Ceramic Transducers Research Articles

Fabrication and properties of thin-shell monolithic piezoelectric ceramic transducers

Monolithic piezoelectric ceramic transducers with hollow thin shell forms (sphere, cylinder, tube and cone) were successfully fabricated from lead zirconate titanate using slip casting method. Stable and well dispersed water based slurries were prepared under basic conditions with 35–45 vol% solid loading using 0.25–0.50 wt% dispersant. Various characteristic vibration modes, such as length extension, radial expansion, etc., were obtained from the thin shell transducers at 50–200 kHz frequencies. The resonance frequencies of these modes were engineered by changing the shape and dimensions of the shells. Comparison of the numerical calculations and experimental results indicates that slip casting is a viable method to obtain hollow thin shells with reasonable electrical properties.

The radial composite piezoelectric ceramic transducer

The radial composite piezoelectric ceramic transducer is presented and analyzed. The transducer consists of two metal thin circular rings and a thickness polarized piezoelectric thin ring which is sandwiched between the two metal rings in the radial direction. The radial vibrations of a metal thin ring and a piezoelectric ceramic thin ring are analyzed. Their electro-mechanical equivalent circuits are obtained. Based on the electro-mechanical equivalent circuits and the radial boundary conditions, the composite electro-mechanical equivalent circuit of a radial composite piezoelectric transducer is obtained and the resonance and the anti-resonance frequency equations are derived. The relationship between the resonance frequency, the anti-resonance frequency, and the effective electro-mechanical coupling coefficient and the geometrical dimensions of the radial composite transducer is analyzed. It is illustrated that the resonance frequencies and the anti-resonance frequencies from the frequency equations are in a good agreement with experimental results.

27 kHz Ultrasonic Complex Vibration Source Using (1, 1) Mode Transverse Vibration Disk with Multiple Transducers of 40 mm Diameter

The configurations of a small-diameter 27 kHz ultrasonic complex vibration source using a (1,1)-mode transverse vibration disk with four bolt-clamped Langevin-type piezoelectric ceramic (PZT) transducers (BLTs) 40 mm in diameter is developed and studied. The vibration source is driven using two power amplifier systems and a circular vibration locus is obtained at a welding tip. A vibration amplitude of 8.5 µmp–0 (peak-to-zero value) is obtained at a driving voltage of 50 Vrms.

Study on the radial vibration of a new type of composite piezoelectric transducer

In this paper, a new type of composite piezoelectric ceramic transducers is studied. The transducer consists of a piezoelectric ceramic thin ring polarized in the thickness direction and a metal thin circular ring. The radial vibration of the transducer is analyzed and its radial electro-mechanical equivalent circuit is obtained. Based on the electro-mechanical equivalent circuit, the resonance and anti-resonance frequency equations are obtained. The relationship between the resonance frequency, the anti-resonance frequency, and the effective electro-mechanical coupling coefficient and the geometrical dimensions is analyzed. Some radial composite piezoelectric transducers are designed and manufactured. The resonance frequencies and anti-resonance frequencies are measured and the effective electro-mechanical coupling coefficient is calculated. It is illustrated that the measured radial resonance frequencies are in good agreement with the theoretical results from the resonance frequency equation. The finite element method is also used to find the resonance frequency and the radial displacement distribution. It is shown that the resonance and anti-resonance frequencies from the finite element method are also in good agreement with those from the analytical method in this paper.

Multi-layer ceramic acoustic transducer

A method for manufacturing a multi-layer acoustic transducer with reduced total electrical impedance. The method is based on the bonding of two piezoelectric ceramic layers with confronting metallized surfaces to a thin electrical conductor, then electrically connecting the top and bottom surfaces to form a wrap-around electrode while a center conductor forms a second electrode. The total electrical impedance of a two-layer ceramic stack comprised of piezoelectric layers connected in this manner is one-fourth that of a solid ceramic element of the same size. This provides for better matching of the acoustic stack impedance to that of the electrical cable, increased penetration depth for imaging within the body, and improved acoustic element sensitivity.

一対の圧電セラミック素子による一様媒質中の対象の3つのパラメータの推定

一対の圧電セラミック素子による一様媒質中の対象の3つのパラメータの推定

Exfoliation detection using structurally integrated piezoelectric ultrasonic transducers

Advanced sensors and sensor network technologies are shaping the future of civilian and military air platform health assessment and monitoring. In this paper, the feasibility of applying a structurally integrated thick-film piezoelectric ceramic ultrasonic transducer for monitoring exfoliation corrosion damage is investigated. The ultrasonic transducer can easily and reliably be deposited on metallic and polymeric structures using a sol-gel spray approach. The change in material thickness due to exfoliation damage is estimated using ultrasonic time-of-flight measurements. Experimental results from two aluminium (Al.7075-T6511) specimens are presented. In comparison, conventional water-coupled ultrasonic tests were also conducted to generate a thickness map for each selected specimen before the integrated transducers were fabricated. Close correlation was obtained between both conventional and integrated thick-film ultrasonic measurements, demonstrating the effectiveness of the integrated thick-film ultrasonic transducer for exfoliation corrosion damage assessment and monitoring.

Correlation between Cyclic Resistance Ratios of Intact and Reconstituted Offshore Saturated Sands and Silts with the Same Shear Wave Velocity

The cyclic liquefaction resistance of intact medium dense specimens of sands and silts obtained from offshore platform sites was compared to that of specimens reconstituted to the same values of shear wave velocity. The shear wave velocity was measured using a new system that is comprised of torsional piezoelectric ceramic ring transducers mounted in a triaxial cell, a multiwave measuring device, and special watertight connectors. The relationship between cyclic resistance ratio and the number of cycles to liquefaction Nf of intact and reconstituted specimens was compared at the same values of consolidation pressure and shear wave velocity. There was good agreement between cyclic resistance ratios of intact and reconstituted specimens with similar values of shear wave velocity if liquefaction is defined as ⩽6% peak-to-peak axial strain. The results of this study support the hypothesis that the cyclic liquefaction resistance of reconstituted specimens may be restored to in situ conditions when their shear ...

Ultrasonic Piezoceramic Transducer Modeling With VHDL-AMS: Application to Ultrasound Nonlinear Parameter Simulations

This paper presents an ultrasonic transducer modeling with very high-speed integrated circuit (VHSIC) hardware description language-analog and mixed signal (VHDL-AMS) IEEE 1076.1 integrated in a global measurement cell modeling dedicated to biological tissue ultrasound characterization. Usual modeling of ultrasonic transducers is based on electrical analogy and is not simulated in the global measurement environment. The ultrasonic transducer modeling proposed is simulated with a nonlinear acoustic load and electronic excitation. The nonlinear B/A parameter is used to characterize a medium with a comparative method. The measurement cell is composed of two piezoelectric ceramic transducers, which are implemented with Redwood's electric scheme. The analyzed medium is placed between the transducers and modeled to take into account the nonlinear propagation with the B/A parameter. The usual transmission line model has been modified to take into account the nonlinear propagation for a one-dimensional (1-D) wave. Simulations of the transducer pulse response and electrical impedance show a VHDL-AMS model that is in good agreement with measurement and compared to the usual personal computer simulation program with integrated circuit emphasis results simulations. Results obtained by simulation of mediums (blood, milk, liver, and human fat tissue) showed good agreement between modeling and experimental measurement, and a maximum error of about 12.5% for B/A measurement-simulation

Study on the radial composite piezoelectric ceramic transducer in radial vibration

A new type of radial composite piezoelectric transducer in radial vibration is developed and analyzed. The radial composite transducer consists of a piezoelectric ceramic thin ring polarized in the thickness direction and a metal thin circular ring. They are connected together and excited to vibrate in the radial direction. The radial vibrations of a piezoelectric ceramic thin ring and a metal thin circular ring are analyzed, respectively. Their radial electro-mechanical equivalent circuits are obtained. Based on the electro-mechanical equivalent circuits and using the boundary conditions between the piezoelectric ceramic thin ring and the metal thin circular ring in the radial direction, the electro-mechanical equivalent circuit of the radial composite piezoelectric transducer is derived out and the resonance frequency equation is obtained. The relationship between the resonance frequency and the geometrical dimensions of the transducer is analyzed. Some radial composite piezoelectric transducers are designed and manufactured. The resonance frequencies and the anti-resonance frequencies, the electro-mechanical equivalent circuit parameters are measured. The effective electro-mechanical coupling coefficient and the mechanical quality factor are calculated. It is illustrated that the measured radial resonance frequencies are in good agreement with the theoretical results from the resonance frequency equation.

Wave velocities and their relation to fabric evolution during the shearing of sands

The fabric of a sand strongly dominates its stress–strain behavior during monotonic and cyclic shearing. In this study, two pairs of piezoelectric ceramic transducers built into a triaxial cell, which are capable of measuring the compressive and shear wave velocities propagating in the axial direction, were developed. A series of triaxial tests using different stress paths were conducted on sand to investigate their mechanical properties and to simultaneously measure the compressive and shear wave velocities. The measured wave velocities varied, depending on stress path and stress state. A new measure, referred to as the fabric index, was derived using elastic theory for a cross-anisotropic material in association with a micromechanics-based stress–strain model. This index was used to evaluate fabric evolution along various stress paths in three types of sand. The effects of confining pressure, current stress ratio, stress path, and stress history on the fabric index are discussed in detail.

Modeling of Piezoelectric Energy Harvesting Using Cymbal Transducers

This study reports the experimental and analytical results on a piezoelectric cymbal with 29 mm diameter and 1 mm thickness operating under force of 70 N in the frequency range of 10–200 Hz. It was found that the generated power increases with the frequency and around 100 mW can be harvested at frequency of 200 Hz across a 200 kΩ resistor. Power generation from the cymbal transducer was modeled by using the theory developed for the Belleville spring. The calculated results were found to be in good agreement with the experimental results. The results indicate that the metal–ceramic composite transducer “CYMBAL” is the most promising structure for harvesting the electric energy from automobile engine vibrations. The metal cap enhances the endurance of the ceramic to sustain high loads along with stress amplification.

Optimized Parallel Interrogation and Protection of Piezo-transducers in Electromechanical Impedance Technique

This article presents some of the practical issues concerning the implementation of the electromechanical impedance (EMI) technique for structural health monitoring (SHM) using piezoelectric ceramic (PZT) transducers. New sensor interrogation algorithms utilizing the sensor multiplexing technique are proposed to reduce the time required in interrogating the PZT patches one-by-one for localizing damage. Environmental effects on the admittance signatures of the PZT patch are considered, and a simple and economical technique is proposed to protect the PZT patches. Finally, practical application of PZT transducers in the monitoring of concrete curing is demonstrated.

Configurations of Large Capacity Ultrasonic Complex Vibration Sources Using Multiple Longitudinal Transducers Installed in Both Sides of a Transverse Vibration Disk

The configurations of large-capacity 27 kHz ultrasonic complex vibration sources with eight longitudinal transducers and the welding characteristics of aluminum alloy plates using the complex vibration systems are studied. Ultrasonic complex systems are effective for various types of metal welding and are essential for new applications in various industries. The vibration source consists of a (2, 1) mode transverse vibration disk (aluminum alloy), a complex transverse vibration horn with a welding tip (stainless steel) which is installed in the center of the disk, and eight bolt-clamped Langevin-type piezoelectric ceramic (PZT) transducers (BLTs) installed normally in both surfaces of the disk at an angle of 90° with respect to each other. The vibration source is driven using two systems at a phase difference of 90°. The transverse vibration rod installed at the center of the disk is driven transversally and the welding tip of the rod vibrates in a circular locus. Weld strength over 2500 N was obtained per welded spot area on 1.2-mm-thick aluminum alloy plates.

Measurement of Sound Speed in Thread

By employing thin wires, human hairs and threads, the measurement of sound speed in a thread whose diameter is smaller than 0.2 mm has been attempted. Preparing two cylindrical ceramic transducers with a 300 kHz resonance frequency, a perforated glass bead to be knotted by a sample thread is bonded to the center of the end surface of each transducer. After connecting these transducers with a sample thread, a receiving transducer is attached at a ceiling so as to hang another transmitting transducer with the thread. A glass bead is bonded to another end surface of the transmitting transducer so that tension, varied with a hanged plumb, can be applied to the sample thread. The time delay of the received signal relative to the transmitting pulse is measured while gradually shortening the thread. Sound speed is determined by the proportionality of time delay with thread length. Although the measured values for metallic wires are somewhat different from the values derived from the density and Young's modulus cited in references, they are reproducible. The sound speed for human hairs of over twenty samples, which varies between 2000 and 2500 m/s, seems to depend on hair quality. Sound speed in a cotton thread is found to approach a constant value under large tension. An advanced measurement system available for uncut threads is also presented, where semi cylindrical transducers pinch the thread.

Embedded piezoelectric ceramic transducers in sandwiched beams

Surface bonded piezoelectric ceramic (PZT) transducers are currently the most prominentarea of research in structural health monitoring using electromechanical impedancemethods. This paper presents a new embedded PZT patch and its interaction with thehost sandwiched beam. Durability and protection from surface finish, vandalismand the environment are important features of the embedment. The paper alsodemonstrates the use of thickness vibration of the PZT patch in electromechanicaladmittance formulations. This embedded PZT–structure interaction model is basedon the new concept of ‘average sum impedance’. The formulations used for thismodel can be conveniently employed to extract the mechanical impedance of any‘unknown’ PZT patch embeddable plane structure. The mechanical impedanceof the structure is obtained from the admittance signatures of the embeddedPZT patch. The proposed model is experimentally verified on sandwiched beams.

Characterization of PZT ceramic transducer embedded in concrete

The characteristics of the PZT ceramic element embedded in concrete are researched. Based on the theory that the physical coefficients of the ceramic change their values under different stress level, a method of measuring the concrete stress by detecting the characteristics of the embedded ceramic element is proposed. The experiment uses a network analyzer to monitor the changes of the parameters during the loading circle in which loadings are applied on a concrete specimen with an embedded PZT ceramic. In order to describe the characteristic change from the aspect of energy losses, three dissipation factors are also obtained from the piezoelectric equations. The experimental results show that although some equivalent parameters show a better monotonicity. But the measurement error analysis indicates that such monotonicity is not reproductive. The piezoelectric dissipation factor performs a relative good monotonicity and reproducibility, and is recommended as stress indicator for stress measurement.

High-temperature piezoelectric film ultrasonic transducers by a sol-gel spray technique and their application to process monitoring of polymer injection molding

Thick-film (90 /spl mu/m) piezoelectric ceramic high-temperature ultrasonic transducers (HTUTs) have been successfully deposited on metallic substrates by a sol-gel spray technique. The gel is composed of fine powders of bismuth titanate dispersed in a lead-zirconate-titanate solution. The films with desired thickness have been obtained through multilayer coating approach. Piezoelectricity is achieved using the corona discharge poling method. The center frequencies of ultrasonic signals generated by these HTUTs are around 10 MHz and their signal-to-noise ratio (SNR) is more than 30 dB in pulse-echo mode at 500/spl deg/C. The main advantages of these new HTUTs are that they 1) are applicable at temperatures higher than 500/spl deg/C, 2) are miniature, 3) can be coated on flat and curved surfaces, 4) do not need ultrasonic couplant, 5) can be operated at low and medium megahertz frequency range with sufficient frequency bandwidth, and 6) have sufficient piezoelectric strength and SNR. The ability of the HTUTs to monitor the polymer injection molding process in real-time at the mold insert of the machine is demonstrated.

Design and fabrication of broadband graded ultrasonic transducers with rectangular kerfs

Broadband ultrasound imaging is capable of achieving superior resolution in clinical applications. An effective and easy way of manufacturing broadband transducers is desired for these applications. In this work, a graded material in which the piezoelectric plate is mechanically graded with rectangular grooves is introduced. Finite element analysis (FEA) demonstrated that the graded piezoelectric material could achieve a broadband, time-domain response resulting from multiple resonant modes. Experimental tests were carried out to validate these theoretical results. Based upon the FEA designs, several single-element transducers were fabricated using either a nondiced ceramic or a diced, graded ceramics. A superior bandwidth of 92% was achieved by the graded transducer when compared to a bandwidth of 56% produced by the nondiced ceramic transducer at the expense of a reduced sensitivity.

Droplet formation and ejection from a micromachined ultrasonic droplet generator: Visualization and scaling

Visualization and scaling of drop-on-demand and continuous-jet fluid atomization of water are presented to elucidate the fluid physics of the ejection process and characterize the modes of operation of a novel micromachined ultrasonic droplet generator. The device comprises a fluid reservoir that is formed between a bulk ceramic piezoelectric transducer and an array of liquid horn structures wet etched into (100) silicon. At resonance, the transducer generates a standing ultrasonic pressure wave within the cavity and the wave is focused at the tip of the nozzle by the horn structure. Device operation has been demonstrated by water droplet ejection from 5to10μm orifices at multiple resonant frequencies between 1 and 5MHz. The intimate interactions between focused ultrasonic pressure waves and capillary waves formed at the liquid–air interface located at the nozzle tip are found to govern the ejection dynamics, leading to different ejection modalities ranging from individual droplets to continuous jet. Specifically, we report the results of high-resolution stroboscopic optical imaging of the liquid–air interface evolution during acoustic pumping to elucidate the role of capillary waves in the droplet formation and ejection process. A basic understanding of the governing physics gained through careful visualization and scaling forms the basis for development of improved theoretical models for the droplet formation and ejection processes by accounting for key fluid mechanical features of the phenomena.