Thermoacoustic Sensor Research Articles

Listening to pulses of radiation: design of a submersible thermoacoustic sensor

Nowadays, various collaborations are creating immense machines to try to track and understand the origin of high-energy cosmic particles (e.g., IceCube, ANTARES, Baikal-GVD, P-ONE). The detection mechanism of these sophisticated experiments relies mainly on an optical signal generated by the passage of charged particles on a dielectric medium (Čerenkov radiation). Unfortunately, the dim light produced by passing particles cannot travel too far until it fades away, creating the necessity to instrument large areas with short spacing between sensors. The range limitation of the optical technique has created a fertile ground for experimenting on the detection of acoustic signals generated by radiation—thermoacoustics. Despite the increased use of the thermoacoustic technique, the instrumentation to capture the faint acoustic signals is still scarce. Therefore, this work has the objective to contribute with information on the critical stages of an affordable submersible thermoacoustic sensor: namely the piezoelectric transducer and the amplifying electronics. We tested the sensor in a 170,{textit{l}} non-anechoic tank using an infrared (lambda =1064,hbox {nm}) Q-switched Nd:YAG laser as a pulsed energy source to create the characteristic signals of the thermoacoustic phenomena. In accordance with the thermoacoustic model, a polarity inversion of the pressure signal was observed when transiting from temperatures below the point of maximum density of water to temperatures above it. Also, the amplitude of the acoustic signal displayed a linear relationship with pulse energies up to (51.1 pm 1.7),hbox {mJ} (R^2 sim 0.98). Despite the use of cost-effective parts and simple construction methods, the proposed sensor design is a viable instrument for experimental thermoacoustic investigations on high-energy particles.

Challenges in practical operational testing of a nuclear powered thermoacoustic sensor

The world’s first nuclear powered, wireless power and temperature sensor was demonstrated in Penn State’s Breazeale Nuclear Reactor during the last week of September 2015. The sensor consisted of a thermoacoustic heat engine powered by nuclear fission designed to acoustically telemeter temperature and neutron flux information. The acoustic frequency of operation and the amplitude of the acoustic signal were proportional to the temperature and the reactor power respectively. The proof-of-concept tests were conducted in the research reactor twice daily over five days. Sensor performance was as expected with the exception that the amplitude of the acoustic signal diminished after each test. In this paper we will present our “wet sock” theory that a seal weld isolating the thermal insulation from the reactor coolant at the hot end of the thermoacoustic sensor failed early in the testing. This allowed water to be drawn in each time the thermoacoustic sensor cooled down reducing the efficiency of the insulation...

Fission-powered in-core thermoacoustic sensor

A thermoacoustic engine is operated within the core of a nuclear reactor to acoustically telemeter coolant temperature (frequency-encoded) and reactor power level (amplitude-encoded) outside the reactor, thus providing the values of these important parameters without external electrical power or wiring. We present data from two hydrophones in the coolant (far from the core) and an accelerometer attached to a structure outside the reactor. These signals have been detected even in the presence of substantial background noise generated by the reactor's fluid pumps.

Design of a Thermoacoustic Sensor for Low Intensity Ultrasound Measurements Based on an Artificial Neural Network.

In therapeutic ultrasound applications, accurate ultrasound output intensities are crucial because the physiological effects of therapeutic ultrasound are very sensitive to the intensity and duration of these applications. Although radiation force balance is a benchmark technique for measuring ultrasound intensity and power, it is costly, difficult to operate, and compromised by noise vibration. To overcome these limitations, the development of a low-cost, easy to operate, and vibration-resistant alternative device is necessary for rapid ultrasound intensity measurement. Therefore, we proposed and validated a novel two-layer thermoacoustic sensor using an artificial neural network technique to accurately measure low ultrasound intensities between 30 and 120 mW/cm2. The first layer of the sensor design is a cylindrical absorber made of plexiglass, followed by a second layer composed of polyurethane rubber with a high attenuation coefficient to absorb extra ultrasound energy. The sensor determined ultrasound intensities according to a temperature elevation induced by heat converted from incident acoustic energy. Compared with our previous one-layer sensor design, the new two-layer sensor enhanced the ultrasound absorption efficiency to provide more rapid and reliable measurements. Using a three-dimensional model in the K-wave toolbox, our simulation of the ultrasound propagation process demonstrated that the two-layer design is more efficient than the single layer design. We also integrated an artificial neural network algorithm to compensate for the large measurement offset. After obtaining multiple parameters of the sensor characteristics through calibration, the artificial neural network is built to correct temperature drifts and increase the reliability of our thermoacoustic measurements through iterative training about ten seconds. The performance of the artificial neural network method was validated through a series of experiments. Compared to our previous design, the new design reduced sensing time from 20 s to 12 s, and the sensor’s average error from 3.97 mW/cm2 to 1.31 mW/cm2 respectively.

Design and Characterization of a Close-Proximity Thermoacoustic Sensor

Although the radiation force balance is the gold standard for measuring ultrasound intensity, it cannot be used for real-time monitoring in certain settings, for example, bioreactors or in the clinic to measure ultrasound intensities during treatment. Foreseeing these needs, we propose a close-proximity thermoacoustic sensor. In this article, we describe the design, characterization, testing and implementation of such a sensor. We designed a 20-mm-diameter plexiglass sensor with a 2-mm-long absorber and tested it against low-intensity pulsed ultrasound generated at a 1.5-MHz frequency, 20% duty cycle, 1-kHz pulse repetition frequency and intensities between 30 and 120 mW/cm2. The sensor captures the beam, converts the ultrasound power into heat and indirectly measures the spatial-average time-average ultrasound intensity (Isata) by dividing the calculated power by the beam cross section (or the nominal area of the transducers). A thin copper sheet was attached to the back face of the sensor with thermal paste to increase heat diffusivity 1000-fold, resulting in uniform temperature distribution across the back face. An embedded system design was implemented using an Atmel microcontroller programmed with a least-squares algorithm to fit measured temperature-versus-time data to a model describing the temperature rise averaged across the back side of the sensor in relation to the applied ultrasound intensity. After it was calibrated to the transducer being measured, the thermoacoustic sensor was able to measure ultrasound intensity with an average error of 5.46% compared with readings taken using a radiation force balance.

Testing a thermoacoustic sensor of high-power microwave pulses

We present the results of testing a new thermoacoustic sensor designed to detect microwave pulses having durations from 3 to 120 ns at wavelengths of 0.8 and 3 cm. Operation of the sensor is based on the effect of generation of acoustic signals during absorption of microwave pulses in a radiotransparent substrate-absorber-liquid layered structure . A thin nanometer-thick film deposited on a substrate is used as an absorber. Microwaves are converted to an acoustic pulse in the film and the adjacent liquid. The pulse is received by a wideband acoustic receiver and then recorded by a digital oscilloscope. It is shown that for a pulse duration of 120 ns, the shape of the signal recorded by the thermoacoustic sensor completely corresponds to the signal of a tube-diode detector of microwave pulses. The response of the thermoacoustic sensor to shorter pulses (3 and 5 ns long) is a pulse with a duration of 18 ns which is determined by a limited frequency band of the acoustic receiver.

A thermoacoustic sensor for recording high-power nanosecond microwave pulses

The operating principle and design of an uncooled noise-immune high-power microwave pulse sensor is described. The sensor operation is based on the effect of acoustic signal generation when microwave pulses are absorbed in a layer structure, in which a thin metal nanometer-thick film is used as an absorber. The sensor is placed in a free space and intended to detect microwave pulses with ∼10- to 100-ns durations in a 10- to 300-GHz frequency band with a pulse repetition rate of up to 5 kHz. For 10-ns-long pulses, the sensor sensitivity is 0.5 V/mJ.

Output intensity measurement on a diagnostic ultrasoundmachine using a calibrated thermoacoustic sensor

A thermoacoustic measurement technique based on the transformation of theincident ultrasonic energy into heat inside a cylindrical absorber is investigated. To enablequantitative acoustic intensity measurements, a thermoacoustic sensor with an absorber 3 mmin diameter is calibrated in the far field of a planar source transducer. For ultrasoundfrequencies in the range from 1 to 9 MHz, the time-averaged intensities are derived frompressure field measurements using a membrane hydrophone. In a second run, measurementsare performed with the thermoacoustic sensor at the same position in the acoustic field andunder the same excitation conditions. The equilibrium temperature enhancement at the rearside of the absorber is determined at each frequency, and the transfer function of the sensor isgiven by the temperature enhancement per ultrasound intensity averaged over the sensor crosssection. The calibrated thermoacoustic sensor is then applied to acoustic output measurementson a diagnostic ultrasound machine at various parameter settings. The results for M-mode andpulse Doppler mode, i.e. for non-scanning beams, are compared with the intensities derivedfrom additional hydrophone measurements. If the spatial averaging effect of thethermoacoustic sensor is taken into consideration, agreement can be observed between theresults of both methods.

Thermoacoustic sensors

The two procedures mainly used for determining ultrasonic power—the sound radiation force method and the planar scanning technique—are complicated, and require a relatively expensive measuring setup. These procedures are therefore unsuitable for the routine inspection of ultrasonic equipment used in medical and technical applications. In contrast to these procedures, the thermoacoustic sensor is well-suited for this purpose. It is of simple design, small in dimension, and its application requires only relatively inexpensive equipment. The ultrasonic power is determined from the heat produced by the ultrasonic signal in a suitable absorbing material. A disadvantage of this first sensor type is that the power of the ultrasonic signal can be determined only if its amplitude spectrum is known. The new thermoacoustic sensor allows the power of ultrasonic signals to be determined even if their amplitude spectra are unknown. When this sensor type is used, the ultrasonic signal first travels a short distance in a weakly absorbing propagation medium before it enters the absorber, where its energy is completely transformed into heat. In this case, the ultrasonic power is determined from the frequency-independent temperature gradient originating in the weakly absorbing propagation medium immediately in front of the absorber.

The thermoacoustic effect and its use in ultrasonic power determination

Abstract In this paper the operation of a thermoacoustic sensor used for the determination of ultrasonic power is described. Its most essential component is an ultrasound-absorbing plate which transforms the incident ultrasonic energy into heat. From the temperature increase measured at the rear surface of the absorber and its thermal and acoustic properties, the absolute value of incident ultrasonic power was determined. In order to be able to estimate the uncertainty of measurement, the experimental results were compared with reciprocity measurements. The good agreement obtained confirms the suitability of the thermoacoustic procedure for determining the absolute value of ultrasonic power and calibrating ultrasonic transducers in the frequency range up to 14 MHz.

Thermoacoustic sensor for ultrasound power measurements and ultrasonic equipment calibration

This paper describes a thermoacoustic sensor developed for measurements of the acoustic power and calibration of ultrasonic transducers in the medical imaging and nondestructive testing frequency range. It is shown that the equilibrium temperature produced by ultrasound absorption in an absorbing material and detected by a copper-constantan thermocouple is proportional to the square of the current applied to the acoustic source. It is also demonstrated that the simultaneous measurement of this current and the corresponding equilibrium temperature at a given frequency allow the transmitting current sensitivity of the acoustic source to be calculated. The sensor thus provides a useful and low-cost alternative to the expensive calibration methods such as those based on the reciprocity technique, the planar scanning technique and the radiation force balance. The principles of the sensor's operation are outlined and its construction and characteristics are described. Experimental data in the frequency range of 1–8 MHz are presented and the advantages and disadvantages of the sensor are discussed.