ABSTRACT

Fugro-UDI have been developing wideband and efficient sonar transducers using 1–3 piezocomposite materials for several years This new material extends the range of material properties which can be achieved by conventional piezoelectric ceramics The material parameters such as the electro-mechanical conversion efficiency mechanical quality factor and electrical impedance can be tailored by varying the quantity and type of both the ceramic and polymer phase within the piezocomposite device This means the transducer material can be customised to suit the wide range of applications in underwater sonar transducers A number of composite transducers have been developed by Fugro-UDI for various applications including echo sounders, side scans and electronically steered systems In each case, the wideband and efficient nature of the composite devices has demonstrated improvements in the detection and imaging capabilities of the sonar system

The paper will discuss the advantages of 1–3 composite materials The test results of a range of composite transducers to be presented which will highlight the improvements which have been made in the performance of sonar systems Finally, the potential of developing new sonar systems by further exploitation of the composite material will be reviewed Since then, subsea, within the Norwegian Continental Shelf, has been a prosperous, growing and successful business

INTRODUCTION

The properties of 1–3 composite materials are now well established and have been reported in the literature since the late 1970's The material consists of piezocomposite pillars embedded m a polymer matrix, as illustrated in Figure 1 Improvements in the electromechanical conversion efficiency is achieved by the reduction in the lateral clamping of the ceramic pillars by the softer polymer material The polymer material also improves the acoustic impedance matching to the waterload by reducing the net density and stiffness of the piezocomposite This means that for a properly designed composite, the bandwidth can be significantly Increased without reducing the efficiency of the device In addition to this, the lossy nature of the polymer reduces lateral excitation of the material This has two man advantages Firstly, the effects of spurious resonances coupling into the thickness mode resonance is reduced significantly The vibrational behaviour of a composite transducer and ceramic transducer of the same dimensions is illustrated in Figure 2 The urn-modal response of the composite block is clearly demonstrated Secondly, the good lateral mechanical isolation permits the use of fabricating monolithic array structures in which the array elements are defined by the electrode patterns, as shown in Figure 3 This reduces the manufacturing complexity of multi-element arrays whilst maintaining a uniform response between array elements It 1s thus possible to manufacture uni-modal, efficient and wideband transducers using simple transducer construction techniques In all cases, the composite element is mounted onto a supportive backing material in which the compressive strength is matched to the particular maximum depth requirement A µ c or thin front layer is used to isolate the front radiating face from the water For wideband applications in which the fractional bandwidth is to exceed 25%, a quarter wavelength matching layer can be easily incorporated into the transducer design

This content is only available via PDF.
You can access this article if you purchase or spend a download.