| ABSTRACT: An
electromagnetic detector is designed to locate an object hidden behind
a separator or a cavity within a solid object. The detector includes a
PRF generator for generating 2 MHz pulses, a homodyne oscillator for generating
a 2 kHz square wave, and for modulating the pulses from the PRF generator.
A transmit antenna transmits the modulated pulses through the separator,
and a receive antenna receives the signals reflected off the object. The
receiver path of the detector includes a sample and hold circuit, an AC
coupled amplifier which filters out DC bias level shifts in the sample
and hold circuit, and a rectifier circuit connected to the homodyne oscillator
and to the AC coupled amplifier, for synchronously rectifying the modulated
pulses transmitted over the transmit antenna. The homodyneoscillator modulates
the signal from the PRF generator with a continuous wave (CW) signal, and
the AC coupled amplifier operates with a passband centered on that CW signal.
The present detector can be used in several applications, including the
detection of metallic and non-metallic objects, such as pipes, studs, joists,
nails, rebars, conduits and electrical wiring, behind wood wall, ceiling,
plywood, particle board, dense hardwood, masonry and cement structure.
The detector is portable, light weight, simple to use, inexpensive, and
has a low power emission which facilitates the compliance with Part 15
of the FCC rules. |