Showing papers on "Temperature coefficient published in 1985"

Microwave Measurement of Dielectric Properties of Low-Loss Materials by the Dielectric Rod Resonator Method

Abstract: Improvements both in accuracy and speed are described for the technique of measuring the microwave dielectric properties of low-loss materials by using a dielectric rod resonator short-circuited at both ends by two parallel conducting plates. A technique for measuring the effective surface resistance R/sub s/ of the conducting plates is proposed to allow the accurate measurement of the loss tangent tan delta. By means of the first-order approximation, the expressions are analytically derived for estimating the errors of the measured values of relative permittivity epsilon/sub r/, tan delta, and R/sub r/, for measuring the temperature coefficient of epsilon/sub r/, and for determining the required size of the conducting plates. Computer-aided measurements are realized by using these expressions. It is shown that the temperature dependence of R/sub s/, should be considered in the tan delta measurement. The copper plates used in this experiment have the relative conductivity of 91.0+-2.7 percent at 20°C, estimated from the measured R/sub s/ value. For a 99.9-percent alumina ceramic rod sample, the results measured at 7.69 GHz and 25°C show that epsilon/sub r/,= 9.687+-0.003 and tan delta = (1.6+-0.2)x 10/sup -5/. The temperature coefficients measured between 25 and 100°C are 112x10/sup -6//°C for epsilon/sub r/, and 23x10/sup -4//°C for tan delta.

Processing of Neodymium-Iron-Boron melt-spun ribbons to fully dense magnets

Abstract: Over-quenched melt-spun ribbons of nominal composition Nd 0.14 (Fe 0.91 B 0.09 ) 0.86 can be compacted to fully dense permanent magnets by hot-pressing at 700-750°C to 100 kPa (-15 kpsi). The resulting material is only slightly magnetically aligned with room temperature magnetics: B_{r}/H_{ci}\simeq 8 kG/19 kOe. Die-upsetting to a thickness reduction of 50% produces B_{r}/H_{ci}\simeq 11 kG/12 kOe and is accompanied by a lateral plastic flow of the ribbons and a corresponding ribbon thickness reduction. The alignment arises from anisotropic grain growth and grain rotation which produces platelet shaped grains oriented perpendicular to the press direction. The temperature dependence of B r for both hot-pressed (MQ2) and die-upset (MQ3) ribbons corresponds to a temperature coefficient of -0.25%/°C. The H ci temperature coefficients are -0.35%/°C and -0.45%/°C, respectively. High temperature aging in air produces negligible loss.

Magnetic properties of the Nd2(Fe1−xCox)14B system

Abstract: We have investigated the magnetic properties of the Nd2(Fe1−xCox)14B system to improve the thermal properties of the Nd‐Fe‐B magnets. Nd2(Fe1−xCox)14B exists in the tetragonal form in the entire range of 0≤x≤1. In this system, the replacement of Fe by Co significantly increases the Curie temperature. The room‐temperature magnetization of Nd2(Fe1−xCox)14B has its maximum value at x=0.1. However, because of the decrease in the anisotropy energy and the saturation magnetization by further substitution of Co for Fe, a reasonable substitution range of Co is suggested to be x<0.2 in the sintered Nd‐Fe‐B magnet. In this range of Co, we have succeeded in improving the reversible temperature coefficient of the remanence for the Nd‐Fe‐B magnets.

Method of making a piezoelectric shear wave resonator

Abstract: An acoustic shear wave resonator comprising a piezoelectric film having its C-axis substantially inclined from the film normal such that the shear wave coupling coefficient significantly exceeds the longitudinal wave coupling coefficient, whereby the film is capable of shear wave resonance, and means for exciting said film to resonate. The film is prepared by deposition in a dc planar magnetron sputtering system to which a supplemental electric field is applied. The resonator structure may also include a semiconductor material having a positive temperature coefficient of resonance such that the resonator has a temperature coefficient of resonance approaching 0 ppm/°C.

MOS Integrated silicon pressure sensor

Abstract: An MOS integrated silicon-diaphragm pressure sensor has been developed. It contains two piezoresistors in a half-bridge circuit, and a new simple signal-conditioning circuit with a single NMOS operational amplifier. The negative temperature coefficient of the pressure sensitivity at the half-bridge is compensated for by a positive coefficient of the variable-gain amplifier with a temperature-sensitive integrated feedback resistor. The sensor was fabricated using the standard IC process, except for the thin diaphragm formation using the N 2 H 4 . H 2 O anisotropic etchant. Tile silicon wafer was electrostatically adhered to the glass plate to minimize induced stress. The -1750 ppm/°C temperature coefficient of sensitivity at the half-bridge was compensated for to less than +190 ppm/°C at the amplifier output in the 0- 70°C range. A less than 20-mV thermal-output offset shift was also Obtained after 26-dB amplification in the same temperature range.

Highly heat-resistant Nd-Fe-Co-B system permanent magnets

Abstract: The magnetic properties and crystal structures of sintered Nd-Fe-Co-B magnets have been investigated over a wide range of chemical composition. Magnetic hardening is performed for samples by a post sintering heat treatment at 500\sim1000\deg C. The curie temperature of these samples are significantly improved with the increase of cobalt content. The sample with the composition of Nd 16 Fe 66 Co 11 B 7 shows remarkable magnetic properties, such as the maximum energy product of 42 MGOe and the reversible temperature coefficient of residual magnetization of 0.02 %/°C, Electron probe microanalysis and x-ray data suggests that the highly heat resistant magnet is produced when cobalt distributes only in the tetragonal matrix phase.

Electronic transport properties of metallic multi-layer films

Abstract: General expressions for the electrical resistivity and the temperature coefficient of resistivity of metallic multi-layer films are derived. It is assumed that the films consist of thin alternating layers of two different metals. The calculations are made within the framework of the Boltzmann kinetic theory. The background mechanisms of scattering of conduction electrons in the layers are described by two different relaxation times. The scattering at the interfaces between the layers is taken into consideration using boundary conditions. The modifications of bulk relaxation times evoked by the presence of the grain boundaries are obtained by means of the Mayadas-Shatzkes method. The analysis shows that the geometrical size effect can be expected when thicknesses of the particular layers become of the same order of magnitude as the mean free paths of conduction electrons in the bulk metals.

Method and apparatus for controlling heater of a gas sensor

Abstract: Energization of a heater built in a gas sensor, such as an oxygen sensor, used in an air/fuel ratio control system of an internal combustion engine, is controlled to maintain the temperature of the same within a desired range. The temperature of the heater is calculated using a measured resistance value of the heater, and engine parameters used for estimating a specific engine operating condition. To this end operating state of the engine is first detected to determine whether it is possible to estimate the actual temperature of the heater, and when possible, a reference resistance value of the heater at a reference temperature such as 0° K. or 0° C. is caluclated using estimated heater temperature and a measured resistance value. Once the initial resistance value is obtained, this is used to calculate actual heater temperature using measured resistance value and a predetermined temperature coefficient.

Self regulating heating device employing positive temperature coefficient of resistance compositions

Abstract: Disclosed is a positive temperature coefficient of resistance (PTC) crosslinked polymeric composition comprising a first polymeric material exhibiting high green strength prior to crosslinking and elastomeric behavior subsequent to cross-linking, and a second polymeric material comprising a thermoplastic, both said materials having dispersed therein conductive particles, e.g., carbon black, and further, said composition exhibiting a rise in resistance with increased temperature at temperatures above the melting point of either material.

Some transport properties of transition metal films

Abstract: Recent experimental measurements reported on the electrical resistivity, temperature coefficient of resistance and thermoelectric power of nineteen transition metal films have been reviewed. All the theoretical models proposed so far to analyse these experimental results have been briefly summarized. Some suggestions for further experimental study on transition metal films are outlined.

Resistivity of liquid, supercooled liquid and amorphous alloys under elevated pressure

Abstract: We present a calculation of the electrical resistivity of liquid, supercooled liquid and amorphous Mg 7 Zn 3 and Ca 7 Mg 3 alloys as a function of temperature and pressure on the basis of the generalized Faber-Ziman theory. The calculation has been performed from first principles, without any adjustable parameter. The theory successfully explains the variation of the electrical resistivity with temperature [positive temperature coefficient (TCR) for CaMg, a generally negative TCR in MgZn with shallow resistivity minima in the liquid and small resistivity maxima and minima in the amorphous phase] and with pressure [positive pressure coefficient (PCR) for MgZn, essentially zero PCR for CaMg] in terms of the partial structure factors, ion-electron potentials and vibrational spectra. We demonstrate the important influence of the thermal expansion upon the calculated resistivity isobars.

Thermistor having a positive temperature coefficient of resistance

Abstract: A thermistor which includes a ceramic sintered body formed of a plurality of inner electrodes alternating with a corresponding plurality of ceramic layers, outer electrodes being connected to specific ones of the inner electrodes. Each ceramic layer a positive temperature coefficient of resistance. The inner electrode layers are obtained by injecting molten base metal having a low melting point such as lead, tin or lead-tin alloy into gap layers previously defined in the sintered body between the laminated ceramic layers from the outside under pressure and hardening the same.

Method and apparatus for determining ice boundary temperature for the de-icing system of an aircraft

Abstract: A method of determining the temperature, preferably the ice boundary temperature, of an electrical resistive heating element of a de-icing system for airplanes, helicopters, and the like, preferably for a fully automatic control of the heating times of the heating elements. Additional temperature sensors are avoided and circuitry costs are substantially reduced by using the resistive heating elements themselves for determining the temperature. The resistance variation due to temperature variations of an element is ascertained by a current-voltage measurement, and a temperature variation of the element is determined from the resistance variation while using the temperature coefficient. The current-voltage measurement may be based on Ohm's law with a following analog or digital processing of the signal.

Temperature self-regulating resistive heating element

Abstract: Disclosed is an improved temperature self-regulating resistive heating element and a method for its fabrication. The element utilizes a positive temperature coefficient (PTC) composition comprising a blend of two partially incompatible crystalline polymers of differing melting points and an electrically conductive filler. The PTC composition does not deform during annealing, this permitting the fabrication of temperature self-regulating resistive heating element with electrodes spaced-apart by not more than 0.100 inch. Heating elements provided by the invention have a smaller cross section, are more flexible, and are less expensive to fabricate than similar prior art elements.

The temperature dependence of threshold voltages in submicrometer CMOS

Abstract: The temperature coefficient of the threshold voltage in long buried-p-channel MOSFET is dV_{th}/dT = 2.02 mV/°C, which is much larger than that in the long enhancement-mode n-channel MOSFET (-1.27 mV/°C). The difference is caused by the charge freeze-out phenomenon in the buried-channel MOSFET. The absolute value of the temperature coefficient of the threshold voltage |dV_{th}/dT| , decreases with decreasing channel length in the n-channel MOSFET, however, it increases with decreasing channel length in the submicrometer p-channel MOSFET. The difference results from the majority-carrier spill-over phenomenon in the buried-p-channel MOSFET.

Models for the thermal expansion coefficient and temperature coefficient of the refractive index in gradient-index glass.

Abstract: In gradient-index glass the variation of glass composition can also cause a variation in the thermal properties across the gradient region. The difference in thermal expansion and dn/dT across the gradient-index region has been modeled. Several examples illustrate how the models can be utilized to select gradient-index glass compositions that will have constant thermal properties within the gradient region. Experimental measurement of the variations of αL and dn/dT in gradient-index glass is presented in a separate paper.

Fibre interferometric sensors

Abstract: A fibre optic gyroscope includes a temperature compensation device 18 adapted to adjust the wavelength of the radiation emitted by the laser 12 to minimise the scale factor temperature coefficient so that the data output by the gyroscope is not influenced by variations in temperature of the fibre. The adjustment is preferably such that the magnitude of the effective wavelength temperature coefficient imparted by the temperature compensation device is equivalent to the magnitude of the difference between the thermo optic coefficient of the fibre and the coil radius temperature coefficient.

Dielectric ceramic composition

Abstract: Disclosed is a dielectric ceramic material having a chemical composition represented by the formula Sr(Ni 1/3 Nb 2/3 )O 3 or (1-x)Sr(Ni 1/3 Nb 2/3 )O 3 .xBaTiO 3 in which x is a positive number of up to 0.3 and also having a perovskite structure. This dielectric material has a small dielectric loss and a large dielectric constant, and the temperature coefficient of the resonance frequency can be controlled to a small value within a certain range. The dielectric ceramic material is valuably used for microwave dielectric ceramics.

Self-temperature controlling type heating device

Abstract: A self-temperature controlling type heating device comprises a positive temperature coefficient ceramic resistor having a thin layer portion, a first electrode provided on one face of the thin layer portion, a second electrode provided on the other face of the thin layer portion opposite to the first electrode, and at least one third electrode provided on the surface of the PTC ceramic resistor in spaced relation to the first electrode. An electric current is allowed to flow between the first and second electrodes to form a heating element, and an electric resistance value between the first and third electrodes is detected to thereby make a temperature control. Thus, a high output is obtained at a low voltage and the control temperature is freely varied.

New cut of quartz for SAW devices with extremely small temperature coefficient

Abstract: A new cut of quartz for SAW devices was discovered by a leaky surface-wave mode. The temperature stability is extremely high and experimental temperature dependence of the phase delay change is within ±10 parts in 106 for the range from −20 to 80°C. The propagation loss is only 2.6×10−4 dB/λ.

Current source with adjustable temperature coefficient

Abstract: In a circuit arrangement for providing a current having a controllable temperature coefficient of current, a diffused resistor (334) is used to set up a reference current in a current source (40) which has a T.C. dependent upon the diffused resistor. A current mirror (352, 354, 356) receives the reference current and passes a portion of it through an ion implanted resistor (360). The output current has a temperature coefficient which is a function of the original temperature coefficient of current and a nonzero algebraic multiple of the temperature coefficient of the implanted resistor. By appropriate selection of the resistor values and types, the T.C. of the output current can be set to any desired value.

Titanium oxynitride layer for use in sensors

Abstract: The electrical properties of titanium oxynitride layers can be changed in a specific manner by admixtures of nitrogen and oxygen to the deposition atmosphere. This makes it possible, in particular, to change in a specific manner the resistivity, the temperature coefficient thereof (TCR) and the K factor and its temperature coefficient (TCK). It is particularly important that the TCR can be both positive (PTC) and negative (NTC), and that it can be negligibly small. This makes the material particularly suitable as a resistor for temperature measurements and for heating (PTC or NTC) and also, for TCR APPROX 0, because of the additionally high K factor, as a material for strain gauges, for example for measuring pressure and force. Because of the good temperature stability this applies up to high temperatures.