End Contact Research Articles

Diffraction of surface electromagnetic waves by the open end of a strip optical microwaveguide

A theoretical study is made of the diffraction of surface electromagnetic waves by the open end of a strip optical microwaveguide. An approximation equivalent to the Kirchhoff approach is used to obtain analytic dependences for the angular distribution of diffracted waves in the far-field zone in the Fraunhofer diffraction case and a study is made of the distribution of electric fields of the diffracted waves in the near-field zone in the Fresnel diffraction case. It is shown that the angular distribution of the diffracted waves depends on the mode index of a strip microwaveguide and it differs considerably for thin-film and graded-index strip microwaveguides in a plane perpendicular to the waveguide. It is shown that in solving of the problem of the end contact between strip microwaveguides and fiber waveguides it is possible to ignore the distortion of the distribution of the electric field of the fundamental mode at the open end of a strip microwaveguide.

Hydrodynamic Lubrication of the Rib-Roller End Contact of a Tapered Roller Bearing

The behavior of the lubricated rib-roller end contact of a tapered roller bearing is studied both theoretically and experimentally. A theoretical hydrodynamic approach was first developed for smooth and rigid surfaces for the particular geometry and kinematic conditions found in this contact. Simultaneous measurements of traction forces and film thicknesses by optical interferometry are performed in a special device made of a flat glass disk and a steel toric specimen which simulates this contact, lubricated with a mineral oil at ambient temperature. Good argeement is noted for both film thickness and traction forces between the hydrodynamic theoretical and experimental results. The experiments which are extended to the elasto-hydrodynamic regime show that central and minimum film thicknesses are lower than the calculated values using classical fully flooded and starved elastohydrodynamic theories. This departure is attributed to side flow effects. Traction curves obtained in this regime, under moderate pressures, show that the oil behavior remains newtonian.

Direct measurements of interfacial contact resistance, end contact resistance, and interfacial contact layer uniformity

A four-terminal microelectronic test structure and test method are described for electrically determining the degree of uniformity of the interfacial layer in metal-semiconductor contacts and for directly measuring the interfacial contact resistance. A two-dimensional resistor network model is used to obtain the relationship between the specific contact resistance and the measured interfacial contact resistance for contacts with a uniform interfacial layer. A new six-terminal test structure is used for the direct measurement of end contact resistance and the subsequent determination of front contact resistance. A methodology is described for reducing the effects of both contact-window mask misalignment and parasitic resistance associated with these measurements. Measurement results are given for 98.5-percent Al/1.5- percent Si and 100-percent Al contacts on n-type silicon.

The Lubrication of the Roller-Rib Contacts of a Radial Cylindrical Roller Bearing Carrying Thrust Load

It is generally assumed by designers that cylindrical roller bearings can only be used to carry radial loads. However, there are a number of applications where, either through accident or design, both radial and thrust loads are successfully carried. For example, the bearings in commercial vehicle gearboxes frequently carry thrust loads. The mechanism of lubrication under these conditions is not fully understood. However, it is now accepted that running-in of the roller end and rib contact is very important. During this period, excessive thrust loading can result in rib scuffing. Experimental work has been carried out to investigate scuffing during running-in and to determine criteria to assist in bearing design. Various possible mechanism of roller-rib lubrication are investigated and it is proposed that a hydrodynamic wedge is created by the combined effect of roller skew and rib wear.

Theory of the flying light spot experiment to determine ambipolar mobility

Theoretical expressions are presented which provide a more general analysis of the flying light spot experiment to determine ambipolar mobility than the standard, one-dimensional, infinite sample theory. We have approximated the semiconductor sample by a semi-infinite bar bounded by a non-ohmic contact. The finite length of the sample traversed by the light spot (the transit length) and the effect of the end contact on the observed carrier distribution have both been considered. The results are illustrated using parameters and device dimensions typical of a prototype Cadmium Mercury Telluride Infra-red detector operating in the 3–5 μm band at 190 K. We show that when contact effects can be neglected that symmetric waveforms are always obtained at the matched condition, regardless of the sample length traversed by the light spot. For short transit lengths the pulses are narrower than the dynamic equilibrium value. A contact with a low interface recombination velocity has an appreciable effect on the observed waveform and results in broadened pulses. When the light spot velocity (VL) and ambipolar velocity (VA) are identical a symmetric waveform is no longer observed. Symmetry occurs when VL<VA. Values of VA deduced using this method, in this situation, would therefore be too low.

A Moving Hot-Spot Configuration for a Seal-Like Geometry, with Frictional Heating, Expansion and Wear

Solutions are obtained for a moving contact patch on the lip of a seal formed by the end contact of two tubes, on a thermal insulator and one a thermal conductor. It is postulated that a patch of uniform pressure [pbar] of width 21 is moving at a speed c on the lip of the conducting body, and that this gives rise to frictional heating, thermal expansion, wear and elastic deformation. Although the relative displacements produced by all of these effects must sum to zero in the contact patch, for this approximate solution the averages of these quantities will be allowed to sum to zero. Results are compared with prior accurate calculations for zero wear case, showing that the approximation is quantitatively reasonable. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference held in Miami Beach, Florida, October 21–23, 1975

Performance Characteristics at the Rib Roller End Contact in Tapered Roller Bearings

Analytical and experimental work is presented to determine the nature of the coefficient of friction at the large rib roller end of a tapered roller bearing. The analytical work considers the dynamic equilibrium of a roller, and it is shown that for normal bearing speeds the inertial forces have negligible effect on the performance at the rib contact. Mathematical expressions for the frictional torque on a detached rib have been derived for the case of axially applied bearing loads. Experimental work has been carried out to obtain the rib torque values for the detached rib of a tapered roller bearing. Experimental information has been presented to show the variation in the value of the coefficient of friction with the sliding speed and the Hertzian stress at the rib contact. It is observed that the condition of lubrication is an important factor influencing the performance at the rib and that for the hydrodynamic condition of lubrication, the value of the rib torque is very low. Presented at the 28th ASLE...

Electrical characteristics of a reduced-area, rhodium-plated, silicon end contact

The apparent linear (ohmic) characteristics, exhibited by a high-purity, p-type, single-crystal specimen of silicon of uniform resistivity (ca. 2200 Ω-cm at room temperature), having rhodium-plated end contacts, were changed to rectifying characteristics by formation of a reduced-area contact at one end (the reduced area was attained by grinding down the original contact). The rectification characteristics improved with decreasing temperature, provided that the temperature is not too low. Voltage-profile and resistivity measurements were made at various temperatures ranging from 116°C to −196°C. These curves show that the maximum of the injection fraction, (Δ n)p 0, and of the resistivity both occur at approximately 90°C. The values of these maxima are respectively 5·5 per cent (total current 10 mA, current density at small-area contact 125 mA/cm 2) and 2980 Ω-cm. The low-temperature voltage contours indicate that the plated contacts, with both small and large area, become good barriers below −68°C. The asymmetry between the large- and small-area contact is much greater at −196°C than at −68°C. At room temperature, the transient behavior manifests the characteristic logarithmic injection curve. Solder and rhodium-plated contacts and transient-current studies indicate that a small amount of injection occurs also at the large-area contact.