Abstract:
A detection device for detecting a blood count parameter of a blood component in a blood vessel comprising a transmitter, a receiver, a loss detector, and a processor. The transmitter injects a first transmit signal into the blood vessel at a first frequency and a second transmit signal into the blood vessel at a second frequency. The receiver receives a first receive signal at the first frequency and a second receive signal at the second frequency. The loss detector determines a first loss value on the basis of the first transmit signal and the first receive signal, and determines a second loss value on the basis of the second transmit signal and the second receive signal. The processor determines a relaxation time constant of the blood component in accordance with the frequency having the greater loss value, and determines the blood count parameter in accordance with the determined relaxation time constant.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the field of detecting a concentration of a blood constituent, for example sugar in blood flowing through a blood vessel. 
     2. Related Technology 
     In order to ascertain a blood picture parameter, such as, for example, a concentration of a blood constituent, blood can be taken invasively. The blood picture parameter can then be ascertained using the taken blood by means of standardized test strips, the electric resistance values of which depend on the concentration of the blood constituent, e.g. blood sugar. By way of example, the respective electric resistance value can be detected using a blood sugar measuring instrument, which carries out a DC current resistance measurement for detecting an electric resistance value of a test strip. The resistance value can be converted into a blood sugar concentration on the basis of a relationship, known per se, between a blood sugar concentration and a resistance value. In order to obtain high detection accuracy, each test strip is provided with calibration data, for example with a reference resistance value or with a corresponding code, as a result of which variations of properties of the test strips can be compensated for. However, a disadvantage of invasive methods is the necessity of taking blood and hence of injuring a patient. Moreover, continuous detection of a concentration of a blood constituent, for example to establish the diurnal variation curve thereof, is complicated. Furthermore, it is not possible to detect a time delay between food being taken and, for example, an increase in the blood sugar accurately by means of the invasive method. Also, particularly in the case of a low concentration of the blood sugar in blood, the time for administering insulin to the patient cannot be ascertained accurately. 
     For noninvasive ascertaining of a blood picture parameter such as, for example, a substance concentration or a substance composition in the blood, use can be made of microwave-spectroscopic methods. Microwave spectroscopy for detecting blood picture parameters is based on coupling a microwave signal into tissue perfused by blood and detecting a frequency-dependent absorption of coupled-in microwave energy. 
     The article “Non-invasive glucose monitoring in patients with Type 1 diabetes: A multi-sensor system combining sensors for dielectric and optical characterization of skin”, Biosensors and Bioelectronics 24 (2009) 2778-2784 by Andreas Caduff et al. describes a multi-electrode arrangement for microwave-based ascertaining of a blood picture parameter. The multi-electrode arrangement comprises a plurality of electrode pairs with different electrode spacings, by means of which different penetration depths of microwave signals can be realized. The blood picture parameter is detected by means of an impedance measurement, i.e. by means of a one-port measurement, and is therefore susceptible to errors in the case of possible impedance maladjustments. As a result of different penetration depths, it is sometimes not possible to distinguish between capillary and venous blood, which can falsify the measurement results. In general, a measurement of a blood picture parameter using venous blood is more precise than a measurement of the blood picture parameter using capillary blood because, for example, blood sugar changes in capillary blood are delayed compared to venous blood. 
     The articles “A microwave frequency sensor for non-invasive blood-glucose measurement”, SAS 2008—IEEE Sensors Applications Symposium, Atlanta, Ga., Feb. 12-14, 2008, by Buford Randal Jean et al. and “Calibration methodology for a microwave non-invasive glucose sensor”, Master&#39;s Thesis, Baylor University, May 2008 by M. McClung describe a further electrode arrangement for ascertaining a blood sugar concentration. What is exploited here is that the dielectric properties of blood depend on a blood sugar content. By pressing a thumb onto the microwave sensor, a change in the relative permittivity of the thumb is measured by a detuning of a resonator. However, blood is displaced by the contact pressure of the thumb, and this can lead to falsification of the measurement results. Moreover, the measurements cannot be carried out continuously. The evaluation of the measurement data for ascertaining the blood sugar content moreover depends on the respective patient and is therefore not reproducible in other patients. Moreover, this method does not allow control of the penetration depth of the microwave power, and so it is not possible to distinguish between capillary and venous blood. Furthermore, the change in the relative permittivity is carried out on the basis of a one-port measurement, which is susceptible in respect of maladjustments. 
     SUMMARY OF THE INVENTION 
     The invention provides an efficient concept for microwave-based, non-invasive ascertaining of a blood picture parameter, in particular of a concentration of blood sugar, in blood flowing through a blood vessel. 
     Accordingly, the invention provides a detection device for detecting a blood picture parameter of a blood constituent of blood in a blood vessel, comprising: 
     a transmitter, which is configured to couple a first transmission signal with a first frequency and a second transmission signal with a second frequency into the blood vessel; 
     a receiver, which is configured to receive a first reception signal at the first frequency and a second reception signal at the second frequency; 
     a loss detector, which is configured to: 
     establish a first loss variable on the basis of the first transmission signal and the first reception signal, and establish a second loss variable on the basis of the second transmission signal and the second reception signal; and 
     a processor, which is configured to ascertain a relaxation time constant of the blood constituent depending on the frequency with the greater loss variable. 
     The invention further provides a method for detecting a blood picture parameter of a blood constituent of blood in a blood vessel, comprising the following steps: 
     coupling a first transmission signal with a first frequency and a second transmission signal with a second frequency into the blood vessel; 
     receiving a first reception signal at the first frequency and a second reception signal at the second frequency; 
     establishing a first loss variable on the basis of the first transmission signal and the first reception signal; 
     establishing a second loss variable on the basis of the second transmission signal and the second reception signal; and 
     ascertaining a relaxation time constant of the blood constituent depending on the frequency with a greater loss variable. 
     The invention is based on the discovery that a blood picture parameter can be established by detecting a relaxation time constant of a blood constituent. By way of example, if the blood picture parameter to be ascertained is a concentration of blood sugar in the blood, a relaxation time constant of a water solution containing sugar is a measure for the concentration of the blood sugar, i.e. for the blood sugar level. 
     The invention is furthermore based on the discovery that the relaxation time constant of the blood constituent can be ascertained by measuring microwave signals coupled into the blood vessel. Here, loss variables of the coupled-in microwave signals are detected. By way of example, the loss variables are represented by the frequency-dependent profile of the complex relative permittivity. 
     The invention is based on the further discovery that a blood vessel such as, for example, a vein or an artery, the fatty tissue surrounding this blood vessel and the layer of skin situated thereover can be considered to be a dielectric waveguide system. Thus, if such a dielectric waveguide system is excited, it is possible to excite different modes or waves types, for example transverse electromagnetic (TEM) waves or transverse electric (TE) waves or transverse magnetic (TM) waves or an HE wave. In the case of a TE mode, there is a component of the magnetic field, different from zero, which points in the propagation direction. By contrast, in the case of a TM mode, there is a component of an electric field, different from zero, which points in the mode propagation direction. Thus, depending on a radiofrequency excitation, it is possible to excite different modes in a dielectric waveguide system, which comprises the blood vessel and the layer of skin, which modes can also propagate in the blood flow direction, as a result of which an accurate detection of a blood picture parameter is possible. 
     The blood vessel, into which the transmission signals are coupled-in and from which the reception signals are decoupled, is interpreted as a dielectric waveguide. The transmission signals are, in particular, embodied as microwave signals. As a result of using microwave signals, a robust measurement methodology is made possible. 
     It is possible to establish at least one blood picture parameter, e.g. the glucose concentration in the blood, by means of the ascertained relaxation time constant ( T ). The blood picture parameter can—like the relaxation time constant ( T ) of the blood constituent—be established continuously. By way of example, for the glucose concentration as a blood picture parameter, this results in an advantage compared to conventional solutions: it becomes possible to ascertain the delay time between food intake of the patient and the blood sugar increase. It follows that it is possible to react quicker to variations in the daily routine of the patient. An alarm can be triggered immediately if it becomes apparent that there is too much or too little sugar. A telemedical link via a communication interface is also possible. 
     By using the first transmission signal, the second transmission signal and, potentially, further transmission signals, a broadband measurement or establishment in respect of the loss variables is possible. 
     In accordance with one aspect of the invention, a detection device for detecting a blood picture parameter of a blood constituent of blood in a blood vessel is proposed, which detection device comprises a transmitter, a receiver, a loss detector and a processor. The transmitter is configured to couple a first transmission signal with a first frequency and a second transmission signal with a second frequency into the blood vessel. The receiver is configured to receive a first reception signal at the first frequency and a second reception signal at the second frequency. The loss detector is configured to establish a first loss variable on the basis of the first transmission signal and the first reception signal. The loss detector is furthermore configured to establish a second loss variable on the basis of the second transmission signal and the second reception signal. The processor is configured to ascertain a relaxation time constant ( T ) of the blood constituent depending on the frequency with the greater loss variable. 
     In particular, the processor is configured to ascertain the relaxation time constant ( T ) of the blood constituent depending on the first frequency if the first loss variable is no smaller than the second loss variable, or to ascertain the relaxation time constant ( T ) of the blood constituent depending on the second frequency if the second loss variable is no smaller than the first loss variable. 
     In accordance with one embodiment, the processor is configured to establish at least one blood picture parameter depending on the ascertained relaxation time constant ( T ). 
     In accordance with one embodiment, the processor is configured to establish at least one blood picture parameter depending on the ascertained relaxation time constant ( T ) by means of a predetermined relationship between the concentration of the blood picture parameter and the relaxation time constant ( T ). 
     In accordance with one embodiment, the predetermined relationship comprises a map of the concentration of the blood picture parameter on the relaxation time constant ( T ). 
     In accordance with one embodiment, the detection device comprises a look-up table, by means of which the predetermined relationship between the concentration of the blood picture parameter and the relaxation time constant ( T ) is mapped. 
     In accordance with one embodiment, the at least one blood picture parameter comprises a glucose concentration in the blood, a lactate concentration in the blood or an oxygen concentration in the blood. 
     In accordance with one embodiment, the loss detector is configured to ascertain the first loss variable and the second loss variable by means of a two-port measurement. 
     Advantageously, the two-port measurement provides a more reliable measurement result than a conventional one-port measurement. 
     In accordance with one embodiment, the loss detector comprises a network analyzer or a power detector. 
     In accordance with one embodiment, the loss detector is configured to ascertain in each case a forward transmission factor S 21  and/or an input reflection factor S 11  in order to ascertain the first loss variable and the second loss variable. 
     In accordance with one embodiment, the loss detector is configured to ascertain in each case the first loss variable and the second loss variable on the basis of the following formula: 
     P loss =1−|S 11 | 2 −|S 21 | 2 , where P loss  denotes the respective loss variable, and where S 11  denotes the input reflection factor and S 21  denotes the forward transmission factor. 
     In accordance with one embodiment, the processor is configured to ascertain the relaxation time constant ( T ) on the basis of the following formula: 
             τ   =     1     2   ⁢   π   ⁢           ⁢     f   A               
where f A  denotes the frequency at which the established loss variable is greater.
 
     In accordance with one embodiment, the loss detector is configured to establish the complex relative permittivity (∈″) at the respective frequency for ascertaining the respective loss variable. 
     In the process, it is, in particular, the imaginary part of the complex dielectric constant or relative permittivity which is evaluated. In particular, those frequencies are considered at which the imaginary part of the complex relative permittivity has a local maximum. As a result, it is possible to separate different polar effects by observing the imaginary part of the complex dielectric constant, which represent the frequency-dependent losses. 
     In accordance with one embodiment, the processor is configured to ascertain the frequency at which the imaginary part of the complex relative permittivity (∈″) is at a maximum and to establish the relaxation time constant ( T ) depending on the ascertained frequency. 
     In accordance with one embodiment, the transmitter is configured to couple at least one transmission signal with a multiplicity of frequencies into the blood vessel. Here, the receiver is configured to receive at least one reception signal with the multiplicity of frequencies. Furthermore, the processor is configured to ascertain the frequency at which the complex relative permittivity (∈″) is at a maximum and to establish the relaxation time constant ( T ) depending on the ascertained frequency. 
     In accordance with one embodiment, the transmitter for coupling-in the first transmission signal or the second transmission signal has at least one transmission antenna, in particular a dipole antenna, a frame antenna or a patch antenna. In accordance with this preferred embodiment, the receiver for receiving the first reception signal and the second reception signal has at least one reception antenna, in particular a dipole antenna or a frame antenna, which is at a distance from the transmission antenna. 
     In accordance with one embodiment, the transmitter is configured to couple the first transmission signal or the second transmission signal into the blood vessel as a transverse electric (TE) wave or as a transverse magnetic (TM) wave, in particular longitudinally or transversely with respect to a blood flow direction. 
     In accordance with one embodiment, the transmitter is configured to couple the first transmission signal and the second transmission signal into the blood vessel successively, in particular by means of a tunable oscillator, or simultaneously, in particular by means of a broadband signal comprising the first transmission signal and the second transmission signal. 
     In accordance with one embodiment, the transmission signal is a broad-edge radiofrequency signal or a sweep signal. 
     In accordance with one embodiment, the transmission signal is formed as a microwave signal. 
     In accordance with one embodiment, the blood vessel is an artery or a vein. 
     In accordance with one embodiment, the transmitter couples the transmission signal into the blood vessel with a power from 0.1 to 1.0 mW. 
     In accordance with one embodiment, the first frequency and the second frequency respectively lie in a frequency range between 1 GHz and 15 GHz. 
     In accordance with one embodiment, the detection device comprises a transmitter with a number of transmission antennas for emitting at least one transmission signal, a receiver with a number of reception antennas for receiving at least one reception signal, the processor and the loss detector. Here, the processor is configured to select a first detection configuration comprising one transmission antenna of the number of transmission antennas and one reception antenna of the number of reception antennas and to select a second detection configuration comprising one transmission antenna of the number of transmission antennas and one reception antenna of the number of reception antennas. Furthermore, the loss detector is configured, if the first detection configuration for emitting a transmission signal is selected, to detect a first loss variable on the basis of the transmission signal and a reception signal and, if the second detection configuration for emitting a transmission signal is selected, to detect a second loss variable on the basis of the transmission signal and a reception signal. Furthermore, the processor is configured to select the detection configuration with the smaller loss variable for detecting the blood picture parameter. 
     By way of example, the transmitter is formed as a transmitter with a broadband pseudo-noise signal, for example as an M-sequence radar. 
     In particular, if the first detection configuration is selected, the transmitter is configured to emit the transmission signal by means of the transmission antenna of the first detection configuration. If the first detection configuration is selected, the receiver is configured to receive the reception signal by means of the reception antenna of the first detection configuration. Furthermore, if the second detection configuration is selected, the transmitter is configured to emit the transmission signal by means of the transmission antenna of the second detection configuration, wherein, if the second detection configuration is selected, the receiver is configured to receive the reception signal by means of the reception antenna of the second detection configuration. Here, the loss detector is configured to detect the first loss variable on the basis of the transmission signal and the reception signal of the first detection configuration and to detect the second loss variable on the basis of the transmission signal and the reception signal of the second detection configuration. 
     In accordance with one embodiment, the first loss variable is an absorption line of a water solution with a blood constituent at the first frequency and the second loss variable is an absorption line of the water solution at the second frequency. 
     In accordance with one embodiment, the first loss variable and the second loss variable define a frequency-dependent profile of absorption lines of a water solution with the blood constituent. 
     In accordance with one embodiment, the first loss variable is an absorption minimum or an absorption maximum in a first frequency range comprising the first frequency, with the second loss variable being an absorption minimum or an absorption maximum in a second frequency range comprising the second frequency. 
     In accordance with one embodiment, the invention relates to a detection device for detecting a blood picture parameter of blood in a blood vessel, comprising a transmitter with a number of transmission antennas for emitting at least one transmission signal, a receiver with a number of reception antennas for receiving at least one reception signal, a processor, which is configured to select a first detection configuration comprising one transmission antenna of the number of transmission antennas and one reception antenna of the number of reception antennas and to select a second detection configuration comprising one transmission antenna of the number of transmission antennas and one reception antenna of the number of reception antennas, a loss detector, which is configured, if the first detection configuration for emitting a transmission signal is selected, to detect a first loss variable on the basis of the transmission signal and a reception signal and, if the second detection configuration for emitting a transmission signal is selected, to detect a second loss variable on the basis of the transmission signal and a reception signal, wherein the processor is configured to select the detection configuration with the smaller loss variable for detecting the blood picture parameter. 
     During the selection of the respective detection configuration, it is preferable for the blood vessel to be excited, wherein the transmission signals are, for example, emitted in the direction of the blood vessel. On the basis of the reception signals, which are received versions of the transmission signals, and on the basis of the transmission signals it is possible, for example, to select that antenna pair, comprising a transmission antenna and a reception antenna, as that detection configuration which is connected with the smallest coupling-in losses. The coupling-in losses can, for example, be detected on the basis of a comparison of the aforementioned loss variables, for example absorption lines or attenuations. 
     In accordance with one aspect of the invention, a method for detecting a parameter of a blood constituent of blood in a blood vessel is proposed. Here, a first transmission signal with a first frequency and a second transmission signal with a second frequency are coupled into the blood vessel. Furthermore, a first reception signal is received at the first frequency and a second reception signal is received at the second frequency. A first loss variable is established on the basis of the first transmission signal and the first reception signal. Accordingly, a second loss variable is established on the basis of the second transmission signal and the second reception signal. Furthermore, a relaxation time constant ( T ) of the blood constituent is established depending on the frequency with a greater loss variable. 
     In accordance with a preferred embodiment, the method comprises the following steps: 
     coupling at least one radiofrequency signal with a multiplicity of frequencies into the blood vessel, 
     ascertaining the frequency at which the imaginary part of the complex relative permittivity (∈″) is at a maximum, establishing the relaxation time constant ( T ) depending on the ascertained frequency, and 
     establishing the blood picture parameter depending on the ascertained relaxation time constant ( T ). 
     Furthermore, a computer program product is proposed, which, on a program-controlled apparatus, prompts at least part of the method as described above for detecting a parameter of a blood constituent of blood in a blood vessel to be carried out. The at least one part, which is embodied as a computer program product, in particular comprises the step of establishing the relaxation time constant ( T ). 
     A computer program product such as a computer program means can, for example, be provided or supplied as a storage medium, such as a memory card, USB stick, floppy disk, CD-ROM, DVD or else in the form of a downloadable file from a server in a network. By way of example, in a wireless communication network, this can be brought about by the transmission of a corresponding file with the computer program product or the computer program means. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further exemplary embodiments will be explained with reference to the attached drawings. In detail: 
         FIG. 1  shows a schematic block diagram of a detection device; 
         FIG. 2  shows a diagram for illustrating the real relative permittivity ∈′ and the complex relative permittivity ∈″ depending on the frequency; 
         FIG. 3  shows a diagram for illustrating a relationship between the relaxation time constant ( T ) and the glucose concentration in the blood; 
         FIG. 4  shows a schematic block diagram of a detection device with a communication device; 
         FIG. 5  shows a schematic flowchart of a method for detecting a blood picture parameter of blood in a blood vessel; 
         FIG. 6  shows a schematic block diagram of an armband; 
         FIG. 7  shows a schematic block diagram of a section of an exemplary embodiment of an armband; 
         FIG. 8  shows a schematic block diagram of a section of an armband; 
         FIG. 9  shows a schematic block diagram of an arrangement of the electrodes of the detection device; 
         FIG. 10  shows a schematic flowchart of a method for operating an armband; 
         FIG. 11  shows a block diagram of a detection device; 
         FIG. 12  shows a model of a cross-section of a human forearm; 
         FIGS. 13A-13D  show antennas; 
         FIG. 14  shows an electric dipole antenna; 
         FIG. 14B  shows an excitation arrangement; 
         FIGS. 15A, 15B  show excitation arrangements; 
         FIG. 16A  shows a loop antenna; 
         FIG. 16B  shows an excitation arrangement; 
         FIG. 17  shows an excitation arrangement; 
         FIG. 18  shows an excitation arrangement; 
         FIG. 19  shows an excitation arrangement; 
         FIG. 20  shows an excitation arrangement; 
         FIG. 21  shows a block diagram of a detection device; 
         FIG. 22  shows a frequency shift of an absorption maximum; 
         FIG. 23  shows a transmission behavior; 
         FIG. 24  shows frequency shifts; 
         FIG. 25  shows a diagram of a method for detecting a blood picture parameter; and 
         FIG. 26  shows a block diagram of a detection device. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a block diagram of a detection device  100  for detecting a blood picture parameter, such as, for example, a concentration of blood sugar or glucose. The detection device  100  comprises a transmitter  101 , which is configured to couple a first transmission signal with a first frequency and a second transmission signal with a second frequency into the blood vessel  103  illustrated schematically in  FIG. 1 . The first transmission signal and the second transmission signal can, for example, together result in a broadband signal. The transmitter  101  can furthermore be configured to couple the first transmission signal and the second transmission signal, one after the other, into the blood vessel  103  in sequence. To this end, the transmitter  101  can have one or more transmission antennas, which, for example, are formed as dipole antennas. 
     The detection device  100  furthermore comprises a receiver  105 , which is configured to receive a first reception signal at the first frequency and a second reception signal at the second frequency. To this end, the receiver  105  can have one or more reception antennas. 
     Furthermore, the detection device  100  has a loss detector  107 , which is, for example, coupled to the transmitter  101  and the receiver  105  and provided for ascertaining a first loss variable on the basis of the first transmission signal and the first reception signal and also a second loss variable the basis of the second transmission signal and the second reception signal. 
     The detection device  100  furthermore has a processor  109 , which is coupled to the loss detector  107  and provided for ascertaining a relaxation time constant  T  of the blood picture parameter depending on the frequency with the greater loss variable. 
     By way of example, the processor  109  will ascertain the relaxation time constant of the blood picture parameter depending on the first frequency if the first loss variable is greater than the second loss variable. Correspondingly, the processor  109  will ascertain the relaxation time constant ( T ) of the blood picture parameter depending on the second frequency if the second loss variable is greater than the first loss variable. 
     The detection device  100  illustrated in  FIG. 1  uses the discovery that a blood vessel such as e.g. a vein, a layer of skin and fatty tissues surrounding a vein can be considered to be a dielectric waveguide. The makeup of a human forearm is described in Netter, F. N. “Atlas der Anatomie” [Anatomical Atlas], Thieme Verlag, 2006. Accordingly, a human forearm in cross-section consists of two bones which are surrounded by muscular tissue. Distributed around the muscular tissue are surface veins. The bones, the muscular tissue and the veins are encapsulated by fatty tissue, which is covered by upper layers of skin. The surface veins are arranged relatively close to the upper layers of skin and separated therefrom by the fatty tissue. 
     By way of example, if the transmitter  101  and the receiver  105 , illustrated in  FIG. 1 , are placed onto the upper layer of skin, the transmitter  101  can be used to couple a transverse electric (TE) wave or a transverse magnetic (TM) wave into the dielectric waveguide system formed by a vein, fatty tissue and a layer of skin. Here, the layer of skin and the fatty tissue can be understood to be a thin-film waveguide. 
     As already explained above, the loss detector  107  is configured to establish a first loss variable on the basis of the first transmission signal and the first reception signal and to establish a second loss variable on the basis of the second transmission signal and the second reception signal. If use is made of further transmission signal and reception signal pairs, the loss detector  107  will accordingly establish further loss variables. 
     In particular, the loss detector  107  is configured to ascertain the loss variables by a two-port measurement. By way of example, the loss detector  107  comprises a network analyzer or a power detector. 
     Furthermore, the loss detector  107  is configured to ascertain in each case a forward transmission factor S 21  and an input reflection factor S ii  in order to ascertain the loss variables. 
     Here, the loss detector will calculate the respective loss variable P loss  by means of the following formula:
 
 P   loss =1 −|S   11 | 2   −S   21 | 2 .
 
     In particular, the loss detector  107  is configured to establish the complex relative permittivity ∈″ for ascertaining the respective loss variable. 
     To this end,  FIG. 2  shows a diagram for illustrating the real relative permittivity ∈′ and the complex relative permittivity ∈″ depending on the frequency f. 
     Here,  FIG. 2  illustrates that the losses represented by the complex relative permittivity ∈″ increase in the frequency range where the real part ∈′ transitions from the higher level to the lower level. This increase in the losses is also referred to as absorption lines in spectroscopy. The effect that can be used in this case is that the frequency at which the excesses of the losses—see local maximum of ∈″ —is displaced with the concentration of the sugar content. 
     By way of example, the human body consists of 80% water. Water has absorption lines, for example at 19 GHz and 50 GHz. The detuning thereof can be ascertained and plotted against the sugar content. The detuning of the resonant frequency at ∈″ is—as illustrated in  FIG. 2 —easier to detect than the change in the plateau of ∈′. In particular, variations in the coupling advantageously do not shift the frequency of the maximum of ∈″. As a result, ascertaining the sugar concentration by observing ∈″ is significantly less susceptible to errors than observing ∈′ or the level change therein. 
     Since such curves as are superimposed in  FIG. 2  in a multiplicity of substances, a separation of the substances by observing the imaginary relative permittivity ∈″ is easier to carry out since each substance can be associated with a specific absorption maximum. However, in the case of the real relative permittivity ∈′, it is only possible to observe the sum of all real relative permittivities ∈′ of all substances involved. 
     As already explained above, the processor  109  is configured to ascertain the relaxation constant  T  of the blood picture parameter depending on the frequency with the larger or maximum loss variable. Furthermore, the processor  109  is configured to establish the blood picture parameter, such as the glucose concentration in the blood, depending on the ascertained relaxation time constants. 
     To this end,  FIG. 3  shows a diagram for illustrating a relationship between the relaxation time constant ( T ) and the glucose concentration C/mol L −1  in the blood. Here, the area denoted by the reference sign  301  in  FIG. 3  shows a critical blood sugar range. 
     Furthermore, the processor  109  is, in particular, configured to calculate the relaxation time constant ( T ) on the basis of the formula 
               τ   =     1     2   ⁢   π   ⁢           ⁢     f   A           ,         
where f A  denotes the frequency at which the established loss variable is at a maximum.
 
     Advantageously, the processor  109  is then configured to ascertain the frequency at which the imaginary part of the complex relative permittivity ∈″ is at a maximum, and at which the relaxation time constant ( T ) is to be established depending on the ascertained frequency. This ascertained frequency is then used by the processor  109  for ascertaining the blood picture parameter, such as the glucose concentration. 
       FIG. 4  shows a schematic block diagram of a detection device  400 . The detection device  400  has an armband  401 , a sensor array  403  attached to the armband  401 , a microprocessor  405 , a microwave circuit  407  for generating the transmission signals, and a communication device  409 . 
     By way of example, the sensor array  403  has a microwave sensor, a temperature sensor and a moisture sensor. 
     By way of example, the microprocessor  405  is configured like the processor  109  in  FIG. 1 . 
     The communication device  409  is configured for providing a communication link between the detection device  400  and a further communication device  411 . By way of example, the communication device  409  comprises a Bluetooth interface. By way of example, the further communication device  411  is a mobile radio device, a smartphone or a GPS-based apparatus. 
       FIG. 5  illustrates a schematic flowchart of an exemplary embodiment of a method for detecting a blood picture parameter, such as, for example, a glucose concentration, of blood in a blood vessel. 
     In step  501 , a first transmission signal with a first frequency and a second transmission signal with a second frequency are coupled into the blood vessel. 
     In step  503 , a first reception signal is received at the first frequency and a second reception signal is received at the second frequency. 
     In step  505 , a first loss variable is established on the basis of the first transmission signal and the first reception signal. 
     In step  507 , a second loss variable is established on the basis of the second transmission signal and the second reception signal. 
     In step  509 , a relaxation time constant of the blood picture parameter is ascertained depending on the frequency with a greater loss variable. The glucose concentration in the blood, for example, can then be ascertained depending on the ascertained relaxation time constant. 
       FIG. 6  shows a block diagram of an exemplary embodiment of an armband  600  with a detection device  601  and a setting device  603 . The detection device  601  is configured to detect a blood picture parameter of blood in a blood vessel of the arm. An example for the blood picture parameter to be detected is the glucose concentration in the blood. 
     The setting device  603  is configured to set a predeterminable contact pressure of the armband  600  on the arm. By setting the predetermined contact pressure of the armband  600 , the setting device  603  can ensure reproducible detections of the blood picture parameter by the detection device  601 . To this end, the setting device  603  is, in particular, configured to set the contact pressure of the armband  600  to the predeterminable contact pressure when the blood picture parameter is being detected by the detection device  601 . 
     In particular, the armband  600  is embodied as an inflatable armband  600 . Here, the setting device  603  in particular has an air pump, which is configured to inflate the armband  600  for setting the predetermined contact pressure. 
     In detail, the detection device  601  comprises electrodes in particular, which are configured to couple at least a radiofrequency signal into the blood vessel. The radiofrequency signal is configured to supply a parameter for detecting the blood picture parameter. An example for such a parameter is formed by the relaxation time constant  T  of the blood picture parameter. Here, the setting device  603  is more particularly designed to set the contact pressure of the electrodes on the arm to the predetermined contact pressure. 
     Furthermore, the setting device  603  can be embodied in such a way that it distributes the contact forces of the armband  600  uniformly on the arm when the blood picture parameter is being detected by the detection device  601 . Furthermore, the setting device  603  is preferably configured in such a way that it ensures uniform contact of the armband  600  while the blood picture parameter is being detected by the detection device  601 . 
       FIG. 7  shows a block diagram of a section of an exemplary embodiment of an armband  700 . The armband  700  has a detection device  701  and a setting device  703 . The detection device  701  and the setting device  703  are embodied at least like the detection device  601  and the setting device  603  of  FIG. 6 . Furthermore, the setting device  703  of  FIG. 7  has a sensor apparatus  705  and a control apparatus  707 . The sensor apparatus  705  is configured to measure a current contact pressure of the armband  700  on the arm. Depending on the measured current contact pressure, the control apparatus  707  sets the predetermined contact pressure on the arm. 
       FIG. 8  shows a block diagram of a section of a further exemplary embodiment of an armband  800 . The armband  800  has a detection device  801  and a setting device  803 . The setting device  803  has a sensor apparatus  805 , a control apparatus  807  and an air pump  811 . The sensor apparatus  805  measures a current contact pressure of the armband  800  on the arm. The control apparatus  807  provides a control signal depending on the measured current contact pressure. By means of the provided control signal, the air pump  811  is controlled for inflating the armband  800 . 
       FIG. 9  illustrates a schematic block diagram of an arrangement  900  of the electrodes  903 ,  905  of the detection device for detecting a blood picture parameter of blood in a blood vessel of the arm. 
     Without loss of generality, the arrangement  900  only shows two electrodes  903  and  905 . In particular, the arrangement  900  is part of the detection device and, for example, embodied as a plate with exemplary dimensions of 5 cm by 2 cm. The electrodes  903 ,  905  for example have a base area of 5 mm by 5 mm. By way of example, the distance between the electrodes  903 ,  905  is 1 to 2 cm. This firstly obtains a strong enough transmission and secondly ensures a sufficiently deep penetration depth into the body. 
       FIG. 10  shows a schematic flowchart of a method for operating an armband with a detection device. 
     In step  1001 , the armband is equipped with a detection device for detecting a blood picture parameter of blood in a blood vessel of the arm. By way of example, the detection device is configured in accordance with one of the exemplary embodiments of  FIG. 6, 7 or 8 . 
     In step  1003 , a predetermined contact pressure of the armband on the arm is set. Hence, reproducible detection of the blood picture parameter is ensured by the detection device. 
       FIG. 11  shows a block diagram of a detection device  1100  for detecting a blood picture parameter such as, for example, a concentration of blood sugar. The detection device  1100  comprises a transmitter  1101 , which is configured to couple a first transmission signal with a first frequency and a second transmission signal with a second frequency into the blood vessel  1103  illustrated schematically in  FIG. 11 . By way of example, together, the first transmission signal and the second transmission signal can result in a broadband signal. The transmitter  1101  can be configured to emit, one after the other, the first transmission signal and the second transmission signal, for example by a frequency sweep. To this end, the transmitter  1101  can have one or more transmission antennas, which can, for example, be embodied as dipole antennas or frame antennas or patch antennas. 
     The detection device  1100  furthermore comprises a receiver  1105 , which is configured to receive a first reception signal at the first frequency and a second reception signal at the second frequency. To this end, the receiver  1105  can have one or more reception antennas. 
     The detection device  1100  furthermore comprises a loss detector  1107 , which, for example, is coupled to the transmitter  1101  and the receiver  1105  and is provided for ascertaining a first loss variable on the basis of the first transmission signal and the first reception signal and also a second loss variable on the basis of the second transmission signal and the second reception signal. 
     The detection device furthermore comprises a processor  1109 , which is coupled to the loss detector  1107  and is provided for ascertaining a first frequency shift of the first loss variable relative to a first reference loss variable and a second frequency shift of the second loss variable relative to a second reference loss variable. The processor  1109  can furthermore be configured to ascertain the blood picture parameter on the basis of the two frequency shifts. 
     The detection device  1100  can furthermore have a storage medium  1111 , which can be accessed by, for example, the processor  1109  and, optionally, the loss detector  1107 . By way of example, the first and the second reference loss variable or a plurality of reference loss variables are stored in the storage medium  1111 . By way of example, the reference loss variables can be absorptions or absorption lines of a water solution with a blood constituent, for example blood sugar. The loss variables detected on the basis of the frequency shifts can be frequency-shifted absorptions or absorption lines such that the blood picture parameter, such as, for example, a concentration of blood sugar, can be established on the basis of the frequency shifts. 
     The detection device  1100  illustrated in  FIG. 11  uses the discovery that a blood vessel, a layer of skin and fatty tissue surrounding the blood vessel of, for example, a human forearm can be considered to be a dielectric waveguide system. By way of example, if the transmitter  1101  and the receiver  1105 , illustrated in  FIG. 11 , are placed onto the upper layer of skin, the transmitter  1101  can be used to couple e.g. a transverse electric (TE) wave or a transverse magnetic (TM) wave into the dielectric waveguide system formed by a blood vessel, fatty tissue and a layer of skin. Here, the layer of skin and the fatty tissue can be understood to be a thin-film waveguide. 
     By way of example, if use is made of a microwave measurement head, as can be employed for ascertaining a complex relative permittivity of materials, it is possible thereby to characterize the substance mixture consisting of skin, fatty tissue and veins. 
     In order to detect a blood picture parameter, it is advantageous to detect substantially only the venous blood. To this end, the transmitter  1101  can be configured to couple the transmission signal in the form of an electromagnetic wave directly into the blood vessel. The transmitter  1101  and the receiver  1105  can each have a plurality of antennas such that, for the purposes of coupling the electromagnetic wave into the blood vessel and decoupling an electromagnetic wave from the blood vessel, it is in each case possible to select that transmission antenna and reception antenna which are connected with the smallest coupling losses. 
       FIGS. 12A to 12C  illustrate a simplified model of a cross-section of a human forearm, e.g. of a wrist, as can be employed, for example, for field simulations or for modeling a dielectric waveguide system. As illustrated in  FIG. 12A , the model comprises a layer of skin  1201 , a blood vessel  1203  and fatty tissue  1205  surrounding the blood vessel  1203 . The model illustrated in  FIG. 12A  forms a dielectric waveguide system comprising the dielectric waveguide illustrated in  FIG. 12B  and the electrical thin-film waveguide illustrated in  FIG. 12C . 
     The dielectric waveguide illustrated in  FIG. 12B  comprises the blood vessel  1203  and the fatty tissue  1205  surrounding the latter. By contrast, the dielectric thin-film waveguide from  FIG. 12C  comprises the layer of skin  1201  and the fatty tissue  1205 . A different dispersive, i.e. frequency dependent, behavior of the respective complex relative permittivity can be attached in each case to the layer of skin  1201 , to the fatty tissue  1205  and to the blood vessel  1203 . Here, the blood vessel  1203  lying at the top is interpreted as a dielectric waveguide, in which, depending on the frequency, different modes or wave types, for example a TE wave, a TM wave, a TEM wave or an HE wave, are able to propagate. Added to the waveguide mechanism in the dielectric waveguide, there is an additional waveguide mechanism in the form of the thin-film waveguide illustrated in  FIG. 12C , which is formed by the upper layer of skin  1201 . 
     A transmission antenna of the transmitter  1101  and a reception antenna of the receiver  1105  can preferably be configured in such a way that they couple microwave power into the blood vessel  1203  in a dedicated fashion and decouple said microwave power again after, for example, a few centimeters. Here, the blood vessel  1203  serves as a measurement length and should therefore be considered as a distributed element and no longer as a concentrated element. The measurement of the loss variables is preferably carried out on the basis of a two-port measurement. Here, particularly when coupling the detection device to a wrist, primary modes can be excited in the dielectric waveguide in accordance with  FIG. 12B  such that an excitation of thin-film waveguide modes in the thin-film waveguide in accordance with  FIG. 12C  is avoided, as a result of which the blood picture parameter can be detected more accurately. 
     In order to excite primary modes in the dielectric waveguide system, it is possible to take into account that, depending on the selected frequency of a transmission signal, different modes can be dominant. It is preferable for mode types, which have a concentration of the fields in the vein  1203 , to be preferred over those modes in which the fields are concentrated in the layer of skin  1201 . What is shown on the basis of the dielectric properties of the dielectric waveguide illustrated in  FIG. 12B  is that for certain types of modes longitudinal components E longitudinal , H longitudinal  are stronger in the propagation direction, i.e. in the direction of a vein extent, than the transverse components E transverse , H transverse , i.e. transverse to the vein extent. Therefore those modes which enable maximum coupling of the microwave power into the blood vessel  1203  are preferably excited in the frequency range to be detected. 
       FIGS. 13A to 13D  illustrate some antennas in an exemplary fashion, which antennas can be used as transmission antennas, i.e. excitation means, or else as reception antennas. 
     The antenna  1301  illustrated in  FIG. 13A  is configured as an electric dipole with a first antenna section  1303  and a second antenna section  1305 . The antenna sections  1303  and  1305  are distanced from one another and are arranged, for example, transversely with respect to the extent of a blood vessel  1307 . The antenna  1301  can be excited by supply lines  1308 . An electric dipole arranged in this manner can, for example, generate an electric field E tangential , which points across the extent of the blood vessel or across the blood flow direction. 
       FIG. 13B  illustrates an antenna  1309 , which can be a frame antenna. By way of example, the frame antenna can have a quadrilateral or round shape. In the arrangement of the frame antenna  1309  with respect to the blood vessel  1307  illustrated in  FIG. 13B , e.g. a magnetic field H tangential  is excited, which points across the extent of the blood vessel  1307  or across the blood flow direction. The antenna  1309  can be excited by supply lines  1310 . 
       FIG. 13C  illustrates an antenna  1311 , which forms an electric dipole with a first antenna section  1313  and a second antenna section  1315 . The antenna sections  1313  and  1315  are distanced from one another and are excited by means of the supply lines  1317  illustrated in  FIG. 13C . The electric dipole formed by the antenna  1311  is arranged in such a way with respect to the extent of the blood vessel  1307  that the sections  1313  and  1315  are arranged parallel to the extent of the blood vessel  1307 . As a result of this, an electric field with the field component E longitudinal , which electric field points in the direction of the extent of the blood vessel, is excited. 
       FIG. 13D  shows a frame antenna  1319 , which can, for example, be formed in the form of a quadrilateral or round frame, which forms a loop antenna, for example as a patch antenna. The frame antenna  1319  is excited by means of supply lines  1320  and is, as illustrated in  FIG. 13D , arranged in such a way with respect to the extent of the blood vessel  1307  or with respect to the blood flow direction that the magnetic field has a component H longitudinal  pointing in the direction of the extent of the blood vessel  1307 . 
     By way of example, the frequency range to be measured in each case conforms to which spectral lines, i.e. which absorption lines, should be detected. By way of example, it is possible to observe the characteristic absorption lines of a substance or else an effect which a specific blood constituent has on the absorption lines of water or of a water solution with a concentration of the blood constituent. 
     The antennas illustrated in  FIGS. 13A to 13D  are either electric dipoles or magnetic frame antennas. Moreover, use can also be made of patch antennas. Electric dipoles dominantly produce an electric field along the axis of the electric dipole. This axis can either, as illustrated in  FIG. 13A , be aligned tangentially with respect to the blood vessel  1307  or the blood flow direction or, as illustrated in  FIG. 13C , be aligned in the direction of the blood vessel  1307  or in the blood flow direction. If it is primarily a magnetic field that should be generated, a frame antenna can be used as excitation means. If a surface vector on the surface spanned by the frame forming the frame antenna is aligned across the blood vessel  1307  or across the blood flow direction, the magnetic field is also aligned across the blood vessel  1307 , as illustrated in  FIG. 13B . By contrast, if the surface vector points in the direction of the blood vessel  1307 , the magnetic field is also aligned in the direction of the blood vessel  1307 , as is illustrated in, for example,  FIG. 13B . The selection of an excitation means illustrated in  FIGS. 13A to 13D  then results in, for example, the dominant excited mode or wave type. 
       FIG. 14A  shows an electric dipole antenna  1401 , which can be used as a transmission antenna or as a reception antenna. The electric dipole antenna  1401  comprises dipole antenna sections  1403  and  1405 , which are arranged in or on a substrate  1408  and can be excited by means of supply lines  1407 . The dipole antenna  1401  can be used as a transmission antenna or as a reception antenna. 
       FIG. 14B  shows an excitation arrangement of a transmission antenna  1409  of a transmitter and of a reception antenna  1411  of a receiver in the direction of an extent of a blood vessel  1413  below a layer of skin  1415 . The transmission antenna  1409  and the reception antenna  1411  are, for example, electric dipole antennas in accordance with  FIG. 14A . In the arrangement illustrated in  FIG. 14B , an electric field with a field component in the direction of the extent of the blood vessel  1413 , or in the blood flow direction, is generated. 
       FIG. 15A  shows an excitation arrangement comprising a transmission antenna  1501  of a transmitter and a reception antenna  1503  of a receiver, across the direction of extent of a blood vessel  1505 , i.e. across the blood flow direction, which lies under a layer of skin  1507 . The transmission antenna  1501  and the reception antenna  1503  can each be formed by e.g. the electric dipole antenna illustrated in  FIG. 14A . In  FIG. 15B , the arrangement of the dipole antenna sections  1403  and  1405  is illustrated in more detail in respect of the blood flow direction. 
       FIG. 16A  shows a loop antenna  1601  with a circular frame  1603  and supply lines  1605  for exciting the circular frame  1603 . The loop antenna  1601  can, for example, be used as a transmission antenna or as a reception antenna. The circular frame  1603  and the supply lines  1605  can be arranged in or on a substrate. 
       FIG. 16B  shows an excitation arrangement with a transmission antenna  1607  of a transmitter and a reception antenna  1609  of a receiver, which can be formed as loop antennas as per  FIG. 16A . By way of example, the loop antennas  1607 ,  1609  are arranged in such a way that the circular frames  1603  are arranged above a blood vessel  1611 , with the supply lines  1605  pointing across the extent of the blood vessel  1611 , i.e. across the blood flow direction. As a result of this, a magnetic field H with a component of the magnetic field pointing across the extent of the blood vessel  1611  is generated on the transmitter side. 
       FIG. 17  shows an excitation arrangement of a transmission antenna  1701  of a transmitter and a reception antenna  1703  of a receiver, with respect to a blood vessel  1705 . By way of example, the transmission antenna  1701  and the reception antenna  1703  can be loop antennas with that shape illustrated in  FIG. 16A . By way of example, they are arranged in such a way that the circular frames  1603  are respectively arranged above the blood vessel  1705  and that the supply lines  1605  extend pointing away from one another, parallel to the extent of the blood vessel  1705 . As a result of this, a field component H pointing perpendicular to the extent of the blood vessel  1705  is generated, which field component points in the direction of a normal of the surface spanned by the circular frame  1603 . 
       FIG. 18  shows an excitation arrangement with a transmission antenna  1801  of a transmitter, which, for example, has the shape of a loop antenna illustrated in  FIG. 16A . By way of example, the transmission antenna  1801  is arranged in such a way with respect to a blood vessel  1803  that a normal of the surface spanned by the frame  1603  points in the direction of the extent of the blood vessel  1803 . By way of example, such an arrangement can be realized at a bend in the blood vessel  1803 . As a result of this, a magnetic field component H pointing in the direction of the extent of the blood vessel  1803  is generated. 
       FIG. 19  shows an excitation arrangement with a transmission antenna  1601 , which, for example, is a loop antenna with the shape illustrated in  FIG. 16A  and can be arranged in a substrate  1901 , for example a polymer substrate. The transmission antenna  1601  is arranged above a blood vessel  1903  in such a way that a normal of the surface spanned by the circular frame  1603  points in the direction of the extent of the blood vessel  1903 . As a result of this, a magnetic field is generated with a field component H pointing in the direction of the extent of the blood vessel  1903 , i.e. in the blood flow direction. 
       FIG. 20  shows an excitation arrangement with a transmission antenna  2001 , which can be a patch antenna with a patch antenna surface  2003  and supply lines  2005 . The patch antenna surface  2003  is, for example, arranged above a blood vessel  2007 , as a result of which an electric field is generated with an electric field component E pointing in the direction of an extent of the blood vessel  2007 , i.e. in the blood flow direction. 
     In accordance with one embodiment, the loss detector  1107  is configured to carry out e.g. a scalar or a vector measurement or a power measurement. In order to ascertain the loss variables, a simple spectroscopic measurement can be carried out, in which the absolute value of the measurement parameter S 21  is detected. 
     By way of example, |S 21 | can be measured by means of the detection device illustrated in  FIG. 21 . The detection device comprises a transmitter with a transmission signal generator  2101 , which can be a tunable oscillator. An output of the transmission signal generator  2101  is connected to a transmission antenna  2103 . The detection device furthermore comprises a receiver with a reception antenna  2105 , the output of which is connected to a loss detector  2107 . By way of example, the loss detector can comprise a power detector. As illustrated in  FIG. 21 , the transmission antenna  2103  and the reception antenna  2105  are arranged above a blood vessel  2109 . The transmitter can correspond to features of the transmitter  1101 , the receiver can correspond to features of the receiver  1105  and the loss detector  2107  can correspond to features of the loss detector  1107 . 
     However, the accuracy when ascertaining the loss variables, i.e. the losses in the waveguide, can be increased further by a further measurement of an absolute value of the measurement parameter S 11 . By way of example, the loss variables can be ascertained on the basis of the following formula:
 
 P   loss =1 −|S   11 | 2   −|S   21 | 2 ,
 
     where P loss  denotes the respective loss variable and where S 11  denotes the input reflection factor and S 21  denotes the forward transmission factor. 
     In order to detect the blood picture parameter, for example a concentration of blood sugar, frequency shifts of the absorption lines of a water solution with sugar can, for example, be examined. By way of example,  FIG. 22  shows a frequency shift of an absorption maximum  2201  at a first blood sugar concentration compared to a frequency shift of an absorption maximum  2203  at a second blood sugar concentration, which is higher than the first blood sugar concentration. Here, a transmission around 6 GHz was detected in an exemplary fashion as loss variable. 
     The frequency shift of the absorption maximum can be considered to be a measure for a blood picture parameter, for example for a blood sugar level. By observing frequency shifts in a number of absorptions of a water solution with sugar, the measurement reliability can be increased still further. 
       FIG. 23  shows, in an exemplary fashion, a broadband transmission behavior of venous blood in a wrist. Here, the profiles  2301  and  2303  clarify different frequency positions of absorption lines at different blood sugar concentrations. In order to detect the blood picture parameter, such as, for example, the concentration of the blood sugar, it is possible, for example, to detect frequency shifts of the absorptions A, B, C, D, E, F and G in a targeted manner. Thus, it is possible, for example, to observe a shift in the direction of higher or lower frequencies depending on blood sugar level, for example in a frequency range between 2 GHz and 12 GHz, for each frequency of an absorption maximum and/or an absorption minimum. 
       FIG. 24  shows, in an exemplary fashion, frequency shifts of the absorptions A, B, C, D, E, F and G illustrated in  FIG. 23  for a blood vessel with a diameter of 6 mm and for a blood vessel with a diameter of 3.4 mm. It is possible to identify that the absorptions for a sugar level variation can have frequency shifts in both positive and negative directions. Detecting a plurality of absorptions or absorption lines therefore makes it possible to detect a blood picture parameter, for example the blood sugar level, more accurately. 
       FIG. 25  shows a diagram of a method for detecting a blood picture parameter of blood in a blood vessel. The method comprises a first transmission signal with a first frequency being coupled  2501  into the blood vessel, a second transmission signal with a second frequency being coupled  2503  into the blood vessel, a first reception signal being received  2505  at the first frequency, a second reception signal being received  2507  at the second frequency, a first loss variable being established  2509  on the basis of the first transmission signal and the first reception signal at the first frequency, a second loss variable being established  2511  on the basis of the second transmission signal and the second reception signal at the second frequency, a first frequency shift of the first loss variable being ascertained  2513  relative to a first reference loss variable, a second frequency shift of the second loss variable being ascertained  2515  relative to a second reference loss variable and the blood picture parameter being ascertained  2517  on the basis of the first frequency shift and the second frequency shift. 
     By way of example, the method illustrated in  FIG. 25  can be executed by the detection device illustrated in  FIG. 11 . 
       FIG. 26  shows a detection device with a transmitter  2601 , which detection device, for example, comprises a tunable oscillator  2602  and a plurality of transmission antennas  2603 . The detection device furthermore comprises a loss detector  2605 , which can, for example, have a power detector. Furthermore, provision is made for a receiver  2606  with a plurality of reception antennas  2607 . 
     One output of the tunable oscillator  2602  can be connected to each antenna input, for example in succession or in any sequence, in a switchable manner, for example by means of a switching matrix  2609 . Analogously to this, each output of a reception antenna of the plurality of reception antennas  2607  can be connected to the loss detector  2605  by means of a switching matrix  2611 . 
     By way of example, the switching matrix  2611  and the switching matrix  2609  can be used to select that pair comprising a transmission antenna and a reception antenna which enables optimum coupling of a microwave signal into a blood vessel  2613  illustrated schematically in  FIG. 26 . The switching matrices  2609  and  2611  are used to select the antenna pairs in succession, starting with, for example, a first transmission antenna  2615  by means of which a transmission signal is emitted. The switching matrices  2609 ,  2611  can have switches, for example transistor switches. 
     On the reception side, the switching matrix  2611  is used to select the reception antennas in succession, starting with, for example, the reception antenna  2617  for receiving a corresponding reception signal, with a loss variable being detected on the basis of the transmission signal and the reception signal. In the next step, the reception antenna  2619  is for example selected, with a loss variable once again being detected by means of the loss detector on the basis of the transmission signal and a reception signal received by the reception antenna  2619 . After this, for example, the reception antenna  2621  is selected, with a further loss variable being detected on the basis of the transmission signal and a reception signal. In the next step, the reception antenna  2623  is selected and a further loss variable is ascertained on the basis of the transmission signal and a reception signal received by the reception antenna  2623 . In the next step, the switching matrix  2609  can, for example, select a further transmission antenna, wherein the aforementioned steps can be repeated. By a comparison of the established loss variables, the smallest loss variable, for example, is selected. In the example illustrated in  FIG. 26 , it is to be expected, for example, that the detection configuration with the transmission antenna  2615  and the reception antenna  2621  is afflicted with the smallest coupling-in losses because the antennas  2615 ,  2621  lie directly above the blood vessel and therefore enable a signal to be coupled into the blood vessel  2613  in an optimum manner. By way of example, the selected detection configuration can be used for detecting a blood picture parameter. The above-described selection steps can be carried out in any sequence. Thus, for example, all or some of the reception antennas  2607  can be tested for the transmission antenna  2615 . 
     The transmission antennas  2603  or the reception antennas  2607  can differ in respect of their location and/or in respect of their field component which should be excited in a dominant fashion. Here, the switching matrices  2609  and  2611  ensure that the optimal excitation type, for example a loop antenna, an electric dipole antenna, a patch antenna, or excitation location can be selected for the respectively selected frequency. 
     By way of example, the detection device illustrated in  FIG. 26  can be integrated in an inflatable armband. Between the detections of the loss variables, which can, for example, take place by measuring the control parameters, air can be allowed to escape from the armband such that the skin is aerated and no sweat is formed. A time interval between the measurements can be variable in this case. By way of example, the measurements can be carried out at intervals of 10 minutes. However, depending on requirement, more frequent measurements can be carried out, wherein the frequency of the measurements can be ascertained, for example, by the times when the meals are taken. 
     Since the transmission or reception antennas, which lie on the skin and can respectively be formed by an electrode plate, can slip, particularly in the pauses between the measurements, the selection of a plurality of excitation means illustrated in  FIG. 26  can ensure that an excitation means which lies over the blood vessel  2613  is selected. Hence that excitation means which enables a maximum of coupling microwave energy into the blood vessel  2613  can be selected by means of the respective switching matrix  2609  and  2611 .