A metal detector includes at least one sensor that enables to detect the magnetic field created by the transmitter, an error detection system that enables to determine the distortion by comparing the detected magnetic field to the ideal function, and a corrective system which enables to eliminate the distortion by the additional magnetic field that is created according to the detected distortion and/or by the current or voltage applied to the transmitter.

The present invention relates to a dual-technology detecting system, comprising: -an archway, -a metal detector housed in a first segment of the side panels, -a millimetre-wave body scanner housed in a second segment of the side panels, said body scanner comprising at least one antenna configured to emit radiant energy, wherein, within the first segment, the internal faces of the side panels are separated by a distance at least equal to 800 mm and smaller than or equal to 900 mm, and within the second segment, a maximum distance between the internal faces of the side panels is larger than or equal to 1000 mm and smaller than or equal to 1200 mm.

A reception compensation apparatus based on airborne transient electromagnetic method is disclosed, and includes a receiver coil, a transmitter coil, at least one compensation coil, and at least one compensation magnetic core, where the transmitter coil is disposed around a periphery of the receiver coil. The at least one compensation magnetic core is disposed around an outer surface of the transmitter coil. The at least one compensation coil is disposed around an outer surface of the compensation magnetic core.

A metal detector detects when a target that is a desirable metal object is located within a medium. A signal is transmitted into the medium. A response signal is received from the medium. The response signal includes a secondary medium response signal from the medium and includes a secondary target response signal from the target when the target is located within the medium. The response signal is amplified to produce an amplified signal. Compensation circuitry perform transmit coil transfer function compensation on the amplified signal to produce a compensated signal. A notch module removes a resistive component of the secondary medium response signal from the compensated signal.

In an embodiment, an inductive proximity sensor includes two receiving coils and one transmitting coil arranged between the two receiving coils. The receiving coils and transmitting coil are each formed from a group of at least two individual coils on carrier boards, which are arranged parallel to one another. The carrier boards have a diameter which is smaller than or equal to 10 mm, and a winding of the receiving coils or the transmitting coil has a cross-sectional geometry in which a ratio of a base width to a height lies in the range from 0.2 to 0.3. An embodiment of a method for detecting an object using an inductive proximity sensor includes generating an alternating field using a transmitting coil of the proximity sensor and sensing, using two receiving coils of the inductive proximity sensor, a change in the alternating field caused by proximity of the object.

Techniques are disclosed relating to sensing an object using an inductive proximity sensor. In an embodiment, an apparatus includes a transmission coil having turns formed on a first circuit board and including a first primary winding having a first winding direction. The apparatus further includes a first sensor coil having turns formed on a second circuit board and including a second primary winding having a second winding direction and a second sensor coil having turns formed on a third circuit board and including a third primary winding having a third winding direction opposite to the second winding direction. The coils are spaced apart from one another in a common axial direction and at least one of the coils includes a compensation winding having at least one turn, where the compensation winding is arranged radially outside of, and has a winding direction opposite to, the same coil's primary winding.

A metal detector includes a balanced coil system with a transmitter coil connected to a transmitter unit, which provides a transmitter signal (s1) with at least one fixed/selectable transmitter frequency or a waveform having at least two different transmitter frequencies. First and a second receiver coils provide output signals to a receiver unit, which can include first and second phase detectors in which the output signals are compared with reference signals that correspond to the at least one transmitter frequency and are offset to each other in phase in order to produce in-phase components and quadrature components, which are forwarded to a signal processing unit to suppress signal components originating from goods or noise, and to process signal components originating from metal contaminants.

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.

According to aspects of the present disclosure, systems and methods for measuring fluid resistivity are described herein. An example system may include a non-conductive tube. The non-conductive tube may be filled with a fluid, such as a formation fluid or drilling fluid, whose resistivity needs to be determined. A transmitter may be disposed around an outer surface of the non-conductive tube. A first receiver may be disposed around the outer surface of the non-conductive tube, and a second receiver may be positioned within a bore of the non-conductive tube. The transmitter may generate a primary electromagnetic field in a fluid within the tube, which may in turn generate an eddy current and a secondary electromagnetic field. The first and second receivers may be used to identify the eddy current and the resistivity of the fluid.

A detection device includes a detection mat having a plurality of detection coils, and at least one pair of groups of detection coils, the pair of groups of detection coils includes first and second groups of detection coils. The first and second group of detection coils comprises first and second first and second impedance values. The detection device includes one or more drive sub-systems and a comparison sub-system. The drive sub-systems are operatively coupled to the detection mat and configured to excite at least one pair of groups of detection coils. The comparison sub-system is operatively coupled to the detection mat and configured to receive a differential current signal from the pair of groups of detection coils, the comparison subsystem is configured to generate a control signal based on the differential current signal.