular, at least one of the first active magnetic bearing and the second active magnetic bearing may be configured to have a mirror symmetry relative to an imaginary mirror plane perpendicular to an axis of a central bore configured to receive the first and second end sections, respectively. Thereby, a simple and efficient design of the first active magnetic bearing and the second active magnetic bearing can be provided. Alternatively, at least one of the first active magnetic bearing and the second active magnetic bearing may not have a mirror symmetry, as described above. Thereby, the design of the first active magnetic bearing and the second active magnetic bearing can be efficiently adapted to the design of the other components of the ventricular assist device. 
     In a preferential configuration, the ventricular assist device comprises a plurality of permanent drive magnets, preferably six permanent drive magnets, fixed to the rotor shaft in a circumferential direction around the rotor shaft. The plurality of permanent drive magnets may be fixed onto an outer circumferential surface of the rotor shaft and/or fixed into the rotor shaft such that an outer surface of the plurality of permanent drive magnets is flush with the outer surface of the rotor shaft. Preferentially, the plurality of permanent drive magnets are fixed to the rotor shaft at a location downstream of the impeller. In other words, the plurality of permanent drive magnets are fixed to the rotor shaft at a location such that during operation of the ventricular assist device, a fluid flows through the impeller prior to flowing past the plurality of permanent drive magnets. Preferentially, the plurality of permanent drive magnets are equally spaced around the rotor shaft in the circumferential direction. 
     Preferentially, the magnetic motor comprises a plurality of magnetic coils, preferably six magnetic coils, arranged in a circumferential direction around the rotor shaft. In particular, the plurality of magnetic coils may be configured to produce a magnetic field to interact with the plurality of permanent drive magnets to cause the rotation of the impeller relative to the longitudinal axis along the rotor shaft. Thereby the magnetic motor is able to adjustably generate a magnetic force on the rotor shaft to control a rotational speed of the impeller. However, neither the rotor shaft, nor the magnetic motor are limited to such a configuration, and other configurations to adjustably generate a magnetic force on the rotor shaft to control a rotational speed of the impeller may be implemented. 
     Preferentially, the control unit may comprise at least one PID controller configured to control at least one of the magnetic motor, the first active magnetic bearing, and the second active magnetic bearing. Furthermore, the control unit and/or the at least one PID controller may be implemented on one or more printed circuit boards, preferentially on one or more encapsulated printed circuit boards. Preferentially, the control unit and/or each of the at least one PID controller may be sealed from outside influences, such as sealed from the fluid to be pumped by the ventricular assist device. For example, the control unit and/or each of the at least one PID controller may each be sealed in a respective protective pod. 
     Preferentially, the ventricular assist device may be substantially cylindrical shaped. In particular, the ventricular assist device may have a total length along the central axis in the operational state of at most 60 mm, preferably at most 45 mm, and at least 20 mm, preferably at least 35 mm. In particular, the ventricular assist device may have a total diameter perpendicular to the central axis in the operational state of at most 40 mm, preferably at most 30 mm, and at least 10 mm, preferably at least 20 mm. 
     One aspect of the disclosure relates to an impeller fixed to a rotor shaft, wherein the impeller is configured to rotate around a longitudinal axis of the rotor shaft. Preferentially, the impeller may comprise any combination of the features described herein and the appended Figures. 
     One aspect of the disclosure relates to a drive unit comprising a magnetic motor configured to cause rotation of an impeller fixed to a rotor shaft around a longitudinal axis of the rotor shaft. Preferentially, the drive unit may comprise any combination of the features described herein and the appended Figures. 
     One aspect of the disclosure relates to an active magnetic bearing configured to bear an end section of a rotor shaft relative to the active magnetic bearing and/or a corresponding drive unit configured to cause rotation of the rotor shaft around a longitudinal axis thereof. Preferentially, the active magnetic bearing may comprise any combination of the features described herein and the appended Figures. While the first active magnetic bearing and the second active magnetic bearing are described as components of a ventricular assist device above, the active magnetic bearing need not be restricted to such an application, and could therefore be used to bear various kinds of rotor shafts. 
     One aspect of the invention relates to a ventricular assist system, comprising a ventricular assist device. The ventricular assist device in particular may comprise: an impeller fixed to a rotor shaft, wherein the impeller is configured to rotate around a longitudinal axis of the rotor shaft; a drive unit comprising a magnetic motor configured to cause rotation of the impeller around the longitudinal axis; a first active magnetic bearing configured to bear a first end section of the rotor shaft relative to the drive unit; a second active magnetic bearing configured to bear a second end section of the rotor shaft relative to the drive unit; and a control unit configured to control the magnetic motor, the first active magnetic bearing and the second active magnetic bearing. 
     Preferentially, the ventricular assist device of the ventricular assist system may comprise any combination of the features of the ventricular assist devices described herein and the appended Figures. 
     Preferentially, the ventricular assist system comprises an external power unit configured to provide power to the ventricular assist device, wherein the power unit comprises a power transmission unit configured to, preferentially wirelessly and transcutaneously, transmit power to the ventricular assist device. Wirelessly and transcutaneously is to be understood in this context such that the power transmission unit may be configured to transmit power over one or more wireless connections that do not require a wire connection through the skin and/or the walls of the blood vessel, such as a vein or artery of a user. The transmission of power may, for example, be provided via an inductive or electromagnetic field. However, alternatively or additionally, the power transmission unit may be configured to transmit power over one or more physical connections, such as one or more wire connections, through the skin and/or the walls of the blood vessel, such as a vein or an artery of a user. Preferentially, the external power unit may be configured to be wearable by a user. For example, the external power unit may be configured as a vest wearable by the user. 
     Preferentially, the external power unit may further comprise an external power storage unit. In particular, the external power storage unit may be configured as any type of power storage unit. Specifically, the external power storage unit may comprise at least one of a battery, such as a LiPo-accumulator, and/or a capacitor, such as a Goldcap capacitor. Preferentially, the external power storage unit is configured to be rechargeable. Preferentially, the external power unit is configured to transmit power stored in the external power storage unit via the power transmission unit to the ventricular assist device. 
     A further aspect of the disclosure relates to an implantation method of a ventricular assist device into a lumen of a blood vessel, comprising providing the ventricular assist device having any combination of features of the ventricular assist devices as described herein and/or in the appended Figures; placing the ventricular assist device fully in the lumen of the blood vessel, such as a vein or artery, preferentially the aorta or pulmonary artery, of a user; and fixing the ventricular assist device to the blood vessel and/or to a wall of the blood vessel. Preferentially, the fixing comprises compressing the blood vessel and/or the wall of the blood vessel around the ventricular assist device to prevent a movement of the ventricular assist device relative to the blood vessel. Alternatively or additionally, the fixing may further comprise providing a fixing means on the ventricular assist device, such that a movement of the ventricular assist device relative to the blood vessel is blocked. Such fixing means may for example comprise friction enhancing elements, biologically acceptable glues, and/or tissue growth elements configured to promote tissue to grow around the ventricular assist device. 
     Preferentially, the implantation method is not limited to the above and may comprise any combination of features described herein and the appended Figures. 
     The invention is further explained in reference to the appended Figures, which show illustrative, exemplary embodiments. In particular, the embodiments shown in the appended Figures are not to be interpreted as limiting the scope of the disclosure. 
    
    
     
       In particular, the Figures show: 
         FIG.  1   : a perspective, exploded view of an exemplary ventricular assist device; 
         FIG.  2   : a perspective view of a ventricular assist device  1  in the operational state; 
         FIG.  3   : a schematic cross-sectional view of an exemplary ventricular assist device  1 ; 
         FIG.  4 A : a cross-sectional view of a first active magnetic bearing  30 A of a ventricular assist device  1 ; 
         FIG.  4 B : a cross-sectional view of a first active magnetic bearing  30 A of  FIG.  4 A  along the line A-A; 
         FIG.  4 C : a cross-sectional view of a second active magnetic bearing  30 B of a ventricular assist device  1 ; 
         FIG.  5   : an organ of balance  50  of a pectinid; 
         FIG.  6   : a schematic view of a first radial sensor unit of the ventricular assist device  1 ; 
         FIG.  7   : a schematic view of a first radial sensor unit of the ventricular assist device  1 ; 
         FIG.  8   : a cross-sectional view of a ventricular assist device  1 ; 
         FIG.  9   : a cross-sectional view of a ventricular assist device  1 ; 
         FIG.  10   : a FEMM (Finite Element Method Magnetics) simulation result of a magnetic field produced by an exemplary first magnetic bearing segment  33 A; 
         FIG.  11   : a cross-sectional view of a fluid flow  1000  through a ventricular assist device  1 ; 
         FIG.  12   : the fluid field  1000  of  FIG.  11    as a perspective, cross-sectional  3 D flow body; 
         FIG.  13   : a cross-sectional view of an exemplary ventricular assist device after implantation into a lumen of a blood vessel; and 
         FIG.  14   : a perspective view of an exemplary impeller geometry; 
         FIG.  15   : a schematic view of magnetic field lines of a permanent magnet. 
     
    
    
     In the following description of the Figures, identical components are provided with identical reference signs, unless otherwise specified for the respective figure description. 
       FIG.  1    shows a perspective, exploded view of an exemplary ventricular assist device  1 . The ventricular assist device  1  is shown to have a substantially cylindrical shape. 
     The ventricular assist device comprises in particular a rotor shaft  10 . The rotor shaft  10  is shown as arranged in the operational state of the ventricular assist device  1  in relation to the drive unit  20 . Specifically, an impeller  11  fixed to the rotor shaft  10  is arranged fully inside the drive unit  20 , and can therefore not be seen in  FIG.  1   . The rotor shaft  10  has a longitudinal axis that is substantially identical to a central axis of the ventricular assist device  1 , wherein the rotor shaft  10  is configured to rotate around the longitudinal axis and/or the central axis. Furthermore, the rotor shaft  10  comprises a non-magnetisable section  190 , a first magnetisable element  191 A, a first non-magnetisable element  192 A, a second magnetisable element  191 B, and a second non-magnetisable element  1926 . The first magnetisable element  191 A and the first non-magnetisable element  192 A may form, in the shown embodiment, a first end section  19 A of the rotor shaft  10 . The second magnetisable element  191 B and the second non-magnetisable element  1926  may form, in the shown embodiment, a second end section  19 B of the rotor shaft  10 . 
     The ventricular assist device  1  further comprises the drive unit  20 . The drive unit  20  is configured to have a substantially cylindrical shape, wherein the impeller  11  of the rotor shaft  10  is arranged within the drive unit  20  in the operational state. The drive unit  20  furthermore comprises a magnetic motor (not shown in  FIG.  1   ) configured to cause rotation of the impeller  11  and the rotor shaft  10  around the longitudinal axis and the central axis during operation of the ventricular assist device  1 . 
     The ventricular assist device  1  further comprises a first active magnetic bearing  30 A. The first active magnetic bearing  30 A is configured to bear the first end section  19 A of the rotor shaft  10  relative to the drive unit  20  and relative to the first active magnetic bearing  30 A. 
     The ventricular assist device  1  further comprises a second active magnetic bearing  30 B. The second active magnetic bearing  30 B is configured to bear the second end section  19 B of the rotor shaft  10  relative to the drive unit  20  and relative to the second active magnetic bearing  30 B. 
     Although the first active magnetic bearing  30 A and the drive unit  20  are shown as separated for illustrative purposes in  FIG.  1   , the first active magnetic bearing  30 A is configured to be fixedly connected to the drive unit  20  on a first side of said drive unit  20  in the operational state of the ventricular assist device  1 . Similarly, the second active magnetic bearing  30 B and the drive unit  20  are shown as separated for illustrative purposes in  FIG.  1   , the second active magnetic bearing  30 B is configured to be fixedly connected to the drive unit  20  on a second side of said drive unit  20  in the operational state of the ventricular assist device  1 . In particular, the first side of the drive unit  20  is located opposite of the second side of the drive unit  20  along the central axis of the ventricular assist device  1 . 
       FIG.  2    shows a perspective view of a ventricular assist device  1  in the operational state. 
     In particular, in the shown embodiment, the first active magnetic bearing  30 A is fixedly connected to the drive unit  20 . Furthermore, the second active magnetic bearing  30 B is fixedly connected to the drive unit  20 . 
     The drive unit  20  may in particular comprise a, preferentially substantially cylindrical, outer body  21 . Specifically, each of the first active magnetic bearing  30 A and the second active magnetic bearing  30 B may be fixedly connected to the outer body  21 . 
     The drive unit may further comprise access covers  22 , wherein each access cover is removably connected to the outer body  21 . In particular, each access cover may configured to be removable to access at least the magnetic motor of the drive unit  20 . 
     The first active magnetic bearing  30 A may comprise in particular a first radial magnetic bearing  31 A configured to adjust a radial position of the first end section  19 A relative to the first radial magnetic bearing  31 A. The first radial magnetic bearing  31 A comprises in the shown embodiment four first bearing segments  33 A, wherein said first bearing segments  33 A are arranged circumferentially, specifically equally spaced, around the central axis and/or the longitudinal axis of the rotor shaft  10  in the operational state of the ventricular assist device  1 . Each of the four first bearing segments  33 A is in particular arranged substantially adjacent the rotor shaft  10  and/or the first end section  19 A in the operational state of the ventricular assist device  1 . 
     Each of the first bearing segments  33 A furthermore comprises a control unit cover  34 A located adjacent to the respective first bearing segment  33 A. Each control unit cover  34 A is in particular configured to seal a corresponding control unit and/or control sub-unit from a fluid to be pumped by the ventricular assist device  1 . 
     Furthermore, the four first bearing segments  33 A are substantially identically constructed. 
     The second active magnetic bearing  30 B may comprise in particular a second radial magnetic bearing  31 B (not shown due to the perspective of  FIG.  2   ) configured to adjust a radial position of the second end section  19 B relative to the second radial magnetic bearing  31 B. The second radial magnetic bearing  31 B comprises in the shown embodiment four second bearing segments  33 B, wherein said second bearing segments  33 B are arranged circumferentially, specifically equally spaced, around the central axis and/or the longitudinal axis of the rotor shaft  10  in the operational state of the ventricular assist device  1 . Each of the four second bearing segments  33 B is in particular arranged substantially adjacent the rotor shaft  10  and/or the second end section  19 B in the operational state of the ventricular assist device  1 . 
     Each of the second bearing segments  33 B furthermore comprises a control unit cover  34 B located adjacent to the respective second bearing segment  33 B. Each control unit cover  34 B is in particular configured to seal a corresponding control unit and/or control sub-unit from a fluid to be pumped by the ventricular assist device  1 . 
     Furthermore, the four second bearing segments  33 B are substantially identically constructed. 
       FIG.  3    shows a schematic cross-sectional view of an exemplary ventricular assist device  1 . 
     In particular, the first active magnetic bearing  30 A comprises at least a first radial magnetic bearing  31 A configured to bear the first end section  19 A (shown as a single end section of the rotor shaft  10  for simplicity) of the rotor shaft  10 . Furthermore, the second active magnetic bearing  30 B comprises at least a second radial magnetic bearing  31 B configured to bear the second end section  19 B (shown as a single end section of the rotor shaft  10  for simplicity) of the rotor shaft  10 . 
     The ventricular assist device  1  further comprises an impeller  11  fixedly connected with the rotor shaft  10 , wherein the impeller  11  is configured to be rotatable with the rotor shaft  10  around the longitudinal axis of the rotor shaft  10  and/or the central axis of the ventricular assist device  1 . The ventricular assist device  1  may further comprise a mounting body  12 , wherein the mounting body  12  is fixedly connected to the rotor shaft  10 . The mounting body  12  is in particular configured such that further elements of the ventricular assist device  1  can easily be mounted on the rotor shaft  10 . However, the mounting body  12  is not essential, and said further elements may also be directly mounted on the rotor shaft  10 . 
     Furthermore, the ventricular assist device  1  comprises a plurality of permanent drive magnets  13 , preferably six permanent drive magnets  13 , wherein each permanent drive magnet  13  is fixedly connected to a bracket  14 . Each bracket  14  is fixedly connected to the mounting body  12 , thereby providing a fixed connection between each of the permanent drive magnets  13  and the rotor shaft  10 . In particular, the six permanent drive magnets  13  are equally spaced in a circumferential direction around the rotor shaft  10  and/or the central axis. In particular, the plurality of permanent drive magnets  13  are fixed relative to the rotor shaft  10  at a location downstream of the impeller  11 . In other words, the plurality of permanent drive magnets  13  are fixed relative to the rotor shaft  10  at a location such that during operation of the ventricular assist device  1 , a pumped fluid flows through the impeller  11  prior to flowing past the plurality of permanent drive magnets  13 . 
     Furthermore, the ventricular assist device  1  comprises an axial sensor arrangement  23  (see for example  FIG.  9   ) configured to determine an axial position of the rotor shaft  10  along the longitudinal axis and/or the central axis in the operational state. In particular, the axial sensor arrangement  23  may comprise any type of sensor capable of detecting and/or measuring the axial position of the rotor shaft  10  along the longitudinal axis and/or the central axis in the operational state relative to the drive unit  20  and/or the first active magnetic bearing  30 A and/or the second active magnetic bearing  30 B. For simplicity, an exemplary sensor is not shown in  FIG.  3   . 
     In particular, the axial sensor arrangement  23  comprises a ring-shaped permanent magnet  15  fixed relative to the rotor shaft  10  in a circumferential direction around the rotor shaft  10 . Specifically, in the shown embodiment, the ring-shaped permanent magnet  15  is fixed to the mounting body  12 , and therewith fixed to the rotor shaft  10 . Furthermore, the ring-shaped permanent magnet  15  may be formed from any possible magnetic material. The ring-shaped permanent magnet  15  may be arranged along the rotor shaft  10  at a location in between the impeller  11  and the plurality of permanent drive magnets  13 . 
     The axial sensor arrangement  23  may further comprise an axial Hall sensor  23 A (not shown in  FIG.  3   ) arranged adjacent the ring-shaped permanent magnet  15  in a direction parallel to the longitudinal axis, wherein the axial Hall sensor  23 A is configured to determine the axial position of the rotor shaft  10 . 
     The first active magnetic bearing  30 A furthermore comprises a first axial magnetic bearing  32 A configured to adjust the axial position of the rotor shaft  10  along the longitudinal axis and/or the central axis. In particular, the first axial magnetic bearing  32 A is configured to adjustably generate a magnetic force on the rotor shaft  10  to adjust the axial position of the rotor shaft  10  along the longitudinal axis and/or the central axis. 
     Furthermore, the rotor shaft  10  comprises a first magnetisable disk  16 , specifically a first ring-shaped planar magnetisable disk  16 , fixed to the rotor shaft  10 , preferably to the non-magnetisable section  190  of the rotor shaft  10 . The first magnetisable disk  16  is fixed to the rotor shaft  10  such that the longitudinal axis is normal to the first magnetisable disk  16 . In particular, the first axial magnetic bearing  32 A may be configured to adjustably generate a magnetic force on the first magnetisable disk  16  to adjust the position of the rotor shaft  10  along the longitudinal axis and/or the central axis. 
     In particular, the first axial magnetic bearing  32 A may comprise a first axial magnetic coil. In particular, the first axial magnetic coil is arranged adjacent the first magnetisable disk  16 . The first axial magnetic coil is wound around the longitudinal axis and/or the central axis in the operational state. Furthermore, the first axial magnetic coil is configured such that the rotor shaft  10  is rotatable with respect to the first axial magnetic coil. Furthermore, a control unit may be configured to control a current to the first axial magnetic coil to adjustably generate a magnetic force on the rotor shaft  10  to adjust the axial position of the rotor shaft  10  along the longitudinal axis and/or the central axis, preferentially based on the axial position of the rotor shaft  10  as determined by the axial sensor arrangement  23 . 
     The second active magnetic bearing  30 B furthermore comprises a second axial magnetic bearing  32 B configured to adjust the axial position of the rotor shaft  10  along the longitudinal axis and/or the central axis. In particular, the second axial magnetic bearing  32 B is configured to adjustably generate a magnetic force on the rotor shaft  10  to adjust the axial position of the rotor shaft  10  along the longitudinal axis and/or the central axis. 
     Furthermore, the rotor shaft  10  comprises a second magnetisable disk  17 , specifically a second ring-shaped planar magnetisable disk  17 , fixed to the rotor shaft  10 , preferably to the non-magnetisable section  190  of the rotor shaft  10 . The second magnetisable disk  17  is fixed to the rotor shaft  10  such that the longitudinal axis is normal to the second magnetisable disk  17 . In particular, the second axial magnetic bearing  32 B may be configured to adjustably generate a magnetic force on the second magnetisable disk  17  to adjust the position of the rotor shaft  10  along the longitudinal axis and/or the central axis. 
     In particular, the second axial magnetic bearing  32 B may comprise a second axial magnetic coil. In particular, the second axial magnetic coil is arranged adjacent the second magnetisable disk  17 . The second axial magnetic coil is wound around the longitudinal axis and/or the central axis in the operational state. Furthermore, the second axial magnetic coil is configured such that the rotor shaft  10  is rotatable with respect to the second axial magnetic coil. Furthermore, a control unit may be configured to control a current to the second axial magnetic coil to adjustably generate a magnetic force on the rotor shaft  10  to adjust the axial position of the rotor shaft  10  along the longitudinal axis and/or the central axis, preferentially based on the axial position of the rotor shaft  10  as determined by the axial sensor arrangement  23 . 
       FIG.  4 A  shows a cross-sectional view of a first active magnetic bearing  30 A of a ventricular assist device  1 . 
     In particular, the first active magnetic bearing  30 A comprises a first radial magnetic bearing  31 A configured to adjust a radial position of the first end section  19 A, specifically of the first magnetisable element  191 A, relative to the first radial magnetic bearing  31 A, and a first radial sensor unit configured to determine the radial position of the first magnetisable element  191 A relative to the first radial magnetic bearing  31 A. The first radial magnetic bearing  31 A is configured to adjustably generate a magnetic force on the first magnetisable element  191 A to control the radial position of the first magnetisable element  191 A relative to the first radial magnetic bearing  31 A. Specifically, the first radial magnetic bearing  31 A is configured to adjustably generate a magnetic force on the first magnetisable element  191 A along a substantially radial direction relative to the longitudinal axis of the rotor shaft  10  and/or relative to the central axis. Specifically, the first radial magnetic bearing  31 A is implemented as an exemplary homopolar magnetic bearing in the shown embodiment. 
     The first radial magnetic bearing  31 A comprises four first bearing segments  33 A, wherein said first bearing segments  33 A are arranged circumferentially and equally spaced around the central axis and/or the longitudinal axis of the rotor shaft  10  in the operational state of the ventricular assist device  1 . In the exemplary cross-section shown, two first bearing segments  33 A are illustrated. Each of the four first bearing segments  33 A is arranged substantially adjacent the rotor shaft  10 , specifically the first magnetisable element  191 A, in the operational state of the ventricular assist device  1 . 
     Furthermore, the first radial sensor unit comprises a first radial sensor configured to measure a capacitance between each of the first bearing segments  33 A, specifically a magnetic yoke  37 A of the respective first bearing segment  33 A, and the first magnetisable element  191 A. Said first radial sensor will be further explained with respect to  FIGS.  5  to  7   . 
     Furthermore, each of the first bearing segments  33 A comprises a magnetic yoke  37 A arranged adjacent the first magnetisable element  191 A in the operational state of the ventricular assist device  1 . The magnetic yoke  37 A may be at least partially formed from a magnetisable material, such as for example magnetisable stainless steel 1.4016. Additionally, each of the first bearing segments  33 A comprises one first radial magnetic coil  36 A, wherein said first radial magnetic coil  36 A is wound around the magnetic yoke  37 A. A close-up view of the magnetic yoke  37 A is illustrated for example in  FIG.  6    below. 
     A control unit of the ventricular assist device comprises a plurality of control sub-units  35 A, wherein each of the first bearing segments  33 A is provided with one of said control sub-units  35 A. Each control sub-unit  35 A is configured to control a current supplied to the respective first radial magnetic coil  36 A of the respective first bearing segment  33 A to adjustably generate a magnetic force on the first magnetisable element  191 A to adjust the radial position of the first magnetisable element  191 A relative to the first radial magnetic bearing  31 A. Each control sub-unit  35 A is in particular implemented on a printed circuit board, and provided with a control unit cover  34 A. Each control unit cover  34 A is in particular configured to seal the corresponding control sub-unit  35 A from a fluid to be pumped by the ventricular assist device  1 . 
     Furthermore, the four first bearing segments  33 A are substantially identically constructed, and substantially equally spaced in a circumferential direction around the longitudinal axis and/or the central axis. 
     Additionally, the first radial sensor unit comprises a first radial Hall sensor arrangement configured to determine the radial position of the first end section  19 A. In particular, the first radial Hall sensor arrangement comprises a first permanent magnet  193 A fixed to the first end section  19 A, specifically fixed to the first non-magnetisable element  192 A of the first end section  19 A, and at least one first radial Hall sensor  38 A arranged adjacent the first permanent magnet  193 A in a radial direction relative to the longitudinal axis and/or the central axis in the operational state of the ventricular assist device  1 . Said first permanent magnet  193 A fixed to the first non-magnetisable element  192 A of the first end section  19 A is not shown in  FIG.  4 A , but will be further explained with respect to  FIG.  9   . The first radial Hall sensor arrangement comprises four first radial Hall sensors  38 A, wherein the four first radial Hall sensors  38 A are equally spaced in a circumferential direction around the longitudinal axis and/or the central axis in the operational state of the ventricular assist device  1 . Specifically, each first radial Hall sensor  38 A is arranged adjacent to one of the first bearing segments  33 A. 
     The first radial Hall sensor arrangement may further be shielded from the first radial magnetic bearing  31 A by one or more shielding elements arranged between the first radial Hall sensor arrangement and the first radial magnetic bearing  31 A. In particular, each first radial Hall sensor  38 A may be shielded from the respective adjacent first bearing segment  33 A by one or more shielding elements. 
       FIG.  4 B  shows a cross-sectional view of a first active magnetic bearing  30 A of  FIG.  4 A  along the line A-A. For brevity, components already discussed with respect to  FIG.  4 A  will not be further discussed for  FIG.  4 B . 
     The first active magnetic bearing  30 A further comprises a structural segment ring  60 . The segment ring  60  may be formed for example from a non-magnetisable material. Furthermore, each of the first bearing segments  33 A are fixedly connected to the segment ring  60 . Furthermore, each of the one or more control unit covers  34 A and/or the respective control sub-units  35 A may also be fixedly connected to the segment ring  60 . Finally, the one or more first radial Hall sensors  38 A may also be mounted on said segment ring  60 . The segment ring  60  therefore acts as a mounting platform for components of the first active magnetic bearing  30 A, and may further be fixedly connected to the drive unit  20 . 
       FIG.  4 C  shows a cross-sectional view of a second active magnetic bearing  30 B of a ventricular assist device  1 . In particular, the second active magnetic bearing  30 B is substantially identically constructed to the first active magnetic bearing  30 A. Thereby, a facile production of the ventricular assist device can be achieved. 
     In particular, the second active magnetic bearing  30 B comprises a second radial magnetic bearing  31 B configured to adjust a radial position of the second end section  19 B, specifically of the second magnetisable element  191 B, relative to the second radial magnetic bearing  31 B, and a second radial sensor unit configured to determine the radial position of the second magnetisable element  191 B relative to the second radial magnetic bearing  31 B. The second radial magnetic bearing  31 B is configured to adjustably generate a magnetic force on the second magnetisable element  191 B to control the radial position of the second magnetisable element  191 B relative to the second radial magnetic bearing  31 B. Specifically, the second radial magnetic bearing  31 B is configured to adjustably generate a magnetic force on the second magnetisable element  191 B along a substantially radial direction relative to the longitudinal axis of the rotor shaft  10  and/or relative to the central axis. Specifically, the second radial magnetic bearing  31 B is implemented as an exemplary homopolar magnetic bearing in the shown embodiment. 
     The second radial magnetic bearing  31 B comprises four second bearing segments  33 B, wherein said second bearing segments  33 B are arranged circumferentially and equally spaced around the central axis and/or the longitudinal axis of the rotor shaft  10  in the operational state of the ventricular assist device  1 . In the exemplary cross-section shown, two second bearing segments  33 B are illustrated. Each of the four second bearing segments  33 B is arranged substantially adjacent the rotor shaft  10 , specifically the second magnetisable element  191 B, in the operational state of the ventricular assist device  1 . 
     Furthermore, the second radial sensor unit comprises a second radial sensor configured to measure a capacitance between each of the second bearing segments  33 B, specifically a magnetic yoke  37 B of the respective second bearing segment  33 B, and the second magnetisable element  191 B. Said second radial sensor will be further explained with respect to  FIGS.  5  to  7   . 
     Furthermore, each of the second bearing segments  33 B comprises a magnetic yoke  37 B arranged adjacent the second magnetisable element  191 B in the operational state of the ventricular assist device  1 . The magnetic yoke  37 B may be at least partially formed from a magnetisable material, such as for example magnetisable stainless steel 1.4016. Additionally, each of the second bearing segments  33 B comprises one second radial magnetic coil  36 B, wherein said second radial magnetic coil  36 B is wound around the magnetic yoke  37 B. 
     A control unit of the ventricular assist device comprises a plurality of control sub-units  35 B, wherein each of the second bearing segments  33 B is provided with one of said control sub-units  35 B. Each control sub-unit  35 B is configured to control a current supplied to the respective second radial magnetic coil  36 B of the respective second bearing segment  33 B to adjustably generate a magnetic force on the second magnetisable element  191 B to adjust the radial position of the second magnetisable element  191 B relative to the second radial magnetic bearing  31 B. Each control sub-unit  35 B is in particular implemented on a printed circuit board, and provided with a control unit cover  34 B. Each control unit cover  34 B is in particular configured to seal the corresponding control sub-unit  35 B from a fluid to be pumped by the ventricular assist device  1 . 
     Furthermore, the four second bearing segments  33 B are substantially identically constructed, and substantially equally spaced in a circumferential direction around the longitudinal axis and/or the central axis. 
     Additionally, the second radial sensor unit comprises a second radial Hall sensor arrangement configured to determine the radial position of the second end section  19 B. In particular, the second radial Hall sensor arrangement comprises a second permanent magnet  193 B fixed to the second end section  19 B, specifically fixed to the second non-magnetisable element  192 B of the second end section  19 B, and at least one second radial Hall sensor  38 B arranged adjacent the second permanent magnet  1936  in a radial direction relative to the longitudinal axis and/or the central axis in the operational state of the ventricular assist device  1 . Said second permanent magnet  193 B fixed to the second non-magnetisable element  192 B of the second end section  19 B is not shown in  FIG.  4 C , but will be further explained with respect to  FIG.  9   . The second radial Hall sensor arrangement comprises four second radial Hall sensors  38 B, wherein the four second radial Hall sensors  38 B are equally spaced in a circumferential direction around the longitudinal axis and/or the central axis in the operational state of the ventricular assist device  1 . Specifically, each second radial Hall sensor  38 B is arranged adjacent to one of the second bearing segments  33 B. 
     The second radial Hall sensor arrangement may further be shielded from the second radial magnetic bearing  31 B by one or more shielding elements arranged between the second radial Hall sensor arrangement and the second radial magnetic bearing  31 B. In particular, each second radial Hall sensor  38 B may be shielded from the respective adjacent second bearing segment  33 B by one or more shielding elements. 
     The second active magnetic bearing  30 B may further also comprise a structural segment ring  60 . The segment ring  60  may be formed for example from a non-magnetisable material. Furthermore, each of the second bearing segments  33 B are fixedly connected to the segment ring  60 . Furthermore, each of the one or more control unit covers  34 B and/or the respective control sub-units  35 B may also be fixedly connected to the segment ring  60 . Finally, the one or more second radial Hall sensors  38 B may also be mounted on said segment ring  60 . The segment ring  60  therefore acts as a mounting platform for components of the second active magnetic bearing  30 B, and may further be fixedly connected to the drive unit  20 . 
       FIG.  5    shows an organ of balance  50  of a pectinid. Specifically, said organ of balance  50  served as the inspiration for the first radial sensor and the second radial sensor. 
     In particular, the organ of balance  50  of the pectinid comprises a fluid-filled central cavity  52 , wherein a movable otolith  54  is arranged. The inner surface of the central cavity  52  is further lined with hair-like receptors  51 , wherein each hair-like receptor  51  is connected to at least one receptor cell  53  of the cavity wall. As the otolith  54  changes position within the central cavity  52 , the otolith  54  comes into contact with one or more of said hair-like receptors  51 , which consequently generate a neural signal. The neural signals are transmitted over the receptor cells  53  and thereto connected neural pathways  55 . Said neural signals are subsequently evaluated by a neural network. 
     Analogous to this, the first radial sensor may, for example, rely on a measured change in capacitance between the first magnetisable element  191 A and a respective first bearing segment  33 A, caused by a movement of the rotor shaft  10  with respect to the first radial sensor. Based on the measured change in capacitance, the first radial sensor consequently determines the position of the first end section  19 A and/or the first magnetisable element  191 A relative to the first radial magnetic bearing  31 A. 
       FIG.  6    shows a schematic view of a first radial sensor unit of the ventricular assist device  1 , wherein the first radial magnetic bearing  31 A is implemented as an exemplary homopolar magnetic bearing in the shown embodiment. 
     In particular, the first radial sensor unit may comprise a first radial sensor configured to measure a capacitance between each of the first bearing segments  33 A and the first end section  19 A, specifically the first magnetisable element  191 A.  FIG.  6    shows two of the four first bearing segments  33 A of the first radial magnetic bearing  31 A. Each first bearing segment  33 A comprises a first magnetic coil  36 A and a magnetic yoke  37 A, wherein the first magnetic coil  36 A is wound around the magnetic yoke  37 A. Furthermore, the magnetic yoke  37 A is separated into two equal halves, wherein said equal halves are separated from one another by an insulating plate  39 A. 
     In particular, the first radial sensor may be configured to measure an absolute value of the capacitance between each of the first bearing segments  33 A and the first magnetisable element  191 A and/or a change of capacitance between each of the first bearing segments  33 A and the first magnetisable element  191 A. Furthermore, the first radial sensor is configured to determine the radial position of the first magnetisable element  191 A based on the measured capacitance between each of the first bearing segments  33 A and the first magnetisable element  191 A. 
     In particular, the rotor shaft  10  is not fixedly connected to the first radial magnetic bearing  31 A and can therefore move in relation to the first radial magnetic bearing  31 A during operation of the ventricular assist device  1 . Specifically, such movement may cause the rotor shaft  10 , in particular the first magnetisable element  191 A, to move closer to one or more first bearing segments  33 A of the four first bearing segments  33 A, while moving away from one or more other first bearing segments  33 A of the four first bearing segments  33 A. In particular, a change in the relative distances between the first magnetisable element  191 A and any of the first bearing segments  33 A causes a change in the capacitance between the first magnetisable element  191 A and the respective first bearing segment  33 A. Specifically, the capacitance may be measured between the two halves of the magnetic yoke  37 A, i.e. at measuring points C 1  and C 2 . Therefore, by measuring the capacitance at measuring points C 1  and C 2  (and the other two corresponding measuring points of the two other first bearing segments not shown) it is possible to determine the distance and/or a change in distance between each of the first bearing segments  33 A and the first magnetisable element  191 A. Based on the determined distance and/or the determined change in distance between each of the first bearing segments  33 A and the first magnetisable element  191 A, it is therefore possible to accurately derive the radial position of the first magnetisable element  191 A relative to the first radial magnetic bearing  31 A. 
     Therefore, the first radial sensor provides four measuring points for the capacitance, while the second radial sensor may provide an additional four measuring points. The equations for determining the radial position of the rotor shaft are therefore an over-constrained system, which allows for an increased accuracy in the determination of said radial position. 
       FIG.  7    shows a schematic view of a first radial sensor unit of the ventricular assist device  1 , wherein the first radial magnetic bearing  31 A is implemented as an exemplary heteropolar magnetic bearing in the shown embodiment, and a corresponding schematic capacitor map. 
     In particular, the first radial sensor unit may comprise a first radial sensor configured to measure a capacitance between each of the first bearing segments  33 A and the first end section  19 A, specifically the first magnetisable element  191 A.  FIG.  7    shows all four of the first bearing segments  33 A of the first radial magnetic bearing  31 A. Each first bearing segment  33 A comprises a first magnetic coil  36 A and a magnetic yoke  37 A, wherein the first magnetic coil  36 A is wound around the magnetic yoke  37 A. Furthermore, each magnetic yoke  37 A is separated from and insulated against its respectively neighbouring magnetic yokes  37 A by four insulating plates  39 A (not shown in  FIG.  7    for simplicity). 
     In particular, the first radial sensor may be configured to measure an absolute value of the capacitance between each of the first bearing segments  33 A and the first magnetisable element  191 A and/or a change of capacitance between each of the first bearing segments  33 A and the first magnetisable element  191 A. Furthermore, the first radial sensor is configured to determine the radial position of the first magnetisable element  191 A based on the measured capacitance between each of the first bearing segments  33 A and the first magnetisable element  191 A. Specifically, the four magnetic yokes  37 A are fixedly arranged in relation to one another, and are furthermore electrically insulated against one another. Therefore, in the shown embodiment, each two neighbouring magnetic yokes  37 A form a first non-variable capacitor CN 1  and a second non-variable capacitor CN 2 , forming a combined non-variable capacitor CN. In particular, the capacitance of the first non-variable capacitor CN 1  and the second non-variable capacitor CN 2  does not change with the movement of the rotor shaft  10  and/or the first magnetisable element  191 A. In particular, insulating plates  39 A may be arranged within each of the first non-variable capacitors CN 1  and/or within each of the second non-variable capacitors CN 2 . 
     In particular, the rotor shaft  10  is not fixedly connected to the first radial magnetic bearing  31 A and can therefore move in relation to the first radial magnetic bearing  31 A during operation of the ventricular assist device  1 . Specifically, such movement may cause the rotor shaft  10 , in particular the first magnetisable element  191 A, to move closer to one or more first bearing segments  33 A of the four first bearing segments  33 A, while moving away from one or more other first bearing segments  33 A of the four first bearing segments  33 A. In particular, a change in the relative distances between the first magnetisable element  191 A and any of the first bearing segments  33 A causes a change in the capacitance between the first magnetisable element  191 A and the respective first bearing segment  33 A. In other words, each of the magnetic yokes  37 A and the first magnetisable element  191 A form a variable capacitor CV. Therefore, by measuring the capacitance across each of the variable capacitor CV, it is possible to determine the distance and/or a change in distance between each of the first bearing segments  33 A and the first magnetisable element  191 A. Based on the determined distance and/or the determined change in distance between each of the first bearing segments  33 A and the first magnetisable element  191 A, it is therefore possible to accurately derive the radial position of the first magnetisable element  191 A relative to the first radial magnetic bearing  31 A. 
       FIG.  8    shows a cross-sectional view of a ventricular assist device  1 , wherein the drive unit  20  has been removed from said ventricular assist device  1 . With respect to components already discussed above, reference is made to the corresponding description sections. 
     The first axial magnetic bearing  32 A comprises a first axial magnetic coil  32 A 1 . The first axial magnetic coil  32 A 1  is arranged adjacent the first magnetisable disk  16 . The first axial magnetic coil  32 A 1  is wound around the longitudinal axis and/or the central axis in the operational state, wherein the first axial magnetic coil  32 A 1  is fixedly connected to the first active magnetic bearing  30 A. In particular, the first axial magnetic coil  32 A 1  is configured such that the rotor shaft  10 , and in particular the non-magnetisable section  190  is rotatable with respect to the first axial magnetic coil  32 A 1 . The control unit, preferentially at least one of the control sub-units  35 A, may be configured to control a current to the first axial magnetic coil  32 A 1  to adjustably generate a magnetic force on the rotor shaft  10  via the first magnetisable disk  16  to adjust the axial position of the rotor shaft  10  along the longitudinal axis and/or the central axis, preferentially based on the determined axial position of the rotor shaft  10 . 
     The first axial magnetic bearing  32 A further comprises a first magnetic pot  32 A 2 . The first magnetic pot  32 A 2  may be formed from any magnetisable material. The first magnetic pot  32 A 2  is configured to contain and/or surround the first axial magnetic coil  32 A 1 , wherein the first magnetic pot  32 A 2  is configured to be open along a surface of the first axial magnetic coil  32 A 1  adjacent the first magnetisable disk  16 . In other words, the first axial magnetic coil  32 A 1  is arranged in the first magnetic pot  32 A 2 , wherein the first magnetic pot  32 A 2  is configured to be open along a surface of the first axial magnetic coil  32 A 1  adjacent the first magnetisable disk  16 . In particular, it is therefore possible to direct and/or orient a magnetic field generated by the first axial magnetic coil  32 A 1 , thereby improving the performance of the first axial magnetic bearing  32 A. 
     The second axial magnetic bearing  32 B comprises a second axial magnetic coil  32 B 1 . The second axial magnetic coil  32 B 1  is arranged adjacent the second magnetisable disk  17 . The second axial magnetic coil  32 B 1  is wound around the longitudinal axis and/or the central axis in the operational state, wherein the second axial magnetic coil  32 B 1  is fixedly connected to the second active magnetic bearing  30 B. In particular, the second axial magnetic coil  32 B 1  is configured such that the rotor shaft  10 , and in particular the non-magnetisable section  190  is rotatable with respect to the second axial magnetic coil  32 B 1 . The control unit, preferentially at least one of the control sub-units  35 B, may be configured to control a current to the second axial magnetic coil  32 B 1  to adjustably generate a magnetic force on the rotor shaft  10  via the second magnetisable disk  17  to adjust the axial position of the rotor shaft  10  along the longitudinal axis and/or the central axis, preferentially based on the determined axial position of the rotor shaft  10 . 
     The second axial magnetic bearing  32 B further comprises a second magnetic pot  32 B 2 . The second magnetic pot  32 B 2  may be formed from any magnetisable material. The second magnetic pot  32 B 2  is configured to contain and/or surround the second axial magnetic coil  32 B 1 , wherein the second magnetic pot  32 B 2  is configured to be open along a surface of the second axial magnetic coil  32 B 1  adjacent the second magnetisable disk  17 . In other words, the second axial magnetic coil  3261  is arranged in the second magnetic pot  3262 , wherein the second magnetic pot  3262  is configured to be open along a surface of the second axial magnetic coil  3261  adjacent the second magnetisable disk  17 . In particular, it is therefore possible to direct and/or orient a magnetic field generated by the second axial magnetic coil  32 B 1 , thereby improving the performance of the second axial magnetic bearing  32 B. 
       FIG.  9    shows a cross-sectional view of a ventricular assist device  1 , as shown in  FIG.  8   , wherein said ventricular assist device further comprises the drive unit  20 . With respect to components already discussed above, reference is made to the corresponding description sections. In particular, for reasons of clarity, reference signs are provided for some features not included in  FIG.  8   . 
     The ventricular assist device  1  comprises an axial sensor arrangement  23  (not marked in  FIG.  9   ) configured to determine an axial position of the rotor shaft  10  along the longitudinal axis and/or the central axis in the operational state. 
     In particular, the axial sensor arrangement  23  comprises a ring-shaped permanent magnet  15  fixed relative to the rotor shaft  10  in a circumferential direction around the rotor shaft  10 . Specifically, in the shown embodiment, the ring-shaped permanent magnet  15  is fixed to the mounting body  12 , and therewith fixed to the rotor shaft  10 . Furthermore, the ring-shaped permanent magnet  15  may be formed from any possible magnetic material. The ring-shaped permanent magnet  15  may be arranged along the rotor shaft  10  at a location in between the impeller  11  and the plurality of permanent drive magnets  13 . 
     The axial sensor arrangement  23  further comprises an axial Hall sensor  23 A arranged adjacent the ring-shaped permanent magnet  15  in a direction parallel to the longitudinal axis, wherein the axial Hall sensor  23 A is configured to determine the axial position of the rotor shaft  10 . 
     In particular, the axial Hall sensor  23 A is fixedly connected to the drive unit  20 , wherein the ventricular assist device  1  is configured such that during rotation of the impeller  11  in the operational state the ring-shaped permanent magnet  15  rotates adjacent to the axial Hall sensor  23 A. Therefore, an axial movement of the rotor shaft  10  along the longitudinal axis and/or the central axis may cause a distance between the axial Hall sensor  23 A and the ring-shaped permanent magnet  15  to change, which causes a change in the magnetic field measured by the axial Hall sensor  23 A. Based on such a measured changed magnetic field and/or change of the magnetic field, the axial Hall sensor  23 A is configured to determine the axial position of the rotor shaft  10 . 
     The drive unit  20  comprises the magnetic motor, wherein the magnetic motor is configured to cause rotation of the impeller  11  around the longitudinal axis. In particular, the magnetic motor of the drive unit  20  comprises a plurality of magnetic coils  24 , preferably six magnetic coils  24 , arranged in a circumferential direction around the rotor shaft  10  in the operational state. In particular, the plurality of magnetic coils  24  are configured to produce a magnetic field to interact with the plurality of permanent drive magnets  13  to cause the rotation of the impeller  11  relative to the longitudinal axis along the rotor shaft  10 . Thereby the magnetic motor is able to adjustably generate a magnetic force on the rotor shaft  10  to control a rotational speed of the impeller  11 . Each of the plurality of magnetic coils may be provided in a recess in the outer body  21  of the drive unit  20 , wherein each of the plurality of magnetic coils  24  is covered in the operational state by a respective access cover  22  of the drive unit. Each access cover  22  may be removably attached to the outer body  21  of the drive unit  20  to substantially seal off the respective recess. 
     The ventricular assist device  1  further comprises a diffusor  70  arranged adjacent the impeller  11 . The diffusor  70  is in particular configured to at least partially reduce and/or remove any swirl produced in a fluid flow caused by the rotation of the impeller  11 . Furthermore, the diffusor as described herein may be further configured aid in the orientation and straightening of the flow generated by the impeller. 
       FIG.  10    shows a FEMM (Finite Element Method Magnetics) simulation result of a magnetic field produced by an exemplary first magnetic bearing segment  33 A, having a first axial magnetic coil  36 A (both the upper cross-section and the lower cross-section of the first axial magnetic coil have been labelled with  36 A) wound around a first magnetic yoke  37 A, on a first magnetisable element  191 A. For the purposes of the simulation, the first magnetic yoke  37 A and the first magnetisable element  191 A are simulated as being formed from magnetisable stainless steel type 1.4016. Furthermore, for the purposes of the simulation, the first axial magnetic coil  36 A comprises 450 windings of copper wire having a wire thickness of 0.5 mm, wherein the first axial magnetic coil  36 A has a depth of 15 mm, and wherein a current of 1 A is passed through the first axial magnetic coil  36 A. Specifically, the simulation determined a net force on the first magnetisable element  191 A of 22.1574 Newton along the y-direction of the coordinate system shown in  FIG.  10   . Furthermore, the simulation determined a net force on the first magnetic element  191 A of −0.005048 Newton along the x-direction of the coordinate system shown in  FIG.  10   . Therefore, the exemplary first magnetic bearing segment  33 A is shown to be able to generate a sufficient magnetic force on the rotor shaft  10  and/or the first magnetisable element  191 A to adjust a radial position of the first magnetisable element  191 A and/or the rotor shaft  10  relative to the first active magnetic bearing  30 A. In particular, the exemplary first magnetic bearing segment  33 A can generate said sufficient magnetic force in the y-direction, while substantially not generating a perpendicular force on the first magnetisable element  191 A. 
       FIG.  11    shows a cross-sectional view of a fluid flow  1000  through a ventricular assist device  1 , wherein only the rotor shaft  10  and the drive unit  20  are shown for simplicity. In particular, the fluid flow  1000  is herein represented by the black flow field, while inflow  1001  is schematically represented by two arrows on the left-hand side of  FIG.  11    and outflow  1002  is schematically represented by two arrows on the right-hand side of  FIG.  11   . 
     Specifically, the geometry of the ventricular assist device  1  is configured such that the flow field  1000  of a fluid pumped by the ventricular assist device  1  through the ventricular assist device  1  in the operational state does not comprise any dead water zones. In particular, said dead water zones are specifically prevented in the ventricular assist device  1  due to the ventricular assist device  1  being configured to have a geometry such that the fluid pumped by the ventricular assist device  1  does not flow over any sharp edges of the ventricular assist device  1 . Thereby, a shear strain on the fluid to be pumped is further significantly reduced, thus causing less damage to live particles in said fluid. 
       FIG.  12    shows the fluid field  1000  of  FIG.  11    as a perspective, cross-sectional  3 D flow body. Specifically, the consistently smooth shape of the flow field  1000  can easily be observed. 
       FIG.  13    shows a cross-sectional view of an exemplary ventricular assist device  1  after implantation into a lumen L of a blood vessel, such as a vein or artery. In particular, the blood vessel may for example be an aorta or pulmonary artery of a user. 
     In particular, the ventricular assist device  1  has been fully implanted into the lumen L of the blood vessel. Specifically, the ventricular assist device  1  has been implanted into the lumen L of the blood vessel, such that the ventricular assist device  1  is fully enclosed in said lumen L. Furthermore, the ventricular assist device  1  is configured to wirelessly and transcutaneously receive power and/or transmission signals from outside the lumen L of the blood vessel. In particular, the ventricular assist device  1  does not comprise a physical connection, such as a wire connection, through the walls W of the blood vessel. 
     The ventricular assist device  1  furthermore comprises two exemplary attachment grooves  41  on an outer surface of the ventricular assist device  1 . Each of the two attachment grooves  41  extends fully around the ventricular assist device  1  in a circumferential direction relative to the central axis. However, the invention is not to be restricted to such a number of possible attachment grooves  41 . In particular, the ventricular assist device  1  may comprise one, two, or more attachment grooves  41 , wherein the number of attachment grooves  41  may be adapted to specific requirements for the ventricular assist device  1 , such as a shape and/or wall thickness of the lumen in which the ventricular assist device  1  is to be implanted. 
       FIG.  13    further shows two fixing elements  40 , wherein said fixing elements  40  may each be a wire or tie. In particular, the two fixing elements  40  are configured to at least partially compress the wall W of the blood vessel between the ventricular assist device  1  and the respective fixing element  40 . Specifically, each of the two fixing elements  40  is arranged adjacent to one of the two attachment grooves  41 , such that the two fixing elements  40  are configured to at least partially compress the wall W of the blood vessel in the respective attachment groove  41  of the ventricular assist device  1 , thereby preventing the ventricular assist device  1  from moving along the lumen L of the blood vessel. 
       FIG.  14    shows a perspective view of an exemplary impeller  11  of the ventricular assist device  1  having an exemplary impeller geometry. Specifically, for illustrative purposes, the impeller  11  of  FIG.  14    is shown separate from the rotor shaft  10 . 
     In particular, the impeller  11  may be formed on or connected to the rotor shaft  10 . The impeller  11  may comprise a plurality of first impeller vanes  11 A at a first end of the impeller  11 . The plurality of first impeller vanes  11 A may in particular be configured such that during rotation of the impeller  11  (in the shown example in the clockwise direction when viewed from the first end of the impeller  11 ) a fluid, in which the impeller  11  is placed, is pumped from the first end of the impeller  11  towards a second end of the impeller  11 . 
     Furthermore,  FIG.  14    shows a perspective view of an exemplary diffusor  70  having an exemplary diffusor geometry, wherein the diffusor  70  may be arranged adjacent the impeller  11 . In particular, the diffusor  70  may be formed around the rotor shaft  10 , wherein the diffusor  70  may be configured to be static with respect to the rotor shaft  10  and the impeller  11 . In particular, the diffusor  10  may be fixedly connected to the drive unit  20  and/or one or more components of the drive unit  20 . In other words, the diffusor  70  may be configured to be static relative to the impeller  11  even during rotation of the impeller  11 . Therefore, in particular, the exemplary diffusor  70  may be physically separate from the exemplary impeller  11 . Furthermore, the diffusor  70  may be formed around the rotor shaft  10 , wherein the diffusor  70  may comprise a base body  72 , wherein the base body  72  may be configured to have a substantially hollow cylindrical shape. In particular, in an operational state of the ventricular assist device  1  the rotor shaft  10  may be at least partially arranged within the base body  72 . In particular, the base body  72  may further be configured such that a fluid pumped by the impeller  11  is prevented from coming into direct, physical contact with the rotor shaft  10  at least while flowing through the diffusor  70 . 
     The exemplary diffusor  70  may comprise one or more stator vanes  71 . The exemplary geometry of the diffusor  70  and/or a geometry of the stator vanes  71  may in particular be configured to at least partially reduce and/or minimize swirl and/or turbulent flow produced in a fluid flow caused by the rotation of the impeller  11 . Furthermore, the exemplary geometry of the diffusor  70  and/or a geometry of the stator vanes  71  may be configured to cause a lowest possible total pressure loss and/or a highest possible static pressure gain of a fluid pumped by the ventricular assist device  1 . The one or more stator vanes  71  may be fixedly connected to the base body  72 . 
     Furthermore, in the shown embodiment, a number of stator vanes  71  is different from a number of impeller vanes  11 A. Specifically, in the shown example, the number of stator vanes  71  is seven and the number of impeller vanes  11 A is six. However, the invention is not to be restricted to such a ratio. In particular, the number of stator vanes  71  may be larger or smaller than the number of impeller vanes  11 A. 
     Furthermore, the number of stator vanes  71  may be identical to the number of impeller vanes  11 A. 
     The shown impeller geometry and the shown diffusor geometry is to be understood as exemplary. Specifically, a plurality of different impeller and diffusor geometries may be implemented. 
       FIG.  15    shows a coordinate system highlighting a difference between an ideal permanent magnet and a commonly produced permanent magnet. 
     In particular, for the shown example, both the ideal permanent magnet and the commonly produced permanent magnet are cylindrically shaped. However, for clarity of the figure, neither one of the magnets is shown in  FIG.  15   . Furthermore, both the ideal permanent magnet and the commonly produced permanent magnet are centred on the origin of the shown coordinate system, such that an axis of both the ideal permanent magnet and the commonly produced permanent magnet is perpendicular to the coordinate axes shown. 
     In particular, the ideal permanent magnet produces a magnetic field that is circular symmetric around the axis of the shown ideal permanent magnet, as represented by the dashed circular trace T 1 . However, commonly produced permanent magnets often contain one or more defects, which cause a distortion of a magnetic field generated by the commonly produced permanent magnet, as represented by the solid trace T 2 , when compared to the magnetic field generated by the ideal permanent magnet. 
     When such a commonly produced permanent magnet is used as a sensor magnet, for example in combination with a Hall sensor, such distortions may result in errors in the measurement signal of the respective sensor. However, this may be addressed by using calibration data, as discussed above, wherein the calibration data may comprise a shape and/or strength of the magnetic field of the commonly produced permanent magnet. The respective sensor may in particular be configured to use the calibration data to account for and thereby compensate possible distortions of the magnetic field. 
     The embodiments described herein and/or shown in the appended Figures are not to be interpreted as limiting the scope of the invention. Therefore, for example, a ventricular assist device may comprise any combination of features described herein and/or shown in the appended Figures. 
     LIST OF REFERENCE NUMERALS 
     
         
         
           
               1  Ventricular assist device 
               10  Rotor shaft 
               11  Impeller 
               11 A Impeller vanes 
               12  Mounting body 
               13  Permanent drive magnet 
               14  Bracket 
               15  Ring-shaped permanent magnet 
               16  First magnetisable disk 
               17  Second magnetisable disk 
               19 A First end section 
               19 B Second end section 
               190  Non-magnetisable section 
               191 A First magnetisable element 
               191 B Second magnetisable element 
               192 A First non-magnetisable element 
               192 B Second non-magnetisable element 
               193 A First permanent magnet 
               193 B Second permanent magnet 
               20  Drive unit 
               21  Outer body 
               22  Access cover 
               23  Axial sensor arrangement 
               23 A Axial Hall sensor 
               24  Plurality of magnetic coils 
               30 A First active magnetic bearing 
               30 B Second active magnetic bearing 
               31 A First radial magnetic bearing 
               31 B Second radial magnetic bearing 
               32 A First axial magnetic bearing 
               32 B Second axial magnetic bearing 
               32 A 1  First axial magnetic coil 
               32 B 1  Second axial magnetic coil 
               32 A 2  First magnetic pot 
               32 B 2  Second magnetic pot 
               33 A First bearing segment 
               33 B Second bearing segment 
               34 A,  34 B Control unit cover 
               35 A Control sub-unit 
               36 A First radial magnetic coil 
               36 B Second radial magnetic coil 
               37 A,  37 B Magnetic yoke 
               38 A First radial Hall sensor 
               38 B Second radial Hall sensor 
               40  Fixing elements 
               41  Attachment grooves 
               50  Organ of balance 
               51  Hair-like receptor 
               52  Central cavity 
               53  Receptor cell 
               54  Otolith 
               55  Neural pathway 
               60  Structural segment ring 
               70  Diffusor 
               71  Stator vanes 
               72  Hollow cylindrical base body 
               1000  Fluid flow 
               1001  Inflow 
               1002  Outflow 
             C 1 , C 2  Measuring point 
             CN, CN 1 , CN 2  Non-variable capacitor 
             CV Variable capacitor 
             L Lumen 
             T 1 , T 2  Trace 
             W Wall