Abstract: A portable magnetic anomaly sensing system includes a non-magnetic support structure defined by a rigid beam and a rigid frame coupled thereto. Triaxial magnetometer (TM) sensors are rigidly coupled to the frame with one TM sensor being positioned at each vertex of a cubic space. Each TM sensor is positioned such that all respective X,Y,Z magnetic sensing axes are mutually parallel to one another. A data acquisition system is mechanically coupled to the beam such that any magnetic elements of the data acquisition system do not adversely affect accuracy of the TM sensors. The data acquisition system samples the sensed magnetic field data from all TM sensors synchronously with a timing signal. A processor is mechanically coupled to the beam such that any magnetic elements of the processor do not adversely affect accuracy of the TM sensors.

Abstract: A data fusion framework is provided for wide-area assessments of unexploded ordnance. One or more wide-area survey data sources representing assessments of geographic sites that may contain unexploded ordnance (UXO) can be analyzed by a data source module as part of the data fusion framework. The data sources can include a geographic registration and a degree of belief and the data source module can register the data sources to a common map grid. A feature layer module can extract a plurality of feature layers from the wide-area survey data sources. A feature map module can generate a plurality of feature maps for each of the plurality of feature layers based on the degree of belief. Finally, a data fusion module can combine the plurality of feature maps and generate a plurality of output maps. This output maps can then be used by UXO site managers to support decisions regarding remediation efforts.

Abstract: A detector for detecting a buried conductor comprises a plurality of antennas B, T. Each antenna B, T has a winding wound around the antenna, the winding being connected to a current source for providing a predefined current in the winding. When the predefined current is applied to the winding an electromagnetic field is generated at the antenna which induces a test current in the antenna. The test current is compared to calibration data stored in the detector to validate the correct operation of the detector.

Abstract: The invention relates to a localization system for localizing an underground object for an earthmoving machine comprising a working part. Said localization system comprises a fastening component and a detector component. The fastening component can be arranged on the working part for example by means of magnets. The detector component is adapted to detect the object using an electromagnetic field that can be associated with the object and is arranged on the fastening component so as to swing like a pendulum, thereby effecting an alignment of the detector component under the effect of gravity. Optionally, the localization system comprises an arithmetic component for deriving a distance information of the object from the detected value. The localization system also comprises a display component for displaying and/or forwarding the detected value and/or the distance information.

Abstract: A detector for locating metallic objects includes a transmit coil (116, 216) and at least two receive coils (112, 114; 212, 214), which are inductively coupled to one another; the at least two receive coils (112, 114; 212, 214) are located coaxial to one another in a plane (126, 226), and the transmit coil (116, 216) is located in a parallel plane with a height offset. Additional compensating windings (130, 132; 230, 232) of at least one of the receive coils (112, 114; 212, 214) are formed adjacent to a transmit coil (116, 216).

Abstract: An arrangement and an associated method are described in which a boring tool is moved through the ground within a given region along a path in which region a cable is buried. The boring tool and the cable transmit a boring tool locating signal and a cable locating signal, respectively. Intensities of the boring tool locating signal and the cable locating signal are measured along with a pitch orientation of the boring tool. Using the measured intensities and established pitch orientation, a positional relationship is determined to relative scale including at least the boring tool and the cable in the region. The positional relationship is displayed to scale in one view. The positional relationship may be determined and displayed including the forward locate point in scaled relation to the boring tool and the cable. Cable depth determination techniques are described including a two-point ground depth determination method.

Abstract: An apparatus for detecting a position of a component in an earth formation is disclosed. The apparatus includes: a transmitter configured to emit a first magnetic field into the earth formation and induce an electric current in the component, the transmitter having a first magnetic dipole extending in a first direction; and a receiver for detecting a second magnetic field generated by the component in response to the first magnetic field, the receiver having a second magnetic dipole extending in a second direction orthogonal to the first direction. A method and computer program product for detecting a position of a component in an earth formation is also disclosed.

Abstract: An apparatus for detecting a position of a component in an earth formation is disclosed. The apparatus includes: a transmitter configured to emit a first magnetic field into the earth formation and induce an electric current in the component, the transmitter having a first magnetic dipole extending in a first direction; and a receiver for detecting a second magnetic field generated by the component in response to the first magnetic field, the receiver having a second magnetic dipole extending in a second direction orthogonal to the first direction. A method and computer program product for detecting a position of a component in an earth formation is also disclosed. Apparatus and methods are also disclosed for estimating a position of a second borehole being drilled relative to an existing first borehole.

Abstract: A metal detection device is capable of effectively detecting a metal mixed in food or the like by generating AC magnetic field simultaneously tuned to respective frequencies by a single transmission coil in response to frequency components of different frequencies without switching an element by a switch or the like. Constituent elements constituting magnetic field generation portion are connected so that a transmission coil L1 and a capacitor C1 resonate in the first frequency F1. Moreover, constituent elements are connected so that the transmission coil L1 and a capacitor C2 resonate in the second frequency F2. Furthermore, constituent elements function so as to effectively separate the capacitor C1 and capacitor C2 so that they do not interfere at least in the same frequency.

Abstract: A portable locator and method for establishing the location of the cable line in a region which includes at least one generally straight electrically conductive cable line extending across the region from which cable line a locating signal includes a first arrangement for measuring a local flux intensity of the locating signal at a first above ground point within the region with the portable locator in a particular orientation at the first above ground point. A second arrangement uses the local flux intensity to establish a cable line angular orientation which limits the possible directions to the cable line relative to the particular orientation of the portable locator at the above ground point. A third arrangement uses the measured local flux intensity to establish an actual direction of the cable line that is selected from the possible directions based on certain characteristics of the locating signal.

Abstract: A technique for locating stationary magnetic objects comprises placing magnetic sensors on a movable platform; for each sensor, measuring a total magnetic field signal in an area of detection; using the sensors to identify a line upon which a target stationary magnetic object is located; and fixing a location of the object by moving the platform in substantially straight lines until the object is detected by at least two of the sensors; using the measured signals to determine a first path on which the object lies; positioning the sensors so that a line connecting two of the sensors intersects the first path on which the object lies; moving the platform along a second path substantially parallel to the first path; recording two positions at which at least two of the sensors detect a maximum total magnetic field signal from the object; and identifying a third path through the two positions.

Abstract: A leak in a membrane on top of a horizontal roof deck is located by applying conductive wires on the membrane underneath the aggregate in a grid pattern. A measuring and switching circuit generates voltage having a positive attached to the roof deck and a negative attached to the wires. The circuit has a relay for each wire which can be switched between a current sensor system and the negative potential. The sensor system is arranged to sense at each of the wires in turn the current flowing from the roof deck through any leak in the membrane to the wire. A microprocessor operates the relays in turn to connect all the other wires to the negative as a shield while each wire is sensed. From the output of the grid the changes in current in the x and y directions are analyzed to locate the leak in the membrane.

Abstract: An electronic metal detector having a transmit coil (1) adapted to transmit an alternating magnetic field associated with a reactive transmit voltage, wherein the transmit voltage signal is selected such that the reactive transmit voltage is approximately constant for at least a time period during which a magnetic field signal to be processed is received by the detector for processing.

Abstract: A pulse induction metal detector having high efficiency and sensitivity. Within the scope of the invention is a high efficiency hand-held metal detector for detecting a metal object, comprising a coil and a source of current flow in the coil. The source is adapted to produce one or more pulses of current in the coil. Preferably, at least two of the pulses are spaced apart in time at least about 20 microseconds during which current flow in the coil is substantially constant. The metal detector also comprises a detecting circuit for detecting a response to the current pulses, and a sampling circuit for sampling the response at predetermined times at least during the time of one of the pulses.

Abstract: A detector for calculating the distortion of an electromagnetic field produced by a buried current carrying conductor comprises three antennas B, M, T. Outputs of two pairs of antennas are compared and the depth of the buried conductor is calculated using two different methods. If there is a significant difference in the two calculated depths then it is deemed that the electromagnetic field produced by the buried current carrying conductor is significantly distorted by the material in which the conductor is buried.

Abstract: An underground digital locating system includes a receiver capable of acquiring a signal produced by an underground object and displaying a digital representation of the orientation of underground object and of its depth. The system includes a carrying case for the digital locating receiver, the carrying case further including a transmitter for energizing underground objects to emit a magnetic field. A method of locating an underground object using the described system is also disclosed, as well as methods of measuring a flux field and translating a flux field signal of an underground object into a visual representation of the underground object on the display screen of the locating receiver.

Abstract: A system for detecting a buried conductor comprises a transmitter for generating a test signal in the buried conductor and a detector for detecting an electromagnetic signal resulting from the test signal flowing in the buried conductor. The transmitter comprises a waveform generator for generating a drive waveform signal, a power supply, an amplifier, connected to the power supply and the waveform generator for producing an output drive signal based on the drive waveform signal and an output circuit for acting on the output drive signal to generate an output signal having a current and a voltage. In-phase and quadrature components of the current and voltage of the output signal are fed back for controlling the amplifier.

Abstract: A detector for calculating a depth of a buried conductor comprises three parallel antennas B, M, T. The second antenna M is spaced a distance s from the first antenna B and the third antenna T is a distance 2s from the first antenna B and a distance s from the second antenna M. The outputs of the first and second antennas B, M are compared and the outputs from the second and third antennas M, T are compared. The depth of the buried conductor is calculated based on the first and second compared values.

Abstract: An underground digital locating system includes a receiver capable of acquiring a signal produced by an underground object and displaying a digital representation of the orientation of underground object and of its depth. The system includes a carrying case for the digital locating receiver, the carrying case further including a transmitter for energizing underground objects to emit a magnetic field. A method of locating an underground object using the described system is also disclosed, as well as methods of measuring a flux field and translating a flux field signal of an underground object into a visual representation of the underground object on the display screen of the locating receiver.

Abstract: A method of determining the nature of a submarine or subterranean reservoir having an electromagnetic characteristic is described. The method comprises analyzing data associated with the application of a time varying electromagnetic field from above the reservoir using a data analysis methodology that does not utilize an estimate of the reservoir's geometry in determining one or more characteristics of the reservoir.

Abstract: There is provided a silicon wafer surface defect evaluation method capable of readily detecting a region where small crystal defects exist, the evaluation method comprising: a rapid heat treatment step of a silicon wafer from a silicon single-crystal ingot in an atmosphere which can nitride silicon at a temperature elevating speed of 10 to 150° C./second from a room temperature to temperatures between not lower than 1170° C. and less than a silicon melting point, holding the silicon wafer at the processing temperature for 1 to 120 seconds and then cooling the silicon wafer to the room temperature at a temperature lowering speed of 10 to 100° C./second; and a step of using a surface photo voltage method to calculate a minority carrier diffusion length on the wafer surface, thereby detecting a region on the wafer surface in which small COP's which cannot be detected at least by a particle counter exist.

Abstract: Discriminating between a cable locating signal and a false cable locating signal is described. A reference signal, which contains a locating signal frequency impressed on it, is transmitted in a way which provides for detection of a phase shift between the locating signal and the false locating signal. Based on the phase shift, a receiver is used to distinguish the locating signal from the false locating signal.

Abstract: An underground digital locating system includes a receiver capable of acquiring a signal produced by an underground object and displaying a digital representation of the orientation of underground object and of its depth. The system includes a carrying case for the digital locating receiver, the carrying case further including a transmitter for energizing underground objects to emit a magnetic field. A method of locating an underground object using the described system is also disclosed, as well as methods of measuring a flux field and translating a flux field signal of an underground object into a visual representation of the underground object on the display screen of the locating receiver.

Abstract: A method for non-invasive mapping (imaging) of the electrical impedance of an object. The present invention provides a method, current density impedance imaging (CDII) which produces an impedance image of object by measuring current density distributions and directly calculating the local impedance values.

Abstract: A pneumatic earth boring tool includes a cylindrical body, a transmitter mounted in the body, the transmitter generating a signal usable for operating the earth boring tool, a linear generator mounted in the body for generating an electrical current to power the transmitter and a rectifier for converting the electrical current produced by the linear generator to direct current. Electrical power generated by the linear generator is used to power the transmitter to generate a signal useful for locating the tool.

Abstract: The invention relates to an inductive proximity switch which has a resonant circuit (Ls, C) comprising a resonant circuit transmission coil (Ls) and a capacitance (C), wherein the resonant circuit transmission coil (Ls) generates an alternating magnetic field which induces a mutual induction voltage in at least one receiving coil (LE), and the oscillation state of the resonant circuit can be influenced by means of a metallic release which enters or moves away from the alternating field. An evaluation circuit is used to obtain a switching signal (uswitch) from the change in the oscillation state of the resonant circuit, wherein the change in the complex coupling between the at least two coils, the transmission coil (Ls) and the receiving coil (LE), can be evaluated, as a switching signal (uswitch), using an auxiliary voltage signal (UHSP) in the presence or absence of the release.

Abstract: An arrangement and an associated method are described in which a boring tool is moved through the ground within a given region along a path in which region a cable is buried. The boring tool and the cable transmit a boring tool locating signal and a cable locating signal, respectively. Intensities of the boring tool locating signal and the cable locating signal are measured along with a pitch orientation of the boring tool. Using the measured intensities and established pitch orientation, a positional relationship is determined to relative scale including at least the boring tool and the cable in the region. The positional relationship is displayed to scale in one view. The positional relationship may be determined and displayed including the forward locate point in scaled relation to the boring tool and the cable. Cable depth determination techniques are described including a two-point ground depth determination method.

Abstract: When a first cable is driven at a locating signal frequency to emit a locating signal, the locating signal can be coupled to a second cable to cause the second cable to generate a false locating signal. As part of discriminating the false signal from the locating signal, the locating signal is generated at the locating signal frequency and phase shifted to produce a phase shifted locating signal frequency. A reference signal is impressed with the phase shifted locating signal frequency. A coupling configuration couples the locating signal frequency onto the first cable to generate the locating signal subject to a coupling configuration phase shift. The phase shifted locating signal, as part of the reference signal, can compensate for the coupling configuration phase shift in the locating signal as emitted by the first cable.

Abstract: To fully characterize the inductive response of an isolated conductive object, such as buried unexploded ordinance, one needs to measure its response to stimulation by primary magnetic fields in three linearly independent (e.g., approximately orthogonal) directions. In one embodiment this is achieved by measuring the response to magnetic fields of three independent transmitters arranged to have magnetic fields that are linearly independent. According to the apparatus and methods employing the system of this invention, multiple transmitters and receivers of known relative position and orientation on a single platform are used. In a preferred embodiment, matched sets of receiver pairs connected in gradient mode are positioned adjacent to closely spaced pairs of transmitting coils, such that a minor displacement of one or both of the receiver coil pairs relative to the paired transmitting coils will not affect the detected secondary signals emitted by a buried metallic object.

Abstract: A real time electronic metal detector including a magnetic transmitter (1) and a receiver (3), wherein the receiver includes approximate sine-wave weighted synchronous demodulation and a switched voltage signal is applied to the magnetic transmitter and the said receiver approximate sine-wave weighted synchronous demodulation is selected to receive synchronously with the switched voltage signal, such that the switched voltage signal and the receiver approximate sine-wave weighted synchronous demodulation may be altered by means of operator selection.

Abstract: A pre-amplifier circuit for connection to an antenna of a human-portable locator includes a differential amplifier/mixer pair and means for allowing a common-mode “phantom” signal to modulate a transfer function of the differential amplifier/mixer pair. The common-mode phantom signal modulates the transfer function of the differential pre-amplifier “onboard” the antenna without the usual requirement for onboard power supply and signal oscillator. This technique uses the same electronic components to provide both pre-amplification and mixing functions, thereby improving circuit performance-to-cost ratio, reducing mixer power consumption, situating the necessary signal oscillator remotely from the mixer, and greatly improving the available system bandwidth by limiting spectral transmission demands to the mixed signal bandwidth alone.

Abstract: A device rotates at least one static magnetic field about an axis, producing a rotating magnetic dipole field, and is movable in relation to the surface of the ground. The field is periodically sensed using a receiver to produce a receiver output responsive to the field. A positional relationship between the receiver and the device is monitored using the output. In one aspect, changing the positional relationship, by moving the device nearer to a boring tool which supports the receiver, causes an increase in accuracy of depth determination. In another aspect, determination of an actual overhead position of the boring tool, and its application, are described. Use of a plurality of measurements over at least one-half revolution of each magnet is disclosed. Establishing a surface radial direction toward a boring tool and resolution of multi-valued parameters is described. Calibration techniques, as well as a three transmitter configuration are also described.

Abstract: A detector for locating a sonde is comprised of a plurality of antennas, a corresponding number of signal isolator modules 1 and a geometrical evaluation module. The magnetic signal generated by the sonde has a fundamental frequency and harmonic frequencies. A frequency spectrum analyzer 29 which forms part of the signal isolator module 1 has frequency bins which are aligned with the fundamental frequency and a plurality of harmonic frequencies of the magnetic signal produced by the sonde. The frequency bins follow variations in the frequency of the magnetic signal produced by the sonde which allows the detector to detect the sonde at a separation of up to 30m.

Abstract: An apparatus and method are described for tracking the position, orientation and/or guiding a sonde as it moves through the ground in a region. The sonde transmits an electromagnetic field received by one detector. The detector includes at least one antenna for measuring at least one component of the intensity of the electromagnetic field and the detector is positioned at a fixed position with the antenna at a particular orientation within the region. Certain initial conditions are determined including the particular orientation and position of the antenna associated with the detector and an initial position and orientation of the sonde. The intensity of the electromagnetic field is obtained at a second position using the detector after the sonde moves a distance to the second position. The coordinate position of the sonde is determined using the initial conditions along with the intensity measured at the second position.

Abstract: A marking tape comprising at least one resonant circuit, each resonant circuit comprising an inductive coil and a capacitor, forming a resonant circuit of a selected frequency, comprises inductive coils and capacitors formed by conductive material layers (2, 3, 4) on the surfaces of a dielectric plastic film (1) and is dimensioned to be wireless detected when positioned in a hidden location. Such marking tape can be produced with low cost and provide a wireless detection of the integrity of a marking tape in a hidden position, e.g. from the surface above a subterranean positioned marking tape.

Abstract: A compact line illuminator for applying an oscillating signal to buried or otherwise inaccessible pipes, cables and conductors so that their location can be traced by detecting an electromagnetic signal emitted by these buried objects. The illuminator includes a circuit for generating a signal suitable for tracing a buried conductor and a holder for a portable power source that can energize the circuit. First and second leads each have a first end connected to the circuit and a second end connected to a corresponding mechanism such as an alligator clip for attaching to a buried conductor. A case encloses the circuit and the portable power source holder and is configured for having the first and second leads wrapped around an exterior of the case. Mechanisms are provided for holding the leads wrapped around the exterior of the case.

Abstract: In a method and system for monitoring an underground cable in a site of interest, multiple samples of magnetic field data and corresponding location data are collected periodically over a sampling period of extended time. The magnetic field data samples and corresponding location data are processed to determine respective topologies of one or more current-carrying conductors in the site and for each of the conductors respective magnetic field data relating to each sampled point are integrated with respect to a predetermined parameter of the respective conductor so as compute an integrated contribution of each sampled span along the respective conductor. The data relating to different conductors in the site are output in a manner that allows determination of a conductor for which the parameter changes during the sampling period.

Abstract: A method of locating a conductive target from a wellbore includes generating a current flowing across an insulated gap in a downhole tool positioned in the wellbore, measuring an azimuthal magnetic field with at least one external magnetometer located proximate the exterior of the downhole tool, measuring a secondary magnetic field using a magnetometer disposed inside the downhole tool, computing at least one of a direction and a distance to the conductive target.

Abstract: In a system in which a transmitter is moved through the ground in a region which includes an electrical conductivity characteristic and the transmitter transmits a locating signal for reception, compensating for skin depth error by measuring the locating signal such that measurements of the locating signal include skin depth error introduced as a result of the electrical conductivity characteristic. Thereafter, the measurements are used in a way which determines a skin depth corrected position of the transmitter. An associated compensation arrangement is also described.

Abstract: A method for determining the location of underground cables and pipes is disclosed. In some embodiments, the method includes measuring a set of electromagnetic field magnitudes and phases at a plurality of positions while traversing a target line parallelly using 3D electromagnetic coil sensors, the 3D electromagnetic coil sensors being orthogonally oriented to the target line, modeling a set of expected complex electromagnetic field magnitudes of a single underground conductor at each of the positions to form a set of values corresponding to a set of individual models for the target line, determining which of the set of individuals models is a best model, determining confidence information at each of the positions based on a comparison between the measured set of complex electromagnetic magnitudes and phases and the best model, and determining parameters at each of positions related to the target line from the best model.

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: A coupled non-linear sensor system is provided for sensing a non-sinusoidal time-dependent target signal. The system comprises an odd number, other than one, of interconnected oscillatory sensors for sensing time-dependent changes in an external magnetic flux generated by the non-sinusoidal time-dependent target signal, the sensors coupled to each other by a coupling parameter characterized by a threshold value, so that each of the sensors oscillates in the presence of the non-sinusoidal time-dependent target signal as the coupling parameter exceeds the threshold value.

Abstract: The present invention provides a locator/monitor capable of locating a boring tool and monitoring the progress of the tool for control purposes. The locator/monitor may be used in expedited locating methodology and straightforward calibration techniques of the present invention. A durable and cost effective pitch sensor is also provided by the present invention. In addition, the present invention provides a slotted transmitter housing formed of an electrically conductive material, where the magnetic field generated by the transmitter is capable of penetrating to the surface.

Abstract: A portable locator for detecting a buried object characterized by an electromagnetic (EM) field emission employing three-dimensional (3D) sensor arrays each having three substantially-identical EM field sensors disposed on a flexible annular wall having a radial centroid defining a sensing axis. The flexible annular sensors are retained in substantial concentricity with the corresponding sensing axes disposed in substantial mutual orthogonality. A pair of 3D sensor arrays disposed on a first axis substantially orthogonal to a second axis defined by another pair of EM field sensors each having a sensing axis disposed along the second axis. The locator introduces a user-reconfigurable user interface (UI) employing a “sticky” ratcheting audio UI and a hollow hinge assembly for redisposing the sensor assembly from an operating to a storage disposition.

Abstract: A system and method for selectively grounding each of a plurality of short-haul buried utility conveyances coupled to a common long-haul buried utility conveyance to enable a conveyance locating signal transmitted through the long-haul conveyance to travel from the long-haul utility conveyance to a selected short-haul utility conveyance. The system includes a first optical switch for selecting each of the plurality of short-haul utility conveyances to be grounded, where the first optical switch is adapted to receive an optical signal and selectively output the optical signal on one of a plurality of optical fibers; and a second optical switch coupled to each of the plurality of optical fibers for grounding each short-haul utility conveyance in response to the optical signal on a corresponding optical fiber.

Abstract: A service tee marker fixture comprises a disk marker and a cylindrical attachment sleeve fastened concentrically to the disk marker and constructed of a flexible material which provides a releasable friction fit with a service tee cap. For certain sleeve materials a stiffener plate is used to secure an end portion of sleeve adjacent to the disk marker. Detents are formed inside the attachment sleeve to grip matching ribs on the cap. An integrally formed inwardly-extending annular flange at an open end of the sleeve helps retain the sleeve on the cap. When installed the wire coil is horizontal and the marker shields the tee, and is further centered over a centerline of the main pipe. A novel method is also disclosed for using the service tee marker fixtures to survey and locate service line end points.

Abstract: At least one antenna array including three mutually orthogonal antennas each sharing a common center point senses an electromagnetic signal emitted by a buried object such as a utility line, pipe or sonde. A circuit at least partially mounted in a housing is connected to the array and determines a location of the buried object by measuring signal strength and field angles in three dimensions without having to align the antenna array relative to the buried object while eliminating nulls and false peaks. A graphical user interface (GUI) has user-friendly icons, symbols, menus, numbers and graphical and auditory representation of signal strength. A SEARCH view indicates signal strength by showing a rotating strength indicator, a trace mode MAP view in which line location is shown by a line that moves side-to-side, and a sonde mode MAP view in which sonde location is shown by a moving line, pole and equator.

Abstract: An above ground locator includes an apparatus for determining the strength of the locating signal at a selected point relative to the boring tool. The apparatus includes an antenna arrangement configured for measuring the strength of the locating signal at the selected point along first and second orthogonally opposed receiving axes to produce first and second received signals. A phase shifting arrangement phase shifts the first and second received signals in a predetermined way to generate first and second phase shifted signals, respectively. Thereafter, a summing arrangement adds the first and second phase shifted received signals to generate an output signal which is a vector sum of the first and second received signals. In one feature, third and fourth signals derived from the first and second signals are used to eliminate balance point ambiguity which is present using the first and second signals alone.

Abstract: Location determination is performed using a transmitter including an elongated generally planar loop antenna defining an elongation axis. The elongation axis is positioned along at least a portion of a path. A magnetic field is then generated which approximates a dipole field. Certain characteristics of the magnetic field are then determined at a receiving position radially displaced from the antenna elongation axis. Using the determined certain characteristics, at least one orientation parameter is established which characterizes a positional relationship between the receiving position and the antenna on the path. The magnetic field may be transmitted as a monotone single phase signal. The orientation parameter may be a radial offset and/or an angular orientation between the receiving position and the antenna on the path. The antenna of the transmitter may be inserted into a first borehole to transmit the magnetic field to a receiver inserted into a second borehole.

Abstract: An electronic metal detector having transmit electronics includes switching electronics arranged and adapted to generate a transmit signal. The transmit electronics includes at least two power sources, and is connected to a transmit coil arranged and adapted to transmit an alternating magnetic field. The switching electronics are adapted and arranged to switch a first voltage of one power source to the transmit coil for at least a first period and also a third period, and to switch a second voltage of the other power source to the transmit coil for at least a second period. Receive electronics are arranged to receive and process a receive magnetic field during at least some of the second period and fourth period to produce an indicator output, at least indicating the presence and a characteristic of some metal targets under the influence of the magnetic field.