[en] By 1982, 10 mm walled targets will require thickness and diameter tolerances of better than +- 100 A over spot dimensions of 10--100 mm. Such targets will be multishell and/or opaque which eliminates optical phase microscopy and severely limits x-ray analysis. In principal, an acoustic phase microscope can provide the necessary resolution, provided the acoustic beam can be coupled to, and focused within, the confines of the wall. In this paper, a shear wave acoustic microscope with an electronically variable focal length is described. A computer code has been used to study the ray optics and diffraction of this design and a spot size with the required dimensions has been obtained