A Fabry Perot Fibre-optic hydrophone for the characterisation of ultrasound fields

• Main Author: Morris, Paul Stephen
• Published: University College London (University of London) 2008
• Subjects: 621.38284
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.500088

This thesis documents the development of a novel fibre optic hydrophone, for the characterisation of medical ultrasound transducers and the measurement of ultrasound induced temperature rises. The transduction mechanism of the hydrophone is based on the detection of acoustically and thermally induced changes in the optical thickness of a Fabry-Perot interferometer deposited at the tip of a single mode optical fibre. The interferometer comprises a layer of Parylene-C sandwiched between two thin gold mirrors. The design of the sensor was optimised using a numerical model of the interferometer transfer function. Through the use of vacuum deposition techniques, a fabrication procedure has been developed which enables batch production of the sensors. A self contained sensor interrogation system has also been developed. The system uses a rapidly tuneable laser developed originally for the telecoms industry to interrogate the sensor and make acoustic and thermal measurement, Control of the system is achieved via a PC using software written in Labview 8.0.