WO2014048799A2

WO2014048799A2 - Sensor arrangement for non-invasive measurements of dielectric permittivity of liquids

Info

Publication number: WO2014048799A2
Application number: PCT/EP2013/069303
Authority: WO
Inventors: Mohamed Ratni; Stefan Koch
Original assignee: Sony Corporation; Sony Deutschland Gmbh
Priority date: 2012-09-25
Filing date: 2013-09-17
Publication date: 2014-04-03
Also published as: WO2014048799A3

Abstract

A sensor arrangement for non-invasive measurements of dielectric permittivity of liquids comprises a signal splitter, a reference path coupled to said signal splitter including a reference sensor comprises a reference fluid container containing a reference fluid, and a measurement path including a measurement sensor that receives the other one of said input signals and comprises a measurement area. A combiner adds a reference signal output on the reference path and a measurement signal output on the measurement path to obtain a sensor signal. A processor determines a change in amplitude and/or phase of said sensor signal compared to one or more reference signals obtained in reference measurements using reference fluids and determines the dielectric permittivity of the measurement fluid from said determined change in amplitude and/or phase of said sensor signal. The reference sensor and the measurement sensor each comprises two or more coupled microstrip lines.

Description

SENSOR ARRANGEMENT FOR NON-INVASIVE MEASUREMENTS OF DIELECTRIC PERMITTIVITY OF LIQUIDS

BACKGROUND

Field of the Disclosure

[0001] The present disclosure relates to a sensor arrangement and a sensing method for non-invasive measurements of dielectric permittivity of liquids, in particular to determine the concentration of biological constituents. Further, the present invention relates to a device for non-invasive measurements of dielectric permittivity of liquids comprising such a sensor arrangement. Description of Related Art

[0002] Non-invasive method for determining dielectric permittivity of liquid solution has attracted many researchers in the last decade. One area of interest for the application is in the field of medical diagnostic, blood analysis and food quality check. Different technologies such as optical, chemical and electromagnetic technologies have, for instance, been applied to detect blood glucose concentration. Some of them succeeded but are still not sufficiently comfortable and convenient. Non-invasive methods typically employ optical or electromagnetic technology. The optical technology has some drawbacks of being non-penetrating and suffering from too low skin depth, while the electromagnetic technology can overcome this obstacle.

[0003] Non-invasive liquid concentration determination has been widely investigated. US 7,315,767 B2 uses a microstrip antenna to measure impedance using a modulated signal at lower frequency. The disadvantage of such a technique is that the antenna is operating in the near field range where the impedance measurement is not very accurate. The frequency used has a very deep skin depth penetration which makes the impedance measurement not precise due to the impedance characteristics of the multiple skin layers. In US 7,371,217 B2 it is described that the capability of such a technique using a rectangular waveguide at high mm-wave frequency. The drawback of using a waveguide is the measurement of the reflection coefficient at a resonant frequency. Such a method might not fulfill the requirements in term of accuracy for blood glucose determination where an order of mmol/liter needs to be determined. Moreover, it is quite difficult to imagine the integration of such sensor into a practical solution for measuring blood glucose concentration.

[0004] WO 2006/107972 A2 discloses a device including a splitter that splits a time varying signal into two substantially equal power signals. A reference capacitor having a fluidic channel between capacitor plates is coupled to one of the equal power signals and a detection capacitor having a fluidic channel between capacitor plates is coupled to the other of the equal power signals. A combiner is coupled to outputs of the reference capacitor and detection capacitor. The signals are shifted 180 degrees from each other in the absence of an analyte in the fluidic channel at or prior to the combiner. In one embodiment the device is formed of microstrip circuit elements, or planar waveguide elements, and operates at microwave frequencies.

[0005] The "background" description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventor(s), to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.

SUMMARY

[0006] It is an object to provide a sensor arrangement and a sensing method for non-invasive measurements of dielectric permittivity of liquids that provide an increase accuracy and sensitivity. It is a further object to provide a device for non-invasive measurements of dielectric permittivity of liquids including such a sensor arrangement.

[0007] According to an aspect there is provided a sensor arrangement and a sensing method for non-invasive measurements of dielectric permittivity of liquids comprising

a signal splitter that splits a millimeter wave or microwave signal into two substantially equal input signals,

a reference path coupled to said signal splitter including a reference sensor that receives one of said input signals and comprises a reference fluid container containing a reference fluid,

a measurement path coupled to said signal splitter including a measurement sensor that receives the other one of said input signals and comprises a measurement area that is configured to contain a measurement fluid or be placed in contact or adjacent to a measurement zone containing said measurement fluid, a phase shifter included in said reference path and/or said measurement path that provides a predetermined phase shift between said two input signals,

a combiner coupled to said reference path and said measurement path that adds a reference signal output on the reference path and a measurement signal output on the measurement path to obtain a sensor signal,

a processor coupled to said combiner that determine a change in amplitude and/or phase of said sensor signal compared to one or more reference signals obtained in reference measurements using reference fluids and that determines the dielectric permittivity of the measurement fluid from said determined change in amplitude and/or phase of said sensor signal,

wherein said reference sensor and said measurement sensor each comprises two or more coupled microstrip lines.

[0008] According to a further aspect there is provided a device for non- invasive measurements of dielectric permittivity of liquids, comprising:

two reference paths coupled to said signal splitter each including a reference sensor that receives one of said input signals and comprises a reference fluid container containing a reference fluid,

a phase shifter included in one or both of said reference paths that provides a predetermined phase shift between said two input signals,

a combiner coupled to said reference paths that adds the reference signal outputs on the reference paths to obtain a reference signal, and

a sensor arrangement as claimed in claim 1, wherein the processor of said sensor arrangement is also coupled to said combiner to obtain said reference signal and is configured to determine a change in amplitude and/or phase of the sensor signal obtained from said sensor arrangement compared to said reference signal and to determine the dielectric permittivity of the measurement fluid from said determined change in amplitude and/or phase of said sensor signal. [0009] According to a still further aspect there is provided a sensing method for non- invasive measurements of dielectric permittivity of liquids, comprising:

splitting a millimeter wave or microwave signal into two substantially equal input signals,

receiving one of said input signals on a reference path including a reference sensor that comprises a reference fluid container containing a reference fluid,

receiving the other one of said input signals on a measurement path including a measurement sensor that comprises a measurement area that is configured to contain a measurement fluid or be placed in contact or adjacent to a measurement zone containing said measurement fluid, wherein said reference sensor and said measurement sensor each comprises two or more coupled microstrip lines,

providing a predetermined phase shift between said two input signals,

adding a reference signal output on the reference path and a measurement signal output on the measurement path to obtain a sensor signal,

determining a change in amplitude and/or phase of said sensor signal compared to one or more reference signals obtained in reference measurements using reference fluids, and

determining the dielectric permittivity of the measurement fluid from said determined change in amplitude and/or phase of said sensor signal.

[0010] Preferred embodiments are defined in the dependent claims. It shall be understood that the claimed sensing method and the claimed device have similar and/or identical preferred embodiments as the claimed sensor arrangement and as defined in the dependent claims.

[0011] One of the aspects of the disclosure is to use, preferably parallel, coupled lines in an interferometric way, preferably at the frequency of water relaxation (water constitutes of more than 60 % of blood). The proposed solution overcomes the disadvantages of many of the known solutions for measuring liquid constituents, e.g. blood glucose, by an improvement of the accuracy and sensitivity using a pair of coupled lines arrays in the sensor arrangement, particularly one coupled line array in the reference sensor and one coupled line array in the measurement sensor. The sensor arrangement preferably operates in the reflectometry type of method. One sensor is used as reference while the other sensor is measuring. Both signals are then compared. The obtained result may then be converted to concentration values.

[0012] Such a method of operation ensures high resolution and accuracy, particularly if a proper coupled line design is optimized. This measurement method can eliminate all the imperfections and mismatch of the circuitry. Moreover, it can compensate for outside parameters which can deteriorate the measurement. Among the different possible application areas glucose monitoring is one application area, but generally "dielectric characterization of liquids" is a common application.

[0013] Thus, the operating mode is based on a non-invasive method using electromagnetic waves. Based on transmitted/and or reflected signal the microwave energy is detected and complex dielectric permittivity is measured.

[0014] In an embodiment the proposed sensor arrangement comprises a millimeter wave generator and a millimeter wave receiver to monitor and detect the transmitted/reflected millimeter wave energy. In this context it shall be noted that radiation is preferably used having a wavelength range in the millimeter wave and/or microwave range. If herein reference is made to either millimeter wave or microwave signals or radiation it shall include both millimeter wave or microwave signals or radiation.

[0015] In a preferred embodiment an in-situ calibration kit (i.e. calibration elements) is included in the proposed device. The calibration kit has been designed and integrated together with the sensor arrangement to avoid calibration mismatch and allow in-situ calibration at any time of the measurement stage. [0016] It is to be understood that both the foregoing general description of the invention and the following detailed description are exemplary, but are not restrictive of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

Fig. 1 shows a schematic diagram of a first embodiment of the proposed sensor arrangement,

Fig. 2 shows an embodiment of an array of coupled microstrip lines,

Fig. 3 shows cross sections of a sensor with air, water and skin layer as overlay,

Fig. 4 shows a schematic diagram of an embodiment of the proposed device,

Fig. 5 shows a schematic diagram of an embodiment of a reference sensor arrangement as used in the proposed device shown in Fig. 4,

Fig. 6 shows a schematic diagram of a second embodiment of the proposed sensor arrangement,

Fig. 7 shows a diagram of the sensor sensitivity versus water permittivity,

Fig. 8 shows a diagram of the sensor insertion loss for a water solution at different permittivity values, Fig. 9 shows a diagram of the sensor insertion loss versus the coupled line gap, and

Fig. 10 shows a flowchart illustrating the proposed sensing method.

DESCRIPTION OF THE EMBODIMENTS

[0018] Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, Fig. 1 shows a schematic diagram of a first embodiment of a sensor arrangement 1 for non-invasive measurements of dielectric permittivity of liquids according to the present disclosure. It comprises a signal splitter 10 that splits a millimeter wave or microwave signal 11 into two substantially equal input signals 12, 13. A reference path 20 is coupled to said signal splitter 10. The reference path 20 includes a reference sensor 21 that receives one of said input signals 12 and comprises a reference fluid container 22 containing a reference fluid, e.g. water (having a well known permittivity) but other liquids could be also used. For instance, if the concentration of a substance which contains alcohol shall be measured, a reference substance with a known concentration of alcohol is preferably used as a reference. The same principle can be used for the determination of the concentration of other substances.

[0019] Further, a measurement path 30 is coupled to said signal splitter 10. The measurement path 30 includes a measurement sensor 31 that receives the other one of said input signals 13 and comprises a measurement area 32 that is configured to contain a measurement fluid or be placed in contact or adjacent to a measurement zone containing said measurement fluid. For instance, a measurement fluid container (similar or equal to the reference fluid container 22) may be provided into which the measurement fluid is filled, or the measurement area may be arranged such that it can be brought into contact with a subject (e.g. skin of a person or animal) to non-invasively measure the dielectric permittivity of blood. [0020] A phase shifter 40 is included in the measurement path 30 to provide a predetermined phase shift, preferably of substantially 180° between said two input signals 12, 13. For this purpose the phase shifter 40 may generally be included in the reference path 20 or the measurement path 30 as a single element, but there may also be several phase shifter elements in both the reference path 20 and the measurement path 30 to obtain the (total) desired phase shift. Further, phase shifter elements may be placed before (as shown in Fig. 1) and/or behind the respective sensor for this purpose. It is generally only relevant, irrespective of the particular implementation that the desired (total) phase shift is obtained by the phase shifter 40.

[0021] A combiner 50 (in particular a power/signal combiner, sometimes also referred to as detector) is coupled to the reference path 20 and the measurement path 30. The combiner 50 adds a reference signal 23 output on the reference path 20 and a measurement signal 33 output on the measurement path 30 to obtain a sensor signal 51. Finally, a processor 60 is coupled to the combiner 50 to determine a change in amplitude and/or phase of said sensor signal 51 compared to one or more reference signals 52 obtained in reference measurements using reference fluids and to determine the dielectric permittivity 61 of the measurement fluid from said determined change in amplitude and/or phase of said sensor signal.

[0022] The reference signals 52 can be obtained in advance reference measurements by the same sensor arrangement while in the measurement area 32 the same reference fluid is present as in the reference fluid container 22. These reference signals 52 are then stored in a storage medium (not shown) and used later during the actual measurement of a measurement fluid.

[0023] In an alternative embodiment the reference signals can be obtained simultaneous to the measurement of the measurement fluid with a separate sensor arrangement as will be explained below. [0024] The reference sensor 21 and the measurement sensor 31 each comprises two or more coupled microstrip lines. An embodiment of an array 70 of several microstrip lines 71-76 is depicted in Fig. 2. The microstrip lines 71-76 are deposited on a surface (i.e. a common microstrip plane) of a substrate 77 which insulates them from a ground layer (not shown) that is generally formed on the opposite surface of the substrate 77. The signal is coupled into the array 70 at a signal input 78 and is coupled out from the array at a signal output 79.

[0025] The microstrip lines are displaced in two orthogonal directions so that there is a gap g between neighboring microstrip lines and that there is coupled line cell length. In this embodiment the size of the gap g between neighboring mictrostrip lines is equal for all gaps, but can also be different for different gaps. The coupled line cell length (i.e. the length of two overlapping microstrip lines) is e.g. in the range of 2 to 3 centimeters. Each array comprises at least two coupled microstrip lines.

[0026] The principle of the transmission type of sensor measures the changes in the transmission phase due to a change of the medium / the surrounding. The sensitivity to a medium change is depending/affected by the change in the phase constant: φ_Δ = φ₂- φι = 1*β₂ - 1* βι = 1 * Αβ y = a+ j wherein φ = the phase constant and / is the length of the coupled microstrip line.

[0027] The coupled microstrip line can be modelled by an equivalent capacitive network. The change in the capacitance of the circuit network implies a change in the phase constant. The impedance characteristics use even and odd mode impedances Zo=(Zo_e*Zo_o)^1/2. The phase constant can be increased by increasing the length of the structure by meander line or hair pin type of structure, or by increasing the phase constant

P-

[0028] In the present case the capacitance which is directly in contact with the surrounding media corresponds to the odd mode capacitance. The odd impedance is related

1/2

to the odd mode capacitance by Z_0o= l/c*(C₀(aii) *C₀) . Hence, in the design the odd mode impedance of the structure is optimized in order to improve the sensitivity.

[0029] Further details regarding the design and function of coupled microstrip lines are generally known in the art and shall not be explained in more detail here.

[0030] The method of operation of the proposed sensor arrangement is based on the interferometer principle as is generally known, e.g. from WO 2006/107972 A2. This technique works by superposing (interfering) the signal waves from different sources on the principle that waves that coincide with the same phase will add to each other while two waves that have opposite phases will cancel each other out. In the proposed sensor arrangement the input signal 11 is split into two branches with equal magnitude but with different phase (preferably in anti-phase, i.e. with a phase shift of 180°. The signals are then added up at the end of the two branches. If both liquids (i.e. reference liquid and measurement liquid) have exactly the same characteristics the resulting signal are two signals in anti-phase. Therefore, the signal is totally cancelled (destructive waves). If a small difference in both liquids exists the transmission characteristics will differ. Therefore, the resulting signal is then added because the signals have a phase difference different from the phase difference of the input signals (e.g. different from 180°). This method of operation increases the resolution of the proposed sensor arrangement.

[0031] The measurement method relies on the measurement of the transmission parameters between the input and the output of the sensor device. It is know that the propagation constant of a coupled microstrip line depends on the permittivity of the substrate. Moreover, it depends also on the dielectric permittivity of the overlay medium. Usually in an electronic circuit the overlay is air as depicted in Fig. 3A (except in stripline where the overlay is substrate with a certain dielectric permittivity). According to the present disclosure the overlay is a liquid under test (as depicted in Fig. 3B) or skin containing blood as liquid under test (as depicted in Fig. 3C), whose permittivity needs to be determined. The overlay will change the propagation characteristics of the coupled mi- crostrip lines. The odd capacitance has been optimized and is very sensitive to overlay changes. This means that when the overlay dielectric permittivity changes, the propagation characteristics and therefore the transmission parameter changes.

[0032] The changes of the propagation constant (phase constant) value due to the overlay dielectric permittivity might be very small. It is therefore difficult to measure the phase values because of uncertainties and resolution, especially at high frequencies, e.g. in the range of GHz. The above explained method of interferometry is therefore used in order to measure amplitude changes due to phase changes.

[0033] Fig. 4 shows a schematic diagram of an embodiment of a device 100 according to the present disclosure. It comprises a reference sensor arrangement 110 and a measurement sensor arrangement 120. The measurement sensor arrangement 120 generally corresponds to the sensor arrangement as shown in Fig. 1. The reference sensor arrangement 110 is also very similar to the sensor arrangement shown in Fig. 1, but instead of the measurement sensor a second reference sensor is provided. An embodiment of the reference sensor arrangement 110 is shown in Fig. 5.

[0034] The reference sensor arrangement 110 comprises a signal splitter 1 11 that splits a millimeter wave or microwave signal into two substantially equal input signals, two reference paths 112, 113 coupled to said signal splitter 111 each including a reference sensor 114, 115 that receives one of said input signals and comprises a reference fluid container containing a reference fluid, a phase shifter 116 included in one or both of said reference paths 112, 113 that provides a predetermined phase shift between said two input signals, and a combiner 117 coupled to said reference paths that adds the reference signal outputs on the reference paths to obtain a reference signal 118.

[0035] Thus, contrary to the measurement sensor arrangement 120 both reference fluid containers of both reference sensors 114, 115 contain the same reference fluid. The obtained reference signals 118 at the output of the combiner 117 of the reference sensor arrangement are used in this embodiment as reference signals 52 (see Fig. 1) and are provided to the processor 60 of the measurement sensor arrangement 120 to determine a change in amplitude and/or phase of the sensor signal (51) obtained (at the output of the combiner 50) from said measurement sensor arrangement 120 compared to said reference signal 151 (52) and to determine the dielectric permittivity of the measurement fluid from said determined change in amplitude and/or phase of said sensor signal (51).

[0036] In order to take into account of the imperfection of the substrate and the tolerances (fabrication imperfections) means for calibration are preferably provided as shown in the embodiment of the device depicted in Fig. 4. A calibration kit including various calibration elements 130, 131, 132, 133 is preferably designed on the same substrate as the reference sensor arrangement 110 and the measurement sensor arrangement 120. The calibration of the device is generally done in a first step before the measurement. The calibration procedure can use any known type of calibration method (full two port, TRL (Thru, Reflect and Line), LRM (Line, Reflect and Match)... etc). The calibration ensures that all the imperfections and tolerances are taken into account in the calibration coefficients. Those are determined trough the procedure and stored. These calibration coefficients are needed to determine the final transmission parameters.

[0037] Switches 140, 141, preferably switch banks, ensure to direct the signal between different calibration elements and to the reference sensor arrangement 110 and the measurement sensor arrangement 120. The calibration can be done at any step of the measurement stage. Moreover, it can be repeated as many times as needed to ensure a good performance and reliable results. The switch 140 also has the role of a power splitter to split the input signal between the reference sensor arrangement 110 and the measurement sensor arrangement 120. The switch 141 also has the role of an adder to add the signals output from the reference sensor arrangement 110 and the measurement sensor arrangement 120.

[0038] In this embodiment, once the calibration is done the coefficients are stored. The measurement can be then performed. In an embodiment, first the measurement is performed with the reference sensor arrangement 110 to obtain reference signals. Then, the actual measurement is done with the measurement sensor arrangement 120. In an alternative embodiment both the reference measurement and the actual measurement are performed simultaneously with the two sensor arrangements 110, 120.

[0039] Fig. 6 shows a schematic diagram of a second embodiment of the proposed sensor arrangement 2. Like elements are assigned like reference signs as in the embodiment shown in Fig. 1. The phase shifter is implemented in this embodiment as two delay lines 13 and 40' providing a phase shift of preferably 180°. In addition to the sensor arrangement 1 the sensor arrangement 2 comprises a temperature sensor arrangement 200 that senses the temperature of the measurement fluid and of the reference fluid. The processor 60 is then configured to take the sensed temperature into account in the determination of the dielectric permittivity of the measurement fluid.

[0040] Preferably, the temperature sensor arrangement 200 comprises a temperature sensing container 201 containing a temperature sensing fluid, in particular water, said temperature sensing container being arranged between (and preferably in contact with) said reference fluid container 22 and said measurement area 32. Further, a temperature sensor 202 is provided that senses the temperature of said temperature sensing fluid.

[0041] The sensor arrangement 2 further comprises a millimeter wave generator 80 that generates said millimeter wave signal and a millimeter wave receiver 90 that receives transmitted or reflected millimeter wave signals. [0042] Fig. 7 shows such obtained results for a liquid under test with an increase of 0.1 , 0.5 and 1% of the value of the pure water permittivity (Debye model). Fig. 8 shows the sensitivity study of the sensor, in particular the insertion loss indicated by the change of an S-parameter magnitude. As can be seen the position of the frequency and the magnitude of the peak (i.e. of the parameter S₂,i which is the transmission coefficient which corresponds to a voltage ratio of the received over the transmitted signal) changes for different values of the water permittivity. Fig. 9 shows the variation of the insertion loss versus the gap of the coupled lines.

[0043] As environmental parameters (e.g. temperature) are influencing the measurement result a re-calibration can be always done during operation. This enables long-term measurements of liquids in e.g. industrial environments (production areas) also.

[0044] Fig. 10 shows a flowchart summarizing the proposed sensing method. Step S 1 provides for splitting a millimeter wave or microwave signal into two substantially equal input signals. Step S2 provides for receiving one of said input signals on a reference path including a reference sensor that comprises a reference fluid container containing a reference fluid. Step S3 provides for receiving the other one of said input signals on a measurement path including a measurement sensor that comprises a measurement area that is configured to contain a measurement fluid or be placed in contact or adjacent to a measurement zone containing said measurement fluid, wherein said reference sensor and said measurement sensor each comprises two or more coupled microstrip lines. Step S4 provides for providing a predetermined phase shift between said two input signals. Step S5 provides for adding a reference signal output on the reference path and a measurement signal output on the measurement path to obtain a sensor signal. Step S6 provides for determining a change in amplitude and/or phase of said sensor signal compared to one or more reference signals obtained in reference measurements using reference fluids. Step S7 provides for determining the dielectric permittivity of the measurement fluid from said determined change in amplitude and/or phase of said sensor signal. [0045] In summary, the present disclosure relates to the field of dielectric permittivity of liquid determination. The operating mode is based on a non-invasive method using electromagnetic waves. Based on transmitted and/or reflected signals the microwave energy is detected and complex dielectric permittivity is measured. The measurement system preferably comprises a microwave energy generator and receiver to monitor and detect the transmitted/reflected microwave energy. Further, an array of microwave coupled microstrip lines, power divider to split/add microwave energy and phase shifter are provided. Thus, a new sensor arrangement, device and method for the determination of permittivity of liquid concentration are provided which further enable integration of an in-situ calibration kit. The calibration kit has been designed and integrated together with the sensor arrangement to avoid calibration mismatch and allow in-situ calibration at any time of the measurement.

[0046] Obviously, numerous modifications and variations of the present disclosure are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

[0047] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single element or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0048] Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A sensor arrangement for non-invasive measurements of dielectric permittivity of liquids, comprising:

a measurement path coupled to said signal splitter including a measurement sensor that receives the other one of said input signals and comprises a measurement area that is configured to contain a measurement fluid or be placed in contact or adjacent to a measurement zone containing said measurement fluid,

a phase shifter included in said reference path and/or said measurement path that provides a predetermined phase shift between said two input signals,

a processor coupled to said combiner that determines a change in amplitude and/or phase of said sensor signal compared to one or more reference signals obtained in reference measurements using reference fluids and that determines the dielectric permittivity of the measurement fluid from said determined change in amplitude and/or phase of said sensor signal,

2. The sensor arrangement as claimed in claim 1, wherein the microstrip lines of the reference sensor and the measurement sensor are respectively deposited on a substrate, in particular on a common substrate, so that they are arranged in a respective microstrip plane, in particular in a common microstrip plane.

3. The sensor arrangement as claimed in claim 2,

wherein the respective microstrip lines of the reference sensor and the measurement sensor are arranged with a gap in between neighboring microstrip lines.

4. The sensor arrangement as claimed in claim 3,

wherein the gaps between the respective microstrip lines of the reference sensor and the measurement sensor all have the same size.

5. The sensor arrangement as claimed in claim 3,

wherein the gaps between the respective microstrip lines of the reference sensor and the measurement sensor have different sizes.

6. The sensor arrangement as claimed in claim 1,

wherein the reference fluid is water.

7. The sensor arrangement as claimed in claim 1,

further comprising a temperature sensor arrangement that senses the temperature of the measurement fluid and of the reference fluid,

wherein said processor is configured to take the sensed temperature into account in the determination of the dielectric permittivity of the measurement fluid.

8. The sensor arrangement as claimed in claim 1,

wherein the temperature sensor arrangement comprises

a temperature sensing container containing a temperature sensing fluid, in particular water, said temperature sensing container being arranged between said reference fluid container and said measurement area, and a temperature sensor that senses the temperature of said temperature sensing fluid.

9. The sensor arrangement as claimed in claim 1,

wherein the measurement area is configured to be in contact with skin of a subject, in particular a person or an animal, wherein the measurement fluid is blood of the subject.

10. The sensor arrangement as claimed in claim 1,

wherein the phase shifter is configured to provide a predetermined phase shift of substantially 180° between said two input signals.

11. The sensor arrangement as claimed in claim 1 ,

further comprising a millimeter wave generator that generates said millimeter wave signal and a millimeter wave receiver that receives transmitted or reflected millimeter wave signals.

12. A device for non-invasive measurements of dielectric permittivity of liquids, comprising:

a sensor arrangement as claimed in claim 1, wherein the processor of said sensor arrangement is also coupled to said combiner to obtain said reference signal and is configured to determine a change in amplitude and/or phase of the sensor signal obtained from said sensor arrangement compared to said reference signal and to determine the dielectric permittivity of the measurement fluid from said determined change in amplitude and/or phase of said sensor signal.

13. The device as claimed in claim 12,

further comprising a controller for controlling the device such that the reference signal and the sensor signal are obtained simultaneously or that the reference signal is obtained first.

14. The device as claimed in claim 12,

further comprising an output switch that switches between said combiner and said sensor arrangement to provide either said reference signal or said sensor signal to an output of said device.

15. The device as claimed in claim 12,

further comprising an input switch that switches said input signals between said signal splitter and said sensor arrangement.

16. The device as claimed in claim 14 and 15,

further comprising calibration elements arranged between said input switch and said output switch, wherein said input switch and said output switch are arranged to switch to one or more of said calibration element for performing a calibration before an actual measurement, wherein said processor is configured to take results from said calibration into account in the determination of the dielectric permittivity of the measurement fluid.

17. A sensing method for non-invasive measurements of dielectric permittivity of liquids, comprising:

receiving one of said input signals on a reference path including a reference sensor that comprises a reference fluid container containing a reference fluid, receiving the other one of said input signals on a measurement path including a measurement sensor that comprises a measurement area that is configured to contain a measurement fluid or be placed in contact or adjacent to a measurement zone containing said measurement fluid, wherein said reference sensor and said measurement sensor each comprises two or more coupled microstrip lines,

providing a predetermined phase shift between said two input signals,