Abstract: An apparatus and method for detecting and locating hidden objects employs a symmetrical array of five directional antennas, including a central transmit antenna and a pair of receive antennas at each side of the transmit antenna, respectively. All of the antennas are pointed in the same general direction toward an object field of interest. The transmit antenna radiates a beam of high-frequency electromagnetic energy, and the receive antennas receive high-frequency electromagnetic energy returned by hidden objects. Each pair of receive antennas has an associated phase detector, the output of which represents the phase difference between receive antenna signals corresponding to the received electromagnetic energy. A circuit determines when the outputs of the phase detectors represent predetermined phase differences and operates indicator devices.

Abstract: An apparatus and method for detecting and locating hidden objects employs a symmetrical array of five directional antennas, including a central transmit antenna and a pair of receive antennas at each side of the transmit antenna, respectively. All of the antennas are pointed in the same general direction toward an object field of interest. The transmit antenna radiates a beam of high-frequency electromagnetic energy, and the receive antennas receive high-frequency electromagnetic energy returned by hidden objects. Each pair of receive antennas has an associated phase detector, the output of which represents the phase difference between receive antenna signals corresponding to the received electromagnetic energy. A circuit determines when the outputs of the phase detectors represent predetermined phase differences and operates indicator devices.

Abstract: Continuous-wave radiation is used to detect a target hidden behind a surface. In an embodiment, a transmitter directs a beam of continuous-wave microwave radiation from a transmitting location, and reflected radiation from the target is received at first and second receiving locations closer to the surface than the transmitting location. The transmitting and receiving locations have spatial relationships such that the phase of reflected radiation received at one receiving location is in quadrature with the phase of reflected radiation received at the other receiving location. In an embodiment, direct transmitted radiation is received at the receiving locations in quadrature.

Abstract: Continuous-wave radiation is used to detect a target hidden behind a surface. In an embodiment, a transmitter directs a beam of continuous-wave microwave radiation from a transmitting location, and reflected radiation from the target is received at first and second receiving locations closer to the surface than the transmitting location. The transmitting and receiving locations have spatial relationships such that the phase of reflected radiation received at one receiving location is in quadrature with the phase of reflected radiation received at the other receiving location. In an embodiment, direct transmitted radiation is received at the receiving locations in quadrature.

Abstract: Continuous-wave radiation is used to detect a target hidden behind a surface. In an embodiment, a transmitter directs a beam of continuous-wave microwave radiation from a transmitting location, and reflected radiation from the target is received at first and second receiving locations closer to the surface than the transmitting location. The transmitting and receiving locations have spatial relationships such that the phase of reflected radiation received at one receiving location is in quadrature with the phase of reflected radiation received at the other receiving location. In an embodiment, direct transmitted radiation is received at the receiving locations in quadrature.

Abstract: Ferromagnetic material of an elongated object, such as a fiber optic cable, is permanently magnetized in a manner that results in a substantially cylindrically symmetric radial external magnetic field around the object. The produced magnetization is substantially greater than natural magnetization of the ferromagnetic material by the earth's magnetic field. The radial external magnetic field varies periodically along the length of the object. If the wavelength of the periodic variations is long compared to the width (diameter) of the object, the strength of the radial external magnetic field decreases approximately inversely with distance from the object for distances that are small compared to the wavelength. The periodic magnetic field variations may have a square wave or a sine wave pattern, for example.

Abstract: Ferromagnetic material of an elongated object, such as a fiber optic cable, is permanently magnetized in a manner that results in a substantially cylindrically symmetric radial external magnetic field around the object. The produced magnetization is substantially greater than natural magnetization of the ferromagnetic material by the earth's magnetic field. The radial external magnetic field varies periodically along the length of the object. If the wavelength of the periodic variations is long compared to the width (diameter) of the object, the strength of the radial external magnetic field decreases approximately inversely with distance from the object for distances that are small compared to the wavelength. The periodic magnetic field variations may have a square wave or a sine wave pattern, for example.

Abstract: A triaxial AC magnetic field analyzer/dosimeter instrument measures the field strength of three mutually orthogonal AC magnetic field components at a plurality of different frequencies in a frequency range of interest and stores corresponding data which may be processed to indicate the field strength at each of the frequencies and/or the sum of the field strengths over the frequency range of interest. The instrument is computer controlled and comprises three measurement channels corresponding to respective magnetic field components, each channel including a sensor coil, a clock controlled, switched capacitor, bandpass filter, and a TRMS detector. The passband of each filter is swept across the desired frequency range by a varying frequency clock.

Abstract: At least one pair of vector gradiometers is employed to locate (and track) magnetic objects or sources. A first signal, S, is produced as a function of the difference in the absolute values of output signals L and R from left and right gradiometers, respectively. The form of the signal depends upon whether the magnetic field associated with the object or source is symmetric or anti-symmetric and is selected in accordance with observations made as the gradiometer pair passes over the magnetic object or source. A second signal, V, is produced as a function of the sum of the absolute values of signals L and R and represents total strength. A third signal, H=S/V, is produced to determine whether the observer is to the left or to the right of the magnetic object or source and is independent of the magnetic field strength and polarity of the magnetic field, even where the polarity and magnetic field strength vary with distance along a linear source.