This invention is related to the method providing computation of the signal frequency components in an acceptable accuracy in contravention of the shifts in the phase and the magnitude information caused by asynchronous sampling of the signals in the process of asynchronous sampling of metal detectors wherein the received signal by the receiver unit (4) divided into time intervals, say timing values those are far shorter than the sampling period and correspond to nearest probable sampling of the ADC (6); providing the computation of the sine and cosine coefficients or exponents of time constant coefficients of the said timing value from previously located or dynamically generated coefficient table; resulting the elimination of the requirement of synchronous sampling and the requirement of the signal period is multiple of the sampling period.

An apparatus (1) for detecting metal is equipped with at least one test device (2) with a non-metallic guide tube (21). Only a proximal end of the guide tube is connected to a pneumatic control unit (3). A distal end of the guide tube has at least one first ventilation port (211). A test article (7), having a known mass of metal, is movable back and forth between the proximal end and the distal end of the guide tube, at least through a section of an electromagnetic field, to verify operation of the metal detection The pneumatic control unit can use air pressure, either elevated above or reduced below the ambient pressure, applied to the proximal end of the guide tube in order to drive the test article back and forth, or only in one direction if it is returned by gravitational force.

A hand-held metal detector coil, including a coil housing which houses aggregate transmit windings and aggregate receive windings. The aggregate transmit windings include a major group of transmit windings that includes a first transmit winding, and the aggregate receive windings include a major group of receive windings that includes a first receive winding; the coil further includes a minor group of windings to null the aggregate receive windings with respect to the aggregate transmit windings. In an absence of external influences, a mutual inductance coupling coefficient between the aggregate receive windings and the aggregate transmit windings, k.sub.TR, is <0.03. A mean location of turns of the major group of transmit windings is further from a bottom plane of the coil housing than a mean location of turns of the major group of receive windings; the first transmit winding has at least part of their cross-sectional winding profile with a first cross-sectional axis longer than a second cross-sectional axis by at least a factor of 3; a mutual coupling constant coefficient between the major group of transmit windings and the major group of receive windings, k.sub.11, is <0.5; and a mean location of turns of the of the first transmit winding is at least 25 mm or more from a bottom plane of the coil housing.

A metal object detecting device for a wireless charging device is provided and includes an object detection coil, a relay and an object detector circuit. The wireless charging device has a transmitter coil, a first digital signal processor and a receiver coil. The object detection coil is disposed above the transmitter coil. The relay is connected to the object detection coil. The object detector circuit is connected to the relay and the first digital signal processor. The transmitter coil transmits a power signal to the receiver coil within a power supplying time. The relay is turned on during an object detection time such that an oscillation signal is generated from the object detection coil and the object detector circuit as a basis for determining whether or not a metal object is close to the wireless charging device.

A metal detection apparatus (9) is tested with a test device (7) having at least one test article (79), movable through a detection zone (60). The test article is moved through the detection zone along a first transfer axis (ca) and a first input signal is measured. A first threshold (th1) is determined, where an amplitude of the first input signal exceeds the first threshold (th1). Then, an identical test article is moved through the detection zone along a further transfer axis (ta; . . . ) and a further input signal is measured and a further threshold (th2; . . . ) is determined, where an amplitude of the further input signal exceeds the further threshold (th2; . . . ). The first or further threshold (th1; th2; . . . ) is selected in the signal processing path (4) whenever the test article is moved along the related transfer axis (ca; ta; . . . ).

For near field communications, inductive coils coupled to each communicating circuit are brought close together so that there is inductive coupling between the two coils. Data signals can then be relayed between the two circuits without any direct connection between them. However, the system is susceptible to common mode noise, such as ambient EMI. In addition to the active coil pairs used for transmitting and receiving data, a pair of passive coils is provided, proximate to the active coil pairs, that is only used for detecting the ambient EMI. The EMI signals detected by the passive coils are processed by a noise detector/processor, and the noise detector processor then controls the transmitters and/or receivers to at least partially compensate for the detected EMI signals. Transmit power or receiver thresholds may be controlled by the noise detector/processor to improve the signal-to-noise ratio, or other compensation techniques can be used.

A metal detector (1) has a drive coil (L61) and at least one detection coil (L62, L63) that detect fluctuations in a magnetic field generated by the drive coil, caused by metallic particles present in an inspected object. A multi-frequency transmitter unit (10) has a converter (4) with a plurality of drive switches (S41, S42; S43, S44) driven by a drive controller (2). The drive switches alternately conduct a drive current through the drive coil to generate an electromagnetic field with two or more different frequency components. A waveform of the drive current is determined, as is at least one pulse-modulated (PXM) signal corresponding to the determined waveform. The determined PXM-signal is determined online or is stored in a memory module (231; 232). The determined PXM-signal is generated and applied to control the drive switches. The drive current can be applied to the drive coil through an admittance unit (5).

A magnetic field sensing apparatus including a magnetic flux concentrator, a plurality of magnetoresistance units, and a plurality of magnetization direction setting elements is provided. The magnetic flux concentrator has a top surface, a bottom surface opposite to the top surface, and a plurality of side surfaces connecting the top surface and the bottom surface. The magnetoresistance units are respectively disposed beside the side surfaces. The magnetoresistance units are electrically connected to form an unchangeable Wheatstone full bridge. The magnetization direction setting elements set the magnetization directions of the magnetoresistance units into three different combinations in three different periods, respectively, so as to enable the unchangeable Wheatstone full bridge to respectively measure the magnetic field components in the three different directions in the three different periods.

This invention is related to the method providing computation of the signal frequency components in an acceptable accuracy in contravention of the shifts in the phase and the magnitude information caused by asynchronous sampling of the signals in the process of asynchronous sampling of metal detectors wherein the received signal by the receiver unit (4) divided into time intervals, say timing values those are far shorter than the sampling period and correspond to nearest probable sampling of the ADC (6); providing the computation of the sine and cosine coefficients or exponents of time constant coefficients of the said timing value from previously located or dynamically generated coefficient table; resulting the elimination of the requirement of synchronous sampling and the requirement of the signal period is multiple of the sampling period.

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.