Carl F. Klein

A model for the relative environmental stability of a series of polyimide capacitance humidity sensors

A capacitance humidity sensor is used as a test device to characterize the performance of 13 polyimide films in relative humidity sensing applications. This sensor has a multilayer, free-standing film construction. It consists of a humidity sensitive polyimide dielectric core and conductive layers consisting of carbon filled polysulfone on each side of the polyimide film to form a capacitor. Thirteen polyimide films, including commercial polyimides and films of novel chemistry, are investigated to determine the long term stability of sensors using the films exposed to 85°C/85% RH for a total of 28 days. Differences in film chemistry are used to interpret trends in the environmental stability of the films.

A differential resonator design using a bossed structure for applications in mechanical sensors

Theory and experimental results are presented of a differential resonator design employing a bossed structure for applications in mechanical sensors. The effects of residual strain, temperature and mechanical load on the resonance frequency are investigated. Mismatches in the resonators are accounted for in the analysis, resulting in a predicted temperature dependence of the offset and of the sensitivity. Experimental data obtained from a macroscopic brass model, mounted on a steel bar and applied as a force sensor, are given. Compared to a design employing a single resonator, the measurements indicate a doubling in force sensitivity and a reduction of both the intrinsic temperature dependence and of the differential thermal expansion effects. The results of this research are directly applicable to micromachined structures in silicon.

Electret and rhodium gas sensors

Abstract The organic gas-sensing characteristics of an electret and a rhodium probe are presented and discussed. The electret consists of a negatively charged PFA polymer layer bonded to a metal back. The electret detects changes in organic gas concentration as a result of dipole-charge and induced dipole-charge interactions between the adsorbed gas and negative charge in the PFA polymer layer. The rhodium-plated probe senses changes in organic gas concentration due to electron donor/acceptor interactions between the adsorbed gas and surface of the probe. The rhodium probe is able to distinguish between strong and weak electron donor gases by the polarity of the response signal.