Abstract: A magnetic sensor 10 includes GMR elements 11-18, and heating coils 21-24 serving as heat generating elements. The elements 11-14 and 15-18 are bridge-interconnected to constitute X-axis and Y-axis sensors, respectively. The heating coils 21, 22, 23, and 24 are disposed adjacent to the elements 11 and 12, the elements 13 and 14, the elements 15 and 16, and the elements 17 and 18, respectively. The heating coils 21-24, when electrically energized, heat mainly the adjacent elements. Therefore, the elements can be heated and cooled in a short period of time in which constant geomagnetism can be ensured. Data for compensation of temperature-dependent characteristic (ratio of change in sensor output value to variation in element temperature) is obtained on the basis of the temperatures of the elements before and after the heating, and the magnetic sensor outputs before and after the heating. Subsequently, the temperature characteristics of the elements are compensated on the basis of the data.

Abstract: A coersive force distribution analyzing, apparatus applies a magnetic field substantially perpendicularly to a sample including a perpendicularly magnetically recordable magnetic thin film. While tow-dimensionally moving the sample, the coersive force distribution analyzing apparatus generates a magnetic flux detection signal in response to a leakage flux generated in a magnetic domain on a sample surface. The apparatus applies, to the sample, a first external magnetic field and a second external magnetic field respectively corresponding to a first threshold and a second threshold selected from a hysteresis characteristic corresponding to average magnetization of the sample. This results in first magnetic domain image data and second magnetic domain image data. The apparatus uses the first and second thresholds to binarize the first and second image data to generate a first coersive force distribution pattern corresponding to the difference between the binarized first and second image data.

Abstract: An arrangement for testing an elongated body 1 or a welded and bonded joint in the body for faults 60 has a device 4, 5 for production of an eddy current in the elongated body 1 or its welded and bonded joint. At least one magnetic field sensor 7 for sensing the magnetic field is provided on the elongated body 1 or the welded and bonded joint. The dimensions of the at least one magnetic field sensor 7 are equal to or less than the fault 60 to be investigated.

Abstract: The present invention discloses a magnetic detecting device comprising an apply coil 1 for generating an alternate magnetic field of variable frequency and a power source 2 for the apply coil; a magnetic sensor 5 for detecting a change in the magnetic field induced by a test object 9 placed at a distance from a surface of said apply coil and toward said test object, said magnetic sensor being provided with a cancel coil 6 for canceling a magnetic field generated at the position of the magnetic sensor by a direct magnetic field and/or said apply coil; a measurement circuit 7 for the magnetic sensor for measuring a detection signal of said magnetic sensor; a lock-in amplifier circuit 8 for detecting an output of said measurement circuit for the magnetic sensor into two signals having the same frequency as that of said apply coil and phases different from each other by 90 degrees; and an analysis means 10 for analyzing a phase change of the output of said magnetic sensor 5 using an output signal from said lock-i

Abstract: Disclosed is a device for detecting defects which are deep in electrically conductive materials in a non-destructive manner, comprising an excitation device provided with induction coils which are used to produce low frequency eddy currents in the material, and a receiving device for the magnetic field of the eddy currents, the magnetic field being modified by the defects, and the receiving device comprising a gradiometer magnetic field sensors with an integrated bridge circuit.

Abstract: A current sensor includes a support structure (12), a magnetic field sensor (11) positioned on the support structure, a primary conductor comprising sandwich (13) including an electrically conducting top layer (13a) and electrically conducting bottom layer (13b), and a layer of magnetic permeable material (13c) interposed between. The magnetic permeable material (13c) is disposed around the magnetic field sensor (11) so that the magnetic field sensor (11) is at least partially surrounded by the magnetic permeable material (13c). The conductor sandwich (13) includes at least one gap (16, 17) between adjacent edges (18, 19). The magnetic field sensor (11) is positioned proximate to the gap and is operable to receive magnetic flux lines resulting from current flowing in the primary conductor.

Abstract: The invention provides a method and apparatus for monitoring subsurface chromium depletion from a steel member, such as a pyrolysis pipe. In the harsh conditions of a pyrolysis furnace, chromium within the pipe 16 migrates towards the pipe surface which results in the formation of a chromium depleted layer 14. This layer can provide useful data about the condition and operation of the furnace. The degree of chromium depletion is measured by using a magnetic source of known strength to create a magnetic field in the surface region of the pipe 16. An estimate of the thickness of the chromium depleted layer 14 is determined from the resultant magnetic flux, which can be measured by a hall element arranged at substantially 45° to the longitudinal axis of the magnet.

Abstract: A sensor signal conditioning circuit and sensor system incorporating the same. In one embodiment, the signal conditioning circuit includes a DC-coupled detector that converts a sensor signal into a discrete level signal. An AC-coupled detector having a dynamic DC threshold input also converts the sensor signal into a discrete level signal and has a startup delay associated with the dynamic DC threshold input. The signal conditioning circuit further includes a device that inhibits the DC-coupled detector responsive to the dynamic DC threshold input reaching a specified threshold voltage level such that the AC-coupled detector provides the detected output during steady-state sensor operation.

Abstract: A non-destructive testing device has an excitation coil with a plurality of conductor ribbons attached to a flexible membrane. A frame supports the membrane and incorporates wheels for translation across a surface to be inspected and resilient suspension for maintaining the membrane with the excitation coil and wheels in intimate contact with the surface, the membrane flexing to maintain contact with a smoothly curved surface as found in aircraft structures. A magnetoresitive (MR) array is supported within the frame inserted in the membrane to be in close proximity to the surface. The MR array detects the magnetic field resulting from the eddy currents created by the excitation coil for identification of cracks or features beneath the surface under inspection.

Abstract: A precisely machined test nest holds a single hard disk drive slider. The test nest is fabricated to contain a micro pickup coil that is positioned to be able to detect magnetic flux from a write element of the slider. The micro pickup coil has highly repeatable and controllable positioning with respect to the write element. This technique also allows local magnetic field to be applied to the read element, and its small size allows excitation at higher frequencies than are currently achievable today. The coil is lithographically defined and integrated into the test nest and used on single slider testers. The low inductance of the coil allows it to be driven at high frequencies. Its position within the test nest ensures good heat sinking and enables large current pulses to be employed.

Abstract: A handheld scanning subsurface detector (1) includes a detector module (2) and a computing unit (3) located in handheld housing (5), a guide (7) for guiding the detector module (2) at a predetermined distance over a to-be-analyzed wall surface (6), at least one path sensor (8) connected to the computing means (3) and connected, in a controlling manner, to the detector module (2) by controlling means (9). A corresponding control method is also described.

Abstract: There is provided an inspection device for the detection of flaws in a component. The inspection device comprises a magnetic field generator, a first array of magnetoresistive sensors and a second array of magnetoresistive sensors, in which the second array is substantially orthogonal to the first array. The signals generated by the first and second arrays are utilized by a processing element to determine a curl of the magnetic field signals effected by the eddy currents including the eddy currents encountering a flaw in the component. The curl of the magnetic field signals is then used to better illustrate the existence of the flaw and various parameters of the flaw. The magnetic field generator comprises a coil or linear arrays of conductors. The inspection device is preferably contained (1) within a hand-held housing or (2) mounted on any automated inspection platform, and advantageously comprises a display for illustration of the detected flaw.

Abstract: An RFEC excitation unit and sensor apparatus and method that facilitate detection of cracks or other anomalies within or under a surface and immediately next to an expected structure (such as a rivet) that would otherwise cause a signal change preventing detection of the cracks. In some embodiments, the apparatus includes actuators and control that move the apparatus and analyze sensed RFEC signals to determine the location of the rivet, and then to rotate (mechanically or electronically) the sensed signal and/or excitation signal to maintain a constant relationship to the edge of the rivet in order that signals from the rivet edge are suppressed and signals from the cracks are detected. In some embodiments, the excitation unit is maintained at the center of the rivet surface, and the sensor is moved around the rivet in a circle centered on the rivet.

Abstract: A device for measuring current comprises a magnetic field sensor (2) for measuring the magnetic field produced by a current I flowing through a current conductor (1) and a yoke (3) of a magnetic material with a relative permeability of at least 100. The magnetic field sensor (2) preferably comprises a semiconductor chip with at least one Hall element and an electronic circuit for the operation of the Hall element. Two magnetic field concentrators (7, 8) separated by an air gap (6) are arranged on a surface of the semiconductor chip such that field lines (9) of the magnetic field (see FIG. 3) that issue from the first magnetic field concentrator (7) in the vicinity of the air gap (6) and impinge on the second magnetic field concentrator (8) in the vicinity of the air gap (6) pass through the at least one Hall element.

Abstract: A planer reader and method of probing the magnetic permeability of a material using a magnetic flux circuit comprises a substrate; a near-circular soft magnetic layer adjacent to the substrate; a gap configured in the soft magnetic layer, wherein the gap creates an opening between two ends of the soft magnetic layer, and wherein the gap is configured to align with a material located a distance from the soft magnetic layer; a magnetic flux generator adapted to provide magnetic flux to the material; and a magnetic sensor adapted to measure the magnetic flux traversing the material. The circuit further comprises an insulator covering the soft magnetic layer, the gap, the magnetic flux generator, and the magnetic sensor. The magnetic flux generator comprises a magnet or a magnetic coil proximate to the soft magnetic layer. Moreover, the soft magnetic layer comprises a soft ferromagnet. In one embodiment, the substrate is flexible.

Abstract: An eddy-current sensor for nondestructive testing according to the present invention includes a planar exciting coil having a pair of current lines in parallel with each other through which exciting currents flow in opposite directions to each other during the testing, for generating an alternative magnetic field applied to a subject to be nondestructively tested by the exciting currents, and at least one MR element positioned on a central axis between the pair of current lines and on the opposite side to the subject in relation to the exciting coil, for detecting a magnetic field generated newly from the subject by an eddy-current induced by the alternative magnetic field.

Abstract: A detector assembly and methods including a magnetoresistive sensor capable of detecting anomalies in the wall of a casing string disposed in a wellbore. Examples of anomalies include gaps between casings such as due to casing joints, air gaps in casing threads such as due to flush casing joints, enlarged casing wall thickness such as due to external casing collars, damaged casing, perforations, and other discontinuities or deformities in the casing. The detector assembly and methods detect perturbations in the earth's magnetic field caused by the anomalies. The detector assembly generates essentially no magnetic or electromagnetic field so that other downhole instrumentation is not affected by its presence.

Abstract: An apparatus for inspecting a metallic post contoured in a single dimension for defects. The apparatus has a clamp having at least one jaw with a surface conforming to the contour to the metallic post. The conforming jaw or jaws also have a plurality of eddy current coils and the probe has at least one sensor configured to sense at least one of position or motion.

Abstract: Magnetic field sensor probes are disclosed which comprise primary or drive windings having a plurality of current carrying segments. The relative magnitude and direction of current in each segment are adjusted so that the resulting interrogating magnetic field follows a desired spatial distribution. By changing the current in each segment, more than one spatial distribution for the magnetic field can be imposed within the same sensor footprint. Example envelopes for the current distributions approximate a sinusoid in Cartesian coordinates or a first-order Bessel function in polar coordinates. One or more sensing elements are used to determine the response of a test material to the magnetic field. These sense elements can be configured into linear or circumferential arrays.

Abstract: The invention relates to apparatus and a method for detecting the condition of the material of a pipeline wall. The apparatus includes means for inducing and detecting magnetic flux at a location on the pipeline and, at said location, sensing means detect whether any change in material condition is on or near the external wall of the pipeline. By analysing the two sets of monitored values a change in condition, such as corrosion, can be detected, located and determined to be at or near the external or internal surfaces of the pipeline wall.

Abstract: An inspection system for detecting flaws in oil and gas well borehole ferromagnetic tubulars. The inspection device operates inside the tubular by first saturating tubular wall with magnetic flux. Flaws in the wall causes flux leakage, and the magnitude of the flux leakage are measured with Hall effect sensors disposed within the inspection device. The magnitude of flux leakage is then related to the amount of ferromagnetic material loss resulting from the flaw. Eddy currents induced in the wall are also measured and combined with the Hall effect sensor measurements to define location and geometric shape of the flaw.

Abstract: A giant magnetoresistive flux focusing eddy current device effectively detects deep flaws in thick multilayer conductive materials. The probe uses an excitation coil to induce eddy currents in conducting material perpendicularly oriented to the coil's longitudinal axis. A giant magnetoresistive (GMR) sensor, surrounded by the excitation coil, is used to detect generated fields. Between the excitation coil and GMR sensor is a highly permeable flux focusing lens which magnetically separates the GMR sensor and excitation coil and produces high flux density at the outer edge of the GMR sensor. The use of feedback inside the flux focusing lens enables complete cancellation of the leakage fields at the GMR sensor location and biasing of the GMR sensor to a location of high magnetic field sensitivity. In an alternate embodiment, a permanent magnet is positioned adjacent to the GMR sensor to accomplish the biasing.

Abstract: The magnetic field intensity distribution of a magnetic material sample, such as a magnetoresistive device, is measured with a probe having a tip portion of a magnetic material to which current is made to flow from a power source to the magnetic material. The probe is scanned relative to the surface of the magnetic material sample in two modes. In a first mode, the probe is scanned by being oscillated in a vertical direction to tap a surface of the sample to be tested. In a second mode, the probe is scanned while being held in contact with the measured surface. Corresponding first and second output signals from the two modes of scanning are processed to calculate the magnetic field intensity distribution of the sample magnetic material.

Abstract: A detector assembly and methods including a magnetoresistive sensor capable of detecting anomalies in the wall of a casing string disposed in a wellbore. Examples of anomalies include gaps between casings such as due to casing joints, air gaps in casing threads such as due to flush casing joints, enlarged casing wall thickness such as due to external casing collars, damaged casing, perforations, and other discontinuities or deformities in the casing. The detector assembly and methods detect perturbations in the earth's magnetic field caused by the anomalies. The detector assembly generates essentially no magnetic or electromagnetic field so that other downhole instrumentation is not affected by its presence.

Abstract: An apparatus for the nondestructive measurements of materials. Eddy current sensing arrays are described which provide a capability for high resolution imaging of test materials and also a high probabilitity of detection for defects. These arrays incorporate layouts for the sensing elements which take advantage of microfabrication manufacturing capabilities for creating essentially identical sensor arrays, aligning sensing elements in proximity to the drive elements, and laying out conductive pathways that promote cancellation of undesired magnetic flux.

Abstract: Products are disclosed for measuring electromagnetic fields. One embodiment has at least two coplanar magneto-resestive sensors. Each magneto-resistive sensor has a sensitive axis in the plane of the at least two coplanar magneto-resistive sensors. The at least two magneto-resistive sensors may be orthogonally arranged about a central point to measure orthogonal components of electromagnetic fields.

Abstract: A detector assembly and methods including a magnetoresistive sensor capable of detecting anomalies in the wall of a casing string disposed in a wellbore. Examples of anomalies include gaps between casings such as due to casing joints, air gaps in casing threads such as due to flush casing joints, enlarged casing wall thickness such as due to external casing collars, damaged casing, perforations, and other discontinuities or deformities in the casing. The detector assembly and methods detect perturbations in the earth's magnetic field caused by the anomalies. The detector assembly generates essentially no magnetic or electromagnetic field so that other downhole instrumentation is not affected by its presence.

Abstract: A magnetic induction device mounted at the wellhead that is capable of measuring changes in magnetic flux can recognize when a tubing joint or casing collar passes in or out of the well. The number of changes in magnetic flux directly correlates to the number of joints and collars that have passed, and therefore an accurate inventory of the number of lengths of casing or tubing that are run into the well can be automatically maintained.

Abstract: A method for detecting breaks in a prestressed wire, rod or bar in prestressed concrete pressure pipe (PCCP), embedded in concrete and/or mortar is described. A remote field eddy current exciter/transformer coupling probe is traversed axially internally through the PCPP so as to create an energy flow path within and external to the wall of the PCPP and to induce a transformer coupling from the prestressing winding thus generating a signal in a detector spaced from and usually approximately coplanar with the exciter. As the exciter traverses a break in the wire, rod or bar, a small signal change is generated in the detector, nearly regardless but not independent of the radial position of the detector relative to the break.

Abstract: A process control method is described which uses measurements from magnetic field sensors to monitor the condition of material, such as from a heat treatment process. The sensors 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. The sensors can be exposed to the same process conditions as the material, such as elevated temperatures, or the shielding layers can be placed between the test material and the sensors to reduce sensor exposure to the processing conditions. Additional property measurements, such as sensor lift-off, can be used to ensure proper sensors operation.

Abstract: A soft-magnetic material is installed on the opposite side of the magnetism sensing face of magnetism sensing devices. This soft-magnetic material is larger than the magnetism sensing face. Then the detection coverage per sensor is enlarged, and the number of sensors and signal processing circuits are reduced across the width of the strip.

Abstract: An inspection system for detecting flaws in oil and gas well borehole ferromagnetic tubulars. The inspection device operates inside the tubular by first saturating tubular wall with magnetic flux. Flaws in the wall causes flux leakage, and the magnitude of the flux leakage are measured with Hall effect sensors disposed within the inspection device. The magnitude of flux leakage is then related to the amount of ferromagnetic material loss resulting from the flaw. Eddy currents induced in the wall are also measured and combined with the Hall effect sensor measurements to define location and geometric shape of the flaw.

Abstract: A magnetic field sensor includes: a Hall element; a voltage amplifier for amplifying an output voltage from the Hall element so as to output an amplified signal; a voltage comparison circuit for receiving the amplified signal; a switch circuit provided between the voltage amplifier and the voltage comparison circuit for inverting a polarity of the amplified signal; and a latch circuit for holding an output signal from the voltage comparison circuit. The voltage comparison circuit inverts a polarity of a hysteresis voltage that determines a reference value of a magnetic field intensity in response to a first synchronizing signal, which triggers a detection of a magnetic field, and a second synchronizing signal following the first synchronizing signal.

Abstract: A method and apparatus for detecting ferrous changes passing axially through a cylindrical space. In one embodiment, the method comprises surrounding the cylindrical space with a nonmagnetic cylinder having an outer wall and a cylindrical axis; creating an alternating magnetic field in the cylindrical space, the magnetic field created by a rotatable permanent magnet; monitoring the magnetic field with magnetic flux sensors placed outside the outer walls; and detecting changes in the magnetic field as ferrous matter passes axially through the cylindrical space. In other embodiments, the apparatus identifies ferrous changes as the tool joints that connect a jointed tubing string as the tubing string is moved in or out of a well bore, or as the presence or absence of a coiled tubing string in the well bore.

Abstract: Inductive sensors measure the near surface properties of conducting magnetic materials. The sensors generally include parallel winding segments to induce a spatially periodic magnetic field in a material under test. The sensors may provide a directionally dependent measure with measurements made in varying orientations of the sensor with respect to the material property variation directions. The sensors may be thin, conformable sensors that can be mounted on a test material and, for example, monitor crack initiation under the sensor. A second sensor may be left in air to provide a reference measurement, or the temperature of the material under test can be varied to verify the response of the individual sensing elements. Sensors can be mounted to materials under test in order to not modify the environment that is causing the stress being monitored.

Abstract: A structure is integrated into the design and manufacture of a magnetic head that allows self-generation of magnetic fields. The structure includes a conductor or conductors placed in close proximity to the read portion of a magnetic head and connected to an externally accessible connection. A high frequency signal is passed through the conductor to generate a magnetic field through the read device and simulate, for example, the head crossing magnetic domains on a magnetic memory disk.

Abstract: A device and method is taught for detection of flaws and localized wall loss in pipes made of ferromagnetic-based material. The device utilizes a magnetic field generator to create a horizontal magnetic field of flux. A pipe is passed through the magnetic field where a magnetic fluctuation detector, for example multiple groups of hall units, identifies fluctuations in the magnetic field.

Abstract: A magnetoresistive sensor has a semiconductor substrate and an insulator over the substrate. A magnetoresistive film is embedded in the insulator responsive material, and a conductive strap is wound into a coil around the magnetoresistive film but not around the substrate.

Abstract: A sensor for detecting defects in a component includes an electric coil fed with a varying electrical current to create a varying magnetic field penetrating at least partly into the component under test, and a defect detector including a magnetoresistor. The above components are accommodated in a protective housing having a detection face disposed near and parallel to a surface of the component under test. The coil has its axis &Dgr; perpendicular to the detection face and the magnetoresistor is in the vicinity of the detection face. The magnetoresistor is a giant magnetoresistor and is disposed so that its sensitivity axis &Dgr;1 sensitive to variations in a magnetic field is parallel to the detection face of the housing.

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: A display apparatus of magnetic flux density for detecting an internal crack of a metal or a shape of the metal includes a three-dimensional magnetic flux focusing unit installed near the metal, for concentrating magnetic flux generated by the metal, a magnetic flux density measurement unit installed near the magnetic flux focusing unit, for measuring changes in magnetic flux density concentrated by the magnetic flux focusing unit, and a display unit electrically connected with the magnetic flux measurement unit, for real-time displaying and storing changes in the magnetic flux density.

Abstract: A method and apparatus for detecting ferrous changes passing axially through a cylindrical space. In one embodiment, the method comprises surrounding the cylindrical space with a nonmagnetic cylinder having an outer wall and a cylindrical axis; creating an alternating magnetic field in the cylindrical space, the magnetic field created by a rotatable permanent magnet; monitoring the magnetic field with magnetic flux sensors placed outside the outer walls; and detecting changes in the magnetic field as ferrous matter passes axially through the cylindrical space. In other embodiments, the apparatus identifies ferrous changes as the tool joints that connect a jointed tubing string as the tubing string is moved in or out of a well bore, or as the presence or absence of a coiled tubing string in the well bore.

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: This invention relates to apparatus for the nondestructive measurements of materials. New eddy current sensing arrays and methods are described which provide a capability for high resolution imaging of test materials and also a high probabilitity of detection for defects and flaws around features such as fasteners. The arrays incorporate unique layouts for the sensing elements, generally have essentially identical sensor arrays with sensing elements aligned in proximity to the drive elements, and conductive pathways that promote cancellation of undesired magnetic flux. These features enable the use of small sense elements that permits high resolution imaging of material properties.

Abstract: Discloses methods to perform magnetic testing of tensioning elements in a pre-stressed concrete cylindcr, such as a pipe or water reservoir and testing apparatus. The apparatus includes magnetic flux production means and detector means disposed proximal to a surface of the cylinder in a plane in common with the magnetic flux production means that is orthogonal to an axis of the cylinder. The apparatus operates over a range of low frequency signals, for example, between 20 and 300 hertz or a pulse. Output of the inspection apparatus includes a signal and distance plot showing the results of testing a cylinder at one or more frequencies. In accordance with another method of analysis, a characteristic of the phase of the output over distance is plotted, including the phase or representations of the in-phase or quadrature components of the received signal in relation to the driving signal.

Abstract: A Barkhausen probe includes a magnetizing field generator, a magnetoresistive magnetic field sensor, a direct current power supply for biasing the magnetoresistive magnetic field sensor and signal conditioning electronics. The Barkhausen probe is capable of generating and sensing the Barkhausen noise emanating from the surface of a cyclic magnetized specimen. The conditioned Barkhausen noise output of the signal conditioning electronics is usable as input to various analysis systems where textural analysis of the material can be performed.

Abstract: A sensor for measuring magnetostriction of and/or magnetic thin film is constructed by depositing a thin film nonferromagnetic electrically insulating layer followed by a thin film layer of a sensor material which is piezoresistive and nonferromagnetic. The insulating and the piezoresistive film can be etched into an appropriate pattern and orientation to provide sensitivity to strain in the magnetic film. The magnetostrictive strain in the magnetic film is induced by a known magnetic field which produces a corresponding strain in the piezoresistive film which can be measured as a change in the electrical resistance which can be detected by external probes or other measuring means. The measurement of the magnetostriction can be performed as a part of the manufacturing process for wafers with a plurality of thin film magnetic heads thereon and does not require that the wafers be removed to a laboratory.

Abstract: A sensor for detecting defects in a component includes an electric coil fed with a varying electrical current to create a varying magnetic field penetrating at least partly into the component under test, and a defect detector including a magnetoresistor. The above components are accommodated in a protective housing having a detection face disposed near and parallel to a surface of the component under test. The coil has its axis &Dgr; perpendicular to the detection face and the magnetoresistor is in the vicinity of the detection face. The magnetoresistor is a giant magnetoresistor and is disposed so that its sensitivity axis &Dgr;1 sensitive to variations in a magnetic field is parallel to the detection face of the housing.

Abstract: An apparatus for the nondestructive measurements of materials. Eddy current sensing arrays are described which provide a capability for high resolution imaging of test materials and also a high probabilitity of detection for defects. These arrays incorporate layouts for the sensing elements which take advantage of microfabrication manufacturing capabilities for creating essentially identical sensor arrays, aligning sensing elements in proximity to the drive elements, and laying out conductive pathways that promote cancellation of undesired magnetic flux.

Abstract: A magnetic non-destructive method and an apparatus for measurement of cross sectional area of elongated ferrous objects such as steel wire ropes and for detecting local flaws is disclosed. A section of a wire rope is magnetized by longitudinally spaced magnetic poles. A magnetic field parameter, e.g. magnetic flux density, is measured in, by at least, one pair of points between the poles of magnetizing device (in an inter-pole area) at the object under test surface. The pair of points is formed by two sensors placed in the inter-pole area along a direct line parallel to the rope axis. The rope cross sectional area corresponds to a sum of the sensor pair signals. Local flaws, such as broken wires and pitting corrosion in the rope, is detected by a first differences of signals of the sensor pair.