Showing papers on "Capacitive sensing published in 2008"

Two-dimensional position sensor

Abstract: A capacitive position sensor for determining the position of an object along first and second directions is described. The sensor comprises a substrate having an arrangement of electrodes mounted on a single surface thereof. The electrodes are arranged so as to define an array of sensing cells arranged in columns and rows to form a sensing area. Each of the sensing cell including a column sensing electrode and a row sensing electrode with the column sensing electrodes of sensing cells in the same column being electrically coupled together and the row sensing electrodes of sensing cells in the same row also being electrically coupled together. Row sensing electrodes of sensing cells at opposing ends of at least one of the rows are connected together by an electrical connection made outside of the sensing area so that there is no requirement for electrical connections to cross within the sensing area, thus providing a capacitive position sensor having a sensing area with electrodes on only one side of a substrate.

Carrier-mediated magnetoelectricity in complex oxide heterostructures.

Abstract: Increasing demands for high-density, stable nanoscale memory elements, as well as fundamental discoveries in the field of spintronics, have led to renewed interest in exploring the coupling between magnetism and electric fields. Although conventional magnetoelectric routes often result in weak responses, there is considerable current research activity focused on identifying new mechanisms for magnetoelectric coupling. Here we demonstrate a linear magnetoelectric effect that arises from a carrier-mediated mechanism, and is a universal feature of the interface between a dielectric and a spin-polarized metal. Using first-principles density functional calculations, we illustrate this effect at the SrRuO3/SrTiO3 interface and describe its origin. To formally quantify the magnetic response of such an interface to an applied electric field, we introduce and define the concept of spin capacitance. In addition to its magnetoelectric and spin capacitive behaviour, the interface displays a spatial coexistence of magnetism and dielectric polarization, suggesting a route to a new type of interfacial multiferroic.

Touch panel and display device using the same

Abstract: An exemplary touch panel includes a substrate, transparent conductive layers, a capacitive sensing circuit, and conductive wires. The transparent conductive layers are disposed on a surface of the substrate and spaced apart from each other. Each transparent conductive layer includes a carbon nanotube layer. The carbon nanotube layer includes carbon nanotubes. The conductive wires respectively electrically connect the transparent conductive layers to the capacitive sensing circuit. A display device using the touch panel is also provided.

Capacitive sensor behind black mask

Abstract: Devices having one or more sensors located outside a viewing area of a touch screen display are disclosed. The one or more sensors can be located behind an opaque mask area of the device; the opaque mask area extending between the sides of a housing of the device and viewing area of the touch screen display. In addition, the sensors located behind the mask can be separate from a touch sensor panel used to detect objects on or near the touch screen display, and can be used to enhance or provide additional functionality to the device. For example, a device having a sensor located outside the viewing area can be used to detect objects in proximity to a functional component incorporated in the device, such as an ear piece (i.e., speaker for outputting sound). The sensor can also output a signal indicating a level of detection which may be interpreted by a controller of the device as a level of proximity of an object to the functional component. In addition, the controller can initiate a variety of actions related to the functional component based on the output signal, such as adjusting the volume of the earpiece.

Touch and force sensing for input devices

Abstract: A device (300) may include a first layer (310), a second layer (320, a third layer (330), a capacitive sensing component (340) coupled to the first layer, and a force sensing component (350) coupled to the first layer (310) and the third layer (330) and configured to detect the amount of force applied to the second layer (320). A method may include monitoring capacitance and voltage at one or more input sensors configured to detect changes in capacitance and to detect changes in applied force, detecting a change in capacitance, activating a capacitance response in response to detecting a change in capacitance, detecting a change in voltage, and activating a force response in response to detecting a change in voltage.

Flexible-foam-based capacitive sensor arrays for object detection at low cost

Abstract: Polymer foams are used in the automotive and construction industries for thermal insulation, vibration attenuation, and pressure absorption, due to their lightweight structure, thermal characteristics and low manufacturing costs. These foams have higher elasticity in their cross sections than bulk polymers, which makes them the preferred mount for capacitive sensor arrays. The authors describe a flexible pressure-sensitive surface mounted on packaging foam. The elastic properties of the foam are presented along with the sensor array’s weight sensitivity. The authors illustrate an inventory management application where objects on display can be detected through their weights.

Enhancement of Ohmic and Stochastic Heating by Resonance Effects in Capacitive Radio Frequency Discharges: A Theoretical Approach

Abstract: In low-pressure capacitive radio frequency discharges, two mechanisms of electron heating are dominant: (i) Ohmic heating due to collisions of electrons with neutrals of the background gas and (ii) stochastic heating due to momentum transfer from the oscillating boundary sheath. In this work we show by means of a nonlinear global model that the self-excitation of the plasma series resonance which arises in asymmetric capacitive discharges due to nonlinear interaction of plasma bulk and sheath significantly affects both Ohmic heating and stochastic heating. We observe that the series resonance effect increases the dissipation by factors of 2-5. We conclude that the nonlinear plasma dynamics should be taken into account in order to describe quantitatively correct electron heating in asymmetric capacitive radio frequency discharges.

Capacitive Circuit Method for Fast and Efficient Design of Wideband Radar Absorbers

Abstract: A simple, fast and efficient method for designing wideband radar absorbers is proposed. The idea is to modify the circuit analog absorber method without perturbing the bandwidth. This is done by utilizing the asymptotic behavior of such an absorber at low frequency and replacing the band-stop resonating frequency selective surfaces with low-pass capacitive ones, which can be synthesized by square patches. It is shown that higher frequencies are not influenced by these modifications. A thin wideband capacitive circuit absorber (CCA) is presented with 28% reduction of thickness and 57% increase of bandwidth in comparison to the Salisbury screen. It is also explained why some optimized metamaterial designs fail to compete with the CCA method. For high permittivity layers, it is shown that the CCA is a better solution than the Jaumann absorber and improvements both in thickness and bandwidth are possible. A three layered ultra wideband (4-24 GHz) CCA is presented with total thickness of 15.1 mm. Finally, a design capable of handling oblique angles of incidence for both polarizations and fulfilling different mechanical, thermal and fabrication constraints is given. The absorption band covers the entire C, X and Ku radar bands (4-18 GHz), showing significant improvement compared to the published circuit analog absorbers. (Less)

Compensation circuit for a tx-rx capacitive sensor

Abstract: A capacitive sensor may include a transmit electrode and a receive electrode capacitively coupled with the transmit electrode. A capacitance sensing circuit senses a capacitance between the transmit and receive electrodes by applying a signal to the transmit electrode and rectifying a current waveform induced at the receive electrode. A compensation circuit reduces the effect of a mutual and parasitic capacitances of the transmit and receive electrode pair by adding a compensation current to the rectified current.

Bistable nanowire for micromechanical memory

Abstract: We present a micromechanical device designed to be used as a non-volatile mechanical memory. The structure is composed of a suspended slender nanowire (width: 100 nm, thickness: 430 nm, length: 8 to 30 ?m) clamped at both ends. Electrodes are placed on each side of the nanowire to (1) actuate the structure during the data writing and erasing mode and (2) determine its position by measuring the capacitive bridge in the reading mode. The structure is patterned by electron beam lithography on a pre-stressed thermally grown silicon dioxide layer. When later released by plasma etching, the stressed material relaxes and the beam buckles by itself to a position of lower energy. These symmetric bistable Euler beams exhibit two stable deformed. This paper presents the microfabrication process and analysis of the static buckling of nanowires. Snapping of these nanowires from one stable position to another by mechanical or electrical means will also be discussed.

A GSM/EDGE/WCDMA Adaptive Series-LC Matching Network Using RF-MEMS Switches

Abstract: To preserve link quality of mobile phones, under fluctuating user conditions, an adaptively controlled series-LC matching circuit is presented for multi-band and multi-mode operation. Following a bottom-up approach, we discuss the design of an RF-MEMS unit cell for the construction of a 5-bit switched capacitor array. To reduce dielectric charging of the RF-MEMS devices their average biasing voltage is minimized by applying a bipolar waveform with a small high/low duty-cycle obtained from a high-voltage driver IC. RF-MEMS capacitive switches are applied because of their high linearity, low loss, large tuning range, and easy control in the discrete domain. Application specific RF-MEMS pull-in and pull-out voltage requirements are derived. An impedance phase detector is used to feed mismatch information to an up-down counter providing robust iterative control. The measured MEMS array capacitance tuning ratio is almost a factor 10. Module insertion loss is 0.5 dB at low-band and high-band. Harmonic distortion is less than -85ndBc at 35 dBm output power and the EVM, measured in EDGE-mode, is less than 1% at 27 dBm . The adaptively controlled module, connected to a planar inverted-F antenna, shows desired impedance correction. For extreme hand-effects the maximum module impedance correction at 900 MHz is -75jOmega.

Vibration damping with negative capacitance shunts: theory and experiment

Abstract: This paper analyzes in detail the enhancement of piezoelectric stack transducers by means of the well known 'negative' capacitive shunting. The stability is thoroughly studied: starting from the electrical admittance curve of the transducer, a method is introduced that quantifies the stability margins of the shunted structure. Two different implementations (series vs parallel) are investigated, and the lack of robustness of the parallel one is demonstrated. Next, this technique is experimentally applied on a truss structure. Its performances are compared with those of passive shunt circuits and with those of an active control law, the so-called Integral Force Feedback or IFF. As expected, the damping introduced by the negative capacitance shunt is larger than the damping obtained with the passive shunts; it remains, however, one order of magnitude smaller than that obtained with the IFF.

Capacitive extensometry for transient strain analysis of dielectric elastomer actuators

Abstract: Dielectric elastomer actuators (DEAs) are promising structural units for artificial muscles and robotic elements. Understanding the safe and failure mode regimes of such DEAs is essential for controlling the actuator. We develop an electrical characterization technique for obtaining information on the transient strain in the actuator and analyze the behavior of the actuator in safe and failure operation regimes, in particular in the pull-in instability mode. Additionally, the technique allows the strain-dependent measurement of the electrode resistance. The current measurement based technique can be also applied for actuator control with feedback loops.

A Monolithic CMOS-MEMS 3-Axis Accelerometer With a Low-Noise, Low-Power Dual-Chopper Amplifier

Abstract: This paper reports a monolithically integrated CMOS-MEMS three-axis capacitive accelerometer with a single proof mass. An improved DRIE post-CMOS MEMS process has been developed, which provides robust single-crystal silicon (SCS) structures in all three axes and greatly reduces undercut of comb fingers. The sensing electrodes are also composed of the thick SCS layer, resulting in high resolution and large sensing capacitance. Due to the high wiring flexibility provided by the fabrication process, fully differential capacitive sensing and common-centroid configurations are realized in all three axes. A low-noise, low- power dual-chopper amplifier is designed for each axis, which consumes only 1 mW power. With 44.5 dB on-chip amplification, the measured sensitivities of x-, y-, and z-axis accelerometers are 520 mV/g, 460 mV/g, and 320 mV/g, respectively, which can be tuned by simply changing the amplitude of the modulation signal. Accordingly, the overall noise floors of the x-, y-, and z-axis are 12 mug/radicHz , 14 mug/radicHz, and 110 mug/radicHz, respectively, when tested at around 200 Hz.

Use of capacitive and GPR techniques for the non-destructive evaluation of cover concrete

Abstract: Two non-destructive techniques, namely ground penetrating radar (GPR) and a more original approach based on capacitive measurement, have been considered in this research project that focuses on the evaluation of cover concrete moisture content. Following a numerical modeling step for the capacitive technique, the two methods were successfully compared during an experimental campaign conducted in the laboratory against several control test slabs.

Capacitive pressure sensor

Abstract: A capacitive pressure comprises a laminated arrangement with a first flexible, electrically insulating carrier film carrying a first capacitor electrode, a second flexible, electrically insulating carrier film carrying a second capacitor electrode and a flexible, electrically insulating spacer film sandwiched between the first and second carrier films. The spacer film has a through-hole or recess therein, with respect to which the first and second capacitor electrodes are arranged opposite one another, in such a way that the first and second electrodes are brought closer together by resilient bending of the first and/or second carrier film into the through-hole or recess under the action of a compressive force acting on the pressure sensor.

A Second-Order Dual X-/Ka-Band Frequency Selective Surface

Abstract: In this letter, a new technique for designing dual-band frequency selective surfaces with arbitrary bands of operation, with second-order band-pass responses at each band of operation, is presented and experimentally verified. The technique is based on utilizing a particular topology of a second-order band-pass microwave filter and synthesizing its constituting elements using periodic structures with inductive, capacitive, or resonant type surface impedances. The result is a low-profile planar structure composed of three metal and two dielectric layers that acts as a spatial version of the dual-band microwave filter.

Nanostructured Metal Oxide Thin Films for Humidity Sensors

Abstract: Capacitive humidity sensors were fabricated using countersunk interdigitated electrodes coated with amorphous nanostructured TiO2, SiO2, and Al2O3 thin films grown by glancing angle deposition. The capacitive response and response times for each sensor were measured. The sensor utilizing TiO2 exhibited the largest change in capacitance, increasing exponentially from ~ 1 nF to ~ 1muF for an increase in relative humidity from 2% to 92%. Adsorption and desorption response times were measured using flow rates of 2.5 l/min and were between 90 ms and 300 ms for the sensors studied here. A simple model of the capacitive response of the devices has been developed and used to calculate the dielectric constant of the combined system of our films and adsorbed water. The obtained dielectric constants are found to be much higher than bulk or literature values for similar systems.

Capacitive humidity sensors on flexible RFID labels

Abstract: Capacitive humidity sensors intended to be used with intelligent RFID tags have been produced from polymer foils and/or thin films. They were successfully tested on experimental platforms well reproducing the real operation conditions. Adequate sensing properties (enough sensitivity, good selectivity and linearity and reasonable response and recovery times) have been achieved. The main requirements for a good match to the target applications, that are also fulfilled, are discussed in connection with the readout options and other practical issues.

Noise reduction in capacitive touch sensors

Abstract: Noise reduction in a one- or two-dimensional capacitive sensor array is achieved by rejecting and re-acquiring noisy signals. The sensor array is formed of crossed X and Y lines for drive and sense functions respectively, each of the X lines being driven in turn to acquire a full frame of data from the sensor array. A controller actuates the X lines in turn and, for each X line, charge is transferred to charge measurement capacitors connected to respective ones of the Y lines. The controller measures a signal value from a first one of the measurement capacitors, and then tests if that Y signal value has a magnitude lying within an acceptable range. If not, the measurement capacitors are all reset without their signal values being measured, and the controller re-drives the same X line to initiate another charge transfer into the measurement capacitors for that X line. It is then attempted once again to acquire Y signal values for that X line. Noisy signal values are thus rejected, and the sensor re-acquires substitute signal values. This is distinct from the approach of acquiring data and then reprocessing it to remove or suppress noisy data as in the prior art.

Integrated touch sensor and solar assembly

Abstract: Integrated touch sensor and solar panel configurations that may be used on portable devices, particularly handheld portable devices such as a media player or phone are disclosed. The integrated touch sensor array and solar cell stack-ups may include electrodes that are used both for collecting solar energy and for sensing on a touch sensor array. By integrating both the touch sensors and the solar cell layers into the same stack-up, surface area on the portable device may be conserved. In addition to being used for capacitive sensing, the integrated touch sensor and solar panel configurations may also be used for optical sensing.

A capacitive vibration-to-electricity energy converter with integrated mechanical switches

Abstract: Due to recent advances in low-power VLSI design technology, it has become feasible to power portable or remote electronic devices by scavenging the ambient energy. The design, fabrication and measurement of a capacitive vibration-to-electricity energy converter are presented in this paper. With a device area constraint of 1 cm2 and an auxiliary battery supply of 3.6 V, the device was designed to generate an output power of 31 µW with an output saturation voltage of 40 V. An external mass of 4 g was needed to adjust the device resonance to match the input vibration of 2.25 m s−2 at 120 Hz. Mechanical contact switches were integrated onto the device to provide accurate charge–discharge energy conversion timing. The device was fabricated in SOI (silicon-on-insulator) wafers by deep silicon etching technology. Parasitic capacitance was minimized by partial back side substrate removal. Resonant frequencies of the fabricated device with and without the external mass agreed with the expected values. Without the external mass, the measured ac output power was 1.2 µW with a load of 5 MΩ at 1870 Hz. Detailed circuit modeling and ac output power measurement of the devices with the external mass attached are in progress.

Dual-Band Capacitive Loaded Frequency Selective Surfaces With Close Band Spacing

Abstract: In this letter, a novel miniaturized dual-band capacitive loaded frequency selective surface (FSS) is presented, in which each periodic cell consist of two neighboring capacitive loaded ring slot resonator with the same dimension. To eliminate the undesired coupling between unit cells, the unit cell is placed in a Faraday cage structure created by arrays of metallic substrate vias. An S-band dual-band FSS with such structures is designed and fabricated, both simulated and measured results show that the proposed FSS provides high transmission with close band spacing at 2.5 and 3.5 GHz, and there is no other resonance frequency up to 15 GHz. Furthermore, the FSS dimension is miniaturized to 0.082 lambda (lambda refer to the resonant wavelength of 2.5 GHz). Also, it is not sensitive to the angle of oblique incidence wave. The design and discussion about dual-band FSS loading with lumped elements is presented for the first time.

A silicon carbide capacitive pressure sensor for in-cylinder pressure measurement

Abstract: This paper reports a research prototype of a low-cost, miniature, mass-producible sensor for measurement of high-pressure at operating temperatures of 300–600 °C, e.g., in-cylinder engine pressure monitoring applications. This all-silicon carbide (SiC) capacitive sensor, i.e., a SiC diaphragm on a SiC substrate, takes advantage of the excellent harsh-environment material properties of SiC and is fabricated by surface micromachining. The sensor is packaged in a high-temperature ceramic package and characterized under static pressures of up to ∼5 MPa (700 psi) and temperatures of up to 574 °C in a custom chamber. An instrumentation amplifier integrated circuit is used to convert capacitance into voltage for measurements up to 300 °C; beyond 300 °C, the capacitance is measured directly from an array of identical sensor elements using a LCZ meter. After high-temperature soaking and several tens of temperature/pressure cycles, packaged sensors continue to show stable operation. For monitoring the dynamic cylinder pressure in the combustion chamber, the sensor is packaged in a custom probe and inserted into the cylinder head of a research internal combustion engine. The sensor efficacy is verified against the reference probe used for monitoring pressure in the research engine.

The effects of nonlinear series resonance on Ohmic and stochastic heating in capacitive discharges

Abstract: The flow of electron and ion conduction currents across a nonlinear capacitive sheath to the electrode surface self-consistently sets the dc bias voltage across the sheath. We incorporate these currents into a model of a homogeneous capacitive sheath in order to determine the enhancement of the Ohmic and stochastic heating due to self-excitation of the nonlinear series resonance in an asymmetric capacitive discharge. At lower pressures, the series resonance can enhance both the Ohmic and stochastic heating by factors of 2–4, with the Ohmic heating tending to zero as the pressure decreases. The model was checked, for a particular set of parameters, by a particle-in-cell (PIC) simulation using the homogeneous sheath approximation, giving good agreement. With a self-consistent Child-law sheath, the PIC simulation showed increased heating, as expected, whether the series resonance is important or not.

A Compact Angular Rate Sensor System Using a Fully Decoupled Silicon-on-Glass MEMS Gyroscope

Abstract: This paper presents the development of a compact single-axis angular rate sensor system employing a 100- mum-thick single-crystal silicon microelectromechanical systems gyroscope with an improved decoupling arrangement between the drive and sense modes. The improved decoupling arrangement of the gyroscope enhances the robustness of sensing frame against drive-mode oscillations and therefore minimizes mechanical crosstalk between the drive and sense modes, yielding a small bias instability. The gyroscope core element is fabricated by through-etching a 100-mum -thick silicon substrate which is anodically bonded to a recessed glass handling substrate. A patterned metal layer is included at the bottom of the silicon substrate, both as an etch-stop layer and a heat sink to prevent heating- and notching-based structural deformations encountered in deep dry etching in the silicon-on-glass process. The fabricated-gyroscope core element has capacitive actuation/sensing gaps of about 5 mum yielding an aspect ratio close to 20, providing a large differential sense capacitance of 18.2 pF in a relatively small footprint of 4.6 mm times 4.2 mm. Excitation and sensing electronics of the gyroscope are constructed using off-the-shelf integrated circuits and fit in a compact printed circuit board of size 54 mm times 24 mm. The complete angular rate sensor system is characterized in a vacuum ambient at a pressure of 5 mtorr and demonstrates a turn-on bias of less than 0.1 deg/s, bias instability of 14.3 deg/h, angle random walk better than 0.115 deg/radic(h), and a scale-factor nonlinearity of plusmn0.6% in full-scale range of plusmn50 deg/s. [2007-0158].

A multichannel portable ECG system with capacitive sensors.

Abstract: Capacitive sensors can be employed for measuring the electrocardiogram of a human heart without electric contact with the skin. This configuration avoids contact problems experienced by conventional electrocardiography. In our studies, we integrated these capacitive electrocardiogram electrodes in a 15-sensor array and combined this array with a tablet personal computer. By placing the system on the patient's body, we can measure a 15-channel electrocardiogram even through clothes and without any preparation. The goal of this development is to provide a new diagnostic tool that offers the user a reproducible, easy access to a fast and spatially resolved diagnostic 'heart view'.

Method to distinguish ferroelectric from nonferroelectric origin in case of resistive switching in ferroelectric capacitors

Abstract: We present investigations on the resistive switching effect in SrRuO3∕PbZr0.2Ti0.8O3∕Pt ferroelectric capacitors. Using a conductive atomic force microscope, the out-of-plane piezoelectric response and the capacitive and resistive current were simultaneously measured as a function of applied bias voltage. We observed two independent switching phenomena, one attributed to the ferroelectric switching process and the other to resistive switching.We show that I-V curves alone are not sufficient in ferroelectric materials to clarify the underlying switching mechanism and must be used with sufficient caution.

Passive stylus for capacitive sensors

Abstract: A passive stylus for capacitive sensors comprises a tip and a shaft. The tip is configured to couple electrically with a capacitive sensing device and to couple physically and electrically with the stylus shaft. The tip comprises a contact surface, a support region, and a flexible region. The contact surface is configured to contact a device surface associated with the capacitive sensing device. The flexible region is disposed between the contact surface and the support region. The flexible region comprises a hardness gradient. The support region is configured to provide structural support to the flexible region.

Capacitive sensing and communicating

Abstract: A device (100) which is placeable on or close to a human or animal body has at least a sensing unit (105) configured to capacitively sense a physiological signal from the human or animal body and capacitively communicate a body coupled communication signal. As sensing and body coupled communication capabilities can be provided by a single sensing unit, disadvantages of previous solutions for sensing and communicating like e.g. clutter of wires or increased costs and power consumption due to extra communication hardware can be alleviated.