Abstract:
A sensor for a contactless electrocardiographic measurement of a person includes an electrode formed of a moisture-permeable material and having a measurement surface and an opposite surface. A moisture generator supplies moisture to the opposite surface, and a moisture sensor detects a moisture content of a microclimate at the measurement surface. A controller receives signals from the moisture sensor and activates the moisture generator based upon the signals to control the moisture content. The moisture generator may be a heating element heating a source of moisture; a pump activated pumping liquid from a reservoir to the electrode; an ultrasonic atomizer for atomizing liquid contained in a reservoir; an actuator varying an amount of a liquid-conducting material in contact with liquid contained in a reservoir; or a Peltier element operable to warm and thereby release moisture from a moisture-storing material adjacent to the electrode.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims foreign priority benefits under 35 U.S.C. §119(a)-(d) to DE 102013219026.3 filed Sep. 23, 2013, which is hereby incorporated by reference in its entirety 
       TECHNICAL FIELD 
       [0002]    The present invention relates to contactless electrocardiographic measurement of a person seated in a motor vehicle, and more specifically to a contactless electrocardiographic sensor having a moisture generator operative to increase the moistness of a microclimate adjacent to the measurement surface of the sensor. 
       BACKGROUND 
       [0003]    Measurement of the electrical potential, or electrical field strength, on the skin of a person by means of electrocardiographic sensors forms the basis of many medical diagnostic methods. In this way, for example, an electrocardiogram (ECG) may be recorded or the heart rate may be determined from the measured electrical potentials. 
         [0004]    In conventional measurement methods for measuring the electrical potential on the skin, the latter is acquired by electrodes which are in direct electrical contact with the surface of the skin. An electrically conductive connection is thus established between the skin, on the one hand, and the electrode, on the other hand. In this case, however, it often proves difficult to ensure a sufficiently good electrical contact between the electrode and the skin, and therefore the body of the person being examined (the subject). Furthermore, the use of such diagnostic methods is also increasingly being provided in application fields in which direct access to the skin of the subject is not available, for example in vehicle applications for monitoring body functions and/or vital parameters of vehicle passengers on seats or bunks. 
         [0005]    For example, U.S. Pat. No. 7,684,854 B2 discloses a sensor for contactless electrocardiographic measurement on a person. The person may in this case be on a stool, in a bed or on a vehicle seat. The electrocardiogram can be recorded from the body of the person wearing clothing without direct contact with the skin. The sensor comprises a flat electrically conductive electrode which comprises a measurement surface facing toward the person and a connection surface which faces away from the person, lies opposite the measurement surface and is electrically connected to a preamplifier. The electrode and the preamplifier of the sensor are enclosed by shielding. 
         [0006]    Another contactless sensor for recording an electrocardiogram of a person is disclosed by EP 2 532 306 A1. The sensor comprises an electrically conductive electrode and a detection device, which is electrically connected to the electrode and is configured in order to amplify the signals received by the electrode. The sensor is intended to be arranged in a vehicle seat and to determine particular physiological parameters of a driver sitting on the vehicle seat. 
         [0007]    DE 20 2012 001 096 U1 discloses capacitive sensors for capacitive recording of vital parameters of a driver of a vehicle. To this end, the sensors are fitted in or on the backrest of the seat of the vehicle. In particular, according to one embodiment it is proposed to arrange the sensors in or on the backrest of the seat while being distributed in two rows separated by a distance corresponding to the width of the spinal column of the driver. In each row, the sensors, with an area of from 16 to 36 cm 2 , are arranged at equal distances of from 1 to 5 cm from one another. In another embodiment, instead of the two separate sensor rows with sensors distributed over the entire height of the seat at a distance of 1-5 cm, two membrane sensors with a width of from 4 to 10 cm are arranged over the entire seat height with a separation corresponding to the spinal column. 
         [0008]    Furthermore, DE 10 2008 049 112 A1 discloses a capacitive textile electrode for measuring body functions and/or vital parameters of persons for vehicle applications, for example in a seat or a bunk, which electrode has a multilayer structure. This comprises two textile layers, each of which has an electrically conductive electrode region, a further textile layer being provided in order to establish a distance between the other two textile layers. 
         [0009]    In general, the electrical conductivity of any clothing (or other material) between the skin of the person and the electrode plays an important role in the signal quality obtained during contactless electrocardiographic measurement. By way of example, when a person gets on/in a vehicle, some period of time may be required until the electrocardiographic sensor is able to record a reliable signal. This is due both to any electrostatic charge of the clothing and the low contact conductance thereof. The electrostatic charge may be discharged relatively slowly, as a result of which the electrostatic charge dominates and attenuates or covers the measurement signal. In general, the conductivity between the skin of the person to be examined and the electrode is substantially influenced by the moisture content of the clothing of the person situated therebetween. The moisture content of the clothing is in turn determined by the microclimate between the electrode surface and the skin of the person to be examined. Thus, for example, it may be the case in a dry surrounding climate, for example in a dry vehicle interior, that the clothing is likewise relatively dry. On the other hand, sweating by the person to be examined leads to a more moist or humid microclimate between the skin of the person and the electrode, leading to an improved signal quality. 
       SUMMARY 
       [0010]    The present disclosure is based on the object of specifying a sensor, a sensor array and a seat or a couch for a contactless electrocardiographic measurement of persons, preferably in the context of vehicle applications, by means of which reliable statements can be made about the bodily functions and/or vital parameters of the person, i.e. which are able to supply a reliable signal with high signal quality at all times. 
         [0011]    It should be noted that the features specified individually in the claims may be combined with one another in any desired technologically meaningful way and disclose further embodiments of the invention. The description, in particular in conjunction with the Figures, characterizes and specifies the invention further. 
         [0012]    According to the invention, a sensor for a contactless electrocardiographic measurement of a person comprises at least one electrically conductive, planar electrode, which comprises an outer or measurement surface facing the person and an opposite, inner surface facing away from the person and lying opposite to the outer surface. Within the meaning of the present invention, “contactless” should be understood to mean that the electrode does not come into direct contact with the skin of the person to be examined (the subject). By way of example, pieces of clothing may be arranged between the subject and the electrode. The electrode may also be electrically insulated from the subject by a layer of insulation lacquer. 
         [0013]    Furthermore, provision is made for a moisture generator on the side of the inner surface of the electrode. Moreover, the electrode is permeable to moisture. In principle, any means or any device capable of releasing moisture under certain conditions, for example in the form of vapor or liquid droplets, may be used as a moisture generator. In this manner it is possible to automatically control the moisture content of the microclimate between the outer surface of the electrode and the skin of the subject, in particular in conjunction with a measurement and regulation apparatus. In particular, moisture which is able to penetrate the moisture-permeable electrode and thus increases the moisture content of the microclimate is released by the moisture generator in the case of a microclimate which is too dry. The moister microclimate improves the signal quality of the measurement signal recorded by the sensor since electrostatic charges can be discharged more quickly. Furthermore, a reliable measurement signal is obtained more quickly by the sensor according to the invention. 
         [0014]    In accordance with an advantageous embodiment disclosed herein, the sensor moreover comprises at least one moisture sensor arranged on the inner surface of the electrode and a controller. The moisture sensor is connected to the controller and acquires the moisture content on the inner surface of the electrode. Furthermore, the controller is configured to control the moisture generator by means of an actuator, depending on the values acquired by the moisture sensor. Accordingly, the controller can cause the moisture generator to release more or less moisture. Thus, a desired moisture content of the microclimate between the outer surface of the electrode and the skin of the subject can be controlled or regulated in a targeted manner. Here, the control, regulation and measurement functions required for this are assumed by the controller. 
         [0015]    A sensor array according to the invention comprises at least two sensors of the type described above. Within the meaning of the present invention, a sensor array should be understood to mean any type of arrangement of a plurality of said sensors. 
         [0016]    In accordance with the present invention, a seat or a couch in a vehicle comprises at least one sensor array of the type according to the invention, as described above, for a contactless electrocardiographic measurement of a person situated on the seat or on the couch. 
         [0017]    Further features and advantages of the invention emerge from the following description of exemplary embodiments of the invention which are not to be understood as being restrictive and which will be explained in greater detail in the following text, with reference being made to the drawing. In detail: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  schematically shows a sensor array and a seat for a vehicle according to the prior art, 
           [0019]      FIG. 2  schematically shows a sensor according to the invention in accordance with a first embodiment, 
           [0020]      FIG. 3  schematically shows a magnified view of the sensor of  FIG. 2 , 
           [0021]      FIG. 4  schematically shows a sensor according to the invention in accordance with another embodiment, 
           [0022]      FIG. 5  schematically shows a sensor according to the invention in accordance with a further embodiment, 
           [0023]      FIG. 6  schematically shows a sensor according to the invention in accordance with a further embodiment, 
           [0024]      FIG. 7  schematically shows a sensor according to the invention in accordance with a further embodiment, 
           [0025]      FIG. 8  schematically shows a sensor according to the invention in accordance with a further embodiment, 
           [0026]      FIG. 9  schematically shows a sensor according to the invention in accordance with a further embodiment, 
           [0027]      FIG. 10  schematically shows a sensor according to the invention in accordance with a further embodiment, 
           [0028]      FIG. 11  schematically shows a sensor according to the invention in accordance with a further embodiment, 
           [0029]      FIG. 12  schematically shows a sensor according to the invention in accordance with a further embodiment, and 
           [0030]      FIG. 13  schematically shows a sensor according to the invention in accordance with a further embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The Figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
         [0032]      FIG. 1  schematically represents a sensor array  20  and a seat  21  for a vehicle for contactless electrocardiographic measurement on a person or subject  22 , according to the prior art. As can be seen, the sensor array consists of a matrix arrangement of six sensors  23  arranged in a 3×2 matrix in a backrest of a vehicle seat, each of which sensors comprises a flat electrically conductive electrode  24 . Another electrode, via which a reference potential is applied to the circuit, is furthermore arranged in the seat surface of the vehicle seat  21 . 
         [0033]    Each electrode  24  comprises an outer or measurement surface  25  facing toward the subject  22 , and an inner or connection surface  26 , facing away from the person and opposite the measurement surface  25 , for the connection of a measuring device  27 . As represented in  FIG. 1 , the measurement surface  25  of the individual electrodes  24  does not directly touch the skin of the subject  22 . Rather, insulation  28  is applied on the measurement surface  25  of each electrode  24  in  FIG. 1 . Furthermore, the clothing  29  worn by the subject person also lies between the subject  22  and the measurement surface  25 . 
         [0034]    The measuring device  27  represented in  FIG. 1  comprises one preamplifier  31 , enclosed by shielding  30 , per sensor  23 . Furthermore, an instrument amplifier  32  amplifies the measurement signal registered by the electrodes  24  of the sensors  23 , followed by a filtering and amplification unit  33  as well as an A/D converter  34 . The digital measurement signal output by the A/D converter  34  may then be processed further in a suitable way, for example by means of a digital computer unit  35 . 
         [0035]      FIG. 2  schematically depicts a control loop for a sensor  36  according to a first embodiment of the invention. The sensor  36  comprises an electrically conductive, planar and moisture-permeable electrode  37 , which comprises a measurement or outer surface  38  facing the person to be examined (the subject) and an inner surface  39  facing away from the subject and opposite from the outer surface  38 . Moreover, the sensor  36  comprises a moisture generator  40  (not explicitly depicted in  FIG. 2 ), which is provided on the side of the inner surface  39  of the sensor  36 . Different embodiments of moisture generators  40 , which are all able to release moisture under certain conditions, for example in the form of liquid vapor or liquid droplets, will still be described in more detail below in conjunction with the remaining Figures. 
         [0036]    As is understood from  FIG. 2 , the control loop in the depicted exemplary embodiment comprises a moisture sensor  41  arranged on the electrode inner surface  39  and an (optional) temperature sensor  42  likewise arranged on the electrode inner surface  39 . Both sensors  41  and  42  are connected to a controller  43 , which controls the moisture generator  40  by means of an actuator  44 . Accordingly, the controller  43  causes the moisture generator  40  to release more or less moisture, depending on the values determined by the sensors  41  and  42 . Thus, a desired moisture content of the microclimate between the electrode outer surface  38  and the skin of the subject can be controlled or regulated in such a targeted manner that a reliable electrocardiographic measurement signal of the sensor  36  is obtained with good signal quality. 
         [0037]      FIG. 3  depicts an embodiment of the sensor  36  from  FIG. 2  in a magnified view. In particular,  FIG. 3  depicts a possible embodiment of the moisture generator  40  in a detailed manner. The moisture generator  40  here comprises a chamber  45  containing a substance  46  which can store moisture and which can emit moisture when heated. By way of example, silica gel or a super absorbent polymer can be used as such a substance. A plurality of heating elements  47  arranged in the chamber  45  can be identified in  FIG. 3 . In the depicted embodiment, the heating elements  47  are completely surrounded by substance  46 , and so said elements can heat the latter. Moreover, further temperature sensors  42 , which can serve to avoid overheating within the chamber  45 , are arranged between the heating elements  47 . A spacer layer  48  which is able to transmit the moisture emitted by the moisture-storing substance may be inserted between the chamber  45  and the inner surface  39  of the electrode  37 . 
         [0038]    Although not depicted in  FIG. 3 , the moisture sensor  41  and the temperature sensors  42  are connected to the controller  43  as described in relation to  FIG. 2 . The controller controls the heating elements  47 , which form the actuator  44  of the moisture generator  40  depicted in  FIG. 2 , in such a way that more or less moisture is released by the moisture generator  40 , depending on the values established by the sensors  41  and  42 . Thus, the moisture content of the microclimate between the outer surface  38  of the electrode  37  and the skin of the subject is controlled or regulated in such a targeted manner that a reliable electrocardiographic measurement signal with good signal quality is recorded via the outer surface  38  of the electrode  37 . 
         [0039]      FIG. 4  depicts a sensor  49  according to the invention in accordance with another embodiment. The sensor  49  substantially differs from the sensor  36  depicted in  FIG. 3  in terms of the arrangement of the heating elements  47 . In the sensor  49  depicted in  FIG. 4 , the heating elements  47  are arranged on the rear walls and the side walls of the chamber  45 , and so there is rear side and lateral heating of the chamber  45  filled with the substance  46  by means of the heating elements  47 . It is likewise feasible to provide only the rear-side of the chamber  45  or only the side walls of the chamber  45  with heating elements  47 . Further temperature sensors  42  can likewise be provided in the chamber  45  and/or on the heating elements  47 , so as to avoid overheating of the heating elements  47  or of the chamber  45 . In the same manner as described above in the explanation of  FIG. 3 , the sensor  49  can also be controlled or regulated by a controller  43 , as depicted in  FIG. 2 , in conjunction with the sensors  41  and  42  and the actuator  44 . 
         [0040]      FIG. 5  depicts a further sensor  50  in accordance with a further embodiment in which the moisture generator  40  comprises a liquid reservoir  51  and at least one heating element  47  which heats the liquid reservoir  51 . Vapor is generated in the liquid reservoir  51  with the aid of the heating element  47 . The vapor passes through a cavity  52  provided between the inner surface  39  and the reservoir  51 . Cavity  52  may contain a vapor-permeable material to conduct the vapor from the reservoir  51  to the inner surface  39  of the electrode  37 . 
         [0041]    Although this has not been depicted in  FIG. 5 , the moisture sensor  41  and the temperature sensor  42  are connected to the controller  43  as described in relation to  FIG. 2 . The controller controls the heating element  47 , which forms the actuator  44  of the moisture generator  40  depicted in  FIG. 2 , in such a way that more or less moisture is released by the moisture generator  40 , depending on the values established by the sensors  41  and  42 . Thus, the moisture content of the microclimate between the outer surface  38  of the electrode  37  and the skin of the subject is controlled or regulated in such a targeted manner that a reliable electrocardiographic measurement signal with good signal quality is recorded via the outer surface  38  of the electrode  37 . 
         [0042]      FIG. 6  depicts a further sensor  53  according to a further embodiment in which the moisture generator  40  comprises a liquid reservoir  51  and a pump  54  which pumps liquid from the reservoir  51 . The water pumped from the reservoir  51  the pump  54  is conducted to the electrode inner surface  39  by a material  55  which can conduct or wick liquid, e.g. a sponge, such that said inner surface is moistened. 
         [0043]    Although this has not been depicted in  FIG. 6 , the moisture sensor  41  is connected to the controller  43  described in relation to  FIG. 2 . The controller controls the pump  54 , which forms the actuator  44  of the moisture generator  40  depicted in  FIG. 2 , in such a way that more or less moisture is released by the moisture generator  40 , depending on the values established by the moisture sensor  41 . Thus, the moisture content of the microclimate between the outer surface  38  of the electrode  37  and the skin of the subject is controlled or regulated in such a targeted manner that a reliable electrocardiographic measurement signal with good signal quality is recorded via the outer surface  38  of the electrode  37 . 
         [0044]    A sensor  56  according to a further embodiment is depicted in  FIG. 7  wherein the material  55  which can conduct or wick liquid, preferably a sponge, is permanently dipped into the reservoir  51 . The sponge  55  conducts the liquid from the reservoir  51  to the inner surface  39  of the electrode  37 . In the exemplary embodiment depicted in  FIG. 7 , the moisture sensor  41  merely has a monitoring function. In this exemplary embodiment, there is no control or regulation of the release of moisture by the moisture generator. 
         [0045]    By contrast, such a control or regulation is made possible in the additional exemplary embodiment of a sensor  57  as depicted in  FIG. 8 . In this case, the actuator  44  serves to dip the material  55  which can conduct liquid, for example a sponge, to a greater or lesser extent into the liquid reservoir  51 , depending on the degree of the desired moisture emission by the moisture generator  40 . By way of example, the actuator  44  is able to move the sponge  55  or the liquid reservoir  51  along the movement trajectory  58  depicted in  FIG. 8 , and therefore able to determine the dipping-in depth of the sponge  55  in the liquid reservoir  51 . 
         [0046]    Although this has not been depicted in  FIG. 8 , the moisture sensor  41  is connected to the controller  43  described in relation to  FIG. 2 . The controller controls the actuator  44  of the moisture generator  40  in such a way that more or less moisture is released by the moisture generator  40 , depending on the values established by the moisture sensor  41 . Thus, the moisture content of the microclimate between the outer surface  38  of the electrode  37  and the skin of the subject is controlled or regulated in such a targeted manner that a reliable electrocardiographic measurement signal with good signal quality is recorded via the outer surface  38  of the electrode  37 . 
         [0047]      FIG. 9  depicts another embodiment of a sensor  59  in which the moisture generator  40  comprises a liquid reservoir  51  and at least one ultrasonic atomizer  60 , which forms the actuator  44  of the moisture generator  40 . The ultrasonic atomizer  60  atomizes the liquid stored in the liquid reservoir  51  and conducts the liquid mist to the inner surface  39  of the electrode  37  such that the latter is moistened as a result thereof. By controlling the ultrasonic atomizer  60  by means of the controller  43  (not depicted in  FIG. 9 ) and by means of the sensors  41  and  42  ( FIG. 2 ) (likewise not depicted here), it is possible to release more or less moisture by the moisture generator  40 . Thus, the moisture content of the microclimate between the outer surface  38  of the electrode  37  and the skin of the subject is controlled or regulated in such a targeted manner that a reliable electrocardiographic measurement signal with good signal quality is recorded via the outer surface  38  of the electrode  37 . 
         [0048]    In the additional exemplary embodiment of a sensor  61  depicted in  FIG. 10 , the liquid mist generated by at least one ultrasonic atomizer  60  is not conducted to the inner surface  39  of the electrode  37  (as in  FIG. 9 ), but rather directly in the direction of the subject by the sensor  61  or their clothing through openings  62  provided in the electrode  37 . Here, the ultrasonic atomizer  60  is once again controlled as described above by means of the controller  43  ( FIG. 2 ) (not depicted in  FIG. 10 ). 
         [0049]    Instead of the ultrasonic atomizer  60  used in the sensors  59  and  61 , use can for example likewise be made of a pump and a spray nozzle as actuators  44  of the moisture generator  40 . 
         [0050]      FIG. 11  depicts a further embodiment of a sensor  63  in which the moisture generator  40  comprises at least one Peltier element  65  and a material  64  which is both permeable to air and able to store moisture. The air-permeable moisture-storing material  64  is arranged adjacent to the electrode inner surface  37 . The Peltier element  65  is arranged adjacent to the air-permeable moisture-storing material  64 . In the exemplary embodiment depicted in  FIG. 11 , a cooling body  66  is moreover arranged adjacent to the Peltier element  65 . The cooling body  66  serves to supply heat to, or dissipate heat from, the Peltier element  65 . 
         [0051]    The inner surface  39  of the electrode  37  is moistened by alternately a) cooling the air-permeable moisture-storing material  64 , whereby water is obtained by condensation from an air flow  67  passing through the cooled material  64 , and b) heating the material  64  to release the condensed water stored in the material  64 . The heating and cooling is brought about by the Peltier element  65 . 
         [0052]    Here, the material which can store moisture can also be separated laterally from the surroundings; in this case, the regeneration is brought about by moisture or a moisture-containing air flow passing through the electrode permeable to moisture. 
         [0053]    The process of obtaining water at the air-permeable moisture-storing material  64  can additionally be supported by a ventilator  68 , as is depicted in the exemplary embodiment of the sensor  63  as shown in  FIG. 12 . Here, the application of surrounding air to the material  64  is performed by the ventilator  68  and preferably is only carried out when obtaining water, i.e. in the cooling phase of the Peltier element  65 . When releasing the water stored in the material  64  by heating by means of the Peltier element  65 , the ventilator  68  is not operating so there is no application of surrounding air. 
         [0054]    The Peltier element  65  is once again controlled by means of the controller  43  ( FIG. 2 ) (not depicted in  FIG. 12 ), as a result of which more or less moisture can be released by the moisture generator  40 . Thus, the moisture content of the microclimate between the outer surface  38  of the electrode  37  and the skin of the subject is controlled or regulated in such a targeted manner that a reliable electrocardiographic measurement signal with good signal quality is recorded via the outer surface  38  of the electrode  37 . 
         [0055]      FIG. 13  depicts a further exemplary embodiment of a sensor  69  in which the moisture generator  40  comprises a compressible material  70  which can store water, for example a sponge, and a displacement apparatus  71 , which is e.g. motor driven, for pressing the compressible water-storage material  70  against the inner surface  39  of the electrode  37 , which is moistened to a greater or lesser extent depending on the contact pressure applied against the inner surface  39 . By way of example, the contact pressure can be measured by a force sensor  72  arranged between the compressible water-storage material  70  and the displacement apparatus  71 . The force sensor  72  is expediently connected to the controller  43  ( FIG. 2 ) (not depicted in  FIG. 13 ), which in turn controls the displacement apparatus  71  of the moisture generator  40  in such a way that more or less moisture can be released by the moisture generator  40  depending on the values established by the force sensor  72 . Thus, the moisture content of the microclimate between the outer surface  38  of the electrode  37  and the skin of the subject is controlled or regulated in such a targeted manner that a reliable electrocardiographic measurement signal with good signal quality is recorded via the outer surface  38  of the electrode  37 . 
         [0056]    Once again, various options are feasible for moistening the water-storage material  70 , for example the already described option by means of a pump and a water reservoir. 
         [0057]    The sensor according to the invention, the sensor array and the seat or the couch were explained in more detail on the basis of several exemplary embodiments depicted in the Figures. However, the sensor, the sensor array and the seat or couch are not restricted to the embodiments described herein, but rather also comprise further embodiments with the same effect. 
         [0058]    In a preferred embodiment, the sensor according to the invention, the sensor array and the seat or the couch are used in a vehicle, in particular in a motor vehicle, for a contactless electrocardiographic measurement of a person. 
         [0059]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.