Showing papers on "Capacitive sensing published in 2003"

Wireless and powerless sensor and interrogator

Abstract: Arrangement and method for monitoring a tire mounted to the vehicle in which a thermal radiation detecting device detects the temperature of the tire at different circumferential locations along the circumference of the tire. The detected temperatures of the tire are analyzed to determine, for example, whether a difference in thermal radiation is present between the circumferential locations of the tire, and if so, an action is effected in response to the analysis. The thermal radiation detecting devices are preferably supplied with power wirelessly, e.g., through an inductive system, a capacitive system or a radio frequency energy transfer system.

RFID device and method of forming

Abstract: A radio frequency identification (RFID) inlay (102) includes a conductive (124) or capacitive connection electrically connecting an antenna (106) to strap leads (116) that are coupled to an RFID chip (110). The conductive connection may include conductive bumps (124) attached to the strap, and/or may include conductive traces, such as conductive ink traces. The capacitive connection may involve putting the antenna and the strap into close proximity, to allow capacitive coupling between the antenna and straps. The connections provide a convenient, fast, and effective way to operatively couple antennas and straps. The RFID inlay may be part of an RFID label or RFID tag.

Fabricating capacitive micromachined ultrasonic transducers with wafer-bonding technology

Abstract: Introduces a new method for fabricating capacitive micromachined ultrasonic transducers (CMUTs) that uses a wafer bonding technique. The transducer membrane and cavity are defined on an SOI (silicon-on-insulator) wafer and on a prime wafer, respectively. Then, using silicon direct bonding in a vacuum environment, the two wafers are bonded together to form a transducer. This new technique, capable of fabricating large CMUTs, offers advantages over the traditionally micromachined CMUTs. First, forming a vacuum-sealed cavity is relatively easy since the wafer bonding is performed in a vacuum chamber. Second, this process enables better control over the gap height, making it possible to fabricate very small gaps (less than 0.1 /spl mu/m). Third, since the membrane is made of single crystal silicon, it is possible to predict and control the mechanical properties of the membrane to within 5%. Finally, the number of process steps involved in making a CMUT has been reduced from 22 to 15, shortening the device turn-around time. All of these advantages provide repeatable fabrication of CMUTs featuring predictable center frequency, bandwidth, and collapse voltage.

Sensor patterns for a capacitive sensing apparatus

Abstract: One embodiment in accordance with the present invention includes a capacitive sensing apparatus. The capacitive sensing apparatus comprises a first set of interdigitated conductive traces. Additionally, the capacitive sensing apparatus comprises a second set of interdigitated conductive traces that are intertwined with the first set of interdigitated conductive traces.

Capacitive Micromachined Ultrasonic Transducers: Theory and Technology

Abstract: Capacitive micromachined ultrasonic transducers ~CMUTs!, introduced about a decade ago, have been shown to be a good alternative to conventional piezoelectric transducers in various aspects, such as sensitivity, transduction efficiency, and bandwidth. In this paper, we discuss the principles of capacitive transducer operation that underlie these aspects. Many of the key features of capacitive ultrasonic transducers are enabled with micromachining technology. Micromachining allows us to miniaturize device dimensions and produce capacitive transducers that perform comparably to their piezoelectric counterparts. The fabrication process is described briefly, and the performance of the CMUT transducers is evaluated by demonstrating characterization results. It is shown that the transduction efficiency as defined by the electromechanical coupling coefficient can be close to unity with proper device design and operating voltage. It is also shown that CMUTs provide large bandwidth ~123% fractional bandwidth! in immersion applications which translate into high temporal and axial resolution. Finally, the feasibility of using CMUTs is demonstrated by showing imaging examples in air and in immersion.

Lattice touch-sensing system

Abstract: This invention is directed to a lattice touch-sensing system for detecting a position of a touch on a touch-sensitive surface. The lattice touch-sensing system may include two capacitive sensing layers, separated by an insulating material, where each layer consists of substantially parallel conducting elements, and the conducting elements of the two sensing layers are substantially orthogonal to each other. Each element may comprise a series of diamond shaped patches that are connected together with narrow conductive rectangular strips. Each conducting element of a given sensing layer is electrically connected at one or both ends to a lead line of a corresponding set of lead lines. A control circuit may also be included to provide an excitation signal to both sets of conducting elements through the corresponding sets of lead lines, to receive sensing signals generated by sensor elements when a touch on the surface occurs, and to determine a position of the touch based on the position of the affected bars in each layer.

Design methodology for Sievenpiper high-impedance surfaces: an artificial magnetic conductor for positive gain electrically small antennas

Abstract: The Sievenpiper high-impedance surface is a periodic structure characterized by a substrate filled with an array of vertical vias, capped by a capacitive frequency selective surface (FSS). It functions as the ideal antenna groundplane for wireless applications because it simultaneously enhances the gain of the antenna as it suppresses the surface waves associated with it (thus reducing the undesired back-lobe and the reactive coupling to nearby circuits). These two properties are known to occur approximately over the frequency bandwidth where the phase of the reflection coefficient of the surface changes from +90/spl deg/ to -90/spl deg/. Since this behavior takes place at frequencies where the unit cell of the structure is small compared to the wavelength, it can be modeled in terms of a layered homogeneous material where each layer has an anisotropic magneto-dielectric tensor. These tensors, readily derived using an effective medium model, can be designed to obtain independent control of the bandwidths of gain increase and surface wave suppression. Based on a transverse resonance model of the effective medium material model, it is shown that Sievenpiper high-impedance surfaces exist that can suppress TE surface waves alone or TM surface waves alone, or both TE and TM surface waves at the same time. Maximum TM surface wave suppression bandwidth is obtained when the distance between the vias in the via array is as close as possible to /spl lambda//2. Maximum TE bandwidth is obtained when the conductors of the capacitive FSS offer maximum blockage to the normal magnetic field of the wave. A reduction of the transverse resonance solution to nearly closed form is used to obtain a simple picture of the design space available when the desired operating frequency is fixed.

Calculation and measurement of electromechanical coupling coefficient of capacitive micromachined ultrasonic transducers

Abstract: The electromechanical coupling coefficient is an important figure of merit of ultrasonic transducers. The transducer bandwidth is determined by the electromechanical coupling efficiency. The coupling coefficient is, by definition, the ratio of delivered mechanical energy to the stored total energy in the transducer. In this paper, we present the calculation and measurement of coupling coefficient for capacitive micromachined ultrasonic transducers (CMUTs). The finite element method (FEM) is used for our calculations, and the FEM results are compared with the analytical results obtained with parallel plate approximation. The effect of series and parallel capacitances in the CMUT also is investigated. The FEM calculations of the CMUT indicate that the electromechanical coupling coefficient is independent of any series capacitance that may exist in the structure. The series capacitance, however, alters the collapse voltage of the membrane. The parallel parasitic capacitance that may exist in a CMUT or is external to the transducer reduces the coupling coefficient at a given bias voltage. At the collapse, regardless of the parasitics, the coupling coefficient reaches unity. Our experimental measurements confirm a coupling coefficient of 0.85 before collapse, and measurements are in agreement with theory.

Intermodulation distortion and power handling in RF MEMS switches, varactors, and tunable filters

Abstract: This paper presents a theoretical and experimental study of the nonlinear effects generated RF-microelectromechanical system (MEMS) varactors and capacitive switches. The theoretical part includes an analytic derivation, as well as an electromechanical model suitable for computer-aided design (CAD) simulation. The simulations agree very well with measurements performed on a 24-GHz three-pole MEMS tunable filter. It is shown that MEMS capacitive components with a spring constant k>10 N/m generate very low intermodulation, as compared to semiconductor devices, and lead to a two-tone third-order intermodulation intercept point (IIP3) greater than +40 dBm for /spl Delta/f>3-5f/sub 0/, where f/sub 0/ is the mechanical resonant frequency. In fact, the IIP3 increases to +80 dBm for a difference signal (/spl Delta/f) of 5 MHz. The CAD model also allows the evaluation of the power-handling capabilities of the tunable filter and, it is seen that, for the case presented here, distortions become significant for an input power greater than +20 dBm. Noise generation due to thermal effects on a movable membrane (Brownian noise) is also modeled and it is shown that the tunable filter results in a very low phase-noise level close to the carrier.

High frequency network multiplexed communications over various lines using multiple modulated carrier frequencies

Abstract: An apparatus is provided for high frequency multiplexed electrical line communication for cable TV, telephone, internet, security and other control applications over the mid and low voltage power lines and directly through the transformers. The apparatus includes a transmitter, a receiver, a modem (14), a multiplexer and multiple couplers (28) at each of two or more locations along an electrical line (18). The couplers have capacitive circuits serially connected with an air-core or dielectric-core transformer (22). The capacitive circuits resonate with the transformer (22) at a preselected frequency. The coupler (28) eliminates noise and is matched to the characteristic impedance of the line at the preselected frequency, which linearizes communication on the line and allows high speed data and voice communication over long distances. Multiple modulators and demodulators are used to produce multiple modulated carrier frequencies.

Single wafer encapsulation of MEMS devices

Abstract: Packaging of micro-electro-mechanical systems (MEMS) devices has proven to be costly and complex, and it has been a significant barrier to the commercialization of MEMS. We present a packaging solution applicable to several common MEMS devices, such as inertial sensors and micromechanical resonators. It involves deposition of a 20 /spl mu/m layer of epi-polysilicon over unreleased devices to act as a sealing cap, release of the encapsulated parts via an HF vapor release process, and a final seal of the parts in 7 mbar (700 Pa) vacuum. Two types of accelerometers, piezoresistive and capacitive sensing, were fabricated. Piezoresistive accelerometers with a footprint smaller than 3 mm/sup 2/ had a resolution of 10 /spl mu/g//spl radic/Hz at 250 Hz. Capacitive accelerometers with a 1 mm/sup 2/ footprint had a resolution of 1 mg/spl radic/Hz over its 5 kHz bandwidth. Resonators with a quality factor as high as 14,000 and resonant frequency from 50 kHz to 10 MHz have also been built. More than 100 capacitive accelerometers and 100 resonators were tested, and greater than 90% of the resonators and accelerometers were functional.

High-Q single crystal silicon HARPSS capacitive beam resonators with self-aligned sub-100-nm transduction gaps

Abstract: This paper reports on the fabrication and characterization of high-quality factor (Q) single crystal silicon (SCS) in-plane capacitive beam resonators with sub-100 nm to submicron transduction gaps using the HARPSS process. The resonating element is made of single crystal silicon while the drive and sense electrodes are made of trench-refilled polysilicon, yielding an all-silicon capacitive microresonator. The fabricated SCS resonators are 20-40 /spl mu/m thick and have self-aligned capacitive gaps. Vertical gaps as small as 80 nm in between 20 /spl mu/m thick silicon structures have been demonstrated in this work. A large number of clamped-free and clamped-clamped beam resonators were fabricated. Quality factors as high as 177000 for a 19 kHz clamped-free beam and 74000 for an 80 kHz clamped-clamped beam were measured under 1 mtorr vacuum. Clamped-clamped beam resonators were operated at their higher resonance modes (up to the fifth mode); a resonance frequency of 12 MHz was observed for the fifth mode of a clamped-clamped beam with the fundamental mode frequency of 0.91 MHz. Electrostatic tuning characteristics of the resonators have been measured and compared to the theoretical values. The measured Q values of the clamped-clamped beam resonators are within 20% of the fundamental thermoelastic damping limits (Q/sub TED/) obtained from finite element analysis.

Charge transfer capacitive position sensor

Abstract: The position of an object, which may be a user's finger, along a body is sensed capacitively. A measurement circuit meters the simultaneous injection of electrical charge into the two ends of the body, which may be shaped as a straight line or as a curve. A computing device computes the ratio of the relative changes in the amount of charge injected into each end of the element. The result of this computation is a one dimensional coordinate number plus a detection state indication, both of which can be fed to another functional element, such as an appliance controller, which interprets the coordinate and detection state as a command or measurement.

Linear Electromechanical Model of Ionic Polymer Transducers -Part I: Model Development

Abstract: A linear electromechanical model is developed for ionic polymer materials. The model is based on an equivalent circuit representation that is related to the mechanical, electrical, and electromechanical properties of the material. Expressions for the quasi-static and dynamic mechanical impedance are derived from beam theory. The Golla-Hughes-McTavish model of viscoelasticity is incorporated into the model to include effects due to a rate dependent modulus. Similar to previous research, the electrical impedance is modeled as a series combination of resistive and capacitive elements. The major contribution of this work is the derivation of an electromechanical coupling term that is related to an effective bending strain coefficient. This parameter is also frequency dependent to model the low-frequency relaxation that has been measured in certain ionic polymer materials. The resulting linear electromechanical model is based on the measurement of the effective permittivity, elastic modulus, and effective stra...

Capacitive sensor systems and methods with increased resolution and automatic calibration

Abstract: Methods and systems for capacitive proximity and contact sensing employ one or more simple sensors (which may be a conductive fiber or pattern of conductive ink) in communication with a microcontroller. Digital signal processing executed by the microcontroller enables resolution enhancement, automatic and continuous calibration, noise reduction, pattern recognition and the configuration of virtual sensors capable of detecting how an object incorporating the sensors is being manipulated.

Experimental evaluation and comparative analysis of commercial variable-capacitance MEMS accelerometers

Abstract: This paper reports the experimental analysis of commercially available variable-capacitance MEMS accelerometers, characterized under standardized tests. Capacitive MEMS sensors of the same low-level input acceleration range with various mechanical sensing element designs, materials, fabrication technologies and price ranges were selected for evaluation. The selected sensors were characterized using ANSI and NIST certified testing equipment and under the same testing conditions; and their sensitivity, resolution, linearity, frequency response, transverse sensitivity, temperature response, noise level and long-term stability were tested and compared. The experimental results are then interpreted to provide an insight to advantages and disadvantages for using a particular mechanical design, fabrication technology, sensor material and the techniques for electronics integration and packaging of each specific sensor design.

Transducer for sensing body sounds

Abstract: An acoustic-to-electrical transducer for sensing body sounds is disclosed. The transducer comprises a capacitive sensor, whereby a stethoscope diaphragm forms one plate of a capacitor, with the second plate of the capacitor being co-planar to the diaphragm. The capacitance of the two plates varies with the distance between them, said distance being modified by motion of the diaphragm in response to sound pressure. The sensor, circuitry, manufacturing methods and improvements are disclosed.

Micro-mechanical capacitive inductive sensor for wireless detection of relative or absolute pressure

Abstract: A micro-mechanical pressure transducer is disclosed in which a capacitive transducer structure is integrated with an inductor coil to form a LC tank circuit, resonance frequency of which may be detected remotely by imposing an electromagnetic field on the transducer. The capacitive transducer structure comprises a conductive movable diaphragm, a fixed counter electrode, and a predetermined air gap between said diaphragm and electrode. The diaphragm deflects in response to an applied pressure differential, leading to a change of capacitance in the structure and hence a shift of resonance frequency of the LC tank circuit. The resonance frequency of the LC circuit can be remotely detected by measuring and determining the corresponding peak in electromagnetic impedance of the transducer.

Efficient charge recovery method for driving piezoelectric actuators with quasi-square waves

Abstract: In this paper, an efficient charge recovery method for driving piezoelectric actuators with low frequency square waves in low-power applications such as mobile microrobots is investigated. Efficiency issues related to periodic mechanical work of the actuators and the relationship among the driving electronics efficiency, the piezoelectric coupling factor, and the actuator energy transmission coefficient are discussed. The proposed charge recovery method exploiting the energy transfer between an inductor and a general capacitive load is compared with existing techniques that lead to inherent inefficiencies. A charge recovery method is then applied to piezoelectric actuators, especially to bimorph ones. Unitary efficiency can be obtained theoretically for purely capacitive loads while intrinsic losses such as hysteresis necessarily lower the efficiency. In order to show the validity of the method, a prototype driving electronics consisting of an extended H-bridge is constructed and tested by experiments and simulations. Preliminary results show that 75% of charge (i.e., more than 56% of energy) can be recovered for bending actuators such as bimorphs without any component optimization at low fields.

A micromachined 2D positioner with electrothermal actuation and sub-nanometer capacitive sensing

Abstract: This paper reports on a multi-purpose two-axis micropositioner with sub-nanometer position sensing for precise feedback control. Along each axis it has an electrothermal actuator, a capacitive position sensor and a displacement amplifier that provides a gain of 3.37 for the sensor. It is fabricated from custom SOI wafers using dry etching, and each component is electrically and thermally isolated by silicon nitride. For a fabricated device of 65 µ mt hickness, the measured displacement sensitivity is 0.333 fF nm −1 ,w hich corresponds to 0.3 nm resolution with available laboratory instrumentation. The range is ≈19 µ ma long each axis for the positioner, which corresponds to 66 µ mt ravel in the sense combs. Using an external parallel inductor, a positioning displacement of 9.6 µ mo ffers as hift of 240 kHz in L–C resonance, corresponding to a sensitivity of 25 Hz nm −1 . (Some figures in this article are in colour only in the electronic version)

Transducer arrays with an integrated sensor and methods of use

Abstract: Methods and systems for obtaining ultrasound and sensing other patient characteristics are provided from summary. One or more sensors (16) are provided in a same transducer probe (10) as an array of elements (14). For example, sensors (16) are formed on a same semiconductor substrate (26), such as a silicon substrate (26), as microelectromechanical devices or a capacitive membrane ultrasonic transducer (CMUT). As another example, a sensor (16) is provided separate from or attached to transducer materials. Possible sensors (16) include temperature, pressure, microphone, chemical and/or other sensors (16).

A new regime for operating capacitive micromachined ultrasonic transducers

Abstract: We report on a new operation regime for capacitive micromachined ultrasonic transducers (cMUTs). Traditionally, cMUTs are operated at a bias voltage lower than the collapse voltage of their membranes. In the new proposed operation regime, first the cMUT is biased past the collapse voltage. Second, the bias voltage applied to the collapsed membrane is reduced without releasing the membrane. Third, the cMUT is excited with an ac signal at the bias point, keeping the total applied voltage between the collapse and snapback voltages. In this operation regime, the center of the membrane is always in contact with the substrate. Our finite element methods (FEM) calculations reveal that a cMUT operating in this new regime, between collapse and snapback voltages, possesses a coupling efficiency (k/sub T//sup 2/) higher than a cMUT operating in the conventional regime below its collapse voltage. This paper compares the simulation results of the coupling efficiencies of cMUTs operating in conventional and new operation regimes.

An Equivalent Circuit Model for Ionic Polymer-Metal Composites and their Performance Improvement by a Clay-Based Polymer Nano-Composite Technique:

Abstract: Ionic Polymer-Metal Composite (IPMC) is a new class of polymeric material exhibiting large strain with inherent soft actuation. The observed motion characteristics of an IPMC subjected to an electric field is highly nonlinear. This is believed to be due primarily to the particle electrodes on the IPMC surface, which is inherently both capacitive and resistive due to particle separation and density. Knowing that the value of resistivity and capacity can be manipulated by the number of metal platings applied to the IPMC, the force response of an IPMC when subjected to an imposed electric field is due to the interaction of an array of capacitors and resistors along with ionic migration. In this effort we attempt to incorporate a capacitive and resistive model into the linear irreversible thermodynamic model. The advantages of using such a model are (i) the possible dynamic predictability of the material itself in connection with capacitive responses; and (ii) the realization of capacitive and resistive effec...

An offset-canceling low-noise lock-in architecture for capacitive sensing

Abstract: We describe an offset-canceling low-noise lock-in architecture for capacitive sensing. We take advantage of the properties of modulation and demodulation to separate the signal from the DC offset and use nonlinear multiplicative feedback to cancel the offset. The feedback also attenuates out-of-band noise and further enhances the power of a lock-in technique. Experimentally, in a 1.5-/spl mu/m BiCMOS chip, a fabrication DC offset of 2 mV and an intentional offset of 100 mV were attenuated to 9 /spl mu/V. Our offset-canceling technique could also be useful for practical multipliers that need tolerance to fabrication errors. We present a detailed theoretical noise analysis of our architecture that is confirmed by experiment. As an example application, we demonstrate the use of our architecture in a simple capacitive surface-microelectromechanical-system vibration sensor where the performance is limited by mechanical Brownian noise. However, we show that our electronics limits us to 30 /spl mu/g//spl radic/Hz, which is at least six times lower than the noise floor of commercial state-of-the-art surface-micromachined inertial sensors. Our architecture could, thus, be useful in high-performance inertial sensors with low mechanical noise. In a 1-100-Hz bandwidth, our electronic detection threshold corresponds to a one-part-per-eight-million change in capacitance.

Compact, low profile, single feed, multi-band, printed antenna

Abstract: Printed circuit (18) and two-shot molding techniques are used to form a metal radiating element (16), a metal ground plane element, a metal antenna feed, a metal short-circuiting strip and metal capacitive loading plates within small antennas that are buried within transmit/receive radio device such as mobile cellular telephones. Balanced and unbalanced, single-feed, two and three band antennas are provided wherein the radiating element (16) is laterally spaced from the ground plane element, to thereby provide an antenna having a very low profile or height, including antennas wherein the ground plane element and radiating element (16) are placed coplanar on the same surface of a PCB (18). A thin dielectric carriage (31) on a PCB allows for placing the metal capacitive loading plates on the sidewalls of the dielectric carriage (31), to thereby provide reactive loading of a radiating element that is on the top surface of the dielectric carriage (31).

Vertical-actuated electrostatic comb drive with in situ capacitive position correction for application in phase shifting diffraction interferometry

Abstract: This research utilizes the levitation effect of electrostatic comb fingers to design vertical-to-the-substrate actuation for optical phase shifting interferometry applications. For typical polysilicon comb drives with 2 /spl mu/m gaps between the stationary and moving fingers, as well as between the microstructures and the substrate, the equilibrium position is nominally 1-2 /spl mu/m above the stationary comb fingers. This distance is ideal for most phase shifting interferometric applications. A parallel plate capacitor between the suspended mass and the substrate provides in situ position sensing to control the vertical movement, providing a total feedback-controlled system. The travel range of the designed vertical microactuator is 1.2 /spl mu/m. Since the levitation force is not linear to the input voltage, a lock-in amplifier capacitive sensing circuit combined with a digital signal processor enables a linearized travel trajectory with 1.5 nm position control accuracy. A completely packaged micro phase shifter is described in this paper. One application for this microactuator is to provide linear phase shifting in the phase shifting diffraction interferometer (PSDI) developed at LLNL which can perform optical metrology down to 2 /spl Aring/ accuracy.

Fast response Humidity Sensors for a Medical Microsystem

Abstract: A fast response humidity sensor was fabricated to equip a medical microsystem for diagnosis of pulmonary diseases. Its main characteristics are reported in this paper. The sensor is based on a capacitor made of a divinyl siloxane benzocyclobutene (BCB) thin film in between parallel plate electrodes. It was fabricated with compatible CMOS technology. It exhibits good linearity, good sensitivity, and a short response time. Equilibrium capacitance variations versus humidity can be considered linear with a linearity error less than 2% of the humidity level. The sensitivity is 0.1 pF by per cent of the humidity level. The device displays a typical adsorption time of 650 ms, a minimum adsorption time of 400 ms, and a desorption time of a few seconds at ambient temperature. Its performances were compared to other types of capacitive humidity sensors fabricated for the same medical use. The static behavior and the dynamic behavior of the device are reported. They are interpreted according to physical processes of gas adsorption and diffusion in and through glassy polymers. The suitability of the conventional Dual-Mode model to explain water sorption in BCB is discussed. This investigation is a starting point in a modeling process to improve the design of the sensor interface circuitry.

Mems scanner with dual magnetic and capacitive drive

Abstract: A MEMS scanning device includes more than one type of actuation. In one approach capacitive and magnetic drives combine to move a portion of the device along a common path. In one such structure, the capacitive drive comes from interleaved combs. In another approach, a comb drive combines with a pair of planar electrodes to produce rotation of a central body relative to a substrate. In an optical scanning application, the central body is a mirror. In a biaxial structure, a gimbal ring carries the central body. The gimbal ring may be driven by more than one type of actuation to produce motion about an axis orthogonal to that of the central body. In another aspect, a MEMS scanning device is constructed with a reduced footprint.

SOI-based HF and VHF single-crystal silicon resonators with SUB-100 nanometer vertical capacitive gaps

Abstract: This paper reports on the fabrication and characterization of single-crystal silicon (SCS) capacitive resonators with operating frequencies in the HF (3-30 MHz) and VHF (30-300 MHz) range. In-plane ultra-stiff SCS resonators with polysilicon electrodes and self-aligned 90 nm vertical capacitive gaps have been fabricated on SOI substrates using a HARPSS-like fabrication process. High frequency side-supported flexural disk resonators and clamped-clamped beam resonators have been implemented and tested. A 3 /spl mu/m thick, 30/spl mu/m in diameter SCS disk resonator exhibited a quality factor of 40,000 in vacuum at 148 MHz. When operated in atmosphere, the same device demonstrated a Q of 8,000.

A contactless capacitive angular-position sensor

Abstract: This paper presents an absolute capacitive angular-position sensor with a contactless rotor. The sensor is mainly composed of three parts: the capacitive sensing element, a signal processor, and a microcontroller. The electrically floating rotor can be either conductive or dielectric. For the dielectric material, we chose plastic, and for the conductive rotor, we chose aluminum. The sensing element has a redundant structure, which reduces mechanical nonidealities. The signal processor has a multicapacitance input and a single output, which is a period-modulated square-wave voltage. The microcontroller acquires output data from the processor and sends them to a PC, which calculates the rotor position. Theoretical analysis, supported by experimental results, show that the sensitivity to mechanical nonidealities of the sensing element is higher in the case of a conductive rotor. The resolution of the capacitive angular-position sensor over the full range (360/spl deg/) was better than 1". The measured nonlinearity was /spl plusmn/ 100" and /spl plusmn/ 300" for the dielectric and the conductive rotor, respectively.