Broadband Piezoelectric Transducer Research Articles

Development of methods and devices for air-coupled ultrasonic through transmission testing of large-sized objects made of polymer composite materials

It is shown that in order to increase the sensitivity of air-coupled ultrasonic through transmission testing of products made of polymer composite materials, it is necessary to develop highly sensitive low-frequency wideband air-coupled piezoelectric transducers. The methods of providing both high sensitivity and a wideband of air-coupled ultrasonic piezoelectric transducer are considered. Air-coupled ultrasonic highly sensitive broadband piezoelectric transducer based on the use of mosaic contact piezoelectric transducer technology, the choice of optimal matching layers and the use of various options for excitation of piezoelectric transmitter have been proposed and developed. It is shown that by use of mosaic air-coupled low-frequency broadband piezoelectric transducers, it is possible to ensure high sensitivity of testing and ensure the accuracy of measurement of acoustic characteristics (ultrasound velocity, density, etc.) with air-coupled ultrasonic low-frequency through transmission testing of large-sized objects made of polymer composite materials.

Anisotropic Acoustodynamics in Gigahertz Piezoelectric Ultrasonic Transducers

In this work, we employed our newly developed optical imaging method to probe detailed acoustodynamic physics in gigahertz unreleased ultrasonic transducers based on an AlN-on-silicon system, revealing mode superposition, anisotropic transduction, and dynamic mode evolution. Superpositioned upon the dominant breathing mode along the vertical direction of the AlN layer, multiple resonant lateral modes are identified, and they are shown to evolve into a surface mode beyond the piezoelectric transduction envelope, with strong anisotropic transduction brought by the shear motion of silicon. This acoustodynamic property is important for verifying and further improving design theories of broadband piezoelectric transducers and thin film piezoelectric-on-substrate systems in general.

Elastic waves in particulate glass-rubber mixtures.

We investigate the propagation of waves in dense static granular packings made of soft and stiff particles subjected to hydrostatic stress. Physical experiments in a triaxial cell equipped with broadband piezoelectric wave transducers have been performed at ultrasound frequencies. The time of flight is measured in order to study the combined effect of applied stress and rubber content on the elastic properties of the mixtures. The bulk stiffness deduced from the wave speed is nonlinear and non-monotonic with the increasing percentage of rubber with a more prominent effect at higher pressures. Moreover, in the frequency domain, a spectral analysis gives insights on the transition from a glass- to a rubber-dominated regime and the influence of rubber particles on the energy dissipation. Mixtures with rubber content below 30% show enhanced damping properties, associated with slightly higher stiffness and lighter weight.

Study on the broadband piezoelectric ceramic transducer based on radial enhanced composite structure

A new type of broadband piezoelectric ceramic transducer is developed and analyzed. The transducer is composed of two radial enhanced composite vibrators with different resonance frequencies stacked along the axial direction. Each vibrator consists of a piezoelectric ceramic stack polarized in the thickness direction and a metal tube, and they are connected and excited to vibrate in the radial direction. On the basis of the radial vibrations of the piezoelectric ceramic thin ring and the metal tube, the electromechanical equivalent circuit of the transducer is derived and the input impedance of the transducer is obtained. The relationship between the resonance frequency and the geometrical dimensions of the transducer is analyzed. The new type of transducer is simulated using the ANSYS software. The simulated resonance frequencies of the transducer are in good agreement with the theoretical results. The transducer exhibits broadband characteristics because of the double stacking of vibrators with different resonance frequencies, and the transducer can be driven under high power because of its radial enhanced composite structure.

Two-dimensional photoacoustic imaging of femtosecond filament in water

We report a first-of-its-kind optoacoustic tomography of a femtosecond filament in water. Using a broadband (~100 MHz) piezoelectric transducer and a back-projection reconstruction technique, a single filament profile was retrieved. Obtained pressure distribution induced by the femtosecond filament allowed us to identify the size of the core and the energy reservoir with spatial resolution better than 10 µm. The photoacoustic imaging provides direct measurements of the energy deposition into the medium under filamentation of ultrashort laser pulses that cannot be obtained by existing techniques. In combination with a relative simplicity and high accuracy, photoacoustic imaging can be considered as a breakthrough instrument for filamentation investigation.

In situ optoacoustic measurement of the pointing stability of femtosecond laser beams

A new method for the in situ acoustic measurement of the beam pointing stability (BPS) of powerful pulsed lasers is tested. A broadband (~6 MHz) piezoelectric transducer placed a few millimeters from the laser spark produces an electric pulse. We show that variation in time of the position of this pulse can be used to assess the BPS down to 1 µrad in a few hundred laser shots. The estimated value coincides well with the BPS estimated using standard measurement in the far field.

Автономный маломощный источник энергии на основе широкополосного пьезоэлектрического преобразователя

Автономный маломощный источник энергии на основе широкополосного пьезоэлектрического преобразователя

Detection and quantification of delamination in laminated plates from the phase of appropriate guided wave modes

Applicability of specific Lamb wave modes for delamination detection and quantification in a laminated aluminum plate is investigated. The Lamb modes were generated in the plate using a broadband piezoelectric transducer structured with a rigid electrode. Appropriate excitation frequencies and modes for inspection were selected from theoretical dispersion curves. Sensitivity of antisymmetric and symmetric modes for delamination detection and quantification has been investigated using the Hilbert–Huang transform. The mode conversion phenomenon of Lamb waves during progressive delamination is observed. The antisymmetric mode is found to be more reliable for delamination detection and quantification. In this investigation, the changes in the phase of guided Lamb wave modes are related to the degree of delamination, unlike other studies, where mostly the attenuation of the propagating waves has been related to the extent of the internal damage, such as cracks and corrosions. Appropriate features for delamination detection and quantification are extracted from the experimental data.

A New Method of Designing Electrical Impedance Matching Network for Piezoelectric Ultrasound Transducer

A new method that is based on genetic algorithm (GA) is developed to design electrical impedance matching network for broadband piezoelectric ultrasound transducer. The new method can both optimize the topology of the matching network and perform optimization on the components at the same time. Results of classical algorithms are referenced to reduce the number of candidate topologies and greatly simplify the calculation process. Some calculation strategies, such as elitist strategy and clearing niche method, are adopted during optimization to make sure that the algorithm can convergence to global optimal result. Simulation results show that the new method has advantages over designing complex impedance matching network.

Optoacoustic monitoring of cutting efficiency and thermal damage during laser ablation

Successful laser surgery is characterized by a precise cut and effective hemostasis with minimal collateral thermal damage to the adjacent tissues. Consequently, the surgeon needs to control several parameters, such as power, pulse repetition rate, and velocity of movements. In this study we propose utilizing optoacoustics for providing the necessary real-time feedback of cutting efficiency and collateral thermal damage. Laser ablation was performed on a bovine meat slab using a Q-switched Nd-YAG laser (532 nm, 4 kHz, 18 W). Due to the short pulse duration of 7.6 ns, the same laser has also been used for generation of optoacoustic signals. Both the shockwaves, generated due to tissue removal, as well as the normal optoacoustic responses from the surrounding tissue were detected using a single broadband piezoelectric transducer. It has been observed that the rapid reduction in the shockwave amplitude occurs as more material is being removed, indicating decrease in cutting efficiency, whereas gradual decrease in the optoacoustic signal likely corresponds to coagulation around the ablation crater. Further heating of the surrounding tissue leads to carbonization accompanied by a significant shift in the optoacoustic spectra. Our results hold promise for real-time monitoring of cutting efficiency and collateral thermal damage during laser surgery. In practice, this could eventually facilitate development of automatic cut-off mechanisms that will guarantee an optimal tradeoff between cutting and heating while avoiding severe thermal damage to the surrounding tissues.

The analysis of broadband piezoelectric transducers on the basis of model of the connected contours

In work calculation of parameters of broadband piezoelectric transducers of medical appointment by means of model of the connected contours is executed. The model allows to carry out calculations on the basis of simple ratios, uniform transducers for different types.Reference 8, figures 11.

The efficiency of a broadband piezoelectric transducer with allowance for losses in the piezoceramic and matching-layer materials

The problem of determining the total (acousto-electric) efficiency of a plate-type broadband piezoelectric transducer, which is loaded into an aqueous medium, was considered. The problem was solved taking the mechanical and dielectric losses in the piezoelectric material and the mechanical loss in a matching-layer material into account. Analytical expressions that determine the efficiency of a transducer and radiated acoustic power with account for losses were obtained. Numerical studies determined the main trends in changes in the total efficiency of this type of transducer in a wide range of values of both the mechanical quality factors of the ceramic and layer materials and the dielectric loss tangent for the ceramic material. These data can be of interest when designing piezoelectric devices for different purposes.

Analysis of unidirectional broadband piezoelectric spherical shell transducers for underwater acoustics

This paper presents an analytical investigation and experimental verification of the properties of unidirectional broadband piezoelectric acoustic transducers utilizing axisymmetric vibrations of both complete and incomplete spherical piezoelectric shells and is a continuation of a previous paper that presented the electromechanical modal analysis part of the problem [J. Acoust. Soc. Am. 130(2), 753-763 (2011)]. The analysis covers the treatment of the acoustic radiation and reception problem by including analysis of the acoustic impedances and diffraction coefficients as a function of geometry and modal excitation as well as providing specific design examples including multimode spherical acoustic transducers with conformal baffles, and transducers made of incomplete shells (e.g., hemispheres and caps) with free circumferential boundary conditions. The energy method is used to obtain equivalent parameters for a multi-contour electromechanical circuit representation of the transducer and to calculate the transducer performance characteristic as sound projectors and as receivers. Experimental results are obtained on representative piezoceramic transducer prototypes and are in good agreement with the analytical results.

Mode-selective excitation and detection of ultrasonic guided waves for delamination detection in laminated aluminum plates

Selective modes of guided Lamb waves are generated in a laminated aluminum plate for damage detection using a broadband piezoelectric transducer structured with a rigid electrode. Appropriate excitation frequencies and modes for inspection are selected from theoretical and experimental dispersion curves. Dispersion curves are obtained experimentally by short time Fourier transform of the transient signals. Sensitivity of antisymmetric and symmetric modes for delamination detection are investigated. The antisymmetric mode is found to be more reliable for delamination detection. Unlike other studies, in which the attenuation of the propagating waves is related to the extent of the internal damage, in this investigation, the changes in the time-of-flight (TOF) of guided Lamb waves are related to the damage progression. The mode conversion phenomenon of Lamb waves during progressive delamination is investigated. Close matching between the theoretical and experimentally derived dispersion curves and TOF assures the reliability of the results presented here.

A Multimodal Transducer for Cardiopulmonary Activity Monitoring in Emergency

This paper is concerned with a new wearable system, which is able to monitor several vital signals and physiological variables in order to determine the cardiopulmonary activity status during emergencies. The innovative system consists of a multimodal broadband piezoelectric transducer based on polyvinylidene fluoride polymer integrated into a textile belt wrapped around the chest. An advanced electronic control unit, floating power supply, and wireless communication support make it suitable for portable monitoring during critical cardiopulmonary failures. The multimodal transducer is innovative in that only one sensitive element is employed to work as either an ultrasound (US) transceiver or piezoelectric sensor. The US transceiver is enabled to work at high frequency, i.e., it is excited by suitable pulses to emit an ultrasonic wave, which penetrates the body and receives the echo signals bouncing off the biological interfaces having different acoustic impedances. The piezoelectric sensor works at low frequency and acquires both signals generated by heart apex movements and the mechanical movement of the chest induced by respiration. This multimodality is allowed by a broadband of sensitivity jointly at a low value of the figure of merit (Q). Moreover, the transducer thickness is thin enough to assure a good adaptability to the biological site, and it is equipped with an advanced control unit enabling to switch from a high to a low working frequency. If jointly used along with an ECG wearable Holter, this transducer can be used to provide an exhaustive picture of the health status of the subject in the diagnostic and prognostic domains.

Requirements for choosing the parameters of broadband transducers for testing objects with high damping of ultrasonic signals

The main concepts of the theory of optimal signal processing as applied to tasks of ultrasonic testing of articles with high integral damping of acoustic vibrations are considered. The conditions for ensuring the optimal transfer coefficient of the receiving section of an ultrasonic flaw detector’s electroacoustic channel are formulated. The requirements for the characteristics of broadband piezoelectric transducers aimed at the insurance of undistorted transmission of ultrasonic signals are formulated.

Electro-acoustical characterization procedure for cMUTs

A procedure for the electro-acoustical characterization in air of cMUTs is reported. First, the measured input electrical impedance of the transducer is used to calculate the transducer parameters at different bias voltages by fitting it with the Mason model. Then, the single membrane equivalent circuit can be calculated. Second, the cMUT impulse response is obtained through a send-and-receive experiment to be compared with the one predicted by the Mason model. In order to minimize the influence of the emitter in the obtained impulse response an ad hoc broadband piezoelectric transducer centered at the resonant frequency of the cMUT was fabricated. Using this transducer, no deconvolution of the impulse response of the emitter in the cMUT reception pulse is necessary. The procedure is tested for two cMUTs with silicon-rich nitride as structural layer and different membrane diameters (60 and 70 μm).

Modeling NDT piezoelectric ultrasonic transmitters

Ultrasonic NDT applications are frequently based on the spike excitation of piezoelectric transducers by means of efficient pulsers which usually include a power switching device (e.g. SCR or MOS-FET) and some rectifier components. In this paper we present an approximate frequency domain electro-acoustic model for pulsed piezoelectric ultrasonic transmitters which, by integrating partial models of the different stages (driving electronics, tuning/matching networks and broadband piezoelectric transducer), allows the computation of the emission transfer function and output force temporal waveform. An approximate frequency domain model is used for the evaluation of the electrical driving pulse from the spike generator. Tuning circuits, interconnecting cable and mechanical impedance matching layers are modeled by means of transmission lines and the classical quadripole approach. The KLM model is used for the piezoelectric transducer. In addition, a PSPICE scheme is used for an alternative simulation of the broadband driving spike, including the accurate evaluation of non-linear driving effects. Several examples illustrate the capabilities of the specifically developed software.

Viscoelasticity of silica aerogels at ultrasonic frequencies

In this letter, the possibility to use a technique based on the analysis of thickness resonances of air-surrounded aerogel plates at ultrasonic frequencies to obtain viscoelastic properties is investigated. These resonances were excited and sensed by airborne ultrasonic waves. Toward this purpose, specially designed air-coupled, high-sensitivity, and broadband piezoelectric transducers were used. Precise and simultaneous measurements of the velocity and attenuation of longitudinal and shear waves at different frequencies, as well as aerogel density, were obtained. It allowed us to afford a full characterization of the viscoelastic properties of these materials at ultrasonic frequencies.

Advanced Ceramic Research at Industrial Research Limited

The Industrial Research Limited (IRL) ceramics research programme has activities in electroceramics, advanced refractories and engineering ceramics aimed both at the initiation and development of new manufacturing enterprises and the uptake by New Zealand industry of advanced ceramic technologies. The research team has considerable expertise and experience in sialon ceramics and composites that has underpinned the development of a new advanced refractory manufacturing capability in New Zealand. The team’s capability in engineering ceramics is based on considerable research into new forming techniques and encompasses new ceramic-metal composites. Increasingly the team is prototyping high value added, high performance ceramic bodies with industry partners. A rapidly growing capability in electroceramics has targeted the communications and electronics industry. Current research includes the prototyping of a new design broadband piezoelectric transducer, suitable for application in high definition sonar.