Capacitive proximity sensors.

摘要

Capacitive proximity sensors (10) are disclosed that can be fabricated in different shapes, sizes and materials used in a wide variety of applications. Each such sensor includes a sensing electrode (11) and a guard electrode (12). The sensor electrode and guard electrode can be parallel conductors separated by an insulating layer (13), such as a double-sided circuit board shaped to suit the application. One such sensor is transparent for use in conjunction with an optical bar-code scanner. Another sensor is annular in shape for use in conjunction with a telephone transmitter. The sensing electrode and the guard electrode are driven in unison by an RF signal (21). The proximity of an object to the sensor is observed by detecting (in 24) changes in the RF current flowing through the sensing electrode caused by the proximity of an object to the sensing electrode. <IMAGE>