GB743063A - Improvements in devices for producing a visible image of the energy distribution of a pressure wave field - Google Patents

Abstract

743,063. Microphones. GIRERD, R. May 19, 1952 [May 18, 1951], No. 12675/52. Class 40 (4). [Also in Groups XXXVIII and XL (b)] In a device for producing a visible image of pressure-wave energy distribution (see Group XXXVIII) comprising a mosaic of electroacoustic transducers, each transducer comprises a rod 2, Fig. 2, tuned to resonance with the mean frequency of the pressure waves being received and supported at a vibration node, one end of the rod being provided with a condenser electrode 30 which co-operates with a fixed condenser electrode 31. If the rod is conductive the end of the rod may constitute electrode 30, but if it is non-conductive, e.g. quartz, glass or ceramic, a conductive electrode is attached thereto. The opposing electrodes may comprise intermeshing coaxial cylinders 33, 34 and 35, 36, Fig. 3A and Fig. 3 (not shown). A D.C. bias voltage 9, e.g. 1,000 v., is applied to one electrode (30 as shown in Fig. 2) and the other electrodes of the transducers are sequentially connected to the indicator by a switch. In other embodiments the condensers are discharged sequentially by arranging them as the shunt capacities of an artificial line, Fig. 4 (not shown) or by making one electrode the base plate of a photo-electric cell of the type disclosed in Specification 743,062, [Group XXXVIII], the cells being sequentially activated by a moving light spot.