Transient Technologies LLC

An Impulse Generator for The Ground penetrating radar

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In last time ground penetrating radars (GPR) are widely used for search and analysis of varied underground objects of natural and artificial origins. Caves and cavities can also be found and investigated with the GPR's aid. Impulse generator is the key unit, which determine GPR's parameters: depth of penetrating, accuracy et al.

Serial power drift diodes are used for generation step voltage with nanosecond rise time. Peak power a few kilowatts and frequency repetition near 20 kHz with portable power supply using have been achieved. Such generator can be used in the simple GPR for caves finding applications.

In recent time an electromagnetic sensing technique by the ground penetrating radars (GPR) are widely used for engineering geophysics tasks decision (DANIELS at al., 1988). GPR utilize a very burst of electromagnetic energy pulses send into the ground from a transmitter antenna located on the surface. Subsurface structures, such as bedding, cementation, changes in moisture and clayey content, cavities, voids, fractures, intrusions man-made objects and many other interface possessing a contrast in dielectric properties cause some of the pulse energy to be reflected back to the surface, while the test of the energy continues to penetrate deeper. The reflected pulse energy is picked up by a receiver antenna on the surface. These signals are then processed and plotted in a distance versus time-depth display. Thus, as the radar antenna is slowly towed across the surface, a continuous cross-sectional 'picture' of subsurface conditions is generated. GPR can be used for mapping geologic strata, aquifers, aquicludes. voids, shallow, bedrock units and fractures, site clearance for drilling, mapping utilities and re-bar, locating underground storage tanks, archaeology et al.

Depth of penetrating is dependent on conditions found at each site. Electromagnetic pulse launched by GPR are attenuated (absorbed or scattered) by certain properties of the site's soil; the most important of which is the electrical conductivity of the material. Generally, better overall penetrating is achieved in dry sandy soils; reduced penetrating is achieved in moist. clay or conductive soils. Considerable depth may be attained in saturated sands or through lake water if the specific conductance of the water is low. Radar penetrating is excellent in massive dry materials such as granite, limestone, and concrete.

GPR operating abilities are depended on impulse transmitter (pulser). antennas, receiving electronics and data processing algorithm using. Pulser for engineering geophysics applications has to generate kilowatts impulse with duration from 1 to 10 nanosecond at a repetition rate more than 10 kHz.

High power impulse generation possibilities by drift diodes are considered and simple pulser for portable GPR for various caves and voids location is proposed.

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