A detection device (100) includes a detection mat (102) having a plurality of detection coils (106), and at least one pair of groups of detection coils (106), the pair of groups of detection coils (106) includes first and second groups of detection coils (106). The first and second group of detection coils (106) comprises first and second first and second impedance values. The detection device (100) includes one or more drive sub-systems (112) and a comparison sub-system (112). The drive sub-systems (112) are operatively coupled to the detection mat (102) and configured to excite at least one pair of groups of detection coils (106). The comparison sub-system (114) is operatively coupled to the detection mat (102) and configured to receive a differential current signal from the pair of groups of detection coils (106), the comparison sub-system (114) is configured to generate a control signal based on the differential current signal.

A detection coil includes a first group of coils, a second group of coils, and a third group of coils that are continuously wound and coaxial, and the second group of coils is located between the first group of coils and the third group of coils. A coil that generates the first magnetic field is coaxial with the first group of coils, the second group of coils, and the third group of coils. A sum of the induced electromotive forces of the first group of coils, the second group of coils, and the third group of coils is zero. When a metal foreign matter exists, a sum of the induced electromotive forces of the first group of coils, the second group of coils, and the third group of coils is not zero.

Provided is a technique for detecting a vehicle type and a traveling direction of a vehicle by an electromagnetic induction sensor.

A sensor unit (10), which is an electromagnetic induction sensor, includes a transmission coil (TX1), a first reception coil (RX1), and a second reception coil (RX2). A magnetic field of a vehicle (90) made of steel attracts a magnetic field emitted from the transmission coil (TX1) (S1). As the vehicle (90) approaches, a state 1 indicated by the broken line changes to a state 2 indicated by the dash-dot line (S2). A reduction in induced voltage and a phase change occur with respect to the induced voltage when the first reception coil (RX1) is in the magnetic field of state 1 (when the vehicle is not detected) (S3). The differential output signals of the second reception coil RX2 and the first reception coil RX1 change according to the advancement of the vehicle and according to the unevenness of the vehicle bottom portion 92 and the metal species (S4). The trajectory image representing a differential output signal in rectangular coordinates of a reception level and a phase difference is different for each vehicle, so the vehicle type may be distinguished.

The method and system are disclosed for operating a metal detector having a balanced coil system with a drive coil that is connected to a transmitter unit which provides a transmitter signal with at least one operating frequency (f.sub.TX), and with first and second detection coils that provide an output signal to a receiver unit that processes a related receiver signal which includes an imbalance signal, and that provides digital in-phase and quadrature components (d.sub.I, d.sub.Q) of the demodulated imbalance signal.

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.

This application relates to a receiving compensation apparatus for an airborne transient electromagnetic method. The receiving compensation apparatus for the airborne transient electromagnetic method in this application includes a received coil, a transmitting coil, compensation coils, and at least one compensation magnetic core, where the transmitting coil is disposed on the periphery of the received coil, the compensation magnetic core is disposed on the transmitting coil, and the compensation coils are disposed on the compensation magnetic core.

A magnetic field sensing system may include a first magnetic field sensing element; a second magnetic field sensing element; means for generating a first magnetic field having a first non-zero frequency; means for generating a second magnetic field having a second frequency; a conductive target positioned to generate a reflected magnetic field in response to the first magnetic field; means for producing a first signal representing the first magnetic field and the reflected magnetic field during a first alternating time period; means for producing a second signal representing the second magnetic field during a second alternating time period; means for calculating an error value as a function of the first and second signals, wherein the error value is based, at least in part, on the second signal during the first time period; and means for applying the error value to the first signal during the first alternating time period.

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.

The method and system are disclosed for operating a metal detector having a balanced coil system with a drive coil that is connected to a transmitter unit which provides a transmitter signal with at least one operating frequency (f.sub.TX), and with first and second detection coils that provide an output signal to a receiver unit that processes a related receiver signal which includes an imbalance signal, and that provides digital in-phase and quadrature components (d.sub.I, d.sub.Q) of the demodulated imbalance signal.

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.