MEASURING DEVICE WITH A PASSIVE COOPERATIVE TARGET

Description

[0001] The present invention relates to a system with a passive cooperative target according to the preamble of independent claim 1 and in its further embodiments within the meaning of the dependent claims.

[0002] The present invention is based on the object of providing a particularly easy-to-use and cost-effective system with a passive cooperative target as a measuring device.

[0003] US 2010 / 066496 A1 discloses an inductively interrogatable identification tag (RFID) comprising two electroacoustic transducers, the first of which is connected to an interrogation unit and the second to a resonator, wherein the first electroacoustic transducer and the second electroacoustic transducer form an acoustic channel and the second electroacoustic transducer forms a passive cooperative target with the resonator, which transmits a response signal upon receipt of an interrogation signal from the interrogation unit via the acoustic channel and the interrogation signal has a higher energy than the response signal.

[0004] Similar to wireless passive measurement using an antenna coupled to surface acoustic wave components, the proposed approach is based on time-domain separation of the transmitted and reflected signals. The wireless sensor system contains an excitation and reception element with signal processing on the active part and a transceiver with an oscillating load on the passive sensor node. The passive sensor node consists of a resonator electrically connected to a radiating element, i.e., an ultrasonic transducer. This object is achieved according to the invention in a measuring device of the type mentioned above by the features of the characterizing part of independent claim 1. Further embodiments of the invention are the subject of subclaims.

[0005] For the purposes of the invention, a system is preferably a measuring device for measuring a desired measurand, such as force, temperature, current, voltage, flow, humidity, or other physical quantities, at a preferably preselected measuring point. Such a system according to the invention comprises a first electroacoustic transducer connected to an interrogation unit. Such an interrogation unit is preferably a software-defined radar system that follows the principle of software-defined radio.

[0006] Software-Defined Radio (SDR) refers to concepts for high-frequency transmitters and receivers in which a small or large portion of the signal processing is performed using software. The analog component can be a straight-through receiver or a superheterodyne receiver. In an SDR, selection and modulation / demodulation, in particular, are implemented using digital signal processing.

[0007] An SDR system performs a large portion of the signal processing with a general-purpose computer, combined if necessary with dedicated hardware such as signal processors and / or FPGAs. Receiver bandwidths of a few tens of MHz can be achieved with general-purpose computers such as PCs. Larger bandwidths and more complex processing algorithms require special processors such as signal processors or FPGAs. A key feature is that the various radio system parameters, such as modulation, different bandwidths, timing behavior, and different channel coding methods, can be implemented simply by changing the software. SDR is used in amateur radio, the military, and mobile communications, among other areas, but also increasingly in civilian applications such as digital broadcast receivers. Here, the flexibility and implementation of different protocol changes in real time are particularly beneficial.A good and clear example is the implementation of base stations for cellular networks as SDRs. These could then be upgraded to new standards cost-effectively within a very short time. The hardware of an SDR consists of at least a transmitter and receiver module, as well as an A / D and D / A converter, and the software-based digital signal processing in between. The signal processing is usually complex, in the sense that a signal path consists of a pair of two parallel real number sequences, which is also referred to as an I / Q signal. The simplest and ideal SDR receiver would consist of an analog-to-digital converter with an antenna. The read data would then be processed by a digital computer directly after the analog-to-digital conversion. The ideal transmitter would look similar: A computer generates a digital data stream via a digital-to-analog converter, and a subsequent antenna transmits it. Operating principles of SDRs

[0008] Today’s SDRs operate according to one of three operating principles: Direct digitization of the input signal

[0009] After minimal analog processing using filters and preamplifiers or attenuators, the input signal is directly digitized. According to the Nyquist theorem, the input signal must be sampled at at least twice the maximum useful frequency for digitization in order to reconstruct the signal. A / D converters with sampling frequencies up to 3.6 GSPS at 12-bit resolution are now available. This enables reception ranges of up to 1500 MHz. Digitization at the intermediate frequency level

[0010] The first stages of such a receiver differ little from a conventional superheterodyne receiver. The analog filters are designed for the largest useful signal bandwidth used. This not only reduces the requirements for large-signal immunity in subsequent processing, it also allows for a drastic reduction in the sampling frequency: For an intermediate frequency bandwidth of, for example, 10 kHz, a sampling frequency of around 20 kHz (subsampling) is sufficient. This concept is now widespread because a sufficiently powerful digital signal processor (DSP) is significantly cheaper than various quartz filters with the required bandwidths. Furthermore, the DSP can also perform other functions such as gain control and demodulation – with significantly better characteristics and more options than conventional analog technology. Direct mixer according to the I / Q process

[0011] A direct mixer receiver is a receiver concept in which the input signal is directly mixed with an oscillator signal of the same carrier frequency and thus demodulated. This is how an audion worked in the 1920s when one wanted to receive Morse code signals. The problem with conventional direct mixers is the lack of image frequency rejection, i.e., a sine signal 1 kHz below the oscillator frequency produces exactly the same output signal as a sine signal 1 kHz above the oscillator frequency. An SDR solves this problem through "complex" signal processing, i.e., by calculating with real and imaginary components, also known as an I / Q signal. The "I" stands for "in phase" and the real part. Q stands for "quadrature" and the imaginary part of the signal. For this purpose, two parallel mixer stages are used in the input section of the direct mixer receiver, whose oscillator signals are phase-shifted by 90°. Such oscillator signals are very easy to generate using digital technology.The output signals of the two mixers are digitized in parallel and then digitally processed, with the Hilbert transform playing a central role. The Hilbert transform ultimately causes a frequency-dependent delay without affecting the signal amplitude, so that the signal is phase-shifted by 90°. A 1 kHz signal is thus delayed by 250 µs, and a 10 kHz signal by 25 µs. The final result is two direct heterodyne signals with a 0° phase shift and a 90° phase shift. By adding or subtracting the two signals, one can switch between the two sidebands.

[0012] The system further comprises at least one second electroacoustic transducer which is electrically connected to a resonator, wherein the first electroacoustic transducer and the second electroacoustic transducer form an acoustic channel and the second electroacoustic transducer is electrically connected to the resonator and forms a passive cooperative target with the resonator, which transmits a response signal upon receipt of an interrogation signal from the interrogation unit via the acoustic channel and the interrogation signal has a higher energy than the response signal.

[0013] A system according to the invention can also comprise an interrogation unit that is a software-defined interrogation unit in the sense of a software-defined radio. In a system according to the invention, the first and / or second electroacoustic transducer can also be a, preferably bidirectional, sound transducer, preferably for ultrasound or infrasound.

[0014] In a system according to the invention, the resonator is a resonator with a high quality factor.

[0015] Furthermore, in a system according to the invention, the resonator can store at least part of the energy of the interrogation signal due to the high quality until an environmental signal reflection of the interrogation signal has decayed.

[0016] In a system according to the invention, the resonator can preferably be a piezoelectric thin-film resonator, a dielectric resonator or a quartz tuning fork resonator.

[0017] The resonator can also be a one-port resonator.

[0018] Furthermore, the resonator according to the invention can have at least one resonance frequency as a function of a measured variable, wherein the resonance frequency is temperature-compensated.

[0019] In a system according to the invention, it has proven particularly advantageous if the response signal is shifted in frequency compared to the interrogation signal.

[0020] In a system according to the invention, the interrogation signal is preferably transmitted by the interrogation unit as at least one rectangular interrogation pulse and / or a beat signal and / or a frequency-modulated interrogation signal.

[0021] Within the scope of the invention, an interrogation pulse can be a pulse or signal with a rectangular envelope in the time domain.

[0022] Furthermore, within the scope of the invention, an interrogation pulse may be a pulse or signal with a rectangular amplitude in the time domain.

[0023] Also, within the scope of the invention, an interrogation pulse may be a pulse or signal with rectangular power in the time domain.

[0024] Furthermore, within the scope of the invention, an interrogation signal can be an interrogation signal whose frequency is periodically increased and decreased with a wide beat signal (also called a dither signal in the technical literature).

[0025] As this frequency-modulated interrogation signal passes over the transponder's resonant frequency each time, the response signal is amplified at resonance and attenuated outside of it. The envelope of the response signal has twice the frequency of the beat signal, since it is attenuated at both the maximum and minimum frequencies. If the frequency of the interrogation signal is locked to the maximum of the second harmonic of the beat frequency in the response signal in the receiver, a PLL can be constructed that allows for extremely precise measurements.

[0026] According to the invention, the frequency-modulated signal can be converted into an amplitude-modulated signal. The details of this wireless conversion from frequency modulation to amplitude modulation by high-frequency resonators for the precise determination of the resonant frequency of passive acoustoelectronic sensors are described in more detail below. The emitted frequency-modulated high-frequency pulses are generated by a pulsed radar for scanning a surface-wave-based sensor. The sharp sign transition of the amplitude-modulated received signal provides a signal to which a feedback loop for monitoring the resonant signal is adjusted.

[0027] A resonator acts like a frequency-to-amplitude modulation converter due to its transfer function. By exciting a narrowband resonator away from its resonant frequency with an FM signal at a rate of the angular frequency ω on one of the resonant edges, the returned signal is an amplitude modulated at ω. At resonant frequency, where the first-order coefficient for a polynomial expansion of the transfer function becomes zero and the second-order coefficient becomes dominant, the frequency modulation at ω becomes an amplitude modulation at 2ω, with a contribution at ω close to zero. Above the resonant frequency, the frequency modulation at ω again becomes an amplitude modulation at ω, but this time with a 90° phase shift of the amplitude modulation with respect to the frequency modulation signal compared to the previous case.

[0028] Within the scope of the invention, in a system the interrogation signal, preferably as at least one rectangular interrogation pulse, can be sent from a signal source which is not the interrogation unit.

[0029] In a system according to the invention, the passive cooperative target does not include any active electronic components. This has the advantage that the system can be used in harsh conditions, such as in environments with very high temperatures or even underwater.

[0030] In a system according to the invention, the passive cooperative target does not include its own power source. This has the advantage that no battery is required. There is also no need to transfer power via inductive transmission or near-field communication (NFC) systems. This makes the system completely energy-autonomous and can be used in harsh conditions, such as in environments with very high temperatures or even underwater.

[0031] Furthermore, in a system according to the invention, the passive cooperative target generates the energy required to transmit the response signal from the interrogation signal via the acoustic channel. This makes the system completely energy-autonomous and can be used in harsh conditions, such as in environments with very high temperatures or even underwater.

[0032] The usability of a system according to the invention underwater as well as in an environment where, for example, a component of the system, namely either the interrogation unit or the passive cooperative target, is located within a Faraday cage, is possible thanks to the acoustic channel. This acoustic channel, in the sense of the invention, is preferably formed from acoustic signals that operate in a frequency range from 1 kHz to 10 THz, preferably a first frequency range from 1 kHz to 10 kHz, in particular 3 kHz to 5 kHz, or also 5 kHz to 10 kHz, or in a second frequency range from 10 kHz to 50 kHz, in particular 10 kHz to 19 kHz, or also 19 kHz to 50 kHz, particularly preferably 20 kHz to 45 kHz or 20 kHz to 25 kHz or 25 kHz to 44 kHz or 44 kHz to 45 kHz. a third frequency range from 50 kHz to 250 kHz, in particular 50 kHz to 100 kHz, or also 100 kHz to 250 kHz, or in a fourth frequency range from 250 kHz to 1 MHz, or in a fifth frequency range from 1 MHz to 10 MHz, or in a sixth frequency range from 10 MHz to 100 MHz, or in a seventh frequency range from 100 MHz to 400 MHz, or in a seventh frequency range from 400 MHz to 600 MHz, or in an eighth frequency range from 600 MHz to 900 MHz, or in a ninth frequency range from 900 MHz to 1 GHz, or in a tenth frequency range from 1 GHz to 5 GHz,or in a further frequency range from 5 GHz to 10 GHz, or also in a frequency range from 1 mHz to 1 kHz, in particular 1 mHz to 0.5 Hz, or also 0.5 Hz to 1 Hz, particularly preferably 1 Hz to 500 Hz, in particular 1 Hz to 100 Hz, preferably also 70 Hz to 95 Hz, or also 100 Hz to 250 Hz, or also 250 Hz to 1 kHz, as well as in further frequency ranges from 20 Hz to 20 kHz, or 20 kHz to 1 GHz, or also 1 GHz to 10 THz. , Sound and / or ultrasonic coupled passive wireless Vibration sensor system

[0033] This paper presents, for the first time, an instrumentation method for passively extracting the resonance frequency of a high-Q resonator via a wireless ultrasonic channel. As a first application, a passive wireless temperature measurement is presented, with a demonstration of the wireless and passive operation of the device. A temperature resolution of 0.17°C and a measurement range of 350 mm were demonstrated.

[0034] Passive wireless sensing is a measurement technique that enables analog wireless measurement of a transducer element.

[0035] In the age of the Internet of Things, this technology has a fair chance of emerging from the current niche of industrial sensor technology for harsh environments and entering the mainstream market. Conventional wireless communication based on electromagnetic wave propagation is ineffective in situations where the sensor node is located in a conductive housing, i.e., a Faraday cage. Therefore, a method based on ultrasonic propagation was recently proposed in the publication by Hagelauer, A.; Ussmueller, T.; Weigel, R. SAW and CMOS RFID transponder-based wireless systems and their applications. In Proceedings of the 2012 IEEE International Frequency Control Symposium (FCS), Baltimore, MD, USA, 21-24 May 2012; pp. 1-6.

[0036] This principle of ultrasound propagation is described in detail in the publication by Hagelauer, A.; Ussmueller, T.; Weigel, R. SAW and CMOS RFID transponder-based wireless systems and their applications. In Proceedings of the 2012 IEEE International Frequency Control Symposium (FCS), Baltimore, MD, USA, 21-24 May 2012; pp. 1-6., which is incorporated herein by reference.

[0037] The work presented here is an attempt to investigate a chip-free approach by adapting a tuning fork resonator with an ultrasonic transducer. First, the concept of wireless interrogation of high-Q resonators is introduced, followed by a description of the experiment testing the following hypothesis: Can ultrasonic transducers and crystal resonators be used as passive wireless sensors? This is then followed by a characterization of the sensing element and a subsequent analysis of its performance. Concept for the wireless sensor system

[0038] Similar to wireless passive sensing with an antenna coupled to surface acoustic wave devices, the presented approach is based on a time domain separation of the transmitted and reflected signal. This is described in detail in the publication by Reindl, L.; Scholl, G.; Ostertag, T.; Scherr, H.; Wolff, U.; Schmidt, F. Theory and application of passive SAW radio transponders as sensors. IEEE Trans. Ultrason. Ferroelectr. Freq. Control 1998, 45, 1281-1292. in its details regarding wireless passive sensing with surface acoustic wave devices, which is expressly incorporated herein by reference. The presented approach is based on a time domain separation of the transmitted and reflected signal. The wireless sensor system contains an excitation and receiving element with signal processing on the active part and a transceiver with an oscillating load on the passive sensor node.The passive sensor node consists of a resonator electrically connected to a radiating element, i.e., an ultrasonic transducer. Quality factor, the main quality factor for a resonator in this application, is defined as: . Q = ω 0 W P where ω 0 is the resonant frequency, W is the energy stored in the resonator, and P is the power dissipation. For resonators coupled to a radiating element, the power dissipation is low due to internal material and resistance losses, and the oscillation time can be longer than ambient echoes, allowing a channel-invariant wireless measurement of the resonant frequency.

[0039] Figure 1 Basic concept of a wireless readout of a resonance frequency using ultrasonic wave propagation.

[0040] External environmental influences such as temperature affect material properties such as the stiffness tensor of a piezoelectric resonator. This causes a frequency shift of the resonance mode, as explained by harmonic perturbation theory. This effect can be used for temperature measurement, passively via a wireless connection, and is demonstrated in Section 4.

[0041] Within the scope of the invention, it is also possible to assign an identification feature (an ID) to a passive cooperative target to enable identification and thus to assign a measured value to a specific measuring point. Details on the functionality and implementation of the signal query and coding, as well as the type, structure, and functionality of the resonators of such a combined identification and / or sensor system, are described in DE 44 13 211 A1, which is expressly incorporated herein by reference.

[0042] Furthermore, details about the functioning and implementation of the signal query and coding as well as the type, structure and functioning of the resonators of such a combined identification and / or sensor system are described in US 5,691,698, to which reference is expressly made here.

[0043] Furthermore, details about the functionality, structure and implementation of the interrogation unit as well as the type, structure and functionality of the sound transducers in the case of ultrasonic transducers of such a combined identification and / or sensor system are described in US 7,061,381 B2, to which reference is expressly made here.

[0044] Furthermore, details about the functioning, structure and implementation of the interrogation unit, the signal interrogation, the signal transmission of the interrogation signal as well as the type, structure and functioning of the energy storage within the resonator in the case of reception of scattered signals from the environment with a longer propagation time than the non-scattered original interrogation signal in the case of electromagnetic signals, which is to be applied analogously with regard to the physical scattering principle of signals within the scope of the invention to the scattering of acoustic signals, are described in detail in DE 10 057 059 A1, to which express reference is made. Conceptual design

[0045] The main focus of the conceptual design is the passive extraction of a resonance frequency using wireless ultrasonic sensing. A temperature-compensated quartz tuning fork resonator with a high Q is used. A temperature-measuring tuning fork resonator will be presented later in this publication to implement the sensor system. The instrumentation setup is described in Figure 2 The commercially available electronic components have a center frequency of 40 kHz and were analyzed using a high-precision impedance measurement.

[0046] Figure 2 Measurement setup with laboratory equipment for conceptual design with a tuning fork resonator.

[0047] A pulse with a width of 0.5 s is applied to the transmitter, resulting in a bandwidth of 2.4 Hz around the resonance. This causes the high-Q resonator to oscillate, enabling time-domain separation of the Tx and Rx. Figure 3represents the measured time-domain signal at the ultrasonic receiver. The excitation frequency decays after the burst in less than 2 ms, and the high-Q resonator begins to oscillate at its resonant frequency. The frequency shift from the excitation to the resonant frequency demonstrates the presented concept. A backscattered signal could be measured with a channel power of 36 dBmV over a distance of 350 mm with a 100 ms burst at 2 Vpp and an SNR of 10 dB.

[0048] Figure 3 Backscattered signal: (a) Excitation pulse width of 0.502 s and ringing of the high-Q-factor resonator at resonance frequency with envelope fitting (red dashed) to decay for Q-factor calculation; (b) Shift from excitation frequency to resonance frequency. Sensor characterization

[0049] The sensor used is a temperature measuring oscillator (TSXO), designed as a tuning fork resonator. With its high Q factor and low frequency in the kHz range, it achieves long oscillation times. For measurements in Figure 4A temperature ramp from -30°C to +90°C is applied to the resonator in a climatic chamber. It is sampled using the burst-mode technique, and the temperature-dependent resonance frequency is measured using an FFT in the unconstrained time frame, shown in Figure 3a as the red area. The excitation frequency is adjusted via the temperature ramp by setting it to the previously obtained resonance frequency, completing the feedback chain of the presented digitally controlled phase-locked loop. This principle of the excitation frequency is adjusted via the temperature ramp by setting it to the previously obtained resonance frequency, completing the feedback chain of the presented digitally controlled phase-locked loop when measuring oscillators or resonators. This principle is described in detail in the publication by Pohl, A.; Ostermayer, G.; Seifert, F.Wireless sensing using oscillator circuits locked to remote high-Q SAW resonators. IEEE Trans. Ultrason. Ferroelectr. Freq. Control 1998, 45, 1161-1168, which is expressly incorporated herein by reference.

[0050] Figure 4 : (a) Characterization of the sensor element's resonant frequency as a function of temperature with a quadratic fit (b) Residuals of the fitted curve in mHz. The TSXO exhibits quadratic temperature behavior with a sensitivity of -1.94 Hz / °C at 25°C. The fitted curve has an R-squared value of 1.0 and 4.3552 as the norm of the residuals with 1819 points. The parabolic patterns in the residual suggest that the main cause of the residuals is the quantization error of the temperature sensor, which is used as a reference with a resolution of 0.1°C. The currently used FFT frequency bandwidth resolution of 0.34 Hz limits the temperature resolution to 0.17°C.

[0051] As Cramer Rao bound as described in detail in the publication Kalinin, V. Comparison of frequency estimators for interrogation of wireless resonant SAW sensors. In Proceedings of the 2015 Joint Conference of the IEEE International Frequency Control Symposium & the European Frequency and Time Forum, Denver, CO, USA, 12-16 April 2015; pp. 498-503 with regard to signal processing and signal evaluation in acoustic components and to which explicit reference is made here, is significantly lower, a better resolution for the temperature can be achieved. conclusion

[0052] This work presents a measurement technique for extracting the resonance frequency of a high-Q resonator using a wireless ultrasonic channel. A conceptual design of the wireless and passive operation of the device is presented, along with a passive wireless temperature measurement. A temperature resolution of 0.17°C and a measurement range of 350 mm were demonstrated. It has been shown that the design and implementation of the proposed system requires careful tuning of the resonance frequency and the impedance between the transducer and the resonator. Additionally, and depending on the ambient noise levels, the Q factor of the resonator must be high (~100,000 ) for precise wireless extraction of the resonance frequency. The new wireless sensing technique presented in this paper has significant potential applications with regard to measurements on moving parts, inside enclosed cavities, and in submerged environments.

[0053] The invention is explained in more detail below with reference to exemplary embodiments illustrated in the figures. It shows: Figure 1 a schematic representation of a system according to the invention with a software-defined radar as an interrogation unit; Figure 2 a schematic representation of the conceptual design of the measurement setup; Figure 3 a time domain measurement of the received signal (returned signal); Figure 5 an illustration of a measurement setup; Figure 4 above: Characterization of the sensor element as a function of temperature. Figure 4 below: a received signal analysis. Figure 6 a measurement diagram of the resonance frequency versus temperature for a 32.8 kHz resonator;

[0054] Figure 1: Measurement setup with a signal generator as a software-defined radar functioning as an interrogation unit for transmitting an acoustic signal via an acoustic transducer, here implemented as an ultrasonic transducer. The ultrasonic transducer transmits the acoustic signal via the acoustic channel to another acoustic transducer, which is connected to a resonator as a cooperative passive target. The resonator stores the received interrogation signal, or rather the energy of the acoustic signal converted into electrical energy by the electroacoustic transducer (namely the resonator), until signals from the environment have decayed.

[0055] The resonator then converts the electrical energy back into acoustic energy and transmits it via the acoustic channel to the first acoustic transducer. Wireless experimental setup: This measurement is performed at a distance of 50 mm using a 10 Vpp interrogation source. A range of up to 1 km was achieved by the authors. List of reference symbols

[0056] 1Software-defined ultrasonic radar 2Microcontroller 3DAC 4Filter 5Tx AMP 6Rx AMP 7Filter 8ADC 9Tx Signal 10Rx Signal 11Ultrasonic sensor / label 12Adapter 13Resonator 14Load 15Function generator Tektronix AFG3102 16Ultrasonic transmitter 17Oscilloscope Rohde&Schwarz RTO1044 18Ultrasonic receiver 19Measurement voltage (V) 20Excitation frequency = 39995.20 Hz 21Pulse duration = 0.502 seconds 22Resonance frequency = 39996.56 Hz 23Decay time = 0.502 seconds 24Quality factor = 101788 25Time (s) 26Measurement voltage (V) 27Time (s) 28Resonance frequency (kHz) 2932.718 kHz Resonator 30Quadratic curve fit 31Residues of the quadratic curve fit (mHz) 32Temperature (°C) 33Function generator 34Ultrasonic transmitter 35Ultrasonic receiver 36Oscilloscope 37Resonator 38Ultrasonic transducer 39Determined resonance frequency (kHz) 40DUT response 41Pt100 reference 42Temperature (°C) 43Time (hours)

Claims

1. System comprising a first electroacoustic transducer connected to an interrogation unit and at least one second electroacoustic transducer electrically connected to a resonator, wherein the first electroacoustic transducer and the second electroacoustic transducer form an acoustic channel and the second electroacoustic transducer is electrically connected to the resonator and forms with the resonator a passive cooperative target which, upon receiving an interrogation signal from the interrogation unit, transmits a response signal via the acoustic channel, and the interrogation signal has a higher energy than the response signal.

2. System according to claim 1, wherein the interrogation unit is a software defined interrogation unit.

3. System according to claim 1 or 2, wherein the first and / or the second electroacoustic transducer is a, preferably bidirectional, transducer, preferably for ultrasound or infrasound.

4. System according to any one of the claims 1 to 3, wherein the resonator is a resonator with a high Q-factor.

5. System according to any one of the claims 1 to 4, wherein the resonator stores at least a part of the energy of the interrogation signal due to the high Q-factor until an environmentally induced signal reflection of the interrogation signal has decayed.

6. System according to any one of the claims 1 to bis 5, wherein the resonator is a thin-film resonator, a piezoelectric thin-film resonator, a dielectric resonator, or a quartz tuning fork resonator.

7. System according to any one of the claims 1 to 6, wherein the resonator is a single-port resonator.

8. System according to any one of the claims 1 to 7, wherein the resonator has at least one resonance frequency as a function of a measured variable.

9. System according to claim 8, wherein the resonance frequency is temperature-response compensated.

10. System according to any one of the claims 1 to 9, wherein the response signal is shifted in frequency relative to the interrogation signal.

11. System according to any one of the claims 1 to 10, in the interrogation signal, preferably as at least one rectangular interrogation pulse and / or a beat signal and / or a frequency-modulated interrogation signal, is transmitted by the interrogation unit.

12. System according to any one of the claims 1 to 11, wherein the interrogation signal is transmitted, preferably as at least one rectangular interrogation pulse, from a signal source which is not the interrogation unit.

13. System according to any one of the claims 1 to 12, wherein the passive cooperative target does not comprise active electronic components.

14. System according to any one of the claims 1 to 13, wherein the passive cooperative target does not comprise its own energy source.

15. System according to any one of the claims 1 to 14, wherein the passive cooperative target generates its energy required to transmit the response signal from the interrogation signal via the acoustic channel.

16. System according to any one of the claims 1 to 15, wherein the acoustic channel is located in a frequency range from 1 kHz to 10 THz, preferably in a first frequency range from 1 kHz to 10 kHz, in particular 3 kHz to 5 kHz, or also 5 kHz to 10 kHz, or in a second frequency range from 10 kHz to 50 kHz, in particular 10 kHz to 19 kHz, or also 19 kHz to 50 kHz, particularly preferably 20 kHz to 45 kHz or 20 kHz to 25 kHz or 25 kHz to 44 kHz or 44 kHz to 45 kHz, a third frequency range from 50 kHz to 250 kHz, in particular 50 kHz to 100 kHz, or also 100 kHz to 250 kHz, or in a fourth frequency range from 250 kHz to 1 MHz, or in a fifth frequency range from 1 MHz to 10 MHz, or in a sixth frequency range from 10 MHz to 100 MHz, or in a seventh frequency range from 100 MHz to 400 MHz, or in an eighth frequency range from 400 MHz to 600 MHz, or in a ninth frequency range from 600 MHz to 900 MHz, or in a tenth frequency range from 900 MHz to 1 GHz, or in an eleventh frequency range from 1 GHz to 5 GHz, or in an expanded frequency range from 5 GHz to 10 GHz, or in a frequency range from 1 mHz to 1 kHz, in particular 1 mHz to 0.5 Hz, or also 0.5 Hz to 1 Hz, in particular preferably 1 Hz to 500 Hz, in particular 1 Hz to 100 Hz, preferably also 70 Hz to 95 Hz, or also 100 Hz to 250 Hz, or also 250 Hz to 1 kHz, as well as in further frequency ranges from 20 Hz to 20 kHz, or 20 kHz to 1 GHz, or also 1 GHz to 10 THz.