Double-electrode capacitive sensor, passenger detector, and passenger protection system

A double-electrode capacitive sensor for detecting a detection object made of dielectric material, the sensor comprising:

• an electrode assembly having a first electrode, a second electrode and an insulation substrate;
• and
• a detection circuit electrically coupled with the first and second electrodes, wherein
• the first electrode faces the detection object,
• the first and second electrodes are overlapped, and the second electrode is coupled with a ground,
• the insulation substrate has a first surface and a second surface,
• the first electrode is disposed on the first surface, and the second electrode is disposed on the second surface, so that the second electrode faces the first electrode in parallel to the first electrode through the insulation substrate,
• the detection circuit applies an alternating voltage between the ground and one of the first and second electrodes,
• the detection circuit detects an electric potential of the other one of the first and second electrodes, or controls the electric potential of the other one of the first and second electrodes to follow the alternating voltage of the one of the first and second electrodes,
• the detection circuit detects a capacitance change between the first electrode and the ground when the detection object approaches the first electrode,
• the detection circuit determines whether the detection object approaches the first electrode based on the capacitance change,
• the detection circuit includes an oscillation circuit and a differential amplifier circuit,
• the oscillation circuit applies the alternating voltage between the ground and the one of the first and second electrodes,
• the differential amplifier circuit alternatingly energizes the other one of the first and second electrodes so that the electric potential of the other one of the first and second electrodes follows the electric potential of the one of the first and second electrodes,
• the differential amplifier outputs a signal corresponding to an energizing current to the other one of the first and second electrodes, and
• the differential amplifier includes a voltage follower circuit for energizing the other one of the first and second electrodes with the electric potential of the other one of the first and second electrodes.

A double-electrode capacitive sensor for detecting a detection object made of dielectric material, the sensor comprising:

• an electrode assembly having a first electrode, a second electrode and an insulation substrate;
• and
• a detection circuit electrically coupled with the first and second electrodes, wherein
• the insulation substrate has a first surface and a second surface,
• the first electrode is disposed on the first surface, and the second electrode is disposed on the second surface,
• the first electrode faces the detection object,
• the first and second electrodes are overlapped so that a periphery of the second electrode is substantially opposite to a periphery of the first electrode,
• the second electrode is coupled with a ground,
• the detection circuit applies an alternating voltage between the ground and the second electrode,
• the detection circuit controls an electric potential of the first electrode to follow the alternating voltage,
• the detection circuit detects a capacitance change between the first electrode and the ground when the detection object approaches the first electrode,
• the detection circuit determines whether the detection object approaches the first electrode based on the capacitance change,
• the detection circuit includes an oscillation circuit and a differential amplifier circuit,
• the oscillation circuit applies the alternating voltage between the ground and the second electrode,
• the differential amplifier circuit alternatingly energizes the first electrode so that the electric potential of the first electrode follows the electric potential of the second electrode,
• the differential amplifier outputs a signal corresponding to an energizing current to the first electrode,
• the differential amplifier includes a voltage follower circuit for energizing the first electrode with the electric potential of the first electrode, and
• a deviation between the periphery of the first electrode and the periphery of the second electrode is in a range between −10% and +10%.