摘要:
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. The sensor geometry consist of a periodic structure with, at any one time, a single sensing element that provides for multiple wavelength within the same sensor footprint.
摘要:
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.
摘要:
Combined wound and micro-fabricated winding constructs are described for the inspection of materials and the detection and characterization of hidden features or flaws. These constructs can be configured as sensors or sensor arrays that are surface mounted or scanned over conducting and/or magnetizable test materials. The well-defined geometry obtained micro-fabricated windings and from carefully wound coils with known winding positions permits the use of model based inversions of sensed responses into material properties. In a preferred embodiment, the primary winding is a wound coil and the sense elements are etched or printed. The drive or sense windings can also be mounted under fasteners to improve sensitivity to hidden flaws. Ferrites and other means may be used to guide the magnetic flux and enhance the magnetic field in the test material.
摘要:
Material condition monitoring may be performed by electromagnetic sensors and sensor arrays mounted to the material surface. The sensors typically have a periodic winding or electrode structure that creates a periodic sensing field when driven by an electrical signal. The sensors can be thin and flexible so that they conform to the surface of the test material. They can also be mounted such that they do not significantly modify the environmental exposure conditions for the test material, such as by creating stand-off gaps between the sensor and material surface or by perforating the sensor substrate.
摘要:
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.
摘要:
Magnetic field based eddy-current sensing arrays measure the near surface properties conducting and magnetic materials. The arrays have a drive winding for imposing the magnetic field in a test material and at least two sense elements for sensing the response of the test material to the magnetic field. Each sense element has distinct leads for connection to impedance measurement instrumentation. The arrays have accurately positioned sense elements and drive winding conductors so that the sense element responses are essentially identical for test materials having uniform properties. The drive windings are typically formed into circular loops for examining material properties in the vicinity of circular features in the test material, such as holes or fasteners. For examining the material, the sensor arrays are rotated around the feature or mounted against a material surface and provide information from multiple locations around the feature to determine if cracks are present or to monitor crack growth.
摘要:
The condition of insulating and semiconducting dielectric materials is assessed by a sensor array that uses electric fields to interrogate the test material. The sensor has a linear array of parallel drive conductors interconnected to form a single drive electrode and sense conductors placed on each side of and parallel to a drive conductor. Subsets of the sense conductors are interconnected to form at least two sense elements sensitive to different material regions. The sense conductors may be at different distances to the drive conductors, enabling measurement sensitivity to different depths into the test material. The material condition is assessed directly from the sense element responses or after conversion to an effective material property, such as an electrical conductivity or dielectric permittivity.
摘要:
Apparatus and methods are described for assessing material condition through magnetic field measurements that provide material property information at multiple depths into the material. The measurements are obtained from sense elements located at different distances from an excitation drive winding, with the area of each sense element adjusted so that the flux of magnetic field through each sense element is approximately the same when over a reference material. These sense element responses can be combined, for example by subtraction, to enhance sensitivity to hidden features, such as cracks beneath fastener heads, while reducing the influence from variable effects, such as fastener material type and placement. Measurement responses can also be converted into effective material properties, using a model that accounts for known properties of the sensor and test material, which are then correlated with the size of the surface breaking or hidden features.
摘要:
Methods and apparatus are described for absolute electrical property measurement of materials. This is accomplished with magnetic and electric field based sensors and sensor array geometries that can be modeled accurately and with impedance instrumentation that permits accurate measurements of the in-phase and quadrature phase signal components. A dithering calibration method is also described which allows the measurement to account for background material noise variations. Methods are also described for accounting for noise factors in sensor design and selection of the optimal operating conditions which can minimize the error bounds for material property estimates. Example application of these methods to automated engine disk slot inspection and assessment of the mechanical condition of dielectric materials are presented.
摘要:
Quasistatic sensor responses may be converted into multiple model parameters to characterize hidden properties of a material. Methods of conversion use databases of responses and, in some cases, databases that include derivatives of the responses, to estimate at least three unknown model parameters, such as the electrical conductivity, magnetic permeability, dielectric permittivity, thermal conductivity, and/or layer thickness. These parameter responses are then used to obtain a quantitative estimate of a property of a hidden feature, such as corrosion loss layer thicknesses, inclusion size and depth, or stress variation. The sensors can be single element sensors or sensor arrays and impose an interrogation electric, magnetic, or thermal field.