SUMMARY

Sensors capable of operation in harsh environments are becoming increasingly important. One specific area of interest is detection and measurement of chemical species at high temperature, especially utilizing a wireless approach. Although fabricating such devices employing micromachining techniques is attractive, traditional material sets for MEMS are frequently unsuitable for use in such extreme environments. As a result, devices fabricated from non-traditional material sets are needed. The primary goal of the proposed research is development of wireless chemical sensors for high temperature environments (T>500°C). To achieve this, a sensing platform has been developed that utilizes a passive wireless resonant telemetry scheme that eliminates the need for onboard power and exposed interconnects. An inductor-capacitor (LC) resonator circuit forms the basis for this wireless platform and chemical detection is achieved through the incorporation of chemically sensitive mixed-oxide dielectrics. Ceramics and refractory metals are used in the fabrication of the sensor body and circuitry. Successful device design requires extensive characterization of material sets to examine the strong non-linear behavior of electrical properties such as permittivity, dissipation factor, and conductivity in relation to temperature, chemical concentrations, and signal frequency. Additionally, fabrication techniques, involving laser micromachining and lamination of ceramic “green tape”, are developed to allow formation of 3-D structures (fluidic channels, cavities, and electrical components) in these non-traditional material sets. As a demonstration of the sensing concept, wireless chemical sensors for detection of carbon dioxide (CO2) and nitric oxide (NO) have been developed. As a continuation of this sensor development, the proposed work will address issues of temperature compensation and incorporation of fluidic sampling networks within the body of the sensors.