Method and apparatus for sensing proximity or position of an object using near-field effects

An electromagnetic system for sensing a position of a movable target having a conductive surface which includes a high region and a low region, the system comprising:

• radio frequency producing means for producing radio frequency energy;
• directional antenna means having an impedance and being connected to the radio frequency producing means for radiating the radio frequency energy toward a region of the target surface opposite the antenna means to thereby charge the target surface, the target surface changing the impedance of the antenna means when the target surface is positioned in a near field of the antenna means;
• detecting means responsive to said antenna means for detecting a value of the impedance of said antenna means;
• translating means responsive to said detecting means for translating the detected antenna means impedance into a position signal;
• comparing means responsive to said translating means for comparing the position signal with a predetermined high and a predetermined low reference signal corresponding, respectively, to the position signal generated when the high surface region and the low surface region are positioned opposite said antenna means;
• determining means responsive to said comparing means for determining the target position from the comparison of the position signal with the high and the low reference signal;
• and
• installing means for installing said antenna means into a housing wall having an aperture formed therein, the housing wall being positioned generally adjacent the target, said installing means comprising:
• a tube positioned in surrounding relation to said antenna means, the tube having an open distal end and open proximal end;
• a ceramic cap transparent to microwave and millimeter-wave energy;
• a sensor connector body affixed to the proximal end of the tube, the sensor connector body having a distal barbed section and a proximal section dimensioned larger than the distal section;
• and
• a flexible plug having an outer diameter dimensioned to form a seal with the housing wall aperture when inserted therein and an aperture extending therethrough dimensioned to sealingly surround the sensor connector body barbed section when the barbed section is inserted therein;
• wherein, in use, the flexible plug is inserted into the housing wall aperture, said antenna means is inserted into the proximal end of the tube sufficiently far so as to generally reach a distal tip of the ceramic cap, the ceramic cap and the rigid tube being inserted through the plug aperture, the sensor connector body barbed section being inserted into the plug aperture sufficiently far that the sensor connector body proximal section is sealingly positioned against a proximal face of the plug, the sensor connector body proximal section remaining on a proximal side of the housing wall.

An apparatus for sensing the proximity of a target using electromagnetic near-field effects, the apparatus comprising:

• an oscillator for providing a radio frequency signal;
• an antenna responsive to said oscillator for directing the radio frequency signal at the target, an amplitude of the radio frequency signal changing with a change in the target position with respect to the antenna when the target is in a near field of the antenna;
• a signal detector responsive to said antenna for detecting a radio frequency signal reflected from the target;
• a low-pass filter responsive to said signal detector for electronically filtering the reflected radio frequency signal and for passing a filtered signal at a predetermined frequency having an amplitude that varies with an amplitude of the reflected radio frequency signal;
• a comparator responsive to said low-pass filter for comparing the filtered signal with a reference signal generated by said signal detector responsive to said antenna and said target;
• and
• determining means responsive to said comparator for determining a proximity signal indicative of a change in target position with respect to the antenna.

A method for sensing a position of a target, the method comprising the steps of:

• radiating radio frequency energy with an antenna having an impedance;
• moving the target sufficiently adjacent the antenna so that the antenna impedance varies with a change in the target position as a result of a near-field effect;
• detecting the change in the antenna impedance in response to the changes in the target position;
• translating the detected change in the antenna means impedance into a position signal;
• comparing the position signal respectively with a reference signal corresponding to the position signal generated when the target is positioned within a predetermined range of the antenna;
• and
• determining the target position from the comparison of the position signal with the reference signal.