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: Methods are described for the use of conformable eddy-current sensors and sensor arrays for characterizing residual stresses and applied loads in materials. In addition, for magnetizable materials such as steels, these methods can be used to determine carbide content and to inspect for grinding burn damage. The sensor arrays can be mounted inside or scanned across the inner surface of test articles and hollow fasteners to monitor stress distributions. A technique for placing eddy-current coils around magnetizable fasteners for load distribution monitoring is also disclosed.

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: Pressurized elastic support structures or balloons are used to press flexible sensors against the surface a material under test. Rigid support elements can also be incorporated into the inspection devices to maintain the basic shape of the inspection structure and to facilitate positioning of the sensors near the test material surface. The rigid supports can have the approximate shape of the test material surface or the pressurization of one or more balloons can be used to conform the sensor to the shape of the test material surface.

Abstract: A dielectrometer with a sensor face that carries an excitation electrode driven with a varying voltage. At least two sensing electrodes and a guard electrode are also carried by the sensor face. The sensing electrodes are adapted for single or multiple penetration depth measurements into a test material. The guard electrode surrounds the sensing electrodes and is at about the same voltage as the sensing electrodes.

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 dielectrometer with a sensor face that carries an excitation electrode driven with a varying voltage. At least two sensing electrodes and a guard electrode are also carried by the sensor face. The sensing electrodes are adapted for single or multiple penetration depth measurements into a test material. The guard electrode surrounds the sensing electrodes and is at about the same voltage as the sensing electrodes.

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: The combination of giant magnetoresistive (GMR) sensing element arrays with shaped field, distributed drive windings provides a deep measurement capability for magnetic and/or conducting materials. Sensor designs are disclosed that use either sinusoidal or first order Bessel function shaped quasistatic field drive designs with a method to provide two magnetic field penetration depths within the same sensor footprint and at the same temporal excitation frequency. An easy to model drive construct supports substantial calibration requirement reduction and rapid generation of sensor response databases called measurement grids used for rapid estimation of multiple properties. Use of one deep penetration drive with an array of GMR sensing elements provides both high-resolution imaging and sensitivity deep into complex structures.

Abstract: A sensor that characterizes welds in materials. The sensor includes a meandering drive winding with at least three extended portions and at least one sensing element placed between an adjacent pair of extended portions. A time varying electric current is passed through the extended portions to form a magnetic field. The sensor is placed in proximity to the test material and translated over the weld region. An electrical property of the weld region is measured for each sensing element location. The weld quality is determined using a feature of the electrical property measurement and location.

Abstract: A method is disclosed for processing, optimization, calibration, and display of measured dielectrometry signals. A property estimator is coupled by way of instrumentation to an electrode structure and translates sensed electromagnetic responses into estimates of one or more preselected properties or dimensions of the material, such as dielectric permittivity and ohmic conductivity, layer thickness, or other physical properties that affect dielectric properties, or presence of other lossy dielectric or metallic objects. A dielectrometry sensor is disclosed which can be connected in various ways to have different effective penetration depths of electric fields but with all configurations having the same air-gap, fluid gap, or shim lift-off height, thereby greatly improving the performance of the property estimators by decreasing the number of unknowns.

Abstract: A method is disclosed for processing, optimization, calibration, and display of measured dielectrometry signals. A property estimator is coupled by way of instrumentation to an electrode structure and translates sensed electromagnetic responses into estimates of one or more preselected properties or dimensions of the material, such as dielectric permittivity and ohmic conductivity, layer thickness, or other physical properties that affect dielectric properties, or presence of other lossy dielectric or metallic objects. A dielectrometry sensor is disclosed which can be connected in various ways to have different effective penetration depths of electric fields but with all configurations having the same air-gap, fluid gap, or shim lift-off height, thereby greatly improving the performance of the property estimators by decreasing the number of unknowns.

Abstract: An instrument and method for providing accurate and reproducible measurement of absolute properties of a material under test without using conductivity or crack calibration standards. The instrument has a sensor designed to minimize unmodeled parasitic effects. To accomplish this, the sensor has one or more of the following features: dummy secondary elements located at the ends of a primary winding meandering, setting back of the sensing element from a connecting portion of the primary winding, or various grouping of secondary elements. The sensing elements of the sensor can be connected individually or in differential mode to gather absolute or differential sensitivity measurements. In addition, the instrumentation is configured such that a significant portion of the instrumentation electronics is placed as close to the sensor head to provide independently controllable amplification of the measurement signals therein reducing noise and other non-modeled effects.

Abstract: A detection apparatus discriminates between metallic mines and other buried objects by detecting the depth of the object, the size, the shape and the orientation of the object and the electrical properties of the object. A magnetometer sensor detects objects containing metal located below the surface of the ground. This apparatus has a plurality of parallel, spaced linear conductor sets disposed in proximity to the ground. The conductor sets have varying numbers of individual conductors. An electromagnetic field is imposed in the ground with a dominant spatial wavelength through the conductor elements. A resulting electromagnetic response of the object in the ground to the imposed magnetic field is sensed.