Showing papers on "Capacitive sensing published in 1986"

Application of capacitance techniques in sensor design

Abstract: By reconsidering the basic principles of capacitance, and also clarifying some of the misconceptions about the principles of guarding, which were correctly described by Kelvin more than a century ago, it is shown how guarded multi terminal capacitor geometries can be designed, analytically precalculated and correctly measured using simplified transformer bridge systems with phase-sensitive detection. An overview is given of the archetypal multi terminal capacitor configurations as well as ways to modify them for practical sensor designs. Detrimental side-effects are discussed and rules for practical designs are given. The possibilities for combining bridge circuits with simultaneous and sequential measurements of complex sensors are described. Expectations for future developments, partly based on silicon microfabrication techniques, are discussed and a comparison of the major aspects of capacitive sensors with resistive strain gauges and inductive sensors is given.

Capacitive pressure-sensing method and apparatus

Abstract: A novel capacitive pressure-sensitive sensing technique and apparatus wherein an elastomeric conductive electrode carrying a two-dimensional array of projections is pressure-deformed against a fixed coextensive cooperative electrode to generate signals, such as tones and sounds in the application to musical instruments, or visual representations, corresponding to the dynamic pressures applied over the two-dimensional surface. A novel drum-like and other musical instruments embodying such novel capacitive sensing techniques and the like are described.

Electromagnetic ignition--an ignition system producing a large size and intense capacitive and inductive spark with an intense electromagnetic field feeding the spark

Abstract: An Electromagnetic Ignition system suitable for adaptation to standard automobile engines including diesel engines, which has been improved by means of a high efficiency RF capacitive spark plug with a projecting antenna tip used for forming very large spark gaps to the plug shell and piston face as well as for coupling high electric fields to the local initial flame plasma, preferably used in combination with shielded high voltage cable including series inductive choke elements and a Capacitive Discharge ignition system incorporating an input capacitor, a SCR switch, an ignition coil with an optimized high current and high output voltage, and preferably a synchronous DC-DC power converter providing "boost power" during ignition so that substantial capacitive, inductive, and electromagnetic energy is supplied to the air-fuel mixture. Preferably the coil has a turns ratio of 50 with the input capacitor having a capacitance between 5 and 10 microfarads and a 400 volts rating. Large output capacitance is provided naturally by existing coil and shielded cable capacitance, supplemented with large plug capacitance of 50 to 250 picofarads, which are charged up to between 15 and 30 Kilovolts prior to breakdown of the wide variable spark gap producing: high frequency capacitive sparks, large inductive spark of several amps; and high pulsed local EM electric field strength of thousands of volts/cm providing a practical, highly efficient ignition system capable of igniting very lean air-fuel mixtures for reducing exhaust emissions and increased engine efficiency.

Capacitive occupancy detector apparatus

Abstract: A capacitive occupancy detector apparatus includes a personnel containment device having first and second electrodes which will define an electric field therebetween which will be intercepted by a person present in the containment device. A detecting device is provided for detecting the capacitance formed between the first and second electrodes and a processor is provided for storing the capacitance at predetermined periods. The difference between the last capacitance detected and a capacitance previously stored is detected to determine the presence of a person when the difference indicates an increase of the capacitance exceeding a first predetermined threshold. A second threshold is set based upon the capacitance which determines the presence of a person so that the subsequent determination of the absence of a person is based upon detecting a decrease of the capacitance with respect to the second threshold.

Method of making silicon capacitive pressure sensor with glass layer between silicon wafers

Abstract: A method of bonding two silicon wafers each having a capacitive plate. Two highly-doped electrically semiconductive feedthrough paths are formed through one wafer, each path contacting one of the capacitive plates. A glass layer is formed on one of the silicon wafers where bonding is desired between the two wafers. The glass layer is anodically bonded to the other of the silicon layers.

Process for manufacturing capacitive devices and capacitive devices manufactured by the process

Abstract: This invention relates to a laminated capacitive element for use in electrical devices such as filtered connectors, said element comprising a laminated body of a metal substrate having one or more layered structures heat bonded to all or a portion of the surfaces thereof, said structures comprising a non-conductive layer composed of a sintered finely divided non-conductive material heat bonded to said metal substrate and a metal conductive layer composed of sintered finely divided metal heat bonded to said sintered non-conductive material

Decoupling capacitor for pin grid array package

Abstract: High frequency noise is decoupled from power supplied to a Pin Grid Array (PGA) package by insertion of a decoupling capacitor between the PGA package and printed circuit board. The decoupling capacitor comprises a multi layer capacitive element sandwiched between a pair of conductors and having a plurality of leads extending from each conductor. In accordance with the present invention, the decoupling capacitor is individually dimensioned and configured to fit under a PGA package and correspond to the power and ground pin configuration of that PGA package.

Infrared detector arrays

Abstract: The capacitive bolometer comprises a detection capacitor having a first-order phase transistion ferroelectric material between two electrodes. The detection capacitor operates during a detection step and a subsequent readout step. During the detection step, a preselected electric field is applied to the detection capacitor to maximize its sensitivity to temperature. A second electric field is applied to the capacitor during the readout step in order to increase responsivity of the detection cell. The detection cells according to the invention can be assembled into disclosed detection arrays.

Vortex flow meter

Abstract: A vortex flow meter for measuring the flow velocity of a fluid in a conduit includes a bluff body disposed in the flow passage of the conduit. The bluff body generates Karman vortices whose recurrence frequency is characteristic of the flow velocity to be measured. In the bluff body a cavity is formed which via passages communicates with the flow passage of the conduit and in the cavity a capacitive vortex sensor is disposed which converts the vortex pressure fluctuations originating from the Karman vortices to capacitance changes. The capacitive vortex sensor includes a first oscillating body in the form of a sensor sleeve which is deflectable by the vortex pressure fluctuations and an electrode holder which is disposed in the sensor sleeve and is formed as second oscillating body but is uncoupled from the vortex pressure fluctuations. The electrode holder carries at least one capacitor electrode which with an opposite electrode portion of the sensor sleeve forms a measured capacitance which varies on the deflections of the sensor sleeve relatively to the electrode holder caused by vortex pressure fluctuations. However, vibrations generated by external interfering influences cause similar deflections of the two oscillating bodies and thus do not result in any capacitance changes. The capacitive vortex sensor is thus insensitive to external vibrations and other interfering influences.

A switched-capacitor interface for intelligent capacitive transducers

Abstract: A novel switched-capacitor circuit has been developed for interfacing capacitive transducers with digital systems. It consists of a differential integrator and a cyclic analog-to-digital converter (ADC). The capacitive transducer is first charged in proportion to its capacitance. This charge is next compared with that stored on a reference capacitor and their difference is converted to a voltage by a differential integrator. The sensitivity of this capacitance-to-voltage conversion is controlled by the rate of the charge accumulation. A binary output is obtained from the resultant voltage by analog-to-digital conversion. The whole operation is insensitive to parasitic capacitances, offset voltages of op amps, and the capacitor values involved in the circuit. Thus the proposed circuit permits an accurate differential capacitance measurement. An error analysis has shown that the resolution as high as 14 bits can be expected by realizing the circuit in a monolithic IC form. Besides the accuracy, it features the small device count integrable onto a small chip area. The circuit is thus suited particularly for the on-chip interface. Its application to a humidity sensor is also presented.

Apparatus for medical treatment by hyperthermia

Abstract: The apparatus comprises a power amplifier (12) ; a remote electrode apparatus (32) receiving a high power electrical supply from the power amplifier ; a power transmission ap­paratus (30) arranged to electrically couple the power amplifier to the remote electrode apparatus for supply of electrical power thereto ; and capacitive matching apparatus (14) for providing real time capacitive matching between the power amplifier and the capacitive load across the elec­trode apparatus. Application in treatment of malignant tumors.

Analysis, Design, and Performance of a Capacitive Pressure Sensor IC

Abstract: Medkcal research has an urgent nieed for a small, accurate, stable, low-power, biocomnpatible, and inexpensive pressure sensor with a zero to full-scale range of 0-300 mmHg. A comparison of fundamenital transducer limits shows that the capacitive device offers better accuracy than the piezoresistive type. Limitations of the on-board circuitry, needed to buffer the transducer capacitor against parasitic capacitanice, hatve previously prevented the realilzation of this accuracy. An integrated circuit (IC) for use with acapacitive pressure transducer was designed, built, and tested. Capacitance is measured by a new ratiomnetric scheme employing an on-chip reference capacitor. The typical random pressure measuarement error due to resolution and nonlinearitiy is ±0.4 mmHlg (with a full-scale of 300 mmHg). The long-term systematic error due to falling battery voltage is ±0.6 mmHg. These figures Were calculated from measurements of temperature, supply dependence, and nonlinearity on completed integrated circuits. The ature compensation of the transducer.

Capacitive-type seed sensor for a planter monitor

Abstract: A sensor apparatus for detecting a flow of material along a given path of travel by detecting a change in the dielectric properties of a portion of the path of travel as the material passes therethrough comprises one or more conductive, plate-like electrodes disposed adjacent the path of travel and generally defining a capacitor having the adjacent portion of the path of travel as a dielectric portion, such that the passage of material to be detected changes the dielectric constant, thereby changing the capacitance. A sensor circuit comprises a tuned circuit having the sensor electrode or electrodes being coupled in circuit therewith. The sensing circuit further comprises an oscillator circuit driving the tuned circuit at a predetermined frequency selected near the resonant frequency of the tuned circuit in the absence of material to be detected. The sensing circuit further includes an AM demodulator circuit coupled to the tuned circuit for developing a sensor circuit signal at a substantially constant level in the absence of material to be detected and a measurable change in signal level when the material to be detected is present.

Fabrication techniques for integrated sensor microstructures

Abstract: Research ef for ts on micromechanical sensors a t the Wisconsin Center for Applied Microelectronics have addressed two fundamental issues: a significant miniaturation of mech nical devices and IC-compatible construction te hniques. The justif ication for this research direction is found in a strong interest in sensor systems or multiple transducers and data extraction circuitry on a single chip.

Capacitive bolometer with improved responsivity

Abstract: The capacitive bolometer comprises a detection capacitor having a first-order phase transition ferroelectric material between two electrodes. The detection capacitor operates during a detection step and a subsequent readout step. During the detection step, a preselected electric field is applied to the detection capacitor to maximize its sensitivity to temperature. A second electric field is applied to the capacitor during the readout step in order to increase responsivity of the detection cell. The detection cells according to the invention can be assembled into disclosed detection arrays.

Structure to provide optical and capacitive contrast on magnetic recording disk

Abstract: A magnetic recording disk is formed on a rigid aluminum substrate coated with a polymeric dielectric layer. A thin film metallic position-indicating track is applied to the upper surface of the dielectric layer. The dielectric material is coated with a magnetic recording medium. A thin film of aluminum forms the patterned capacitive and optically reflective track. The dielectric layer is composed of a very similar material to the matrix material in the magnetic recording medium. The disk can be flexible or floppy and it is not necessary to have the extra dielectric layer in such a case, where the substrate is a dielectric.

Analysis, design, and performance of micropower circuits for a capacitive pressure sensor IC

Abstract: An integrated circuit has been designed, built, and testing as part of a capacitive pressure transducer. High-accuracy compact micropower circuits utilizing a standard bipolar IC process without any special components or trimming are used. The key circuits for achieving this performance are a Schmitt trigger oscillator and a bandgap voltage reference. The sensor circuits consume 200 /spl mu/W at 3.5 V, can resolve capacitance changes of 300 p.p.m., measure temperature to /spl plusmn/0.1/spl deg/C over a limited temperature range, and presently occupy 4 mm/SUP 2/ on a 2 mm/spl times/6 mm implantable monolithic silicon pressure sensor. Further scaling of the sensor is discussed showing that a reduction of area by a factor of 4 is achievable.

Propagation of Partial Discharge and Noise Pulses in Turbine Generators

Abstract: Changes with time in the partial discharge (PD) activity originating in a generator stator's insulation system provide information about the electrical integrity of the stator winding. It is desirable to measure PD during normal service to minimize costs. To do this successfully, the influence of electrical interference must be reduced. Tests are reported which characterize the nature of discharge and noise pulses when using capacitive couplers mounted on each of the phase leads and an RF current transformer mounted on the neutral lead for signal detection. Significant differences between PD and electrical noise have been observed.

Switched-capacitor filter having digitally-programmable capacitive element

Abstract: A method and circuitry for time-sharing a digitally-programmable capacitive element, particularly in conjunction with a switched-capacitor filter circuit. The method includes: selecting a first capacitance value for the capacitive element; initializing the charge on the capacitive element; connecting the capacitive element to first preselected nodes of an electronic circuit; disconnecting the capacitive element from the first preselected nodes of after any charge transfer has substantially been completed; changing the capacitance of the capacitive element to a new desired value; initializing the charge on the capacitive element; and then connecting the capacitive element to other preselected nodes of the electronic circuit. A biquad switched-capacitor filter circuit is configured to use such method in its operation.

Study and Application of Nonlinear Turn-Off Snubber for Power Electronic Switches

Abstract: A nonlinear capacitive turn-off snubber is discussed. Customarily, only linear capacitors are used in high-frequency power electronic switches. However, ceramic ferro-electric materials, with ratios of initial to final capacitance of nearly 30, are found suitable and are investigated. The energy stored in these nonlinear capacitors, with an initial capacitance of 300 nF, amounts to only about 1.1 mJ at 300 V compared to 13.5 mJ in a 300-nF linear capacitor. As far as the power switch is concerned, the difference in switching behavior and switch turnoff loss between these two cases is negligible. This nonlinear snubber is analyzed approximately by assuming an exponential relation between capacitance and voltage, as well as with a more accurate analysis by means of a computer program. The latter uses an exact capacitance-voltage curve stored on a data file. Computed values correlated well with experimental measurements. As the dielectric losses in the ceramic material are very important, careful calorimetric measurements in situ revealed an energy loss in the capacitor of 135 ?J per turn-off cycle, taken at 500 Hz, 30 A, and 300 V.

Batch method of making miniature capacitive force transducers assembled in wafer form

Abstract: A batch method for fabricating semiconductive capacitive force transducers is disclosed wherein a first wafer of silicon or fused silica is recessed by etching to define a array of force transducer structures, each including a deflectable portion supported from a surrounding frame portion. The first wafer is thermoelectrically bonded between a pair of glass or quartz plates, each plate having an array of electrode structures for capacitively sensing deflection of the individual force transducers. Each electrode structure includes a lead portion passing over the frame portio of the transducers and being spaced from the frame to provide a gas communication passageway through the frame to the capacitive gap between the electrode structure and the deflectable portion of each transducer. The composite assembled wafers are notched along cleave lines generally outlining the individual transducer structures. The notching along the cleave lines is preferably performed by sawing or scribing with the saw kerf or scribe lines extending only partially through the plates so as not to contaminate the individual transducer devices. The individual transducer structures are then cleaved from the composite wafer so as not to introduce contaminants into the individual transducers.

Capacitive gravity sensor

Abstract: An inclinometer includes two coplanar electrodes positioned within a chamber of a metallic housing containing a high relative dielectric constant fluid and a gas With the inclinometer positioned on a level surface equal areas of the two electrodes are immersed in the dielectric fluid creating two equal capacitors formed by the electrodes and the metallic housing When the inclinometer is rotated through an inclination angle, unequal areas of the electrodes are immersed in the fluid causing a capacitance differential that is a measure of the inclination angle

Water level controller for a boiler

Abstract: A water level controller for a boiler has electrical probe means (capacitive or conductive) to be arranged in the boiler to detect electrically the water level therein. An oscillator circuit generates an oscillator signal which first and second circuit means receive. When a capacitance probe is used, the first circuit means has a variable gain amplifier in which the gain is determined by variations in the capacitance of the probe according to the water level. The second circuit means comprises a variable gain amplifier in which the gain is determined by a variable resistance the value of which is representative of the desired operating water level. Third circuit means obtains a difference signal resultant from the output signals of said first and second circuit means, which is representative of the difference between the actual water level in the boiler and the desired operating level of the water in the boiler. Relays open and close the water supply respectively. Fourth circuit means energize said relays to open or to close the water supply, in response to the difference signal.

Manipulation of Central Axis Heating Patterns with a Prototype, Three-Electrode Capacitive Device for Deep-Tumor Hyperthermia

Abstract: Measurements of initial temperature elevations produced by a prototype, three-electrode capacitive heating device operating at 13.56 MHz were made at selected points along vertical and horizontal axes in beef phantoms. Adjustment of the net power supplied by the three generators driving the upper and lower two electrodes of the device permitted significant manipulation of the distribution of initial temperature elevations along the vertical "central" axis of the beef phantoms. For example, in a 17 cm thick phantom, the ratio of initial temperature elevations at central axis depths of 1 and 8 cm below the upper surface was reduced from 3.2 to 0.5, through appropriate redistribution of power to the three electrodes.

Inclination and acceleration sensor utilizing electrostatic capacitive effects

Abstract: A sensor includes a common electrode, and a plurality of detecting electrodes which are electrically independent from each other. The common electrode has a spherical shape. The detecting electrodes are arranged oppositely to the common electrode so as to form a spherical space between the common electrode and them. In the spherical space, a viscous fluid is housed so as to permit it to move freely therein. The viscous fluid moves according to the direction and angle of inclination or the direction and size of acceleration. By means of the movement of the viscous fluid, electrostatic capacity between the common electrode and each detecting electrode varies. The electrostatic capacity of each detecting electrode is detected by a detecting apparatus.