Microwave sensor for identifying the surface properties of a workpiece and associated method

A sensor for identifying the surface properties of a workpiece, the sensor comprising:

• a microwave generator for producing microwave signals at a predetermined frequency;
• microstrip sensing means comprising:
• a dielectric substrate for supporting propagation of microwave signals, said dielectric substrate having opposed first and second surfaces;
• and
• a microstrip sensor comprised of a layer of conductive material disposed on the first surface of said dielectric substrate for transmitting microwave signals produced by said microwave generator from a first end portion to a second end portion such that the workpiece can influence the strength of the transmitted microwave signals, wherein the first end portion is coupled to said microwave generator and is spaced apart from the second end portion, and wherein said microstrip sensor further includes a center segment extending between and electrically connecting the first and second spaced apart end portions;
• a detector, coupled to the second end portion of said microstrip sensor, for detecting the microwave signals on said microstrip sensor;
• and
• surface properties determining means, responsive to said detector means, for determining the surface properties of the workpiece based upon the strength of the detected microwave signals such that workpieces having different impedances to the propagation of microwave signals can be distinguished.

A method of identifying the surface properties of a workpiece comprising the steps of:

• transmitting microwave signals having a predetermined frequency and a predetermined power level to the workpiece;
• receiving microwave signals in response to the transmitted microwave signals;
• filtering the received microwave signals to remove received microwave signals having a frequency outside of a predetermined range of frequencies about the predetermined frequency of the transmitted microwave signals;
• and
• comparing the power level of the received microwave signals, following said filtering step, to high and low predetermined power levels such that workpieces which have different impedances to the propagation of microwave signals can be distinguished.