A sensor for the location of metallic objects and also an associated method comprise a plurality of transmitting coils (2.1, 2.2) and at least one receiving coil (1.9) which are arranged such as to be inductively coupled to one another and overlap to a partial extent for the purposes of decoupling the interaction therebetween, whereby there can be obtained a point of optimal cancellation of the interaction. Due to the fact that a flow of current is passed through the transmitting coils (2.1, 2.2) by a sensor electronic system, equal flows of current through the transmitting coils have an effect upon the at least one receiving coil (1.9) which results in a local point of optimal cancellation which moves in a first direction when there is a flow of current in a first transmitting coil (2.1), whereas it moves in another direction when there is a flow of current in a further transmitting coil (2.2), and due to the fact that there is provided a control circuit for the regulation of the currents in the transmitting coils which leads to a displacement of the local point of optimal cancellation which causes cancellation of the received signal, a simple and effective sensor is thereby produced.

A balanced coil system (2) of a metal detection system has a transmitter coil (21) connected to a first transmitter unit (1), to provide a transmitter signal (s1) comprising at least first and second operating frequencies (f.sub.TX1, f.sub.TX2). First and second receiver coils (22, 23), which compensate one another when the system is in balance, provide output signals (s22, s23) to a receiver unit (3). The respective operating frequencies are applied separately together each with a monitoring frequency (f.sub.MON) to inputs of first and second modulation units (52, 53), which provide first and a second modulated monitoring signals (s.sub.M1, s.sub.M2), each comprising a first or second modulated monitoring frequency (f.sub.MM1, f.sub.MM2) without a carrier. When applied to a summation unit (54), the modulated monitoring signals result in a combined output signal (s.sub.M12) that is applied to a monitoring coil (24), inductively coupled with at least one of the receiver coils.

The invention provides for a metal detector (100, 300) with at least a first coil (102) for generating a first magnetic field (108) along a first direction (119). The first coil is a split coil with a first (104) and a second (106) portion (104). A coil power supply (110) separately supplying time varying electrical power to the coil portions. At least one electrical sensor (116, 118) measures electrical data (136) descriptive of the electrical power supplied to at least the first coil portion and the second coil portion. The coils are controlled such as to move a field-free region in a predetermined pattern within a measurement zone. If metal is detected, the pattern is modified for refining localisation of the metallic object.

A line locator system that includes a metal detector is disclosed. In accordance with some embodiments of the invention, the line locator system includes a digital signal processor in a housing; a line locator portion mounted in the housing and coupled to the digital signal processor; and an active metal detector mounted in the housing and coupled to the digital signal processor.

An antenna arrangement. The arrangement uses four conductive loops, each within a distinct plane from the other conductive loops. The four conductive loops have a common center point. Each loop is within a dipole magnetic field, and detects a component thereof. By balancing the signals received between matched pairs of the conductive loops, the difference between the signals can be used to guide the antenna arrangement to a null point—that is—a point in the magnetic field where each pair of conductive loops is balanced. The antenna arrangement can further be used to determine the depth of the dipole field source using the magnitude of the field.

A metal detector 20 includes a detection signal acquisition unit 31, a threshold value setting and updating unit 32, and a determination unit 33. The detection signal acquisition unit 31 acquires a detection signal that changes according to the detection strength for a rebar W1 contained in concrete W, on the surface of the concrete W. The threshold value setting and updating unit 32 sets a threshold value in order to determine the presence or absence of the rebar W1 on the basis of the maximum value and/or the minimum value included in the acquisition results for the detection signal acquired by the detection signal acquisition unit 31. The determination unit 33 determines the presence or absence of the rebar W1 by using the threshold value set in the threshold value setting and updating unit 32.

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 means to enable the inspection of industrial materials in order to see hidden structural defects that can lead to an early failure, using electromagnetic fields and harmonic waves.

A metal detector 20 includes a detection signal acquisition unit 31, a threshold value setting and updating unit 32, and a determination unit 33. The detection signal acquisition unit 31 acquires a detection signal that changes according to the detection strength for a rebar W1 contained in concrete W, on the surface of the concrete W. The threshold value setting and updating unit 32 sets a threshold value in order to determine the presence or absence of the rebar W1 on the basis of the maximum value and/or the minimum value included in the acquisition results for the detection signal acquired by the detection signal acquisition unit 31. The determination unit 33 determines the presence or absence of the rebar W1 by using the threshold value set in the threshold value setting and updating unit 32.

A system for metal detection comprises a single aperture comprising two or more sets of detection coils that surround the perimeter of the aperture. A flow path of materials passes through the aperture. Each set of detection coils comprises a transmitter and two receiver coils, with the transmitter coil located between the two receiver coils. Each set of detection coils is at a different angle relative to the flow path.