Acoustic Particle Velocity Sensor Research Articles

Sensitivity enhancement of thermal acoustic particle velocity sensor based on metal film optimization

Thermal acoustic particle velocity sensors find widespread application in sound field measurements and sound source localization, owing to their capacity to capture vectorial information. This paper focuses on enhancing the sensitivity of detecting weaker signals by elevating the temperature coefficient of resistance (TCR) in the platinum thin film on the sensor's sensing wires. The study delves into the impact of annealing on the TCR of Pt thin films applied to small-sized elongated wires for thermal acoustic particle velocity sensors. The augmented effects of annealing Pt thin films with three adhesion layer metals—Chromium (Cr) and Titanium (Ti), previously commonplace in this sensor, and the newly introduced Tantalum (Ta) are scrutinized. Additionally, the influence of the deposition of Au electrodes, employed for wire bonding, both before and after annealing, on the annealing effect is also explored. In conclusion, a Pt thin film annealing process tailored for thermal acoustic particle velocity sensors is proposed, along with the recommendation of the optimal adhesion layer metal. This approach results in a substantial 20 % improvement in the TCR of the Pt thin film on the sensing wires, coupled with a corresponding 2.2 dB increase in sensor sensitivity.

Acoustic Characterization around the CalWave Wave Energy Converter

Sound generated by marine energy (ME) installations in the ocean environment remains a particular concern for environmental permitting despite the limited evidence showing low levels of ME sounds relative to other anthropogenic sounds. In an effort to increase understanding of potential environmental effects of marine energy projects and help reduce barriers to marine energy deployments, a new acoustic monitoring technology, the NoiseSpotter®, was developed and recently demonstrated around CalWave’s operational scaled xWave™ wave energy converter (WEC). The NoiseSpotter® improves upon traditional acoustic sensing techniques by use of a cost-effective, compact array of acoustic particle velocity sensors that characterizes, classifies, and provides accurate location information for anthropogenic and natural sounds in real time. Results are presented from co-deployments of NoiseSpotter® with the operational CalWave WEC that were conducted over a 9-day period in fall 2021 offshore of Scripps Research Pier in San Diego, California, USA. The multi-day deployment of the NoiseSpotter® at 100 m from the CalWave WEC revealed a rich library of sounds that include: Low-level (~95 dB re 1 µPa relative to an ambient noise floor between 80-90 dB re 1 µPa) sounds from the WEC associated with the deliberate actuation of mechanical components, Sounds from a hovering helicopter, Marine mammal vocalizations, and, Small boat engines. Sound levels from the WEC were placed within the context of ambient sounds, and reveal little deviation from the ambient soundscape. The azimuthal anisotropy of WEC sound was investigated via deployments along four cardinal directions around the WEC. While a noticeable increase was observed along the north-south orientation, the sound levels along all directions still showed little deviation relative to the ambient noise floor. Analysis of low-level WEC sounds in conjunction with exploratory machine learning techniques demonstrate the utility of directional acoustic sensing in distinguishing marine energy sounds from the myriad other sounds in the surrounding ocean environment.

An analytical model of three-hot-wire acoustic particle velocity sensors

A thermal-based acoustic vector sensor consisting of three heated wires can detect acoustic particle velocity instead of pressure. This paper proposes an analytical model for calculating the temperature distribution and acoustic-caused temperature perturbation of the sensor with a three-hot-wire configuration. In this model, the nonlinear effect caused by non-uniform thermal conductivity is considered. The nonlinear effects will not only affect the temperature of the three hot wires, but also the frequency response of the sensor. Based on the stationary temperature distribution calculated by the nonlinear model, we correct the heat diffusion coefficient in the acoustic perturbation model. The nonlinear stationary model and the corrected perturbation model are found to be in good agreement with the numerical results. Furthermore, we design a chip to measure the temperature distribution of the three heated wires and compare the sensitivity of the sensor with the corrected model. The experimental results can verify the proposed model. This study provides a theoretical basis for sensor performance optimization.

Analysis and design of 2-dimensional acoustic particle velocity horns

A two-dimensional acoustic horn packaged with a 2-D acoustic particle velocity sensor (APVS) is presented. The particle velocity amplification factor of the 2-D acoustic horn is analyzed theoretically and experimentally. The experimental results show a good agreement with the theoretical expectations. Compared with the previous horn model, this model considers the gain attenuation at low frequency and the influence of chip assembly deviation. As the particle velocity distribution changes greatly in the boundary layer, the assembly deviation of the chip has a great influence on the package gain. Furthermore, a microphone and the 2-D particle velocity sensor was packaged in the acoustic horn to detect the acoustic pressure and 2-D particle velocity at one point. The acoustic horn has an omnidirectional response for acoustic pressure. By using the mode domain beamforming, the direction of the incident wave was estimated with this two-dimensional sound intensity probe.

Design and Optimization of Sensitivity Enhancement Package for MEMS-Based Thermal Acoustic Particle Velocity Sensor.

In this paper, small-sized acoustic horns, the sensitivity enhancement package for the MEMS-based thermal acoustic particle velocity sensor, have been designed and optimized. Four kinds of acoustic horns, including tube horn, double cone horn, double paradox horn, and exponential horn, were analyzed through numerical calculation. Considering both the amplification factor and effective length of amplification zone, a small-sized double cone horn with middle tube is designed and further optimized. A three-wire thermal acoustic particle velocity sensor was fabricated and packaged in the 3D printed double cone tube (DCT) horn. Experiment results show that an amplification factor of 6.63 at 600 Hz and 6.93 at 1 kHz was achieved. A good 8-shape directivity pattern was also obtained for the optimized DCT horn with the lateral inhibition ratio of 50.3 dB. No additional noise was introduced, demonstrating the DCT horn’s potential in improving the sensitivity of acoustic particle velocity sensors.

Acoustic Particle Velocity Sensor With Improved Time-Domain Resolution

This letter presents a comparison of acoustic particle velocity sensor versus conventional microphone in terms of a time-domain resolution. To the best of the authors' knowledge, this is the first conceptual reasoning of a superior time-domain resolution of an acoustic particle velocity sensor. This letter also discloses an engineering solution with an outline of an in-house technological process, allowing a mechanically strong monolithic sensing element chip to be built.

Battlefield acoustics: Applications and challenges

Some primary objectives of research and development for battlefield acoustic sensing include the optimization of sensors, arrays, and signal processing algorithms for the detection, localization, and classification of diverse broadband and transient threats in complex environments. Time-difference-of-arrival and frequency domain signal processing techniques using distributed microphone arrays allow sound source localization and tracking through triangulation in the 3-D space. This presentation will introduce general applications of broadband acoustic and infrasonic microphone arrays, acoustic particle velocity sensors, geophones, propagation environment effects and wind mitigation methods.

<b>Analytical Method of Noise Contribution Ratio in Railway Vehicle Using Small Speaker and Acoustic Particle Velocity Sensor</b>

<b>Analytical Method of Noise Contribution Ratio in Railway Vehicle Using Small Speaker and Acoustic Particle Velocity Sensor</b>

Superdirectivity solutions of circular arrays with acoustic particle velocity sensors

This paper presents analytical superdirectivity solutions for circular arrays with acoustic particle velocity sensors (APVSs) based on the eigenbeam decomposition and synthesis theory. The main findings are summarized as follows. (1) The optimal beampattern, the global directivity factor, and the total error sensitivity function of circular APVS arrays, like those of circular arrays with pressure sensors, can also be expressed as the sums of eigenbeams, their directivity factors, and their error sensitivity functions, respectively. (2) The directivity factor increases but robustness decreases with an increase in the order number at low frequencies, and the reduced-rank technique can be used to synthesize robust superdirective beampatterns by truncating some high-order eigenbeams. (3) The limit theoretical maximum directivity factor and optimal beampattern are derived, which provide the upper bound of performance for circular APVS arrays and show that this type of arrays also has good potential for improving directivity. The reduced–rank technique is applied for circular APVS arrays to obtain robust high-order superdirectivity in simulations, which shows good performance for improving the robustness.

All-fiber acoustic particle velocity sensor based on graphene-coated four-core fiber.

A graphene-coated four-core fiber (FCF)-based acoustic particle velocity (APV) sensor for the detection of acoustic location is proposed and experimentally demonstrated. A graphene film is coated on the cross section of the FCF, which can be heated through a 532-nm laser. Due to the antisymmetric temperature distribution of the graphene induced by the APV, the reflection power of different fiber cores in the FCF is modulated, and the acoustic source direction can also be located based on the vector characteristic of the APV. The experimental results show that the figure-of-eight directional response of the graphene-coated FCF with a directional sensitivity of 0.56mV/deg is achieved. The all-fiber vector acoustic sensor possesses the potential for applications in structural health monitoring, partial discharges, public security, etc.

Three‐hot‐wire acoustic particle velocity sensor with improved detection capability

This Letter proposes a novel 3-hot-wire acoustic particle velocity sensor with high sensitivity and low self-noise for the first time. Three parallel wires, covered with platinum film, are suspended on silicon substrate by MEMS process. The middle wire works as a heater and the left and right ones work as both heaters and temperature sensors. Compared with the 1-hot-wire and 2-hot-wire counterparts, this sensor has higher sensitivity and lower self-noise, showing its potential for sound source localisation, acoustic camera and so on. The self-noise of the sensor is about 15 dB / Hz at 1 kHz and the relative direction sensitivity is as high as 42 dB.

Design of unidirectional acoustic probes with flexible directivity patterns using two acoustic particle velocity sensors.

This letter proposes a method of designing unidirectional acoustic probes with flexible directivity patterns using two acoustic particle velocity sensors. The closed-form weighting vector of this two-sensor array is accurately derived by finding the minimum mean square error approximation to a desired directivity pattern that is expressed in a general form. Different unidirectional acoustic probes can be obtained by properly selecting the desired directivity pattern, and the previously proposed particle velocity gradient-based design approach can be thought of as a special case of the proposed method. Simulations and experimental results demonstrate the good performance of the proposed method.

The application of acoustic particle velocity sensors to airborne infrasonic signals

Infrasound arrays, because of the wavelengths involved and the necessity for minimal spatial aliasing, can be quite large, e.g. an array layout often used for beamforming for frequencies up to 10 Hz is a centered, 17-m radius equilateral triangle. Available real estate is often limited such that optimally sized arrays are not possible. An acoustic particle velocity sensor, in principle, can perform the same job as a large infrasound array, but in a much smaller package (less than the size of a single infrasound sensor) since it provides, in post processing, a direct measurement of the wavefront normal. However, localized meteorological perturbations to the wavefront normal could cause significant bearing estimate errors when using a particle velocity sensor. Recently, as part of the characterization of a mobile infrasound source and during the collection of sounds from space station resupply rockets, acoustic particle velocity sensors were positioned next to infrasound sensors in order to test the concept of using these sensors for accurate pointing at infrasound frequencies. Results from these experiments will be discussed.Infrasound arrays, because of the wavelengths involved and the necessity for minimal spatial aliasing, can be quite large, e.g. an array layout often used for beamforming for frequencies up to 10 Hz is a centered, 17-m radius equilateral triangle. Available real estate is often limited such that optimally sized arrays are not possible. An acoustic particle velocity sensor, in principle, can perform the same job as a large infrasound array, but in a much smaller package (less than the size of a single infrasound sensor) since it provides, in post processing, a direct measurement of the wavefront normal. However, localized meteorological perturbations to the wavefront normal could cause significant bearing estimate errors when using a particle velocity sensor. Recently, as part of the characterization of a mobile infrasound source and during the collection of sounds from space station resupply rockets, acoustic particle velocity sensors were positioned next to infrasound sensors in order to test the concept...

Towards acoustic particle velocity sensors in air using entrained balloons: Measurements and modeling.

In this article, the feasibility of using balloons for the measurement of acoustic particle velocity in air is investigated by exploring the behavior of an elastic balloon in air as it vibrates in response to an incident acoustic wave. This is motivated by the frequent use of neutrally buoyant spheres as underwater inertial particle velocity sensors. The results of experiments performed in an anechoic chamber are presented, in which a pair of laser Doppler vibrometers simultaneously captured the velocities of the front and back surfaces of a Mylar balloon in an acoustic field. From phase measurements, the motion is described in terms of contributions from odd-order vibration modes (including bulk translation) and even-order vibration modes. The measured entrainment factors for the balloon are seen to be in good agreement with a physical model based on the scattering from an entrained rigid sphere. This demonstrates the feasibility of using entrained balloons for direct measurement of acoustic particle velocity in air.

A wider bandwidth technique of an estimation method for acoustic transmission using an acoustic particle velocity sensor

A wider bandwidth technique of an estimation method for acoustic transmission using an acoustic particle velocity sensor

Small aperture acoustic methods to locate transients

Acoustic microphone arrays have been used in battlefield environments to detect and locate continuous wave targets like helicopters and ground vehicles, and for transient events like gunshots, mortars, rockets and explosions. Depending on the application, source bandwidth, propagation distance, and required localization accuracy, these arrays can vary their sensor separation greatly. Unattended ground sensors, manned- and unmanned-platforms, and Soldier-worn systems can all benefit from very small apertures if performance can be maintained. A commercially available acoustic particle velocity sensor, approximately one-half an inch in diameter, showed good transient localization at a field experiment. Data will also be presented from a small cluster-array of cardioid microphones.

Toward acoustic particle velocity sensors in air using entrained balloons: Measurements and modeling

Acoustic particle velocity sensors for underwater applications typically work by measuring the motion of a small, neutrally buoyant body entrained in the acoustic field. Motivated by this, we have investigated the use of balloons for acoustic particle velocity measurements in air by exploring the behavior of an elastic balloon vibrating in response to an incident acoustic wave. In this presentation, we will present the results of experiments performed in an anechoic chamber, in which a pair of laser Doppler vibrometers simultaneously captured the velocities of the front and back surfaces of a Mylar balloon in an acoustic field. From phase measurements, the motion is described in terms of contributions from odd-order vibration modes (including bulk translation) and even-order vibration modes. The measured entrainment factors for the balloon at low frequencies are seen to be in good agreement with a physical model based on the scattering from an entrained, rigid sphere. This demonstrates the feasibility of using balloons for direct measurement of acoustic particle velocity in air.

A 2D acoustic particle velocity sensor with perfectly orthogonal sensitivity directions

A two-dimensional acoustic particle velocity sensor as well as the required interfacing electronics have been designed and realized. The novel crossed-wire sensor structure provides a direct two-dimensional measurement and, contrary to current 2D particle velocity sensors, the sensitive directions are exactly orthogonal to each other due to the inherent symmetry of the sensor. This new design of size 1.0mm×2.5mm×0.5mm dissipates only half the power required by current one-dimensional particle velocity sensors, has comparable bandwidth at modest 15dB higher selfnoise. Furthermore, it requires no directivity calibration, which was difficult to achieve in previous designs. The devices are relatively easy to fabricate, smaller and mechanically more robust than existing parallel-wire particle velocity sensors, resulting in better resistance against harsh fabrication steps and, consequently, higher fabrication yield.

Acoustic particle velocity sensor: Application to infrasonic detection

Infrasonics is the study of low-frequency acoustics that is below the normal limit of human hearing. Infrasound has the ability to propagate extremely long ranges and is often utilized to monitor naturally occurring phenomena and explosives. Acoustic particle velocity sensors have shown promise in detection and localization of transient signals in the audio range such as small arms fire, mortars, and rocket propelled grenades. Ideally, this sensor can be used to detect various targets spanning a broad range of frequencies to include that of infrasound. The primary objective of this research is to characterize the acoustic vector sensor’s localization performance for infrasonic sources given varying atmospheric conditions using algorithms developed at the Army Research Laboratory (ARL).

Characterization and modeling of CMOS-compatible acoustical particle velocity sensors for applications requiring low supply voltages

Acoustic particle velocity sensors have been obtained applying simple low resolution micromachining steps to chips fabricated using a standard microelectronic process. Each sensor consists of four silicided polysilicon wires, suspended over cavities etched into the substrate, and connected to form a Wheatstone bridge. Full compatibility of the micromachining procedure with the original process is demonstrated by integrating a simple pre-amplifier on the same chip as the sensors and showing that both blocks are functional. Proper design of the sensing structures allows them to operate with a single 3.3V power supply. Sensitivity and noise measurements, performed to estimate the sensor detection limit, are described. Excess noise with a flicker-like behavior, not ascribable to the amplifier, is found when the bridges are biased in working conditions. In addition, the dependence of the sensitivity on the dc bias voltage of the bridges is investigated, comparing the experimental data with the results of a simple analytical model and finite element method simulations.