Fast contactless vibrating structure characterization using real time field programmable gate array-based digital signal processing: Demonstrations with a passive wireless acoustic delay line probe and vision

Abstract

Vibrating mechanical structure characterization is demonstrated using contactless techniques best suited for mobile and rotating equipments. Fast measurement rates are achieved using Field Programmable Gate Array (FPGA) devices as real-time digital signal processors. Two kinds of algorithms are implemented on FPGA and experimentally validated in the case of the vibrating tuning fork. A first application concerns in-plane displacement detection by vision with sampling rates above 10 kHz, thus reaching frequency ranges above the audio range. A second demonstration concerns pulsed-RADAR cooperative target phase detection and is applied to radiofrequency acoustic transducers used as passive wireless strain gauges. In this case, the 250 ksamples/s refresh rate achieved is only limited by the acoustic sensor design but not by the detection bandwidth. These realizations illustrate the efficiency, interest, and potentialities of FPGA-based real-time digital signal processing for the contactless interrogation of passive embedded probes with high refresh rates.

Passive radar for measuring passive sensors: direct signal interference suppression on FPGA using orthogonal matching pursuit and stochastic gradient descent

“…At a sampling rate of 125/4=31.25 MS/s or 32 ns/cycle, convergence will require 64 µs of data acquisition, well below typical time constants for temperature or chemical sensing using passive wireless SAW sensors. Furthermore, for faster physical quantities such as strain sensing, 19 the sensor environment is expected not to vary significantly over sub-100 µs durations and the DSI identification using SGD considered to be still valid for extracting sensor echoes whose phase is representative of stress levels in the sensor. Fig.…”

Reader Architectures for Wireless Surface Acoustic Wave Sensors

“…However, the mandatory high bandwidth is also its huge disadvantage: the architecture is too costly and complex due to the necessary fast sampling and switching circuitry [ 72 ] and the required broadband excitation is not always compatible with the strict ISM band limits, especially not in the limited 868 MHz frequency band. Some prototypes have been built and evaluated [ 26 , 29 , 59 , 73 , 74 , 75 , 76 ]; however, this principle is only used in absolute exceptions when the very highest sampling rates are required for reflective delay line SAWs. A measurement update rate up to 250 kSa/s, which was only limited by the acoustic sensor design but not by the detection bandwidth, could be demonstrated in [ 76 ], but with a high hardware effort using 40 ns transmit pulses and a real-time field-programmable gate array (FPGA) signal processing.…”

“…Some prototypes have been built and evaluated [ 26 , 29 , 59 , 73 , 74 , 75 , 76 ]; however, this principle is only used in absolute exceptions when the very highest sampling rates are required for reflective delay line SAWs. A measurement update rate up to 250 kSa/s, which was only limited by the acoustic sensor design but not by the detection bandwidth, could be demonstrated in [ 76 ], but with a high hardware effort using 40 ns transmit pulses and a real-time field-programmable gate array (FPGA) signal processing. Almost all of today’s readers for reflective delay line sensors use one of the FDS or hybrid architectures, shown in Section 4 , which are easier and more economical to implement.…”

Local oscillator phase noise limitation on the resolution of acoustic delay line wireless passive sensor measurement

“…At a large enough distance, the receiver Low Noise Amplifier (LNA) phase noise dominates the local oscillator phase noise and the measurement uncertainty increases with increasing interrogation distance since the returned power decreases. 4 At short range, as is applicable in a multitude of industrial environments in which the sensor is confined close to the antenna linked to the interrogation unit (e.g., motor rotor to stator distance), the local oscillator phase noise dominates. Its contribution is dependent on the local oscillator noise floor b 0 and the emitted power P E : the range d beyond which the LNA dominates over the oscillator phase noise is 4…”

“…Phase noise 10 is a central characteristics provided by the time and frequency analysis community when characterizing an oscillator: it defines the phase fluctuation as a function of the frequency offset from the carrier, or in other words the phase fluctuation over a duration equal to the inverse to the frequency offset from the carrier. Having demonstrated the wireless interrogation of acoustic delay lines either using a stroboscopic pulsed approach 1 or a wideband pulsed approach, 4 we here investigate how the performance of the local oscillator actually affects the physical quantity measurement resolution. 5 Although further processing might improve the physical quantity estimate, 6 the raw input remains the core limiting factor of the measurement resolution.…”