A metal detection apparatus has a passage channel (100) through which products (P) that may contain metal contaminants (C) pass. The apparatus has at least one transmitter unit (1) that provides transmitter signals to a transmitter coil (2) that is inductively coupled to a first and a second receiver coil (31; 32). The receiver coils are balanced and connected separately or combined to an input of a receiver unit (4). The transmitter coil has at least two coil sections (211, 212; 221, 222) that are arranged inclined to one another, with each coil section generating at least a first and a second magnetic field (M.sub.y; M.sub.Z). Each of the first and the second receiver coils has at least a first coil section (311; 321) that is engaged in the first magnetic field and at least a second coil section (312; 322) that is engaged in the second magnetic field.

An intruding metal detection method for a supplying-end module of an induction type power supply system having a supplying-end coil includes: obtaining a previous peak trigger voltage measured during a previous measurement period and setting a reference voltage to be equal to the previous peak trigger voltage; interrupting at least one driving signal of the induction type power supply system to stop driving the supplying-end coil during a measurement period, to generate a coil signal of the supplying-end coil; measuring a first peak of the coil signal within an oscillation cycle of the coil signal, to obtain a first peak trigger voltage; comparing the first peak trigger voltage with the reference voltage; and determining that there is no intruding metal existing in a power supply range of the induction type power supply system when the first peak trigger voltage is equal to or close to the reference voltage.

A metal detection apparatus is provided which includes a balanced coil system with a transmitter coil connected with coil terminals to a transmitter unit, and receiver coils connected to an input of a receiver unit, whose output is connected to a signal processing unit. The transmitter unit includes a controllable frequency generator providing an input signal with a selectable operating frequency to the input of an amplifier stage, whose output is connected to an adaptation unit, which includes a coupling transformer with at least one primary and secondary coil having a transformer coil terminal and transformer tappings. The adaption unit includes tuning capacitors having capacitor terminals and switching devices, with which the secondary coil of the coupling transformer and at least one of the tuning capacitors is connectable to the transmitter coil Individually selectable resonator channels are provided, which when selected, each include the transmitter coil, tapped windings of the secondary coil of the coupling transformer, one of the tuning capacitors connected by a first semiconductor switching device and a second semiconductor switching device, controllable by a channel selector such that one of the resonator channels is always selectable.

A metal detection apparatus is disclosed which includes a balanced coil system with a transmitter coil and receiver coils. A coupling transformer with an input winding is energized by an input signal with a selected operating frequency and an output winding with tappings, each pair of which is selectable to define a partial winding consisting of the turns extending between the selected pair. Individually selectable excitation circuits for energization of the transmitter coil, each including a semiconductor switching device. Individually selectable tuning capacitors, each including an electro-mechanical relay.

An intruding metal detection method for a supplying-end module of an induction type power supply system having a supplying-end coil includes: obtaining a previous peak trigger voltage measured during a previous measurement period and setting a reference voltage to be equal to the previous peak trigger voltage; interrupting at least one driving signal of the induction type power supply system to stop driving the supplying-end coil during a measurement period, to generate a coil signal of the supplying-end coil; measuring a first peak of the coil signal within an oscillation cycle of the coil signal, to obtain a first peak trigger voltage; comparing the first peak trigger voltage with the reference voltage; and determining that there is no intruding metal existing in a power supply range of the induction type power supply system when the first peak trigger voltage is equal to or close to the reference voltage.

The invention concerns a system (1) and a method for scanning a person (2) before access to a restricted access area (3) comprising a processing unit (14) and a metal detector (10, 70) for detecting metal in the shoes (20) or in a waist portion of the person walking on a surface (15). The processing unit controls an indication unit (12, 13) for: letting the person walk towards the restricted area if a first scan indicates the probability of the presence of metal lower than a first threshold; in case of a probability higher than the first threshold, prompting the person to carry out a second scan close to a mark (11) on the carpet; and prompting the 10 user to remove his shoes or object if the first scan indicates a probability higher than a second threshold, or if the second scan indicates a probability higher than a third threshold.

A foreign matter detecting device comprises a first yoke portion and a second yoke portion which adjoin a permanent magnet respectively. The both yoke portions are arranged while interposing a reference space therebetween. Further, a detour yoke portion is arranged. A magnetic resistance of the first detour space being smaller than a magnetic resistance of the predetermined reference space, and magnetic resistances of the second detour space and the first detour space being larger than the magnetic resistance of the predetermined reference space. A detection signal in relation to the foreign matter is outputted on the basis of a magnetic flux density provided in at least any one of spaces of the reference space and the first detour space, corresponding to an amount of retention of the foreign matter in a retaining portion which is provided so that the foreign matter is retained in the second detour space.

A foreign object detector includes detection coils between a transmitter coil in a transmitter device and a receiver coil in a receiver device, a power supply circuit that supplies AC power having a predetermined frequency to each detection coil through a feeder coil located to be electromagnetically coupled to each detection coil, and a detection circuit that detects, while power to be transmitted to the receiver coil is being supplied to the transmitter coil, a criteria voltage to be a criterion for foreign object detection output from each detection coil at a start of power supply from the power supply circuit and outputs a signal to stop power supply to the transmitter coil in response to the criteria voltage for any detection coil deviating from a predetermined range. The transmitter device transmits power to the receiver device contactlessly.

A foreign matter detecting device comprises a first yoke portion and a second yoke portion which adjoin a permanent magnet respectively. The both yoke portions are arranged while interposing a reference space therebetween. Further, a detour yoke portion is arranged. A magnetic resistance of the first detour space being smaller than a magnetic resistance of the predetermined reference space, and magnetic resistances of the second detour space and the first detour space being larger than the magnetic resistance of the predetermined reference space. A detection signal in relation to the foreign matter is outputted on the basis of a magnetic flux density provided in at least any one of spaces of the reference space and the first detour space, corresponding to an amount of retention of the foreign matter in a retaining portion which is provided so that the foreign matter is retained in the second detour space.

A method of operation of a variable frequency metal detector having a driver circuit for establishing an alternating magnetic field in a coil system so as to generate an output signal at a given frequency, said driver circuit comprises a plurality of switches being arranged to cause the coil system to be driven at a frequency determined by the operation of the plurality switches, the method comprising the steps of generating an adjustable balance signal, combining the adjustable balance signal with the output signal of the detector, and varying the adjustable balance signal so as to provide a compensated signal whereby the output signal and/or the adjustable balance signal is filtered to remove one or more harmonics.