Wideband Piezoelectric Transducers Research Articles

Optimization of the Design of Multifrequency Annular Arrays for Very Wide Band Operation

This paper presents an optimization design strategy for wideband piezoelectric transducers based on a kerfless multifrequency annular array with two elements, made out of a 1-3 connectivity piezo-composite disk. The disk is machined by reducing the thickness within a circular section at the centre of the disk faces, so that two elements are obtained: an inner and thinner disk and an outer ring. They are designed to meet two main criteria: i) both elements present a different resonant frequency, being the inner disk the higher frequency element and ii) the individual frequency bands of the elements overlap to build up an overall frequency response that approximate to the sum of the individual frequency bands. The objective of this research is to determine the optimum configuration of both elements, in particular the relative elevation of the inner disk, so that cross-talk between elements and the appearance of undesired modes is minimized while frequency bandwidth is optimized. Towards this end, the response of different configurations is calculated using a finite element method. DOI: http://dx.doi.org/10.5755/j01.eie.22.5.16350

Laser optoacoustic diagnostics of femtosecond filaments in air using wideband piezoelectric transducers

New opportunities in ultrasound diagnostics of femtosecond laser filaments with wideband piezoelectric transducers are considered. Transverse spatial resolution better than 100 microns is demonstrated in the single and regular multiple filamentation regime making path toward 3D filament tomography. The simple analytical model of the cylindrical acoustic source fitted well with the experimental data.

Modeling of Acoustic Emission Signals Generated in On Load Tap Changer

The paper deals with mathematical modeling of acoustic emission signals which are generated in on load tap changers. In power engineering area acoustic emission method is commonly used for diagnosis purposes. Authors in their research works apply it for detection of defects occurring in on load tap changers, which are important elements of power transformers. The acoustic emission method is based on measurements performed by use of wideband piezoelectric transducers that are mounted on transformer tank surface. The registered signal is then analyzed in the time, frequency, and time frequency domains or is evaluated with computer expert systems for diagnosis purposes. Depending on indicators device technical condition can be determined. The contribution given by the authors in this paper is proposal of a mathematical model, which describes envelope of the measured acoustic emission signal.

Optoacoustic technique for thickness measurement of submicron metal coatings

The new nondestructive method for thickness measurement of submicron metal coatings on transparent substrate is developed. The method is based on the optoacoustic (OA) transformation in the system, where the coating is covered by an optically transparent liquid. Theoretical treatment of the problem consists of two steps. At the first step laser-induced thermal field in the system is calculated, taking into account the large thermal conductivity of the metal film and partial heat diffusion into the liquid. At the second step the system of wave equations for scalar potential of vibration velocities is solved. Heat sources, determined at the first step, are free form of wave equations. Three chrome coatings of different thickness (approximately 0.2, 0.3, and 0.6 μm) deposited on the quartz substrate are tested experimentally. Two different organic liquids (acetone and ethanol) are used to cover chrome coatings. Nanosecond diode-pumped Nd:YAG laser operated at the main harmonic is used to perform OA transformation (laser pulse duration is τ L = 12 ns, the laser energy is about 0.2 mJ). Two detection modes are used. In forward mode laser pulse irradiates the film from the side of the substrate and in backward mode—from the side of the liquid. Detection of induced ultrasonic pulses is performed by the wide-band piezoelectric transducer in the liquid in both cases. The thickness of the coatings is determined by the least squares fitting of the theoretical dependencies of spectral transfer functions of OA transformation to experimental data. It is demonstrated, that the developed technique can be used for measurement of metal coatings thickness within the range from 50 nm to 5 μm with the error about 50 nm.

Photoacoustic depth profiling of layered samples†

A photoacoustic sensor for the indirect detection of acoustic waves on the basis of a prism was developed. This wide-band piezoelectric transducer allows temporal resolutions of better than nanoseconds. Owing to the finite acoustic velocity it is possible to distinguish between sound waves generated in different layers. Suitable samples were built up to estimate the depth profiling capabilities of the developed sensor. For a simple experiment the lower limit for the depth resolution in an aquatic system is about 30 µm, corresponding to a temporal resolution of 20 ns. Only qualitative results were obtained with more complex layered samples.

Design of Ultrasonic Transducers with Multiple Acoustic Matching Layers for Medical Application

For high-efficiency wide-band piezoelectric transducers, a design method based on the synthesis theory of multiple-mode filters is presented. This design method has the advantages that it retains phys- ical intuition and can find optimum values of these matching layers by using iterative calculation techniques. An air-backed disk transducer with triple matching layers has been built to illustrate this design ap- proach, and good agreement between theory and experiment has been achieved. The transducer has SS-percent 6-dB fractional bandwidth, 3.2-dB round trip insertion loss, and less than l-dB passband ripple. Moreover, a prototype linear array probe with triple matching layers has been produced and has been used in an ultrasonic diagnostic equip- ment. Ultrasonograms with high resolution were obtained.