Acoustic Pressure Sensor Research Articles

An analytical model of spatial correlation between vector fields of surface generated noise in a stratified ocean.

Traditionally, hydrophone-based acoustic pressure information has been utilized for underwater detection, but the advent of vector sensors has enabled the utilization of particle velocity of sound waves. A vector sensor adds three-axis particle velocity vector components to the conventional acoustic pressure sensor, representing spatial correlation not as a scalar function but as a matrix of four vector components. While analytical solutions exist for vector sensor spatial correlation in the case of simple isotropic noise, such noise fails to reflect the medium properties of the ocean, such as sound speed or density. Previous investigation reflecting the ocean environment derived a pressure spatial correlation model for surface generated noise in a stratified ocean, but this model is limited in the applicability to vector sensors. In this work, we extend the pressure spatial correlation model to vector fields, and by comparing with isotropic noise, we have confirmed that ocean environmental factors significantly influence the spatial correlation of vector sensors.

Recent Advances in Ferroelectret Fabrication, Performance Optimization, and Applications.

The growing demand for wearable devices has sparked a significant interest in ferroelectret films. They possess flexibility and exceptional piezoelectric properties due to strong macroscopic dipoles formed by charges trapped at the interface of their internal cavities. This review of ferroelectrets focuses on the latest progress in fabrication techniques for high temperature resistant ferroelectrets with regular and engineered cavities, strategies for optimizing their piezoelectric performance, and novel applications. The charging mechanisms of bipolar and unipolar ferroelectrets with closed and open-cavity structures are explained first. Next, the preparation and piezoelectric behavior of ferroelectret films with closed, open, and regular cavity structures using various materials are discussed. Three widely used models for predicting the piezoelectric coefficients (d33) are outlined. Methods for enhancing the piezoelectric performance such as optimized cavity design, utilization of fabric electrodes, injection of additional ions, application of DC bias voltage, and synergy of foam structure and ferroelectric effect are illustrated. A variety of applications of ferroelectret films in acoustic devices, wearable monitors, pressure sensors, and energy harvesters are presented. Finally, the future development trends of ferroelectrets toward fabrication and performance optimization are summarized along with its potential for integration with intelligent systems and large-scale preparation.

Design, fabrication and experimental analysis of piezoresistive bidirectional acoustic sensor

PurposeIdentification of the direction of the sound source is very important for human–machine interfacing in the applications such as target detection on military applications and wildlife conservation. Considering its vast applications, this study aims to design, simulate, fabricate and test a bidirectional acoustic sensor having two cantilever structures coated with piezoresistive material for sensing has been designed, simulated, fabricated and tested.Design/methodology/approachThe structure is a piezoresistive acoustic pressure sensor, which consists of two Kapton diaphragms with four piezoresistors arranged in Wheatstone bridge arrangement. The applied acoustic pressure causes diaphragm deflection and stress in diaphragm hinge, which is sensed by the piezoresistors positioned on the diaphragm. The piezoresistive material such as carbon or graphene is deposited at maximum stress area. Furthermore, the Wheatstone bridge arrangement has been formed to sense the change in resistance resulting into imbalanced bridge and two cantilever structures add directional properties to the acoustic sensor. The structure is designed, fabricated and tested and the dimensions of the structure are chosen to enable ease of fabrication without clean room facilities. This structure is tested with static and dynamic calibration for variation in resistance leading to bridge output voltage variation and directional properties.FindingsThis paper provides the experimental results that indicate sensor output variation in terms of a Wheatstone bridge output voltage from 0.45 V to 1.618 V for a variation in pressure from 0.59 mbar to 100 mbar. The device is also tested for directionality using vibration source and was found to respond as per the design.Research limitations/implicationsThe fabricated devices could not be tested for practical acoustic sources due to lack of facilities. They have been tested for a vibration source in place of acoustic source.Practical implicationsThe piezoresistive bidirectional sensor can be used for detection of direction of the sound source.Social implicationsIn defense applications, it is important to detect the direction of the acoustic signal. This sensor is suited for such applications.Originality/valueThe present paper discusses a novel yet simple design of a cantilever beam-based bidirectional acoustic pressure sensor. This sensor fabrication does not require sophisticated cleanroom for fabrication and characterization facility for testing. The fabricated device has good repeatability and is able to detect the direction of the acoustic source in external environment.

Modeling and testing of a highly sensitive surface acoustic wave pressure sensor for liquid depth measurements

The fluid depth/level measurement application extends from industry to domestic contexts. This article explores the underutilized potential of Surface Acoustic Wave (SAW) sensor-based devices for liquid depth and pressure measurements. Experiments conducted at room temperature address design challenges using a quartz Y34° cut single-port resonator. Theoretically predicted longitudinal strain sensitivity of −1.15 kHz/μStrain (−1.32 ppm/μStrain) was reduced to −421 Hz/μStrain (-0.48 ppm/μStrain) due to adhesive layer thickness. Numerical simulations investigate the effect of adhesive thickness on strain transfer from a cantilever to the Surface Acoustic Wave (SAW) sensor's top surface. The sensor is tested on a cantilever and integrated into a 20 μm thick diaphragm-based depth gauge, achieving a depth sensitivity of 42 Hz/mm (0.048 ppm/mm). This sensitivity results from bending of the SAW sensor under hydrostatic pressure, causing compression at the top SAW surface, which was an interesting observation. Additional numerical investigations confirm this behavior, aligning well with experimental findings. The article summarizes the comprehensive study of the SAW resonator’s performance and effect of adhesive thickness and provides a guide for designing thin diaphragm-based SAW pressure and depth sensors. It also identifies the device’s high sensitivity compared to other sensors in the literature and outlines potential avenues for future research.

Self-Mixing Interferometer for Acoustic Measurements through Vibrometric Calibration.

The Self-Mixing Interformeter (SMI) is a self-aligned optical interferometer which has been used for acoustic wave sensing in air through the acousto-optic effect. This paper presents how to use a SMI for the measurement of Sound Pressure Level (SPL) in acoustic waveguides. To achieve this, the SMI is first calibrated in situ as a vibrometer. The optical feedback parameters C and α in the strong feedback regime (C≥4.6) are estimated from the SMI vibrometric signals and by the solving of non-linear equations governing the SMI behaviour. The calibration method is validated on synthetic SMI signals simulated from SMI governing equations for C ranging from 5 to 20 and α ranging from 4 to 10. Knowing C and α, the SMI is then used as an acoustic pressure sensor. The SPLs obtained using the SMI are compared with a reference microphone, and a maximal deviation of 2.2 dB is obtained for plane waves of amplitudes ranging from 20 to 860 Pa and frequencies from 614 to 17,900 Hz. The SPL measurements are carried out for C values ranging from 7.1 to 21.5.

On the mixed acoustic and vibration sensors for the cross-correlation analysis of pipe leakage signals

Pipe leak detection can be carried out by various acoustic/vibration sensors, such as acoustic pressure, velocity and acceleration sensors. The purpose of this study is to investigate the effectiveness of the mixed acoustic/vibration sensors for the determination of pipe leakage. Firstly, a propagation and attenuation model of leakage signal in the liquid-filled pipeline is established based on frequency response functions. Further, the expressions of the cross-correlation function of different sensor types are derived with respect to the differential properties of Fourier transform. Then, the influence of signal-to-noise ratio (SNR) on the cross-correlation function is analyzed. Numerical simulation is employed to generate pressure, velocity and acceleration signals by differentiating the leakage source signals. Simulation results indicate that the use of pressure sensor acts as low-pass filtering operation, whereas the velocity and acceleration sensors act as band-pass filtering. Finally, experimental work is carried out on a medium density polyethylene (MDPE) pipe. Leakage signals are collected synchronously by hydrophones and accelerometers. Experimental results show that the cross-correlation function of hydrophones fluctuates slowly with peak value being less obvious, while the cross-correlation function of accelerometers fluctuates rapidly and has a sharper peak. In comparison, there is a compromise in the fluctuation for the sake of peak sharpness in the cross-correlation function of the mixed sensors, indicating that the corresponding cross-correlation result are less affected by background noise.

Temperature-compensated surface acoustic wave internal pressure sensor for nondestructive structural inspection of spent fuel canisters

Temperature-compensated surface acoustic wave internal pressure sensor for nondestructive structural inspection of spent fuel canisters

Experimental mode decomposition investigation on 3-stage axial flow compressor stall phenomena using aeroacoustics measurements

Safely operating compressors is quite critical. Rotating stall is highly undesirable and affects negatively the performance and stability of aero-engine compressors. It is important to identify a precursor of such rotating stalling phenomena observed on the compressor. In this work, we conduct experimental measurements on a 3-stage axial flow compressor by using 8 acoustic pressure sensors. Emphasis is being placed on applying different mode decomposition methods such as Proper Orthogonal Decomposition (POD) and Empirical Mode Decomposition (EMD) on these acoustics data to shed lights on the stall phenomena. Comparison is then made between these methods and conventional means like continuous wavelet (CWA), and PSD (Power Spectrum Density) analyses to achieve a timely detection of stall inception and the energy distribution before and after stall occurred. It is found from POD that the dominant acoustic modes contributing to more than 90% of the total fluctuation energy are changed from 3 to 4, when the stall occurred. The EMD investigation shows that the compressor stall is associated with a few low-frequency IMFs (intrinsic mode function). Time evolutions of such IMFs are observed to grow from negligible amplitude disturbances into limit cycles. Additionally, applying CWA reveals that the stall cell is originated from the first stage and then propagates circumferentially and axially to the second and third stage. Finally, PSD analysis shows that the stall frequency related to the spike-type stall cell exists only on the first stage. This is different from the blade passing frequency as observed on all stages of the compressor. In summary, the present work offers alternative acoustic measurements to examine the dynamic instability of a compressor stall with advanced signal-processing techniques applied.

A method of in-situ monitoring multiple parameters and blade condition of turbomachinery by using a single acoustic pressure sensor

In this paper, a method of using a single acoustic pressure sensor to evaluate multiple physical parameters (pressure, rotation speed, temperature) of the turbomachinery and monitor the condition of rotating blades in-situ through the interpretation of dynamic acoustic pressure generated by the rotating components is proposed. The time-domain response of dynamic acoustic pressure is transformed by Fast Fourier Transform (FFT) to obtain the rotation frequency of the blade and calculate the rotation speed of turbomachinery, the standing wave method is adopted to measure the temperature of the rotating equipment synchronously with the dynamic acoustic pressure. Furthermore, the formula for calculating the distance between the rotating blade tip and the case based on the acoustic attenuation model is derived, which can demonstrate the change of blade tip clearance, even blade wear, and fracture. Finally, a fan test-bed with seven blades is built for test verification, the results show that the rotation speed and temperature measured based on dynamic acoustic pressure are consistent with the measured results of commercial instruments, and it is also effective and accurate to measure the change of tip clearance and predict the wear and fracture of blade through the time-domain response of dynamic acoustic pressure. Therefore, in-situ dynamic acoustic pressure measurement with a single sensor is a promising method that can be used for both parameter evaluation and condition monitoring of turbomachinery.

Design and analysis of SAW pressure sensing element based on IDT/AlN/Mo/diamond multilayered structure

The multilayer structure of surface acoustic wave sensor is an important development direction of surface acoustic wave devices in recent years. In this paper, the IDT/AlN/Mo/diamond structure of surface acoustic wave pressure sensing element is modeled and simulated. The influence of the thickness of AlN and IDT on pressure coefficient frequency andK2were simulated and analyzed. The performance of surface acoustic wave pressure sensing element is compared when the metal layer is Mo, no metal layer and the metal layer is Pt. Finally, the relationship between frequency variation and pressure of the designed multilayer surface acoustic wave pressure sensing element is obtained. This research provides a good guidance for the design of surface acoustic wave pressure sensor.

The influence of temperature on the pressure sensitivity of surface acoustic wave pressure sensor

This paper illustrates the effect of temperature on AlN-based surface acoustic wave (SAW) pressure sensor. The resonance frequency of the SAW pressure sensor at different temperatures and pressures have been simulated and extracted in the COMSOL Multiphysics software, and the pressure coefficient of frequency (PCF) was obtained as 157.31 ppm/MPa through the linear fitting. The PCF at room temperature was experimentally measured to be 101.46 ppm/MPa in the pressure range of 0 MPa to 2 MPa. In addition, the effect of temperature on PCF has been investigated by simulation analysis and it was found that PCF increases with temperature due to thermal mismatch between different films rather than the effect of temperature on the Young's modulus. The experimental findings have proved the increase of PCF with temperature and the obtained data are found in good agreement with simulation results.

A point sound source location and detection method based on 19-element hemispheric distributed acoustic pressure sensor array

To solve the key problem of diagnosing the operating condition of an oil transfer pump unit in a 3D closed space, this paper presents an approach for a point sound source location and detection method based on a hemispheric distributed sound pressure sensor array. The array model consists of 19 sound pressure sensors acting in the radial direction and uniformly distributed over the hemispherical surface. A spatial rectangular coordinate system is established by taking the projection point of the central sensor arranged at the apex of the hemisphere to the ground as the origin of the spatial coordinates. With reference to the central sensor, the point sound source is located by selecting the maximum measured sound level and its spatial coordinate in each of the three layers of sensors surrounding it as parameters and using a triangular or a quadrilateral area location algorithm based on virtual instrument technology. According to the location of the source, the A-weighted sound level of the sound source point is derived by the inversion of the sound field distribution law. Results show that the triangular and quadrilateral area location algorithms are both effective. The errors in location become larger for a measured sound source far from the centre.

Highly sensitive thick diaphragm-based surface acoustic wave pressure sensor

Diaphragm-based Surface acoustic wave (SAW) pressure sensors are of great interest to fulfill high-pressure sensing requirements in industrial and commercial applications. These sensors are developed with a thick diaphragm, can endure considerable pressure but adversely result in low sensitivity and affect device accuracy. The trade-off between diaphragm thickness and sensitivity is the major problem in designing pressure sensors for high-pressure sensing ranges. This work proposed a highly sensitive pressure sensor design based on one port SAW resonator with AlN/Mo/SOI multilayer structure. The sensor utilizes a 50 μm thick rectangular diaphragm and has been fabricated with simple microfabrication techniques, making it cost-effective and easy to implement in pressure sensing equipment. Finite element analysis (FEA) has been performed for analyzing diaphragm to locate IDTs based on bending, uniformity of stress distribution and induced strain type. The developed sensor exhibits good performance characteristics, including high sensitivity (up to 129.17 ppm/MPa), wide pressure sensing range (up to 2 MPa), and good repeatability with linear behavior for applied pressure range. Additionally, this work has presented a novel approach to enhance pressure sensitivity based on increased velocity without compromising sensing range. The obtained sensitivity has been enhanced up to 228.46 ppm/MPa by modifying the primarily developed sensor design such that the SAW propagation direction becomes parallel to the induced strain direction. With the proposed novel concept, the sensitivity has been significantly improved by 76.87 % compared to the primarily developed sensor. Besides improved sensitivity, the modified sensor also shows the best repeatability and linearity. All these performance characteristics pave the way to make this design a good choice for high-pressure sensing applications.

Engineering Caged Microbubbles for Controlled Acoustic Cavitation and Pressure Sensing

Acoustic microbubbles (MBs) are an important class of biomaterials that play an increasingly prominent role in advanced applications such as contrast and super-resolution imaging, sonoporation, drug delivery, microrobotics, and biosensors. The ability to control and regulate acoustic cavitation of MBs by ultrasound (US) pulses is fundamental to achieve these applications. However, most MBs are coated with a soft shell that may undergo alteration (e.g., rupture or dissolution) under insonification and result in unintended acoustic responses. This work introduces a system of stable polymeric caged MBs in which the gas core is encapsulated within a rigid but nanoporous shell, so that their acoustic response is regulated by both shell compressibility and metastructure (i.e., porosity), thus permitting high control over their cavitation behaviors via pulse manipulation. These caged MBs are fabricated via a method of interfacial nanoprecipitation. Fabrication parameters can be varied to manipulate shell elasticity and porosity and subsequently control a wide range of acoustic properties such as tuning resonance frequency, controlling modes of nonlinear cavitation. Furthermore, the cavitation of caged MBs can be manipulated to develop tunable acoustic pressure sensors. These caged MBs offer insight of the acoustic–material relationship to design acoustic biomaterials for US-guided diagnostic and therapeutic technologies.

Experimental investigation on axial compressor stall phenomena using aeroacoustics measurements via empirical mode and proper orthogonal decomposition methods

In this work, we conduct experimental investigations on a single-stage axial compressor to shed lights on the dynamic stall phenomena via aeroacoustic measurements. For this, 8 acoustic pressure sensors are installed equally around the circumference of the compressor intake. The acoustic pressure data are simultaneously logged in real-time. Classical and conventional Fourier-transform based methods reveal that the compressor stall will occur beyond a critical pressure ratio or a flow coefficient as illustrated on a compressor map. However, there is no warning precursor obtained from the conventional signal analysis methods. Further investigations are conducted using a number of advanced signal processing techniques, such as empirical mode decomposition (EMD) and proper orthogonal decomposition (POD) and continuous wavelet (CW) methods. EMD analysis reveals that the compressor stall is corresponding to a low-frequency intrinsic mode function (IMF). It is growing rapidly from negligible amplitude random disturbances to limit cycle oscillations. POD shows that the number of the dominant acoustic modes contributing to more than 98.5% of the total fluctuation energy is changed from 3 to 7, when the stall occurs. This is insightful for low-order modeling of the compressor stall phenomena. Finally, applying CW transform could provide a warning of 0.05 s precursor on the tested axial compressor. In general, the present work opens up an alternative approach to study the dynamic physics of a compressor stall by applying an array of acoustic sensors with proper advanced data-processing methods implemented.

Enhanced acoustic pressure sensors based on coherent perfect absorber-laser effect

Lasing is a well-established field in optics with several applications. Yet, having lasing or huge amplification in other wave systems remains an elusive goal. Here, we utilize the concept of coherent perfect absorber-laser to realize an acoustic analog of laser with a proven amplification of more than 104 in terms of the scattered acoustic signal at a frequency of a few kHz. The obtained acoustic laser (or the coherent perfect absorber-laser) is shown to possess extremely high sensitivity and figure of merit with regard to ultra-small variations of the pressure (density and compressibility) and suggests its evident potential to build future acoustic pressure devices such as precise sensors.

Protection and Identification of Thermoacoustic Azimuthal Modes

Abstract This paper first characterizes the acoustic field of two annular combustors by means of data from acoustic pressure sensors. In particular, the amplitude, orientation, and nature of the acoustic field of azimuthal order n are characterized. The dependence of the pulsation amplitude on the azimuthal location in the chamber is discussed, and a protection scheme making use of just one sensor is proposed. The governing equations are then introduced, and a low-order model of the instabilities is discussed. The model accounts for the nonlinear response of M distinct flames, for system acoustic losses by means of an acoustic damping coefficient α and for the turbulent combustion noise, modeled by means of the background noise coefficient σ. Keeping the response of the flames arbitrary and in principle different from flame to flame, we show that, together with α and σ, only the sum of their responses and their 2n Fourier component in the azimuthal direction affect the dynamics of the azimuthal instability. The existing result that only this 2n Fourier component affects the stability of standing limit-cycle solutions is recovered. It is found that this result applies also to the case of a nonhomogeneous flame response in the annulus, and to flame responses that respond to the azimuthal acoustic velocity. Finally, a parametric flame model is proposed, depending on a linear driving gain β and a nonlinear saturation constant κ. The model is first mapped from continuous time to discrete time, and then recast as a probabilistic Markovian model. The identification of the parameters {α,β,κ,σ} is then carried out on engine time-series data. The optimal four parameters {α,σ,β,κ} are estimated as the values that maximize the data likelihood. Once the parameters have been estimated, the phase space of the identified low-order problem is discussed on selected invariant manifolds of the dynamical system.

Mechanical defects diagnosis for gas insulated switchgear using acoustic imaging approach

Mechanical faults are major fault types in gas insulated switchgear (GIS). The vibration and acoustic signature provide valuable health indicator for GIS. This paper proposes a novel mechanical defect detection and identification approach for GIS using acoustic imaging. The vibration modals of a three-phase-in-one-tank GIS bus tube under different natural frequencies are investigated. An acoustic pressure sensor matrix is designed to obtain the acoustic intensity nephogram of the GIS. The gray-level co-occurrence matrix (GLCM) is used to extract the characteristics of the nephogram. Five eigenvalues, including angular second moment, contrast, entropy, correlation, and inverse different moment, are analyzed for three types of mechanical defects (i.e., loose anchor bolts, loose disc insulator bolts, and poor switchgear contact). A mechanical defect diagnostic approach for GIS is developed using the variation percentage of the averaged values of contrast as the key indicator. The effectiveness of the approach is validated using experimental data.

Finite element simulation for sensitivity measurement of a shear horizontal surface acoustic wave micro pressure sensor with a groove structure

Shear horizontal surface acoustic wave (SH-SAW) sensors have great application potential due to their advantages of easy integration, miniaturization and suitability in liquid environments. In this paper, the finite element method is used to analyse a new SH-SAW micro pressure sensor, in which there are many groove structures along the direction of wave propagation on the delay path. We use the transient response simulation method to calculate and analyse the output voltage signal at the output interdigital transducer and surface average stress at the delay path of this new SH-SAW sensor, and its pressure sensitivity is analysed by uniformly applying an appropriate surface pressure on the resonant beam formed after grooving. The simulation results show that the surface average stress can be enhanced in a certain range of groove depth during the vibration of the groove structure. When the groove depth and width are set to 0.7 μm and 0.5 μm, respectively, the sensitivity of the SH-SAW sensor with a groove structure is four times higher than that of the traditional SH-SAW sensor. The increase of pressure sensitivity is the result of the increase of average stress caused by the groove structure. The new groove structure SH-SAW sensor provides a new basis for research on high-sensitivity micro-pressure sensors and lays a foundation for subsequent device design and manufacture.

Research of SAW Temperature and Pressure Dual Parameter Measuring Sensor Based on Delay Line Type

Surface acoustic wave (SAW) temperature and pressure sensors have been rapidly developed. A surface acoustic wave sensor with a dual-port delay line structure was designed and optimized by COMSOL software. The temperature and pressure measurement accuracy of the sensor is studied. In the signal measurement system, the signal is processed by the mixing detection method and the phase detection method. The perturbation quantity of pressure and temperature can be obtained by analyzing the perturbation relation between frequency and pressure, phase, and temperature. The results show that the sensitivity of the sensor is 339.175 kHz/N in the micro-pressure measurement of 0–0.2 N. The frequency error after optimization is between –3.3 and 4 kHz, and the error rate is 2.95%. In the case of 25–95°C, the sensitivity of the sensor is 0.045861 rad/°C. It lays a foundation for the research of the SAW multi-parameter measuring sensor.