Showing papers on "Capacitive sensing published in 2009"

Rational design of high-responsivity detectors of terahertz radiation based on distributed self-mixing in silicon field-effect transistors

Abstract: In search of novel detectors of electromagnetic radiation at terahertz frequencies, field-effect transistors (FETs) have recently gained much attention. The current literature studies them with respect to the excitation of plasma waves in the two-dimensional channel. Circuit aspects have been taken into account only to a limited degree. In this paper, we focus on embedding silicon FETs in a proper circuitry to optimize their responsivity to terahertz radiation. This includes impedance-matched antenna coupling and amplification of the rectified signal. Special attention is given to the investigation of high-frequency short-circuiting of the gate and drain contacts by a capacitive shunt, a common approach of high-frequency electronics to induce resistive mixing in transistors. We theoretically study the effect of shunting in the framework of the Dyakonov–Shur plasma-wave theory, with the following key results. In the quasistatic limit, the capacitive shunt induces the longitudinal high-frequency field neede...

A Multifunctional Capacitive Sensor for Stretchable Electronic Skins

Abstract: We present a stretchable and multifunctional capacitive sensor made of gold thin films embedded in silicone rubber. The mechanical compliance of the gold films and silicone membranes allow the device to be bent, folded, or stretched without damage, making it a suitable candidate for electronic skin applications. The device can detect strains up to 20%, human touch, and pressure up to 160 kPa, and reliably function when it is held stretched or relaxed.

Capacitive control panel

Abstract: A control panel for proximity and force sensing, includes a cover layer, a first electrode layer including a first force sensor electrode, a second force sensor electrode positioned in a second electrode layer or on a support layer, and a dielectric substrate at least a portion of which is compressible and is positioned between the first and second force sensor electrodes. The support layer is positioned to support at the vicinity of the second force sensor electrode support location so that compression of the dielectric substrate and the separation of the first and second force sensor electrodes depends on the magnitude of a force applied to the cover layer. Touch sensor electrodes are positioned on one or more of the electrode layers such that their capacitance depends on proximity of an object such as a finger. Controllers measure the capacitance of the force and touch sensor electrodes respectively and output force and touch proximity signals.

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 ultrawideband CCA is presented with total thickness of 15.1 mm.

Dual-Mode Capacitive Proximity Sensor for Robot Application: Implementation of Tactile and Proximity Sensing Capability on a Single Polymer Platform Using Shared Electrodes

Abstract: In this paper, we report a flexible dual-mode capacitive sensor for robot applications which has two sensing capabilities in a single platform; tactile and proximity sensing capability. The sensor consists of a mechanical structure based on PDMS (Polydimethylsiloxane) and a mesh of multiple copper electrode strips. The mesh is composed of 16 top and 16 bottom copper strips crossed each other to form a 16 times 16 capacitor array. The proposed sensor is able to switch its function from tactile sensing to proximity sensing or vice versa by reconfiguring the connection of electrodes. The tactile sensing capability has been demonstrated already and reported in our previous paper (Lee et al.,, 2006); therefore, in this paper, we will demonstrate the feasibility of the proximity sensing capability and the dual-mode operation of the proposed sensor in detail. The capacitance change caused by an approaching object has been estimated through simulation of multiple two-dimensional models as an initial study. The measured data have shown similar trends with the simulation results. We tested various materials from conducting metals to a human hand for proximity measurement. The fabricated sensor could detect a human hand at a distance up to 17 cm away from the sensor. We also have successfully demonstrated the feasibility of dual-mode operation of the proposed sensor in real-time exploiting a custom designed PCB, a data acquisition pad, and Labview software.

Capacitive sensing device for use in a keypad assembly

Abstract: One embodiment in accordance with the present invention includes a capacitive sensing device for use in a keypad assembly of an electronic system. The capacitive sensing device includes a substantially transparent single sheet capacitive sensor. The substantially transparent single sheet capacitive sensor is configured to be disposed within the keypad assembly without requiring the formation of key post holes therethrough. Additionally, the substantially transparent single sheet capacitive sensor has a flexibility which enables desired tactile response during use of keys of the keypad assembly.

Assembly of a capacitive acoustic transducer of the microelectromechanical type and package thereof

Abstract: A microelectromechanical-acoustic-transducer assembly has: a first die integrating a MEMS sensing structure having a membrane, which has a first surface in fluid communication with a front chamber and a second surface, opposite to the first surface, in fluid communication with a back chamber of the microelectromechanical acoustic transducer, is able to undergo deformation as a function of incident acoustic-pressure waves, and faces a rigid electrode so as to form a variable-capacitance capacitor; a second die, integrating an electronic reading circuit operatively coupled to the MEMS sensing structure and supplying an electrical output signal as a function of the capacitive variation; and a package, housing the first die and the second die and having a base substrate with external electrical contacts. The first and second dice are stacked in the package and directly connected together mechanically and electrically; the package delimits at least one of the front and back chambers.

Resonant Magnetic Field Sensors Based On MEMS Technology.

Abstract: Microelectromechanical systems (MEMS) technology allows the integration of magnetic field sensors with electronic components, which presents important advantages such as small size, light weight, minimum power consumption, low cost, better sensitivity and high resolution. We present a discussion and review of resonant magnetic field sensors based on MEMS technology. In practice, these sensors exploit the Lorentz force in order to detect external magnetic fields through the displacement of resonant structures, which are measured with optical, capacitive, and piezoresistive sensing techniques. From these, the optical sensing presents immunity to electromagnetic interference (EMI) and reduces the read-out electronic complexity. Moreover, piezoresistive sensing requires an easy fabrication process as well as a standard packaging. A description of the operation mechanisms, advantages and drawbacks of each sensor is considered. MEMS magnetic field sensors are a potential alternative for numerous applications, including the automotive industry, military, medical, telecommunications, oceanographic, spatial, and environment science. In addition, future markets will need the development of several sensors on a single chip for measuring different parameters such as the magnetic field, pressure, temperature and acceleration.

Small-Signal Model-Based Control Strategy for Balancing Individual DC Capacitor Voltages in Cascade Multilevel Inverter-Based STATCOM

Abstract: This paper presents a new feedback control strategy for balancing individual DC capacitor voltages in a three-phase cascade multilevel inverter-based static synchronous compensator. The design of the control strategy is based on the detailed small-signal model. The key part of the proposed controller is a compensator to cancel the variation parts in the model. The controller can balance individual DC capacitor voltages when H-bridges run with different switching patterns and have parameter variations. It has two advantages: 1) the controller can work well in all operation modes (the capacitive mode, the inductive mode, and the standby mode) and 2) the impact of the individual DC voltage controller on the voltage quality is small. Simulation results and experimental results verify the performance of the controller.

Temperature, humidity and gas sensors integrated on plastic foil for low power applications

Abstract: Temperature, gas and humidity resistive/capacitive sensors on plastic substrates, suitable for mobile applications, like smart RFID tags, have been produced and investigated. The sensor concept is providing simple, versatile and low power solutions for temperature, humidity and gas detection. The device structure was devised together with the data evaluation strategies based on the latest generation ΣΔ analog (resistance and capacitance) to digital converters. The possibility of developing gas sensors on humidity sensitive substrates, having temperature corrected responses is demonstrated. The proposed sensor is aimed to evolve towards “flexible and full plastic” implementations.

Capacitive humidity sensor design based on anodic aluminum oxide

Abstract: Capacitive humidity sensors based on anodic aluminum oxide (AAO), a material used as a sensing layer for high sensitivity, were investigated. The AAO film has many nanosized pores, giving it a large surface area for absorbing water vapor. Effects of design factors and heating were investigated. A thick porous layer or big pore diameter increases sensitivity because of increase in contact surface area. An electrode of rectangular spiral-shaped type tends to have a slightly higher hysteresis than the interdigitated type, but the rectangular spiral-shaped type is efficient and sensitive if the hysteresis and nonlinearity are reduced by controlling design factors or heating. Although heating reduced the sensitivity, it improved performance parameters such as nonlinearity, hysteresis, response time and temperature dependence. Also, a porous electrode would show a higher sensitivity than a nonporous electrode because of the larger surface area.

Single sided capacitive force sensor for electronic devices

Abstract: A capacitive force sensor (100) includes a substrate (101) having at least one electrode pair (102,103) defining a capacitance disposed thereon. The substrate (101) is fixed relative to a first plate (106). A drive circuit (104) is configured to apply a voltage relative to a circuit ground (105) to the electrode pair (102,103). The first plate (106) is separated from a second plate (107) that is coupled to circuit ground (105) by a compliance member (108,109). The compliance member (108,109) is configured to oppose a compression force (110) while allowing the first plate (106) to physically move relative to the second plate (107). A capacitive detection circuit (111) is then configured to detect a change the capacitance when the compliance member (108,109) is compressed. The compression force (110) is then determined from the change in capacitance and the spring constant of the compliance member (108,109).

A flexible capacitive tactile sensing array with floating electrodes

Abstract: In this work, we present the development of a capacitive tactile sensing array realized by using MEMS fabrication techniques and flexible printed circuit board (FPCB) technologies. The sensing array, which consists of two micromachined polydimethlysiloxane (PDMS) structures and a FPCB, will be used as the artificial skin for robot applications. Each capacitive sensing element comprises two sensing electrodes and a common floating electrode. The sensing electrodes and the metal interconnect for signal scanning are implemented on the FPCB, while the floating electrode is patterned on one of the PDMS structures. This special design can effectively reduce the complexity of the device structure and thus makes the device highly manufacturable. The characteristics of the devices with different dimensions are measured and discussed. The corresponding scanning circuits are also designed and implemented. The tactile images induced by the PMMA stamps of different shapes are also successfully captured by a fabricated 8 × 8 array.

Input detection system for a portable electronic device

Abstract: A proximity input detection system for an electronic device. In one embodiment, the present invention utilizes an inductive field sensor to detect a change in a magnetic field when an input device with a coil is within a threshold distance. In another embodiment, the present invention utilizes a capacitive sensor which can locate the position of an electrically conductive object which is within a threshold distance. The capacitive sensor can also be used, for example, as a switch to activate the device if a user picks it up. The present invention allows user inputs to be detected without actually touching the electronic device. The present invention can also be used to detect inputs through intervening non-metallic layers such as a protective cover or another display of the device without using additional input sensors.

A Novel Level Measurement Technique Using Three Capacitive Sensors for Liquids

Abstract: The liquid level in a tank should be measured for most applications. In this paper, a new capacitive method is presented to detect the liquid level. Existing methods are generally approximations based on the large difference between the dielectric constants of the liquids and the air. The method proposed here eliminates the effect of air and gives the accurate reading of the liquid level in the tank. The main advantage of the method is that it can directly be applied to any kind of nonconductive liquid without calibration. The method is based on the measurements of capacitances of three parallel plate capacitive structures, which are designated as level, reference, and air sensors. It is mathematically proven that the method completely eliminates different factors, which affect the readings, such as air and temperature. The capacitance measurements are performed using a capacitance-to-digital converter integrated circuit, which can measure very small capacitances up to plusmn4 fF error. The result of a computer simulation, which demonstrates the performance and limitations of the proposed structure, is also provided.

Textile-Based Capacitive Sensors for Respiration Monitoring

Abstract: Respiration monitoring in everyday life enables the early detection of the diseases and disorders that can suddenly manifest in a life threatening episode. Long-term monitoring can extend the capabilities of healthcare providers if reliability can be achieved economically. In this paper, the potential for using capacitive sensing to serve as an inexpensive method for long-term respiration sensing is explored. This paper proposes new designs of capacitive sensors for respiration sensing and describes the design and fabrication of a prototype textile-based capacitive-sensor respiration belt. Two capacitive sensors were designed and fabricated for detecting chest or abdominal circumference changes of up to 60 mm. These sensors gave good linearity, and the respiration measurements obtained with these new sensors show that they are capable of measuring respiration rate, and possibly lung function parameters.

A Capacitive Humidity Sensor Based on Multi-Wall Carbon Nanotubes (MWCNTs).

Abstract: A new type of capacitive humidity sensor is introduced in this paper. The sensor consists of two plate electrodes coated with MWCNT films and four pieces of isolating medium at the four corners of the sensor. According to capillary condensation, the capacitance signal of the sensor is sensitive to relative humidity (RH), which could be transformed to voltage signal by a capacitance to voltage converter circuit. The sensor is tested using different saturated saline solutions at the ambient temperature of 25 °C, which yielded approximately 11% to 97% RH, respectively. The function of the MWCNT films, the effect of electrode distance, the temperature character and the repeatability of the sensor are discussed in this paper.

Parasitic feedthrough cancellation techniques for enhanced electrical characterization of electrostatic microresonators

Abstract: Capacitive parasitic feedthrough is an impediment that is inherent to all electrically interfaced micron scale resonant devices, resulting in increased challenges to their integration in more complex circuits, particularly as devices are scaled to operate at higher frequencies for RF applications. In this paper, a technique to cancel the undesirable effects of capacitive feedthrough that was previously proposed is here developed for an on-chip implementation. The method reported in this paper benefits from the simplicity of its implementation, and its effectiveness is demonstrated in this paper. This technique is demonstrated for two disk-plate resonators that have been excited in the wine glass mode at 5.4 MHz, though applicable to almost any electrically interfaced resonator. Measurements of the electrical transmission from these resonators show that the magnitude of the frequency response of the system is enhanced by up to 19 dB, while the phase is found to shift through a full 180° about the resonant frequency. This method is proposed as a useful addition to other techniques for enhancing the measured response of electrostatic micromechanical resonators.

Touch sensor panels with reduced static capacitance

Abstract: Capacitive touch panels may include a plurality of positive voltage lines that are driven at a first phase. These positive voltage lines may be used to provide the drive capacitance signal sensed by one or more sense regions. The touch panels may also include a plurality of negative phase voltage lines that are driven at a phase that is different than the first phase. Both the positive and negative voltage lines may cross-under one or more sense regions. The negative phase voltage lines are able to counter act and reduce the static capacitance in the sense regions.

Input device with capacitive force sensor and method for constructing the same

Abstract: Input devices which include a capacitive force sensor, along with methods of making and using such, are provided. The input device includes a structural component having first and second substantially opposing sides, a plurality of sensor electrodes located on the first side of the structural component, the plurality of sensor electrodes configured to capacitively sense positional information associated with user input in a sensing region, a first capacitive electrode located on the second side of the structural component, the first capacitive electrode being configured to capacitively couple to a second capacitive electrode that is separated from the first capacitive electrode by a gas and moveable relative to the first capacitive electrode, and a biasing member configured to be physically coupled to the structural component such that a force associated with the user input causes a change in a separation distance between the first and second capacitive electrodes based on the force.

A capacitive touch interface for passive RFID tags

Abstract: This paper presents a novel method for incorporating a capacitive touch interface into existing passive RFID tag architectures without additional parts or changes to the manufacturing process. Our approach employs the tag's antenna as a dual function element in which the antenna simultaneously acts as both a low-frequency capacitive fringing electric field sensor and also as an RF antenna. To demonstrate the feasibility of our approach, we have prototyped a passive UHF tag with capacitive sensing capability integrated into the antenna port using the WISP tag. Finally, we describe how this technology can be used for touch interfaces as well as other applications with the addition of a LED for user feedback.

Repetitive High-Voltage Solid-State Marx Modulator Design for Various Load Conditions

Abstract: The analysis of a solid-state Marx modulator (S2M2) topology, which have been developed for repetitive high-voltage (in kilovolts) applications, needing positive or negative rectangular pulses, is presented. The proposed topology benefits from the intensive use of semiconductors, allowing kilohertz operation with different load conditions. In addition to resistive loads, capacitive loads can be discharged to ground after each pulse and inductive loads can be clamped and the energy recovered to the main capacitors. Furthermore, the presented topology and proposed switching sequence enables the use of typical half-bridge semiconductor structures currently integrated in modular packages, which is advantageous for circuit assembling and triggering the semiconductors. Discussion on the advantages and limitation will be given. Finally, experimental results of some modulator features will be presented.

Design and optimization of an ultra thin flexible capacitive humidity sensor

Abstract: In this paper we present the design and fabrication of a humidity sensor on ultra thin (8 μm) flexible polyimide substrate. The ultra thin flexible substrate can be preserved also when a read-out electronic interface is integrated by using Polycrystalline Silicon Thin Film Transistors technology. The sensor device is a capacitor where a thin layer of [bis(benzo cyclobutene)] is used as a dielectric sensitive material between two metal electrodes. The electrode layout has been designed with the aid of numerical simulations in order to optimize the sensor performances. The fabricated sensor has shown sensitivity to relative humidity of 0.38%/RH% and a linearity of 0.996 in the range of 10–90 RH%. Furthermore, measurements regarding the sensor response time, different bending and bias voltage effects have been performed.

Fabricating capacitive micromachined ultrasonic transducers with a novel silicon-nitride-Based wafer bonding process

Abstract: We report the fabrication and experimental testing of 1-D 23-element capacitive micromachined ultrasonic transducer (CMUT) arrays that have been fabricated using a novel wafer-bonding process whereby the membrane and the insulation layer are both silicon nitride. The membrane and cell cavities are deposited and patterned on separate wafers and fusion-bonded in a vacuum environment to create CMUT cells. A user-grown silicon-nitride membrane layer avoids the need for expensive silicon-on-insulator (SOI) wafers, reduces parasitic capacitance, and reduces dielectric charging. It allows more freedom in selecting the membrane thickness while also providing the benefits of wafer-bonding fabrication such as excellent fill factor, ease of vacuum sealing, and a simplified fabrication process when compared with the more standard sacrificial release process. The devices fabricated have a cell diameter of 22 mum, a membrane thickness of 400 nm, a gap depth of 150 nm, and an insulation thickness of 250 nm. The resonant frequency of the CMUT in air is 17 MHz and has an attenuation compensated center frequency of ~9 MHz in immersion with a -6 dB fractional bandwidth of 123%. This paper presents the fabrication process and some characterization results.

Methods and apparatuses to test the functionality of capacitive sensors

Abstract: Some embodiments include apparatus and methods to test a device having a driving layer and a sensing layer. A test signal is applied to electrodes of the driving layer in a capacitive load state, with a capacitive load applied, and in an ambient state, without a capacitive load applied. Measured values are obtained at the sensing layer for each state. The measured values are compared with threshold values. A report is generated when a measured value violates a threshold. In one embodiment, the driving layer and the sensing layer form multiple capacitive electrodes within a touch sensor. The measured values are related to mutual capacitance values of the touch sensor.

Interfacing Differential Capacitive Sensors to Microcontrollers: A Direct Approach

Abstract: This paper is a continuation of a previous work with regard to the direct connection of differential sensors to microcontrollers without using intermediate electronics between them. This paper focuses on the measurement of differential capacitive sensors, whereas the previous work dealt with the resistive counterparts. The proposed circuit is analyzed, and the main limitation seems to be the fact that the magnitude of the input parasitic capacitances of the microcontroller is similar to or even higher than the sensor capacitances. Methods to overcome this limitation are proposed, particularly when measuring low-value differential capacitive sensors such as microelectromechanical system (MEMS) sensors. Experimental tests of the circuit have been carried out by measuring a commercial capacitive accelerometer working as a tilt sensor. Although such a sensor has a low value (1.5 pF) and low sensitivity (0.105 pF/g), the measurement has shown a nonlinearity error of 1% full-scale span (FSS), which is a remarkable value considering the simplicity of the circuit.

Capacitive Sensor Gloves

Abstract: A glove usable to activate a capacitive touch screen comprises a body configured to cover the palm and back of the hand and a plurality of finger sheaths configured to cover the fingers and thumb. An electrically conductive material is disposed preferably at the tip of at least one of the finger sheaths. The conductive material may be a thin sheet of conductive material, a disc of conductive material, or a fibrous conducting material woven into the fabric of the finger sheath. When the tip of the finger sheath is brought toward contact with a capacitive touch screen, the electrically conducting material effects the touch screen in a manner similar to the tip of a bear fingertip to cause the touch screen to recognize the gloved touch.

Successive approximation a/d converter

Abstract: A successive approximation A/D converter, has a main DAC having a capacitive element group coupled to a top node and a switch group; a comparator comparing voltage of the top node with comparison reference voltage; a correction DAC generating correction voltage in accordance with a capacitance error of a capacitive element pair to be balanced in the main DAC, and supplying the correction voltage to the top node; and a control circuit generating internal digital input for controlling the switch group and a correction code for controlling the correction voltage, and outputting a successive approximation result by the comparator when the A/D conversion is performed. The control circuit measures a capacitance error of the capacitive element pair to be balanced, and determines an offset-removed capacitance error where an offset generated in the measurement is removed from the capacitance error.