Details of Grant 

EPSRC Reference:	GR/J10624/01
Title:	SILICON-BASED DEVICES FOR ULTRASONIC TRANSDUCTION IN AIR
Principal Investigator:	Hutchins, Professor D
Other Investigators:
Researcher Co-Investigators:
Project Partners:
Department:	Sch of Engineering
Organisation:	University of Warwick
Scheme:	Standard Research (Pre-FEC)
Starts:	01 October 1993	Ends:	30 September 1995	Value (£):	83,506
EPSRC Research Topic Classifications:	Electronic Devices & Subsys. Instrumentation Eng. & Dev.
EPSRC Industrial Sector Classifications:
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Panel History:
Summary on Grant Application Form
(i) Investigate silicon as a backplate material for ultrasonic air-coupled transducers;(ii) Establish whether apodisation and focussing can be achieved;(iii) Measure the response and characteristics of the devices;(iv) Perform trial NDT experiments.Progress:A range of silicon backplates have been fabricated using micromachining techniques. Here, an anisotropic etch has been used to produce a backplate from a silicon wafer that contains a series of cylindrical pits, of 50 microns depth and diameter, separated by 100 microns. A thin polymer membrane is then placed over the surface, trapping air in a controlled fashion. An excitation voltage causes the membrane to move, and ultrasonic transients are generated. In detection, a d.c. bias is applied to the device, and membrane motion causes the capacitance, and hence the charge on the backplate, to vary, forming the detected signal. The devices have been tested as sources using a wide bandwidth miniature hyrdophone, adapted for use in air. This has demonstrated that the devices have a bandwidth of 2MHz, and this is an excellent result. It has been found that the emitted ultrasonic field is that expected from a plane piston source, and hence the device is operating as expected, with a uniform amplitude across its front face. By changing the way the membrane is clamped, it has been possible to produce apodisation, where the amplitude of membrane motion decreases uniformly from the centre outwards. This leads to a much more uniform beam, which is a desirable feature in applications. Additional work has produced annular transducers. These are expected to focus on-axis, and experimental profiles have shown this to be the case. With regard to the original objectives, (i) is complete, as is most of (ii) and (iii). Work is currently under way to enhance the focussing of the devices using a zone plate apodization scheme. In addition, we are looking at more advanced silicon processing methods, such as laser machining, to give a range of backplate topographies. When this work is complete, the final phase will look at the use of these devices for ultrasonic imaging in various samples, for potential industrial implementation
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Organisation Website:	http://www.warwick.ac.uk