The design and implementation of an ultrasonic dynamic
focusing annular array system is described. The array is designed
for use as a contact transducer and for eventual incorporation
into the head of a real-time mechanical scanner.
A solution for the continuous wave field of a focused thin
ring array is used to examine the effects of the number of rings,
ring arrangement and apodisation of the array aperture on its focal
plane response. Other aspects of array design are also considered.
A suitable method of array fabrication, based on printed circuit
board techniques, is described.
The design and implementation of an electronic system for the
generation, detection and processing of the array signals is given.
Digital techniques are used to implement the dynamic delays.
The dynamic focusing capabilities of the array are confirmed
experimentally. Dynamic focusing of the reception response of the
array is usually combined with a fixed focus on transmission. The
compromise of fixed focusing on transmission may be overcome by
applying the idea of Synthetic Aperture Imaging. An effective
dynamic focus is then achieved on both transmission and reception.
This novel application to annular arrays is investigated
experimentally, and significant advantages are confirmed, however,
at the expense of a lower pulse repetition frequency.