Resolution reflection acoustic microscope

The limits zmjn and zmax are the values of defocus at which the reflected rays just fill the area of the transducer thus for zmin < z < zmax all the reflected rays that enter the lens fall on the transducer, while for values of defocus outside that range some of the rays miss it altogether. The value z0 is the defocus at which the geometrically reflected rays are focused on the transducer at this point, as indeed at z = 0, ray optics breaks down because it does not allow for diffraction, although it does correctly predict the position of a minimum in V(z) at z0. The approximate expressions are valid when D/n > q, as is usually the case in a high-resolution acoustic microscope. In the approximation for z0, the quantity Ft is the ratio of the separation between the transducer and the back focal plane of the lens D — q/n) to the Fresnel distance for the transducer (na /Ao),... 

Anyone who has successfully used a microscope to image properties to which it is sensitive will sooner or later find himself wanting to be able to measure those properties with the spatial resolution which that microscope affords. Since an acoustic microscope images the elastic properties of a specimen, it must be possible to use it to measure elastic properties both as a measurement technique in its own right and also in order to interpret quantitatively the contrast in images. It emerged from contrast theory that the form of V(z) could be calculated from the reflectance function of a specimen, and also that the periodicity and decay of oscillations in V(z) can be directly related to the velocity and attenuation of Rayleigh waves. Both of these observations can be inverted in order to deduce elastic properties from measured V(z). 

We used 900-MHz scanning acoustic microscopy to assess the acoustic impedance with a micrometer resolution. Acoustic microscopy measures the amphtude of a high frequency ultrasonic pulse reflected from the surface of a materM. The microscope is calibrated with a set of materials which have... 

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