United Kingdom Atomic Energy Authority

Parmeko Limited

Michael A Flemming

Graham N Plested

John D McCann

James H Stephen

A method of characterizing a material uses an element in which microwaves can propagate and can resonate, such as a weakly-coupled isolated microstrip device or a microwave cavity, arranged so that fringing fields from the element interact with the material. Microwaves are coupled into the element at a frequency near a resonance, and a modulating signal is applied so as to modulate the response of the element. Measurements of both the mean response and the modulation of the response enable the dielectric constant and dielectric loss of the material to be determined. Modulation may be applied to the frequency of the microwaves, or to the electrical parameters of the element.

Material characterization

A microwave probe for determining properties of a fluid medium, and particularly for separating measuring dielectric constant and dielectric loss, comprises an insulating substrate metallized on one face, an electrically isolated, ring-shaped, resonant element defined on the opposite face, and shielded means to couple microwaves into and from the element such that the element can undergo a resonance. The resonant frequency depends on the dielectric constant of an adjacent medium, while the Q-factor of the resonance depends on the dielectric loss of the medium. In one method of operation microwaves are coupled into the element to force an oscillation, and the driving frquency is varied to obtain a resonance.

Microwave probe

An apparatus and a method are provided for measuring the thickness (d) of a thin layer (12) of a non-metallic material on the surface of another medium (14). A transmitter (16) causes a beam of microwaves to be incident on the exposed surface (15) at an angle of incidence greater than 30.degree., and at least one fixed detector (18) monitors a component of the reflected microwave beam polarized in an appropriate plane. In one case the angle of incidence is equal to the Brewster angle (B) for the lower medium, which is water, and the detector monitors the amplitude of the vertically plane polarized component, which is a rapidly varying function of the thickness. In another case the angle of incidence is about 45.degree., and the monitored component is cross-polarized relative to the incident beam. The apparatus is suitable for detecting layers less than 1 mm thick of pollutants such as oil or kerosene on water before such water is discharged into the environment.

Method and apparatus for thin layer monitoring

A surveillance system transmits a microwave carrier signal through a surveillance zone (14). Two low frequency energy fields are also established in the zone being produced by respective pairs of closely spaced apart low frequency signals radiated from opposite sides of the zone. A receptor reradiator in the zones receives these signals and reradiates a reply signal to a receiver the reply signal consisting of the microwave carrier signal amplitude modulated in accordance with the instantaneous value of the low frequency fields at the location of the receptor reradiator. The receiver separates out preselected intermodulation products and activates an alarm only when the preselected intermodulation products are present.

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Abingdon, United Kingdom

Michael A Flemming