Transducer Configuration Research Articles

Wireless frequency-tuned generation and measurement of torsional waves using magnetostrictive nickel gratings in cylinders

The objective of this work is to experimentally investigate the possibility of using a magnetostrictive nickel grating for frequency-tuned wireless generation/measurement of elastic torsional waves in a non-ferromagnetic aluminum cylinder. In doing so, the effects of the grating size and distance on the frequency-tuning characteristics are studied. Although the employed transduction principle is the magnetostrictive principle used in the existing surface acoustic wave devices which are magnetostrictively transduced, the magnetostrictive nickel grating in our transducer configuration served not as electrical conductors but as deforming elements. The transduction frequency was controlled by the grating distance and the wireless wave generation/measurement was carried out employing solenoid coils encircling a nickel-grated cylinder. In addition, two small permanent magnets were installed to adjust the wave propagation direction.

Theoretical and Experimental Studies of Longitudinal Guided Wave Generation in Hollow Cylinders by Multielement Transducers

Numerical simulation and experimental investigation on defect detection in pipes using ultrasonic guided waves are carried out in the paper. In theoretical analysis, normal mode expansion method is used to quantify the coupling between the applied boundary loadings and acoustic field. The general results are specialized to the loading configuration of multielement transducers. Several important conclusions can be drawn about the design of transducers to generate guided wave modes in pipes. The importance of design parameters such as the number of elements, the ratio of gap width to element width, and the length of each element is discussed in detail. The experimental study demonstrates the use of practical axisymmetric loading in generating axisymmetric longitudinal guided waves, which is particularly useful in the inspection of tubing or piping.

A flexible piezoelectric transducer design for efficient generation and reception of ultrasonic Lamb waves

This paper describes the development of a flexible piezoelectric transducer for the generation and detection of ultrasonic symmetrical Lamb waves in plate-like structures. This piezoplatelet transducer structure comprises an array of miniature piezoceramic plates embedded within a soft setting polymer filler material, combining the efficiency of the active piezoceramic phase with a degree of flexibility, which is a function of the platelet/polymer dimensions. For many condition-monitoring applications, the generation of ultrasonic Lamb waves is often appropriate, and this was achieved by incorporating interdigital design techniques via the transducer electrode pattern. The performance of the piezoplatelet transducer structure was evaluated using a combination of linear systems and finite-element modeling, substantiated by experimental results. Importantly, the transducer is shown to operate as an ensemble of platelets, each operating in the thickness mode and well decoupled from neighboring piezoelectric elements. Using this transducer configuration, an unimodal s1 Lamb wave, at 1.45 MHz, has been generated and detected in a 3-mm thick steel plate. Furthermore, a propagation distance of almost 1 m was recorded for s0 Lamb wave generation/detection in a fiber-reinforced composite plate.

Estimation of the flow profile correction factor of a transit-time ultrasonic flow meter for the feedwater flow measurement in a nuclear power plant

A new method to estimate the flow profile correction factor (FPCF) for a transit-time ultrasonic flow meter (UFM) having a diametral transducer configuration is introduced in this work. For the adaptation of a diametral UFM for a feedwater measurement, the optimized flow profile correction factor is obtained through experiments and a simulation in actual flow conditions. The log function curve fitting is performed on a combined data set; the velocity ratio of UFM reading versus standard fluid measurement at low flow velocity, UFM reading versus standard fluid measurement at medium flow velocity, and UFM reading versus clean Venturi measurement at high flow velocity. Through an uncertainty analysis, the uncertainty of the FPCF is calculated. The resultant uncertainty of the new FPCF is 0.335%. This value is approximately half the value presented by UFM manufacturers. By adaptation of a diametral UFM with the new FPCF proposed in this work, feedwater flow measurement in nuclear power plants (NPPs) can be easily performed at lower cost than either chordal or cross-correlation UFM.

Torsional wave experiments with a new magnetostrictive transducer configuration

For the efficient long-range nondestructive structural health inspection of pipes, guided waves have become widely used. Among the various guided wave modes, the torsional wave is most preferred since its first branch is nondispersive. Our objective in this work is to develop a new magnetostrictive transducer configuration to transmit and receive torsional waves in cylindrical waveguides. The conventional magnetostrictive transducer for the generation and measurement of torsional waves consists of solenoid coils and a nickel strip bonded circumferentially to test pipes. The strip must be premagnetized by a permanent magnet before actual measurements. Because of the premagnetization, the transducer is not suitable for the long-term on-line monitoring of pipes buried underground. To avoid the cumbersome premagnetization and to improve the transduction efficiency, we propose a new transducer configuration using several pieces of nickel strips installed at 45 degrees with respect to the pipe axis. If a static bias magnetic field is also applied, the transducer output can be substantially increased. Several experiments were conducted to study the performance of the proposed transducer configuration. The proposed transducer configuration was also applied for damage detection in an aluminum pipe.

Estimation of the density, the wave speed and the acoustic impedance function in ultrasound imaging

In this paper, we derive integral equations for estimating the density function ρ and the wave speed function c or the acoustic impedance function from boundary measurement data. A nonlinear integral equation for the special case ρ = const and c ≠ const is discussed in detail. We show that the inverse problem of estimating the acoustic impedance function from boundary data measured via a zero-offset transducer configuration can be decomposed into two successively solvable inverse problems. The first inverse problem corresponds to the estimation of the spherical mean function of the acoustic impedance function from a set of one-dimensional integral equations. The second inverse problem corresponds to the estimation of the acoustic impedance function which is closely related to the estimation of the electromagnetic absorption function in transparent media. We conclude the paper with some numerical experiments.

Optimization of transducer configuration for bulk acousto-optic tunable filters

In the present paper, we discuss the effect of an easily implemented type of transducer electrode segmentation on the electrical and optical performance of bulk acousto-optic filters. Segmentation consisting in transducer upper electrode shaping allows realization of filters with very large interaction length with transducer electric impedances not far from the 50 Ω of the generator output’s standard impedance. Detailed experimental investigation of the influence of the electrode shape on the electrical, acoustical and acousto-optical performance has been effectuated through comparison of filters with segmented and non-segmented transducer electrodes. It was demonstrated that the positive effect of the electrode segmentation on the electrical behavior and optical wavelength dependent throughput uniformity is reduced by increased optical aperture inhomogeneity and somewhat decreased optical resolution. Practical application of both segmented and non-segmented transducers has its justification depending on the application type and available electronic environment.

In-room sound reproduction using active control: Simulations in the frequency domain and comparison with wave field synthesis

Active sound control simulations were performed for progressive sound field reproduction over a ‘‘large’’ area using multiple monopole loudspeakers. The model is limited to the simulation of the acoustical output of the prescribed loudspeaker array in a simple room, and is based on achieving an optimal control in the frequency domain. This rather simple approach is chosen for this first feasibility study concerning a limited number of possible configurations of sensing microphones and loudspeakers. Other issues of interest concern the comparison with wave field synthesis, the control mechanisms and transducer configurations. As it is demonstrated, in-room reproduction of sound field using active control can be achieved with a residual normalized squared error below 2% while open-loop wave field synthesis gives more than 100% of error in the same situation. Usage of active control technique suggests the possibility to automatically overcome the room’s natural dynamics. A special surrounding configuration of sensors is introduced for a sensor-free listening area. [Work supported by NSERC, NATEQ, VRQ, and Université de Sherbrooke.]

A high power ultrasonic array based test cell

This paper describes the use of finite element (FE) analysis as a tool in the design process for laboratory based ultrasonic test cells. The system was designed to incorporate an array of ultrasonic transducers to provide a pressure focus in the centre of the cell and importantly, operate both above and below the cavitation threshold of the load medium. Furthermore, the cell incorporates a coolant jacket to accommodate temperature control of the load material associated with the process. A 2D FE model corresponding to a slice through the operational plane of the cell was developed and used to investigate the influence of cell wall material and thickness, transducer configuration, rotation of a metallic stirrer blade and heat transfer fluid on the cell acoustic response. Importantly, experimentally measured pressure field maps demonstrate good correlation with the FE predicted fields. A final manufactured test cell is shown to produce a highly focussed region of cavitation. Finally, the importance in accurately representing the acoustic properties of the constituent materials used in such FE models is demonstrated through an illustrated example.

Thermo-mechanical stress effect on 1–3 piezocomposite power transducer performance

This paper deals with the emission performance of 1–3 piezoelectric composite power transducers made with a hard PZT (Navy III) and epoxy resins with a high glass–rubber transition temperature. Following the “dice and fill” technique, various composite transducers with 30 and 50% PZT volume fractions were fabricated with an air backing and no front matching layer with resonance operating frequencies around 500 kHz. The transducers were first evaluated under isothermal conditions, with a low emission duty cycle. Efficiencies as high as 95% were monitored as a function of the instantaneous input power up to a 60 W/cm 2 density. The effect of the polymer matrix mechanical losses and the fabrication conditions is then discussed. For the transducer thermal stability, the case of long duty cycle or continuous emission was considered in a second evaluation. In this case the transducer working temperature and axial radiated pressure were monitored as functions of the input power density up to 40 W/cm 2. It is shown that the transducer efficiency and working temperature were strongly dependent on the type of resin used but also on the PZT material, even for hard PZT compositions. A composite transducer configuration with strongly improved thermal stability was investigated demonstrating a working temperature higher than 90 °C and an extended power range (30–40 W/cm 2). The composite thermal breakdown mechanism was analyzed and the effect of the curing-induced thermo-mechanical stresses on the PZT mechanical losses was considered in relation to the composite working temperature. Measurements of the composite mechanical losses versus the temperature were obtained and related to the variation of the PZT mechanical losses with the stresses due to the composite transducer temperature change. It is found that the thermally induced stress can strongly influence the PZT ceramic mechanical losses and that it can be the reason for a thermal breakdown taking place at a temperature much lower than the epoxy resin transition.

Application of theoretical modeling to multichannel active control of cooling fan noise

Multichannel active control has been applied to the global reduction of tonal noise from a cooling fan. In order to achieve consistent far-field attenuation of multiple harmonics of the blade passage frequency (BPF) of the fan, an analytical model has been applied to the control system in order to determine appropriate transducer configurations. The results of the modeling show that the additional global reduction possible by locating acoustically compact secondary sources coplanar with a compact primary source rapidly lessens as the number of symmetrically placed sources is increased beyond three. Furthermore, the model suggests that there are locations in the extreme near field of the sources that can be considered ideal for the minimization of far-field radiated power. Experiments carried out show that a four-channel control system is more effective than a two-channel system at achieving far-field attenuations, especially at the higher harmonics of the BPF for the fan tested. In addition, greater far-field mean-square pressure attenuations are achieved with the error microphones located along the calculated ideal regions than for nonideal placement.

Automatic generation of intelligent instruments for IEEE 1451

In this work we present the design of a smart transducers interface module (STIM) that meets the IEEE 1451 normative. The improvement of this prototype is that it can work with any configuration of transducers without the necessity of changing the software and hardware of the STIM. The system automatically adapts its functions from the transducers electronic data sheets (TEDS). We only need to write the appropriate TEDS of our transducers configuration in a non-volatile memory of the STIM. We also have developed a PC TEDS editor that allows us to introduce them in a friendly way in a PC and save them into the STIM through the parallel port.

Optimal Design of Three-IDT Type SAW Filter By using Variable Neighborhood Search.

An optimal design approach for Surface Acoustic Wave (SAW) filters is presented. The frequency response characteristics of SAW filters are governed primarily by their geometrical structures, i.e., the configurations of respective interdigital transducers (IDTs) arranged on piezoelectric substrates. First of all, for realizing a desirable bandpass filter, the structural design of a three-IDT type SAW filter, which consists of three IDTs and two reflectors, is formulated as a combinatorial optimization problem. In order to simulate the frequency response of the SAW filter, the least equivalent circuit model of IDT is employed. Then, a variable neighborhood search based on the k-degree-neighborhood is proposed for solving the optimization problem. Changing the number of examined variables in the process of local search, it avoids being trapped in the first local optimal solution found. Computational experiments conducted on the practical design problem of the three-IDT type SAW filter demonstrate the usefulness of the proposed variable neighborhood search.

Methods of experimental investigation of acoustic interaction between electroacoustical transducers in array

Determination of acoustic loading conditions on projectors in underwater arrays is needed to predict the performance of the array. Nonuniform distribution of the acoustic loading over the radiating surface of the array is generated due to acoustic interactions between the projectors, and often causes performance degradation of the directivity patterns and the transmit frequency response. In the electromechanical equivalent circuit model of such an array, the influence of the neighboring transducers can be considered as the mutual radiation impedance that is inserted in series with the self-radiation impedance. The mutual radiation impedance depends on the configuration of the transducer, the mode of vibration, velocity distribution, and the geometry of the array. We present experimental techniques to determine the mutual radiation impedance as an intrinsic property of a given transducer and array configuration. Two experimental methods are presented: the Z method and the V method. The methods are based on the measurements of the input impedances and on the output voltages of the interacting transducers. For the two methods, analytical investigations based on the electromechanical equivalent circuit analysis will be presented along with supporting experimental results on cylindrical transducers. [Work supported in part by ONR 321SS Lindberg and BTECH Acoustics.]

The disappearance of ultrasound contrast bubbles: observations of bubble dissolution and cavitation nucleation

The destruction process of biSphere™ and Optison™ ultrasound (US) contrast microbubbles were studied at 1.1 MHz. High-amplitude tone bursts caused shell disruption and/or fragmentation of the microbubbles, leading to dissolution of the freed gas. The bubble destruction and subsequent dissolution process was imaged with a high pulse-repetition frequency (PRF) 10-cycle, 5-MHz bistatic transducer configuration. Three types of dissolution profiles were measured: In one case, biSphere™ microbubbles showed evidence of dissolution through resonance, during which a temporary increase in the scattering amplitude was observed. In another case, both biSphere™ and Optison™ microbubbles showed evidence of fragmentation, during which the scattering amplitude decreased rapidly. Finally, in some cases, we observed the impulsive growth and subsequent rapid decay of signals that appear to be due to cavitation nucleation. Simulations of bubble dissolution curves show good agreement with experiments. (E-mail: matula@apl.washington.edu)

Bio-acoustic thermal lensing and nonlinear propagation in focused ultrasound surgery using large focal spots: a parametric study

It is well known that the acoustic properties of soft tissue have a dependence on tissue temperature. This is of particular interest in focused ultrasound surgery since the mechanism of action of focused ultrasound surgery is to kill targeted tissue by inducing localized heating by ultrasound absorption, and hence cautery of that tissue. However, the act of localized heating induces a change in the acoustic properties of the targeted tissue and tissue surrounding it. This phenomenon distorts the incoming acoustic wavefront, and has been termed the thermal lens effect for this reason. Furthermore, nonlinear effects in acoustic propagation become non-negligible at the ultrasound intensities required for therapeutic action.This paper examines the importance of the thermal lens effect and nonlinear tissue properties by simulating a variety of clinically applicable phased array transducer configurations that have not yet been appropriately analysed using a full three-dimensional nonlinear treatment of acoustic propagation. The significance of the thermal lens effect is characterized by comparing the simulation of coupled acoustic and thermal propagation with an uncoupled treatment; neglecting thermal lensing typically produces a movement of 1 to 2 mm in the predicted position of the focus towards the transducer.The results also show that the classical methods of acoustic propagation can produce grossly erroneous results under certain clinically relevant transducer configurations and that an acoustic field scan with a hydrophone may not accurately predict therapeutic effect.

Simulations of circular 2D phase-array ultrasonic imaging transducers

Theoretical simulations of the pulse–echo beam forming of two-dimensional (2D) circular planar phase-array ultrasound transducers were conducted for the optimization of the effective architectures. These results were compared with equivalent linearly reticulated 2D phase-array transducer configurations. It is predicted that ultrasound imagers based on circular 2D phase-array transducers will outperform the other architectures for several medical applications. This study was motivated by the recent demonstration of micromachining of high-density circular as well as linear reticulated 2D phase-array transducers, to achieve real-time high-resolution completely electronic steerable volumetric medical noninvasive ultrasound imaging.

Ultrasonic measurement of gas flow using electrostatic transducers

Ultrasonic gas flowmeters typically use narrowband piezoelectric transducer arrangements for interrogating the flow of gas in a pipe. In this work, the suitability of broadband electrostatic transducers operating at frequencies of up to 1 MHz for ultrasonic measurement of gas flow has been investigated. The transit time method of ultrasonic gas flow measurement was adopted and experiments were carried out using a laboratory test rig capable of producing a range of gas flowrates up to 17.5 m/s. The test rig also allowed easy interchange of different prototype flowmetering sections. Times of flight of ultrasonic waves interrogating the gas flow were measured using separate send/receive electrostatic transducer arrangements. Two flowmeter configurations were considered. The first interrogated the flow at 45° in contra-propagating upstream and downstream directions. The second consisted of an upstream interrogation at 45° to the gas flow and an interrogation made normal to the flow direction. k factors correlating the fluid velocity along the ultrasonic path with the mean fluid velocity in the pipe were calculated using experimental ultrasonic data and anemometer measurements. All transducer configurations were numerically modelled using the computational fluid dynamics software package FLOTRAN © (ANSYS Inc.). Theoretical gas flow velocities for both transducer arrangements were subsequently compared with experimental values and found to be in excellent agreement. A flow-dependent frequency shift of the received ultrasonic signals was also observed simultaneously with the transit time measurement.

Feasibility study for real time three dimensional Doppler intracardiac echocardiography.

Using catheter-mounted two-dimensional array transducers, we have obtained real-time three-dimensional color flow and spectral Doppler ultrasound images in phantoms. We have constructed several transducers operating at 5 MHz with up to 137 channels inside a 12 French catheter lumen. The transducer configuration may be side scanning or beveled with respect to the long axis of the catheter lumen. We have also included six electrodes to acquire simultaneous electrocardiograms. We have measured Doppler signals in two phantoms, a string phantom and a pulsatile flow phantom. Using an open chest sheep model, we inserted the catheter into the cardiac chambers to study the utility of in vivo 3D intracardiac Doppler echocardiography.

Real-time three-dimensional intracardiac echocardiography

Using catheter-mounted 2-D array transducers, we have obtained real-time 3-D intracardiac ultrasound (US) images. We have constructed several transducers with 64 channels inside a 12 French catheter lumen operating at 5 MHz. The transducer configuration may be side-scanning or beveled, with respect to the long axis of the catheter lumen. We have also included six electrodes to aquire simultaneous electrocardiograms. Using an open-chest sheep model, we inserted the catheter into the cardiac chambers to study the utility of in vivo intracardiac 3-D scanning. Images obtained include a cardiac four-chamber view, mitral valve, pulmonic valve, tricuspid valve, interatrial septum, interventricular septum and ventricular volumes. We have also imaged two electrophysiological interventional devices in the right atrium, performed an in vitro ablation study, and viewed the pulmonary veins in vitro. (E-mail: edl@duke.edu)