Simple and low-cost object detection method based on observation of effective permittivity change

The permittivity of a material is generally larger than that of air. When an object is present near an electric wire, the effective permittivity of the space around the wire becomes larger than that without the object. It follows that in the presence of an object, the velocity of the signal propagating along the wire decreases and the propagation delay time increases. This change can be easily detected by a simple electronic circuit composed of standard semiconductor devices. The principle of this object detection method can be used not only for proximity sensors but also for the detection or measurement of phenomena involving changes in permittivity.