Capacitive sensor for non-contacting gap and dielectric medium measurement

A non-contact capacitive sensor and sensor circuit assembly comprising:

• a sensor plate configured to be displaced from a surface and to measure a capacitance of a gap between the surface and sensor plate;
• an active shield plate over said sensor plate and insulated from said sensor plate, wherein a high frequency input signal is applied to the active shield plate and sensor plate;
• an effective ground shield plate connected through a first resistor to a ground, arranged over said active shield plate to sandwich the active shield plate between the ground shield plate and the sensor plate, and insulated from the active shield plate;
• a second resistor connected between the ground shield plate and the active shield plate to provide a direct current (dc) path through the sensor, and
• the sensor circuit receiving as an input a signal from of the sensor plate and generating an output indicative of the gap.