Dielectric, piezoelectric and acoustical properties of high performance piezorubber composite hydrophone

It is well known that conventional piezoelectric ceramics are hard and brittle materials in nature. These possess high acoustic impedance causing great acoustical mismatching when used in conjunction with radiating media like water or human tissues. To overcome this problem a number of composite systems based on piezoceramic and polymers have been suggested with different connectivity patterns [1, 2]. Such composites offer better acoustic coupling in low density medium like water. Being relatively flexible, most of the composites can be used to form non-planar transducers without the need for machining or grinding. The concept of composite materials has also been extended for the cancellation of reflected and transmitted sound in one dimension by single and double layers of piezoelectric material subjected to a normally incident wave in a fluid [3]. Active piezocomposite coatings for active underwater sound reduction have also been developed [4]. However, the present work is aimed to develop a piezorubber composite hydrophone with much higher piezoelectric voltage constant (g33) than their ceramic counterparts [5-7]. Special attention was focused on the development of hydrophones with omnidirectional broad band characteristics. This was achieved by adopting a 0-3 connectivity pattern consisting of lead zirconate-lead titanate ceramic powder loaded in a rubber matrix. The effects of the relative amounts of individual constituents, grain size of the ceramic powder and poling conditions on dielectric and piezoelectric properties have been studied. Composite hydrophones of cylindrical shape have been fabricated and their electroacoustic sensitivity has been evaluated analytically as well as experimentally. The donor doped lead zirconate-lead titanate (PZT) was synthesized using a conventional mixed oxide route by pre-reacting the oxides of lead, zirconium and titanium at 900 °C. The powders were pressed into disc-shaped specimens and sintered at 1220 °C for 4 h. These sintered discs were then crushed to form powder. The X-ray diffraction (XRD) patterns of the powders confirmed the formation of a perovskite phase. These materials were used to obtain powders of average particle size 30, 50 and 80/xm. The ceramic filler powder was uniformly dispersed in commercial chloroprene rubber dissolved in toluene. A small quantity of carbon (1.0 wt%) was added to facilitate the poling. The resulting mixture has been used to prepare specimens of desired dimensions. The mixture was