METHOD AND APPARATUS FOR EXPLORATION OF THE FOREFIELD IN THE COURSE OF WORKING OF COAL-SEAMS

摘要

1481436 Acoustical inspection apparatus RUHRKOHLE AG 10 Sept 1974 [12 Sept 1973] 39366/74 Heading G1G The Specification describes a method and apparatus for the exploration of the forefield in the course of working coal seams in mines comprising generating simultaneously, a number of monochromatic coherent audible sound impulses which are focused into the coal seam as a sound ray with a lobar radiation pattern, and detecting and measuring the echo times of reflections from boundary surfaces. The apparatus 6 is arranged at the coal face 5, and comprises pulse generator 7 to feed pulses through individual phase shifters 15 to transmitting transducers 9, arranged spatially at a pitch of (2n+1) #/4 where # is the acoustic wavelength in the seam, to produce lobe pattern 12. It is stated that the low frequency monochromatic pulses suffer low attenuation and are only reflected from discontinuities having an orthogonal surface component to the beam direction. The phase differences applied to the separate TX transducers 9 may be varied to produce a variation in or scanning of the beam direction and conversely, the echo signals may be received directionally by RX transducers 10, arranged at a pitch of 2n#/ 4 , to the same effect. The echo time is measured in device 11 and may be displayed, e.g. on an oscilloscope, recorded, or stored for display on a storage screen.