Robert E. Hetrick

Resonant vibrating structures with driving sensing means for noncontacting position and pick up sensing

A vibration type sensor can make a noncontacting measurement of position or pick up the passage of an object past a point. The sensor has a coil of wire placed on a vibrating structure. As an object with an attached magnet approaches the coil, an emf is induced in the coil indicating position. Alternatively, the magnet remains fixed with respect to the vibrating coil while a material of high magnetic permeability approaches the coil and magnet combination thereby perturbing the magnetic field and changing the induced emf. This method can be used to obtain a linear variation of sensor output with position or to enable the use of the device as a pickup sensor.

Resonant vibrating structure with electrically driven wire coil and vibration sensor

A vibration type sensor can make a noncontacting measurement of position or sense the passage of an object past a point. The sensor has a coil of wire placed on a vibrating structure. A power supply causes current to be passed through the coil at the resonant frequency of the vibrating structure. As an object with an attached magnet approaches the coil, a force is exerted on the current carrying coil thereby exciting the structure at its resonant vibrational frequency. A piezoelectric bimorph is attached to the structure so that it flexes with the structure producing an emf output proportional to the vibrational amplitude. As the object moves, the field strength at the coil, the amplitude of the vibration and the induced emf change. The latter quantity is used to sense the motion of the object. Alternatively, the magnet remains fixed with respect to the coil while a material of high magnetic permeability approaches the coil and magnet combination thereby perturbing the magnetic field and changing the induced emf. This method can be used to obtain a linear variation of sensor output with position or to enable the use of the device as a timing sensor.

Oxygen Sensing by Electrochemical Pumping

An oxygen pumping structure using ZrO2 electrochemical cells is described for measuring the percentage of O2 in a high‐temperature gaseous environment. The device output is linearly proportional to the O2 percentage, has a weak dependence on temperature, and does not require a reference atmosphere.

Oscillations in the emf of solid‐state electrochemical oxygen sensors

Oscillations have been found in the emf of ZrO2 electrochemical cells used for high‐temperature oxygen sensing in nonequilibrium CO,O2 environments. This behavior is shown to arise from an oscillation in the platinum‐catalyzed oxidation of CO. The use of a ZrO2 cell provides a new technique for studying oscillating reactions of this type.

Effect of Surface Electric Fields on Radiative Recombination in CdS

Photoluminescence (edge emission) in a variety of CdS single crystals has been studied under the influence of the surface field generated near the Au–CdS interface of an Au–CdS Schottky‐barrier diode. Experimentally, above bandgap radiation is incident upon a semitransparent Au film evaporated on an air‐cleaved CdS surface. Free electrons and holes are generated within the region of the high barrier field which extends on the order of 0.5 μ into the crystal bulk. Variations of diode bias as small as 2.5 V were found to be sufficient to alter the luminescence efficiency by nearly two orders of magnitude. A model is presented (emphasizing the rapid removal of photoinjected free carriers from the barrier) which qualitatively accounts for the major features of the observed effects.

Oscillatory-mode oxygen sensor

A high-temperature (∼ 800°C) O<inf>2</inf>sensor is described based on O<inf>2</inf>pumping and sensing with ZrO<inf>2</inf>, O<inf>2</inf>-concentration cells. The cells are incorporated in a ceramic structure that defines an enclosed volume which communicates with a gaseous ambient of interest by means of a small leak. An oscillatory pumping procedure is described whose period is proportional to at least the first power of the desired ambient O<inf>2</inf>-partial pressure over a substantial pressure range. The device has potential application for monitoring engine air-to-fuel ratio based on the O<inf>2</inf>content of exhaust gas.

Oscillations in the electrical resistivity of TiO2 induced by solid/gas interactions

Abstract We report the discovery of an oscillatory variation in the resistivity of rutile exposed to a nonequilibrium mixture of CO and O2 at elevated temperatures. Our data suggest that the electrical oscillations result from a corresponding modulation in the degree of reduction of the TiO2 material; the latter is caused by a chemical oscillation in the catalytic oxidation of CO and in the concentration of adsorbed CO and oxygen species on the solid surface.

Wavelength dependence of the surface photovoltage in vacuum cleaved CdS

Abstract A report is made of the first spectral response measurements of the surface photovoltage in conducting CdS single crystals cleaved in ultra-high vacuum. The spectra were obtained with a recently developed electron beam technique which is sensitive to periodic changes in the surface potential as small as 1 μV. After cleavage, systematic studies of the response were made as a function of surface treatment including air exposure and electron bombardment. Of particular interest is the structure in the photovoltage response at photon energies less than the bandgap and the variation of this structure with surface treatment. The origin of these spectra is discussed in terms of optical excitation from intrinsic and extrinsic surface states and from impurities occurring within the surface barrier region.

Electron Beam Technique for Measuring Microvolt Changes in Contact Potential

A low voltage electron beam technique is reported which when coupled with ac detection is capable of measuring periodic changes in contact potential as small as 1.0μV. This sensitivity, which exceeds by a factor greater than 100 the reported sensitivities obtained by other methods, should enhance the usefulness of the contact potential measurement for detailed surface studies, especially in the case of semiconductors. The potential of the technique is demonstrated in the context of high resolution photovoltage measurements in n‐type CdS which may allow for a sensitive form of surface state or surface barrier spectroscopy.

A vibrating cantilever magnetic-field sensor

Abstract A magnetic-field sensor is described in which a planar coil, photolithographically fabricated on a silicon cantilever blade, is caused to vibrate at a resonance frequency of the blade using a piezoelectric driver. In the presence of a magnetic field, an e.m.f. is induced in the coil proportional to the field strength. Operation is analogous to that of an a.c. generator. A reciprocal device, analogous to an a.c. motor, is also possible in which an a.c. current in the coil results in a vibration of the blade with amplitude proportional to the magnetic field and a corresponding output from the piezoelectric element. Applications, required electronics and advantages of this method are discussed.