| 摘要 |
1,254,328. Ultrasonic holography; sound directing appliances. HOLOTRON CORP. 24 Feb., 1969 [6 March, 1968], No. 9808/69. Headings H4D and H4X. Two ultrasonic beams are combined to form a hologram by directing one against a first side of a thin plate at an angle of incidence to obtain reflection of the beam, and directing the second beam at the second side of the plate at a critical angle of incidence to obtain transmission of the second beam through the plate. For obtaining an acoustic hologram of an object 19 (Fig. 2) at least part of which is immersed in liquid 11, a reference beam and an object beam are respectively transmitted through and reflected from plate 39 to interfere and form a hologram at detecting surface 23. If the angle of incidence of a beam on the plate is one of a plurality of critical angles, the plate will vibrate in a symmetric natural mode (Fig. 3A) or in an asymmetric natural mode (Fig. 3B) and will be transparent to the incident energy; at other angles it will reflect the energy. Small adjustments near a critical angle may be made with screw 45 to tilt the plate about pivot 51 and so control the relative intensities of the two beams reaching surface 23 for optimizing the hologram. The hologram may be recorded on film or reconstructed by illumination as in Specification 1,194,543 (see Division H4). By forming the hologram first with one and then with another ultrasonic frequency and illuminating it with light of at least two colours, coloured reconstructions of the hologram can be obtained as in Specification 1,200,948 (see Division H4). |
