Composite Ultrasonic Transducer Research Articles

0.36BiScO3-0.64PbTiO3/Epoxy 1-3-2 High-Temperature Composite Ultrasonic Transducer for Non-destructive Testing Applications.

The development of high-temperature nondestructive testing (NDT) requires ultrasonic transducers with good temperature resistance and high sensitivity for improved detection efficiency. Piezoelectric composite can improve the performance of transducers because of its high electromechanical coupling coefficient and adjustable acoustic impedance. In this study, 1-3-2 composites and 1-3-2 high-temperature composite ultrasonic transducers (HTCUTs) based on 0.36BiScO3-0.64PbTiO3 (BSPT), which are preferred piezoelectric materials at 200°C-300°C, and high-temperature epoxy with a center frequency of 6 MHz were designed and fabricated. From 25°C to 250°C, 1-3-2 composites show a higher electromechanical coupling coefficient kt especially at high temperatures (~0.53 at 25°C, and ~0.64 at 250°C) than monolithic BSPT (~0.5). The signal of the pulse-echo response of 1-3-2 HTCUTs is distinguishable up to 250 °C and remains stable (Vpp~500 mV) below 150°C, exhibiting higher sensitivity (improved by 7 dB) than that of monolithic BSPT high-temperature ultrasonic transducers (HTUTs). Bandwidth has been greatly enhanced especially at high temperatures (~103250°C) compared with that of monolithic BSPT HTUTs(~30250°C). To verify the excellent performance, B-mode scanning imaging measurement of a stepped steel block and defect location detection of a steel block were performed, showing the potential for high-temperature NDT applications.

BiScO3-PbTiO3 based high temperature piezoelectric ceramics composite ultrasonic transducer

Utilizing the electrical resonance method, matrices encompassing elastic, piezoelectric, and dielectric properties were calculated for 0.36BiScO3-0.64PbTiO3 (BSPT) ceramics. The design parameters for the BSPT/epoxy 2-2 composite material were meticulously elucidated through simulations conducted via COMSOL software. Characterization outcomes unveil that the synthesized composite material exhibits diminished acoustic impedance and heightened electromechanical coupling in comparison to its piezoelectric ceramic counterparts. Subsequent to the design and fabrication of ultrasonic transducers employing both BSPT ceramics and BSPT/epoxy 2-2 composite material, a thorough investigation into their electrical and acoustic attributes ensued at ambient temperature and 200 °C. Test results manifest that the BSPT/epoxy 2-2 composite high temperature ultrasonic transducer (CHTUT) demonstrates a center frequency and bandwidth of 4.52 MHz and 54.71%, respectively, at room temperature. While, at 200 °C, these parameters are 3.54 MHz and 80.79%. The HTUT, under parallel scrutiny, exhibits a center frequency and bandwidth of 4.65 MHz and 34.23% at room temperature, respectively, and 4.52 MHz and 29.65% at 200 °C. These findings prove the robust ultrasonic performance of the CHTUT, even under elevated temperatures, with the BSPT ceramic based counterpart demonstrating superior temperature stability. Furthermore, the results of an imaging experiment involving steel step blocks at both room temperature and 200 °C align consistently with the acoustic test outcomes.

Ultrabroad-bandwidth ultrasonic transducer based on Sm-doped PMN-PT ceramic/epoxy 1–3 composite

Ultrasonic transducers for nondestructive testing (NDT) require wide bandwidth and high sensitivity to obtain good axial resolution and strong signal reception, which requires active materials with high electromechanical coupling performance. In this work, 2.5 mol% Sm-doped Pb(Mg1/3Nb2/3)O3-30PbTiO3 (PMN-30PT:2.5Sm) piezoelectric ceramics with excellent piezoelectric properties (d33 =1065 pC/N, and k33 = 77 %) were synthesized and a ceramic/epoxy 1–3 composite ultrasonic transducer was fabricated. The center frequency is around 2.3 MHz, the − 6 dB bandwidth reaches 135.9 %, and the insertion loss is −18.7 dB. Compared with the transducer made of PZT-5H composite, the −6 dB bandwidth is increased by 45.3 % and the insertion loss is increased by 2.2 dB. The imaging experiments also show that the PMN-30PT:2.5Sm ceramic transducer has a better axial resolution (at −6 dB).

LiNbO3-based sol-gel composite ultrasonic transducer poled at low temperatures

A LiNbO3 (LN) based sol-gel composite could be suitable for high temperature ultrasonic transducer application at 700 °C, however, poling requires high temperature above 550 °C and it shows relatively low signal strength. In order to realize the polarization temperature reduction of an LN-based sol-gel composite ultrasonic transducer, alumina (AO) and strontium doped titanium oxide (TO) were chosen as sol-gel phase material, and LN/AO and LN/TO films were fabricated onto Inconel substrates. In each polling process, corona discharge after heat treatment in the furnace at 400 °C and at 200 °C was executed for LN/AO and LN/TO, respectively. Ultrasonic measurements up to 700 °C were performed and both transducers were able to confirm the reflected echoes and ultrasonic performance stability at 700 °C. Especially LN/TO showed the highest signal strength compared to previously developed high temperature lead-free sol-gel composite materials, Bi4Ti3O12 (BiT)/BiT and CaBi2Ta2O9 (CBTa)/BiT.

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.

Radial Vibration Characteristics of Piezoelectric Ceramic Composite Ultrasonic Transducer

Different from the existing equivalent circuit analysis method of the transducer, based on the vibration theory of the mechanical system and combined with the constitutive equation, this paper analyzes the radial vibration characteristics of the transducer. The piezoelectric ceramic composite ultrasonic transducer is simplified as a mechanical model of a composite thick wall tube composed of a piezoelectric ceramic tube and a metal prestressed tube. The mathematical model of radial vibration of the transducer is established, which consists of the wave equation of radial coupling vibration of the piezoelectric ceramic tube and the metal prestressed tube, the continuity conditions, and the boundary conditions of radial vibration of composite thick wall tube. The characteristic equation and the mode function of radial vibration are derived. The calculated results of natural frequency are in good agreement with the existing experimental results. Based on the analytical method and the difference method, the numerical simulation models of radial vibration are established, and the amplitude-frequency characteristic curves and the displacement responses are given. The simulation results show that the amplitude-frequency characteristic curves and the displacement responses of the two methods are the same, which verifies the correctness of simulation results. Through the simulation analysis, the influence rule of the transducer’s structure sizes on its radial vibration natural frequency is given: when the thickness of the metal prestressed tube and the piezoelectric ceramic tube are constant, the natural frequency decreases with the increase of the inner diameter of the piezoelectric ceramic tube; when the outer diameter of the metal prestressed tube and the inner diameter of the piezoelectric ceramic tube are constant, the natural frequency decreases with the increase of the thickness-to-wall ratio. The calculation method of natural frequency based on elastic vibration theory is clear in concept and simple in calculation, and the simulation models can analyze the mechanical vibration of the transducer.

Polarity effect of corona discharge poling for sol-gel composite-based ultrasonic transducers

Corona discharge was produced in air atmosphere by applying positive and negative high voltage to a needle to investigate the poling effects for two kinds of sol-gel composite materials, Pb(Zr, Ti)O3(PZT)/PZT and Bi4Ti3O12 (BiT)/PZT. Concerning piezoelectric constant d33, only polarity was different. The samples poled by negative corona discharge showed superior temperature durability above certain temperatures even though no significant difference was observed regarding ultrasonic performance characteristics such as center frequency, 6 dB frequency bandwidth. When the pulse voltage supplied by pulser/receiver increased, that difference starting temperature decreased and negative corona poling effect increased. Negative corona discharge poling was effective to improve thermal durability of sol-gel composite ultrasonic transducers when normal pulser/receiver with negative excitation pulse voltage was used for measurements.

High-performance potassium sodium niobate piezoceramics for ultrasonic transducer

Ultrasonic transducers can be used as medical diagnostic imaging and nondestructive testing. This work presents phase structure engineered high-performance potassium sodium niobate [(K,Na)NbO3, KNN]-based ceramics and its potential application on ultrasonic transducer. A connection among structural engineering, electrical properties, and prototype device designing was established in lead-free KNN-based ceramics. Structural elucidation through atomic resolution polarization mapping by Z-contrast imaging indicates that the nanoscale balanced multiple phase coexistence (R-O-T) is the origin of both enhanced piezoelectricity and improved temperature stability: high d33 of 500 pC/N and improved in-situ temperature stability of d33 (less than 24% variation for d33 from 25 to 100 °C), together with the improvement of electromechanical coupling coefficient (kp~0.5 and kt~0.55). Based on the high-performance ceramics, a 1–3 composite ultrasonic transducer with a center frequency of 5 MHz is produced, and a bandwidth of 81% at −6 dB is substantially higher than that of PZT-based transducers at the same center frequency. We believe the novel way to improve electrical properties through structural engineering could open a new road to promote the practical application of KNN-based ceramics.

Preparation and Performance Test of Orthotropic Piezoelectric Composite Material Ultrasonic Phased Array Transducer

Preparation and Performance Test of Orthotropic Piezoelectric Composite Material Ultrasonic Phased Array Transducer

Analysis and experimental validation of longitudinally composite ultrasonic transducers.

The longitudinally cascaded piezoelectric ultrasonic transducer is studied which is composed of two longitudinally sandwiched piezoelectric transducers connected together mechanically in series and electrically in parallel. When the losses and load are taken into account, the electromechanical equivalent circuit of the transducer is obtained; the input electric impedance is analyzed and the resonance/anti-resonance frequency equations are obtained assuming one dimensional longitudinal vibrational theory. The relationship among the resonance/anti-resonance frequency, the effective electromechanical coupling coefficient, the mechanical quality factor and the electro-acoustic efficiency with the geometrical dimension, the losses, and the load is analyzed. Two longitudinally composite transducers are designed, made, and measured. It is shown that the theoretical resonance/anti-resonance frequencies, the effective electromechanical coupling coefficient, and the mechanical quality factor are in good agreement with the experimental results. It is expected that this kind of composite transducer can be used in large power and high intensity ultrasonic applications, such as ultrasonic liquid processing, ultrasonic metal machining, and ultrasonic welding and soldering.

A 2D dual-mode composite ultrasonic transducer excited by a single piezoceramic stack

A 2D composite ultrasonic transducer with two resonance modes is proposed by using a central coupling metal block, a piezoceramic stack and four outer metal cylinders. With the introduction of the dual-mode equivalent mechanical coupling coefficient and the 2D longitudinal force transform coefficient, a novel equivalent circuit model is developed for the design and analysis of the 2D coupled vibration of the transducer. After verifying the proposed equivalent circuit model with the FE method and the corresponding experiments, the vibration characteristics of the proposed transducer are investigated by using the equivalent circuit mode, the FE methods, and the experiments. The results demonstrate that the proposed transducer has the advantage of generating 2D ultrasonic radiation with two different fundamental resonance modes, which is useful in some new ultrasonic applications such as ultrasonic emulsification, ultrasonic defoaming and ultrasonic sonochemistry where multi-frequency and multidimensional sound radiation is needed.

Ultrasound Imaging of Pipeline Crack Based on Composite Transducer Array

Cracks, especially small cracks are difficult to be detected in oil and gas transportation pipelines buried underground or covered with layers of material by using the traditional ultrasonic inspection techniques. Therefore, a new composite ultrasonic transducer array with three acoustic beam incidence modes is developed. The space model of the array is also established to obtain the defect reflection point location. And the crack ultrasound image is thus formed through a series of small cubical elements expanded around the point locations by using the projection of binarization values extracted from the received ultrasonic echo signals. Laboratory experiments are performed on a pipeline sample with different types of cracks to verify the effectiveness and performance of the proposed technique. From the image, the presence of small cracks can be clearly observed, in addition to the sizes and orientations of the cracks. The proposed technique can not only inspect common flaws, but also detect cracks with various orientations, which is helpful for defect evaluation in pipeline testing.

Fabrication of PMN-PT/Epoxy 2–2 Composite Ultrasonic Transducers and Analysis Based on Equivalent Circuit Model

Single-crystal (1 − x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN-PT) has great potential for use in ultrasonic applications; however, it is challenging to achieve both broad bandwidth and high sensitivity owing to the mismatch in acoustic impedance between the piezoelectric materials and loading medium. Fabrication of a matching layer for transducers is challenging owing to the increase in the center frequency of the transducer. In this study, a 2–2 PMN-PT-crystal composite was designed and fabricated, exhibiting desirable piezoelectric properties and lower acoustic impedance compared with single-crystal PMN-PT. Transducers based on the 2–2 PMN-PT composite were fabricated and analyzed in detail to investigate their sensitivity and bandwidth. Moreover, the effects of a backing layer on the transducer were investigated. The measured results showed that the bandwidth improved from 21.28% to 35.54% at the cost of reduced sensitivity of the transducer. Systematic analysis of this phenomenon using an equivalent circuit based on the Mason model is presented.

0.36BiScO3–0.64PbTiO3/Epoxy 1–3 Composite for Ultrasonic Transducer Applications

In this paper, 0.36BiScO3–0.64PbTiO3 (BSPT) were chosen as piezoelectric materials because of their higher Curie temperature and comparable piezoelectric properties to commercially available lead-zirconate-titanate polycrystalline ceramics. To get a broader bandwidth, BSPT/epoxy 1–3 composite was fabricated using the dice and fill method to alleviate the acoustic impedance matching problems. The design of the BSPT/epoxy 1–3 composite was guided by W. A. Smith theory to get largest electromechanical coupling coefficients. Finite element simulation was utilized for optimal transducer design. 10-MHz transducers were fabricated using BSPT/epoxy 1–3 composite and monolithic BSPT ceramics with the same fabrication process. Electrical and acoustic properties of the transducers were characterized systematically. The monolithic BSPT ceramics ultrasonic transducer has a center frequency of 10.57 MHz, a electromechanical coupling coefficients of 0.579, and a bandwidth of 24.31%. The BSPT/epoxy 1–3 composite ultrasonic transducer has a little lower center frequency (8.93 MHz), a larger effective electromechanical coupling coefficients (0.608), and a broader bandwidth (41.59%). The simulation result matched well with measured parameter, which indicate the BSPT/epoxy 1–3 composite is a potential material in application of high frequency and high resolution.

A 3D model of new composite ultrasonic transducer

A three-dimensional (3D) model of a high-power ultrasonic, composite, unidirectional transducer is proposed in this paper. The proposed 3D Matlab/Simulink model of the composite transducers predicts the thickness and the radial modes of oscillation as well as their mutual couplings. This longitudinal, prestressed, asymmetrical, piezoelectric transducer, which consists of two active piezoelectric layers, front, back and central oscillating metal mass, is realized. Due to its special structure, the central mass is not bounded using a bolt and performs unidirectional piston motion as compression and expansion occur in cycles keeping the axial dimension of the transducer roughly constant because of mutually opposite polarization of active elements. The electromechanical equivalent circuit of the transducer, representing one-dimensional (1D) model, is derived first and is also presented in this paper, while the resonance frequency equation is obtained analytically. Few composite transducers are designed and manufactured. Their resonance frequencies are measured and compared with the analytically obtained results for a large number of electrical connection combinations. In order to demonstrate the capabilities and limitations of the 1D model, comparison with the results from the 3D model are made. Results show that the measured frequencies are in good correspondence with the analytically obtained from 1D model only for the thickness modes and from the 3D model for the thickness and the radial modes of oscillation and their mutual coupling.

Transparent lead lanthanum zirconate titanate (PLZT) ceramic fibers for high-frequency ultrasonic transducer applications

This paper presents fabrication of transparent lanthanum zirconate titanate (PLZT) fibers using extrusion technique. The diameter of the sintered PLZT fiber is about 400-μm, and the fibers exhibit very good transparency. Measured dielectric constant, remnant polarization and coercive field of PLZT fiber were found to be 2340, 22.5-μC/cm2, and 9.8-kV/cm, respectively. The transparent piezoelectric materials may exhibit great potential for Photoacoustic (PA) imaging and hybrid intravascular imaging combining OCT and ultrasound imaging by using the transparent fiber as the path of light propagation and ultrasonic transducer material. In our study, these transparent PLZT fibers were designed to fabricate two types of high-frequency ultrasonic transducers: small aperture single PLZT fiber/epoxy composite and large aperture 1–3 PLZT fiber/epoxy composite ultrasonic transducers. Besides, a 20-μm tungsten wire phantom and the cornea of the porcine eye were also imaged with the 1–3 PLZT fiber/epoxy composite ultrasonic transducer to demonstrate its imaging capability.

Radial Vibration of a Regular Polygon Composite Piezoelectric Ultrasonic Transducer

Radial Vibration of a Regular Polygon Composite Piezoelectric Ultrasonic Transducer

Air-Coupled Ultrasonic Transducers Based on an Application of the PMN-32%PT Single Crystals

Application of air-coupled ultrasonic measurements is problematic due big acoustic transduction losses of conventional ultrasonic air-coupled transducers. One of the ways to solve this problem is application of more efficient ultrasonic transducers made of PMN-32 %PT crystals. The objective of this work was development of novel effective air-coupled ultrasonic transducer with PMN-32% PT crystal plates. The high electromechanical factor of the transverse extension mode enables to achieve a good performance of air-coupled transducers. The developed and investigated ultrasonic transducer possesses in a transmission mode 10 times better efficiency than a PZT composite ultrasonic transducer.

Sol-gel composite ultrasonic transducers

Sol-gel composite ultrasonic transducers

Micromachining techniques in developing high-frequency piezoelectric composite ultrasonic array transducers

Several micromachining techniques for the fabrication of high-frequency piezoelectric composite ultrasonic array transducers are described in this paper. A variety of different techniques are used in patterning the active piezoelectric material, attaching backing material to the transducer, and assembling an electronic interconnection board for transmission and reception from the array. To establish the feasibility of the process flow, a hybrid test ultrasound array transducer consisting of a 2-D array having an 8 × 8 element pattern and a 5-element annular array was designed, fabricated, and assessed. The arrays are designed for a center frequency of ~60 MHz. The 2-D array elements are 105 × 105 μm in size with 5-μm kerfs between elements. The annular array surrounds the square 2-D array and provides the option of transmitting from the annular array and receiving with the 2-D array. Each annular array element has an area of 0.71 mm(2) with a 16-μm kerf between elements. The active piezoelectric material is (1 - x) Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT)/epoxy 1-3 composite with a PMN-PT pillar lateral dimension of 8 μm and an average gap width of ~4 μm, which was produced by deep reactive ion etching (DRIE) dry etching techniques. A novel electric interconnection strategy for high-density, small-size array elements was proposed. After assembly, the array transducer was tested and characterized. The capacitance, pulse-echo responses, and crosstalk were measured for each array element. The desired center frequency of ~60 MHz was achieved and the -6-dB bandwidth of the received signal was ~50%. At the center frequency, the crosstalk between adjacent 2-D array elements was about -33 dB. The techniques described herein can be used to build larger arrays containing smaller elements.