Fluid monitoring system and method for monitoring presence or condition of a fluid using dielectric constant of the fluid

Abstract

A fluid monitoring system for monitoring the presence or condition of a specific fluid (9) in a device (10) for storing or conducting a fluid (9) using the dielectric constant properties of the fluid (9), the system comprising: a device (10) for storing or conducting a fluid (9); a detector component (1) which is an integral part of the device and comprises a component body (2) and a passive antenna (3), preferably in the form of an open loop resonator (30), placed on a surface (4) of the component body (2); and a reader device (5) comprising a reader device antenna (6); wherein the reader device (5) is adapted to emit an electromagnetic output signal (7) with a predetermined output power and over a predetermined frequency range via the reader device antenna (6) to the passive antenna (3) of the detector component (2) and to measure a reflected signal (8) over the predetermined frequency range reflected from the passive antenna (2); and wherein the reader device (5) is further adapted to compare the measured reflected signal (8) with at least one reference signal of at least one known reference fluid to determine the presence or condition of a specific fluid (9) in the device (10).

Description

Technical Field

[0001] This invention relates to a fluid monitoring system for monitoring the presence or condition of a specific fluid in a device for storing or conducting fluid, utilizing the dielectric constant properties of the fluid, and a method for monitoring the presence or condition of the fluid. It also relates to a sealing component for such a fluid monitoring system. Background Technology

[0002] An open-loop resonator is a conductive, non-magnetic material structure with gaps in the loops. It is primarily used as an array on metamaterials to modify their properties. Open-loop resonators can also be used to measure certain conditions of materials or their surrounding environment.

[0003] WO20040709 describes a contact lens-embedded sensor system for monitoring high intraocular pressure and glaucoma conditions. The contact lens has an embedded sensor comprising at least two open-ring resonator-type resonator rings. An antenna is coupled to the contact lens for communication with an electronic readout device to measure the resonant frequency of the sensor. The system is configured to determine the deformation of the contact lens and the embedded sensor due to intraocular pressure. US2018042479 relates to a similar open-ring resonator-based strain sensor located on a flexible substrate, such as a contact lens, for detecting changes in intraocular pressure.

[0004] US2019298234 describes a dielectric sensor comprising at least one open-loop resonator configured to be located within the oral cavity of a subject and to be biologically responsive to at least one physiological variable, such as glucose concentration, ethanol concentration, salinity, pH, and temperature. The open-loop resonator may include a first resonator ring, a second resonator ring arranged together with the first resonator ring in an open-loop resonator configuration, and a dielectric interlayer inserted between and in contact with the first and second resonators.

[0005] WO19036812 describes a sensor and method for measuring the physical properties of fluids in a microfluidic system. The microfluidic chip has a thin, deformable membrane that separates the microfluidic channel from a microwave resonator sensor. The membrane deforms in response to a load generated by the interaction between the membrane and the fluid. The load can be fluid pressure in the channel, or shear stress or surface stress generated by the interaction between the membrane and the fluid. The deformation of the membrane changes the dielectric constant in the region near the sensor. The change in dielectric constant leads to a change in the sensor's electrical parameters, thereby allowing the measurement of fluid properties, such as flow rate or biological or chemical characteristics. Furthermore, a microwave sensor with enhanced sensitivity for characterizing fluids in microfluidic channels is provided. The sensor has a rigid and very thin layer in the microfluidic chip, for example, in the range of 10 μm to 100 μm, allowing the sensor to be positioned very close to the microfluidic channel, enabling very high-resolution sensing.

[0006] US2017284968 describes an apparatus for detecting at least one condition of interest (e.g., the presence of a bubble) associated with a pipe. In some embodiments, the sensor includes an antenna, an open-loop resonator, a frequency generator capable of generating frequencies in the microwave range, and a detection element. The detection element can estimate at least one parameter of the received microwave energy to determine whether the condition of interest exists.

[0007] US2016091544 generally relates to sensors for sensing the chemical and physical properties of a sample or environment, and more specifically, to sensors comprising microwave planar open-ring resonators. Planar open-ring resonators detect changes in the nearby medium by means of changes in the electric field above the resonator substrate. The sample is positioned relative to the coupling gap of the resonator. Summary of the Invention

[0008] One object of the present invention is to provide a fluid monitoring system comprising a detector or sensor component and a reading device for monitoring the presence or state of a specific fluid in a pre-existing device, wherein the integrated component body of the pre-existing device can be modified into the detector or sensor component of the fluid monitoring system. Another object of the present invention is to provide a fluid monitoring system for detecting or distinguishing different specific fluids. Yet another object of the present invention is to provide a fluid monitoring system for detecting potential fluid leaks, detecting the presence of unwanted fluids, or detecting changes in fluid within a device to control fluid stability, storage life, or loss.

[0009] At least one objective of the present invention is achieved by a fluid monitoring system and a sealing component.

[0010] A fluid monitoring system that utilizes the dielectric constant of a fluid to monitor the presence or condition of a specific fluid in a device for storing or conducting fluid includes: the device for storing or conducting fluid; a detector component having a component body and a passive antenna, the passive antenna preferably disposed on the surface of the component body in the form of an open-loop resonator; and a reader device (e.g., a network analyzer) including a reader device antenna. The reader device is adapted to transmit an electromagnetic output signal with a predetermined output power and within a predetermined frequency range to the passive antenna of the detector component via the reader device antenna, and to measure the reflected signal within the predetermined frequency range reflected from the passive antenna. The reader device is also adapted to compare the measured reflected signal with at least one reference signal of at least one known reference fluid to determine the presence or condition of a specific fluid in the device.

[0011] By comparing a measurement signal of a specific fluid with a reference signal of a known reference fluid, it is possible to determine the actual fluid present in the device, such as whether the actual fluid is the desired fluid, or whether the fluid in the device has deteriorated over time, for example, in the case of pharmaceutical or food products. The at least one reference signal may be a library of reference signals of known reference fluids, which includes the specific fluid and, for example, known deterioration states of undesirable or desired fluids.

[0012] The detector component can be a sealing component of the device. A sealing component is understood to be a device component that provides a fluid seal within the device, for example, between two parts of the device. The present invention is based on the idea that most devices used for storing or conducting a particular fluid also include a sealing component of an elastic material or other material (e.g., a membrane made of plastic), said plastic being selected from polybenzimidazole (PBI), polyimide (PI), thermoplastic polyimide (TPI), polyamide-imide (PAI), polyethersulfone (PES), polyphenylene sulfone (PPSU), polyetherimide (PEI), polysulfone (PSU), polyetherketone (PEK), polyarylene etherketone (PAEK), polyphenylene sulfide (PPS), perfluoroalkoxy polymer (PFA), ethylene tetrafluoroethylene (ETFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polybutylene terephthalate (PBT), or polyetheretherketone (PEEK), having at least one surface facing and in contact with the fluid. By providing a passive antenna to the seal, this component can be cost-effectively manufactured and integrated into existing devices. Preferably, the passive antenna is located on the fluid-facing surface. However, if the dielectric constant of the fluid is still detectable, the sealing membrane can be thin enough to place the passive antenna on the fluid-repellent surface. Examples of such sealing membranes are described in WO2016012233 or WO2017121668 of the same applicant. In another application, the passive antenna can be arranged on the “dry side” (i.e., the side away from the fluid) of the membrane for pumping or metering fluid, even if the membrane is too thick for measuring the dielectric constant of the conductive fluid. This arrangement can be used to detect the presence of a specific fluid on the “dry” side, for example, for leak detection.

[0013] Reader devices can be adapted to calculate the reflection coefficient over a predetermined frequency range using reflected and output signals. The reflection coefficient, often referred to as S11 and measured in dB, is the ratio of the response or reflected signal to the output signal reflected from a passive antenna. Changes in the dielectric constant of the fluid near the detector or sensor components alter the resonant frequency of the open-loop resonator by changing the electric field around it, which in turn causes a change in the reflected signal. To change the resonant frequency, the fluid does not necessarily need to be in direct contact with the passive antenna.

[0014] Monitoring systems can be used to detect desired or unwanted fluids within equipment. Undesired fluids can be fluids that may damage elastic materials in sealing components, or incorrect fluids (e.g., gasoline instead of diesel; or gasoline replacing an additive, drug, or incorrect liquid in a medical device) or unwanted fluids filling or passing through the equipment. By detecting changes in the fluid relative to its original state or properties, the monitoring system can be used to monitor the stability, shelf life, or wear of the fluids within the equipment.

[0015] The term "device" is also understood here to mean, for example, a container used for medicines. The terms sensor and detector are used synonymously.

[0016] In some embodiments, the elastic material of the component body may be a thermosetting elastomer or a thermoplastic elastomer. The elastomer material may be, for example, synthetic or natural rubber, such as butyl rubber, isoprene rubber, butadiene rubber, halogenated butyl rubber (e.g., brominated butyl rubber), ethylene-propylene terpolymer, silicone rubber, fluoroelastomers or perfluoroelastomers, chlorosulfonates, polybutadiene, butyl rubber, chloroprene rubber, nitrile rubber, polyisoprene rubber, nitrile rubber, copolymer rubbers such as ethylene-propylene (EPR), ethylene-propylene-diene monomer (EPDM), acrylonitrile-butadiene (NBR or HNBR), and styrene-butadiene (SBR), blends such as ethylene or propylene-EPDM, EPR, or NBR, and combinations thereof. The term “synthetic rubber” should also be understood to include materials that can be broadly classified alternatively as thermoplastic or thermosetting elastomers, such as polyurethanes, silicones, fluorosilicones, styrene-isoprene-styrene (SIS) and styrene-butadiene-styrene (SBS), as well as other polymers that exhibit rubber-like properties, such as plasticized nylon, polyolefins, polyesters, ethylene vinyl acetate, fluoropolymers, and polyvinyl chloride.

[0017] In some embodiments, the detector component may be a sealing component of a device for containing, conducting, or processing fluid, and the surface of the sealing component may face the fluid.

[0018] In some embodiments, the passive antenna is a double-open-ring resonator with two concentrically arranged rings, preferably circular. A double-open-ring resonator (SRR) has a pair of closed rings made of non-magnetic metal with openings or small gaps on opposite sides. These rings can be concentric or square, with gaps as needed. Magnetic flux through the metal rings induces rotating currents in the rings, which generate their own magnetic flux to enhance or counteract the incident field (depending on the resonant characteristics of the SRRs). This field mode is dipole. The small gap between the rings produces a large capacitance value, which lowers the resonant frequency.

[0019] The geometric parameters of the double-open-ring resonator can be within the following ranges: outer ring radius r: 30 mm to 60 mm, preferably about 46 mm; outer ring w1 width: 1 mm to 3 mm, preferably about 2 mm; inner ring width w2: 1 mm to 3 mm, preferably about 2 mm; gap width between rings wg: 1 mm to 3 mm, preferably 1.8 mm; gap size of outer ring d1: 1 mm to 3 mm, preferably about 1.8 mm; gap size of inner ring d2: 1 mm to 3 mm, preferably about 1.8 mm; ring layer thickness h: 10 mm to 100 mm.

[0020] In some embodiments, the passive antenna can be placed by printing, for example using known printing techniques such as screen printing, aniline printing, gravure printing, letterpress printing, inkjet printing, piezoelectric inkjet printing, aerosol jet printing, stencil printing, offset printing, squeegee printing, rotary screen printing, intaglio printing, digital printing, capillary printing, electrohydrodynamic printing, imprinting, microcontact printing, laser printing, coating or lamination techniques.

[0021] In some embodiments, the material used for the passive antenna can be selected from the group consisting of conductive polymers, carbon, organometallic compounds, metal precursors, and metal nanopowders. Preferably, the material enhancing the antenna is a stretchable material, such as stretchable silver ink. This material can be selected from metallic inks and / or metal salt inks, such as Ag / AgCl, Cu and Ni, non-metallic inks, such as carbon-based inks (graphene, carbon nanotubes), PEDOT:PSS, and combinations thereof. This material can be combined with a stretchable carrier material (e.g., polysiloxane or PU or fluorinated elastomer). Good results have been achieved with silver-siloxane polymer compositions.

[0022] In some embodiments, a passive antenna placed on the surface of a component body may be covered with a dielectric layer of dielectric foil, dielectric ink, or varnish, which is different from the material of the component body. Dielectric ink typically consists of an organic polymer or ceramic in a solvent. Novel insulating 2D nanomaterials such as hexagonal boron nitride further provide temperature and electrochemical stability. The dielectric foil may consist of an organic polymer and may include ceramic powder. The material of the passive antenna may be a stretchable material, such as a stretchable ink or paste. Good results have been achieved using dielectric ink based on a siloxane polymer composition filled with alumina, resulting in translucent and stretchable films.

[0023] In some embodiments, the predetermined frequency range of the output signal may be 400MHz to 1600MHz, preferably 800MHz to 1000MHz, or approximately 2.4GHz, and / or the predetermined power of the output signal may be adjusted to obtain a good reflected signal. The frequency range also depends on the limitations of the corresponding mechanism.

[0024] In some embodiments, the reader device antenna of the reader device may be a circularly polarized antenna.

[0025] In some embodiments, at least one reference signal is at least one predetermined reflection signal for air, water, or any fluid, which may be a desired or undesired fluid in the device. Therefore, the calculated reflection coefficient can be used as a reference.

[0026] In some embodiments, the device for storing or guiding a particular fluid may be a storage container or a device for metering or pumping fluid.

[0027] The present invention also relates to a sealing component for a fluid monitoring system, wherein the sealing component is a detector component of a device for storing or conducting fluid, and comprises a component body made of an elastomeric material, preferably a thermosetting elastomer or a thermoplastic elastomer, or a film of plastic selected from polybenzimidazole (PBI), polyimide (PI), thermoplastic polyimide (TPI), polyamide-imide (PAI), polyethersulfone (PES), polyphenylene sulfone (PPSU), polyetherimide (PEI), polysulfone (PSU), polyetherketone (PEK), polyaryletherketone (PAEK), polyphenylene sulfide (PPS), perfluoroalkoxy polymer (PFA), ethylene tetrafluoroethylene (ETFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polybutylene terephthalate (PBT), or polyetheretherketone (PEEK), and a passive antenna, preferably in the form of an open-loop resonator, disposed on the surface of the component body. The sealing component may have the features described above.

[0028] The present invention also relates to a method for monitoring the presence or condition of a specific fluid in a device for storing or conducting fluid using the fluid monitoring system described above, comprising the steps of: a.) transmitting an electromagnetic output signal having a predetermined output power and within a predetermined frequency range to a passive antenna of a detector component via a reader device antenna; b.) measuring a reflected signal reflected from the passive antenna; c.) comparing the measured reflected signal with at least one reference signal of at least one known reference fluid to determine the presence or condition of the specific fluid in the device.

[0029] The reflection coefficients within a predetermined frequency range can be calculated using the reflected and output signals, and then compared with a reference set of reflection coefficients. Attached Figure Description

[0030] The invention will now be described in more detail with reference to the embodiments shown in the accompanying drawings. These drawings illustrate:

[0031] Figure 1 A passive antenna for a fluid monitoring system is a double-open-ring resonator with two concentrically arranged rings.

[0032] Figure 2 This is a schematic diagram of a fluid monitoring system;

[0033] Figure 3 Test containers for monitoring fluids using a fluid monitoring system; and

[0034] Figure 4A graph showing different reflection measurements for different fluids. Detailed Implementation

[0035] Figure 1 An example of a circular double-open-ring resonator with two concentric open-rings 30, 31 is shown, which can be used as such Figure 2 The passive antenna 3 in the fluid monitoring system shown.

[0036] The geometric parameters of the double-open-ring resonator can be within the following ranges: outer ring radius r: 30 mm to 60 mm, preferably about 46 mm; outer ring w1 width: 1 mm to 3 mm, preferably about 2 mm; inner ring width w2: 1 mm to 3 mm, preferably about 2 mm; gap width between rings wg: 1 mm to 3 mm, preferably 1.8 mm; gap size of outer ring d1: 1 mm to 3 mm, preferably about 1.8 mm; gap size of inner ring d2: 1 mm to 3 mm, preferably about 1.8 mm; ring layer thickness h: 10 micrometers to 100 micrometers.

[0037] The fluid monitoring system includes a detector or sensor component 1, which includes a passive antenna 3 and a reader device 5. The reader device 5 can transmit an electromagnetic output signal 7 with a predetermined output power and within a predetermined frequency range. The output signal 7 is transmitted via a reader device antenna 6 of the reader device 5, which is typically in the form of a circularly polarized antenna. The reader device 5 may include a network analyzer.

[0038] The reflected signal 8 from the passive antenna 3 depends on the resonant frequency of the passive antenna 3, which is in turn affected by the fluid 9 present near the passive antenna 3. The dielectric constant of the fluid 9 affects the electric field between rings 30 and 31, thereby changing the resonant frequency. The change in the resonant frequency can be best observed through the so-called reflection coefficient measured over the transmission frequency range (see...). Figure 4 ).

[0039] The reader device uses the reflected signal 8 and the output signal 7 to calculate the reflection coefficient within a predetermined frequency range. The reflection coefficient, usually referred to as S11 and expressed in dB, is the ratio of the reflected signal 8 to the output signal 7. By changing the electric field around the open-loop resonator, the change in the dielectric constant of the fluid near the passive antenna alters the resonant frequency of the open-loop resonator, which in turn causes a shift in the resonant peaks 81, 81', and 81" as shown below. Figure 4 The curve is shown in the figure. Figure 4 The resonance peaks 81, 81', and 81" in the signal refer to different fluid samples. These signals can be used as known reference signals in a reference signal library for comparison with measurement signals of a specific fluid in the device.

[0040] Typically, the parameters of the passive antenna 3 are set to obtain a high response of the output signal or reflection coefficient within a predetermined frequency range, which is typically 400MHz to 1600MHz, preferably 800MHz to 1000MHz, or approximately 2.4GHz. The frequency range also depends on the limitations of the corresponding mechanism. The power of the output signal is adjusted to obtain a good reflected signal.

[0041] Figure 3 A simple device 10 or container is shown for measuring the reflectance of fluid 9 using a fluid monitoring system. Device 10 includes a container wall 11 and a sensor or detector component 1.

[0042] The detector component 1 includes a component body 2 and a passive antenna 3, which is placed on the surface 4 of the component body 2 facing the fluid 9. If the component body 2 is made of an elastic material, the detector component 1 can be used as a sealing component in the device 10.

[0043] Figure Labels

[0044] 1. Detector components, sensor components

[0045] 2 main components

[0046] 3 passive antennas

[0047] 30 Open-ring resonator

[0048] 31 Open-loop resonator

[0049] 4 surfaces

[0050] 5 Reader devices

[0051] 6 Reader device antennas

[0052] 7 Output Signal

[0053] 8 reflected signals

[0054] 9 fluids

[0055] 10. Equipment (containing, conducting, or processing fluids)

[0056] 11 container wall

[0057] 81, 81', 81” resonance peaks

Claims

1. A fluid monitoring system for monitoring the presence or condition of a specific fluid (9) in a device (10) for storing or conducting fluid (9) by utilizing the dielectric constant properties of the fluid (9), said system comprising: Device (10) for storing or conducting fluid (9); A detector component (1), which is a sealing component of the device, is configured to provide a fluid seal of the device to prevent leakage and has at least one fluid-facing surface. The detector component (1) includes a component body (2) and a passive antenna (3). The component body (2) is made of a thermosetting elastomer or a thermoplastic elastomer, and the passive antenna (3) is placed on a surface (4) of the component body (2). Reader device (5) including reader device antenna (6); The reader device (5) is adapted to transmit an electromagnetic output signal (7) with a predetermined output power and in a predetermined frequency range to the passive antenna (3) of the detector component (1) via the reader device antenna (6), and to measure the reflected signal (8) in the predetermined frequency range reflected from the passive antenna (3); and The reader device (5) is also adapted to compare the measured reflected signal (8) with at least one reference signal of at least one known reference fluid to determine the presence or condition of a specific fluid (9) in the device (10).

2. The fluid monitoring system according to claim 1, characterized in that, The reader device is adapted to use the reflected signal (8) and the output signal (7) to calculate the reflection coefficient within a predetermined frequency range.

3. The fluid monitoring system according to claim 1 or 2, characterized in that, The main body (2) of the component is made of an elastic material or a plastic film, wherein the plastic is selected from polybenzimidazole (PBI), polyimide (PI), thermoplastic polyimide (TPI), polyamide-imide (PAI), polyethersulfone (PES), polyphenylene sulfone (PPSU), polyetherimide (PEI), polysulfone (PSU), polyetherketone (PEK), polyaryletherketone (PAEK), polyphenylene sulfide (PPS), perfluoroalkoxy polymer (PFA), ethylene tetrafluoroethylene (ETFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polybutylene terephthalate (PBT), or polyetheretherketone (PEEK).

4. The fluid monitoring system according to claim 1 or 2, characterized in that, The main body (2) of the component is made of thermosetting elastomer or thermoplastic elastomer.

5. The fluid monitoring system according to claim 1 or 2, characterized in that, The passive antenna (3) is a double-open-loop resonator (30, 31) with two concentrically arranged loops.

6. The fluid monitoring system according to claim 5, characterized in that, The ring is a circular ring.

7. The fluid monitoring system according to claim 1 or 2, characterized in that, Passive antennas (3) are placed using printing, coating or lamination techniques.

8. The fluid monitoring system according to claim 1 or 2, characterized in that, The passive antenna (3) placed on the surface (4) of the component body (2) is covered with a dielectric layer of dielectric foil or dielectric ink or paint that is different from the material of the component body (2).

9. The fluid monitoring system according to claim 1 or 2, characterized in that, The passive antenna (3) is made of a stretchable material.

10. The fluid monitoring system according to claim 9, characterized in that, The stretchable material is stretchable ink or paste.

11. The fluid monitoring system according to claim 1 or 2, characterized in that, The predetermined frequency range of the output signal is 400MHz to 1600MHz.

12. The fluid monitoring system according to claim 1 or 2, characterized in that, The predetermined frequency range of the output signal is 800MHz to 1000MHz.

13. The fluid monitoring system according to claim 1 or 2, characterized in that, The predetermined frequency range of the output signal is 2.4 GHz.

14. The fluid monitoring system according to claim 1 or 2, characterized in that, The reader device antenna (6) is a circularly polarized antenna.

15. The fluid monitoring system according to claim 1 or 2, characterized in that, The at least one reference signal is at least one predetermined reflected signal (8) for air, water or any fluid, the fluid being a desired or undesired fluid in the device (10) (9).

16. The fluid monitoring system according to claim 1 or 2, characterized in that, Devices used to store or guide a particular fluid are storage containers or devices used to meter or pump fluid.

17. A sealing component for a fluid monitoring system according to any one of claims 1 to 16, wherein the sealing component is a detector component of a device for storing or conducting fluid, and comprises a component body (2) and a passive antenna (3), wherein the component body (2) is made of an elastomeric material or a plastic film selected from polybenzimidazole (PBI), polyimide (PI), thermoplastic polyimide (TPI), polyamide-imide (PAI), polyethersulfone (PES), polyphenylene sulfone (PPSU), polyetherimide (PEI), polysulfone (PSU), polyetherketone (PEK), polyarylene etherketone (PAEK), polyphenylene sulfide (PPS), perfluoroalkoxy polymer (PFA), ethylene tetrafluoroethylene (ETFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polybutylene terephthalate (PBT), or polyetheretherketone (PEEK), and the passive antenna (3) is disposed on the surface (4) of the component body (2).

18. The sealing component according to claim 17, characterized in that, The main body (2) of the component is made of thermosetting elastomer or thermoplastic elastomer.

19. The sealing component according to claim 17, characterized in that, The passive antenna (3) is in the form of an open-loop resonator (30, 31).

20. A method for monitoring the presence or condition of a specific fluid (9) in a device (10) for storing or conducting fluid (9) using the fluid monitoring system according to any one of claims 1 to 16, comprising the following steps a. Transmit an electromagnetic output signal (7) with a predetermined output power and in a predetermined frequency range to the passive antenna (3) of the detector component (1) via the reader device antenna (6). b. Measure the reflected signal (8) reflected from the passive antenna (3) within a predetermined frequency range; c. The reflected signal (8) measured in a predetermined frequency range is compared with at least one reference signal of at least one known reference fluid to determine the presence or condition of a specific fluid (9) in the device (10). The at least one reference signal is a reference signal library, which includes reference signals of a known reference fluid measured over a predetermined frequency range. The known reference fluid includes a specific fluid as well as a known undesirable fluid or a specific fluid in a deteriorated state.

21. The method according to claim 20, characterized in that, The reflection coefficient within a predetermined frequency range is calculated using the reflected signal (8) and the output signal (7).

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