Sonic sensor and its question

Abstract

The present invention relates to a method of interrogating an acoustic wave sensor, comprising transmitting, by an interrogator, an interrogating radio frequency signal by a transmit antenna to the acoustic wave sensor; receiving, by the interrogator, a response radio frequency signal from the acoustic wave sensor by a receive antenna; processing, by a processing means of the interrogator, the received response radio frequency signal to obtain in-phase and quadrature components in both the time domain and the frequency domain; determining, by the processing means, perturbations in the obtained in-phase and quadrature components in both the time domain and the frequency domain; and determining a value of a measurand based on the perturbations detected by the processing means.

Description

[Technical field]

[0001] The present invention relates to passive sensors of the acoustic wave type, in particular passive surface acoustic wave or bulk acoustic wave sensors, and the interrogation thereof. [Background technology]

[0002] Sensors are becoming increasingly important and more ubiquitous in everyday life. Microelectromechanical systems (MEMS) are an attractive option to meet the demand for improved sensor performance along with reduced size and cost. Surface acoustic wave (SAW) sensors, and to a lesser extent bulk acoustic wave (BAW) sensors or Lamb or Love wave acoustic sensors, offer particularly advantageous options due to the variety of measurable ambient parameters including, for example, temperature, pressure, strain and torque.

[0003] Acoustic wave sensors convert electrical signals into mechanical / acoustic waves using the piezoelectric effect. SAW-based sensors are built on single-crystal piezoelectric materials such as quartz (SiO2), lithium niobate (LiNbO3), lithium tantalate (LiTaO3), langasite (LGS), or polycrystalline piezoelectric materials such as aluminum nitride (AlN) or zinc oxide (ZnO), in particular deposited on silicon, or even on piezoelectric materials, in particular piezo-on-insulator (POI) composites, which include a layer of a single-crystal material, for example lithium tantalate or lithium niobate, and optionally bonded to a supporting substrate, for example silicon, by a bonding layer, for example a silicon oxide layer (generally any combination of single-crystal piezoelectric material and non-piezoelectric substrates is used for specific properties such as thermal stability or acoustic quality). The transducer is an interdigital transducer (IDT), in the case of surface acoustic waves, which converts the electrical energy of the electrical signal into acoustic wave energy. The acoustic waves travel across the surface (or bulk) of the device substrate via a so-called delay line to another transducer, in particular an IDT, which converts the acoustic waves into a detectable electrical signal. In some devices, mechanical absorbers and / or reflectors are provided to prevent interference patterns and reduce insertion losses. In some devices, the other (output) IDT is replaced by a reflector that reflects the generated acoustic waves back to the (input) IDT. This reflector can be coupled to an antenna for remote interrogation of the sensor device. Advantageously, the measurement can be performed completely passively, i.e. the sensor does not need to be powered by a power source.

[0004] A particular class of acoustic sensors comprises resonators that exhibit a resonant frequency that varies according to different ambient conditions. For example, a conventional surface wave resonator comprises an electroacoustic transducer with an interdigital comb placed between Bragg mirrors. At the resonant frequency, the synchronization condition between the reflectors is met and it is possible to obtain a coherent addition of the various reflections occurring under the reflectors. A maximum acoustic energy is then observed in the resonant cavity and, from an electrical point of view, a maximum amplitude of the current allowed by the transducer. A differential acoustic wave sensor may comprise two or more resonators that exhibit different resonant frequencies or a resonator that operates in multimode (several resonant frequencies), the difference in the measured frequencies reflecting the variations of an ambient parameter, for example temperature or strain.

[0005] However, despite recent engineering processes, the entire interrogation process, where the interrogator transmits a suitable radio frequency signal that is received by the sonic sensor via a receiving antenna, converted by the transducer into a surface acoustic wave (or bulk wave, in the case of bulk sonic sensor type devices), retransmitted via a radiating antenna, and converted into a radio frequency signal that is received and analyzed by the interrogator, still poses tough technical problems. In particular, radio frequency noise present in the commonly used ISM (industrial, scientific, medical) bands, e.g., those with center frequencies of 434 MHz or 2.45 GHz, causes reading / interpretation errors that affect the quality of the generation and analysis of the response spectrum provided by the sensor device. In particular, intermittent parasite / spurious echoes, such as WiFi, Bluetooth, GSM emissions, can adversely affect the quality of the spectral response, leading to reading errors or interference with the required signal. Persistent background white noise can adversely affect time domain measurements. Another problem is related to the relative motion between the sensor device and the interrogator, which causes parasites and affects the resonant frequency of resonator type sonic sensors. Summary of the Invention [Problem to be solved by the invention]

[0006] It is therefore an object of the present invention to provide a means for interrogating acoustic sensors with improved signal quality, e.g. improved signal to noise ratio, compared to the state of the art. [Means for solving the problem]

[0007] The present invention addresses the above objectives by providing a method of interrogating an acoustic sensor (and sensing a measurand by an acoustic sensor) comprising the steps of: transmitting, by an interrogator, an interrogating radio frequency signal by a transmitting antenna to the interrogated acoustic sensor (the acoustic sensor receiving the interrogating radio frequency signal by its own antenna); receiving, by the interrogator, by a receiving antenna (which may or may not be the same as the transmitting antenna) a reply radio frequency signal from the acoustic sensor (transmitted by an antenna included in the acoustic sensor device, which may or may not be the same as the antenna used to receive the interrogating radio frequency signal); processing, by a processing means of the interrogator (e.g. being or including a CPU or a microcontroller) to obtain in-phase and quadrature components in both time and frequency domains; detecting, by the processing means, perturbations in the obtained in-phase and quadrature components in both time and frequency domains; and determining, based on the perturbations detected by the processing means, a value of the measurand, which is an ambient parameter, e.g. temperature, strain, pressure or torque of a rotation axis.

[0008] The acoustic wave sensors may be surface acoustic wave sensors or bulk acoustic wave sensors and may include delay line structures as well as single or multiple resonator structures.

[0009] Thus, processing / analysis of the received response radio frequency signal is performed by determining the in-phase and quadrature components in both the time and frequency domains, and depending on noise / perturbations that may be present in at least one of the domains, further processing is performed in the time domain or the frequency domain, or both mentioned domains.

[0010] According to an embodiment, if the perturbation in the frequency domain exceeds a first predefined threshold, the value of the measurand is determined in the time domain, and conversely, if the perturbation in the time domain exceeds a second predefined threshold, the value of the measurand is determined in the frequency domain (e.g. the second threshold is the same as the first threshold).

[0011] The received response radio frequency signal may typically be processed in frames, and frames that contain perturbations exceeding a predefined threshold may be removed as defective frames when determining the value of the measurand. Removing defective frames makes the overall process more robust and provides more reliable results for the measurement of the measurand.

[0012] In particular, the value of the measurand can be determined in the time domain and / or in the frequency domain based at least in part on the phase of the received response radio frequency signal. Since the phase is very sensitive to the variations of the measurand, it can be advantageously used to measure the measurand in both the time domain and the frequency domain. However, if the resonant frequency is detected as a local maximum of the spectral coefficient, it can be shown that, according to the definition of resonance, the phase corresponding to the resonant frequency is necessarily zero (all contributions within the resonator sum in phase at the resonant frequency). In the time domain, if the sensor represents free space moving, for example in a delay line or a cavity resonator, the phase of the time domain signal corresponding to the maximum amplitude will change with the variations of the environmental parameters or with the sensor position.

[0013] In both cases a) where the perturbations in the time domain do not exceed the second predefined threshold, and b) where the perturbations in the frequency domain do not exceed the first predefined threshold, the translational and / or rotational movement of the acoustic sensor relative to the interrogator can be determined in both the time and frequency domains based on the obtained in-phase and quadrature components, effects caused by the movement of the acoustic sensor relative to the interrogator can be taken into account and / or the initial position of the acoustic sensor can be reliably determined.

[0014] The determination of the perturbation in all of the above embodiments may include dynamically determining the variance or standard deviation of the in-phase and quadrature components obtained over the entire respective frame. The variance or standard deviation of the in-phase component I and the quadrature component Q over a particular frame, for example the first frame, of N consecutively sampled frames is calculated and represents an initial threshold value. For the next frames (N+1, N+2, etc.), the variance or standard deviation of the in-phase and quadrature components over the entire respective frame (both in the time domain and in the frequency domain) is also calculated. If the variance or standard deviation of the next frame is decreasing, the threshold value is updated by the variance or standard deviation of the next frame. If the variance or standard deviation of the next frame is greater than the variance or standard deviation of the previous frame, the variance or standard deviation of the previous frame is used as the threshold value. In the analysis performed subsequently, frames that exceed the thus obtained threshold value are rejected and are not taken into account in the process step of determining the value of the measurand based on the determined perturbation of the method of the present invention for interrogating an acoustic sensor.

[0015] The above object is also addressed by providing a system for sensing a measurand comprising an acoustic wave sensor (e.g. a surface acoustic wave or bulk acoustic wave sensor having one or more antennas), and an interrogator comprising a processing means, a transmitting antenna and a receiving antenna (which may or may not be realized by one and the same antenna) and configured to transmit an interrogating radio frequency signal to the acoustic wave sensor by means of the transmitting antenna and to receive a response radio frequency signal from the acoustic wave sensor by means of the receiving antenna, wherein the processing means of the interrogator is configured to process the received response radio frequency signal to obtain in-phase and quadrature components in both time and frequency domains, detect perturbations of the obtained in-phase and quadrature components in both time and frequency domains, and determine a value of the measurand (ambient parameter) based on the detected perturbations.

[0016] According to an embodiment, the processing means is configured to determine the value of the measurand in the time domain if the perturbation in the frequency domain exceeds a first predefined threshold, and the value of the measurand in the frequency domain if the perturbation in the time domain exceeds a second predefined threshold (e.g. the same as the first predefined threshold). Furthermore, the processing means may be configured to process the received response radio frequency signal in frames, whereby when determining the value of the measurand, frames containing perturbations exceeding the predefined threshold are removed. Furthermore, the processing means may be configured to determine the value of the measurand in the time domain and / or in the frequency domain based at least in part on the phase of the received response radio frequency signal (and its temporal evolution during the monitoring process). If the resonant frequency is detected as a local maximum of the spectral coefficients, it can be shown that, according to the definition of resonance, the phase corresponding to the resonant frequency is necessarily zero (all contributions within the resonator are summed in phase at the resonant frequency). If in the time domain the sensor represents free space moving, for example in a delay line or a cavity resonator, the phase of the time domain signal corresponding to the maximum amplitude is changing due to the variation of the environmental parameters or the position of the sensor.

[0017] According to a further embodiment, the processing means of the Interrogator are configured to determine a translational and / or rotational movement of the acoustic sensor relative to the Interrogator based on the in-phase and quadrature components obtained in both the time and frequency domains if a) the perturbations in the time domain do not exceed a second predefined threshold and b) the perturbations in the frequency domain do not exceed the first predefined threshold. Furthermore, the processing means may be configured to (dynamically) determine the perturbations by determining the variance or standard deviation of the in-phase and quadrature components obtained over the respective frames.

[0018] In all of the above embodiments, the acoustic wave sensor may comprise one transducer configured to convert the interrogating radio frequency signal into an acoustic wave, in particular a surface acoustic wave, two resonant cavities, and a Bragg mirror structure, thus providing a hybrid acoustic wave sensor that allows to combine a delay line architecture with a resonant architecture and easily provides detection data that can be processed in both the time and frequency domains. In all of the above embodiments, the system may be configured to perform the steps of the embodiments of the method of the present invention for interrogating the above acoustic wave sensor.

[0019] Additional features and advantages of the present invention will now be described with reference to the drawings, in which reference is made to the accompanying figures which are intended to illustrate preferred embodiments of the invention, it being understood that such embodiments do not represent the full scope of the invention. [Brief description of the drawings]

[0020] [Figure 1] 1 illustrates an acoustic wave sensor device in which the present invention may be implemented according to an embodiment; [Diagram 2] The examples show the different susceptibilities of the response radio frequency signal provided by the acoustic wave sensor to noise in the time and frequency domains. [Diagram 3] 1 illustrates the effect of sensor movement on the determined resonant frequency of a resonator acoustic wave sensor device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The present invention provides a technique for remote interrogation of passive acoustic sensors, in particular surface acoustic wave sensor devices, characterized by a high signal-to-noise ratio. The technique can be applied to any interrogator configured to determine the spectral and impulse responses from an interrogating acoustic sensor. While in the art the response radio frequency signal received by the interrogator is processed in either the time or frequency (spectral) domain, here a technique is provided that in principle provides processing in both domains depending on the actual interrogation conditions, e.g. noise perturbations. In particular, if it is determined that a heavy parasite is present in one of the domains, the other one of the domains can be used to process / analyze the required signal.

[0022] FIG. 1 shows an exemplary hybrid acoustic wave sensor device, where a) a delay line structure, where the measurand affects the speed of the propagating acoustic wave and / or the geometric length of the propagation path, and b) a resonant approach, where the resonant frequency / frequency is affected by the measured value, are each known per se in the art and implemented in combination with each other. The hybrid acoustic wave sensor device comprises one transducer for converting the received radio frequency signal into an acoustic wave, in this case a surface acoustic wave (SAW). However, the invention is not limited to SAW sensors, but can also be applied, for example, to bulk acoustic wave sensors. Furthermore, the hybrid acoustic wave sensor device comprises two cavities and a mirror. The sensor device provides a high quality factor Qf, which corresponds to the ratio between the center frequency and the full width at half maximum of the band pass used in the interrogation process. The high quality factor Qf ensures a sufficiently high resolution of the detected data samples. A comb-shaped response can be obtained in the response radio frequency signal, both in the time domain and in the frequency domain. In the differential operation mode, the signal obtained from the delay line structure can be compared with the signal obtained from the resonator structure.

[0023] The interrogation signal transmitted by the interrogator may represent, for example, a frequency-stepped continuous wave signal or a linear frequency modulated continuous wave signal. The response radio frequency signal transmitted by the sensor device is received by the interrogator and may be processed by the interrogator in the time domain or in the frequency domain, the processing including the determination of the in-phase and quadrature components (real and imaginary parts) of the response radio frequency signal. The received response radio frequency signal is mixed by the processing means with the interrogation radio frequency signal according to the so-called IQ protocol known in the art to then extract the in-phase I and quadrature Q from which the coefficients and phases can be derived.

[0024] Therefore, changes in detected ambient parameters (measurands), e.g., temperature, strain, pressure, or torque of a rotating axis, can be detected either by frequency shifts, which can vary from peak to peak, and thus detection can be done in the time domain, either on absolute or relative frequency values, or by modification of the time of flight, or by differential phase changes from one echo to another, or both.

[0025] When processing in the frequency domain, the frequency band of the sensor is sampled in several steps performed in succession and the sensor value is determined from the amplitude and phase / frequency difference between the transmitted interrogating and replying radio frequency signals. When processing in the time domain, the frequency band of the sensor is sampled in one single step at a time. Therefore, faster sampling has to be performed in the interrogator, but on the plus side, a higher measurement update rate can be obtained. Furthermore, a high dynamic range can be achieved due to the time division multiplexing between the transmitted interrogating and replying radio frequency signals.

[0026] Although the time and frequency domains are mathematically interconnected by the (inverse) Fourier transform, perturbations (noise parasites and spurious bursts) may be significantly present only in one of the domains while the other domain is not significantly affected. For example, intermittent parasites such as WiFi, Bluetooth, or GSM emissions may be present in the frequency domain but generate only some bursts in the time domain. These bursts do not significantly affect the time domain information reconstructed by the inverse Fourier transform once all the spectral data has been acquired (the interrogator / reader may operate like a vector network analyzer detecting S11 responses). In other situations, persistent white background noise may affect the time domain measurements that do not significantly hide the spectral information. According to the invention, depending on the actual interrogation conditions, either time domain information or frequency domain information or both domain information may be acquired and used to monitor the measurement quantities.

[0027] The quality of the measurements can be determined by a statistical process based on the calculation of the variance or standard deviation of the in-phase and quadrature values ​​at each sampling frame and appropriate thresholding. If the calculated variance or standard deviation exceeds a certain predefined threshold, the measurement is rejected for further processing, i.e., analysis for the determination of ambient parameters. Figure 2 shows the occurrence of different signatures in the frequency and time domain of the resonator signal. The top row shows the spectral response of the quadrature and in-phase components of the received response radio frequency signal, the coefficients of these components, and the enhanced coefficients obtained by some post-processing. The in-phase component is given by I=Ycosφ and the quadrature component by Q=Ysinφ, where Y denotes the amplitude, φ denotes the phase, and the coefficients are calculated by the following formula:

number

[0028] The resonance peaks are clearly identifiable. Perturbation bursts are present at the last two resonances, as can be seen in the top row of Figure 2. After thresholding, the corresponding frames can be removed. The middle row shows the quadrature and in-phase components in the time domain. These data are not affected by the perturbations present in the frequency domain and can be directly used to determine the ambient parameters (temperature in this case), as shown in the bottom row of Figure 2.

[0029] Thresholding to remove defective (perturbed) frames can be performed as follows: The variance or standard deviation of the in-phase component I and the quadrature component Q over a certain frame of the N sampled frames, for example the first frame, is calculated and represents an initial threshold value. For the next frames, the variance or standard deviation of the in-phase component I and the quadrature component Q over the respective frame is also calculated. If the variance or standard deviation of the next frame is decreasing, the threshold value is updated by the variance or standard deviation of the next frame. If the variance or standard deviation of the next frame is greater than the variance or standard deviation of the previous frame, the variance or standard deviation of the previous frame is used as the threshold value. In the subsequent analysis, frames exceeding the threshold value thus obtained are rejected (defective frames).

[0030] It should be noted that the detection sensitivity in both the frequency and time domains, and in both the delay line and resonator approaches, is usually limited to a few kHz for bandwidths of a few MHz, and around 30 or 50 ns for chronograms of a few μs. In this context, better sensitivity can be achieved by using the phase of the received response radio frequency signal. In a coherent system, the phase can be obtained by φ=arctan(Q / I). For example, at 2.45 GHz, a time domain variation of 0.1 ns translates to π / 2 radians. This magnification effect exists in both the time and frequency domains and can be used in both the delay line and resonator approaches. In the latter case, it is similar for single- or multi-resonant architectures operating within or outside the allowable Bragg band. For example, the measurand can be measured directly or differentially based on the phase variation measured for resolved peaks in the spectral range, and then the temporal evolution of the phase of the phase difference between the peaks resolved in time in the context of a multi-sensor interrogation can be monitored. It should be noted that ambiguities arise when the phase shift exceeds 360°. This ambiguity problem can be solved, for example, by providing multiple reflectors at known positions and evaluating their phase differences to resolve the ambiguity.

[0031] Another source of accuracy limitation of detection by sonic sensor devices is the movement of the sensor relative to the interrogator. Figure 3 shows the effect of translational and rotational movements of the resonating sensor on the resonant frequency. Indeed, it has been observed that a linear displacement of the sensor by ±x leads to a shift of the resonant frequency f0, so that the determined resonant frequency obtained by measurement is given by f=f0(1+a cos(2πx / λ)) with λ being the wavelength. The parameter a can be found experimentally from measurements and depends on how the antennas are coupled on the interrogator and sensor sides. For example, a for the maximum frequency variation around f0=2.45 GHz is about 18 kHz. Similarly, rotating the sonic sensor by θ shifts the resonant frequency f0, so that the determined resonant frequency obtained by measurement is given by f=f0(1+a cos(θ)). This accuracy problem can in principle be solved by phase shift control of the antenna of the sensor device, using two antennas for the sensor device detuned by 180°, and / or by moving the acoustic sensor in an initialization step by λ / 2 and calibrating the resonant frequency to f0=(f0(x)+f0(x+λ / 2)) / 2 to compensate for the linear motion.

[0032] In fact, since the fluctuations are periodic, if we consider two frequency points to be in antiphase, the average value of the two corresponding frequencies is automatically equal to f0: f(x)+f(x+λ / 2)=f0(1+a cos(2πx / λ))+f0(1+a cos(2πx / λ+π))=2f0.

[0033] On the other hand, if valid (sufficiently unperturbed) signals are obtained in the time and frequency domains, the results of the two domains can be compared with each other to check the consistency of the obtained information. For example, if some phase rotation is determined from the measurement data in the time domain and no significant deviation of the resonant frequency is determined from the measurement data in the frequency domain, it can be concluded that some relative movement of the sensor device with respect to the interrogator has occurred. By unwrapping the phase information, it is possible to determine the distance the sensor has moved in a translational and / or rotational manner. A translational movement leads to a change in the unwrapped phase, whereas a rotation leads to a rotational phase movement even when the phase is unwrapped.

[0034] Indeed, when a resonator sensor device is subject to variations in the ambient parameters to be detected, e.g. thermal variations, for a linearly behaving sensor device, the phase of the time domain echo varies linearly, i.e. the resonant frequency decreases linearly over time, so the phase is shifted downwards. The true phase (without periodic -π / +π wrapping) can be obtained by unwrapping the phase, resulting in a linear phase change. A similar effect is observed when moving the sensor closer to or farther away from the interrogator, since the phase rotations of the RF link accumulate and have a similar effect on the sensor. Experimental measurements have shown that when the sensor is rotating, the phase stays in the -π / +π range, so that after unwrapping the phase stays in the -π / +π range. This is due to the fact that if the position of the sensor device remains approximately the same (no significant translational motion), the overall average phase does not actually change.

[0035] All the above-described embodiments are not intended as limitations, but serve as examples to illustrate the features and advantages of the present invention. It is understood that some or all of the above features can also be combined in different ways.

Claims

1. 1. A method of interrogating an acoustic sensor, comprising: said acoustic wave sensor comprising a transducer adapted to convert an interrogation radio frequency signal into an acoustic wave, in particular a surface acoustic wave, two resonant cavities and a Bragg mirror structure; The method comprises: transmitting, by an interrogator, an interrogating radio frequency signal via a transmitting antenna to said sonic sensor; receiving, by said interrogator, a receiving antenna, a response radio frequency signal from said sonic sensor; processing said received response radio frequency signal by a processing means of said interrogator to obtain in-phase and quadrature components in both the time and frequency domains; detecting, by said processing means, noise perturbations of said obtained in-phase and quadrature components in both the time domain and the frequency domain; determining a value of a measurand based on the received response radio frequency signal by the processing means, the measurand being a temperature, strain, pressure or torque measurand; wherein the value of the measurand is determined in the time domain if the noise perturbation in the frequency domain exceeds a first predetermined threshold, and the value of the measurand is determined in the frequency domain if the noise perturbation in the time domain exceeds a second predetermined threshold.

2. 1. A method of interrogating an acoustic sensor, comprising: said acoustic wave sensor comprising a transducer adapted to convert an interrogation radio frequency signal into an acoustic wave, in particular a surface acoustic wave, two resonant cavities and a Bragg mirror structure; The method comprises: transmitting, by an interrogator, an interrogating radio frequency signal via a transmitting antenna to said sonic sensor; receiving, by said interrogator, a receiving antenna, a response radio frequency signal from said sonic sensor; processing said received response radio frequency signal by a processing means of said interrogator to obtain in-phase and quadrature components in both the time and frequency domains; detecting, by said processing means, noise perturbations of said obtained in-phase and quadrature components in both the time domain and the frequency domain; determining a value of a measurand based on the received response radio frequency signal by said processing means; and if the noise perturbation in the time domain does not exceed a second predetermined threshold and the noise perturbation in the frequency domain does not exceed a first predetermined threshold, then a translational and / or rotational movement of the acoustic sensor relative to the interrogator is determined based on the obtained in-phase and quadrature components in both the time domain and the frequency domain.

3. 3. The method of claim 1 or 2, wherein the received response radio frequency signal is processed in frames and, when determining the value of the measurand, frames containing noise perturbations exceeding a predetermined threshold are eliminated.

4. A method according to any one of claims 1 to 3, wherein the value of the measurand is determined in the time domain and / or the frequency domain based at least in part on a phase of the received response radio frequency signal.

5. A method according to any one of claims 1 to 4, wherein the determining of the noise perturbation comprises determining the variance or standard deviation of the obtained in-phase and quadrature components over each frame.

6. 1. A system for sensing a measurand, comprising: an acoustic wave sensor comprising a transducer adapted to convert an interrogation radio frequency signal into an acoustic wave, in particular a surface acoustic wave, two resonant cavities and a Bragg mirror structure; an interrogator comprising a processing means, a transmitting antenna and a receiving antenna, the interrogator being configured to transmit an interrogating radio frequency signal to the sonic sensor by the transmitting antenna and to receive a reply radio frequency signal from the sonic sensor by the receiving antenna; said processing means of said interrogator processing said received response radio frequency signal to obtain in-phase and quadrature components in both the time and frequency domains; detecting noise perturbations of the obtained in-phase and quadrature components in both the time domain and the frequency domain; determining a value of a measurand based on the received response radio frequency signal; The system, wherein the processing means is configured to determine the value of the measurand in the time domain if the noise perturbation in the frequency domain exceeds a first predetermined threshold, and to determine the value of the measurand in the frequency domain if the detected noise perturbation in the time domain exceeds a second predetermined threshold.

7. 1. A system for sensing a measurand, comprising: an acoustic wave sensor comprising a transducer adapted to convert an interrogation radio frequency signal into an acoustic wave, in particular a surface acoustic wave, two resonant cavities and a Bragg mirror structure; an interrogator comprising a processing means, a transmitting antenna and a receiving antenna, the interrogator being configured to transmit an interrogating radio frequency signal to the sonic sensor by the transmitting antenna and to receive a reply radio frequency signal from the sonic sensor by the receiving antenna; said processing means of said interrogator processing said received response radio frequency signal to obtain in-phase and quadrature components in both the time and frequency domains; detecting noise perturbations of the obtained in-phase and quadrature components in both the time domain and the frequency domain; determining a value of a measurand based on the received response radio frequency signal, the measurand being a temperature, strain, pressure, or torque measurand; the processing means is configured to determine a translational and / or rotational movement of the acoustic sensor relative to the interrogator based on the obtained in-phase and quadrature components in both the time domain and the frequency domain if the noise perturbation in the time domain does not exceed a second predetermined threshold and if the noise perturbation in the frequency domain does not exceed a first predetermined threshold.

8. 8. A system as claimed in claim 6 or 7, wherein the processing means is arranged to process the received response radio frequency signal in frames, and when determining the value of the measurand, frames containing noise perturbations exceeding a predetermined threshold are eliminated.

9. A system according to any one of claims 6 to 8, wherein the processing means is configured to determine the value of the measurand in the time domain and / or the frequency domain based at least in part on a phase of the received response radio frequency signal.

10. A system according to any one of claims 6 to 9, wherein the processing means is arranged to determine the noise perturbation by determining the variance or standard deviation of the obtained in-phase and quadrature components over each frame.

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