GB1503734A - Acoustic microscopes - Google Patents

Abstract

1503734 Acoustic microscopes LELAND STANFORD JUNIOR UNIVERSITY BOARD OF TRUSTEES 14 Feb 1975 [15 Feb 1974] 6382/75 Heading G1G [Also in Division H4] An acoustic microscope comprises a transmitting transducer and a receiving transducer coupled to respective solid wave-propagating members which define respective acoustic lenses, the focal points of the two lenses being coincident in a fluid within which an object to be examined can be traversed, the ratio of the acoustic velocities in the solid and liquid being chosen such that the lens system has negligible spherical aberration. The Fig. 1 microscope includes thin-film Piezo-electric transducers 14, 36 of zno, cds or lithium niobate on wave-propagating members 16, 34 of sapphire, fused quartz, cds or yttrium aluminium garnet. Concavities 18, 32 in the members act with liquid (water or helium) 20 as acoustic refractors with a common focus F where object O to be examined is positioned. Transducer 14 is driven by a "chirp" signal, or at one or more discrete (sequential) frequencies, via co-axial line 12 by RF generator 10 operating in the band 400 MHz to > 1 GHz. The object is moved in X and Y directions by a loudspeaker 24 and hydraulic ram 23, in synchronism with the scanning of a CRT 28, and micrometer 22 provides adjustment of the objects vertical position. The through-transmission signal from transducer 36 modulates the CRT brightness. The several acoustic frequencies may be used to modulate the colour of the CRT display. Aplanatic lenses can be used instead of the simple acoustic refractors 18, 32. In the Fig. 5 embodiment, wave-propagating members 64, 80 provide several acoustic paths between parallel-energized transducers 58, 60, 62 and receiving transducers 82, 84, 86 via focal points F of the acoustic refractors formed by the curved interfaces between members 64, 80 and members 98. The latter members guide movement of the object O through the focal points in turn. It is stated that by appropriately delaying the signals from the receiving transducers to account for this movement, the received signals can be added at 92 to enhance the signal-to-noise ratio of the signal to be displayed at 94. In various modifications the acoustic signal reflected by object O, rather than transmitted through it, is used, Fig. 4 (not shown) and instead of sensing the received signal intensity its phase is sensed relative to the R.F generator signal or to a signal obtained using a reference acoustic path, Fig. 6 (not shown). The phase data can be used in the manner of acoustic holography to provide a three-dimensional display.