Position and electromagnetic field sensor

Abstract

A position and electromagnetic field sensor is provided. The sensor relies upon an oscillator such as a Robinson marginal oscillator to generate an rf or microwave electromagnetic field. As an inhomogeneously-shaped object, such as a metallic toothed wheel, for example, moves through the resultant field, the field experiences a change in electric or magnetic susceptibility. This in turn causes energy losses in the oscillator the magnitude of which can be output as a d.c. signal related thereto. To detect non-moving objects which nevertheless generate an electromagnetic field or have attached to them a source thereof, the sensor may also include a giant or colossal magnetoresistive structure located adjacent the oscillator coil, the structure having an imaginary magnetic susceptibility which is strongly dependent upon the magnitude and direction of the field generated by or at the object to be sensed.

Description

RELATED APPLICATIONS [0001] This application is a divisional application of application Ser. No. 10 / 211,543, filed Jan. 16, 2003, which is a National Stage of International Application PCT / GB01 / 01085, filed Mar. 13, 2001. Application Ser. No. 10 / 211,543 is hereby incorporated by reference in its entirety.BACKGROUND OF INVENTION [0002] This application relates to a sensor for detecting the position of an object and / or an electromagnetic field associated with that object. SUMMARY [0003] In embodiments of a first aspect of the present invention, there are provided a susceptibility sensor for detecting relative movement between an inhomogeneously-shaped object to be sensed and the sensor, comprising: an oscillator including a sensor electromagnetic field generator; and an output arranged to provide a signal which varies in dependence upon the change in the electrical properties of the said oscillator; the sensor being arranged such that relative movement between the object to be sensed ...

AI Technical Summary

Benefits of technology

[0004] Using variations in electric or magnetic susceptibility provides a number of advantages. Firstly, the object to be detected may be formed of a very wide range of materials, such as ferromagnets, non-ferromagnets, metals, and even insulators such as ceramics or plastic materials. Secondly, the sensor has a very high sensitivity, relative to previous motion sensors, and this sensitivity is independent of the speed at which the relative movement of the object and sensor takes place.

[0008] It is preferable that the coil is non-planar. The use of a non-planar coil provides particular advantages such as the ability to focus the sensitive region, and to obtain a better spatial resolution.

[0010] The oscillator is preferably a self-oscillating, closed loop oscillator, such as a Robinson marginal oscillator, a Van der Pol marginal oscillator or any oscillator variant with intermediate characteristics. In the case of the Robinson marginal oscillator in particular, it is preferable that an oscillator loop and limiter detector is employed. This potentially allows operation from the uhf region to d.c., and is insensitive to amplitude noise.

[0011] The use of an oscillator loop together with a limiter detector is likewise particularly advantageous when the limiter detector includes Gallium Arsenide or High Electron Mobility Transistors. The use of such devices allows operation up to the GH2 regime which in turn provide increased spatial resolution.

[0013] Such a sensor may be constructed using a discrete sensor element, in close proximity to a microwave stripline or uhf tank circuit comprising a coil and capacitor. Such a sensor is highly versatile, and can detect both changes in the electric or magnetic susceptibility of the object to be sensed, or changes in magnitude or direction of the object electromagnetic field associated with the object to be sensed, or both. The sensor itself requires no modification and the output can generate a signal regardless of which parameter of the object to be sensed is changing. If the object to be sensed is moving, but has no object electromagnetic field associated with it, then the sensor of the preferred embodiment effectively ignores the presence of the sensor element, whose electric or magnetic susceptibility remains constant in that case.

Problems solved by technology

In use, the sensor electromagnetic field is presented with a change in electric or magnetic susceptibility, which may cause a variation in electromagnetic energy losses within the oscillator.

Although there are particular advantages associated with a composite sensor having both a sensor element and means for generating a sensor electromagnetic field, allowing monitoring of both moving objects and objects having an electromagnetic field associated with them that changes with time, the sensor need not necessarily allow monitoring of moving objects.

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