Abstract: A metal detector including transmit electronics having a plurality of switches for generating a repeating transmit signal cycle for transmission by a transmit coil. The repeating transmit signal cycle includes at least a high voltage period, and at least a low voltage period, the low voltage period followed by a substantially zero voltage period. The output impedance of the transmit electronics is less than three times the equivalent series resistance of the transmit coil during the low voltage period and the substantially zero voltage period.

Abstract: A metal detector including transmit electronics having a plurality of switches for generating a repeating transmit signal cycle for transmission by a transmit coil. The repeating transmit signal cycle includes at least a high voltage period, and at least a low voltage period, the low voltage period followed by a substantially zero voltage period. The output impedance of the transmit electronics is less than three times the equivalent series resistance of the transmit coil during the low voltage period and the substantially zero voltage period.

Abstract: This invention relates to metal detectors used to detect metal targets in soils wherein the detector is insensitive to signals induced by a received magnetic field due to perpendicular components of a uniform conducting half-space, including metal detectors simultaneously capable of suppressing signals due to components of substantially log-uniform viscous superparamagnetic soil, and including metal detectors using repeating transmit signal cycles resembling a pulse induction-like waveforms. It discloses signal processing, in particular synchronous demodulation functions which may simultaneously substantially suppress signals due to perpendicular components of a uniform conducting half-space in a received magnetic field, signals due to components of substantially log-uniform viscous superparamagnetic soil, and signals due to a movement of the receive coil with respect to a static magnetic field.

Abstract: A metal detector transmitting, through a transmit coil, a repeating transmit signal cycle, which includes at least one receive period and at least one non-zero transmit coil reactive voltage period; and sensing a current in the transmit coil during at least one receive period to control a magnitude and/or duration of the at least one non-zero transmit coil reactive voltage period such that the average value of the current during at least one receive period of every repeating transmit signal cycle is substantially constant, and the current during at least one receive period is substantially independent of the inductance of the transmit coil.

Abstract: A metal detector with improved magnetic soil response cancellation is disclosed.

Abstract: An electronic metal detector having, a transmit coil arranged and adapted to transmit an alternating magnetic field associated with a reactive transmit coil voltage, the transmit coil being connected to transmit electronics arranged and adapted to generate a transmit signal, the transmit electronics having at least two power sources, a first power source and a second power source, wherein the first power source is adapted and arranged to connect to the transmit coil for at least a first period, and the second power source is adapted and arranged to connect to tie transmit coil for at least a second period, the said transmit electronics including at least one servo control negative feedback loop, a first servo control negative feedback loop, which is adapted and arranged to monitor a transmit coil current for at least part of the said first period, and to control at least part of the said transmit signal, the transmit electronics being adapted and arranged to control the transmit signal to produce the reactive

Abstract: An electronic metal detector having a transmit coil (1) adapted to transmit an alternating magnetic field associated with a reactive transmit voltage, wherein the transmit voltage signal is selected such that the reactive transmit voltage is approximately constant for at least a time period during which a magnetic field signal to be processed is received by the detector for processing.

Abstract: A highly flexible real-time metal detector platform which has a detection capability for different targets and applications, where the operator is able to alter synchronous demodulation multiplication functions to select different types or mixtures of different types to be applied to different synchronous demodulators, and also different waveforms of the said synchronous demodulation multiplication functions; examples of the different types being time-domain, square-wave, sine-wave or receive signal weighted synchronous demodulation multiplication functions. The operator can alter the fundamental frequency of the repeating switched rectangular-wave voltage sequence, and an operator may alter the waveform of the repeating switched rectangular-wave voltage sequence and corresponding synchronous demodulation multiplication functions.

Abstract: A real time electronic metal detector including a magnetic transmitter (1) and a receiver (3), wherein the receiver includes approximate sine-wave weighted synchronous demodulation and a switched voltage signal is applied to the magnetic transmitter and the said receiver approximate sine-wave weighted synchronous demodulation is selected to receive synchronously with the switched voltage signal, such that the switched voltage signal and the receiver approximate sine-wave weighted synchronous demodulation may be altered by means of operator selection.

Abstract: An electronic metal detector having transmit electronics includes switching electronics arranged and adapted to generate a transmit signal. The transmit electronics includes at least two power sources, and is connected to a transmit coil arranged and adapted to transmit an alternating magnetic field. The switching electronics are adapted and arranged to switch a first voltage of one power source to the transmit coil for at least a first period and also a third period, and to switch a second voltage of the other power source to the transmit coil for at least a second period. Receive electronics are arranged to receive and process a receive magnetic field during at least some of the second period and fourth period to produce an indicator output, at least indicating the presence and a characteristic of some metal targets under the influence of the magnetic field.

Abstract: A class-D audio amplifier switching output stage with reduced distortion including, application of damping to the power supply voltage nodes in the form for example of a low inductance damping snubber circuit including a first resistor in series with a second capacitor connected via a low inductance path between the power supplies connecting the output switching devices.

Abstract: An electronic metal detector having a transmit coil (1) adapted to transmit an alternating magnetic field associated with a reactive transmit voltage, wherein the transmit voltage signal is selected such that the reactive transmit voltage is approximately constant for at least a time period during which a magnetic field signal to be processed is received by the detector for processing.

Abstract: An electronic class-D amplifier with intrinsically low distortion employing modulation of the slopes of a triangular-wave carrier reference signal; the modulation being in proportion to the derivative of the input signal. The negation of the distortion is most successful if this derivative signal is shifted in phase and gain to compensate for the closed loop phase and gain of the amplifier. The amplifier includes a pulse width modulator which includes an oscillator (5) with at least one integrator and a first comparator (6), at least one servo-loop amplifier (3), an input signal processor (4) which processes and modifies the input amplifier signal. An output signal of the oscillator produces a carrier reference signal (13) which includes at least positive and negati derivative components, which are modulated by an output of the input signal processor (4) which is applied to a modulation input of the oscillator (5), whereby at least the symmetry of the carrier reference signal is modulated.

Abstract: An electronic class-D amplifier including a pulse width modulator and a servo-loop amplifier characterized in that there is provided a sample and hold element which samples a signal at the sample input when a sample command signal is applied to a control input, and holds the value of the last sampled value of the signal at the sample input when a hold command signal is applied to the control input, and the output of the sample and hold element is connected to a modulation input of the pulse width modulator wherein a negative feedback path connects an output of the output switching stage to an input of the servo-loop amplifier.

Abstract: An electronic class-D amplifier including a one servo-loop amplifier plus pulse width modulator, and a controlled delay stage including a delay modulation input, and a negative feedback path connects an output of the output switching stage to an input of the servo-loop amplifier wherein the forward gain of an output switching stage, the forward gain of the servo-loop amplifier plus pulse width modulator and controlled delay stage, and a carrier reference output signal's mean frequency, and modulation gain of the controlled delay stage, and the gain of the negative feedback path, are selected to lower the distortion of a signal at the amplifier output relative to a signal applied to the amplifier input.

Abstract: An ultra-low distortion electronic amplifier wherein the global dominant pole is formed by the selection of circuit and component arrangement within the input stage, such that the global dominant pole, is of third order, at audio frequencies. This audio power amplifier implements a high order global dominant pole with the use of operational amplifiers, and this high order dominant pole is distributed across both the voltage amplification stage and input stage without adverse reduction in the slew rate. The amplifier has increased negative feedback at audio and ultrasonic frequencies, giving a reduction in distortion across the entire audio band and some of the lower ultrasonic band.

Abstract: Metal detection apparatus containing at least two inductive coils one of which acts as a transmit coil and all of which act as receive coils and processing circuitry wherein a proportion of the first receive electronic signal and a proportion of the second receive electronic signal may be selected to produce various first resultant linear combination signals for the purpose of improved interference cancelling.

Abstract: A metal detector apparatus including a transmit coil which transmits a magnetic field, transmit timing control circuitry which also includes timing for a semiconductor switch, and receive signal circuitry and receive signal processing circuitry, with a transmit coil damping network including at least one resistor connected in series with the semiconductor switch across the transmit coil, and timing control circuitry which generates a timing sequence which is selected so that for at least some of the time no transmit field is generated and at least during part of the transmit signal, the first semiconductor switch is controlled to be off and is turned on before the cessation of the transmit field.

Abstract: A metal detector with a transmit coil which transmits a magnetic field, transmit timing control circuitry, and receive signal circuitry and receive signal processing circuitry, and a low voltage and a high voltage power supply. The timing sequence generated within the transmit timing control circuitry produces control signals such that there are at least two different transmit periods, a short and a long period, and such that there are periods when no current flows through the transmit coil. The timing sequence is such that an average transmit coil energy at termination of the long periods is similar to that of an average transmit coil energy at termination of the short periods.

Abstract: Metal detection apparatus wherein a transmit coil will transmit magnetic pulses, and the processing circuitry will weight a receive signal more heavily soon after a transmit pulse transition and less heavily after a longer period following the transmit pulse transition.