Abstract: A metal detector has multiple transmit and receive coils for producing multiple detection fields. In one embodiment, a transmit coil is combined with two receive coils in a configuration that enables the detector to generate two detection fields, one being substantially narrower than the other. The transmit coil is inductively balanced with the receive coils such that the transmit coil induces minimum signals in each of the two receive coils. A metal target lying within a detection field changes the coupling between transit and receive coils and produces signals in the receive coils. The received signals are utilized to identify the target's presence within one or both of the detection fields. The use of two detection fields, substantially different in size, enables the metal detector to search over a broad area for object detection and then narrow the search to more precisely locate the detected object.

Abstract: A metal detector utilizes digital signal processing and a microprocessor to process buffers of information which is received at a periodic rate. Both high and low gain phase quadrature and in-phase signals are provided via a multiplexer to an analog-to-digital converter from a first receive antenna. A second receive antenna provides phase quadrature and in-phase signals also through the multiplexer to the analog-to-digital converter. The received signals are averaged, decimated and low pass filtered to eliminate noise and reduce the quantity of data which must be processed. A threshold (triggering) processing operation is performed to determine whether a valid target signal is present in the data. If not, no further processing is performed. The in-phase and quadrature components are processed using Fourier transforms to select a frequency band which includes the energy for the target signal. The energy in this frequency band is utilized to determine the identification of the target.

Abstract: A metal detector utilizes digital signal processing and a microprocessor to process buffers of information which is received at a periodic ram. Both high and low gain phase quadrature and in-phase signals are provided via a multiplexer to an analog-to-digital converter from a first receive antenna. A second receive antenna provides phase quadrature and in-phase signals also through the multiplexer to the analog-to-digital converter. The received signals are averaged, decimated and low pass filtered to eliminate noise and reduce the quantity of data which must be processed. A threshold (triggering) processing operation is performed to determine whether a valid target signal is present in the dam. If not, no further processing is performed. The in-phase and quadrature components are processed using Fourier transforms to select a frequency band which includes the energy for the target signal. The energy in this frequency band is utilized to determine the identification of the target.