Composite Transducer Research Articles

Wireless Power Transmission for Implantable Medical Devices Using Focused Ultrasound and a Miniaturized 1-3 Piezoelectric Composite Receiving Transducer.

Wireless power transmission (WPT) using ultrasound is a promising way for wirelessly recharging implantable medical devices (IMDs). However, the transmitted power using ultrasound so far is insufficient for driving the existing IMDs. Moreover, the size of the receiving transducer is larger, which is not suitable for implantation. To increase the output power and reduce the size of the implantable receiver, this article presents a method of combining focused ultrasound with a miniaturized 1-3 piezoelectric composite receiving transducer to produce higher electrical power. An analytical fluid-structure interaction model is constructed to fully understand the operating mechanism of the receiving transducer under ultrasonic force. In our experiments, a miniaturized 1-3 piezoelectric composite receiving transducer with a diameter of 3.7 mm was used. The output power generated from the receiving transducer reached 60 mW at a distance of 150 mm. In vitro and in vivo animal experiments proved that the miniaturized transducer could successfully receive focused ultrasonic energy and convert it to electrical power. The method presented and the electrical power that we obtained can provide a valuable reference for wirelessly charging of IMDs.

Experimental validation of axially polarized multilayer piezoelectric composite cylindrical transducers with adjustable multifrequency

The axially polarized multilayer piezoelectric composite cylindrical transducers with adjustable multifrequency capability have been proposed by adjusting the external electric resistance and the ratio of piezoelectric layer numbers between the actuator part and the sensor part, which have promising potential in designing the novel cymbal transducer for underwater sound projector and ultrasonic radiator applications. In the previous studies, the multilayer models were established to guide the design of the transducers with arbitrary layer number, and analyzed the dynamic characteristics theoretically. In this work, an experimental study is performed to validate the theoretical models and predictions. Piezoelectric rings with multiple concentric annular electrodes are designed to characterize the multilayer piezoelectric composite cylindrical transducers. The top surface of the piezoelectric rings is divided into two separate parts. One part is covered by multiple concentric annular electrodes, corresponding to the piezoelectric layers, and the other part is uncovered, corresponding to the elastic layers. Four prototypes are fabricated and each consists of four concentric annular electrodes. The impedance spectra are measured by the impedance analyzer to obtain the resonance and anti-resonance frequencies. Effects of two adjusting methods on the dynamic characteristics are evaluated experimentally. The experimental results basically coincide with the theoretical ones. This comprehensive experimental work assures the feasibility of using axially polarized multilayer piezoelectric composite cylindrical transducers with adjustable multifrequencies and confirms the benefit of the developed theoretical models for guiding the fabrication and optimization of this type of transducers.

Multifrequency ultrasonic transducers based on dual vibration and harmonic mode

Multifrequency ultrasonic transducers have broad application prospects in the field of biomedical due to their high imaging resolution and detection depth. This paper proposed a design method of triple frequency single-element transducers by finite element method(FEM). The triple frequency transducers are based on contour mode, thickness mode and the third harmonic of thickness mode. Nine micro single element transducers with different widths and matching layers were fabricated and characterized to verify the design method. The traditional 30 MHz single frequency transducer and 2.3 MHz 1–3 piezoelectric composite transducer were used to compare with high frequency part and low frequency part of the triple frequency transducers, respectively. The pulse-echo characteristics of the triple frequency transducers have impressive low and middle frequency part. The high frequency part is similar with traditional transducer except the sensitivity is 0.5 times. The results certify the feasibility of a triple-Frequency transducer based on dual vibration and harmonic modes.

Ultra-wide operation band of the high-frequency underwater acoustic transducer realized by two-layer 1-3 piezoelectric composite.

In this paper, the two-layer 1-3 composite transducer using an unconventional part-excitation method is presented to achieve the ultra-wide operation band for the high-frequency underwater devices, in which the part-excitation refers to the method that only the lower-layer is excited, while the upper-layer in contact with the propagation medium is not excited. This method is first proposed by analyzing the longitudinal vibration modes of one piezoelectric rod in the 1-3 composite and finally, we conclude that if the excited lower-layer can be controlled to have thickness given by 3l/2n, where l is the whole thickness of the two-layer rod and n (n > 1) denotes the number of the coupled modes, then first n order modes can be activated simultaneously to form an ultra-wide operation band containing n response peaks. Finite element method (FEM) is employed to investigate the two-layer 1-3 composite with a thickness of 10 mm. The results show that when the thickness of the excited lower-layer is 3 mm (n = 5), the transducer attains the ultra-wideband by coupling five resonances, nearly covering the frequency range from 100 kHz to 1 MHz. According to the difference of response level, the whole band can be divided into multiple local wide bands. A prototype transducer is fabricated based on the FEM results, and the measured results show that the whole band contains three wide bands, covering the frequency ranges 125-295 kHz, 300-480 kHz, and 500-915 kHz, respectively.

High-frequency wide beam underwater transducer based on 1–3 piezocomposite

In order to increase the beam width of high-frequency underwater transducer, ellipsoidal cap and spherical cap transducer based on 1–3 piezocomposite were designed and fabricated. Finite element simulation was used to analyze transmitting voltage response level and beam directivity curve of the transducer. The transducer was fabricated by the curved 1–3 piezoelectric composite. Compared with spherical cap transducer, the elliptical spherical cap transducer has the advantage of wide beam opening angle and relatively smooth directivity curve. Both simulation and experiment results showed the potential of a broad covered area of the composite transducer in underwater environment.

Wideband and wide beam piezoelectric composite spherical cap transducer for underwater acoustics

A new class of piezoelectric composite spherical cap transducer that produces a wide beam and bandwidth was developed for underwater acoustics. A finite element analysis (FEA) simulation was used to design the transducer. Electroacoustic response measurements in water were made on a transducer to evaluate the performance characteristics and then compared with the FEA results. The measured results show the transducer can provide a 112° beamwidth and a usable frequency band from 215 kHz to 355 kHz. The maximum transmitting voltage response (TVR) of the transducer is 161.7 dB re 1µPa/V@1m at 255 kHz.

Theoretical calculation model of emission performance for 1-3 piezoelectric composite transducer

1-3 piezoelectric composite has been widely used in underwater acoustic high frequency transducer because of its excellent high frequency characteristics. Resonance frequency, transmitting voltage response and bandwidth are three key parameters to measure the emission performance of 1-3 piezoelectric composite transducer. In order to predict these parameters, the theoretical model of 1-3 piezoelectric composite transducer is established based on the electromechanical equivalence principle and acoustic field theory. According to the theoretical model, numerical calculation method is used to calculate the emission performance parameters of the transducer. The theoretical calculation agrees well with the experiment, and the maximum error is less than 7.9%. It shows that the theoretical model established in this paper is reasonable and can accurately predict the emission performance of 1-3 piezoelectric composite transducer.

Large-dimension piezoelectric ceramic composite transducer with point-defect, square-lattice phononic crystal

<p indent=0mm>To improve the longitudinal working efficiency of large-dimension sandwich piezoelectric ceramic composite transducers (PccTs), reduce the strong coupling between longitudinal and transverse vibrations, and improve the longitudinal displacement distribution uniformity of the front radiation end of the transducer, three rows and three columns of two-dimensional (2D) air cylindrical holes arranged in a square lattice parallel to the axial direction of the transducer were fabricated on the front cover plate of a large-dimension sandwich PccT. By changing the radius of the air cylindrical hole in the center of the 3×3 supercell, a point defect is introduced to construct 2D square lattice near-periodic phononic crystals based on the abnormal radius point defect. This design can use the incomplete bandgap of the crystal in the radial direction to suppress the transverse vibration of the large-dimension PccT and can use the Anderson localization characteristics of the point defect to adjust the intensity and phase of the local sound field to further improve the uniformity of the displacement distribution of the radiation surface of the front cover plate. In addition, the influence of the structural parameters of the air cylindrical hole with the point defect on the longitudinal resonance frequency and the longitudinal vibration displacement distribution is analyzed. The simulation results show that the large-dimension PccT based on point defect, phononic crystals can suppress the axial stray modal of the transducer, significantly optimize the longitudinal relative displacement distribution of the radiation surface, and improve the performance of large-dimension PccTs.

Study on the bending vibration of bimorph rectangular transducer based on type 2-2 piezoelectric composites

In order to improve the acoustic radiation capability of piezoelectric ultrasonic transducer in gas, a bimorph rectangular transducer based on type 2-2 piezoelectric composites is proposed in this paper, which is composed of two piezoelectric composite rectangular slices with thickness polarization. First, the bending vibration of the rectangular transducer is divided into two bending vibrations of the thin rods in the x and y directions using the equivalent elastic method. When the mechanical coupling coefficient is introduced and combined with the anisotropic piezoelectric equations, the resonance frequency equations of the thickness-polarized transducer are derived with simply supported boundary conditions. Then the bending vibration of the transducer is numerically simulated. The results show that the resonance frequency obtained by the analytical method is in good agreement with the numerical simulation results. Finally, the influence of geometrical size and two-phase volume ratio on the bending vibration performance of the transducer is analyzed. Compared with the piezoelectric bimorph transducer, the piezoelectric composite bimorph transducer has a larger bending vibration displacement amplitude, a larger transmitting voltage response, a lower resonant frequency and better acoustic radiation capability.

A Dual-Frequency Lens-Focused Endoscopic Histotripsy Transducer.

A forward-looking miniature histotripsy transducer has been developed that incorporates an acoustic lens and dual-frequency stacked transducers. An acoustic lens is used to increase the peak negative pressure through focal gain and the dual-frequency transducers are designed to increase peak negative pressure by summing the pressure generated by each transducer individually. Four lens designs, each with an f -number of approximately 1, were evaluated in a PZT5A composite transducer. The finite-element model (FEM) predicted axial beamwidths of 1.61, 2.40, 2.84, and 2.36 mm for the resin conventional, resin Fresnel, silicone conventional, and silicone Fresnel lenses, respectively; the measured axial beamwidths were 1.30, 2.28, 2.71, and 2.11 mm, respectively. Radial beamwidths from the model were between 0.32 and 0.35 mm, while measurements agreed to within 0.2 mm. The measured peak negative was 0.150, 0.124, 0.160, and 0.160 MPa/V for the resin conventional, resin Fresnel, silicone conventional, and silicone Fresnel lenses, respectively. For the dual-frequency device, the 5-MHz (therapy) transducer had a measured peak negative pressure of 0.136 MPa/V for the PZT5A composite and 0.163 MPa/V for the PMN-PT composite. The 1.2-MHz (pump) transducer had a measured peak negative pressure of 0.028 MPa/V. The pump transducer significantly lowered the cavitation threshold of the therapy transducer. The dual-frequency device was tested on an ex vivo rat brain, ablating tissue at up to 4-mm depth, with lesion sizes as small as [Formula: see text].

Spherical-Omnidirectional Piezoelectric Composite Transducer for High- Frequency Underwater Acoustics.

Spherical-omnidirectional acoustic source has become a powerful tool to provide a near-ideal omnidirectional beam pattern for acoustic tests and communications. Current spherical-omnidirectional acoustic sources do not combine an omnidirectional beam pattern with a high transmitting voltage response (TVR) in the frequency range of above 200 kHz. This work presents the design, fabrication, and measurements of a high-frequency spherical-omnidirectional transducer that can provide a near-ideal omnidirectional beam pattern and a high TVR. The active element of the transducer consists of six identical square coupons with spherical curvature 1-3 piezoelectric composites operating in thickness mode. Electroacoustic responses of the fabricated transducer in water were measured. The measured resonance frequency of the transducer was 280 kHz. The maximum TVR was 161.3 dB re 1 μ Pa/V@1 m. The horizontal and vertical beamwidths of the transducer were 360° and 346°, respectively. Measurements show that the spherical piezoelectric composite transducer has a favorable spherical-omnidirectional behavior and a high TVR at high frequency. These results demonstrate that the spherical piezoelectric composite transducer is potentially a strong candidate for a high-frequency underwater acoustic source that requires an omnidirectional response.

Development of a novel non-contact piezoelectric wind energy harvester excited by vortex-induced vibration

Wind energy harvesting using piezoelectric transduction is becoming a promising alternative for battery-free portable and wireless electronics. A novel non-contact vortex-induced vibration-based piezoelectric wind energy harvester using an indirectly excited composite piezoelectric transducer is investigated to enhance the reliability and environmental adaptability in this paper. It is very different from the most existing vortex-induced vibration-based piezoelectric wind energy harvesters where piezoelectric cantilever beams interacted directly with the airflow. Herein, wind energy harvesting from vortex-induced vibration of a composite piezoelectric transducer embedded in a cylindrical shell was explored theoretically and experimentally. Furthermore, a pre-bending vibrator subjected only to unidirectional compressive stress was employed to further enhance the reliability of the piezoelectric transducer. To verify the feasibility of the proposed principle and design, a prototype of the non-contact piezoelectric wind energy harvester was fabricated and tested in terms of vibration characteristics, wind speed bandwidth and output power. The results showed that the wind speed bandwidth, vibration displacement and output voltage were increased with the enhancing transducer mass and the decreasing shell mass as the wind speed increased. There was an optimal load resistance of 300 kΩ to maximize the output power. At the wind speed of 40.0 m·s−1 and transducer mass of 65 g, the maximum power of 1.438 mW was recorded in terms of a single piezoelectric pre-bending beam. Meanwhile, the non-contact piezoelectric wind energy harvester could be effectively operated within a wide wind speed range from 5.5 m·s−1 to 40.0 m·s−1 (namely wind speed bandwidth of 34.5 m·s−1) when an output voltage of 5 V was used as the reference value.

Detection of torsional guided wave generation using macro-fiber composite transducers and basis pursuit denoising

In engineering structures, such as large fluid-filled pipelines, continuous monitoring for damage detection is needed. To address this issue, we study the generation of guided waves in pipes by using a circumferential strip of macro fiber composite transducer to generate and detect torsional and flexural lower modes. The propagated elastic waves and their resulting reflected and mode-converted signals at the interaction wave discontinuity are post-processed with basis pursuit denoising using a Gabor dictionary to improve signal identification. Numerical results are obtained and experimentally tested on a stainless-steel pipe A-36 (43.6 and 48.2 mm in inner and outer diameter). It was found that the proposed method makes it possible to identify an artificial discontinuity by detecting the scattered wave and converted modes of a propagated torsional wave.

1Pb3-3 Fundamental study of 2-2 ceramic-air composite transducers for air-coupled ultrasonic measurement

1Pb3-3 Fundamental study of 2-2 ceramic-air composite transducers for air-coupled ultrasonic measurement

Fabrication and high acoustic performance of high frequency needle ultrasound transducer with PMN-PT/Epoxy 1-3 piezoelectric composite prepared by dice and fill method

In this paper, we reported the fabrication and high acoustic performance of high frequency needle ultrasound transducer based on 0.70Pb(Mg1/3Nb2/3)O3-0.30PbTiO3 single crystal/Epoxy 1–3 piezoelectric composite, which was prepared by using the dice and fill (DAF) method. The as-prepared 0.70PMN-0.30 PT/Epoxy 1–3 composite has high thickness extension mode electromechanical coupling coefficient with the value of 67.3 %. The transducer is designed by PMN-PT/Epoxy 1–3 piezoelectric composite with a dimension of 550 μm × 450 μm × 35 μm. The fabricated transducer has not only a high center frequency larger than 42 MHz, but also high bandwidth of -6 dB of 90.6 %, the insertion loss with the value of 16 dB and excellent transmitting sensitivity of 314 mV/V. The results are in good agreement with the values simulated by PiezoCAD software. In addition, the acoustic performance of the transducer was also obtained by measuring the acoustic filed distribution in purified water. The -3 dB acoustic beam dimension width, the value of focal length and the acoustic power were 0.38 mm × 0.42 mm, 2.3 mm and 4.4 × 10−3mW, respectively. The performance PMN-PT/Epoxy 1–3 piezoelectric composite ultrasound transducer fabricated by dice and fill method (DAF) achieved the effect of ultrasonic transducer fabricated by deep reactive ion etching (DRIE). The excellent acoustic performance demonstrated that the DAF prepared PMN-PT/Epoxy 1–3 piezoelectric composite have great industry application potential in high frequency ultrasonic electronics, such as microelectronics NDT and biomedical imaging.

A new broadband radial vibration ultrasonic transducer based on 2-2 piezoelectric composite material

Radial vibration transducer has the advantages of large radiation area, high radiation efficiency, uniform radial radiation, and wide range of action. Therefore, it is widely used in the technical fields of ultrasonic liquid treatment such as underwater acoustics, ultrasonic degradation and sonochemistry. On the other hand, the 2-2 piezoelectric composite material is one of the most commonly researched piezoelectric composite materials with the best development prospects. Compared with traditional pure piezoelectric ceramics, this new type of material has the advantages of low impedance, low mechanical quality factor, and frequency bandwidth. Therefore, in this paper we propose a new broadband radial vibration ultrasonic transducer based on 2-2 piezoelectric composite material, which is mainly composed of an inner metal ring and an outer piezoelectric ceramic composite ring. First, the Newnham series-parallel theory and the uniform field theory are used to derive the equivalent parameters of the 2-2 piezoelectric composite material. Second, the radial vibration of the combination of the metal ring and the radially polarized piezoelectric composite ceramic ring are analyzed by the analytical method. The six-terminal electromechanical equivalent circuit of the transducer is obtained, and the frequency equation of the transducer is also obtained. And then the relationship between the resonant frequency and anti-resonant frequency of the transducer, as well as the effective electromechanical coupling coefficient, geometric size, and two-phase volume ratio are analyzed. It is concluded that in order to obtain higher electromechanical conversion efficiency, the design of the transducer radius ratio should be as close as possible to 0.35. Although the higher proportion of polymer phase will lead the electromechanical conversion efficiency to decrease, it can also bring better acoustic matching ability. Therefore, the lower proportion of polymer phase can be selected in the transducer design. The finite element method is used to numerically simulate the radial vibration of the new transducer. The results show that the resonance frequency and anti-resonance frequency obtained by the analytical method are in good agreement with the numerical simulation results. In addition, the acoustic field of the transducer under water is simulated numerically. The results show that compared with the traditional pure ceramic radial transducer, the new composite radial transducer has a large emission voltage response amplitude, the working bandwidth is nearly doubled, and the acoustic matching is better.

Theoretical analysis and experimental validation of radial cascaded composite ultrasonic transducer* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11674206 and 11874253).

A radial cascaded composite ultrasonic transducer is analyzed. The transducer consists of three short metal tubes and two radially polarized piezoelectric ceramic short tubes arranged alternately along the radial direction. The short metal tubes and the piezoelectric ceramic short tubes are connected in parallel electrically and in series mechanically, which can multiply the input sound power and sound intensity. Based on the theory of plane stress, the electro-mechanical equivalent circuit of radial vibration of the transducer is derived firstly. The resonance/anti-resonance frequency equation and the expression of the effective electromechanical coupling coefficient are obtained. Excellent electromechanical characteristics are determined by changing the radial geometric dimensions. Two prototypes of the transducers are designed and manufactured to support the analytical theory. It is concluded that the theoretical resonance/anti-resonance frequencies are consistent with the numerical and experimental results. When R 2 is at certain values, both the anti-resonance frequency and effective electromechanical coupling coefficient corresponding to the second mode have maximal values. The radial cascaded composite ultrasonic transducer is expected to be used in the fields of ultrasonic water treatment and underwater acoustics.

Properties of PMN-PT single crystal piezoelectric material and its application in underwater acoustic transducer

In order to further understand the characteristics of PMN-PT piezoelectric single crystal materials, the piezoelectric constant d33, impedance and frequency characteristics of PMN-PT piezoelectric single crystal elements under different pressures are studied in this paper, and the performances of PMN-PT piezoelectric single crystal elements are compared with PZT-4 piezoelectric ceramic elements. The non prestressed PMN-PT piezoelectric single crystal sandwich dipole transducer is studied and compared with PZT-4 piezoelectric ceramic sandwich dipole transducer of the same size. The matching layer broadband PMN-PT piezoelectric single crystal circular composite rod transducer is studied. The stress distribution of the transducer under 10 N pressure is calculated, and the problem of local crack of the piezoelectric single crystal element is solved from the structural design. The results show that the PMN-PT piezoelectric single crystal material has obvious advantages in low frequency performance, acoustoelectric and electroacoustic conversion efficiency, and can improve the emission and reception performance of acoustic transducer at the same time. The maximum transmitting voltage response and receiving sensitivity of the non prestressed sandwich dipole transducer can reach 144 dB and −166 dB respectively. Compared with piezoelectric ceramic transducer, the resonance frequency is reduced by about 3 kHz, and the transmitting and receiving performance are improved by 3 dB and 6 dB respectively. The matching layer broadband PMN-PT piezoelectric single crystal circular composite rod transducer has a transmitting voltage response of more than 136 dB, fluctuation of less than 5 dB, receiving sensitivity of more than −176 dB and fluctuation of less than 6 dB in the frequency range from 20 kHz to 40 kHz. The research results of this paper have important reference value and guiding significance for the popularization of PMN-PT piezoelectric single crystal material and its application in acoustic transducer.

Parylene coating for 13 MHz 1-3 composite transducer performance enhancement

1-3 piezoelectric composite material is widely applied in medical ultrasound transducers. The acoustic impedance mismatching still exists between composite materials and human tissue, this mismatching limits the performance of the 1-3 composite transducer. In this work, Parylene coating technique is employed to enhance the performance of a 1-3 piezoelectric composite transducer whose center frequency is 13 MHz. Theory and simulation analysis is carried out to estimation and optimize the influence of the Parylene coating layer. Pulse- echo experiment is performed to verify the hypothesis of theory and simulation. The experiment results confirm that the performances of the transducer are effectively enhanced by Parylene coating and the optimum thickness of the coating Parylene layer is about 39.5 μm. Compared to the uncoated 1-3 composite transducer, the echo amplitude of 39.5 μm Parylene coated transducer increases 98.8%, the value of −6 dB pulse width decreases 39.5%, the value of −20 dB pulse width decreases 22.7%, the bandwidth increases 51.9%, and the center frequency is not affected. These results prove the feasibility and effectiveness of the Parylene coating layer in transducer performance enhancement.

Design of 2D Sparse Array Transducers for Anomaly Detection in Medical Phantoms.

Aperiodic sparse 2D ultrasonic array configurations, including random array, log spiral array, and sunflower array, have been considered for their potential as conformable transducers able to image within a focal range of 30–80 mm, at an operating frequency of 2 MHz. Optimisation of the imaging performance of potential array patterns has been undertaken based on their simulated far field directivity functions. Two evaluation criteria, peak sidelobe level (PSL) and integrated sidelobe ratio (ISLR), are used to access the performance of each array configuration. Subsequently, a log spiral array pattern with −19.33 dB PSL and 2.71 dB ISLR has been selected as the overall optimal design. Two prototype transducers with the selected log spiral array pattern have been fabricated and characterised, one using a fibre composite element composite array transducer (CECAT) structure, the other using a conventional 1–3 composite (C1–3) structure. The CECAT device demonstrates improved coupling coefficient (0.64 to 0.59), reduced mechanical cross-talk between neighbouring array elements (by 10 dB) and improved operational bandwidth (by 16.5%), while the C1–3 device performs better in terms of sensitivity (~50%). Image processing algorithms, such as Hough transform and morphological opening, have been implemented to automatically detect and dimension particles located within a fluid-filled tube structure, in a variety of experimental scenarios, including bespoke phantoms using tissue mimicking material. Experiments using the fabricated CECAT log spiral 2D array transducer demonstrated that this algorithmic approach was able to detect the walls of the tube structure and stationary anomalies within the tube with a precision of ~0.1 mm.