METHOD AND DEVICE FOR ELECTROSTATICALLY INVESTIGATING SURFACE AND SUB-SURFACE STRUCTURES

摘要

An electrostatic detection device for examining a surface structure and / or an underground structure comprises a central electrically conductive and square sensor plate, and four side sensor plates electrically connected elongate and rectangular to each other and each disposed adjacent and parallel to an edge of the central plate. This detector plate pattern is applied on the surface, and the central and side plates are then electrically charged at different rates, the loading rate of the central plate being affected by the absolute permittivity of the electric field structure being examined. A differential amplifier (49) amplifies the difference between voltages on the central and side plates as said plates are loading, and a peak detector (61) detects the higher the amplitude of this amplified difference voltages and displays a voltmeter (4). Since the absolute permittivity of the structure being examined is a function of at least one characteristic thereof, and as the voltage difference is affected by the rates of charge of the central and side plates themselves affected by the absolute permittivity of the electric field , the output signal from the peak detector (61) is representative of this feature of the controlled structure.