Vibration Transducer Research Articles

Design of piezoelectric transducers using topology optimization

Among other applications piezoelectric transducers are widely used for acoustic wave generation and as resonators. These applications require goals in the transducer design such as high electromechanical energy conversion for a certain transducer vibration mode, specified resonance frequencies and narrowband or broadband response. In this work, we have proposed a method for designing piezoelectric transducers that tries to obtain these characteristics, based upon topology optimization techniques and the finite element method (FEM). This method consists of finding the distribution of the material and void phases in the design domain that optimizes a defined objective function. The optimized solution is obtained using sequential linear programming (SLP). Considering acoustic wave generation and resonator applications, three kinds of objective function were defined: maximize the energy conversion for a specific mode or a set of modes; design a transducer with specified frequencies and design a transducer with narrowband or broadband response. Although only two-dimensional plane strain transducer topologies have been considered to illustrate the implementation of the method, it can be extended to three-dimensional topologies. Transducer designs were obtained that conform to the desired design requirements and have better performance characteristics than other common designs.

On the sound radiated by electrical equipment : an active structural acoustic control of harmonic sound

In this paper a technique is presented for the active structural acoustic control of harmonic sound radiated from an electrical machine. In the study, we consider the noise radiated by the heat-exchanger enclosure of a a large size induction motor; the sound is radiated harmonically by the enclosure panels, excited by structure borne vibrations. The control source is a spatially distributed piezoelectric ceramic patch actuator attached to the enclosure panels, and the sensor is a vibration transducer or a microphone. A digital controller and digital processing software are designed based on a feedback algorithm. The paper describes: the functional characteristics of the piezoelectric patch actuators for this application, the finite element model of the enclosure for determining the optimum system configuration, the experimental dynamic analysis to map the panel vibrations, the baseline noise measurements, and the implementation of the control algorithm. Final results are presented showing a 20 dB noise reduction of the harmonic sound radiated from the electrical machine.

Thick-film strain transducers made using piezoelectric paint

This paper describes the manufacture and testing of a novel strain transducer based on piezoelectric paint for use in structural vibration monitoring. This is a form of thick-film sensor, similar in structure to conventional thick-film sensors based on piezoelectric ink. However, the use of paint avoids two problems associated with the ink based manufacturing process: screen printing and high temperature curing. The materials selection and application techniques development are outlined for the three principal components of the transducer: the resin binder, the piezoelectric material and the electrode. The final design comprised a sprayable suspension of milled PZT powder in lacquer (the piezoelectric paint) with a gold electrode formed by physical vapour deposition. The transducers were tested for variability and for dynamic properties (bandwidth and dynamic range). It was found that there is considerable scatter between the output sensitivities of individual transducers, but that the dynamic properties were very consistent. It is shown that the techniques developed form the basis for a viable low cost vibration transducer in the range 20 - 600Hz.

Vibration transducer device for stringed musical instruments

A vibration transducer device for stringed musical instrument comprising a magnetic field generating bar, metal strings of the musical instrument and an electronic circuit is described herein. The electronic circuit amplifies a minute electric voltage induced in the metallic strings by the magnetic field when the metallic strings are vibrating.

Ultrasonic motor using a one-dimensional longitudinal-torsional vibration converter with diagonal slits

Characteristics of ultrasonic rotary motors using a longitudinal-torsional vibration converter 15 mm to 50 mm in diameter are described. To obtain large torque, ultrasonic motors using one-dimensional longitudinal-torsional converters with diagonal slits are proposed. The converters have rather simple and tough structures and are driven using only a longitudinal vibration transducer. The vibration converters are made of metal materials and have diagonal slits cut along the converter circumference adjacent to a nodal position of longitudinal vibration. The ultrasonic motors consist of a vibration converter with a driving part at its free edge, and a rotor part pressed statically to a driving surface using corned disk springs. Vibration characteristics and vibration loci at driving surfaces of these motors are measured under loaded and nonloaded conditions and under forward and reverse rotating conditions. Maximum torques over 0.3 to 23 N m were obtained by the converters 15 to 50 mm in diameter and at frequencies of 80 to 23 kHz. Maximum revolution obtained was over 550 rpm using a 15 mm diameter motor of 56 kHz.

Load Characteristics and Vibration Loci at the Driving Surfaces of Ultrasonic Rotary Motor using a Longitudinal-Torsional Vibration Converter

Characteristics of ultrasonic rotary motors using a longitudinal-torsional vibration converter, 15 to 50 mm in diameter, are studied. To obtain a large torque, ultrasonic motors using one-dimensional longitudinal-torsional converters with diagonal slits are proposed. The converters have simple and tough structures and are driven using only a longitudinal vibration transducer. The vibration converters are fabricated from metal materials and have diagonal slits cut along the converter circumference, adjacent to a nodal position of longitudinal vibration. The ultrasonic motors consist of a vibration converter having a driving part at its free edge, and a rotor part statically pressed to the driving surface using corned disk springs. The vibration characteristics and vibration loci at the driving surfaces of these converters and motors are measured under loaded and nonloaded conditions and at forward and reverse rotating conditions, using two laser Doppler vibrometers. Vibration locus shapes are changed according to the load conditions and frequencies. Maximum torques of over 0.2 N·m are obtained by the converters, 15 to 20 mm in diameter, and at frequencies of 56 to 65 kHz. The maximum revolution speed obtained is over 550 r.p.m. using a 15-mm-diameter motor of 56 kHz.

The design of a vibration transducer to monitor the integrity of dental implants.

Bone-anchored titanium implants are being used increasingly to provide support for prostheses replacing missing teeth in edentulous and partially dentate patients. A technique is required to monitor bone formation at the implant-tissue interface during healing, and also to check whether there has been bone loss from around the top of the implant. One possible method is to screw a beam into the implanted fixture and to measure the first flexural resonance frequency of the resulting system. This resonance frequency is affected by both the exposed length of fixture and the stiffness of the interface between the implant and the bone. This paper describes the design of a beam-like transducer for clinical trials of the technique. The sensitivity of the transducer resonance frequency to the changes of interest is dependent on the thickness and length of the beam element. However, the choice of these dimensions is constrained by the need to avoid closely spaced resonances. The performance of different transducer shapes and the influence of the thickness and length of the beam element in the transducer has been studied. The results have been used to finalize a transducer design for the clinical trials.

Vibration transducer using an optical cavity comprising birefringent mirrors

We have developed an optical-cavity system comprising birefringent mirrors for a vibration transducer. To obtain a dispersive-shape signal necessary for reading out the information of mirror vibration, we measure the polarization change of the cavity transmission light caused by the natural birefringence appearing on interferential mirrors; this effect is enhanced by the cavity resonance. Since there are no additional polarization-changing elements inside the cavity, we can achieve the high finesse that is indispensable for a highly sensitive vibration measurement. The principle and an experimental demonstration of the system are reported here.

Body-felt sound unit and vibration transmitting method therefor

The invention relates to a body-felt sound unit having a vibration transmitting member (2) imbedded in a human body support member (8), for example, a chair, a bed, etc., and an electro-mechanical vibration transducer (4) attached to the vibration transmitting member (2), the transducer (4) generating mechanical vibration on receipt of a low-frequency current, thereby transmitting the vibration to the human body (9). The vibration transmitting member (2) comprises a flat plate- or net-shaped member (3) of a relatively large area, and the electro-mechanical vibration transducer (4) is attached to the vibration transmitting member (2) such that the direction of vibration generated from the transducer (4) coincides with the direction of the width of the vibration transmitting member (2) so as to transmit transverse vibration to the vibration transmitting member (2). Even if the vibration transmitting member (2) is thin, the apparent rigidity becomes high, so that the transmission of vibration is effectively made.

Calibration. Primary—Secondary—Field

The primary calibration of acoustic and vibration transducers are well standardized and confirmed by a round-robin inter-laboratory test. Secondary calibration is also very common with traceability to primary calibration. Examples of setups for microphone and accelerometer secondary calibration are discussed regarding accuracy, frequency response testing, etc. Field check methods using reference sources and other methods like Phantom calibration are discussed regarding advantages and shortcomings.

A novel method for characterizing contact-mode shear wave transducers in immersion

The dominating shear motion of a contact-mode shear wave transducer is often accompanied by a weak parasitic longitudinal mode due to its finite size and constrained boundary conditions. The amplitude and phase of this out-of-plane vibration may be exploited for determining the shear polarization direction and for detecting any asymmetry or distortion of the shear transducer’s vibration pattern. In practice, the contact-mode shear probe is immersed in water and energized by an rf pulser to serve as the transmitter. A C-scan is then made of the face of the shear transducer using a focused longitudinal wave transducer as the receiver. The resulting image shows the out-of-plane longitudinal vibration of the shear transducer. For commercial contact-mode shear probes, this pattern usually consists of two crescent-shaped regions of higher vibration amplitude but of opposite phase. A line bisecting the two crescents and passing through their centers defines the shear polarization direction. Finite-element modeling of the shear displacement of a circular disk with constrained boundary confirmed the experimentally observed behavior. This approach provides a simple method for characterizing commercial shear wave transducers. [Work supported by Center for NDE, Iowa State University.]

Design simulation of composite transducers

Many advanced transducers, such as those for medical ultrasound imaging, are made of composite materials. These composites contain both piezoelectric active and inactive constituents and therefore have a nonuniform surface vibration profile. This nonuniform surface vibration will in turn influence many characteristics of the acoustic beam pattern produced by the transducer, such as the focusing ability, sidelobes, and the near-field pressure distribution. These complex transducer systems cannot be modeled properly using equivalent circuit models due to the 3-D nature of the transducer vibration. A 3-D finite-element modeling scheme will be given in this presentation. The modeling contains two stages: First, a finite-element method is used to study the nonuniform structural vibrations of the composite transducer and obtain the surface velocity and displacement distributions; second, this surface velocity and displacement information will be fed to the Helmholtz integral to derive the transducer radiation pattern. It is also possible to compute directly the near-field pressure distribution using FEM. Accurate predictions on the transducer behavior are obtained. In addition, stress and electric field concentrations inside the transducer can be calculated. Comparison with experimental results will be shown via an animation.

Load characteristics of ultrasonic rotary motor using a longitudinal-torsional vibration converter with diagonal slits. Large torque ultrasonic rotary motor

The characteristics of an ultrasonic rotary motor using a longitudinal-torsional vibration converter with a large torque are studied. To obtain a large torque, ultrasonic motors using a slitted longitudinal-torsional vibration converter are proposed. The converters have rather simple structures and are driven using only a longitudinal vibration transducer. The vibration converters have 8 to 16 diagonal slits of 45 ° and 0.5 to 1.0 mm width. The designed ultrasonic motors consist of a vibration converter with a driving part at its free edge, and a rotor part pressed statically to a driving surface using corned disk springs. Characteristics of these motors are measured under loading by various weights. Maximum torques over 0.3 to 23 Nm were obtained by converters of 15 to 60 mm in diameter and of 56 to 23 kHz in frequency. Maximum revolution obtained was over 290 r.p.m. using a 15 mm diameter motor of 56 kHz.

The reconstruction of transducer vibration patterns from the amplitude distribution of the radiated pressure field alone

The reconstruction of transducer vibration patterns can readily be achieved by the well-established technique of applying a back projection algorithm to measurements of the complex pressure distribution over a plane parallel to the source plane. The fidelity of the reconstruction depends upon the accuracy and the precision of the pressure measurements. Pressure amplitude measurements can be made with reasonable accuracy over a large dynamic range using piezoelectric hydrophone probes, but phase measurements may be significantly less accurate, particularly at low pressure intensities. It is therefore of interest to explore the possibilities of source reconstruction from amplitude measurements alone. This contribution reports on the results of source reconstruction achieved by the application of the Gerchberg-Saxton phase recovery algorithm. The use of simulated data enabled some criteria for successful reconstruction to be established. Its potential as a viable technique is discussed in the light of the results to be presented.

Comparison of Absolute Sensitivity Limits of Various Ultrasonic and Vibration Transducers

Comparison of Absolute Sensitivity Limits of Various Ultrasonic and Vibration Transducers

Rationale and utilization of temporomandibular joint vibration analysis in an orthopedic practice.

Temporomandibular joint vibration analysis (JVA) is the electronic recording of TMJ sounds, or, more accurately, vibrations occurring in the joint. Utilizing vibration transducers called accelerometers, a characteristic wave pattern is created for the various types of internal joint vibrations (conditions). Whereas the human ear cannot hear many of the frequencies that occur in the TMJ's, the accelerometers record all frequencies with equal efficiency. Once a vibration has been recorded, then it can be compared to other types of vibrations. This may make it possible to categorize the various types of internal conditions, and then, to monitor the joint status throughout treatment. Sample patients are shown with the initial and then progress joint vibration analyses. This electronic device may help answer the questions of whether orthodontic treatment helps, harms, or has any affect on the internal health of the TMJ. It may also be used to monitor different types of orthodontic treatment to help determine whether one type is more beneficial to the TMJ or not.

The Development of Vibration Analysis Using Contact Transducers Applied To Periodic Machine Condition Monitoring

Recent trends in industry indicate the importance and efficient use of portable vibration analysis as part of an integrated machine condition monitoring program. This paper concentrates on machine vibration analysis and the influence of the various mounting techniques associated with vibration transducers. The vibration signal quality is considered throughout and emphasis is placed on the effect of the applied mounting force when collecting vibration data manually. Also, the types of vibration software systems and the choice of transducer for optimum results are discussed.

Vibration and pressure fluctuation monitoring transducers and instruments for technical diagnostic systems of power-generating units

Vibration and pressure fluctuation monitoring transducers and instruments for technical diagnostic systems of power-generating units

Mode frequency and damping changes due to chemical treatments of the violin bridge

Hammer‐impact modal analysis using a microphone as a no‐load vibration transducer was performed on violin bridge blanks chemically treated two different ways to extract free–free vibrational mode frequencies, dampings and shapes for comparison with untreated bridges. Data were taken for both in‐plane (IP) and out‐of‐plane (OP) vibrations over a 0–20 kHz range. Average effects of these chemical treatments on mode frequency and damping were determined from IP and OP single‐point excitation on six Formalization (FA), six Resorcin/formaldehyde (RE) bridges, and eight untreated (UN) maple violin bridge blanks. All the bridges exhibited three well‐defined IP modes and six OP modes. Few significant changes were observed between the frequency and damping parameters of the IP and OP mode shapes, although the RE treated bridge exhibited a possibly unique doublet at ∼9 kHz. Since no mode frequency variations ≳1.5% were found, even though the RE treatment increased bridge masses 9.1%, it was concluded that the combined mass/stiffness changes of the wood were related to the acoustic effects observed with these bridges [H. Yano and K. Minato, 1222–1227 (1992)].

Use of an eddy-current probe to study the transient vibration of a piezoelectric transducer

A method employing an eddy-current probe is proposed for determining the displacements in piezoelectric transducers working under nonsteady conditions. A description is given of experimental equipment tested in the excitation of a piezoceramic cylinder by electrical pulses. Measurements are compared with theoretical data obtained within the framework of the models of linear electroelasticity and thin shells.