Charles Robert Harrington

An air flow sensor based on interface thermal wave propagation

An air flow sensor that uses a flow‐induced change of temperature oscillation phase at an air‐solid interface is described and analyzed. The sensor is fabricated on silicon coated with polyimide. The source and detector of temperature oscillations are integrated on the same substrate but spatially separated. A narrow strip of metal film driven by ac is the source. A PbTe thin‐film thermocouple is the detector. Device operation in still air is analyzed and compared with experiment. The temperature oscillation amplitude and phase on an interface with an oscillating strip heat source is derived for interface thermal resistance and for a layered substrate. Interference between thermal oscillations propagating from source to detector through the solid and through the air is predicted and observed with a 53‐μm‐thick polymide layer. In contrast, with a 16‐μm‐thick polyimide layer, interference that varies with frequency is not seen, also in agreement with theory. Experimental demonstration of flow response is al...

An on-vehicle fuel driveability index sensor

The driveability of a vehicle is important to both drivers and vehicle manufacturers. Good driveability can provide drivers with a better driving experience and can result in lower vehicle emissions. The driveability is closely related to the volatility of the fuel used, which is characterized by the driveability index (DI). A sensor of fuel DI has been fabricated and tested on a vehicle. One version is a metal sensor which has an interdigitated cube structure. The sensor element is located in the vapor dome of the fuel tank and is bathed in fuel while the fuel pump is on. After the pump is turned off, a reproducible volume of fuel is retained between the capacitor plates in the sensor element. The sensor element heats the fuel sample, causing it to evaporate while the temperature and remaining liquid volume are monitored. Fuels with different volatility yield differing evaporation rates. By monitoring the fuel level rate of decline as a function of its temperature, a characteristic curve related to the fuel volatility is measured. Six nonoxygenated fuels were used to test the sensor concept. It was found that there was a good correlation between the sensor result and the fuel DI.