Quantitative acoustic microscopy of plastics using low speed coupling fluids

Conventional acoustic microscopes can not generate a V(z) curve with Rayleigh wave interaction on materials with a low speed of sound such as plastics. To perform this type of acoustic microscopy on such materials, one needs to use a coupling fluid with a very low speed of sound. This poses practical difficulties: high attenuation in the coupling fluid, lens design complexities, high precision needed in the Z translation stage, temperature stability of the quickly evaporating coupling fluid, and absorption of coupling fluid into the test specimen. A new coupling fluid with suitable speed of sound and attenuation factor is introduced. A 250 MHz lens and measurement system design, addressing the problems listed above, are discussed. An example of a V(z) curve collected on epoxy is introduced, and it is shown that both Rayleigh and lateral compressional waves are responsible for V(z) characteristics. This is the first time that such measurements on plastics with Rayleigh wave dominance have been reported.