Modulated scatterer microwave telemetry inside automobile engines and transmissions

Measuring temperature and pressure inside automobile engines and transmissions poses a difficult set of problems. Since the measurement transducers are mounted on moving parts inside sealed housings, it is generally impossible to simply connect the transducers to the laboratory instrumentation with wires. We have had some success with infrared telemetry links for piston-mounted transducers with the infrared receiver mounted inside the engine crankcase, but optical scattering in the oil-covered engine is very low, so a short-direct path between the infrared LED and receiver is needed. Inside an automatic transmission there are no direct paths, so an alternative telemetry link that can propagate around corners must be used. Other constraints on the telemetry system are operation in a severe mechanical environment with high temperature, pressure and vibration; small size and weight so that the instrument package does not interfere with the operation of the engine or transmission; and long battery life, since the engine or transmission must be disassembled to change batteries. Our current telemetry systems use either low-powered FM transmitters or modulated scatterers operating between 2 and 3 GHz. Since the entire environment is electromagnetically enclosed, there is no potential for interference to or from other services operating at these frequencies.