City Research Online

Abstract

An ultrasonic transducer converts acoustic signals into electrical signals and vice versa. Here practical attempts at fabricating ncn—uniformly excited, wide-band ultrasonic transducers are presented.

New transducers to directly replace conventional, uniformly�excited, wide-band transducers were produced by varying the piezoelectric excitation of transducer elements as a function of their radius i.e. apodisation. To do this it was necessary to re-examine the technology of poled ferroelectric or piezoelectric ceramics of PZT and PMN.

The construction of wide-band transducers is analysed in terms of the KLM transmission line model and their acoustic fields are described by the plane— and edge-wave model. The impulse response method is applied to transducers and useful forms of non-uniform excitation are described.

Details are given of measuring the planar electromechanical coupling factor of a piezoelectric element and of how standard photofabrication methods using photoresist were adapted to cope with the comparatively rough surfaces of ceramics working right up to and including the edges of the substrates. The poling apparatus designed to apply various poling regimes under conditions of constant
temperature and time are detailed. Fabrication methods for producing wide-band transducers based on using a centrifuge to apply the required damping are given. The wide-band excitation and receiving system is described.
Computer-calculated results illustrate the effect of various types of transducer excitation ranging from the theoretical to the practically-attainable. Measured results confirm these calculations and also present some of the physical characteristics of the piezoelectric ceramics. Both uniformly and non-uniformly excited transducers are considered.

The thesis concludes that it is possible to make non-uniformly excited transducers by controlling the strength of the piezoelectric excitation within the transducer element.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science > QC Physics
Departments:	School of Science & Technology School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

Export

Downloads