Abstract: Methods and Apparatus for detecting the presence of a conductor near an inductive coupling loop are disclosed. The method includes supplying an excitation to the coupling loop, measuring the signal distortion induced by the excitation signal, and monitoring the distortion in the signal for a change in harmonic content.

Abstract: A locator or signaling device and a detector system for locating lost dentures includes a button or insert that can be mounted on the surface of an existing denture. An insert can also be implanted in a new denture. The internal signaling component is surrounded by a resin layer that can be used to bond the locator button to the existing denture and will also isolate the internal signaling component form the denture wearer's oral cavity. The internal signaling component is responsive to an electromagnetic field and emits a detectable signal when the denture is located with a specified interrogation zone or search area. Signaling components having magnetic characteristics that are altered by an incident variable electromagnetic field can be employed. The preferred location for the locator, locator strip, marker or button is on the interior lingual surface of the flange of a mandibular or lower denture.

Abstract: An apparatus and method for the repeatable detection and recording of low-threshold molecular electromagnetic signals. The sample material and detection apparatus are contained with a magnetically shielded faraday cage to shield them from extraneous electromagnetic signals. The detection apparatus includes a detection coil and Super Conducting Quantum Interference Device (“SQUID”). White noise is injected external to the SQUID and the signals emitted by the sample material enhanced by stochastic resonance.

Abstract: A magnetic sensor of orthogonal flux-gate type is provided with a cylindrical core made of a soft magnetic material; an internal conductor that is placed inside the core; a detection coil wound up on the core; and an external conductor that is placed around the core and electrically connected to the internal conductor. A high-frequency current is allowed to flow through the internal core so that a magnetic field to be measured which resides around the detection coil is changed and the intensity and direction of the magnetic field to be measured is detected on the basis of an output of the detection coil. Since the external conductor is placed on the periphery of the core, it is possible to prevent the magnetic flux formed by the core from magnetizing any space, and consequently to concentrate the magnetic field on the core.

Abstract: Described are methods for monitoring of stresses and other material properties. These methods use measurements of effective electrical properties, such as magnetic permeability and electrical conductivity, to infer the state of the test material, such as the stress, temperature, or overload condition. The sensors, which can be single element sensors or sensor arrays, can be used to periodically inspect selected locations, mounted to the test material, or scanned over the test material to generate two-dimensional images of the material properties. Magnetic field or eddy current based inductive and giant magnetoresistive sensors may be used on magnetizable and/or conducting materials, while capacitive sensors can be used for dielectric materials. Methods are also described for the use of state-sensitive layers to determine the state of materials of interest. These methods allow the weight of articles, such as aircraft, to be determined.

Abstract: An eddy current inspection probe provides multiple interchangeable configurations for enabling an inspector to reach most or all portions of most or all turbine blades within a combustion turbine by inserting the probe through an inspection port, without disassembling the turbine. The probe shaft contains the electronic signal wire for the inspection tip and a port for a video probe, thereby facilitating use of the video probe and protecting these components. The inspection tip connector at the end of the main shaft is pivotally secured to the shaft, and may be set at any desired angle by using a semirigid or rigid member passing through the shaft, and connected to lever within the handle. Any one of a plurality of probe tips and shaft extensions may be selected to configure the inspection probe to reach a desired location within the turbine.

Abstract: A method for distinguishing between a semi-soft magnetic material, having a magnetic saturation field H sub s ranging from 100A/m to 3000 A/m, and a soft magnetic material, having a magnetic saturation field H sub s ranging from 3 A/m to 100 A/m, includes (a) emitting an electromagnetic drive signal of one or more particular frequencies to an article so that any present semi-soft magnetic material or soft magnetic material in the article go into saturation for both positive and negative magnetic fields; (b) detecting an electromagnetic detection signal (20) emanating from the article; (c) measuring time or relative phase delays (A, B) between one or more reference points of the drive signal and points at which positive and negative peaks of the detection signal occur; (e) comparing the measured time or relative phase delays with values which are typical for semi-soft magnetic or soft magnetic features in order to make a decision whether the material is soft magnetic or semi-soft magnetic.

Abstract: Metal detection apparatus containing at least two inductive coils one of which acts as a transmit coil and all of which act as receive coils and processing circuitry wherein a proportion of the first receive electronic signal and a proportion of the second receive electronic signal may be selected to produce various first resultant linear combination signals for the purpose of improved interference cancelling.

Abstract: A metal detector apparatus including a transmit coil which transmits a magnetic field, transmit timing control circuitry which also includes timing for a semiconductor switch, and receive signal circuitry and receive signal processing circuitry, with a transmit coil damping network including at least one resistor connected in series with the semiconductor switch across the transmit coil, and timing control circuitry which generates a timing sequence which is selected so that for at least some of the time no transmit field is generated and at least during part of the transmit signal, the first semiconductor switch is controlled to be off and is turned on before the cessation of the transmit field.

Abstract: A monitoring device is for monitoring changes in at least one characteristic of a coating, and uses an electromagnetic field generator, a magnetic field sensor positioned within the magnetic field of the field generator and a signal generator for generating an alternating signal of a selected frequency for driving the magnetic field generator. The selected frequency causes resonant fields to be generated within a coating sample to be monitored, thereby altering the magnetic field detected by the magnetic field sensor. The magnetic field sensor output is monitored over time, and this enables changes in at least one characteristic of the sample to be monitored over time. This device detects magnetic resonance within a sample as a tool for analysing the characteristics of the sample. In this way, the curing characteristics of the sample can be evaluated by monitoring the concentration of the selected component over time.

Abstract: This invention relates to the method and apparatus for indicating roller wear in a media handling device. Such structures of this type, generally, employ the use of variable inductance to determine roller wear. The media transport roller has a non-conductive surface with a conductive core. Located just above the conductive core is a rod containing a power coil that is driven by AC excitation and a pick-up coil. The pick-up coil is connected to circuitry that measures the inductance. As the media transport roller wears, the conductive core moves closer to an inductive pick-up unit. The measured output voltage from the pick-up unit depends upon the distance between the core and the pick-up unit. This inductance change can then be correlated to media transport roller wear and relayed to the user through the use of an LED or other similar types of numerical/graphical displays.

Abstract: A detector for finding metal objects being disposed in garbage includes a driving coil, a receiving coil, and a voltage detector. The driving coil encircles an opening formed in a ring-like lid for the trashcan. The controller connects to the driving coil and oscillates a driving current in the driving coil. A receiving coil is disposed parallel to the driving coil and has an current induced therein from the driving current in the driving coil. The voltage detector connects to the coil and detects changes in voltage of the inducted current when a metal object passes through the driving coil and the receiving coil. The coils can be constructed from a flat ribbon coil containing a plurality of parallel wires. The flat ribbon coil can be supported under a trashcan lid by a support.

Abstract: A metal detector with a transmit coil which transmits a magnetic field, transmit timing control circuitry, and receive signal circuitry and receive signal processing circuitry, and a low voltage and a high voltage power supply. The timing sequence generated within the transmit timing control circuitry produces control signals such that there are at least two different transmit periods, a short and a long period, and such that there are periods when no current flows through the transmit coil. The timing sequence is such that an average transmit coil energy at termination of the long periods is similar to that of an average transmit coil energy at termination of the short periods.

Abstract: A magnetic flux detector has a core member and an armature member. The core member generates a magnetic flux by an exciting coil receiving an excitation current controlled by an excitation current controller. The magnetic flux detector also has a search coil provided in a magnetic path for the magnetic flux, and a magnetic flux calculator, which determines the magnitude of the magnetic flux by measuring an electromotive force induced in the search coil by a change in the magnetic flux. The excitation current controller controls the excitation current to increase from zero to a predetermined value during a first predetermined time period and then to decrease to zero during a second predetermined time period. The magnetic flux calculator determines the magnitude of the magnetic flux based on the integrated electromotive forces during the first and second time periods.

Abstract: A method for estimating a thickness profile of a substrate sample that has undergone a chemical-mechanical polishing (CMP) process includes obtaining initial and terminating resistance and reactance measurements from the sample. Initial eddy current measurement values are obtained while an eddy current probe is positioned at an initial distance relative to the substrate sample, and terminating values are obtained while the eddy current probe is positioned at a modified distance relative to the sample. An intersecting line can be calculated using the initial and terminating resistance and reactance measurements. An intersecting point between a previously defined natural intercepting curve and the intersecting line may also be determined. A reactance voltage of the intersecting point may be located along a digital calibration curve to identify a closest-two of a plurality of calibration samples.

Abstract: A sensor for monitoring a conductive film in a substrate during chemical mechanical polishing generates an alternating magnetic field that impinges a substrate and induces eddy currents. The sensor can have a core, a first coil wound around a first portion of the core and a second coil wound around a second portion of the core. The sensor can be positioned on a side of the polishing surface opposite the substrate. The sensor can detect a phase difference between a drive signal and a measured signal.

Abstract: A temperature sensing apparatus including a sensor element made of a magnetically soft material operatively arranged within a first and second time-varying interrogation magnetic field, the first time-varying magnetic field being generated at a frequency higher than that for the second magnetic field. A receiver, remote from the sensor element, is engaged to measure intensity of electromagnetic emissions from the sensor element to identify a relative maximum amplitude value for each of a plurality of higher-order harmonic frequency amplitudes so measured. A unit then determines a value for temperature (or other parameter of interst) using the relative maximum harmonic amplitude values identified. In other aspects of the invention, the focus is on an apparatus and technique for determining a value for of stress condition of a solid analyte and for determining a value for corrosion, using the relative maximum harmonic amplitude values identified.

Abstract: The present invention provides an apparatus and method for measuring the resistivity of a sample of cement-based material. A transformer is formed with a primary coil, a secondary formed by means of a sample of said cement-based material, means for supplying a voltage to said primary, means for measuring the voltage induced in said sample, and means for measuring the current induced in said sample. The resistance of the sample can be measured and thus the resistivity of the concrete sample can be calculated.

Abstract: This invention relates to the method and apparatus for indicating roller wear in a media handling device. Such structures of this type, generally, employ the use of variable inductance to determine roller wear. The media transport roller has a non-conductive surface with a conductive core. Located just above the conductive core is a rod containing a power coil that is driven by AC excitation and a pick-up coil. The pick-up coil is connected to circuitry that measures the inductance. As the media transport roller wears, the conductive core moves closer to an inductive pick-up unit. The measured output voltage from the pick-up unit depends upon the distance between the core and the pick-up unit. This inductance change can then be correlated to media transport roller wear and relayed to the user through the use of an LED or other similar types of numerical/graphical displays.

Abstract: A method and system for detecting or measuring defects in a rope having ferromagnetic tension members includes a magnetic field exciter and an array of magnetic flux sensors corresponding to the tension members in a known relationship. Measurements of magnetic flux leakage are indicative of defects. Another aspect of the invention includes a method and system for detecting or measuring defects in an elevator rope having electrically conductive tension members, whereby measured electrical resistance in the tension members is indicative of defects.

Abstract: A vibrating sample magnetometer controls an electromechanical drive using both ac and dc control and a position sensor. Absolute position sensing is used in a feedback loop to control both an alternating current (ac) drive and a direct current (dc) drive to the electromechanical drive. Improved performance and stability results.

Abstract: The invention subject of this invention pertains to device and methods for transmitting electromagnetic signals into or through magnetically permeable and electrically conductive materials. The invention also teaches the method and apparatus for receiving a return signal from or through the material, thereby permitting information to be collected on matter on the opposite side of the material. The subject invention teaches various techniques for creating EM wave transparencies in materials such as carbon steel and iron. The invention further teaches methods and apparatus for varying, in a controlled manner, the size of the transparency, the creation of multiple transparencies, the sequential opening and closing of the transparencies, utilization of one or more transmitting and receiving devices, each of which may be located at its own transparent opening.

Abstract: The present invention relates to a device for measuring the value of a parameter relating to an electrically conductive object. Such a parameter can be the electric conductivity or the degree in which the material has changed under the influence of external conditions. Alternatively the parameter is the quality of a weld or the thickness of the object.

Abstract: A magnetic flux detector comprises a core member 12 and an armature member 11, and the core member 12 generates a magnetic flux by an exciting coil 13 when the exciting coil receives an excitation current controlled by an excitation current controller 30. The magnetic flux detector further comprises a search coil 14, which is provided in a magnetic path for the magnetic flux, and a magnetic flux calculator 40, which determines the magnitude of the magnetic flux by measuring an electromotive force induced in the search coil 14 by a change in the magnetic flux. The magnetic flux calculator 40 has a potential setup resistor 43, whose resistance B is sufficiently larger than the internal resistance A of the search coil 14 (approximately A=B/3˜B/30).

Abstract: An exciting coil is constructed by winding a winding in a groove formed on the outer circumference of a circular ring member, and a detecting coil in the shape of a polygon (such as a triangle and a pentagon) when seen from the front is positioned. One side of the detecting coil is placed in a diameter direction of the exciting coil, inside the exciting coil, and the vertex opposite to the one side is placed apart from the exciting coil so that the detecting coil is orthogonal to the exciting coil. A side surface of the exciting coil on the side opposite to the vertex is placed to face the surface of a test material, and used as a flaw detection surface.

Abstract: In a transient electromagnetic or pulse induction type metal detecting apparatus having a receiving coil attached to a sensor, a method and apparatus is disclosed of determining a null point comprising determining a series of post transient output values for the sensor at predetermined times; forming a summation of the output values or their negatives; and altering the predetermined times so as to minimise the summation.

Abstract: The present invention provides an apparatus and method for measuring nonferrous electrical resistance measurement. The method includes providing a nonferrous material, inducing a magnetic field on the nonferrous material, measuring the remote magnetic field of the nonferrous material, and comparing the measured remote magnetic field to a standard.

Abstract: Apparatus and methods for measuring cross sectional area and flaws in a continuous sucker rod string as the string is conveyed within a borehole. These measured parameters are useful is monitoring the physical integrity of the sucker rod string. A magnet is used to saturate an increment of continuous sucker rod, and a coil is used to measure induced flux. Cross sectional area of the rod increment is computed from the flux measurement. One or more Hall effect transducers are used to measure leakage from the increment as a function of distance along the increment. This measurement is used to detect and quantify the type of flaw within the rod increment being investigated. The process is repeated as the sucker rod string is conveyed into or out of the borehole.

Abstract: The system and the method are used for detecting a level of liquid metal at a given location, such as a launder set between an holding furnace and a casting pit. The system comprises an emitter coil and a receiver coil in a side-by-side configuration and in close proximity of the location. In use, an AC signal is applied to the emitter coil for producing an alternating magnetic flux. At least a part of the magnetic flux passes through the location where the level of liquid metal needs to be measured and goes back into the receiver coil. The signal in the receiver coil is monitored and the data are conveyed to a control module which determines the level of liquid metal from the variation of the signal in the receiver coil. The coils of the system are advantageously provided with respective core elements having a high magnetic permeability and which are configured and disposed to channel the magnetic flux.

Abstract: An inspection system include a transmitter and a receiver configured for communication with a remotely positioned processing means. The transmitter and receiver are arranged as a mobile apparatus configured for insertion into any duct, conduit, pipeline, mining shaft, or the like, or any diameter or cross section. The transmitter is configured to transmit an electromagnetic signal to induce an electromagnetic response in the duct and the electromagnetic response is detected by the receiver. The mobile apparatus is self-powered and processes the electromagnetic response prior to communicating the processed response to the remotely positioned processing means as a discrete signal.

Abstract: A field generator/detector including at least one super-toroidal conductor and a device to energize the super-toroidal conductor to generate varying electric and magnetic fields. Where conductor has a length l, the super-toroidal conductor is energized with at least one frequency component equal to or greater than 2c/l, where c is the speed of light in free space. Then the near field generated at this frequency close to the super-toroidal conductor has a strongly inhomogeneous spatial distribution similar or more complex than that generated by four or more electric charges and/or current loops. At any particular moment in time, the amplitudes of the electric and magnetic fields components of such a complex field change significantly over a distance comparable with the smallest winding feature of the super-toroidal conductor. The field generator/detector may be used in a sample analyzer having a chamber and a sample holder within the chamber.

Abstract: The invention concerns a method and apparatus for determining the hydride content in an electrically conductive substrate by generating a first electromagnetic alternating field that at least partly penetrates the substrate which in turn produces a second alternating field that reacts with the first field. The first field is set at at least two different frequencies and measurement at the frequencies of the combined alternating field formed by the interaction of the first and second fields determines the hydride content in the substrate.

Abstract: The present invention provides an apparatus and method for measuring nonferrous electrical resistance measurement. The method includes providing a nonferrous material, inducing a magnetic field on the nonferrous material, measuring the remote magnetic field of the nonferrous material, and comparing the measured remote magnetic field to a standard.

Abstract: An inductive measurement is carried out of the distance between a workpiece (3) and a working head (1), which bears an induction coil (8), through which an alternating current flows and which is part of a resonance circuit whose oscillation frequency is monitored for changes which occur as a consequence of changes in the distance between the workpiece (3) and working head (1). In this case, the working head (1) acts on the workpiece (3) with a material (2) having a dielectric constant greater than 1. The frequency of the alternating current is in the megahertz region or just therebelow. Last but not least, the induction coil is screened from external electric fields in order to avoid the influence of parasitic capacitances.

Abstract: The present invention relates to a head tester for testing heads having a read element and a write element. The tester comprises a substrate on which a read coil is positioned to be sensitive to the write element of the head. A write coil is also formed on the substrate and this coil is positioned such that the read element of the head to be tested is sensitive to the write coil.

Abstract: An electromagnetic induction coil includes a casing with high magnetic permeability with a magnet disposed within the casing. The magnet has a central hole. A core with high magnetic permeability is disposed within the central hole of the magnet. The core is in physical contact with the casing. A multi-loop coil of conductive wire is disposed within the central hole of the magnet encircling the core. The multi-loop coil is insulated from the magnet.

Abstract: The present invention provides an apparatus and method for measuring the resistivity of a sample of cement-based material. A transformer is formed with a primary coil, a secondary formed by means of a sample of said cement-based material, means for supplying a voltage to said primary, means for measuring the voltage induced in said sample, and means for measuring the current induced in said sample. The resistance of the sample can be measured and thus the resistivity of the concrete sample can be calculated.

Abstract: This invention is a method for nondestructively determining the deterioration of determining ferromagnetic materials by quantifying the change in brittleness with aging of the materials. This invention supposes acquirement of an embrittlement coefficient b by measuring a magnetic susceptibility &khgr;b of ferromagnetic materials under a magnetic field having a specified intensity H. And the coefficient b of the ferromagnetic materials is calculated by putting the intensity H and the susceptibility &khgr;b into an equation: b=&khgr;bH2. By the coefficient b, a correlation between the coefficient b and a referenced embrittlement factor of materials like said determining materials is obtained previously. Said coefficient b of said determining materials in the initial and the deteriorated states is acquired. The factor corresponding to the coefficient b is obtained from the correlation. It is possible to quantify the change by comparing the values of the factor in the initial and deteriorated states.

Abstract: A surgical sponge is provided and adapted to prevent unaccounted disposal thereof. The sponge includes an absorbent pad and a visually identifiable member attached to the pad. The visually identifiable member assists in identification and accounting in a surgical environment. Finally, a metallic tag of sufficient size is incorporated with the sponge to provide detection by a metal detector device upon disposal of the sponge.

Abstract: A device for carrying out measurements of a quantity through measuring the influence upon a magnetic field generated through a basic signal in a region of measurement (16) has a first member (7) adapted to change the polarity of the basic signal in a regular way on the basis of the length of the time for regularly repeating the basic signal, or a multiple thereof, and a second member (9) adapted to change the polarity of a detection signal in connection with the treatment of this detection signal synchronizedly with the polarity change of the first member.

Abstract: A magnetic field sensor that can be manufactured using the technology of surface micromechanics, having a conductor loop that has at least one deformable segment; a deformation device for deforming the deformable segment of the conductor loop with a predeterminable time dependence; a voltage sensing device for sensing the voltage induced at the ends of the conductor loop upon deformation in the presence of a magnetic field; and a magnetic field determining device for determining the present static and/or dynamic magnetic field in consideration of at least the time dependence of the deformation.

Abstract: An apparatus is provided for quantitatively measuring groups of magnetic particles. The particles are complexed with substances to be determined and are excited in a magnetic field. The magnetizations of the magnetic particles are thereby caused to oscillate at the excitation frequency in the manner of a dipole to create their own fields. These fields are inductively coupled to at least one sensor such as sensing coils fabricated in a gradiometer configuration. The output signals from the sensing coils are appropriately amplified and processed to provide useful output indications.

Abstract: An apparatus for detecting the presence or absence of foreign matter in a product is provided which includes a reaction signal generating circuit 2 for outputting a reaction signal associated with the product by detecting a change in pattern of distribution of magnetic fluxes when the product P is passed through an alternating magnetic field; a determining circuit 10 for comparing a value of the reaction signal at a predetermined phase point p1 with a threshold value SH to thereby determine the presence or absence of the foreign matter in the product; and a sensitivity adjusting circuit 12A for adjusting a sensitivity of the reaction signal generating circuit 2 so that the value of a first test reaction signal A at the predetermined phase point p1, which is obtained when a product P added with foreign matter of a minimum size to be detected is passed through the alternating magnetic field, attains a desired level relative to the threshold value SH.

Abstract: An apparatus that measures electrical impedance. The apparatus includes a signal generator controlled by a master microcontroller, a plurality of data acquisition channels, each channel containing a microcontroller, a host computer that processes and stores measured values, and a communication line between the host computer and the master microcontroller.

Abstract: A magnetic flux detector comprises a core member 12 and an armature member 11, and the core member 12 generates a magnetic flux by an exciting coil 13 when the exciting coil receives an excitation current controlled by an excitation current controller 30. The magnetic flux detector further comprises a search coil 14, which is provided in a magnetic path for the magnetic flux, and a magnetic flux calculator 40, which determines the magnitude of the magnetic flux by measuring an electromotive force induced in the search coil 14 by a change in the magnetic flux.

Abstract: An improved non-obtrusive weapon detection system and method used in discriminating between a concealed weapon made of a ferromagnetic material. The system provides a high probability of detection of hand guns and other types of weapons with a low false alarm rate. The detection of the weapon is accomplished by measuring a total electromagnetic field. The total field being the sum of an incident electromagnetic field and an electromaetic field scattered from the object. The system uses a magnetic field transmitter, which transmits a low intensity electromagnetic signal. The electromagnetic signal illuminates a volume wherein the weapon, called a target, may or may not be carried by a person. The electromagnetic signal is in a form of a sudden steplike change in a constant magnetic field, called a “time-domain” excitation. The waveform or step pulse of the time-domain excitation is called a Heaviside step pulse.

Abstract: The present invention relates to a device for measuring the value of a parameter relating to an electrically conductive object. Such a parameter can be the electric conductivity or the degree in which the material has changed under the influence of external conditions. Alternatively the parameter is the quality of a weld or the thickness of the object.

Abstract: A method for setting the trigger power of transmitter diodes that transmit data via optical paths allows the transmission power to be adjusted and adapted to the communication distance. The trigger power is determined for the present communication distance on the basis of a test signal before data transmission begins. A circuit arrangement implementing the method includes a driver circuit with a switching device that switches a circuit junction point selectively to a supply voltage or to a constant reference voltage, a voltage-controlled resistor which delivers the driver current and is controlled from the circuit junction point, and a voltage-controlled measuring resistor which delivers a measured current with a fixed relationship to the driver current and is controlled from the circuit junction point. Since the set trigger power can be reduced, the power consumption for data transmission can be reduced considerably.

Abstract: A hand tool has a handgrip attached to a ground-piercing probe, which is manually insertable in the soil. The probe has a chamber in which at least one inductor is positioned and connected to metal detection circuitry. The preferred circuitry has a pulse generator applying current pulses to an inductor for inducing eddy currents in a buried target object. After the pulse terminates, the decaying coil voltage is sampled at different times to detect both the presence and range of the object, as well as the type of metal in the object. An asymmetric magnetic field pattern about the probe is aligned with a direction pointing indicium on the handgrip and provides directional sensitivity. The coil voltage samples are applied to signaling circuitry, which provides an audible signal which is a series of bursts of an audio tone. The pitch of the audio tone signals the presence, range and bearing of the buried metal object, while the pulse rate of the bursts signals the metal type.

Abstract: A hand tool has a handgrip attached to a ground-piercing probe, which is manually insertable in the soil. The probe has a chamber in which at least one inductor is positioned and connected to metal detection circuitry. The preferred circuitry has a pulse generator applying current pulses to an inductor for inducing eddy currents in a buried target object. After the pulse terminates, the decaying coil voltage is sampled at different times to detect both the presence and range of the object, as well as the type of metal in the object. An asymmetric magnetic field pattern about the probe is aligned with a direction pointing indicium on the handgrip and provides directional sensitivity. The coil voltage samples are applied to signaling circuitry, which provides an audible signal which is a series of bursts of an audio tone. The pitch of the audio tone signals the presence, range and bearing of the buried metal object, while the pulse rate of the bursts signals the metal type.