Showing papers on "Capacitive sensing published in 1996"

Capacitive Sensors: Design and Applications

Abstract: Preface Introduction Electrostatics Capacitive Sensor Basics Circuit Basics APPLICATIONS Capacitive Micrometers Proximity Detectors Motion Encoders Multiple Plate Systems Miscellaneous Sensors DESIGN Circuits and Components Switched Capacitor Techniques Noise and Stability Hazards PRODUCTS Electret Microphone Accelerometer StudSensor Proximity Detector Vernier Caliper Graphic Input Tablet Camera Positioner Digital Level References Appendix 1--Capacitive Sensors in Silicon Technology Appendix 2--Dielectric Properties of Various Materials Index

A surface micromachined electrostatic ultrasonic air transducer

Abstract: Airborne ultrasound has many applications such as, ranging, nondestructive evaluation, gas flow measurement, and acoustic microscopy. This paper investigates the generation and detection of ultrasound in air at a few MHz. Conventional plane piston lead zirconium titanate (PZT) based transducers perform poorly for this application due to the lack of proper matching layer materials. Electrostatic, or capacitive, transducers promise higher efficiency and broader bandwidth performance. The device structure in this work consists of a capacitor where one plate is a circular silicon nitride membrane coated with gold and the other is a rigid silicon substrate. By applying a voltage between the membrane and the silicon substrate, an electrostatic force is exerted on the membrane which sets it in motion, thus generating a sound wave in air. Presented here is an electrical equivalent circuit model for electrostatic transducers which is based on the early work of Mason (1942). The electrostatic transducers were designed and constructed for operation at 1.8 and 4.6 MHz. The transducers were fabricated using standard micromachining techniques. An optical interferometer was used to measure the peak displacement of the 1.8 MHz electrostatic transducer at 230 /spl Aring//V. A transmit-receive system was built using two electrostatic transducers. The system had a signal to noise ratio of 34 dB at a transducer separation of 1 cm. Each transducer had a 3-dB bandwidth of 20%, and a one-way insertion loss of 26 dB. There is excellent agreement between the measured device performance and theoretical predictions.

Implantable stimulator with replenishable, high value capacitive power source and method therefor

Abstract: The implantable stimulator (10), in accordance with the principles of the present invention, utilizes a high value, small sized capacitor (36) having at least a capacitive rating of 0.1 farads which is completely contained within the implantable stimulator (10). This high value, small size capacitor (36) or series of capacitors enables the implantable stimulator to deliver, on a controlled and continual basis, electric stimulation pulses to targeted tissues over at least an 8 hour period. Further the capacitive power source is replenished via an external, RF coupled device (20) on a daily or other long-term periodic basis. During the replenishying cycle, the energy contained in the battery of the external transmitter is transferred to the internal capacitive power source in the implantable stimulator. The method includes providing, on an exclusive basis, power to an implantable stimulator via a high value capacitive source during at least an 8 hour cycle of substantially continued delivery of electric stimulation pulses to targeted tissue. The method includes incorporating and containing a capacitive device in the implantable stimulator wherein the capacitive device has a capacitive rating of at least 0.1 farads.

Implantable capacitive absolute pressure and temperature monitor system

Abstract: A capacitive pressure and temperature sensing system for providing signals representative of the magnitude of body fluid absolute pressure at a selected site and ambient operating conditions, including body temperature, at the site. An implantable lead having a sensor module formed in its distal end is coupled to a monitor that powers a sensor circuit in the sensor module and demodulates and stores absolute pressure and temperature data derived from signals generated by the sensor circuit. The sensor module is formed with a pickoff capacitor that changes capacitance with pressure changes and a reference capacitor that is relatively insensitive to pressure changes. The sensor circuit provides charge current that changes with temperature variation at the implant site, alternately charges and discharges the two capacitors, and provides timing pulses having distinguishable parameters at the end of each charge cycle that are transmitted to the demodulator. The demodulator detects and synchronizes the timing pulses and derives pressure and temperature analog voltage values representative of the intervals between the timing pulses which are digitized and stored in the monitor. The monitor may also be coupled with other sensors for measuring and storing related patient body parameters, e.g. blood gas, EGM, and patient activity.

Surface micromachined accelerometers

Abstract: Surface micromachining has enabled the cofabrication of thin-film micromechanical structures and CMOS or bipolar/MOS integrated circuits. Using linear, single-axis accelerometers as a motivating example, this paper discusses the fundamental mechanical as well as the electronic noise floors for representative capacitive position-sensing interface circuits. Operation in vacuum lowers the Brownian noise of a polysilicon accelerometer to below 1 /spl mu/g//spl radic/(Hz). For improved sensor performance, the position of the microstructure should be controlled using electrostatic force-feedback. Both analog and digital closed-loop accelerometers are described and contrasted, with the latter using high-frequency voltage pulses to apply force quanta to the microstructure and achieve a very linear response.

Characteristics of micromachined switches at microwave frequencies

Abstract: This article reviews the fundamental characteristics of micromechanical membrane switches operating at microwave frequencies. The construction and theory of operation of capacitive membrane switches is reviewed. Measurement and modeling of the electromechanical and microwave properties of these switches are presented. The inherent advantages of these switches relative to semiconductor switches is discussed.

Capacitive touch sensor

Abstract: A capacitive touch sensor (15) includes a plurality of horizontal sensor bars (105) arranged in a single direction The touch sensor (15) receives differential sensor signals from the sensor array (20) to reduce proximity effects and noise associated with conventional capacitive touch sensors The touch sensor (15) also utilizes an isolation circuit or floating interface to reduce the effects of external interference and increase the accuracy of touch sensing and localization The bars (105) are preferably comprised of indium tin oxide oriented in the machine direction of roll for superior linearity The touch sensor (15) may be utilized with display screens (22) having thick dielectrics and also eliminates the need for a rear guard layer

Lcd with bus lines overlapped by pixel electrodes and photo-imageable insulating layer therebetween

Abstract: This invention is related to an active matrix liquid crystal display (AMLCD) having a high pixel aperture ratio. The display has an increased pixel aperture ratio because the pixel electrodes are formed over the insulating layer so as to overlap portions of the array address lines. Both the manufacturability and capacitive cross-talk of the TFT-based device are improved due to the use of a photo-imageable insulating layer between the pixel electrodes and the address lines. Both the manufacturability and capacitive cross-talk of the TFT-based device are improved due to the use of a photo-imageable insulating layer between the pixel electrodes and the address lines. According to certain other embodiments, the insulating layer may be BCB (either photo-imageable or not) and/or have a dielectric constant less than about 3O

Computer input stylus method and apparatus

Abstract: A system comprising a conductive stylus used in conjunction with a capacitance sensitive touch pad, said system providing at least two different signals to an associated computer system. The stylus is a pen-like device having an actuable switch which when actuated substantially increases the capacitive disturbance caused by the conductive stylus on the touch pad. Before actuation, the stylus creates a capacitive disturbance sufficient for circuitry in the touch pad to measure as crossing a first predefined capacitive disturbance threshold when the foam covered conductive stylus tip is brought in contact with the surface of the touch pad. When the switch is actuated, the capacitive disturbance measured by the touch pad increases sufficient to cross a second predefined capacitive disturbance threshold. An associated computer program for drawing on a computer display places a cursor on the display when the first threshold is crossed. The computer program begins drawing on the display beginning at the cursor location when the switch is actuated causing the second threshold to be crossed. Placing a conductive foam cover over the conductive stylus tip results in the measured capacitive disturbance being amplified to thereby increase the magnitude of the capacitive disturbance of the stylus.

Dynamic admittance of mesoscopic conductors : discrete-potential model

Abstract: We present a discussion of the low-frequency admittance of mesoscopic conductors in close analogy with the scattering approach to dc conductance. The mesoscopic conductor is coupled via contacts and gates to a macroscopic circuit which contains ac-current sources or ac-voltage sources. We find the admittance matrix which relates the currents at the contacts of the mesoscopic sample and of nearby gates to the voltages at these contacts. The problem is solved in two steps: we first evaluate the currents at the sample contacts in response to the oscillating voltages at the contacts, keeping the internal electrostatic potential fixed. In a second stage an internal response due to the potential induced by the injected charges is evaluated. The self-consistent calculation is carried out for the simple limit in which each conductor is characterized by a single induced potential. Our discussion treats the conductor and the gates on equal footing. Since our approach includes all conductors on which induced fields can change the charge distribution, the admittance of the total response is current conserving, and the current response depends only on ac-voltage differences. We apply our approach to a mesoscopic capacitor for which each capacitor plate is coupled via a lead to an electron reservoir. We find an electrochemical capacitance with density-of-state contributions in series with the geometrical capacitance. The dissipative part of the admittance is governed by a charge-relaxation resistance which is a consequence of the dynamics of the charge pileup on the capacitor plates. We specialize on a geometry displaying an Aharonov-Bohm effect only at nonzero frequencies. For a double barrier with a well coupled capacitively to a gate the low-frequency admittance terms may have either sign, reflecting either a capacitive or a kinetic-inductive behavior. The validity of a second-quantization-current-operator expression which neglects spatial information is examined for perfect leads in both the frequency and the magnetic-field domain. \textcopyright{} 1996 The American Physical Society.

Silicon three-axial tactile sensor

Abstract: A novel three-axial tactile sensor based on the differential capacitive principle is presented. The sensor is fabricated using IC processing and bulk-micromachining technology. Normal and shear forces are detected by capacitor arrays under force mesas. Experimental devices show sensitivities of 0.13 pF g −1 to normal forces, and 0.32 pF g −1 to shear forces in a force range of 0–1 g. The device has a spatial resolution of 2.2 mm. Its maximum dynamic response frequency is 162 Hz. The force range and sensitivity can be adjusted by changing the membrane thickness. A dynamic measurement range of more than 100 can be obtained using detection circuits with a resolution of 10 fF.

Capacitive responsive electronic switching circuit

Abstract: A capacitive responsive electronic switching circuit comprises an oscillator providing a periodic output signal having a frequency of 50 kHz or greater, an input touch terminal defining an area for an operator provide an input by proximity and touch, and a detector circuit coupled to the oscillator for receiving the periodic output signal from the oscillator, and coupled to the input touch terminal. The detector circuit being responsive to signals from the oscillator and the presence of an operator's body capacitance to ground coupled to the touch terminal when in proximity or touched by an operator to provide a control output signal. Preferably, the oscillator provides a periodic output signal having a frequency of 800 kHz or greater. An array of touch terminals may be provided in close proximity due to the reduction in crosstalk that may result from contaminants by utilizing an oscillator outputting a signal having a frequency of 50 kHz or greater.

Apparatus for determining and recording injection doses in syringes using electrical capacitance measurements

Abstract: An apparatus for electrically determining and recording the dose of an agent delivered with a syringe of the type having a barrel for holding the agent and a plunger for expelling the agent. The syringe includes a capacitive element having first and second conducting surfaces arranged such that the capacitance of the capacitive element varies in dependence upon the dose of agent contained in the barrel. An input terminal and an output terminal located on the outside of the syringe are electrically connected to the first and second conducting surfaces, respectively. The apparatus produces a voltage difference across the terminals, thereby charging the capacitive element. A capacitance meter measures the capacitance and a microprocessor calculates the dose from the measured capacitance. The calculated dose is recorded by a digital memory unit.

High value capacitive, replenishable power source

Abstract: The implantable device includes a power supply including a high value, small sized capacitor having at least a capacitive rating of 0.1 farads which is completely contained within the implantable device. This high value, small size capacitor or series of capacitors enables the implantable device to deliver, on a controlled and continual basis, electric energy over at least an eight hour period. Further, the capacitive power source is replenished via an external, RF coupled device on a daily or other long term periodic basis. During the replenishing cycle, the energy contained in the battery of the external transmitter is transferred to the internal capacitive power source in the implantable device. The method includes providing, on an exclusive basis, power to an implantable device via a high value capacitive source during at least an eight hour cycle of substantially continual delivery of electric energy. The method includes incorporating and containing a capacitive device in the implantable device wherein the capacitive device has a capacitive rating of at least 0.1 farads. The capacitive device captures and stores a pre-determined amount of coulombs of electrical energy. This electrical energy is utilized to power the implantable device during at least an eight hour cycle during substantial continual delivery of electrical energy. The replenishment unit can be programmed to interrogate the implanted device and reprogram the implanted device upon detection of a lower power status signal. Also, automatic as well as manually commanded replenishment routines are established between the replenishment unit and the implanted device. Data transmission, error detection routines are established for the programming of the implanted device.

Pen drawing computer input device

Abstract: A method and system are provided for drawing or writing using an input device in computer systems. The system provides an absolute-coordinate drawing mode, in which the user may draw written strokes to which the computer system display is responsive, and a relative-coordinate repositioning mode, in which the user may figuratively “pick up the pen” and reposition the beginning of a following written stroke. The system enters the drawing mode in response to a user command, and remains in the drawing mode in response to continued written strokes. The system enters the cursor mode after a selected time period occurs with no written strokes, or in response to other user commands. In the drawing mode, a coordinate system for the touchpad is mapped to a coordinate system for a selected window on the display. The mapping is selected so that an initial position of a written stroke in the window corresponds to a final position selected during the cursor mode, so that the user is able to reposition the input device when it has (or is about to) “run off the edge” of an input tablet which is relatively smaller than the display. The system uses either a resistive touchpad input tablet, or a capacitive touchpad input tablet in conjunction with a passive stylus input device having a flexible conductive writing tip. The system alternatively provides a signature mode, in which the user is able to make a simple drawing, such as a handwritten signature.

Micromachined Z-axis vibratory rate gyroscope

Abstract: A microfabricated gyroscope to measure rotation about an axis perpendicular to the surface of the substrate. The driving electrodes, X-axis sensing electrodes, and Y-axis sensing electrodes may all be fabricated from a signal structural layer. The gyroscope includes movable sensing electrode fingers which are positioned between paired stationary sensing electrode fingers. The position of the proof mass along the Y-axis is measured by a capacitive bridge. A voltage differential may be applied between the pairs of stationary electrode fingers to reduce the quadrature error, and a bias voltage may be applied between the movable and stationary electrode fingers to adjust the Y-axis resonant frequency.

Scanning force microscopy in the dynamic mode using microfabricated capacitive sensors

Abstract: We report on the first successful operation of a scanning force microscope using microfabricated capacitive force sensors. The sensors, which are made from single crystal silicon on insulator wafers, consist of a cantilever spring with integrated tip at the free end and an electrically insulated counter electrode. Dynamic force gradient sensing is the preferred operating mode. Here, tip–sample interactions are detected by letting the sensor act as a resonator in a phase controlled oscillator setup and measuring corresponding shifts of the oscillation frequency. Experiments were performed in vacuum using a standard tunneling microscope. A Cr grating on a quartz substrate served as the test sample. Topographic images showing details on a 10 nm scale were obtained operating at a constant force gradient of the order of 0.01 N/m. In addition, critical design parameters are discussed based on an analysis of the electromechanical properties of the sensors.

Capacitively loaded PIFA

Abstract: A planar inverted-F antenna is described that is provided with a capacitive load that allows the dimensions of the antenna to be reduced from a conventional λ/4 to λ/8. To maintain good bandwidth and impedance matching in spite of the presence of the capacitive load, a capacitive feed is also provided.

Electrostatic forces and their effects on capacitive mechanical sensors

Abstract: This paper describes the electrostatic forces developed between the plates of capacitive mechanical sensors built in crystalline silicon and their effects on the measurement and the fabrication process. In single capaciti sensors the electrical forces can introduce offset errors in the measuring process, or can cause the collapse of the sensing structure or jeopardize the functionality of the final device due to the sticking or even bonding of the movable parts. Also it is investigated how the limits are affected when scaling down the dimensions of the sensors. Finally, some solutions to avoid the negative effects of the electrostatic forces are proposed.

Implantable cardioverter defibrillator having a high voltage capacitor

Abstract: The present invention is an implantable cardioverter defibrillator (ICD) system that is electrically connected to two or more implantable discharge electrodes for implantation into a human patient for treating cardiac dysrhythmias. The ICD system has a battery system and a stepup transformer for charging a capacitive storage system in response to a cardiac dysrhythmia detected by a sensing system. A plurality of electrodes are provided which are adapted to be implanted into a human patient. A primary capacitive energy storage system is provided and is corrected to the stepup transformer for storing and delivering a high voltage output of at least 1500 volts. A stepdown transformer is also provided which is connected between the primary capacitive energy storage system and the electrodes for reducing the high voltage output of the primary capacitive energy system to a safe level for the heart.

A novel low-cost capacitive-sensor interface

Abstract: This paper describes the design of a new capacitive sensor interface. The interface is based on the use of a novel type of oscillator whose frequency is insensitive to low- and high-frequency interfering signals by the application of a third order high-pass filter and special dither techniques. The fully integrated 0.7 /spl mu/m CMOS circuit shows an inaccuracy of less than 100 aF with respect to a 2 pF reference capacitor over a -30/spl deg/ to +70/spl deg/C temperature range. The applied measurement concept guarantees high stability, high accuracy and a negligible influence of parasitic capacitances without the need for calibration.

Surface-micromachined capacitive differential pressure sensor with lithographically defined silicon diaphragm

Abstract: A capacitive surface-micromachined sensor suitable for the measurement of liquid and gas pressures was fabricated. The structure consists of a polysilicon stationary electrode suspended 0.7 /spl mu/m above a 20-/spl mu/m-thick lightly doped silicon diaphragm formed by a patterned etch stop. The a priori patterning of the buried etch stop yields diaphragm widths independent of wafer thickness variations with excellent alignment. The design described here has a pressure range of 100 PSI, a nominal capacitance of 3.5 pF with a full scale span of 0.8 pF, and a temperature coefficient of 100 ppm/spl deg/C/sup -1/. Each device, including a matched reference capacitor, occupies 2.9 mm/sup 2/, yielding approximately 2000 devices per 100-mm wafer.

Void fraction measurements in gas - liquid flows using capacitance sensors

Abstract: Void fraction measurements for vertical flow in a small diameter tube (9.53 mm) were taken using two non-intrusive capacitive void fraction sensors. The sensors were needed to measure the void fraction of water - air two-phase flow under normal gravity and microgravity conditions. Void fraction data were collected with: (1) a sensor having helical wound electrodes that was used to collect data under normal gravity and microgravity conditions, (2) a sensor having concave plate electrodes, used to collect data at normal gravity. This paper covers the calibration results for both sensors and some of the problems associated with the helical wound design. Nonlinearity in the helical sensor is addressed, with improvements shown in the concave plate sensor. Comparisons are made between the capacitive sensors, quick-closing valves and a gamma densitometer.

Capacitively coupled bi-directional data and power transmission system

Abstract: A power and data transfer system includes a portable device (1) with a first contact circuit formed from a pair of contact pads (24 and 25) having an outer surface covered with a dielectric material. A processing unit (14) is coupled to the first contact circuit. A host unit (2) has a second circuit including a second pair of contact pads (20 and 21) which are also covered with a dielectric material. A host processing unit is coupled to the second contact circuit. The first and second contact circuits are adapted to form a capacitive interface when the portable device is positionned proximate the host unit. The capacitive interface transmits power signals from the host unit to the portable device. The same contacts are used to transmit bidirectional data signals between the portable device and the host unit.

Heating mode transition induced by a magnetic field in a capacitive rf discharge.

Abstract: We show that a recently proposed pressure model of collisionless heating in capacitive rf discharges predicts that a small magnetic field ({approximately}10 G) applied transverse to the electric field will induce a heating mode transition from a pressure-heating dominated state to an Ohmic-heating dominated state. This prediction is confirmed by kinetic simulations and experiments. {copyright} {ital 1996 The American Physical Society.}

Micromachined ultrasonic transducers: 11.4 MHz transmission in air and more

Abstract: The fabrication and modeling of novel, capacitive, ultrasonic air transducers is reported. Transmission experiments in air at 11.4, 9.2, and 3.1 MHz are shown to correspond with theory. The transducers are made using surface micromachining techniques, which enable the realization of center frequencies ranging from 1.8 to 11.6 MHz. The bandwidth of the transducers ranges from 5% to 20%, depending on processing parameters. Custom circuitry is able to detect 10 MHz capacitance fluctuations as small as 10−18 F, which correspond to displacements on the order of 10−3 A, in a bandwidth of 2 MHz with a signal to noise ratio of 20 dB. Such detection sensitivity is shown to yield air transducer systems capable of withstanding over 100 dB of signal attenuation, a figure of merit that has significant implications for ultrasonic imaging, nondestructive evaluation, gas flow and composition measurements, and range sensing.

An interface circuit for high-accuracy signal processing of differential-capacitance transducers

Abstract: For high-accuracy signal processing of differential-capacitance transducers, an interface circuit is developed. The architecture is based on the idea that the ratio of one of the transducer capacitances to its total capacitance represents the offset binary equivalent of the physical quantity under measurement. An op amp-based capacitance-to-voltage converter is commonly used for capacitance detection and an analog-to-digital converter is used for the ratiometric operation. A circuit analysis shows that the interface can detect the capacitance change as small as 0.01% of the total capacitance. Experimental results are also given to confirm the analysis.

Short vertical 160 meter band antenna

Abstract: A physically short broad-bandwidth multiband vertical antenna with 50 ohm input impedance and 25 foot square footprint for 160, 80, 40 and 17 meter radio bands Low ohmic resistance due to the small physical size combined with system impedance transformation and capacitive input coupling provide radiation resistance corresponding to an efficiency of about 85 percent The 2:1 SWR bandwidth is 50 kHz on 160 meters and 87 kHz on 80 meters A 30 foot mast, top hat capacitive load, and a plurality of parallel vertical skirt wires depending from the top hat around the mast are electrically connected together at the top of the mast An impedance transforming multi-tap coil is connected between mast and ground Skirt wires are in two sets separately fed at their lower ends by separate coaxial cable coupling capacitors for operation on different bands A 50 ohm feed line, skirt wires, coupling capacitors and impedance transforming coil all have terminal connections on a mast-base insulator End-pruning of coaxial cable capacitors combined with coil tap selection tunes the antenna for desired portions of the 160 and 80 meter bands for input impedance matching without additional matching devices Skirt wire sets, downwardly tensioned and spaced from the mast, are connected to input capacitors by separated crossed metal spreaders at the mast-base insulator Additional reactance-reducing components facilitate improved operation at 40 meters More independent center frequency tuning for both 160 and 40 meter bands is obtained by connecting the impedance transformation coil from ground to a higher point on the mast via an additional skirt system

A high-frequency plasma process wherein the plasma is excited by an inductive structure in which the phase and anti-phase portions of the capacitive currents between the inductive structure and the plasma are balanced

Abstract: A process for fabricating a product (28, 119). The process comprises the steps of subjecting a substrate to a composition of entities, at least one of the entities emanating from a species generated by a gaseous discharge excited by a high frequency field in which the vector sum of phase and anti-phase capacitive coupled voltages from the inductive coupling structure substantially balances.