Abstract: A hermetically sealed metal detector includes a plastic housing with an integrally formed diaphragm having a predetermined area and a thickness that enables vibration thereof by an internal acoustic transducer. An alert signal audibly drives the transducer in response to a metal detector circuit. The acoustic transducer is positioned to align the transducer output port adjacent to the interior surface of the diaphragm, which enables coupling of the acoustic signal through an air gap to vibrate the diaphragm. A cover is disposed about the diaphragm on the exterior of the housing. The cover has a vent formed therethrough for enabling passage of the acoustic energy to the exterior of the housing. Light and battery hermetic sealing are also presented.

Abstract: A hand-held metal detector and soil excavation device useful for locating and retrieving metallic objects concealed in soil or other materials. The device includes a housing with a hand-grip portion and an elongated probe portion. There is an excavation tool connected to the housing that is useful for moving soil to locate metallic objects that are sought. The device also includes a metal detector circuit located within the housing, that operates to generate an alert signal when the probe portion is moved into proximity of metallic objects.

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.

Abstract: A metal detector is provided with circuitry for producing a plurality of vector signals derived from a target signal. Each of these vector signals corresponds to a phase characteristic of target signals. These vector signals define phase ranges which correspond to classifications of targets. Upon detection of a target signal, the metal detector generates first and second phase detected signals which in turn generate a plurality of vector signals. These vector signals are digitized and within a microprocessor a determination is made through slope analysis to determine which range includes the principal phase of the detected target signal. The vector signals which define the identified range are then utilized in algebraic calculations to define one of a plurality of subphase ranges within each range. This identified subphase range identifies a segment in a linear display which is illuminated to show the determined characteristic for the detected object.

Abstract: A hobby-style metal detector includes a two-piece stem interconnected by a hand grip and provided with an arm rest. A search coil is positioned at the lower end of the first section of the stem and an electronic housing is mounted on the first stem section near the hand grip. A metal detector circuit, a display and operator controls are provided with the electronic housing. A second housing is detachably connected to the second section of the stem in conjunction with the arm rest. The second housing contains batteries and can be detached and clipped to the operator's belt to reduce the weight carried by the operator's arm. A speaker can further be included within the second housing thereby removing additional weight from the arm carried unit. A cable is provided to extend from the second housing to the electronic package for providing the battery power to the metal detector circuit. When a speaker is provided in the second housing, a further line is provided in the cable for the detection signal.

Abstract: A metal detector circuit includes a transmit coil (12) and a receive coil (56) arranged in a balanced induction configuration in an electromagnetic field. The receive signal from the receive coil (56) is input to electronic switches (146, 148) which receive quadrature reference inputs from a phase shift circuit (112). The phase demodulated outputs of the switches (146, 148) are passed through amplifiers and input to an analog-to-digital converter (324) to produce digital signal samples which are transmitted through a bus (326). The bus (326) is connected to random access memory (414, 416) and a read only memory (418) which includes a stored signal processing program. A microprocessor (374) is connected to the bus (376) for receiving the digital signal samples and the stored program from memory (418). The microprocessor (374) executes the stored signal processing program to produce a digital output signal which is transmitted through the bus (326) to a digital-to-analog converter (360).

Abstract: A metal detector circuit of the balanced induction type is utilized to detect hidden metal objects. A receive signal is provided with two fixed concurrent phase shifts relative to the transmit signals. Each of the phase shifted receive signals is synchronously demodulated to produce first and second vector signals. The vector signals are combined in a summation circuit to produce a third vector signal. The first and third vector signals are then selectively combined by an operator to produce a fourth vector signal having a desired vector range between minimum and maximum vector angles. The metal detector circuit of the present invention provides a response for objects having a phase response signal outside the selected phase range. The first and fourth vector signals are each differentiated twice then level detected. The outputs from the level detection process are logic signals which are input to an AND gate.

Abstract: A metal detector is disclosed which has a transmit coil, a receive coil, and circuit means for detecting metal objects due to a change in the magnetic coupling between the coils. Circuit board arrangement techniques are disclosed which enable the close placement of the transmit and receive coils and the circuit board, thereby allowing packaging of the metal detector in a small package. A low battery voltage indicator circuit is provided to warble an audio indicator signal to indicate sufficient battery voltage. In the event the battery voltage drops below a certain level, the warbling of the indicator signal ceases and a steady tone is generated thereby indicating a low battery voltage condition.

Abstract: A metal detector is disclosed which has a transmit coil, a receive coil, and circuit means for detecting metal object due to a change in the magnetic coupling between the coils. Circuit board arrangement techniques are disclosed which enable the close placement of the transmit and receive coils and the circuit board, thereby allowing packaging of the metal detector in a small package. A low battery voltage indicator circuit is provided to warble an audio indicator signal to indicate sufficient battery voltage. In the event the battery voltage drops below a certain level, the warbling of the indicator signal ceases and a steady tone is generated thereby indicating a low battery voltage condition.

Abstract: A low drift rate tuning circuit (10) is operated in conjunction with a feedback network (36). An operational amplifier (12) is connected to first and second power supply buses (18, 20). The negative input terminal (16) of the amplifier is connected to the lower voltage supply bus (20). The output of the amplifier (12) is connected to an inverting amplifier (51). The output from the circuit (10) is connected as the input of the feedback network (36) and the input to the circuit (10) is connected to the output of the feedback network (36). In the seek mode the circuit (10) balances the voltages at the input terminals of the operational amplifier (12). In the balance condition the common mode input voltage to the operational amplifier (12) is essentially zero at which voltage the input leakage current is at a minimum. With the leakage current reduced to a minimum the circuit is made more stable by reason of reduced drift over time.

Abstract: A metal detector (10) is disclosed which has a transmit coil (48) and a receive coil (150) for detecting a metal object due to a change in the magnetic coupling between the coils (48, 150). The metal detector (10) has a plurality of operating modes and for each mode an operating parameter is selected and stored. Each operating parameter is used to generate a demodulation signal. A multiposition switch (36) is manipulated by an operator to select one of the operating modes. A logic circuit (191) is provided to route the demodulation signals to a demodulation circuit (110) to operate on a receive signal from the receive coil (150). An audible signal produced by the metal detector (10) is inhibited when operating modes are changed. An automatic tuning circuit (228) has selectable slewing rates for nulling the output from the metal detector (10).

Abstract: A metal detector (10) is disclosed which has a transmit coil (48) and a receive coil (150) for detecting a metal object due to a change in the magnetic coupling between the coils (48, 150). The metal detector (10) has a plurality of operating modes and for each mode an operating parameter is selected and stored. Each operating parameter is used to generate a demodulation signal. A multiposition switch (36) is manipulated by an operator to select one of the operating modes. A logic circuit (191) is provided to route the demodulation signals to a demodulation circuit (110) to operate on a receive signal from the receive coil (150). An audible signal produced by the metal detector (10) is inhibited when operating modes are changed. An automatic tuning circuit (228) has selectable slewing rates for nulling the output from the metal detector (10).