Performance of periodic piezoelectric composite arrays incorporating a passive phase exhibiting anisotropic properties

This paper explores the minimisation of interelement cross talk in 1-D and 2-D periodic composite array structures through the incorporation of a passive phase exhibiting anisotropic elastic properties. Initially the PZFlex finite element code was used to monitor array aperture response as a function of material properties. It is shown that in array structures comprising passive polymer materials possessing low longitudinal loss and high shear loss, inter-element mechanical cross talk is reduced, without a concomitant reduction in element sensitivity. A number of polymer materials with the desired properties were synthesised and their elastic character confirmed through a program of materials characterisation. Finally, a range of experimental devices exhibiting improved directional response, as a result of a significant reduction in interelement cross talk, are presented and the predicted array characteristics are shown to compare favourably in each case

Investigating the influence of the constituent materials on the performance of periodic piezoelectric composite arrays

This paper describes a theoretical investigation into the influence of the constituent materials on periodic composite array transducer performance. A finite element (FE) model, configured in PZFlex, is used to analyze the performance of a wedge coupled array transducer operating into a steel component. Here, the improvements offered by new single crystal piezoelectric materials are compared to standard PZT‐based configurations. In addition, new passive polymer materials, possessing low longitudinal loss and high shear loss, are evaluated for their potential to significantly reduce inter‐element mechanical cross talk. The FE results illustrate the potential for the next generation of array transducers incorporating these new materials and this is highlighted in the A‐scan predictions from simulated defects

The high frequency flexural ultrasonic transducer for transmitting and receiving ultrasound in air

Flexural ultrasonic transducers are robust and low cost sensors that are typically used in industry for distance ranging, proximity sensing and flow measurement. The operating frequencies of currently available commercial flexural ultrasonic transducers are usually below 50 kHz. Higher operating frequencies would be particularly beneficial for measurement accuracy and detection sensitivity. In this paper, design principles of High Frequency Flexural Ultrasonic Transducers (HiFFUTs), guided by the classical plate theory and finite element analysis, are reported. The results show that the diameter of the piezoelectric disc element attached to the flexing plate of the HiFFUT has a significant influence on the transducer's resonant frequency, and that an optimal diameter for a HiFFUT transmitter alone is different from that for a pitch-catch ultrasonic system consisting of both a HiFFUT transmitter and a receiver. By adopting an optimal piezoelectric diameter, the HiFFUT pitch-catch system can produce an ultrasonic signal amplitude greater than that of a non-optimised system by an order of magnitude. The performance of a prototype HiFFUT is characterised through electrical impedance analysis, laser Doppler vibrometry, and pressure-field microphone measurement, before the performance of two new HiFFUTs in a pitch-catch configuration is compared with that of commercial transducers. The prototype HiFFUT can operate efficiently at a frequency of 102.1 kHz as either a transmitter or a receiver, with comparable output amplitude, wider bandwidth, and higher directivity than commercially available transducers of similar construction

Modal analysis and nonlinear characterization of an airborne power ultrasonic transducer with rectangular plate radiator

Some industrial processes like particle agglomeration or food dehydration among others can be enhanced by the use of power ultrasonic technologies. These technologies are based on an airborne power ultrasonic transducer (APUT) constituted by a pre-stressed Langevin-type transducer, a mechanical amplifier and an extensive plate radiator. In order to produce the desired effects in industrial processing, the transducer has to vibrate in an extensional mode driving an extensive radiator in the desired flexural mode with high amplitude displacements. Due to the generation of these high amplitude displacements in the radiator surfaces, non-linear effects like frequency shifts, hysteresis or modal interactions, among others, may be produced in the transducer behavior. When any nonlinear effect appears, when applying power, the stability and efficiency of this ultrasonic technology decreases, and the transducer may be damaged depending on the excitation power level and the nature of the nonlinearity. In this paper, an APUT with flat rectangular radiator is presented, as the active part of an innovative system with stepped reflectors. The nonlinear behavior of the APUT has been characterized numerically and experimentally in case of the modal analysis and experimentally in the case of dynamic analysis. According to the results obtained after the experiments, no modal interactions are expected, nor do other nonlinear effects

Ultrasonic Transducer And Method For Using Same

An improved ultrasonic transducer fabricated on a silicon base has a piezoelectric layer of polyvinylidene fluoride-trfluroethylene copolymer. The piezoelectric layer is sandwiched between two conductive electrodes, all of which are supported on a dielectric layer on top of the silicon base. At least one of the electrodes forms a Fresnel zone plate to focus the ultrasonic signals from the transducers. To improve the performance of the transducer, the silicon base behind the active area is removed, leaving the dielectric layer as a membrane to support the electrodes and the piezoelectric layer. The resulting void in the silicon base is filled with an acoustically matched backing, such as an epoxy, to enhance the wideband performance of the transducer. The transducer is especially suited for characterizing anatomical structures or features requiring very high resolution.Georgia Tech Research Corp.Medical College Of Georgia Research Institut

An analytical model of a longitudinal-torsional ultrasonic transducer

The combination of longitudinal and torsional (LT) vibrations at high frequencies finds many applications such as ultrasonic drilling, ultrasonic welding, and ultrasonic motors. The LT mode can be obtained by modifications to the design of a standard bolted Langevin ultrasonic transducer driven by an axially poled piezoceramic stack, by a technique that degenerates the longitudinal mode to an LT motion by a geometrical alteration of the wave path. The transducer design is developed and optimised through numerical modelling which can represent the geometry and mechanical properties of the transducer and its vibration response to an electrical input applied across the piezoceramic stack. However, although these models can allow accurate descriptions of the mechanical behaviour, they do not generally provide adequate insights into the electrical characteristics of the transducer. In this work, an analytical model is developed to present the LT transducer based on the equivalent circuit method. This model can represent both the mechanical and electrical aspects and is used to extract many of the design parameters, such as resonance and anti-resonance frequencies, the impedance spectra and the coupling coefficient of the transducer. The validity of the analytical model is demonstrated by close agreement with experimental results

Printing High Viscosity Fluids using Ultrasonic Droplet Generation

A new printing technology based on ultrasonic actuation (~1 MHz) is presented that has the potential to print high viscosity fluids. In this paper, we describe the print-head’s operating principles and construction. Acoustic focusing in the nozzles produces high pressure gradients that help eject the fluid which, under the proper conditions, forms droplets. Two types of models are presented to attempt to predict print-head behavior over a range of conditions. The first model borrows from simple fully developed, laminar flows to estimate printing conditions based on fluid properties, as well as printing pressures. The second model captures the dynamic behavior of the print-head to estimate cavity resonances that lead to acoustic focusing and potentially droplet generation. We report on experiments with several types of fluids that demonstrate the technology’s potential.Mechanical Engineerin