Differential Capacitor Research Articles

Micromachined capacitive accelerometer

Abstract A capacitive accelerometer has been fabricated from Si 110 wafers using the silicon micromachining technique. The sensor basically consists of an elastically suspended plate between two fixed capacitor plates, forming a differential capacitor. The central plate is equipped with several slits, which reduces the air damping and enhances the dynamic behaviour. A sensor with a sufficient number of slits detects accelerations up to 1000 Hz with a signal deviation of less than 10%, while a sensor with no slits reaches the same deviation already around 50 Hz. The experimental data have been fitted with the theoretical curve, and the damping and resonance frequency are determined for different numbers of slits.

Ceramic sensor technology for the measurement of mechanical quantities at high temperature

Abstract Differential capacitor sensors with variable airgap geometry enable mechanical quantities to be measured at temperatures up to 900 °C. In this paper it will be shown that ceramics, preferably alumina, are multi-purpose materials for capacitive sensors. The descriptions of technological approaches concern laser machining, sputter coating and reaction soldering of alumina components, electrical connections and alumina in cables; new sensors for strain and displacement are given as examples.

A noncontacting human tremor sensor and measurement system

A two-dimensional noncontacting displacement transducer has been developed for the primary purpose of measuring human hand tremor. No electrical or mechanical connections are required. The device consists of a square frame with each side representing a capacitor plate. A test subject's hand inserted into the center of the frame forms the moving plate of two separate differential capacitor systems (horizontal and vertical axes) used in bridge configurations with 100-kHz excitation and appropriate signal conditioning. Sensitivity is 2 V/cm over a typical dynamic range. Clinical evaluations indicate that the device is sensitive enough to quantify differences in normal tremor and provides discriminating results in patients with neurologic disorders.

A Differential Capacitor Circuit for Very High and Low Dielectric Q-Factor Measurement at High Frequencies

This paper presents an electronic circuit system that is capable of measuringdielectric Q-factor Qx (= 1/tan δ) ranging from 0.01-10 at measuring frequencies 100 kHz-30 MHz, and from 10-105 at 1-300 MHz. For measurement of very high loss materials, a tripartite differential capacitor is used as a variable resistor to substitute for low Rx, and for measurement of very low loss materials, an ordinary differential capacitor connected in series with two fixed deposited fim resistors is used to substitute for high unknown resistance Rx. An important characteristic of the circuit is its capability of measuring capacitance and resistance of high loss materials accurately.

Thermal expansion of copper, silver, and gold below 30 K

A variable transformer technique has been used to determine the linear thermal expansion coefficients of the noble metals from 4 to 30 K. The precision of the data initially was ±0.04 A, and this was later increased to ±0.015 A, resulting in a sensitivity of approximately 2×10−11 for relative length changes of a 10-cm-long sample. The results agree at all temperatures (to better than 5%) with those of White and Collins who used a differential capacitor technique. The differences are 2% or less above 20 K for Cu, above 8 K for Ag, and at all temperatures for Au. The differences between the two sets of data for the three metals are not systematic (αWC greater for Cu, less for Ag) and may be due to differences in sample purity since much larger low-temperature anomalies were found within each set for certain samples of Cu and Ag. The resulting electronic Gruneisen parameters γe and theT=0 lattice Gruneisen parameters γ0 are as follows: $$\begin{gathered} copper \gamma _{\text{e}} = 0.91 \pm 0.05 \gamma _{\text{0}} = 1.67 \pm 0.02 \hfill \\ silver \gamma _{\text{e}} = 1.18 \pm 0.15 \gamma _{\text{0}} = 2.29 \pm 0.03 \hfill \\ gold \gamma _{\text{e}} = 1.6 \pm 0.5 \gamma _{\text{0}} = 2.96 \pm 0.04 \hfill \\ \end{gathered} $$ The values of γ0 are in reasonable (5% at worst) agreement with elastic constant values.

Ferromagnetic and spin wave resonance at high pressure

A 4-electrode multi-port precision differential capacitor for testing the gravitational reference sensor (GRS) electronics of the ST7 spacecraft has been built and tested. The differential capacitor has a tunable and intentional mismatch of 2 aF out of ∼2 pF total nominal capacitance, and holds stable for time-periods on the order of hours.The capacitor has two electrodes representing a pair of nominally identical drive plates, one electrode representing the metallic proof-mass, and one electrode acting as a non-contact pickup. The required adjustability has been achieved by introducing two pairs of grounded micrometers located between the drive and the ‘proof-mass’ electrodes for making coarse and fine adjustments. The capacitance is changed by advancing or retracting the micrometer spindles in the electric flux path to alter the capacitive coupling of each arm. The change in capacitance by coarse adjustment is 30 fF for each arm of the capacitor. The fine adjustment has a range of 1 fF with a setting resolution of 2 aF per arm. This mechanism of changing the capacitance achieves the fine control, repeatability and stability required to test the ST7 electronics.

Creep of Highly Anisotropic, Low-density Polyethylene

A SYSTEMATIC study of the creep properties of polymers possessing known anisotropy does not seem to have been attempted, probably because of the experimental difficulties involved. The few results reported are usually measurements of the creep extension in the direction of the applied tensile stress, made by following the separation of the specimen grips. End effects make this an unsatisfactory arrangement, especially when small samples are used. We have therefore developed an apparatus for measurement of the creep strain of specimens having a gauge length of as little as 0.5 in. The extensometer uses a linear displacement differential capacitor transducer, with a sensitivity better than 10−5 in., in a counter-balanced arrangement to reduce specimen loading to a minimum. The transducer sensitivity is equivalent to a strain of 2 × 10−5 for a gauge length of 0.5 in. The creep load is applied to the specimens using a lever loading system based on a well-proved design1. The results reported are for creep in the time range 5–100 s after application of the load. Other tests have shown that the transducer and control unit are stable, within the limit of sensitivity, for a period of at least 5 months.

差動容量式変位変換器

差動容量式変位変換器

Kinetic Friction of Textile Yarns: Improved Measuring Instrument

A versatile instrument for measuring the kinetic friction of textile yarns over any test object is described. The instrument incorporates new features for more precise friction evaluation, such as a feedback control for continuous testing and an accurate system for applying constant input tensions of any desired value. The instrument collects friction data continuously, using the established technique of measuring the input and output yarn tensions over the test object, by use of differential capacitor transducers accurate to ±0.1 g. Using Howell's model of kinetic friction, the relationship describing the dependence of the friction force F on the normal load W for a worsted yarn over metal has been shown to be given by F=0.637 W0.782. Kinetic measuring of yarn/metal, yarn/yarn friction can be performed on most types and counts of yarn.

Novel displacement detector and its application in a recording thermobalance

A transducer has been developed to detect changes in position of a balance beam. Its operation is based upon a differential capacitor. Variations in capacitance are made to produce directly a d.c. voltage corresponding in sign to the sense of deflexion of the balance beam. The construction of the transducer is described, and its application in automatic apparatus for thermogravimetric analysis is illustrated by results obtained on the dehydration of copper sulphate and the decomposition of quinoline phosphomolybdate. The sensitivity of the instrument can be varied in nine steps to give full-scale deflexions from 10 to 5000 mg. An accuracy of about 1.5 mg or 0.75% of full scale was obtained for the 200 mg range.

Pulse registration as a means of evaluating peripheral vascular patency and vasomotor activity ∗

T IlE REGIS'RAlltN of the volume pulses from various pare of a limb has been found to he an accurate and simple method of demonstrating local vascular patches and clianges in blood vessel tones :. The method has the following advantages over others previously employed; particularly the measurement of skin temperature_ (1) The sensing pneumatic cuff of the device embraces the total cross section of the limb at each level examined, so that the resultant pulse trace reflects changes in the deep as well as the superficial arteries . (2) The cuff, are easily applied to aire level of the limb, from a digit upward, avoiding examination of the digits alone. where tones is subject to great spontaneous variations, and allowing also an appraisal of the circulation over the entire limb . t31 With this method . the reactivity of the part may he tested by direct heating, or cooling . Such a direct application of thermal changes is more efficient than indirect methods in inducing change, in tone, and more nearl' approximates the environmental stres_es from which the syrriptomtt of some patients arise The urethod Iias been used in differentiating functional from organic disease, an well as in evaluating the degree of spasm or the flexibility of the arterial systeur when permanent structural changr_s are present . The study has reinforced the concept that vascular tonus is the sum of all constrictive and vasodilatory influences. We have further been impressed by the universality (if the vasoconstrictive response to cold as an expression of both functional and organic arterial disease . METHOD Pulse Regislralion and Quantilation : This aspect of the method has been detailed in a former publication,' but it may be summarized here. The apparatus consists of a series of pneumatic cuffs, two of which may be connected simultaneously to the transducing unit (the Infraton Pulse Oseillograph d . A pressure of 30 mm . Hg is used in the pneumatic system. The transducing element is a differential capacitor; the output of which is fed into a direct writing Sanborn recorder . A paper speed of 25 mm . per second is used throughout . While simple inspection of the curves allows a good estimate of change in pulse configuration and an approximation of ampliurde and slope, a quantitative evaluation of these two factors is available . ']'his is made possible by calibration of the height of pulse defection for each cult application through a device that displaces a known volume of air in the pneumatic system . The degree of displacement of the recording pen is noted . With this calibration, the pulse trace can be expressed in two parameters . The first is mean pulse deflection (mean change in vohune in cubic millimeters during one pulse cycl(-). noted as 1) in the illustrations . In arriving at this value Lhe area under a pulse trace is measured by a planirneter . In this way the difference between a sustained and an acuminate pulse is taken into account . 'I 'he second parameter is the systolic slope (rate of systolic increase in volume of the pulse in cubic millimeters per se(ond), noted as 55 in the figures . The Iractions shtnvn in some of the figures dlrnote the attenuation of the recording used for the particular pulse trace icproduced . Induction of Vasodilatation and VasocoruUict,orc Patients were examined after resting from ten to thirty minutes in a morn in which the temperature was kept 1 )brained I'roni Medical F .leetronies Development Co., Long Island, New York .