Transducer Bandwidth Research Articles

Wideband laser-ultrasound transducer for shear waves: Design and tests on isotropic materials and rock samples

Wideband laser-ultrasound transducer for shear waves: Design and tests on isotropic materials and rock samples

Performance enhancements of Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystal/epoxy 1–3 composite by alternating current polarization

Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystal/epoxy 1–3 piezoelectric composite was designed to decrease acoustic impedance and to improve the electromechanical property, which was vital to the ultrasound transducers. The piezo-/dielectric properties of the PMNT/epoxy 1–3 composites prepared by the different poling methods were measured. It was found that piezoelectric coefficient d33, dielectric constant ε33T/ε0, and electromechanical factor kt of composites exhibited the significant increases of 16.41%, 6.89%, and 1.97% under optimized alternating current polarization (ACP), compared with those of the samples using direct current polarization (DCP). The domain patterns suggested that the remarkable regular striped domain and high domain wall density of the ACP sample could result in performance enhancements. The ACP composite-based transducer's bandwidth (BW) and relative sensitivity (RS) were improved by 6.27% and 1.93 dB. These results indicated that the ACP effectively enhances the piezoelectric composite's performances, and BW and RS of the transducer based on ACP piezoelectric materials are improved simultaneously.

Design and Preparation of Double-Harmonic Piezoelectric Composite Lamination.

In this work, a new type of double-harmonic piezoelectric composite laminated structure is designed. Two bending vibration frequencies are generated by designing the structure with non-equal length and non-equal width, and the response is relatively consistent at the frequency point of the double-harmonic vibration. Firstly, the finite element software ANSYS is used to establish the simulation model of double-harmonic piezoelectric composite lamination. Two bending vibration frequencies are generated by using the non-equal length structure design, and the variation law of the conductance curve with the laminated structure is analyzed. Then, according to this law, the structure is optimized, and a non-equal width structure is further proposed in this work. Different double-harmonic piezoelectric composite laminations are prepared for comparison. The simulation and experimental results show that the value of the corresponding conductance curve at the two vibration frequency points can be increased or reduced by changing the lamination width. Then, the same conductance peak can be obtained to have a relatively consistent response at the double-harmonic frequency point. This will provide a good choice for expanding the transducer bandwidth and developing the broadband energy collector.

Enhancement of Ultrasonic Transducer Bandwidth by Acoustic Impedance Gradient Matching Layer.

High-performance broadband ultrasound transducers provide superior imaging quality in biomedical ultrasound imaging. However, a matching design that perfectly transmits the acoustic energy between the active piezoelectric element and the target medium over the operating spectrum is still lacking. In this work, an anisotropic gradient acoustic impedance composite material as the matching layer of an ultrasonic transducer was designed and fabricated; it is a non-uniform material with the continuous decline of acoustic impedance along the direction of ultrasonic propagation in a sub-wavelength range. This material provides a broadband window for ultrasonic propagation in a wide frequency range and achieves almost perfect sound energy transfer efficiency from the piezoelectric material to the target medium. Nano tungsten particles and epoxy resin were selected as filling and basic materials, respectively. Along the direction of ultrasonic propagation, the proportion of tungsten powder was carefully controlled to decrease gradually, following the natural exponential form in a very narrow thickness range. Using this new material as a matching layer with high-performance single crystals, the −6 dB bandwidth of the PMN-PT ultrasonic transducer could reach over 170%, and the insertion loss was only −20.3 dB. The transducer achieved a temporal signal close to a single wavelength, thus there is the potential to dramatically improve the resolution and imaging quality of the biomedical ultrasound imaging system.

Favorite problems on acoustic transducers and linear systems theory

Practitioners of acoustics sometimes forget how lucky we are that the vast majority of acoustic phenomena and devices we encounter in daily life are linear and solutions using linear systems theory work very well for predicting behavior and designing devices. Typical examples are microphones, loudspeakers and acoustic propagation at sufficiently low excitation levels. One might contrast this to a viscous dashpot, which is also commonly modeled as a linear device. The sliding seals in all viscous dashpots render them essentially-nonlinear from the start. One favorite problem I give year after year, in various forms, is reported here. A generic acoustic transducer, based on a linear simple harmonic oscillator is presented and often the system response function is given in the problem statement. Derivation of the transfer function could be a problem from earlier or later in the class. The students are asked to predict the time domain output of the transducer, subject to a periodic forcing composed of a sawtooth wave, using frequency-domain convolution and Fourier series. Various sub-questions explore the effect of transducer bandwidth and damping on the output signal. A variation of this problem using time-domain convolution is also a favorite. Predictions can be compared to measurements.

Polyphase codes for multiplexed acoustic signalling and sensing on pipes

Transmission of acoustic signals between distributed sensor nodes may be useful for status monitoring of elongated structures such as pipelines. In principle, coded signals can be used in an asynchronous multiplexed system, provided the signals are distinguishable. However, multimode effects complicate signal propagation, so any such codes should be short. A search for polyphase code families with properties suitable for acoustic code division multiple access is presented. Algorithms for reduction of search space to allow use of a laptop for code discovery are described. Short codes of base 6 are shown to outperform codes of bases 2, 3, 4 and sets suitable for systems with 2 and 3 users are identified. The codes have similar properties to Barker codes but larger sidelobes. Their use is demonstrated by simulation and experiment at kHz frequencies using an air-filled copper pipe, an electromagnetic acoustic transducer (EMAT) and a microphone designed to excite and detect the mode. Low loss propagation over 25 m is achieved with a 20 kHz carrier. Excellent agreement between experiment and theory is demonstrated, with performance limited by transducer bandwidth.

Agile offset frequency locking for single-frequency fiber lasers

Single frequency fiber lasers (SFFLs) have seen increasing applications in state-of-the-art quantum technologies, which usually require precise and stable offset frequency locking (OFL). However, limited by the piezoelectric transducer bandwidth in SFFLs and the loop bandwidth of the OFL, the large-gap jumping between two locked offset frequencies will take an undesirable amount of time. In order to diminish that consuming time, we developed an agile offset frequency locking system based on a hybrid loop of a feed-forward path and a feedback path. In accordance with the experimental demonstration, we characterized the performances of the offset frequency locking system, as frequency-locking stability with an Allan deviation of 3.2 × 10−14 at 1 s averaging time and jumping agility with a duration of 0.6 ms at 1.3 GHz frequency gap, which is a factor of 60 faster than that without the feed-forward path. This mechanism can find direct applications in existing quantum metrology experiments with SFFLs where high-speed frequency jumping or sweeping is needed.

Kirigami Engineering of Suspended Graphene Transducers.

The low mass density and high mechanical strength of graphene make it an attractive candidate for suspended-membrane energy transducers. Typically, the membrane size dictates the operational frequency and bandwidth. However, in many cases it would be desirable to both lower the resonance frequency and increase the bandwidth, while maintaining overall membrane size. We employ focused ion beam milling or laser ablation to create kirigami-like modification of suspended pure-graphene membranes ranging in size from microns to millimeters. Kirigami engineering successfully reduces the resonant frequency, increases the displacement amplitude, and broadens the effective bandwidth of the transducer. Our results present a promising route to miniaturized wide-band energy transducers with enhanced operational parameter range and efficiency.

Superconducting-qubit readout via low-backaction electro-optic transduction.

Entangling microwave-frequency superconducting quantum processors through optical light at ambient temperature would enable means of secure communication and distributed quantum information processing1. However, transducing quantum signals between these disparate regimes of the electro-magnetic spectrum remains an outstanding goal2-9, and interfacing superconducting qubits, which are constrained to operate at millikelvin temperatures, with electro-optic transducers presents considerable challenges owing to the deleterious effects of optical photons on superconductors9,10. Moreover, many remote entanglement protocols11-14 require multiple qubit gates both preceding and following the upconversion of the quantum state, and thus an ideal transducer should impart minimal backaction15 on the qubit. Here we demonstrate readout of a superconducting transmon qubit through a low-backaction electro-optomechanical transducer. The modular nature of the transducer and circuit quantum electrodynamics system used in this work enable complete isolation of the qubit from optical photons, and the backaction on the qubit from the transducer is less than that imparted by thermal radiation from the environment. Moderate improvements in the transducer bandwidth and the added noise will enable us to leverage the full suite of tools available in circuit quantum electrodynamics to demonstrate transduction of non-classical signals from a superconducting qubit to the optical domain.

Spectral Ultrasound Imaging of Speed-of-Sound and Attenuation Using an Acoustic Mirror

Speed-of-sound and attenuation of ultrasound waves vary in the tissues. There exist methods in the literature that allow for spatially reconstructing the distribution of group speed-of-sound (SoS) and frequency-dependent ultrasound attenuation (UA) using reflections from an acoustic mirror positioned at a known distance from the transducer. These methods utilize a conventional ultrasound transducer operating in pulse-echo mode and a calibration protocol with measurements in water. In this study, we introduce a novel method for reconstructing local SoS and UA maps as a function of acoustic frequency through Fourier-domain analysis and by fitting linear and power-law dependency models in closed form. Frequency-dependent SoS and UA together characterize the tissue comprehensively in spectral domain within the utilized transducer bandwidth. In simulations, our proposed methods are shown to yield low reconstruction error: 0.01 dB/cm⋅MHzy for attenuation coefficient and 0.05 for the frequency exponent. For tissue-mimicking phantoms and ex-vivo bovine muscle samples, a high reconstruction contrast was achieved. Attenuation exponents in a gelatin-cellulose mixture and an ex-vivo bovine muscle sample were found to be, respectively, 1.3 and 0.6 on average. Linear dispersion of SoS in a gelatin-cellulose mixture and an ex-vivo bovine muscle sample were found to be, respectively, 1.3 and 4.0 m/s⋅MHz on average. These findings were reproducible when the inclusion and substrate materials were exchanged. Bulk loss modulus in the bovine muscle sample was computed to be approximately 4 times the bulk loss modulus in the gelatin-cellulose mixture. Such frequency-dependent characteristics of SoS and UA, and bulk loss modulus may therefore differentiate tissues as potential diagnostic biomarkers.

A Comparison of Adaptive Ultrasound Reflectometry Calibration Methods for Use in Lubrication Films

Adaptive calibration for ultrasound reflectometry methods used in the detection of lubrication film thickness is of great research interest. This is mainly due to the versatile non-destructive implementation of the technology in industrial applications, allowing for measurements of the lubrication film thickness, which directly relates to the friction, wear, and overall efficiency of the system. This study reviews and compares a curve fitting, extended Kalman filter, and resonance frequency detection adaptive calibration approach. Furthermore, the study compares two different regression models, used for the curve fitting and the extended Kalman filter approach. The study compares the methods and regression models based on both a theoretical and experimental analysis. The experimental analysis is based on data with varying lubrication film thickness. The lubrication film thickness is varied such that the resonance frequency is both detectable and non-detectable within the ultrasound transducer bandwidth. It is found that all three methods give results very similar to those achieved through manual calibration. However, since the extended Kalman filter approach is the only method that allows for continuous calibration, this method is found to have the greatest potential of the methods compared.

Spectroscopically resolved photoacoustic microscopy using a broadband surface plasmon resonance sensor

Photoacoustic spectroscopic analysis allows for evaluating biological microscopic features, such as morphology and viscoelasticity, which offers the opportunities of comprehensively understanding the biological specimens. However, an ongoing challenge arises from inadequate response to the photoacoustic impulses owing to limited bandwidth of the piezoelectric transducer. Here, we develop spectroscopically resolved optical-resolution photoacoustic microscopy (OR-PAM) by incorporating a broadband surface plasmon resonance sensor (∼169.5-MHz bandwidth) as the ultrasonic detector. The photoacoustic spectra from polystyrene and polymethyl methacrylate microspheres represent the close dependence upon the density and sound speed in addition to the diameter. The photoacoustic structural images of the two types of microspheres with the same morphology manifest the nearly identical appearances, while the photoacoustic spectroscopic analysis permits them to be clearly distinguished because of the different densities and sound speeds. The results suggest that, by simultaneously revealing the anatomic structures and acoustic spectra, our spectroscopically resolved OR-PAM system is potentially valuable in characterizing the microscopic features of biological samples at a cellular level.

Effects of Composition Segregation in PMN-PT Crystals on Ultrasound Transducer Performance.

This study investigates the relationship between the composition segregation in lead magnesium niobate-lead titanate (PMN-PT; PMN-29%PT, PMN-29.5%PT, PMN-30%PT, PMN-30.5%PT, and PMN-31%PT) single crystals within morphotropic phase boundary (MPB) and the corresponding ultrasonic transducer performance through PiezoCAD modeling and real transducer testing. For five crystals with compositions distributed across the main body of a crystal ingot, the piezoelectric coefficient and free relative permittivity values were measured to vary by over 30%, whereas the transducer bandwidth and center frequency values were modeled to change by less than 10%. For the single-element ultrasonic transducers fabricated using those crystals without matching layers, the variations of -6-dB bandwidth, insertion loss, receiver-free field voltage response, and center frequency were measured to be 9.61%, -15.23%, 9.76%, and 1.41%, respectively, confirming the modeling results. Using the Mason and Krimholtz, Leedom, and Matthaei (KLM) models, it is found that the relatively stable transducer performance can be attributed to the relatively consistent electromechanical coupling coefficient, acoustic impedance, and clamped relative permittivity originated from the stable elastic compliance properties among the crystals of various compositions. It is expected that the relatively stable performance could be extended to multielement transducers with matching layers for the same contributing mechanisms. Our results suggest that it is possible to use crystal plates of different compositions within the MPB region, obtained from one and the same ingot, to fabricate a batch of ultrasonic transducers that will exhibit a similar performance, significantly reducing the cost of materials.

Planar ultrasonic transducer based on a metasurface piezoelectric ring array for subwavelength acoustic focusing in water

The development of a new ultrasonic transducer capable of improved focusing performance has become a necessity to overcome the limitations of conventional ultrasonic transducer technology. In this study, we designed and optimized a metasurface piezoelectric ring device, and using multiphysics finite element analysis, we examined the performance of a planar ultrasonic transducer consisting of this device, a matching layer, a backing layer, and housing in producing a needle-like subwavelength focusing beam in water. For practical experiments, a metasurface piezoelectric ring device was fabricated using a laser ablation process. Subsequently, using a pulse-echo test, we found that the − 6 dB bandwidth of a planar ultrasonic transducer with a center frequency of 1.0 MHz was 37.5%. In addition, the results of an ultrasonic-focusing performance test showed that the full width at half-maximum of the axial subwavelength focusing beam was 0.78λ, and the full lateral width at half-maximum of the subwavelength lateral focusing beam was 7.03λ at a distance of 10.89λ. The needle-like focused ultrasonic beam technology implemented with a piezoelectric ring array based new planar ultrasound transducer is expected to be used in high-resolution imaging devices or medical ultrasound focusing devices in the future.

Super-resolution acoustic focusing based on the particle swarm optimization of super-oscillation

The spatial resolution of conventional waves is restricted by the diffraction limit of half wavelength. Hence, how to construct super-resolution acoustic beams with a smaller focal radius is one of the major challenges in recent studies. In the present paper, the super-resolution acoustic focusing method is proposed based on the superposition of multi-frequency super-oscillation beams and the Particle Swarm Optimization (PSO), which can improve the spatial resolution concurrently with good controllability. Based on the diffraction effect of traditional ultrasound fields, the acoustic lens of Fresnel zone plane (FZP) at the center frequency is designed by the half-wave zone method. Multiple acoustic beams at several preset frequencies within the transducer bandwidth are sent out to build the super-oscillation focal area by the pressure superposition. The radius of the super-resolution focal spot constructed by the PSO algorithm with optimized amplitudes and phases is less than the half wavelength at the center frequency, which is even smaller than the focal radius at the highest frequency. Furthermore, the focal radius is also proved to decrease with the increase of the number of multiple frequencies and the center frequency. The favorable results demonstrate the feasibility of super-resolution acoustic focusing based on the PSO of super-oscillation, and provide an applicable strategy for the high-resolution acoustic imaging and manipulation.

A Fabry–Perot Fiber-Optic Array for Photoacoustic Imaging

Photoacoustic imaging is an emerging noninvasive and nonionizing imaging modality with high contrast and high resolution, which originates from the photoabsorption selectivity and the broadband response of the photoacoustic signals. However, sensing of the photoacoustic signal is currently limited by the bandwidth of piezoelectric ultrasound transducers. The optical ultrasound sensors based on Fabry–Perot (F–P) interference exhibit broader bandwidth than piezoelectric transducers, which is expected to be a promising alternative. At present, nevertheless, the parallel sensing and processing of ultrasound signals using the fiber-optic ultrasound sensor is still a challenge. Here, we propose a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times16$ </tex-math></inline-formula> fiber-optic array based on F–P interference, which enables parallel sensing for imaging with a volume rate of 10 Hz. We experimentally demonstrated that the fiber-optic array ultrasound sensor exhibited a pressure nonlinearity of <3.64%, and −6 dB bandwidth from ~0 to 18.3 MHz. High-definition imaging is achieved by this sensing array without mechanical scanning. As the ultrasound sensing realized by optics, the photoacoustic imaging system is potentially an all-optic system with broadband response.

Design and implementation of half-space radiation high frequency broadband “spherical” transducer based on anti-sound baffle and circuit matching

In underwater acoustic communication engineering applications, it is sometimes necessary to place the communication transducers underwater. This usually requires the transducers to have the ability to radiate in half-space. At the same time, in order to reduce the transmission error rate, it is also necessary that the transducers have the ability to operate in a wide band. The spherical piezoelectric transducers have full space radiation, and high power and energy density. The design of spherical transducer by using anti-sound baffle and circuit tuning can meet the requirements of underwater communication transducers. In this work, we analyze the directivity of a spherical transducer by comparing the simulations and theoretical computations. In addition, the broadband performance of a spherical transducer is analyzed based on series inductance tuning. Finally, a half-space broadband spherical transducer prototype is manufactured and its performance is tested and verified by performing experiments. The experimental results show that the bandwidth of the spherical transducer can be increased by series inductance. Moreover, the results show that the distance from the center of the spherical transducer to the anti-sound baffle and the working frequency have a significant effect on the directivity of a spherical transducer. The test results of transducer prototype show that the directivity angle of the transducer is greater than 180°, and the operating bandwidth is around 18 kHz–54 kHz.

Development of a Compact Photoacoustic Tomography Imaging System with Dual Single-Element Transducers for Image Enhancement

ObjectiveThis paper proposes a new photoacoustic computed tomography (PACT) imaging system employing dual ultrasonic transducers with different frequencies. When imaging complex biological tissues, photoacoustic (PA) signals with multiple frequencies are produced simultaneously; however, due to the limited bandwidth of a single-frequency transducer, the received PA signals with specific frequencies may be missing, leading to a low imaging quality.MethodsIn contrast to our previous work, the proposed system has a compact volume as well as specific selection of the detection center frequency of the transducer, which can provide a comprehensive range for the detection of PA signals. In this study, a series of numerical simulation and phantom experiments were performed to validate the efficacy of the developed PACT system.ResultsThe images generated by our system combined the advantages of both high resolution and ideal brightness/contrast.ConclusionThe interchangeability of transducers with different frequencies provides potential for clinical deployment under the circumstance where a single frequency transducer cannot perform well.

Measuring the sound speed in deep-sea first sediment layer using a high-frequency submersible sub-bottom profiler: Method and sea trial application

In the study of sedimentary acoustics, measuring sound speed in the first layer sediment is a key issue. To solve this problem, we proposed a method for measuring the sound speed in the deep-sea first-layer sediment using a high-frequency submersible sub-bottom profiler. In this method, we obtained the reflection data of deep-sea sediments near the bottom using a wide-band narrow-beam single transducer and obtained the profile of deep-sea sediments using the reflection compression method. The first sediment layer was extracted according to the layer structure information, and the sound speed of the first sediment layer was directly measured. The transducer feasibility of the high-frequency submersible sub-bottom profiler operating at high pressure in deep sea was verified through high hydrostatic pressure tests in the laboratory. We designed a laboratory reflection compression measurement device to simulate the first layer of deep-sea sediments and verified the effectiveness of the measurement method. This method also was used to process deep-sea sediment data acquired by the Deep-Sea Warrior manned submersible.

A Novel Coupled Piezoelectric Micromachined Ultrasonic Transducer Based on Piston Mode.

This article presents a piezoelectric micromachined ultrasonic transducer (pMUT) modified with a piston diaphragm term as piston diaphragm pMUT (PD-pMUT). The transmission sound pressure level (SPL) and the frequency bandwidth of the modified transducer can be remarkably improved by adding a piston diaphragm on the central circular diaphragm. In this work, a lumped model, an acoustic resonance model, and an equivalent circuit model are established to study the multiresonance mechanism. The second resonance peak is contributed by the interference acoustic wave generated between the circular and piston diaphragms. This work demonstrated a simulated far-field average SPL up to 132.2 dB in the single modified piston diaphragm structure and a 28.1%-6-dB frequency bandwidth by theoretical analysis and parameter optimization. The bandwidth is 3.31 times of the traditional pMUT with aluminum nitride (AlN) in air. In addition, the PD-pMUT has a -6-dB frequency bandwidth of up to 66%, which is 1.4 times of traditional pMUT in the liquid-coupled operation. The proposed PD-pMUT provides a new approach for the application of high transmission power and broad bandwidth transducers.