Recent results and trends in health monitoring with Surface Acoustic Waves (SAWs)

This paper presents recent results based on the use of Surface Acoustic Waves (SAWs) for active sensors for health monitoring of a variety of structures. In the first example, SAWs were used in an acoustic waveguide effect in the fluid filled space between two surfaces. The effect was demonstrated for flat plates and for concentric cylinders. Pressure vessels with concentric cylinders are used in the power industry, where the position of an industrial lead screw is an important parameter. Wave travel over a length of up to 2 meters could be observed with little energy loss into the fluid. The second example, presents the use of Electromagnetic Acoustic Transducers (EMAT) for the rapid health monitoring of railroad wheels. In the third example, surface hugging wedges were used with conventional transducers to launch and detect SAWs for crack detection and mapping measurements on pressure vessel valve stems. The fourth example deals with health monitoring of living biomedical cells. In this case SAWs at hypersonic frequencies (1GHz) were employed to image and monitor the health of the cells as the temperatures were raised. While these examples are still laboratory projects, some of them are finding their way into industrial applications.