Applications of Laser-Generated Ultrasound Using AN Interferometric Sensor.
Available from UMI in association with The British Library. To complement non-contacting ultrasonic generation using lasers, it is ideal to have a remote, non-contacting detector. An interferometer, based on the Michelson design, has been constructed for the purpose of this thesis, enabling laser generated ultrasonic displacements of the order of 25 pm to be resolved. The design and operation of this device is described fully, and its performance compared with two other non-contacting devices, namely a capacitance transducer and an electromagnetic acoustic transducer (EMAT), and a contacting piezoelectric probe. Experimentally observed waveforms, from laser generation of ultrasound in both the thermoeleastic and plasma regimes, are shown to be in excellent agreement with wave propagation theory. The depth estimation of surface breaking defects by the detection of Rayleigh surface waves, generated in both the thermoelastic and plasma regimes, is described, and an empirical formula is given which is valid for narrow slots of <0.3 mm width. The experimentally determined mechanism for the interaction of Rayleigh waves with slots is also compared with a theoretical computer model. The measurement of ultrasonic velocity at elevated temperatures has been investigated in a number of materials, namely dural, aluminium, stainless steel, iron and graphite. Data is presented for non-contact ultrasonic detection at temperatures of up to 1000 degrees centigrade in iron and stainless steel. Finally, the measurement of the thickness of thin metal sheets is investigated using both a pulse-echo technique, and Lamb waves.
- Pub Date:
- Physics: Condensed Matter; Physics: Electricity and Magnetism