Variable frequency seismic wave generator - utilises adjustment of partial vacuum in cylinder in which piston operates, with pressure indicated on external gauge

摘要

A non-explosive source of variable frequency seismic waves is provided by a piston in a cylinder in which a partial vacuum exists. Pressure vaia tion allows tuning of the acoustic wave frequency. A seismic wave generator (10) mounted on a lorry comprises a cylinder (1 2) with a piston release mechanism (14) at the upper end operated by the excitation of coils (338, 340). A pressure buffer(16) is located at the lower end. Holes (304) in an upper plate (302) allow entry of air to a space (306) above the piston (308). A pin (318) protruding from the rear face of the piston has a conical section (322) which engages the release mechanism. A partial vacuum in the cylinder (12) is achieved via connections (350) to a vacuum pump (366) via a valve (368) which is closed when the required frequency is obtained.