Ceramic Transducers Research Articles

The Cavermod Device: Force Measurements

The Cavermod device, as described in the companion paper (Filali et al., 1999), allows us to produce the axial collapse of a cavitating vortex at high velocities. From a global point of view, we can consider that it produces a high momentum in the axial direction. Large forces, concentrated on a small area and able to produce erosion pits on hard materials, result from the sudden momentum stopping against a solid wall. In this paper, the results of the forces measurements are given. Four different measurements devices are used to analyze the Cavermod performance in both cases of long and short vortex: dislocations in MgO (Magnesium Oxide) single crystal, two special piezoelectric ceramic transducers and a PVDF film transducer. Special attention is given to the PVDF film response which is found twice the response of other devices. In addition, an attempt is made to interpret the temporal force signal given by a ceramic transducer in terms of local erosive pressure.

Ceramics into next millennium

AbstractOverpopulation is the overriding problem of the twenty-first century, and water is key to human survival. Irrigation, desalination, filtration, and aquaculture are the key technologies and, given the natural abundance of oxides, ceramics are the key materials. High strength saline cements, semipermeable membranes, antibacterial coatings, limestone farming, accretion chemistry, and sonar systems for massive fish farms are concepts worthy of consideration in the twenty-first century. All will involve the use of vast amounts of oxide materials, mainly cement, concrete, synthetic coral, together with ceramic membranes and transducers. The scaling up process for engineering megaworks will be matched by equally interesting scaling down processes in which ceramic, electronic, and optical components are made smaller and smaller until they disappear inside integrated inorganic systems which rival biological systems both in scale and complexity. The age of engineering microworks is upon us, and in the comin...

Functional composites for sensors, actuators and transducers

Following the trend in structural applications, composite structures are being used more commonly in transducer applications to improve acoustic, mechanical and electrical performance of piezoelectric devices. Functional composite transducers for actuators and sensors generally consist of an active ceramic phase incorporated with a passive polymer phase, each of which has a phase transition associated with it. In this paper, several polymer–piezoelectric ceramic composite transducers, mostly designed for sensing hydrostatic waves, are discussed based on the connectivity of the constituent phases. Also discussed are some recent examples of metal–ceramic composites, and single element ceramic transducers with modified shapes for improved performance. A comparison of these designs is given based on their hydrophone figure of merit (dh·gh).

Ultrasonic Measurement of the Dynamic Elastic Moduli of Small Metal Samples

Abstract Ultrasonic velocity measurements were used to determine the dynamic elastic moduli of small metal samples to a 2σ measurement uncertainty of better than 1%. The samples were cylindrical in shape, possessing nominal diameters of 12 mm and thicknesses of 6 mm. Aluminum, titanium, and stainless steel compositions were examined. In the longitudinal wave measurements, a 20-MHz quartz piezoelectric element transducer was employed in pulse-echo mode using a tone-burst excitation. These longitudinal time-of-flight measurements were made with a repeatable 2σ measurement uncertainty of ≤1.0 ns. Shear time-of-flight measurements, using a 10-MHz contact ceramic piezoelectric element transducer subjected to tone-burst excitation, were made with a repeatable 2σ measurement uncertainty of ≈2.0 ns. NIST calibration facilities provided measurements for the density and lengths of these samples, as needed for the moduli calculations. Results indicate that the measurement uncertainties for elastic moduli measurements of this type can be kept quite small.

Time Temperature Stability of Magnetic Properties of Ceramic Magnetic Temperature Transducers

Three ceramic magnetic compositions within the CuZnTi ferrite system, having the Curie temperatures centered around 60, 80 and 100°C, respectively, were investigated in order to determine the time-temperature stability of their main magnetic properties. Permeability and the slope of permeability around their Curie points were determined on ring shaped samples, before and after being subjected to long term (over 6000 h) ageing at their Curie temperature and for a shorter time of about 50 h at higher temperatures up to 700°C. Rates of changes of 33, 66 and 100 ppm h −1 of the maximum slopes of permeability were found for the samples aged at 60, 80 and 100°C, respectively. The samples aged at temperatures higher than 200°C show a rather sudden decrease of maximum slope of permeability, but no shift of the Curie temperature and the working point, corresponding to the temperature where the slope has the maximum value. This is the most interesting result as concerns the use of such magnetic temperature sensors for the construction of highly sensitive temperature controllers, for example ultrathermostats. The results are discussed in terms of the migration processes of the cations, especially Cu 2+, from metastable positions on which they were frozen during the rapid cooling of the sample from the sintering temperature, to the more stable ones, namely the octahedral sites into the spinel lattice. ©

Temperature elevations computed for three-layer and four-layer obstetrical tissue models in nonlinear and linear ultrasonic propagation cases

The authors computed temperature elevations in a three-layer and a four-layer tissue model, assuming the crucial obstetrical case when the ultrasonic pulse propagating through the abdomiinal wall and the fluid-filled bladder penetrates into soft fetal tissues.To consider nonlinear propagation, the authors applied a new theory of nonlinear increase of absorption recently developed by the first author. Computations were carried out for pulses with a carrier frequency of 3 MHz, duration time of 1.33 μs, and pulse repetition frequency of 3.3 kHz. Similar computations were carried out for a four-layer tissue model corresponding to the third trimester of gestation. The ceramic piezoelectric transducer 2 cm in diameter radiated the ultrasonic beam focused at a distance of 6.5 cm. The intensities at the radiating transducer (at the source) were I SAPA= 10 and 5 W/cm 2. Temperature elevations and distributions were determined numerically for various values of low-amplitude absorption coefficients assumed to be the same as attenuation coefficients. It was shown in the three-layer tissue model that the maximum temperature elevation can be about 50% higher for nonlinear than for linear propagation.The maximum fetal temperature elevation in this case was 2.36°C for nonlinear and 1.84°C for linear propagation. The temperature elevation in the abdominal wall was lower than those temperatures when the attenuation of the abdominal wall was assumed to be a low value of 0.05 Np/cm.MHz (0.45 dB/cm.MHz). However, when it was increased to 0.16 Np/cm.MHz (1.4 dB/cm.MHz), the temperature elevation of the abdominal wall reached 3.2°C and the maximum fetal elevation was 1.65°C. In such cases, the abdominal wall became the principal source of heat production. In this case, the difference between fetal temperature elevations for nonlinear and linear propagation was only about 10%. The results obtained in the four-layer tissue model, in which the uterus tissue also was represented, show that temperature elevations in this case are about 3.6 times lower than in the three-layer tissue model, with comparable attenuation of the abdominal wall. Differences between nonlinear and linear propagation in the four-layer tissue model are negligible. The temperature elevations obtained were proportional to the pulse repetition frequency, without changing temperature distributions in the ultrasonic beam. In this manner, fetal temperature elevations can be reduced by reducing the repetition frequency.

A New, Low-Power Consumption, One-Dimensional Sonic Anemometer-thermometer.

A low power (0.1W) and light weight (probe weight 270g and circuit weight 80g) one-dimensional sonic anemometer-thermometer was developed. The measuring span of the anemometer is 10cm, sound frequency is 40kHz and alternation frequency of the sound direction is 78Hz. The low power consumption was attained by using ceramic transducers, which can be driven by low voltage pulses (5V peak-to-peak) and by adapting CMOS logic to the circuit.A field test was carried out in a coniferous forest with a commercial sonic anemometer and a fine thermocouple thermometer. Comparison of the output signal and spectra from each sonic anemometer indicated good agreement.The characteristics of the sonic anemometer-thermometer are low power consumption and light weight. These features are useful for measurements from a small tethered balloon or at places where the electrical power is limited.

Flexural Piezoelectric Transducers with Frequency Agility Obtained via Membrane Loads

Broadband transducers find uses in many applications. One approach to increasing the bandwidth of a flexural transducer is to add damping to the device, usually decreasing its sensitivity in the process. An alternative approach, useful in some applications, involves active tuning of the natural frequency of a high-sensitivity narrowband device. In this research, membrane loads were used to alter the natural frequencies and electromechanical coupling coefficients of three-layer (trilaminar) piezoelectric ceramic transducers. A coupling coefficient is a measure of the effectiveness with which a piezoelectric material or device converts electrical energy to mechanical energy or vice versa. Applying in-plane loads increased the effectiveness of the transducers by increasing their operating frequency range, while maintaining high coupling coefficients. Two types of trilaminar flexural piezoceramic transducers were studied: beams and disks. The measured electrical impedance of individual devices was used to determine shortand open-circuit natural frequencies, and then coupling coefficients. In addition, finite element models were developed and used to predict the same quantities. Rotational springs were used in these models to account for non-ideal experimental boundary conditions, while reduction of the piezoelectric material coupling accounted for loss of performance due to stress depoling and aging. Good agreement between experimental data and theory was obtained. Significant changes in natural frequencies, as well as increases in coupling coefficients were obtained for both beam and disk transducers. Experiments with the trilaminar piezoceramic beams yielded a 36% change in frequency, with an accompanying 38% increase in coupling coefficient. Experiments with the disks yielded a change in frequency of 13%, and an increase in coupling coefficient of 15%. These results demonstrated the feasibility of using membrane loads to improve the frequency-agility of flexural piezoceramic transducers. Candidate applications include acoustic transducers and pneumatic valves.

Prolonged Paralysis After a Test Dose of Mivacurium in a Patient with Atypical Serum Cholinesterase

Prolonged Paralysis After a Test Dose of Mivacurium in a Patient with Atypical Serum Cholinesterase

Shaping of focused ultrasonic beams to expedite thermal necrosis in tumor therapy

Ultrasonic tumor therapy employing focused beams shows great promise for treating tumors by producing spatial matrices of thermal-necrosis lesions. A practical problem involves the long time required to treat extended tumor volumes. To treat ocular tumors, our laboratories are investigating beams with asymmetric shapes to expedite the production of lesion matrices. The beams are generated using rectangular strip electrodes plated on spherical-cap ceramic transducers. The phase and amplitude of the strip excitation voltages are controlled to launch beams whose focal-zone patterns consist of a sequence of lobes confined within elliptical, rather than circular, cross sections. A simple theoretical model has shown that thermal diffusion between these lobes can produce lesions with elliptical cross sections; lesion matrices would be readily produced by translating such transducers along the short axis of the lesion cross section, thereby causing necrosis in broad regions. The concept has been verified in in-vitro experiments (in liver and the ocular lens) and in in-vivo exposures of human tumor explants in nude mice. [Work supported by NIH Grant EY10369.]

Development of a novel system for measurement of the angular scattering of ultrasound by inhomogeneous materials

Measurements of the ultrasonic scattering cross-section of inhomogeneous materials are frequently limited to the determination of backscattering, as this geometry is the easiest to realise experimentally and corrections for instrumentation effects can be derived straightforwardly. However, this approach cannot characterise materials in as complete a manner as measurements of scattering as a function of angle. A novel means of measuring angular scattering of inhomogeneous materials such as biological tissues and tissue mimics has been developed which uses a focused bowl ceramic single-element transducer as transmitter and a pvdf needle probe hydrophone as the receiving transducer. The use of two dissimilar devices for angular measurements requires that the differential scattering cross-section of specimens be derived from first principles for each experimental arrangement. It is shown that such a system can make precise and accurate determinations of the angular scattering of ultrasound by specimens consisting of glass beads in agar.

Driving Electric Field Effects on Piezoelectric Transducers

Electromechanical properties for lead zirconate-titanate Pb(ZrxTi1-x)O3 (PZT) based ceramic and lithium niobate LiNbO3 (LN) crystal piezoelectric transducers were studied from a driving electric field viewpoint. The vibration velocity linearly increases with the driving field for a 128°-rotated Y-cut LN transducer and its maximum vibration velocity which can be used is 2.7 m/s when driven with the driving field of 7 ×102 V/m. The transducer is mechanically broken when driven with a higher field. The vibration velocity for the PZT based ceramic transducer initially increases with an increasing field and then gradually converges onto a certain value accompanied by heat generation. These phenomena are caused by the decrease in the mechanical quality factor with an increasing field. The 0.45PbZrO3–0.45PbTiO3–0.10Pb(Mn1/3Sb2/3)O3 ceramic transducer is capable of generating 0.68 m/s with 5.5 ×103 V/m.

Synthetic phased arrays for intraluminal imaging of coronary arteries

A 64-element, high efficiency, ceramic piezoelectric array transducer operating at 20 MHz has been constructed for ultrasonic intraluminal imaging. The array is mounted on the surface of a 1.2 mm diameter catheter appropriate for coronary artery applications. Integrated into the catheter tip is a custom analog chip set permitting complete data capture from the array. That is, on each firing any combination of array elements can be selected independently as transmitter or receiver. Using data acquired in this way, a complete phased array aperture (i.e., independent transmit and receive apertures) can be synthesized. Reconstruction hardware based on a custom application specific integrated circuit (ASIC) has been designed and built to produce real-time images. Beam forming coefficients are derived using an optimal filtering approach accounting for the circular geometry of the array. Simulated and measured beam patterns for this system are compared. In addition, images of coronary anatomy acquired with the real-time system are displayed demonstrating the marked image quality improvement compared to previous synthetic aperture intraluminal systems.

Q-Value Control of Piezoelectric Vibrator Using Operational Amplifier Circuit

In application of a piezoelectric vibrator to some electronic devices such as gyro-sensors and piezoelectric ceramic transducers, it is very useful if the value of the resonance quality factor (Q-value) can be controlled electrically. For achievement of such an ideal, application of a negative impedance converter circuit (NIC circuit) to a piezoelectric vibrator is considered in this work. We applied several negative circuit elements to a piezoelectric vibrator in order to control the Q-value and achieve high performance of it. That is, this work deals with Q-value control of a piezoelectric vibrator by series connection of the NIC circuit, consisting of an operational amplifier, to the vibrator.

Characteristics of Two-Vibration-System Ultrasonic Plastic Welding with 90 kHz and 20 kHz Vibration Systems at Right Angles

The direct welding characteristics of an ultrasonic plastic welding system with an upper 90 kHz longitudinal welding tip with a small vibration amplitude and a lower 20 kHz low frequency torsional vibration welding tip with a large vibration amplitude at right angles are studied. By using a combination of high and low vibration frequency systems with small and large vibration amplitude welding tips, the welding characteristics are improved, resulting in a smaller required vibration amplitude and less damage to the specimens due to vibration than those using conventional systems. The two-vibration-system welding equipment consists of a 90 kHz upper longitudinal vibration source with six bolt-clamped Langevin-type piezoelectric ceramic (lead-zircon-titanate; PZT) transducers 15 mm in diameter, a 20 kHz torsional vibration system 40 mm in diameter and a welding frame. The total required velocity amplitude of the two-vibration-system welding equipment is decreased and the welding characteristics are improved significantly compared to those of conventional one-vibration-system for both soft and hard plastic sheet welding.

The acoustical properties of fluid in a wall-driven elastic tube

The acoustics of a fluid in a long cylindrical tube is analyzed. The tube’s wall is thin, elastic, and externally driven by a phased array of ring-shaped piezoelectric ceramic transducers. The rings influence the radial motion of the tube’s wall. Applications of the theory to an active wall impedance tube and a toroidal tube are considered. In the toroidal tube, a digitally controlled electronic system drives the transducer array with a fixed wave number and a continuously variable frequency. If the tube wall were rigid, the fluid pressure reaches a resonant maximum when the wave number and frequency of the driven transducer array matches that allowed by the dispersion relation of sound in the homogeneous fluid. Experimentally determining the fluid’s homogeneous sound speed is more difficult, however, when the wall is not rigid. The idea of using the tube’s external airborne sound to noninvasively measure a fluid’s sound speed is introduced. The theory predicts a minimum in the external sound. At this minimum, the wall is effectively rigid and the transducer array’s phase velocity equals the homogeneous fluid’s phase velocity. Preliminary experimental efforts to make an elastic wall rigid are briefly described.

Effect of diameter-to-thickness ratio of crystal disks on the vibrational characteristics of ultrasonic ceramic transducers

The processes of generation and detection of ultrasonic waves through solids and fluids using piezoelectric ceramic (PZT) transducers essentially require the efficient launching of compressional waves into adjoining media. This primarily depends upon the distribution of vibrational amplitude over the radiating surface of the transducer which, on the other hand, is a function of the diameter-to-thickness ( D t ) ratio of the transducer element (ceramic disk) used. Studies are reported on the vibrational amplitude characteristics of PZT-5 ceramic transducers for airborne applications in the megahertz frequency range employing the phase-locked laser interferometry technique, where ceramic disks with the D t ratio ranging between 2 and 11 have been used. Variations of displacement amplitude behaviour with the change in D t values are discussed. Observed results would be of significant use in fabricating ultrasonic transmitters and receivers to produce the desired surface distribution of vibrational amplitude suitable for specific applications.

Analysis of a three-layered piezoelectric ceramic transformer filter

A transformer filter is fabricated with three piezoelectric ceramic disk transducers and two sheets of thin insulator. Its equivalent circuit is derived from the Mason's model of a thickness-driven piezoelectric transducer. The electric input near its fundamental resonance frequency is applied to the center transducer and the output voltages across the left and right transducers are connected in parallel or in series to the resistor load. The load characteristics at resonance frequencies under various resistor loads and the frequency characteristics near the resonance frequency under no load have been investigated. Moreover, symbolic expressions for input impedances, voltage ratios, resonance frequencies, phase angles between the input and output voltages, and bandwidths have been derived. The values calculated from those symbolic expressions are shown to agree well with the measurement values. >

Optimization of Signal-to-Noise Ratio for Multilayer Pzt Transducers

In medical ultrasound imaging, two-dimensional (2-D) array transducers are desirable to implement dynamic focusing and phase aberration correction in two dimensions as well as volumetric imaging. Unfortunately, the small size of a 2-D array element results in a small clamped capacitance and a large electrical impedance near the resonance frequency. This results in poor signal-to-noise ratio (SNR) of the array elements. It has previously been demonstrated that transducers made from multilayer PZT ceramics have lower electrical impedance and greater SNR than comparable single layer elements. A simplified circuit model has been developed to optimize the SNR for multilayer ceramic (MLC) transducers. In this model, an electronic transmitter excites the array element and in the receive mode, the element drives a coaxial cable load terminated by a high impedance preamplifier. The transducer impedance is Zt/N2, where N is the number of piezoelectric layers. Maximum transmit signal is obtained when N = Ntx such that the transducer impedance, Zt/Ntx2, is matched to the source impedance. Maximum receive signal is obtained when N = Nrx such that the transducer impedance, Zt/Nrx2, is matched to the coaxial cable reactance. For maximum pulse-echo signal, the transducer should be designed with N = square root of Ntx Nrx, the geometric mean of Ntx and Nrx. Using this optimization technique, a 1.5-D array was designed with 3 layers for maximum pulse-echo SNR. Results of simulations from the simplified circuit analysis were consistent with those of the KLM model. The 3 layer array was fabricated as well as a single layer control array. The measured transmit signal and receive signal agreed with the simulation results.

Optimization of Signal-to-Noise Ratio for Multilayer PZT Transducers

In medical ultrasound imaging, two-dimensional (2-D) array transducers are desirable to implement dynamic focusing and phase aberration correction in two dimensions as well as volumetric imaging. Unfortunately, the small size of a 2-D array element results in a small clamped capacitance and a large electrical impedance near the resonance frequency. This results in poor signal-to-noise ratio (SNR) of the array elements. It has previously been demonstrated that transducers made from multilayer PZT ceramics have lower electrical impedance and greater SNR than comparable single layer elements. A simplified circuit model has been developed to optimize the SNR for multilayer ceramic (MLC) transducers. In this model, an electronic transmitter excites the array element and in the receive mode, the element drives a coaxial cable load terminated by a high impedance preamplifier. The transducer impedance is Z t/N 2, where N is the number of piezoelectric layers. Maximum transmit signal is obtained when N = N tx, such that the transducer impedance, Z t/N tx 2, is matched to the source impedance. Maximum receive signal is obtained when N = N rx such that the transducer impedance, Z t/N rx 2 is matched to the coaxial cable reactance. For maximum pulse-echo signal, the transducer should be designed with N = [formula] the geometric mean of N tx and N rx. Using this optimization technique, a 1.5-D array was designed with 3 layers for maximum pulse-echo SNR. Results of simulations from the simplified circuit analysis were consistent with those of the KLM model. The 3 layer array was fabricated as well as a single layer control array. The measured transmit signal and receive signal agreed with the simulation results.