Near-field scanning acoustic microscope

A traditional scanning acoustic microscope (SAM) has been modified to operate in the near-field mode. A pinhole in a thin shim of brass defines the resolution of the instrument, which can be as small as 0.1 lambda . In an edge scan experiment, a 125- mu m-thick brass shim with a pinhole size of 125 mu m, a SAM operating at 3 MHz, and a transducer with an F-number of 0.7 are used. The improvement in resolution corresponds to using a transducer with an F-number of 0.2. The results of measurements of the line response of the system, using steel pinholes of several thicknesses and diameters at different linewidths and operating frequencies and showing the details of the design of the instrument, are presented.<
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