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Pulsed wave (PW) Doppler ultrasound is routinely used in the clinic to assess blood flow. Our annual Doppler quality assurance tests revealed unexpectedly large errors in measurement of maximum velocity, exceeding our tolerance (error >20%), when using certain scanners with small Doppler sample volume dimensions. The aim of this study was to assess the dependence of maximum velocity estimates on PW Doppler sample volume size. A flow phantom with known steady flow was used to acquire maximum velocity estimates (maximum velocities of 24, 39 and 85 cm/s and sample volume range of 0.3–20 mm) with a variety of transducers and scanners in clinical use (51 probes from 4 manufacturers). Selected acoustic outputs were characterized using free-field hydrophone measurements. All maximum velocity estimates were within our tolerance for sample volume sizes ≥1.5 mm, although maximum velocity estimates typically increased with decreasing sample volume size. Errors exceeding our tolerance were commonly found for one manufacturer when using smaller sample volumes, resulting in up to 75% overestimation. Although intrinsic spectral broadening based on transit time considerations may help explain our findings, the sample volume dependence raises potential clinical concerns that users should be aware of and which manufacturers should consider addressing.

The Focused Ultrasound Foundation has developed a low-cost, validated, open-source hydrophone scanner for the spatial characterization of ultrasound transducers. Assembly instructions and a MATLAB control graphical user interface are provided such that the device can be easily replicated for less than $1000 in roughly 40 person-hours. The low-cost scanning tank's performance was compared with data collected with a commercial automated scanning tank. Pressure measurements of a focused transducer and a planar transducer had less than a 10% difference between the two scanning systems. Two-dimensional automated scans (20 × 20 mm at 0.25-mm resolution) took the low-cost scanning tank 45 min compared with the commercial system's 30 min. A reproducibility study found that the low-cost scanner made consistent peak negative pressure measurements as reflected by the low coefficient of variation for both focused (1.88%) and planar (0.98%) transducers. The low-cost scanner described here is a viable alternative for ultrasound laboratories needing efficient, accurate characterization of ultrasound transducers.

This letter presents a high-performance scandium-doped aluminum nitride (Sc x Al 1-x N, x = 9.5%) piezoelectric MEMS hydrophone. The doping of Sc increases the piezoelectric constants of the piezoelectric sensing layer and hence results in better receive sensitivity for the ScAlN-based piezoelectric MEMS hydrophone. The sensing cells of the MEMS hydrophone sensor are designed in a bioinspired honeycomb structure for achieving high fill-factor and thus a large receive sensitivity. The top electrodes of the sensing cells are split into the inner and outer sections with optimized size ratios for differential readout, which further enhances the sensor’s sensitivity. The receive sensitivity is improved even further by reducing the top oxide thickness on the sensing diaphragm. The best measured receive sensitivity of the reported MEMS hydrophone with differential readout is −164.5 dB (re: 1 V/ $\mu $ Pa). An equivalent noise density as low as 44 dB (re: $1 ~\mu $ Pa/ $\surd $ Hz) at 1kHz is achieved. These metrics are much better than those of state-of-the-art bulk piezoceramic hydrophones as well as other reported piezoelectric MEMS hydrophones.

The paper deals with the cavitation at tongue of a pump-turbine in pump mode, including the typical patterns, unsteady behaviors, and the influence on pump performance and fluid-borne noise. Visualization experiments were conducted under different flow rates and rotational speeds for variation cavity regimes. The results show the patterns can be divided into three regimes with cavitation development: bubble cavitation, cloud cavitation, and lock cavitation for the gas-lock phenomenon and performance plummet. The rotor-stator interaction and jet-wake flow could affect the cavitation generation. The blade passing effect is the leading cause of bubble clusters periodic collapsing or shedding at the early stages of cavitation, while playing a small role as cavities become thick and evaporation rate rises. The combined action of the attached vortex (re-entrant jet) and the depression by pressure gradient outside cavity surface account for the shedding at the developed cloud cavitation stage. Based on the noise measurement by hydrophone at the outlet, the broadband sound in the range of 1000 HZ-2000 Hz can be used for cavitation detection since it can be rarely influenced by operating conditions under non-cavitation.

In this article, we present a high-performance aluminum nitride (AlN)-based microelectromechanical system (MEMS) hydrophone sensor, in which the sensing cells are designed and arranged as an innovative honeycomb architecture for achieving large acoustic pressure sensitivity and high fill-factor. An $8\times9$ array of $360~{\mu }\text{m}$ in characteristic size, 0.92-MHz MEMS hydrophone sensor is developed based on an AlN-on-cavity silicon-on-insulator (CSOI) platform. The size of the MEMS hydrophone sensor is 3.2 mm $\times3.2$ mm. The MEMS hydrophone sensor and its preamplification circuit are integrated on a printed circuit board and packaged together with an acoustically transparent material, in order to meet the stringent requirements of underwater applications. The packaged MEMS hydrophone is fully characterized through using an industry-standard hydrophone calibration instrument. The MEMS hydrophone achieves an acoustic pressure sensitivity of −178 dB (re: 1 V/ $\mu$ Pa), with a maximum nonlinearity of 0.1%, and a noise resolution of 58.7 dB (re: 1 $\mu$ Pa/Hz). The measurement results show that the reported MEMS hydrophone sensor with bioinspired honeycomb structure is compared favorable with advanced commercially available bulky hydrophones.

During underwater acoustic detection, the positioning accuracy of the bionic cilia MEMS vector hydrophone is affected by its own sensitivity. MEMS vector hydrophone operate in different temperature environments, so studies on the environmental temperature and the sensitivity of the MEMS vector hydrophone are of great significance. In this paper, based on the sensitivity of the MEMS vector hydrophone at room temperature (22°C), its sensitivity variation is studied within the temperature range of 0–40°C. The relationship between the temperature and the piezoresistor in the MEMS vector hydrophone is theoretically analyzed, and it is concluded that the sensitivity change is within ±0.6dB. The sensitivity change of MEMS vector hydrophone is proved to be within ±0.3 dB via COMSOL 5.4 simulation software, and the MEMS vector hydrophone is verified experimentally by the hydrophone temperature characteristic testing system. The results show that the variation of the sensitivity is within ±0.5 dB, which is basically consistent with the theoretical analysis results and simulation results. It can be said that under normal non-extreme ambient temperature, the operating temperature has little effect on the sensitivity of the MEMS vector hydrophone.

We developed a piezoelectric micromachined cantilever acoustic vector (PEMCAV) sensor. We modeled the device using a "lumped" approach that considers fluid-structure interaction, the piezoelectric effect, and the mechanical impedance of the cantilever. Due to the high flexibility, the influence of the medium is significant, so fluid-structure interaction must be considered in theoretical modeling. We compared the model data to experimental results. The design parameters optimized using the derived analytical open-circuit sensitivity equation are presented, and the physical characteristics of the sensor are discussed. We used a micromachining technique to fabricate the sensor, added a preamplifier, and tested it using a reference hydrophone under a frequency range of 100 Hz-1 kHz. The analytical predictions and experimental results were in good agreement with respect to frequency response and the directivity of the sensor. Even when the sensor was much smaller than the wavelength ( ka≪1), the proposed sensor exhibited a typical cosine directivity pattern, and the measured sensitivity at 100 Hz was -194 dBV/μPa.

A mathematical model is necessary to analyze sensor performance and optimize its design. However, most of the existing models of piezoelectric micro-machined hydrophones are incomplete and too complex to understand. There has been no mathematical model for the sensitivity of piezoelectric hydrophones. To address this shortcoming, this paper proposes a mathematical model of a piezoelectric micro-machined hydrophone. The stresses in the piezoelectric layer and static displacement of the diaphragm under uniform sound pressure are derived. In addition, the resonant frequency and sensitivity of the hydrophone are analyzed. The finite element simulation is used to verify the validity of the proposed mathematical model. On the basis of the mathematical model and simulation, the diaphragm radius, top electrode area, and piezoelectric film thickness are optimized. Furthermore, the hydrophone is fabricated, and its morphology is observed. The impedance-frequency spectrum of the hydrophone is measured by HIOKI IM3536 LCR impedance analyzer. The tested resonant frequency is 0.5 MHz, which is relatively close to the calculated result of 0.537 MHz, so the validity of the proposed mathematical model is further validated. Also, the reason why the test result is less than the calculated result is explained. The effective electromechanical coupling coefficient derived from the impedance curve is 7.5%. The developed mathematical model can provide a useful guide for designing high performance piezoelectric micromachined hydrophone and make preliminary predictions of its characteristics.

The existing MEMS bionic vector hydrophone has the problems of low-sensitivity and narrow-working band, and the sensitivity and working bandwidth cannot be improved simultaneously by changing the single microstructural parameter. In this paper, the MEMS bionic vector hydrophone microstructural parameters (length, width and height of cantilever, side length of the center block, height and radius of the rigid cylinder) have been optimized simultaneously to obtain a higher sensitivity at the almost same working bandwidth. Firstly, through the mechanical analysis of the microstructure, the objective function and feasible region are established to optimize the parameters of the microstructure, and a set of optimized parameters is obtained. Secondly, the optimized structure is verified by ANSYS simulation, and then, the optimized four-beam structure is fabricated by the MEMS manufacturing technology. Finally, these two kinds of hydrophones (the previous one and the optimized one) are produced, and their performance tests are carried out. The testing results show that the performances of the optimized hydrophone have been greatly improved, exhibiting a receiving sensitivity of −181.2 dB@1 kHz (increasing by 6.5 dB, 0 dB reference 1 V/μ Pa), the frequency response ranging from 20 Hz to 1 kHz which is the same working bandwidth as before, and a good dipole directivity. The optimization researches in this paper provide a method and idea for the performance improvement of the following MEMS vector hydrophone.

The technique of phase contrast imaging, combined with tomographic reconstructions, can rapidly measure ultrasonic fields propagating in water, including ultrasonic fields with complex wavefront shapes, which are difficult to characterize with standard hydrophone measurements. Furthermore, the technique can measure the absolute pressure amplitudes of ultrasonic fields without requiring a pressure calibration. Absolute pressure measurements have been previously demonstrated using optical imaging methods for ultrasonic frequencies below 2.5 MHz. The present work demonstrates that phase contrast imaging can accurately measure ultrasonic fields with frequencies up to 20 MHz and pressure amplitudes near 10 kPa. Accurate measurements at high ultrasonic frequencies are performed by tailoring the measurement conditions to limit optical diffraction as guided by a simple dimensionless parameter. In some situations, differences between high frequency measurements made with the phase contrast method and a calibrated hydrophone become apparent, and the reasons for these differences are discussed. Extending optical imaging measurements to high ultrasonic frequencies could facilitate quantitative applications of ultrasound measurements in nondestructive testing and medical therapeutics and diagnostics such as photoacoustic imaging.

In the present study, a novel hybrid method was considered to identify and measure inertial cavitation activity using acoustic and optical emissions from violent bubble collapses. A photomultiplier (PMT) tube and a calibrated cylindrical needle hydrophone were used to simultaneously detect sonochemical luminescence (SCL) signals and acoustic emissions, respectively, during sonication. A cylindrical focusing ultrasound transducer operating at 398.4 kHz was employed to produce a dense cavitation bubble cloud at the focus. The results clearly showed that a similar trend between the PMT output (i.e., the SCL results) and the broad band acoustic emissions started to appear at the frequencies considered above the fourth harmonic of the sonication frequency. The experimental observation suggests that the occurrence of inertial cavitation can be monitored using the high pass spectral acoustic power and the cut-off frequency can be effectively chosen with the aid of sonochemical luminescence measurement. The hybrid method is expected to be useful for cavitation dosimetry in various medical and industrial applications.

The nonlinear pressure profile at the focus of an ultrasonic beam radiated into water at a frequency of 2.0 MHz and having a shock front with amplitude of 50 MPa is reconstructed for the first time using Raman lidar signals. This is possible due to the relationship between the degree of deformation of the O–H stretching vibration band in the Raman spectrum of water, the amplitude of elastic scattering, and the pressure at the sounding site. The lidar profile is in good agreement with a PVDF hydrophone profile.

Underwater acoustic ranging and detection usually require hydrophones to have high sensitivity at narrowband operating frequencies. Different from traditional sensitization methods with the help of new materials and solid/liquid resonance structure, this paper proposes a low-cost, high-sensitivity hydrophone based on a resonant air cavity containing an affordable MEMS microphone inside to sense the focused acoustic waves transmitted from the external water across the solid shell into the air cavity. Both finite element simulations and experiments are carried out to test its acoustic sensing performances. Resonance frequency and directivity of the proposed hydrophone are determined by the air cavity size and the acoustic mode, but is independent of the solid shell, which facilitates the precise designability. The sensitivity of the developed hydrophone at the resonance frequency is up to −157 dB re 1V/ $\mu $ Pa calibrated by commercial standard hydrophone TC4013. Finally, several further considerations, improvements and applications on the proposed hydrophone are discussed.

We have developed and experimentally implemented an adaptive laser vector-phase hydroacoustic measuring system, which allows one to determine the total acoustic intensity vector. A receiving element of the measuring system comprises six spatially separated fibre-optic coil-type sensors. Signals from the sensors are phase demodulated by using a six-channel adaptive holographic interferometer based on dynamic holograms multiplexed in a photorefractive CdTe crystal. Performance of the developed measuring system has been experimentally tested by determining the bearing and localisation of a source of a weak hydroacoustic field.

The mechanical properties of biological tissues are fingerprints of certain pathologic processes. Ultrasound systems have been used as a non-invasive technique to both induce kilohertz-frequency mechanical vibrations and detect waves resulting from interactions with biological structures. However, existing methodologies to produce kilohertz-frequency mechanical vibrations using ultrasound require the use of variable-frequency, dual-frequency and high-power systems. Here, we propose and demonstrate the use of bursts of megahertz- frequency acoustic radiation to observe kilohertz-frequency mechanical responses in biological tissues. Femoral bones were obtained from 10 healthy mice and 10 mice in which osteoporosis had been induced. The bones’ porosity, trabecular number, trabecular spacing, connectivity and connectivity density were determined using micro-computed tomography (μCT). The samples were irradiated with short, focused acoustic radiation pulses (f = 3.1 MHz, t = 15 μs), and the low-frequency acoustic response (1–100 kHz) was acquired using a dedicated hydrophone. A strong correlation between the spectral maps of the acquired signals and the μCT data was found. In a subsequent evaluation, soft tissue stiffness measurements were performed with a gel wax-based tissue-mimicking phantom containing three spherical inclusions of the same type of gel but different densities and Young's moduli, yet with approximately the same echogenicity. Conventional B-mode ultrasound was unable to image the inclusions, while the novel technique proposed here showed good image contrast.

Purpose The aim was to quantitatively validate the hybrid angular spectrum (HAS) algorithm, a rapid wave propagation technique for heterogeneous media, with both pressure and temperature measurements. Methods Heterogeneous tissue-mimicking phantoms were used to evaluate the accuracy of the HAS acoustic modeling algorithm in predicting pressure and thermal patterns. Acoustic properties of the phantom components were measured by a through-transmission technique while thermal properties were measured with a commercial probe. Numerical models of each heterogeneous phantom were segmented from 3D MR images. Cylindrical phantoms 30-mm thick were placed in the pre-focal field of a focused ultrasound beam and 2D pressure measurements obtained with a scanning hydrophone. Peak pressure, full width at half maximum, and normalized root mean squared difference (RMSDn) between the measured and simulated patterns were compared. MR-guided sonications were performed on 150-mm phantoms to obtain MR temperature measurements. Using HAS-predicted power density patterns, temperature simulations were performed. Experimental and simulated temperature patterns were directly compared using peak and mean temperature plots, RMSDn metrics, and accuracy of heating localization. Results The average difference between simulated and hydrophone-measured peak pressures was 9.0% with an RMSDn of 11.4%. Comparison of the experimental MRI-derived and simulated temperature patterns showed RMSDn values of 10.2% and 11.1% and distance differences between the centers of thermal mass of 2.0 and 2.2 mm. Conclusions These results show that the computationally rapid hybrid angular spectrum method can predict pressure and temperature patterns in heterogeneous models, including uncertainties in property values and other parameters, to within approximately 10%.

This paper describes the design, characterization, and testing of a compact hydrophone capable of measuring acoustic signals from cardiomyocytes. Our hydrophone consists of a nanofabricated photonic-crystal diaphragm externally-mounted to the facet of an optical fiber to form a pressure-sensitive Fabry-Pérot cavity. Our hydrophone can operate in small liquid volumes less than 5 mm deep and incorporates a microchannel to vent air during immersion. The venting channel is designed to optimize bandwidth and sensitivity. Modeling and experimental results in water show a bandwidth from 50 Hz to 18 kHz and a minimum detectable pressure of $3~\mu Pa/ \sqrt {Hz}$ . We demonstrate the sensitivity to simulated bio-acoustic sources with nanometer-scale displacements.

A high-performance fiber optic interferometric hydrophone based on a push–pull mandrel structure, with high sensitivity and wide-frequency response, is designed and developed. Each arm of the Michelson interferometer is a fiber coil wrapped onto a separate but concentric thin elastic tube as the sensing arm to detect acoustic pressure wave. The fiber optic hydrophone is fabricated and examined experimentally, demonstrating its capacity to detect very low-frequency underwater acoustic pressure variation. The theoretical design is validated experimentally, with results showing that the push–pull fiber optic hydrophone has an average sensitivity of −134.39 dB re rad/ $\mu$ Pa within the frequency range of 1 Hz–2 kHz, which is 5.67 dB higher than that of the analogous one-sensing-arm fiber optic interferometric mandrel hydrophone that we made for comparison. The push–pull fiber optic hydrophone has a minimum detectable pressure (MDP) of 25.37 $\mu {\mathrm {Pa}}/\sqrt {{\mathrm {Hz}}}$ at 1 kHz, about 15 dB lower than the deep-sea state zero (DSS0) level. At 10 Hz, the MDP is ~1.71 mPa/ $\sqrt {{\mathrm {Hz}}}$ , which is nearly 7 dB lower than the acoustic ambient noise in the ocean at low frequency. The sensitivity and the MDP of the push–pull fiber optic hydrophone have been doubled and improved by about 20% at 1 kHz, respectively, compared to other state-of-the-art flat response fiber optic hydrophones.

One of the tasks of the COOMET 786/RU/19 pilot comparisons is to check the correctness of the hydrophone model proposed in VNIIFTRI, consisting of an advance line and a minimum-phase part, including the effect of sound diffraction and resonance properties of the active element. This model makes it possible to use the Hilbert transform to obtain the phase-frequency response from the amplitude-frequency response as well as for inverse operation. The results of measuring experiments performed using facilities of the State Primary Standard GET 55-2017 are presented. For many practical tasks, it is not necessary to obtain the phase-frequency response for an acoustic center of the receiver. It is enough to determine the shape of the phase-frequency response using much less laborious methods. The question of which of the characteristics is expedient to determine during calibration - for an acoustic center, or for a point on the surface of an active element, deserves a discussion among specialists performing acoustic measurements.

Majority of the sensors for underwater application use acoustic waves for detection, communication and navigation of submersibles. Hydrophone, used for sensing acoustic signals in water, has piezoelectric material within which responds to acoustic pressure by generating electric potential. Different types of hydrophones having different shapes can be manufactured depending on their applications. An omni-directional hydrophone can be developed using a spherical piezoelectric material as active material. This paper describes the design and development of a spherical hydrophone using lead zirconate titanate-4 (PZT-4) hollow sphere, having Receiving Sensitivity (RS) − 205 ± 0.6 dB ref 1 V/µPa in the frequency band 0–10 kHz. Analytical modelling of the piezoelectric sphere is done to fix its dimensions for the desired output and numerical analysis is done in COMSOL Multiphysics to validate the result. Since the spherical hydrophone is manufactured by encapsulating the piezoelectric sphere with polymer to give water-tight insulation, numerical analysis of the piezoelectric sphere coated with a polymer is done to calculate the RS of the hydrophone. Fabrication of a spherical hydrophone is done by rubber encapsulation of the piezoelectric sphere using compression moulding technique and its RS is measured in water. RS values obtained from numerical analysis and experiment are having a good agreement in the frequency band 0–10 kHz.

Objective: There may be a need to perform dynamic skull aberration corrections during the non-invasive high-intensity transcranial treatment with magnetic resonance imaging (MRI) -guided focused ultrasound in order to accurately and rapidly restore the focus in the brain. Methods: This could possibly be accomplished by using an ultrasound-based correction method based on the skulls’ thickness resonance frequencies. The focus of a 500 kHz transducer was centered in the ex vivo human skull caps at different temperatures. The pulse-echoed signals reflected from the skulls were analyzed in the frequency domain to reveal the resonance frequencies for the phase shift calculation. The accuracy was compared to both hydrophone and computed tomography (CT) based analytical methods. Results: Around 73% of the measurements (n = 784) were in the optimal constructive interference region, with a 15° decrease in the average phase error compared to the previous study. In the best implementation, it performed approximately the same or better than the CT based analytical method currently in clinical use. Linear correlation was found between the resonance frequencies or skull induced phase shifts and the skull temperature with an average rate of −0.4 kHz/°C and 2.6 deg/°C, respectively. Conclusion: The ultrasound based resonance method has shown the feasibility of detecting heating-induced changes of skull phase shift non-invasively and accurately. Significance: Since the technique can be made MRI compatible and integrated in the therapy arrays, it may enable temperature tracking and adaptive focusing during high-intensity transcranial ultrasound treatments, to prevent skull overheating and preserve the transcranial focusing integrity.

Objective: This paper aims to develop a miniaturized forward-looking ultrasound transducer for intracavitary tissue ablation, which can be used through an endoscopic device. The internal ultrasound (US) delivery is capable of directly interacting with the target tumor, resolving adverse issues of currently available US devices, such as unintended tissue damage and insufficient delivery of acoustic power. Methods: To transmit a high acoustic pressure from a small aperture (

The effects of voltage and current pulse durations of underwater discharge on shock wave generation are reported. In this article, underwater discharges were generated by using a magnetic pulse compression (MPC) circuit. The compression number of the MPC circuit was varied from two compressions to one and no compression; also the capacitance of an output peaking capacitor connected in parallel to discharge electrodes (load) was varied from 10 to 6 and 2 nF. As a result, electric pulses with different rise time/duration and variable peak voltages and currents were obtained and applied to generate shock waves. The shock waves were quantitatively measured with optical principles using a fiber optic probe hydrophone (FOPH) pressure transducer. By reflecting the generated shock waves from a reflector, uniform shock waves were produced, which made it possible to accurately measure the shock waves. The maximum pressure of the generated shock wave after the reflection was in the range of 40 MPa. The energies of the output shock waves were calculated from the pressure histories and the electrical to shock wave energy conversion efficiency was calculated from the electrical energy used to generate the shock waves. The results indicated that the rise time of voltage and current significantly affects the electrical energy that can be delivered to generate the shock waves. For the range of the electric pulse durations of 100 to 500 ns of this article, the shock waves pressures were independent of the pulse duration for the same input energy consumed during the rise and full width at half maximum times of the current. The method presented here gives possibility to select the shock wave profile, which would be crucial for successful medial applications.

For marine bioacoustics applications, the sounds by aquatic animals must be recorded with a high precision and minimal noise in order to extract valuable information. For such marine applications, we propose and demonstrate an optical fiber microtip-based hydrophone. The hydrophone design consists of an extrinsic Fabry–Perot interferometer, which utilizes fiber microtip and processed aluminum foil as two partially reflecting mirrors. The packaged optical fiber hydrophone of dimensions 1.4 cm $\times1.4$ cm $\times 2$ cm, with a microtip diameter of 31.23 $\mu \text{m}$ and natural rubber diaphragm of 6 mm diameter, shows a high sensitivity of 8.94 nm/mPa or −41.42-dB re 1 nm/ $\mu $ Pa at 1 kHz. The hydrophone shows an excellent signal-to-noise ratio, and the noise-limited minimum detectable pressure is as low as $0.388~\mu $ Pa/ $\surd $ Hz at 1 kHz. The linear working range of the hydrophone is 0–3950 Hz. The experimental results show that the proposed optical fiber hydrophone can very accurately detect the click trains produced by dolphins for echolocation. Furthermore, depending on the applications, the performance parameters of the proposed hydrophone can be tailored by changing the diaphragm thickness and diameter, thus opening a new platform to study the marine environment.

At present, the field of applications of powerful ultrasound is expanding intensively, and the improvement of equipment and technological processes continues. With that, the key factor in the effect of ultrasonic vibrations on processes in liquids and liquid-like media is cavitation, i.e. the phenomenon of formation, pulsation and collapse of gas microbubbles under the influence of variable pressure. The widespread introduction of promising ultrasound technologies is largely constrained by the fact that the patterns of cavitation generation are not well understood, and the data known in the literature are contradictory and are characterized by low reproducibility. This paper describes an innovative method for studying ultrasonic cavitation. In order to increase the reproducibility of the results and the reliability of the conclusions about the correlation of various cavitation effects, it is proposed to register simultaneously the parameters characterizing these effects. An installation designed to implement this method has been developed and tested. The installation provides the ability to register the full output signal of the hydrophone, the intensity of the glow generated in the cavitation region - sound luminescence, the cavitation noise spectrum and its individual components. Technical characteristics of the installation allow you to adjust the rate of development of the cavitation region by varying the duration and period of the ultrasound pulses. It is possible to conduct experiments both in low-frequency (LF) and high-frequency (HF) fields as well as in interacting HF and LF ultrasonic fields. During the testing of the installation, the results were obtained that are of considerable interest from the point of view of refining the ideas about the mechanism for generating cavitation effects. It was found that preliminary treatment of the liquid in an ultrasonic field with the aim of its degassing for 15–20 min provides a significant increase in the reproducibility of measurements, especially for liquids with a high gas content. Based on a comparison of the time dependences of the signals of the cavitation sensor and the photomultiplier output, the characteristic stages of the development of the cavitation region are distinguished, which differ in the dynamics of the development of the cavitation region and in the composition of the cavitation noise spectra recorded.

Background: Despite a wealth of literature on medical high-intensity focused ultrasound (HIFU), there are knowledge gaps related to therapeutic ultrasound in the presence of bone obstructions. In particular, the literature on detailed imaging of ultrasonic wave-scattering at bones to validate numerical models is still sparse. Objective: Experimentally investigate the ultrasonic energy deposition in areas surrounding flat and curved bone-like obstructions. Methods: Imaging from a diffraction-based shadowgraph method is used to visualize ultrasound wave propagation in laboratory water tank experiments. The experiments are performed with no obstruction, varying partial obstruction, and with complete obstruction by bone-like constructs. In addition, hydrophone measurements and numerical simulations are performed for similar bone obstruction configurations, and the results are compared. Results: The shadowgraph technique produces high-resolution images of the wave transmission through and reflection from bone-like constructs. There is generally good agreement between experimental findings and numerical results. In particular, hydrophone measurements match closely with simulation data for both obstructed and unobstructed cases. Also, shadowgraph images qualitatively confirm simulation and hydrophone measurements. Conclusions: Overall, the results of this work demonstrate the utility of shadowgraph imaging in the development and evaluation of novel treatments in the field of therapeutic ultrasound.

It has been demonstrated for the first time that pulsed laser Raman spectroscopy can be used for diagnostics of a local acoustic pressure profile with a peak pressure drop of 50 MPa and a carrier frequency of 2.0 MHz in the focus of an ultrasound beam propagating in water. A 527-nm 10-ns laser pulse has been focused into the waist of the ultrasound beam at an angle of 90°. Backscattered photons have been recorded in a gated spectrum analyzer. It has been found that the Raman spectra at the times corresponding to the maximum and minimum acoustic pressures are significantly different. This feature has been used for point-to-point reconstruction of the acoustic pressure profile; for this purpose, the delay between the ultrasound and laser pulses is consequently increased with a step of 50 ns. It has been shown that, within the measurement error, the resulting changes in the position of the center of the stretching OH vibration band of water molecules in the Raman spectrum reproduce the acoustic pressure profile directly measured using a PVDF hydrophone at the laser sensing point. The results obtained can be used to develop a new method for remote diagnostics of the time profile of acoustic pressure and monitoring the local dynamic of the compression-tension processes in water up to critical pressures corresponding to the cavitation rupture, when the use of the hydrophone can lead to its damage.

Blend of chloroprene rubber (CR) and bromobutyl rubber (BIIR) is used for encapsulation of piezo sensors used in sea water. Conventional encapsulation method of these sensors involving high temperature vulcanisation (HTV) often leads to deterioration of piezo properties due to thermal degradation. This paper reports a low temperature vulcanisation (LTV) technique carried out at 90 °C for CR-BIIR blend using chlorinated polyethylene (CPE) as compatibiliser and LTV system consisting of modified di-o-tolyl guanidine and thiocarbanilide as accelerators and ZnO as curing agent. The conventionally used scavenger MgO was eliminated and only ZnO was used to boost the cure reaction. Properties specific to sonar sensors, namely, acoustic transparency, electrical resistivity, water absorption and physico‑mechanical properties were evaluated besides evaluation of morphology. The results are found to compare better than the conventional blend. Accelerated thermal ageing at 70 °C for 7 days yielded 97 % retention of tensile strength. The technique was implemented in a PZT hydrophone sensor and was successfully underwater tested.

A microelectromechanical systems piezoelectric transducer capable of measuring static accelerations and acoustic vibrations has been designed and proposed. The transducer is composed of a circular plate on a pillar, which is fixed at the centre and free at the rim so that it resembles a flat cap mushroom. An annular piezoelectric layer has been employed to convert the vibration-induced stress of the plate to a potential difference. The proposed structure has been compared with diaphragm piezoelectric transducers and hydrophones and its superior performance has been verified. Analytical models for both static and dynamic accelerations have been developed, discussed and the output voltage has been formulated, which is in a very good agreement with the finite element analysis. Results show that the maximum sensitivity is achieved when there is an annular piezoelectric layer on the plate around the pillar perimeter. The effect of different geometrical parameters on the transducer performance has been studied. The proposed flat cap mushroom shape piezoelectric transducer could achieve −186.5 dB sensitivity and a very wide bandwidth. Another important advantage of the proposed structure is that by controlling the pillar radius and without changing the plate size, the sensitivity can be enhanced.

Cavitation bubble cloud formation due to the backscattering of high-intensity focused ultrasound (HIFU) from a laser-induced bubble in various water temperatures and dissolved oxygen (DO) has been investigated. A laser-induced bubble generated near the geometrical focus of HIFU is utilized to yield intense negative pressure by the backscattering. Optical observation with a high-speed video camera and pressure measurement with a fiber-optic probe hydrophone are conducted simultaneously to understand the forming process of a bubble cloud and corresponding pressure field by the backscattering. Optical observation shows that a bubble cloud grows stepwise forming multiple layers composed of tiny cavitation bubbles, and the cavitation inception position is consistent with the local minimum pressure position simulated with the ghost fluid method. The bubble cloud grows larger in the opposite direction of HIFU propagation, and the absolute value of the cavitation inception pressure decreases with an increase in water temperature. The linear correlation between cavitation inception pressure and water temperature agrees with that given by Vlaisavljevich, Xu, Maxwell, Mancia, Zhang, Lin, Duryea, Sukovich, Hall, Johnsen, and Cain [IEEE Trans. Ultrason. Ferroelectr. Freq. Control 63, 1064-1077 (2016)]. However DO has minor dependence on the cavitation inception pressure when DO is degassed sufficiently. Furthermore, the gas nucleus size that might exist in the experiment has been estimated by using bubble dynamics.

The special features of the implementation and the main sources of measurement uncertainty of the power of an ultrasound beam in water are examined by the method of plane scanning of the cross-section of a beam. The methods of evaluating the effect of deviations from the conditions of a plane wave and a far field were refined. Methods of decreasing the laboriousness of measuring beams with rotational symmetry are substantiated. The results are presented for the comparison of the values of the power of ultrasound emission of a round piston emitter, obtained by the plane scanning method and by the reference method of equilibration of emission force. The sufficiently good concurrence of the results provides evidence of the potential possibility of increasing the precision of hydrophone calibrations by the methods of plane (raster or diametral) scanning.

Many researchers have considered air quality degradation due to the emission of fine particles from industrialized and urban areas during recent decades. Recently, the European Parliament has had concerns about ensuring a healthy human environment. Therefore, the experimental and theoretical investigations of the dynamics of fine particulate matter are for determining efficient monitoring and cleaning air from industrially generated air pollutants. These investigations also imply the use of alternate methods that stimulate fine particle agglomeration. One of the methods is the use of acoustics. Many experimental investigations of particles with a diameter between 1 and 10 μm have proven that the use of acoustic agglomeration increases the particle size. Then, conventional air filters can be used to collect the larger particles. This process improves the collection efficiency of the particles. Particulate agglomeration chamber consisting of an acoustic field generator and an inner part was created for the test particles of diesel engines (range from 0.3 to 10 μm). Modeling of its elements was performed using Comsol multifunctional software. This sound pressure level is enough [1] to lead the acoustic agglomeration process of particles in the measurable range from 0.3 to 10 μm. The sound pressure level reach this value (130–140 dB) at the acoustic agglomeration zone. Additionally, the theoretical evaluation of the agglomeration time of two sub-micron particles enabled the estimation of efficient agglomeration of particles with sizes between 0.3 and 10 μm during the measurement period. A starting value of 136 dB of sound pressure level (SPL) was created in the experimental chamber with the turbulence condition, where SPL values were measured by using the Bruel&Kjaer measurement system “Type 9727” with hydrophone 8104. The observation concentrations of diesel engine exhaust particles in the experimental chamber with and without acoustic influence were performed using Particle Concentration Analyzer 4 APC ErgoTouch Pro 2. The results of experimental research shows that the acoustic agglomeration effect formed the proper conditions for the agglomeration of particles of all diameters (0.3, 0.5, 1.0, 3.0, 5.0 and 10 μm).

Acoustoelectric effect (AE) in a non-degenerate fluorinated single walled carbon nanotube (FSWCNT) semiconductor was carried out using a tractable analytical approach in the hypersound regime , where q is the acoustic wavenumber and is the electron mean-free path. In the presence of an external electric field, a strong nonlinear dependence of the normalized AE current density , on ( is the electron drift velocity and is the speed of sound in the medium) was observed and depends on the acoustic wave frequency, , wavenumber q, temperature T and the electron-phonon interactions parameter, . When , decreases to a resonance minimum and increases again, where the FSWCNT is said to be amplifying the current. Conversely, when , rises to a maximum and starts to decrease, similar to the observed behaviour in negative differential conductivity which is a consequence of Bragg’s reflection at the band edges at T=300K. However, FSWCNT will offer the potential for room temperature application as an acoustic switch or transistor and also as a material for ultrasound current source density imaging (UCSDI) and AE hydrophone devices in biomedical engineering. Moreover, our results prove the feasibility of implementing chip-scale non-reciprocal acoustic devices in an FSWCNT platform through acoustoelectric amplification.

Laser-induced acoustic (LIA) technology is of significance for the communication from the air platform to the underwater platform. This paper describes a method of nonlinear LIA in the liquid based on the mechanism of optical breakdown. Acoustic signals with high energy were generated by using a Nd: YAG pulsed laser with 10 ns width. A PZT hydrophone was used to receive the LIA signals for cases of the linear and nonlinear regime in the water. Meanwhile, simulation of LIA in a distance of 400 m between laser spot on the water surface and the hydrophone was performed by the COMSOL Multiphysic software. The simulated results show the communicated ability of LIA technology in the long distance.

In a growing number of applications, fast and localized pressure measurement in aqueous media is desired. To perform such measurements, a custom-made single-mode fiber-optic probe hydrophone (FOPH) was designed and used to measure the pressure pulse generated by laser-induced breakdown (LIB) in water. The sensor enabled sub-nanosecond pressure rise time measurement. Both the rise time and the duration of the shockwave were found to be shorter in the direction perpendicular to the breakdown generating laser beam, compared to the shockwave observed in the parallel direction. Simultaneous high-frame-rate imaging was used to qualitatively validate the novel hydrophone data and to observe the shockwave evolution. The measurements were performed also on pressure pulses emitted during the generation of miniature ( [Formula: see text] diameter) laser-induced bubbles at very small distances (down to [Formula: see text]), further demonstrating the capabilities of the small-size sensor and the ability to measure locally. The results improve understanding of LIB shockwave characteristics dependence on laser pulse energy and duration.

Ferroelectret films are soft cellular solids capable to trap dielectric dipoles within the pores. These dipoles together with the large material compressibility give rise to a measurable piezoelectric response. They have been used to produce air-coupled ultrasonic transducers (200 kHz to 600 kHz) and recent works have shown the possibility to use them in water immersion. The main advantage is the large bandwidth and the main drawback is the poor sensitivity. This suggests the possibility of using these materials for wide-band reception, in particular, to make hydrophones. Due to the very low acoustic impedance of ferroelectret films (about 0.08 MRayl), thickness resonances under water immersion are completely damped out. Therefore, unlike conventional PVDF hydrophones, no upper frequency limit in the frequency band of the FE film hydrophone is expected due to these resonances, being the only limit the attenuation in the material. Present work is aimed to study the response of FE film as hydrophone and to explore the frequency range of the reception band in water immersion operation.

Acoustic lenses are widely used in focused ultrasound transducers to produce high acoustic intensity at the focal point. However, acoustic lenses are usually curved or curled, and when air or bubbles gather near the curved surface, the transducer may be damaged as a result of heating or cavitation. In addition, their non-planar structure may cause difficulties to develop multilayer lens to reduce the F-number further. In this work, we develop a focused annular ultrasound transducer with a planar acoustic lens, which is made of a velocity gradient matching layer. KLM model simulation is used to design the piezoelectric part of the transducer. Finite element analysis (FEA) simulation is used to predict the acoustic field distribution, following by hydrophone measurement verification using a motion stage. The result shows that the planar lens achieves a focusing distance of 62 mm, with a lower F-Number of 2.81 comparing to the natural focusing at 78.5mm.

In the measurement of acoustic pressure from medical ultrasonic instruments with a hydrophone, waveform recovery by deconvolution based on a wide-band calibration of the hydrophone has been proposed. To study the deconvolution method, we numerically simulated a hydrophone as well as a nonlinearly propagated focused ultrasonic wave to be received by the hydrophone. Deconvolution with a proper extrapolation of the pressure to voltage sensitivity in frequency domain perfectly recovered the pressure waveform except for a small vicinity of the positive peak, while scaling by the sensitivity at the primary frequency overestimated both negative and positive peak pressures about 5%. Deconvolution underestimated the positive peak pressure by 0-8%, which decreased monotonously as the frequency to start extrapolation increased above 4 times the primary frequency.

This paper reports a compact sonoporation device for 24 and 96 well cell culture plates. The proposed device is designed to be used in in vitro studies on adherent cells. K-Wave toolbox was used to model the pressure field and determine a uniform region where cells could be then exposed to ultrasound. The uniformity was confirmed using measurements by a needle hydrophone. The sonoporation device, which included six 30 mm planar transducers, was designed and built. The cell culture plate was placed in the sonoporation device at a height where cells were exposed to uniform acoustic pressure. Three embodiments of the sonoporation device working at 330 kHz, 500 kHz and 1 MHz were built. The results show that more than 80% of the well-area had a measured acoustic pressure at a set value ±25%. The sonoporation device was validated on a dermal mouse fibroblast model. The exposures were performed at 50% duty cycle, 7Hz repetition frequency and pressure values from 0 kPa to 50 kPa for a total exposure time of 1 and 3 minutes. Live/dead viability test showed that the tested conditions did not significantly affect mortality rate, except for 1 MHz, where an increase in death rate was observed.

In order to meet the needs of phase generated carrier (PGC) demodulation technology for interferometric fiber optic hydrophones, we proposed an optical microfiber all-optical phase modulator (OMAOPM) based on the photo-induced thermal phase shift effect, which can be used as a phase carrier generation component, so as to make the modulation efficiency and working bandwidth of this type of modulator satisfy the requirements of underwater acoustic signal demodulation applications. We analyzed the modulation principle of this modulator and optimized the structural parameters of the optical microfiber (OM) when the waist length and waist diameter of OM are 15 mm and 1.4 μm, respectively. The modulation amplitude of the modulator can reach 1 rad, which can meet the requirements of sensing applications. On this basis, the fiber optical hydrophone PGC-Atan demodulation system was constructed, and the simulated underwater acoustic signal test demodulation research was carried out. Experimental results showed that the system can demodulate underwater acoustic signals below 1 kHz.

Underwater ultrasonic communication is a methods of sending and receiving messages for underwater level. Nowadays there is a lot application that have been discovered for example telecommunication between submarines There are several ways to communicate underwater level but the most common communication using hydrophone. Hydrophone can be build based on sensing element using piezoelectric material or capacitive material. Currently hydrophones based piezoelectric material are low sensitivity and narrow bandwidth. This will affect the sonar application when used the low performance of hydrophones. This project is aimed to design, simulate and characterize a new backing layer structure for piezoelectric ultrasonic transducer applied in underwater communication using finite element analysis (FEA). The study was included a different types of backing layers that applied for a new structure backing layer. There were 3 types of backing layer constructed, namely wood (pine), plastic (acrylic) and metal (titanium). The frequency ranges of 1 kHz to 100 kHz were applied in simulation. Piezoelectric ultrasonic transducer with titanium 21S metal has wide bandwidth of 53.7 %. The transmitting voltage response of the device was 110 dB rel 1 μPa/V. The material of titanium 21S metal has improved transducer performance where it was the highest performance between other materials.

Hydrophones with three different resonant cavities (microscope slide, cavity with 9.8 mm diameter and 5.7 mm[Formula: see text] curve surface, and cavity with 14 mm diameter and 6.5 mm[Formula: see text] curve surface) and with two different electrode structures (interdigital electrode, without the interdigital electrode but with top–bottom structure) were designed and fabricated. Zinc oxide (ZnO) film was deposited on indium–tin oxide/glass as seed layer and ZnO nanocolumns were grown as the piezoelectric material. Grown ZnO nanocolumns were used in all samples as the sound receiver of all designed hydrophones to enhance the sensing effect and efficiency of fabricated hydrophones. The electrode mask was then adhered on the surfaces of ZnO nanocolumns to complete the electrodes of designed resonant cavity. While measuring the hydrophones without interdigitated electrode, the measurement probes were contacted directly on the substrate and on the top layer of the material. Finally, the resonant cavities in all designed hydrophones were encapsulated using epoxy resin to finish the package of the fabricated hydrophones, and then the sound receiving performance of the hydrophones was evaluated in the water and the results were well compared in this study.

Highlights • Ultrasonic cavitation is recorded by high-speed camera and hydrophone in a gas-expanded liquid system. • Content of CO2 has an important influence on evolution of bubble cloud. • Cavitation intensity depends on ultrasonic power and gas content. • The combination of ultrasound and gas-expanded liquid system greatly promotes mass transfer., Due to the tunability in mass transfer, solvation and solubility, gas-expanded liquids show advantages over traditional organic solvents in many characteristics. Ultrasonication is a commonly used method to promote heat and mass transfer. The introduction of ultrasonic technology into the gas-expanded liquid system can promote the polymerization of polymer monomers, enhance extraction efficiency, and control the growth size of nanocrystals, etc. Although acoustic cavitation has been extensively explored in aqueous solutions, there are still few studies on cavitation in organic liquids, especially in gas-expanded liquid systems. In this article, the development of cavitation bubble cloud structure in CO2-expanded N, N-dimethylformamide (DMF) was observed by a high-speed camera, and the cavitation intensity was recorded using a spherical hydrophone. It was found that the magnitude of the transient cavitation energy was not only related to input power, but also closely related to CO2 content. The combination of ultrasound (causing a rapid alternation of gas solubility) and gas-expanded liquid system (causing a decrease in viscosity and surface tension of liquids) is expected to provide a perfect platform for high-speed mass transfer.

Generally, the beam width of planar hydrophone is limited by its wavelength size, that is, when the receiving aperture is fixed, the beam width at a certain frequency is also fixed. When the working frequency is increased, in order to meet the beam width index, the receiving area of the hydrophone must be reduced accordingly, which reduces the capacitance value of the hydrophone and the ability of anti-interference and anti-current noise of the hydrophone. Large area receiving is one of the biggest advantages of PVDF hydrophone, so how to improve the beam width without reducing the receiving area is an important problem to be solved. Therefore, a circular arc backed PVDF hydrophone is proposed in this paper, which can improve the directivity of the hydrophone and make the beam width no longer limited by its wavelength size. The beam width can be adjusted by changing the shape and radian of the arc backing, so that it can be applied to different frequencies.

DFB fiber laser is cross sensitive to sound pressure signal and vibration signal. To the actual demand of the towed thin linear array based on DFB fiber laser hydrophone, the probe of symmetrical sensitized DFB fiber laser hydrophone was designed and packaged. In this paper, the sound sensitivity and acceleration sensitivity of the probe were calculated by finite element simulation respectively, and the experimental verification was carried out. Second, by acoustic vibration coupling experiment to simulate the actual working conditions, the probe was motivated by acoustic signal and acceleration signal, and the coupling experiment under acceleration sensitivity conform to the separate calculation of acceleration sensitivity. It preliminarily verified the sensor unit had both the high-pressure sensitivity and the low acceleration sensitivity. It was a foundation for the towed thin line array cable formation based on DFB fiber laser hydrophone.