Micropower RF material proximity sensor

An apparatus for detecting a level of material in a container, comprising:

• an oscillator which oscillates at a nominal frequency and produces an oscillator signal;
• an antenna coupled to the oscillator which is resonant at the nominal frequency of the oscillator and which has a characteristic impedance which depends on proximity of the material in the container to the antenna;
• and
• a detector coupled to the oscillator which detects changes in the oscillator signal as a result of changes in the characteristic impedance of the antenna caused by proximity to the antenna of the material in the container.

An apparatus for detecting a proximity of a material, comprising:

• an antenna which is resonant at a nominal frequency and has a characteristic impedance which depends on proximity to the antenna of the material;
• a transistor having a first terminal coupled to the antenna to provide theretogether a radio frequency resonant circuit which oscillates at the nominal frequency at which the antenna is resonant with an amplitude dependent on the characteristic impedance of the antenna, a second terminal receiving a bias potential and a third terminal;
• a detector coupled to the transistor which detects changes in the oscillation of the resonant circuit as a result of changes in the characteristic impedance of the antenna caused by changes in materials in proximity to the antenna;
• and
• a control circuit coupled to the third terminal of the transistor which turns the transistor on and off with a duty cycle to produce a sequence of bursts of oscillations at the nominal frequency.

A method for detecting proximity of a material to a particular location, comprising:

• placing an antenna having a characteristic impedance which depends on materials in proximity to the antenna in the particular location;
• establishing a resonating signal at a nominal frequency in the antenna;
• and
• detecting changes in the resonating signal at the nominal frequency as a result of changes in the characteristic impedance of the antenna caused by changes in materials in proximity to the antenna.