Showing papers on "Capacitive sensing published in 1988"

Patch-clamp techniques for time-resolved capacitance measurements in single cells.

Abstract: Two methods are described for estimation of passive cell parameters such as membrane capacitance, membrane conductance and access resistance in tight-seal whole cell recording. Both methods are restricted in their application to cases where the cell under study can be approximated by a simple three-component network with linear properties over some voltage range. One method, referred to as the time domain technique, requires only standard electrophysiological equipment and a computer. Parameters are derived from an analysis of capacitive transients during square wave stimulation. It is readily adaptable to wide variations in experimental parameters. Particurlarly, it is equally applicable to the “slow whole-cell” configuration (access resistance in the range 100 MΩ to 1 GΩ) and to normal whole-cell measurements (access resistance typically 10 MΩ). The other method applies a sine wave command signal to the cell and employs a lock-in amplifier to analyse the resulting current signal. Two modes of operating the lock-in amplifier are described. One mode provides an output signal directly proportional to small changes in capacitance at maximum resolution (1–10 fF). The other mode, in conjunction with a digital computer, supplies estimates of all passive cell parameters, as does the time domain technique, but with a large amount of data reduction performed by the lock-in amplifier itself. Due to the special hardware, however, this method is not as flexible as the time domain technique.

Optimized capacitive sensor for chemical analysis and measurement

Abstract: An apparatus for detecting the presence and/or measuring the concentration of an analyte (24) in the fluid medium (22) is disclosed. The apparatus relies on biospecific binding between a biochemical binding system (20) and the analyte (24) to change the dielectric properties of a capacitive affinity sensor. The biological affinity sensor is optimized by: adjusting the thickness and dielectric properties of a passivation layer (16) to generally match the impedance of the biological binding system (20, 21); and minimize the double layer capacitance so that bulk capacitance changes associated with the biological binding system (20, 21) are maximized.

A 1024-element high-performance silicon tactile imager

Abstract: A 32*32-element capacitive silicon tactile imager, for use in precision robotics applications where high density and high resolution are important, is discussed. The silicon chip measures 1.6 cm*1.6 cm, and is organized in an X-Y matrix of 1024 capacitor elements on 0.5-mm centers. The process uses two boron diffusions (deep and shallow) followed by a silicon-to-glass electrostatic bonding step and subsequent unmasked wafer dissolution. This results in a thick center plate for the sense capacitor supported by thinner beams. Only four noncritical masking steps for silicon and two for glass are required. A measured force sensitivity of 0.27 pF/gmf/element, temperature sensitivity of less than 3o p.p.m./ degrees C, and maximum operating force of approximately=1 gm/element has been obtained. A discrete data acquisition system used with the device offers over 6 b of force resolution, and the imager can be read at a rate of 15-20 mu s/element, offering an effective frame rate of 5.1 ms. >

Measurement of head/disk spacing with a laser interferometer

Abstract: A multichannel heterodyne laser interferometer was built to measure the head-disk spacing in magnetic disk drives. The main advantage of the present method compared to white light interferometry and capacitive measurements is that neither the disk nor the slider need be transparent or conductive. The interferometer is described, including the optics and electronics. Experimental results on head-disk spacing during the take-off, flying and landing processes are presented and discussed. It is concluded that the present system is capable of making the desired measurement with minimum modification of the slider. It has a resolution of 2.5 nm and a bandwidth of DC to about 40 kHz. >

Analytical method for evaluating surface charge distribution on a dielectric from capacitive probe measurement-application to a cone-type spacer in +or-500 kV DC-GIS

Abstract: The measurement of surface charging on a spacer in a +or-500-kV HVDC gas-insulated switchgear (GIS) is performed by a capacitive probe set inside the gas tank. The various factors that cause measurement errors are examined using a simple model. An analytical method to correct the measurement errors and transform the probe output into the charge distribution on the surface of the spacer is developed. The method is an extension of a numerical method for 3-D surface charge calculation. It is shown that the charge distributions from the probe measurement agree fairly well with dust figures. >

Capacity responsive control circuit

Abstract: A capacitive detecting circuit for detecting transient capacitive changes such as that of a person moving into proximity of a sensing element. A sensing element is coupled to a threshold level controlled amplifier supplied with relatively high frequency signals from an oscillator through a high input impedance. A detector circuit is coupled to the amplifier output to detect D.C. variations in the level control loop caused by transient capacitive changes and provide a control output signal representative of such change.

The electroquasistatics of the capacitive touch panel

Abstract: The capacitive touch panel, a high-resolution position sensor intended for computer displays, must be safe and inexpensive and must sense position accurately in spite of electrical noise, dirt, or direct electrostatic discharge. The implementation discussed uses a quasi-static electric field, applied to a semiconducting coating on the panel surface. A touch draws current from the surface. This current can be used to compute position. If the computation is performed properly, the computed position is independent of touch current and panel coating resistivity. The electroquasistatic basis for position measurement with a capacitive touch panel and a system to implement it are described. >

A digital readout technique for capacitive sensor applications

Abstract: The difference between two capacitors is measured digitally using a charge redistribution technique incorporating a comparator, MOS switches, a successive approximation register, and a digital-to-analog converter. The technique is insensitive to comparator offset and parasitic capacitance, and the effect of MOS switch charge injection is measured and canceled. Extensive measurements have been made from test chips fabricated in 3- mu m CMOS technology. Detection of percent differences of >

Capacitive incremental position measurement and motion control

Abstract: A capacitance based, high resolution, incrementally encoding, position measuring system employs an array of identical replicated electrodes that are driven in unison from an RF source and mounted in proximity to a patterned monolithic reference ground plane of arbitrary size. Motion of such position-sensing arrays is monitored by measuring both the sums and the differences of the electrode displacement currents in such a way as to provide incrementally encoding position signals in both one and two dimensions together with a continuous measurement of the height of the sensor array above the patterned ground plane. In various modifications, the system and methods are applied both to one dimensional linear, as well as to two dimensional planar and two dimensional cylindrical motion measurement and control. Various techniques for eliminating the effects of spurious capacitances are also disclosed.

Variable capacitance push-button switch

Abstract: In a capacitive-type switch having two capacitive levels, a relatively thin blade of a desired dielectric material is interposed between two capacitive plates by downward actuation of a push-button switch so that the plates become separated by the blade. When the push button is released, the blade is removed from between the two capacitive plates and a high capacitance level is once again achieved.

Conductivity effects on capacitance measurements of two-component fluids using the charge transfer method

Abstract: Describes an investigation into the effects of component conductivity on capacitance measurements of two-component fluids using the charge transfer method. Various capacitance sensor systems are represented using three typical equivalent circuit models according to their electrode configurations and the type of mixture between the electrodes. The effects of conductive elements on the measurement of these models are analysed theoretically and tested experimentally using a capacitance transducer based on the charge transfer method. It is shown that the conductance effects can be reduced by using semiconductor switches with low ON resistance and fast commutation time to control the charge and discharge of the sensor. Measurements of glass bead concentration in water-based conductive slurries from an industrial wet peening process and water contentin oil/water mixtures are described as practical applications.

A theoretical study of transducer noise in piezoresistive and capacitive silicon pressure sensors

Abstract: An analysis of the effect of noise introduced by the transduction process on the minimum detectable signal (MDS) of piezoresistive and capacitive pressure sensors has been performed. MDS is first introduced as an appropriate figure of merit for comparing different sensor transduction schemes. Analyses are then performed to determine the minimum MDS theoretically achievable for a broad range of generic transducer circuits. The results of the analyses indicate that noise in the transduction process is not a limiting factor in the performance of properly designed integrated silicon sensors. >

Method and apparatus for driving capacitive display device

Abstract: This invention relates to gradation display by pulse width control method (PWM method) in every pixel in a capacitive display apparatus such as liquid crystal display apparatus. The driving voltage applied to the electrodes is variable slowly, and the number of grada­tions of gradation display by PWM method is increased. Since the capacitive display apparatus is used, as going away from the drive circuit of the electrode for each electrode, the driving pulse is more influenced by the capacity, and its persisting duration is extended. As a result, even in identical gradation data, uneven colors may occur. In this invention, the pulse width applied to the electrodes is gradually decreased as scanning of the electrodes is promoted. Therefore, the brightness of the capacitive display apparatus may be made uniform over the entire screen surface.

Capacitive pressure sensor with third encircling plate

Abstract: A pressure sensor (210) utilizing capacitance variations to sense pressure variations of the silicon-glass-silicon type (FIG. 3) including a conductive silicon substrate (212), a conductive silicon diaphragm (211) and a glass dielectric layer (213) therebetween forming a spacing wall (216) between them, in which dielectric drift and parasitic (non-pressure sensitive) capacitance is minimized by including a very thin, third, symmetrical, silicon, capacitive plate (220) in the glass wall (216). The third conductive plate encircles the central region (Cc) of the sensor and is located outside of it. Improved assembly techniques, including all symmetrical planar layers, for higher manufacturing yield and better long term reliability are also disclosed.

LC filter device having magnetic resin encapsulating material

Abstract: An LC filter device includes a dielectric substrate having opposing sets of coil electrode patterns and capacitor electrode patterns. Each set of coil electrode patterns forms an inductive element, and each set of capacitor electrode patterns forms a capacitive element. The inductive and capacitive elements are interconnected to form an LC circuit configuration. The dielectric substrate is encapsulated by a resin coating. The resin coating includes a magnetic material, such as a high frequency ferrite powder, to increase the inductance of the LC filter and to reduce the stray capacitance of the LC filter.

Membrane touch control panel assembly for an appliance with a glass control panel

Abstract: An appliance with a glass control panel is provided with a membrane touch control panel assembly which simulates the appearance of a glass capacitive touch panel, and which can tolerate relatively harsh temperature environments such as on the backsplash of a range.

Capacitively commutated brushless DC servomotors

Abstract: There are disclosed both one and two-dimensional, high resolution, brushless DC servomotors that are linear, rotary, planar and cylindrical in nature. All of these employ a capacitive method for deriving the required position and motor commutation information. In suitable circumstances, particularly two-dimensional planar motors on air bearings, the method allows the use of the motor ferromagnetic cores themselves as the capacitive position sensing elements. This leads to a particularly simple and compact type of sevomotor design. In addition, since such motors can move at high speed, there are also disclosed two transformer coupled methods for handling the current drive to the motor windings. Both methods are simple, energy efficient, applicable to motors of any number of phases, and in addition, handle motor direction reversals automatically.

The Design And Calibration Of A Semiconductor Strain Gauge Array

Abstract: A semiconductor s t r a i n gauge a r r a y , c o n s i s t i n g o f d i g i t a l l y addres sab le r e s i s t o r ed t o measure t h e mechanical t e d du r ing i n t e g r a t e d c i r c u i t This paper d i s c u s s e s s t r a i n t h e convers ion o f measured p r i n c i p a l stresses on t h e An automated test s e t u p or t h e convenient de te rmit a m e c o e f f i c i e n t s and t h e o f r e s i s t a n c e . For t h i s nding j i g was des igned and cons t ruc t ed so t h a t it could be c o n t r o l l e d from wi th in an environmental chamber. The s t r a i n gauge w i l l be used t o map t h e p r i n c i p a l stress f i e l d s c h a r a c t e r i s t i c o f i n t e g r a t e d c i r c u i t assembly and f a t i g u e l i f e t e s t procedures. I n t r o d u c t i o n During t h e assembly o f i n t e g r a t e d c i r c u i t s , mechanical stresses a r e imparted on to t h e d i e . These stresses r e s u l t from t h e mismatch i n thermal expansion between t h e va r ious assembly m a t e r i a l s , i.e., t h e s i l i c a f i l l e d epoxy molding compound, t h e copper leadframe and t h e s i l i c o n i n t e g r a t e d c i r c u i t . Undes i rab le consequences o f t h e s e mechanical stresses inc lude pass iva t ion , encaps u l a n t and d i e c racking . The aim o f t h e p r e s e n t work is t o provide a t o o l which can map t h e p l ana r stress t e n s o r over t h e s u r f a c e o f t h e i n t e g r a t e d c i r c u i t . Due t o t h e q u a n t i t y o f measurements and c a l c u l a t i o n s r equ i r ed fo r stress mapping, an automated d a t a a c q u i s i t i o n and a n a l y s i s system was implemented. This system was designed around an IRM AT pe r sona l computer, a Data Trans l a t ion DT2801-5716 d a t a a c q u i s i t i o n board, a high s t a b i l i t y Ke i th l ey 220 programmable c u r r e n t sou rce and t h e ASYST programming language. Add i t iona l ly , a RANSCO environmental chamber was used i n t h e p i e z o r e s i s t a n c e c a l i b r a t i o n experiments. The TP86 S t r a i n Gauge The b a s i c stress senso r is an a r s e n i c i m p l an ted resistor rosette c o n s i s t i n g o f 4 r e s i s t o r s o r i e n t e d a t Oo, 45O, 90° and 1 3 5 O , f i g . 1. The compact size o f t h e rosette s t r u c t u r e (220x220p2) is necessa ry i n o r d e r t o make l o c a l i z e d p r i n c i p a l stress c a l c u l a t i o n s . In o r d e r t o i n v e s t i g a t e t h e i n f l u e n c e o f d i e s i z e upon stress, d i e dimensions of 2 . 5 ~ 2 . 5mm2 4 . 5 ~ 4 . 5mm2 6 . 5 ~ 6 . 5mm2, 2. 5x4.5mm2 and 4.5x6.5mm2) a r e a v a i l a b l e . The t o t a l number o f r e s i s t o r s chosen f o r a p a r t i c u l a r d i e s i z e is implemented i n "powers o f 2" due t o mul t ip l ex ing requi rements the 2 . 5 ~ 2 . 5mm2 and 2 . 5 ~ 4 . 5m2 d i c e i n c o r p o r a t e 128 t o t a l resistors; t h e 4.5x4.5mm2 and 4 . 5 ~ 6 . 5mm2 d i c e i n c o r p o r a t e 256 r e s i s t o r s ; and t h e 6.5x6.5m2 d i e i n c o r p o r a t e 512 r e s i s t o r s . 2.5mm2, s t r a i n gauge d i e is shown i n f i g . 2. The arrangement of t h e 128 r e s i s t o r , 2 . 5 ~ The sed t o addres s i n d i v i d u a l resisned i n t h e l a r g e r e c t a n g u l a r f e a t u r e s on t h e t o p and r i g h t edges o f t h e d i e . S ince t h e h ighes t stress l e v e l s a r e expected a t t h e d i e co rne r s , t h e s t r a i n gauge arrangement i s map t h i s r eg ion wi th t h e h ighes t e t te d e n s i t y on t h e Process ing o f t h e senso r invo lves t h e unusual combination of MOS t echnology, f o r t h e s e l e c t i o n l o g i c , and (111) o r i e n t a t i o n s i l i c o n , f o r piezoFig. 1 The b a s i c s t r a i n gauge rosette ( 2 2 0 ~ 220p2). Also shown a r e t h e primed and unprimed c o o r d i n a t e systems used f o r c a l c u l a t i o n s i n t h i s paper. F ig . 2 The 2.5x2.5mr2, 128 r e s i s t o r , TP86 s t r a i n gauge. CH2560-1/88/0000-0185$01.00@1988 IEEE 18

Thin-film microwave filter

Abstract: A thin-film, lumped element filter utilizing spiral inductors and capacitive pi networks is disclosed. The filter is fabricated from a planar dielectric substrate having a ground plane on one side thereof and two thin-film metal layers and an insulation layer disposed therebetween on the opposite side of the dielectric substrate. The metal and insulation layers are configured to form one or more capacitive pi networks and spiral inductors, which are electrically interconnected to form the filter.

Position measurement apparatus for capacitive touch panel system

Abstract: A capacitive touch panel system (10) having a faceplate (14) with an electrically conductive layer (20) of a consistent resistivity employs a position measurement apparatus (12) to generate an address signal indicative of a position (46) on the faceplate in contact with a stylus (48). The position measurement apparatus includes a position measurement signal source (62) that generates a square-wave measurement signal of substantially constant frequency and a preselected magnitude. The position measurement signal is applied to a first pair of opposed electrodes (36) and (40) and a second pair of opposed electrodes (38) and (42) positioned along respective side margins (26, 30, 28, and 32) of the faceplate. The resistivity of the conductive layer establishes effective resistances of R x and R y between the respective first and second pairs of electrodes. Position measurement subcircuits (60a-60d) measure currents drawn through the electrodes whenever the stylus contacts the conductive layer, thereby to form an address signal indicative of the location at which the stylus contacts the faceplate.

Capacitive sensors for measuring the pressure between the foot and shoe

Abstract: A test was conducted of a Hercules Orthoflex capacitive sensor used to measure pressure distribution under the foot for gait analysis and sensory substitution. Maximal nonlinearity for the sensor is 16%, and maximal hysteresis is 10% over the pressure range 0 to 1.3 MPa. Seven transducers in each shoe determine the distribution of pressure. >

Capacitive absolute position measurement device

Abstract: The invention relates to an absolutely measuring position measurement device for rotary or linear movements, which consists of a capacitive measurement transducer and an electronic control and evaluation circuit. In order to obtain highly accurate position and speed measurement at a favourable price, the output signal from a linearly operating capacitive measurement transducer is converted by a timed electronic evaluation into a digital position signal and an analog tachometer signal in each case with high accuracy and quality.

Hand held weighing scale

Abstract: A scale arranged and constructed of relatively small size to be hand held and portable for use in weighing relatively light articles such as fish and the like. The scale operates on a capacitance measuring concept wherein an initial capacitance between two conductive, spaced and insulated plates is measured with a change in distance between the two plates caused by a load is measured and, through a logic circuit, converted to a digital read-out. The capacitance sensor unit for the measuring of the capacitance caused by the load includes a stationary plate and a moveable plate insulated from each other with proper leads connecting the plates to the logic circuit. The entire capacitance measuring device is provided in a sandwiched arrangement to provide a small and compact unit. The logic circuitry provides for digital readout and provides automatic zeroing.

Coupling of discharge currents between conductors of electrical machines owing to laminated steel core

Abstract: Over the past few years, a number of techniques have evolved for detecting discharges in the insulation systems of electrical machines by measuring the discharge currents flowing at the machine terminals The propagation of these currents through the winding, from the discharge site to the terminals, is influenced by the capacitive and inductive coupling between the conductors of the winding The paper is concerned solely with the inductive component of that coupling, through the laminated steel stator core of the machine It describes how this coupling makes a significant contribution to the equivalent circuit for the propagation of discharge currents containing frequencies from 20 kHz to 20 MHz

Car phone antenna assembly

Abstract: A car phone antenna assembly which comprises a whip, a base mounted on a window of a car and a coupling unit having the structure for a capacitive tuning circuit. The coupling unit further comprises a coupling plate which acts as a coupling capacitor together with the base, first and second inductor members, and a variable capacitor member which can fine tune the resonant frequency of the antenna assembly.

Capacitive sensor and electronic circuit for non-contact distance measurement

Abstract: A novel thin, three-terminal capacitive transducer which is positioned in a clearance gap to be measured is presented. This transducer comprises an insulated assembly having three parallel conductive planes with the first and second plane each containing a single electrode and the third plane containing a pair of spaced electrodes. Preferably, each electrode is composed of a thin layer of copper mounted on an insulated substrate such as an epoxy-glass composite. An air space is provided between each of the pair of electrodes in the third plane and the single electrode in the second plane. Another important feature of the present invention is a novel electronic circuit for use in conjunction with the novel three terminal capacitive transducer. This circuit provides a means of "synthetic resonance" whereby a small capacitance (such as generated by the three-terminal capacitive sensor of this invention) functions as if it were at or near series resonance with a synthesized large inductance. This is achieved by using a synthesized network (which is a variation of a known twin-tee circuit) in the feedback path of a high gain amplifier, thereby inverting the normal rejection notch into a resonance-like peak at a frequency determined mathematically.

Frequency dependent identification of materials

Abstract: Packaged materials are tested in a capacitive sensor which has plates whose spacing can be accurately adjusted, and whose plates are segmented so that selected segments can be employed. An a.c. voltage is applied across the capacitive plates at accurately known amplitude, phase, and frequency for a number of frequencies. A ratio bridge is tied to each number of frequencies. A ratio bridge is tied to each of the segments and provides outputs that reflect the a.c. voltage and current, both capacitive and ohmic. A zero-crossing detection method or time domain method can be employed to provide precise amplitude and phase, or a quadrature or phase-sensitive detection method can provide amplitude and phase, or a quadrature or phase-sensitive detection method can provide amplitude and phase of the a.c. current through each segment. Values of capacitance, conductance, frequency dependence of capacitance, and frequency dependent of conductance are compared to stored values of a number of known objects of the target class.

Digital load shift compensation

Abstract: A digital weighing scale is compensated for the effects of off-center loading by determining the position of the load and calculating a corrected weight value according to such position. Position sensing transducers (16,17) are mounted on the load cell to provide information regarding the position of the load on the weighing scale. An expression for corrected weight as a function of load position and magnitude is determined for the particular scale and stored. The expression is used to calculate corrected weight according to the magnitude and position of each weight placed on the scale. The load cell may include a counterforce of substantially any type including single bending beam, dual bending beam or capacitive structure, and the load magnitude and position sensors may be of substantially any type including strain gages and capacitive sensors.

Capacitive keyswitch membrane with self contained sense-to-ground capacitance

Abstract: A membrane capacitive keyboard of the type including a first flexible dielectric sheet and a second dielectric sheet having electrically conductive patterns thereon which form an array of capacitors and connecting matrices of drive and sense conductors. The patterns on the sheets include a first array of capacitor plates on an inner surface of the first sheet and a second array of capacitor plates on the outer surface of the second sheet. A third array of electrically floating capacitor plates is formed by a third pattern on the inner surface of the second sheet. The sense conductors are capacitively coupled to ground through coupling capacitor plates connected to the sense conductors and a common capacitor plate overlaying the coupling capacitor plates.