NON-INVASIVE DETERMINATION OF GLUCOSE

Abstract

The present invention relates to the non-invasive determination of glucose in blood, in particular to the non-invasive determination of glucose in capillary blood.

Claims

1. A device for the non-invasive determination of glucose in the blood of a test subject, wherein the device comprises: (a) a unit for receiving a body region to be examined, originating from the test subject, (b) a radiation source for generating terahertz radiation, in particular terahertz radiation in a wavelength region of from approximately 0.1 mm to approximately 5 mm, from approximately 0.12 mm to approximately 5 mm, or from approximately 0.1 mm to approximately 1 mm, for irradiating the body region to be examined, (c) a unit for acquiring radiation from the body region to be examined, comprising: (i) a unit for acquiring reflected terahertz radiation from the body region to be examined, which unit is designed for acquiring terahertz radiation in a wavelength range in which the intensity of the reflected terahertz radiation changes in a manner dependent on the glucose concentration, (ii) a unit for acquiring the body's own IR radiation from the body region to be examined, which unit is designed for separate acquisition of IR radiation in at least two different wavelengths or wavelength ranges in the wavelength region of from approximately 8 μm to approximately 12 μm, at a first wavelength or a first wavelength range the intensity of the body's own IR radiation being substantially independent of the glucose concentration, and at a second wavelength or a second wavelength range the intensity of the body's own IR radiation changing in a manner dependent on the glucose concentration, and the unit being optionally additionally designed for unspecific acquisition of the body's own IR radiation, and (d) (i) an element for measuring the temperature in the body region to be examined, (ii) optionally an element for adjusting the temperature in the body region to be examined, (e) (i) an element for measuring the temperature in the acquisition unit (c), (ii) an element for adjusting the temperature in the acquisition unit (c), it being provided for the temperature in the acquisition unit (c) to be lower than the temperature in the body region to be examined, and (f) a unit which is designed for temperature-compensated evaluation of the signals originating from the acquisition unit (c), and for determining the glucose concentration on the basis of the evaluated signals, the unit being optionally additionally designed for selective evaluation of the body's own IR radiation, which originates from capillary blood vessels of the dermis of the body region.

2. The device according to claim 1, wherein the radiation source for generating terahertz radiation (b) comprises an antenna, in particular a patch or a dipole antenna.

3. The device according to claim 1, wherein the radiation source for generating terahertz radiation (b) is designed to radiate a frequency-modulated or pulse-modulated terahertz radiation.

4. The device according to claim 1, wherein a focusing lens, e.g. a spherical lens, an aspherical lens or a Fresnel lens is arranged in the beam path between the radiation source for generating terahertz radiation (b) and the body region to be examined, the focusing lens consisting of a material that is substantially transparent for terahertz radiation.

5. The device according to claim 4, wherein the focusing lens is designed to focus the radiation, generated by the terahertz radiation source (b), on a predetermined zone of the body region to be examined, in particular on a zone containing capillary blood.

6. The device according to claim 1, wherein the unit (c) (i) is designed to acquire a broadband spectrum in the terahertz range, in particular within a frequency range of from approximately 0.12 mm to approximately 5 mm (corresponding to 60 GHz to approximately 2.5 THz).

7. The device according to claim 1, wherein the unit (c) (i) is designed to bring about single-step or multi-step amplification, in particular two-step amplification of the terahertz radiation reflected from the body region to be examined.

8. The device according to claim 1, wherein the unit (c) (i) is designed for combined acquisition of reflected terahertz radiation from the body region to be examined and terahertz radiation radiated into the body region to be examined, and in the unit (c) (i) in particular being designed for acquiring frequency-modulated and pulse-modulated signals.

9. The device according to claim 1, wherein the device does not contain an external source for generating IR radiation.

10. The device according to claim 1, wherein the unit for receiving the body region to be examined (a) comprises an element which is thermally insulating, at least in part, with respect to the unit (c) for acquiring radiation, and is intended for deposition of the body region to be examined, and contains a region that is transparent for terahertz radiation in particular from approximately 0.12 mm to approximately 5 mm (corresponding to approximately 60 GHz to approximately 2.5 THz) or in a sub-range thereof, and for IR radiation in the wavelength region in particular of from approximately 8 μm to 12 μm or in a sub-range thereof.

11. The device according to claim 1, wherein the unit for receiving the body surface region to be examined (a) comprises means, e.g. sensors, for acquiring and/or monitoring the contact position and/or contact pressure of the body region to be examined, in particular means for acquiring and/or monitoring a contact pressure in the range of approximately 0.5-100 N, preferably in the range of approximately 1-50 N, and particularly preferably approximately 20 N being provided.

12. The device according to claim 1, wherein the unit for acquiring the body's own IR radiation (c) (ii) comprises at least one first sensor, at least one second sensor, and optionally at least one third sensor, the first sensor being designed for acquiring IR radiation of a first wavelength or a first wavelength range in the region of from approximately 8 μm to approximately 12 μm, where the intensity of the body's own IR radiation is substantially independent of the glucose concentration, the second sensor being designed for acquiring IR radiation of a second wavelength or a second wavelength range in the region of from approximately 8 μm to approximately 12 μm, where the intensity of the body's own IR radiation changes in a manner dependent on the glucose concentration, and the third sensor being designed for referencing the body's own IR radiation.

13. The device according to claim 12, wherein the unit for acquiring the body's own IR radiation (c) (ii) comprises two or more second sensors which are designed for acquiring IR radiation of different wavelengths or wavelength ranges, where the intensity of the body's own IR radiation changes in a manner dependent on the glucose concentration.

14. The device according to claim 1, wherein the unit for acquiring radiation (c) is in contact with a thermally conductive carrier, in particular the unit for acquiring terahertz radiation (c) (i) and the unit for acquiring IR radiation (c) (ii) being in contact with the same thermally conductive carrier.

15. The device according to claim 1, wherein a temperature is provided in the acquisition unit (c) which is at least 5° C., at least 6° C. or at least 7° C., and up to 15° C., less than the temperature of the body region to be examined.

16. The device according to claim 1, wherein the device is provided for sequential acquisition of terahertz radiation and IR radiation, in particular initially acquisition of the body's own IR radiation without irradiation of the body region to be examined being performed, and subsequently irradiation, of the body region to be examined, with terahertz radiation, and acquisition of the reflected terahertz radiation, being performed.

17. The device according to claim 1, wherein the unit (f) is provided for temperature-compensated evaluation of the signals on the basis of the temperature values measured and optionally set by the elements (d) and/or (e).

18. The device according to claim 1, wherein the unit (f) is provided for combined evaluation of the signals from the terahertz acquisition unit (c) (i) and the IR acquisition unit (c) (ii).

19. The device according to claim 1, for non-invasive quantitative determination of glucose in the blood of a test subject.

20. Method for non-invasive quantitative determination of glucose in the blood of a test subject, comprising the steps of: (i) irradiating a body region originating from the test object with terahertz radiation, in particular in a wavelength region of from approximately 0.1 mm to approximately 5 mm, from approximately 0.12 mm to approximately 5 mm, or from approximately 0.1 mm to approximately 1 mm, and acquiring reflected terahertz radiation by means of a unit for acquiring terahertz radiation from the irradiated body region in a wavelength range in which the intensity of the reflected terahertz radiation changes in a manner dependent on the glucose concentration, (ii) separate acquisition of the body's own IR radiation from a body region originating from the test subject by means of a unit for acquiring IR radiation of at least one first wavelength or one first wavelength range in the wavelength region of from approximately 8 μm to approximately 12 μm, where the intensity of the body's own IR radiation is substantially independent of the glucose concentration, and of at least one second wavelength or one second wavelength range in the wavelength region of from approximately 8 μm to approximately 12 μm, where the intensity of the body's own IR radiation changes in a manner dependent on the glucose concentration, and optionally unspecific acquisition of the body's own IR radiation from the irradiated body surface region, for referencing, the temperature in the region of the unit for acquiring IR radiation being lower than the temperature of the body region to be examined, (iii) combined evaluation of the signals acquired according to (i) and (ii) taking account of the temperature of the body region to be examined and the temperature in the region of the units for acquiring terahertz radiation and IR radiation, and optionally selective evaluation of the body's own IR radiation from capillary blood vessels of the dermis of the body region taking place, and (iv) determining the glucose concentration on the basis of the evaluated signals.

21. Method according to claim 20, wherein the determination of the glucose is carried out by acquiring the body's own IR radiation from a fingertip of the test subject, without excitation by an external source of IR radiation.

Description

[0107] FIG. 1 schematically shows the advantages of a combined evaluation of measuring signals from the terahertz range and the IR range, as a result of which the accuracy of the measurement can be increased by improved association of the measuring signals with a specific analyte.

[0108] FIG. 1a shows the absorption spectra of alcohol (red), glucose (green), fructose (blue) and an unknown substance (yellow) in the IR wavelength range of from approximately 8 μm to approximately 10 μm. When using IR sensors (e.g. thermopiles) having a wavelength of 8.5 μm (reference wavelength) and 9.6 μm (analyte-specific wavelength), it is possible to reliably distinguish between glucose and the unknown substance. In contrast, distinguishing between glucose and fructose is difficult. FIG. 1b shows an absorption spectrum in the terahertz wavelength range of 400 μm to 100 μm (corresponding to a frequency of from 0.5 to 4.0 THz) of glucose (black), fructose (red; dotted) and the unknown substance (yellow). In the terahertz range, it is possible to reliably distinguish glucose and fructose, whereas the absorption spectra of glucose and the unknown substance overlap. In the case of a combination of the absorption spectra in the IR range and the terahertz range, an improved distinction of the individual substances is possible, which brings about an increase in the measuring accuracy.

[0109] FIG. 2 is a schematic view of an embodiment of the device. The device contains a source for terahertz radiation (100), e.g. a femtosecond laser having a wavelength of 800 nm, the radiation of which is first guided through a semipermeable beam splitter (102) and is split, there, into partial beams (104a) and (104b). The partial beam (104a) is converted, in a mixer (106), e.g. a gallium arsenide crystal, into terahertz radiation (108), which is guided through an optical device (110), e.g. a prism (on a body region (112) to be examined, e.g. a fingertip. The radiation reflected out of the body region is guided via the optical element (110), a further mixer (114), e.g. a gallium arsenide crystal, and optionally a further semipermeable beam splitter (116), into a terahertz sensor (118), e.g. a photo diode, which is designed for acquiring a spectrum in the terahertz range. The partial beam (104b) from the beam splitter (102) can optionally be guided, for the purpose of referencing, via a delay element (120), into the mixer (114), and from there into the photodiode (118). The device furthermore contains an IR acquisition unit (120) having one or more IR sensors which are designed for acquiring the body's own IR radiation from the body region (112) to be examined. The measuring signal from the IR sensor (120) is guided into an evaluation unit (124), e.g. a CPU. The evaluation is performed in the unit (124) in combination with the measuring signal from the terahertz sensor (118), optionally following a fast Fourier transform in the unit (128). In the evaluation unit (124), from the combined terahertz and IR measuring signals a value (126) for the concentration of the analyte, e.g. glucose, determined, which can then be displayed in a suitable manner, e.g. by means of a display (not shown).

[0110] The device furthermore contains a carrier element (130), e.g. a metal carrier such as copper, which is provided for receiving at least the IR acquisition unit (120) and optionally further elements, such as the optical device (110) and/or the terahertz sensor (118). The temperature of the carrier element (130) can be stabilized using suitable means, in order to allow for a temperature-compensated measurement of the IR signal and optionally of the terahertz signal.

[0111] FIG. 3 shows a further embodiment of the device. The device contains a terahertz transceiver chip (200) which emits terahertz radiation (202) into the body region (204) to be examined, e.g. a fingertip, and is designed for acquiring the terahertz radiation (206) reflected therefrom. The measuring signal from the chip (200) is guided to the evaluation unit (212), e.g. a CPU, via a fast Fourier transform unit (210). The device furthermore contains at least one IR sensor (214) for acquiring the body's own IR radiation (216) from the body region (204) to be examined. The measuring signal acquired by the at least one IR sensor (214) is guided into the evaluation unit (212) and evaluated there in combination with the terahertz measuring signal.

[0112] FIG. 4 is a detailed view of an embodiment of the IR acquisition unit. A body region (14), to be examined, of a test subject, is introduced into the device.

[0113] In this case, a body region having a good supply of blood, such as a fingertip, is preferably selected. The body region (14) rests on a support element (16) which thermally isolates and contains a region (16a) which is optically transparent, at least in part, i.e. at least in the region of the measuring wavelengths, for the IR radiation (20) originating from the body region (14). The support element (16) contains means (16b) for determining the temperature of the body region to be examined, such as a fingertip (14), e.g. a temperature sensor. Furthermore, means, e.g. sensors, for acquiring and/or monitoring the contact position and/or the contact pressure of the body region to be irradiated may be provided (not shown). The support element can furthermore contain a temperature adjustment element (not shown).

[0114] IR radiation (20) from the body region (14) to be examined originates at least in part from the blood capillaries, close to the surface, in the region of the dermis (18), which capillaries are located at a distance of from approximately 2.5 to 3 mm from the body surface. An analyte located in the blood capillaries or optionally in adjacent tissue absorbs the radiation in the range of the specific absorption band thereof, the extent of the absorption correlating with the concentration of the analyte.

[0115] The device furthermore contains a first sensor (22a) and a second sensor (22b) for separate acquisition of the body's own IR radiation at different wavelengths or wavelength ranges (20) in the region of preferably 8-12 μm. The first and the second sensor can be designed as bolometers or thermopiles. Optionally, the first and the second sensor can also consist of arrays of individual sensor elements, e.g. 8×8 individual sensor elements.

[0116] The first sensor (22a) is designed for selective acquisition of the body's own radiation having a first wavelength or a first wavelength range from an absorption minimum of glucose, a first filter element (24a) being provided which is selectively permeable for radiation having the first wavelength or having the first wavelength range. That is to say that the signal measured by the first sensor is substantially independent of the glucose concentration. The second sensor (22b) is in turn designed for selective acquisition of the body's own radiation (20) having a second wavelength or a second wavelength range from an absorption band, preferably in the region of an absorption maximum of glucose, a second filter element (24b) being provided which is selectively permeable for radiation having the second wavelength or having the second wavelength range. This means that the signal acquired by the second sensor is dependent on the glucose concentration. Two or more second sensors may optionally be provided, which can acquire radiation having different wavelengths or wavelength ranges. For the determination of glucose it is possible for example for two second sensors to be used, which in each case separately acquire IR radiation in the range of 9.1 μm and 9.6 μm.

[0117] The filter elements (24a, 24b) are expediently arranged such that they rest directly on the relevant sensors (22a, 22b).

[0118] The device optionally furthermore comprises a third sensor (22c) which is designed for unspecific acquisition of the body's own IR radiation (20) and serves for referencing, e.g. for referencing the body temperature in the body region (14) to be examined.

[0119] The sensors (22a, 22b and optionally 22c) can optionally be equipped with optical lens elements, e.g. biconvex lenses, in particular spherical lenses, in order to allow for focusing of the impinging body's own IR radiation.

[0120] The sensors (22a, 22b and optionally 22c) are in thermal equilibrium, in that they are in contact with a block (32) made of a conductive material, e.g. metal, or are embedded therein, e.g. in that they are arranged in a depression of the block. Alternatively, the thermally conductive material can also be designed as a plate or foil.

[0121] Furthermore, means (26) for determining the temperature of the block (24) containing the sensors (22a, 22b and optionally 22c), e.g. a temperature sensor, and means (28) for adjusting the temperature of the block (24) containing the sensors (22a, 22b and optionally 22c), e.g. cooling and/or heating elements, are provided.

[0122] The signals originating from the sensors (22a, 22b and optionally 22c), and the temperatures determined by the elements (16b) and (26) are transmitted to a CPU unit (30), if required an adjustment of the temperature for the sensors (22a, 22b and 22c) to a value that is lower than the temperature of the body region to be examined, and a temperature-compensated evaluation of the signals, being performed. The glucose concentration is determined on the basis of said evaluation. The result can then be shown in a display (32).

[0123] The inside (34) of the measuring system can be coated or equipped, entirely or in part, with a surface made of a material which does not reflect the IR radiation (20) originating from the body region (14) and/or which absorbs the IR radiation (20) originating from the body region (14).

[0124] The measuring system can furthermore comprise a coating or a housing which brings about electrical and/or thermal insulation with respect to the surroundings.

[0125] An alternative embodiment for separate acquisition of the body's own IR radiation at different wavelengths is shown in FIG. 5. The absorption curve of glucose in the region between 8 and 14 μm is shown as a bold line (G). For the purpose of separate acquisition of IR radiation having two different wavelengths, from this region, two sensors are used, which comprise different combinations of bandpass, highpass and/or lowpass filter elements. In one embodiment, the two sensors contain a wide bandpass filter (C) having a permeability in the region between 8 and 14 μm. In the case of the first sensor, the filter (C) is combined with a highpass filter (A) which is permeable for IR radiation having a wavelength of approximately 8.5 μm or less. A sensor that is equipped with the filters (A) and (C) will therefore acquire a signal from the region of 8-8.5 μm, which is substantially independent of the concentration of glucose. The second sensor is equipped with a combination of the bandpass filter (C) with a lowpass filter (B), which is permeable for IR radiation having a wavelength of 8.5 μm or more. The signal acquired by said sensor comprises an absorption band of glucose located in the region of approximately 9-10 μm, and is therefore dependent on the glucose concentration. Differential evaluation of the signals acquired by the two sensors makes it possible for the glucose concentration to be determined.

[0126] In another embodiment, a first sensor can also be equipped with the bandpass filter (C) and the highpass filter (A), while a second sensor is equipped only with the bandpass filter (C). The signal acquired by the first sensor is independent of the glucose concentration, while the signal acquired by the second sensor changes with the glucose concentration.

[0127] FIG. 6 is a schematic cross-sectional view of a further embodiment of the IR acquisition unit of the device. In this case, the body region, to be examined, of the test subject (not shown), is arranged on a thermally insulating support element (66) which contains a region (66a) which is optically transparent for IR radiation, at least in part. The optically transparent region (66a) is for example an Si or Ge slice. The support element (66) is provided with a temperature sensor (66b) and optionally with a temperature adjustment element (not shown), which preferably comprises a Peltier element. In this case, the temperature of the body region can for example be set to a range of approximately 28-38° C. The support element (66) preferably contains means, e.g. sensors (68), for acquiring and/or monitoring the contact pressure, such as a load cell, as well as, optionally, sensors for acquiring and/or monitoring the contact position, such as a camera and/or a pulse sensor. Expediently, a contact pressure of approximately 1-50 N, e.g. approximately 20 N, is set.

[0128] The device furthermore contains a first IR sensor (70a) and a second IR sensor (70b) for acquiring the body's own IR radiation (72) having different wavelengths in the region of 0.7-20 μm, preferably of 3-20 μm, from the body region examined. The first and the second sensor can in each case be designed as a bolometer or as a thermopile. Optionally, the first and the second sensor can also consist of arrays of individual sensor elements.

[0129] The first sensor (70a) can be designed for selective acquisition of the body's own IR radiation having a first wavelength, from an absorption minimum of the analyte, for example, a first filter element (74a), e.g. a bandpass filter having a narrow permeability being provided, which is selectively permeable for radiation having the first wavelength, in which the signal is substantially independent of the concentration of the analyte to be determined. For the determination of glucose, the first wavelength is for example 8.1±0.3 μm and/or 8.5±0.3 μm, preferably 8.1±0.2 μm and/or 8.5±0.2 μm, particularly preferably 8.1±0.2 μm, and/or 8.5±0.1 μm. The second sensor (74b) is in turn designed for selective acquisition of the body's own IR radiation (72) having a second wavelength from an absorption band, preferably in the region of an absorption maximum of the analyte to be determined, a second filter element (74b), e.g. a bandpass filter having narrow permeability, being provided which is selectively permeable for radiation having the second wavelength. During the determination of glucose, the second wavelength is for example 9.1±0.3 μm, 9.3±0.3 μm and/or 9.6±0.3 μm, preferably 9.1±0.2 μm, 9.3±0.2 μm and/or 9.6±0.2 μm, particularly preferably in the region of 9.1±0.1 μm, 9.3±0.1 μm, and/or 9.6±0.1 μm. Two or more second sensors may optionally be provided, which can acquire radiation having different wavelengths or wavelength ranges. For the determination of glucose it is possible for example for two second sensors to be used, which in each case separately acquire IR radiation in the region of 9.1 μm or 9.3 μm and 9.6 μm.

[0130] The filter elements (74a, 74b) are expediently in direct contact with the sensors (70a, 70b).

[0131] Alternatively, instead of bandpass filters having narrow permeability, the combination, shown in FIG. 5, of a bandpass filter having wider permeability and a highpass and/or a lowpass filter, can be used.

[0132] Optical focusing elements, e.g. lens elements, can be arranged in the beam path of the body's own IR radiation (72), between the body part to be examined and the sensors (70a, 70b and optionally 70c). For example, the sensors (70a, 70b) can optionally be equipped with optical lens elements, e.g. biconvex lenses, in particular spherical lenses, in order to allow for focusing of the impinging body's own IR radiation.

[0133] The device optionally furthermore comprises a third sensor (70c) which is designed for unspecific acquisition of the body's own IR radiation (72) and serves for referencing, e.g. for referencing the body temperature in the body region to be examined. The third sensor (70c) can be designed as a bolometer or thermopile.

[0134] Optionally a partition wall (78) can be arranged between the first sensor (70a) and the second sensor (70b).

[0135] The sensors (70a, 70b and optionally 70c) are in thermal equilibrium, in that they are in contact with thermally conductive material, e.g. a block (76), a plate, or a film made of metal.

[0136] Furthermore, an element (80) for determining the temperature of the block (76) containing the sensors (70a, 70b and 70c) is provided, e.g. a temperature sensor. Furthermore, an element (82) for adjusting the temperature of the block (76) containing the sensors (70a, 70b and 70c) is provided, e.g. a cooling and/or heating element.

[0137] The signals originating from the sensors (70a, 70b and optionally 70c), and the temperatures determined by the elements (66b) and (80) are transmitted to a CPU unit (84) for temperature-compensated evaluation of the signals. The concentration of the analyte is determined on the basis of said evaluation, and the result can then be shown in a display (86). The CPU unit can furthermore be used for controlling the elements (68, 82).

[0138] Optionally, the inner surface of the measuring system can be coated with a material which is non-reflective for IR radiation and/or which absorbs IR radiation. Furthermore, the measuring system can comprise a thermal insulation with respect to the surroundings.

[0139] FIG. 7 shows a particularly preferred arrangement of sensors in the IR acquisition unit. In this case, four IR sensors (90a, 90b, 90c and 90d) are provided, which are arranged together in a depression of a metal block (not shown) and are thus thermally equilibrated. Preferably, each of the sensors consists of an array of a plurality of, e.g. 8×8, individual sensor elements. The sensors (90a, 90b) are provided for selective acquisition of IR radiation having a wavelength from an absorption band of the analytes to be determined, and are therefore equipped with corresponding filter elements. For the determination of glucose, the sensor (90a) can be provided for selective acquisition of IR radiation having a wavelength of approximately 9.6 μm, e.g. 9.6±0.1 μm and the sensor (90b) can be provided for selective acquisition of IR radiation having a wavelength of approximately 9.1 μm, e.g. 9.1±0.1 μm or approximately 9.3 μm, e.g. 9.3±0.1 μm. The sensor (90c) is provided for selective acquisition of IR radiation having a wavelength from an absorption minimum of the analytes to be determined, and are therefore equipped with corresponding filter elements. For the determination of glucose, the sensor (90c) can be provided for selective acquisition of IR radiation having a wavelength of approximately 8.5 μm, e.g. 8.5±0.1 μm. The sensor (90d) does not contain a filter element, and is used for referencing.

[0140] FIG. 8 shows a particularly preferred embodiment of a terahertz transceiver element comprising a focusing lens. A terahertz transceiver element (100) contains a terahertz radiation source (102), e.g. an antenna, and a terahertz acquisition unit (104).

[0141] Terahertz radiation (106) emitted by the radiation source (102) is guided through a focusing lens (108), e.g. a spherical lens. The lens consists of a material that is transparent for terahertz radiation, such as polypropylene.

[0142] The radiation (106) is focused by the lens (108) on a predetermined zone (112) of the body region (110) to be examined, e.g. a finger (capillary blood region or saturated tissue). The focusing preferably takes place at a predetermined penetration depth, e.g.

[0143] a penetration depth of 3-4 mm. The radiation (114) reflected from the focusing zone (112) is in turn guided through the lens (108), focusing on the terahertz acquisition unit (104) taking place.

[0144] FIG. 9 shows a particularly preferred embodiment for the evaluation of a terahertz measuring signal. The frequency of a terahertz signal is modulated over a range (f0 . . . f1) which contains an absorption band of glucose as the analyte to be determined. The modulation can take place continuously, e.g. by means of voltage variation using a voltage-controlled oscillator (VCO), or discontinuously.

[0145] The frequency-modulated terahertz signal reaches an antenna, e.g. a patch antenna (PA), and is radiated there to the body region (K) to be examined, e.g. a finger. This can be achieved by means of a lens (see e.g. FIG. 8) or a waveguide. Here, the terahertz radiation is reflected and reaches a sensor (S), e.g. a patch antenna or a dipole, and from there reaches a preamplifier, e.g. an LNA.

[0146] Subsequently, the signal is guided to a mixer (X) which multiplies the received signal and the transmit signal. On account of the distance to the body region and back again, the received signal has a different path length from the transmit signal. On account of the frequency modulation and the different path length and transit time for the received signal and the transmit signal, a frequency difference which is proportional to the transit time difference (e.g. path length difference of approximately 50 mm, corresponding to a transit time difference of 166 psec) results at the mixer. As a result a mixed signal (sin(fa)*(fb)=sin(fa+fb) and sin(fa-fb) results, the difference being the useful signal, which is further amplified by an amplifier (AMP). One or more phases of the signal are guided to an A/D converter and evaluated by a CPU.

[0147] The evaluation preferably comprises a fast Fourier transform (FFT), performed continuously, for filtering out undesired parasitic signals. Thus a different spectrum results, in each case, on the THz transmitter, as the frequency (f0 . . . f1) increases, in a manner controlled by the voltage input. The signal corresponding to the beam path to the capillary layer and back can be identified by its characteristic transit time difference, and tapped. As a result, a characteristic curve progression is obtained, which corresponds to the reflection and absorption spectrum of glucose in the capillary blood. A comparative measurement at the absorption maxima and the absorption minima of glucose gives the glucose content in the capillary blood.

[0148] Alternatively to the frequency modulation, the terahertz signal can also be irradiated onto the body region to be examined as a pulse-modulated signal, signal pulses, in particular discrete signal pulses having a different frequency in each case, being radiated in at predetermined time intervals.