Abstract: This invention is for a pulse induction metal detector which uses combinations of the signal detected during non-transmission of the magnetic field to eliminate those contributions to the signal due to the remanent magnetization of ferrites and asynchronous magnetic fields within the target volume.

Abstract: An apparatus and method for supplying a regulated direct electric current comprises a switch mode regulator having an input for receiving a varying source of electrical power. A linear regulator provides a source of low noise direct current and has an input connected so as to receive a voltage that is dependent upon an output of the switch mode regulator. A first servo-loop provides a first control signal to the switch mode regulator. The first control signal is varied according to a variation in the voltage across the linear regulator. A second servo-loop provides a second control signal to the linear regulator. The second control signal is varied according to the difference between a voltage that is related to an output of the linear regulator and a reference voltage. The second servo-loop has a higher gain than the first servo-loop when both of the servo-loops are operating at frequencies that are within their operating frequency ranges.

Abstract: This invention is for a method of an apparatus to perform metal discriminatory detection comprising the application of a multi period rectangular wave form to a transmitter coil, processing received signals by combining received components measured during different selected periods with respect to the transmitted signal in a manner based upon the predictable characteristics of ground constituents and thereby to provide an output signal which will be selectively indicative of a metal object within a target volume and substantially distinguishable from any signal arising from any electrically non-conducting ferrite in the target volume.

Abstract: A metal detector apparatus and a metal detection method for detecting and discriminatory interrogating a metal target buried in the ground. The detector includes a transmitter for providing a first varying magnetic field including at least two frequency components and a receiver for providing a resultant voltage dependent upon a second magnetic field resulting from the combined effects of the ground and metal targets buried in the ground, upon the first alternating magnetic field. The detector samples at least three voltage measurements of the resultant voltage over three different time periods to provide three sampled values which are then processed by a microprocessor to provide three average ground balanced signals from which at least two ratios are calculated and compared against a pre-defined response.

Abstract: An apparatus and method for ultrasonic cleaning is disclosed in which a transducer (35) in a liquid bath is driven by electronic circuitry causing rapid change of frequency to limit development of high concentration for any significant period of time. The electronic circuitry uses two field effect transistors (19 and 20) driving a square wave into an inductor (31) and capacitor (32) in series with a transformer inductor (33) which is coupled in parallel to the transducer (35) the inductor (31) and capacitor (32) and the transformer inductor (33) which is coupled in parallel to the transducer (35) being selected to be resonant at a mean driving frequency.

Abstract: An arrangement to determine whether a tennis ball is "in" or "out" on a playing surface, which includes both a transmit coil and a receive coil beneath the playing surface and a modified tennis ball to have a non-zero magnetic permeability, so that an alternating signal can be transmitted from the transmit coil and re-radiated from the tennis ball, which can then be detected by the receive coils, and can be synchronously demodulated and resistive and reactive components of the signal analysed to discriminate the ball from other influences. The receive coils can be wound to avoid electro-magnetic interference from far fields.

Abstract: A means and arrangement to assist in determining the location of a ball relative to a line of a game surface is disclosed. The arrangement utilizes transmit and receive coils buried beneath lines on a game surface. Overlapping transmit coils operate at different frequencies and include filtering means to make each transmit coil substantially independent of the other transmit coil.

Abstract: A conducting metal discriminating detection apparatus which uses at least two different frequencies and in preference 3 to interrogate a target. The detection apparatus distinguishes reactive and resistant components of each of the received signals and combines these in such a way as to avoid effects of background such as ironstone in one case or salt water in another.

Abstract: An apparatus is described for detecting metal objects in an interrogated environment. An alternating magnetic signal is transmitted, and received by a receiving coil. The signal is amplified, and is then synchronously demodulated based on a transmitted frequency. The synchronously demodulated signals are low-pass filtered, and then changes in the amplitude of these low-pass filtered signals are detected. The outputs are cross-correlated and interrograted, and are used to control a controlled phase shifter. The output of the controlled phase shifter is used as a reference input to a first one of the synchronous demodulators, and a shifted transmitted signal is used as a reference to the second synchronous demodulator.

Abstract: A sensing head for a metal detector including means for magnetic transmission and detection of a retransmitted signal from a target by means of at least one coil, the head being characterized in that at least some of the conductor material forming the coil and providing for passage of current through the coil is such as to provide for such passage wherein the arrangement is such or the selection of conductor material is such as to restrict the magnitude of eddy currents in the conducting material. Coils wound from wires in parallel, and in particular, Litz wires, are disclosed.