Group Velocity Of Acoustic Waves In Plates Of Electronic Materials
In this study the propagation and dispersion characteristics of plate acoustic waves (PAW) in electronic materials are investigated experimentally. Plate acoustic waves are elastic waves that travel along a plate with thickness comparable to the wavelength of the waves. Lamb waves, a type of plate acoustic wave, have particle motion in the direction of propagation and normal to the plate. Unlike an infinite medium, plates support two sets of Lamb wave modes (symmetric and anti-symmetric) with unique velocities which depend on the relationship between the wavelength and the thickness of the plate. Out of this, two zero order modes (so and ao) in several electronic material plates are studied here. This kind of study has practical applications particularly in non-destructive testing. Lamb waves are propagated through plates of glass, brass, aluminium and lithium niobate. The delay of propagation of Lamb waves through the plates is measured and the group velocities of the so and a o modes are then computed and plotted against the frequency and the thickness of the plate. These results compare well with the theoretical results obtained from published work. Group velocities of PAW in all of them are found to be similarly dispersive. The so mode has a low dispersion when the product of frequency and thickness is lower than approximately 1MHz-mm whereas the ao mode is less dispersive when the same product is higher than about 1MHz-mm, a characteristic which is usually exploited in industry. Thus it can be concluded that the experimental work matches well with the theory and the analysis can be useful in industrial applications such as testing the uniformity of materials and defect detection.
Acoustic, Group Velocity, Lamb Waves, Lithium Niobate, Paw, Plates, Physics
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