US 7,113,087 B1 · Proximity sensing based on antenna impedance variation

Abstract

Proximity of a user body part can be detected by measuring the effects such proximity has on antenna impedance mismatches. The amount of mismatch affects the amount of RF signal energy reflected back into a transmission line connecting the antenna to a RF signal source. A directional coupler has a main line electrically connected to the transmission line, as well as a coupled line. The directional coupler produces a signal on its coupled line in relation to the magnitude of reflected energy on the transmission line; the amount of reflected energy varies in response to how well the antenna impedance matches the transmission line impedance. A signal detector is electrically connected to the coupled line, and responds to signals produced in the coupled line by the main line. The signal detector output is then used to determine whether a body part is in proximity. Other aspects the invention include an adaptive algorithm to adjust a threshold for proximity determination.

Claims43

Dependent claims

A proximity detection system for sensing the presence of an object or body portion in contact with or close proximity to another object, comprising:

a radio frequency (RF) signal source providing RF signals;
a transmission pathway connected to the RF source;
an antenna connected to the transmission pathway;
a directional coupler having a main line in electrical communication with the transmission pathway and a coupled line, the directional coupler producing a signal on the coupled line which varies in response to changes in antenna and transmission line impedance matching caused by presence of an object or body portion;
a signal detector in electrical communication with the coupled line and responsive to signals produced in the coupled line by the main line, wherein the signal detector produces an output signal that is within an output range, the output range corresponding to a range of antenna-transmission line impedance mismatch;
and
a controller in communication with the signal detector, the controller configured to provide, in relation to the output signal, a state signal indicative of the presence or absence of an object or body portion in contact with or close proximity to another object.

4 more elements

Dependencies are inferred from the claim text.

Proximity sensing based on antenna impedance variation

Life of this patent

Proximity sensing based on antenna impedance variation

Life of this patent

Abstract

Claims43