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US 2004/0103725 A1Published application
Stress sensor
AssigneeQuinetiq Limited
InventorsGeorge Jiri Tomka, Jonathan Geoffrey Gore, Mark Gregory Maylin, James Carl Milne
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AssigneeQuinetiq Limited
InventorsGeorge Jiri Tomka, Jonathan Geoffrey Gore, Mark Gregory Maylin, James Carl Milne
Estimating the term…
A stress or magnetic field sensor comprises a generally elongate magnetically soft amorphous or nanocrystalline electrically resistive element and biasing means for applying to the element a bias magnetic field of which the component directed along the length of the sensor has an amplitude variation pattern along the element. A periodically varying pattern has the effect of reducing the sensitivity of a stress sensor to external ambient fields (FIG. 3 shows that with a sawtooth bias field the sensitive portions a of a sensor move to positions b in the presence of an ambient field, but their number remains the same). A ramped bias field enables the position of the sensitive region of the sensor to be controlled, for measuring local stress, or for mapping an external magnetic field. Control of the regions where the sensor is active may include selective conductive coating of portions of its length. Potential uses of the stress sensor include a pressure sensor, embedment in moving parts (using rf communication) such as vehicle tyres, aircraft wings or machine parts, and in structures such as bridges where stray magnetic fields are a problem.
A sensor comprising a generally elongate magnetically soft amorphous or nanocrystalline electrically resistive element and biasing means for applying to the element a bias magnetic field, the component of said field directed along the length of the sensor having a spatially substantially varying pattern of amplitude along the element.
A sensor according to any preceding claim wherein said amplitude variation is periodic.
A sensor according to any preceding claim wherein said element has portions along its length coated with a relatively highly conducting material.
A sensor according to any preceding claim wherein said element is in the form of a wire, ribbon or fibre.
A sensor according to any preceding claim wherein said element is melt spun.
A sensor according to any preceding claim wherein said element exhibits a small negative magnetostriction.
A sensor according to any preceding claim wherein the element is formed of a cobalt rich alloy.
A sensor according to any preceding claim wherein the element is embedded in a matrix.
A sensing device comprising a sensor according to any preceding claim and current supply means for supplying an alternating current to the element.
A method of reducing the sensitivity of the impedance of a generally elongate magnetically soft amorphous or nanocrystalline stress sensor element to external magnetic fields, the method comprising applying along the sensor element a bias magnetic field, the component of said field directed along the length of the sensor having a spatially substantially varying amplitude pattern along the element.
A method of measuring stress in an object by securing thereto a stress sensor comprising a generally elongate magnetically soft amorphous or nanocrystalline stress sensor element, supplying an ac current to the element, and measuring the impedance of the element, wherein a bias magnetic field with an amplitude which varies with position along the element, the component of said field directed along the length of the sensor having a spatially substantially varying amplitude pattern along the element to reduce its sensitivity to external magnetic fields.
A sensor element substantially as hereinbefore described with reference to FIGS. 6 and 7 of the accompanying drawings.
Dependencies are inferred from the claim text.