Showing papers on "Capacitive sensing published in 2011"

Capacitive power transfer for contactless charging

Abstract: The simplicity and low cost of capacitive interfaces makes them very attractive for wireless charging stations. Major benefits include low electromagnetic radiation and the amenability of combined power and data transfer over the same interface. We present a capacitive power transfer circuit using series resonance that enables efficient high frequency, moderate voltage operation through soft-switching. An included analysis predicts fundamental limitations on the maximum achievable efficiency for a given amount of coupling capacitance and is used to find the optimum circuit component values and operating point. Automatic tuning loops ensure the circuit operates at the optimum frequency and maximum efficiency over a wide range of coupling capacitance and load conditions. An example interface achieves near 80% efficiency at 3.7 W with only 63pF of coupling capacitance. An automatic tuning loop adjusts the frequency from 4.2 MHz down to 4MHz to allow for 25% variation in the nominal coupling capacitance. The duty cycle is also automatically adjusted to maintain over 70% efficiency for light loads down to 0.3 W.

Capacitive tactile sensor array for touch screen application

Abstract: In this paper, we propose and demonstrate a transparent and flexible capacitive tactile sensor which is designed for multi-touch screen application with force sensing. A sensor module is composed of 2D array tactile cells with a spatial resolution of 2 mm to measure the touch force at multiple positions. The device is fabricated by using transparent materials on a transparent plastic substrate. The optical transmittance of the fabricated tactile sensor is approximately 86% in the visible wavelength region, and the maximum bending radius is approximately 30 mm. The cell size is 1 mm × 1 mm, and the initial capacitance of each cell is approximately 900 fF. The tactile response of a cell is measured with a commercial force gauge having a resolution of 1 mN. The sensitivity of a cell is 4%/mN within the full scale range of 0.3 N.

Terahertz responsivity of field effect transistors versus their static channel conductivity and loading effects

Abstract: We study the broadband photovoltaic response of field effect transistors on terahertz radiation. A simple physical analytical model of the response is developed. It is based on plasma density perturbation in the transistor channel by the incoming terahertz radiation. The model shows how the non-resonant detection signal is related to static (dc) transistor characteristics. We analyze loading effects related to capacitive, inductive, and resistive coupling of the detector to the read-out circuit as a function of modulation frequencies and loading resistors. As we show, the proposed physical model completed by loading effects fully describes the experimental results on the non-resonant sub-terahertz detection by all studied III-V (GaAs, GaN) and silicon based transistors. Field effect transistors were recently proposed as the best terahertz detecting pixels for fabrication of low cost focal plane arrays for terahertz imaging. This article gives prospects for electrical simulation of these transistors and their optimal integration in the focal plane arrays.

Detection of microdroplet size and speed using capacitive sensors

Abstract: a b s t r a c t Detection of the presence, size and speed of microdroplets in microfluidic devices is presented using commercially available capacitive sensors which make the droplet based microfluidic systems scalable and inexpensive. Cross-contamination between the droplets is eliminated by introducing a passivation layer between the sensing electrodes and droplets. A simple T-junction generator is used to generate droplets in microchannels. Coplanar electrodes are used to form a capacitance through the microfluidic channel. The change in capacitance due to the presence of a droplet in the sensing area is detected and used to determine the size and speed of the droplet. The design of a single pair of electrodes is used to detect the presence of a droplet and the interdigital finger design is used to detect the size and speed of the droplet. An analytical model is developed to predict the detection signal and guide the experimental optimization of the sensor geometry. The measured droplet information is displayed through a Labview interface in real-time. The use of capacitance sensors to monitor droplet sorting at a T-junction is also presented. The discussions in this paper can be generalized to any droplet detection application and can serve as a guideline in sensor selection.

Gas sensors based on gravimetric detection—A review

Abstract: These last 10 years, smaller, less expensive, and higher performance sensors are required for gas sensing applications. To date no true detection principle has been recognized as the best candidate for such application. Microsytems or Micro/Nano Electro Mechanical Systems (M/NEMS) used as gravimetric detectors are among the probable candidates. The technology can indeed be manufactured en masse and can provide multi-gas analysing platform. In this paper, we present a comprehensive overview of micro/nano sensors based on the gravimetric effect to detect an absorbed gas on top of their surfaces. The paper provides a comparison between different electromechanical devices (Bulk Acoustic Wave, Surface Acoustic Wave, Capacitive Micro-machined Ultrasonic Transducer, Micro/Nano cantilevers) with an introduction to gas adsorption mechanisms, material selection, detection principles and design guidance useful to researchers or engineers.

Real-time measurement of the three-axis contact force distribution using a flexible capacitive polymer tactile sensor

Abstract: In this paper, we report real-time measurement results of various contact forces exerted on a new flexible capacitive three-axis tactile sensor array based on polydimethylsiloxane (PDMS). A unit sensor consists of two thick PDMS layers with embedded copper electrodes, a spacer layer, an insulation layer and a bump layer. There are four capacitors in a unit sensor to decompose a contact force into its normal and shear components. They are separated by a wall-type spacer to improve the mechanical response time. Four capacitors are arranged in a square form. The whole sensor is an 8 × 8 array of unit sensors and each unit sensor responds to forces in all three axes. Measurement results show that the full-scale range of detectable force is around 0‐20 mN (250 kPa) for all three axes. The estimated sensitivities of a unit sensor with the current setup are 1.3, 1.2 and 1.2%/mN for the x-, y- and z-axes, respectively. A simple mechanical model has been established to calculate each axial force component from the measured capacitance value. Normal and shear force distribution images are captured from the fabricated sensor using a real-time measurement system. The mechanical response time of a unit sensor has been estimated to be less than 160 ms. The flexibility of the sensor has also been demonstrated by operating the sensor on a curved surface of 4 mm radius of curvature. (Some figures in this article are in colour only in the electronic version)

Touch detection techniques for capacitive touch sense systems

Abstract: A technique for recognizing and rejecting false activation events related to a capacitance sense interface includes measuring a capacitance value of a capacitance sense element. The measured capacitance value is analyzed to determine a baseline capacitance value for the capacitance sensor. The capacitance sense interface monitors a rate of change of the measured capacitance values and rejects an activation of the capacitance sense element as a non-touch event when the rate of change of the measured capacitance values have a magnitude greater than a threshold level, indicative of a maximum rate of change of a touch event.

Inductive and capacitive excitation of the characteristic modes of small terminals

Abstract: In this paper we present concepts for the selective excitation of orthogonal modes of small terminals by inductive and capacitive coupling elements. The concepts can be used to implement an efficient MIMO (Multiple Input Multiple Output) antenna system based on the TCM (Theory of Characteristic Modes). Both coupling concepts are discussed with respect to their ability to excite specific modes separately. An important result obtained is that inductive couplers offer advantages over capacitive couplers in exciting the desired modes purely even when they are not close to their modal resonance.

Capacitive stylus for a touch screen

Abstract: A system comprising a sensing device and a capacitive sense array configured to track the position of a stylus and synchronize the capacitive sense array to the stylus transmit signal. The system is configured to track the position of both a stylus and a passive touch object. The system is further configured to track the position of the stylus using self capacitance sensing and track the position of the passive touch object using mutual capacitance sensing. The system further configured to modulate the stylus transmit signal to include additional data to support additional stylus functions.

In situ growth of continuous thin metal–organic framework film for capacitive humidity sensing

Abstract: A large-scale continuous thin film of Cu3(BTC)2 on polished Cu slice is prepared through a method of homogenous nucleation. The film shows high phase purity and homogeneity and can be set up for capacitive humidity sensing. As a sensor, the MOF film shows good capacitive humidity sensor properties.

Synchronizing a stylus with a capacitive sense array

Abstract: A system and method for tracking a stylus on a capacitive sense array. The system comprising the capacitive sense array configured to detect a presence of the stylus, a processing device to generate a synchronization signal, and a transmitter to transmit the synchronization signal to the stylus to synchronize the stylus to the capacitive sense array. The system further comprises a magnetic antenna configured to inductively transmit the synchronization signal to the stylus, wherein the magnetic antenna is disposed around the outer edges of the capacitance sense array, according to an embodiment of the invention.

Force and true capacitive touch measurement techniques for capacitive touch sensors

Abstract: Methods, systems, and apparatus relate to touch sensors that are configured to measure a true capacitive touch and a force applied to the sensor from a user. Some implementations involve the measurement of force and true capacitive touch simultaneously in a touch capacitive sensor.

Electric-Field Intrabody Communication Channel Modeling With Finite-Element Method

Abstract: Electric-field intrabody communication (EF-IBC) is a promising new scheme for the data exchange among wearable biomedical sensors. It uses the body as the signal transmission media. Compared with existing body area network (BAN) schemes, EF-IBC can achieve higher data rate with less transmission power. Until now, the detailed EF-IBC channel mechanism is not well understood. In this work, finite-element method (FEM) is utilized for the first time to investigate the EF-IBC channel. A circuit-coupled FEM model is established for the EF-IBC channel. The FEM model is extensively verified by experimental measurements. The new physical model enables the revelation of characteristics and effects of different components in the EF-IBC channel. The FEM investigation finds that the capacitive return path is critical to the characteristics of the EF-IBC channel. Parameters of the capacitive return path are quantitatively measured. The investigation also finds that the body plays an important role to the return path capacitance. The forward body path can be well modeled by a cascade of π-shaped circuits. Based on the FEM model of the EF-IBC channel, a simplified circuit model is derived to provide an efficient tool for the transceiver design.

Capacitive touch system using both self and mutual capacitance

Abstract: Systems and methods for determining multiple touch events in a multi-touch sensor system are provided. The system may have a touch sensor including nodes defined by a plurality of electrodes, which may comprise a first and second set. The method may include measuring self capacitance for at least two electrodes, detecting a touched electrode, and measuring the mutual capacitance for only a subset of the nodes (e.g., fewer than all of the nodes and including at least the nodes corresponding to the touched electrodes) resulting in the detection of two or more touched nodes. The self capacitance measurements may be performed on each of the electrodes, and the touched electrodes may comprise electrodes from both the first and second sets. Alternatively, the self capacitance measurements may be performed only on electrodes in the first set, and the touched electrodes may comprise electrodes from only the first set.

Smart scanning for a capacitive sense array

Abstract: A method and apparatus scan a plurality of scan groups in a capacitive sense array to generate signals corresponding to a mutual capacitance between the electrodes. Each of the plurality of scan groups is formed from a subset of the plurality of electrodes. A processing device identifies a scan group where the generated signal is affected by a presence of a conductive object. The processing device individually scans the subset of the plurality of sense elements in the identified scan group to determine a location of the conductive object.

Capacitance scanning proximity detection

Abstract: A method and apparatus for scanning a first set of electrodes of a capacitive sense array using a first sensing mode to identify a presence of an object in proximity to the capacitive sense array, where scanning using the first sensing mode identifies objects not in physical contact with the capacitive sense array. The first set of electrodes is scanned using a second sensing mode to determine a location of the object in relation to the capacitive sense array, where rescanning using the second sensing mode determines locations of objects in physical contact with the capacitive sense array.

A capacitive intrabody communication channel from 100 kHz to 100 MHz

Abstract: Intrabody communication (IBC) uses the human body as a signal transmission medium. In the capacitive coupling IBC approach, the signal is transmitted through the body, and the signal return path is closed through the environment. The received signal level is affected by the orientation of the transmitter with respect to the receiver, the number of ground electrodes connected to the body, the size of the receiver ground plane, and the surrounding environment. In this paper, we present a characterization of the capacitive IBC channel in the frequency range from 100 kHz to 100 MHz, obtained using a network analyzer and a pair of baluns. In order to better understand the transmission path in the frequency range of interest, we analyze the intrabody channel transmission characteristics using different electrode arrangements, test persons, environments, and body positions and movements. The transmission gain increases with frequency for 20 dB/dec and depends on the transmitter to the receiver distance, and the electrode arrangements. For a proper IBC configuration, the variations of the environment, test persons, body positions, and movements affect the transmission gain less than 2 dB.

Readout system for MEMs-based capacitive accelerometers and strain sensors, and method for reading

Abstract: A method and an electronic readout circuit for measuring a capacitance of a MEMS sensor are disclosed In one aspect, the readout circuit includes: an input stage for receiving a first signal from the sensor and for presenting a second signal; a charge amplifier stage for amplifying and integrating the second signal; and a control logic for controlling the readout circuit according to a predefined timing relation synchronized to actuation voltages applied to the sensor for generating the first signal The readout circuit may further includes a first switching unit for applying a first reference voltage to the sensor and a second switching unit for applying the second signal to the charge amplifier stage, wherein the first and the second switching units are controlled according to the predefined timing relation such that a plurality of the second signals are accumulated

Force sensing capacitive hybrid touch sensor

Abstract: A method for detecting a magnitude of force applied to a capacitive sensor array may comprise receiving a plurality of capacitance measurements affected by a contact at a touch-sensing surface, and determining a magnitude of a force applied to the touch-sensing surface at a location of the contact based on the location of the contact and a capacitance measurement of the first plurality of capacitance measurements

A Highly Sensitive Capacitive Touch Sensor Integrated on a Thin-Film-Encapsulated Active-Matrix OLED for Ultrathin Displays

Abstract: This paper presents ultrathin and highly sensitive input/output devices consisting of a capacitive touch sensor (Cap-TSP) integrated on thin-film-encapsulated active-matrix organic light-emitting diodes (OLEDs). The optimal structure of the electrically noise-free capacitive touch sensor, which is assembled on a thin-film-encapsulated active-matrix OLED (AMOLED) display, is obtained by investigating the internal electrical field distribution and capacitance change based on the Q3D Extractor model. Electrostatic simulations have verified malfunction-free electrical signals for 4-in diagonal-sized capacitive touch sensors on AMOLEDs possessing a 100-μm-thick optically clear adhesive (OCA, er = 1.4) layer. The prototype OLED platform using the capacitive touch sensors exhibits an overall thickness of 1.2 mm, which is the lowest thickness for commercially available OLED platforms.

Capacitive behavior of pentacene-based diodes: Quasistatic dielectric constant and dielectric strength

Abstract: The capacitive behavior of pentacene films was investigated in the metal-semiconductor-metal (MSM) diode structure. Impedance analysis of diodes with a thick pentacene layer up to 1012 nm showed a full depletion of the organic layer. This observation allowed us to regard the MSM diode as a parallel-plate capacitor in the reverse-bias regime without current flow. Under forward-bias, the diode was evaluated through frequency-dependent impedance measurements by using an equivalent circuit composed of a single parallel resistance-capacitance circuit. The analysis of the data in both the reverse and forward bias regime led us to electrical methods for quantifying dielectric properties of pentacene.

Touch screen with transparent capacity sensing medium and related display device and computing system

Abstract: A touch panel having a transparent capacitive sensing medium configured to detect multiple touches or near touches that occur at the same time and at distinct locations in the plane of the touch panel and to produce distinct signals representative of the location of the touches on the plane of the touch panel for each of the multiple touches is disclosed.

Resistive and capacitive response of nitrogen-doped TiO2 nanotubes film humidity sensor

Abstract: Dielectric oxides are traditionally used to fabricate resistive surface humidity-sensing devices, as well as capacitive sandwich-structured sensors. In the present work, relative humidity (RH) sensors were fabricated by employing vertically aligned TiO2 nanotubes array (TNA) film produced using electro-chemical anodization of Ti foil followed by a nitrogen-doping process, simultaneously showing resistive and capacitive humidity-sensing properties in the range of 11.3–93.6%. For the sample formed at optimized experimental conditions, the capacitance (CS) and resistance (RS) of the as-fabricated RH sensors made from nitrogen-doped TiO2 nanotubes film could be simultaneously obtained. Both the resistive and capacitive sensitivity (KR and KC) of the as-fabricated TiO2 nanotube RH sensors show distinct dependence on the frequency of alternating current (AC) voltage signal and RH. At higher water coverage, water–water interaction will result in lowering of the water dissociation barrier, leading to an increase of conductance. With the increase of RH, the polarization of as-adsorbed water molecules will also occur, causing a sharp increase of capacitance. For an explanation of the frequency response of both CS and RS, ionic transport, as well as the polarization effect, should be comprehensively considered. The changes of capacitance and resistance at different temperatures are plausibly caused by thermal expansion and surface state modification by adsorption and desorption of oxygen and water.

Touch sensor with force-actuated switched capacitor

Abstract: This disclosure provides apparatus, systems and methods of fabricating force-sensitive switches. In some implementations, an array of force-sensitive switches and local capacitors of a combined sensor device may be used to connect the local capacitor into associated projected capacitive touch (PCT) detection circuitry. In some implementations, each capacitor may be formed with a thin dielectric layer to achieve a high capacitance increase when the force-sensitive switch is closed, e.g., by the pressing of a stylus or finger. In some implementations, the same PCT detection circuitry can be used to detect changes in mutual capacitance when touched with a finger (touch mode) and changes in sensel capacitance when the force-sensitive switch is depressed (stylus or fingerprint mode).

A touch controller using differential sensing method for on-cell capacitive touch screen panel systems

Abstract: A touch controller is proposed for on-cell capacitive touch screen panel systems. The proposed IC adopts the differential sensing method to enhance the dynamic range of sensing voltage and to be robust to display noise. The measurement results show that the maximum reporting rate, jitter tolerance, and signal-to-noise ratio (SNR) are 140 Hz, ±0.3 mm, and 12 dB, respectively, when evaluated with a 13.3-inch wide extended graphics array (WXGA) liquid crystal display (LCD) panel with the on-cell touch screen. The proposed IC fabricated via 0.35 μm CMOS process technology occupies a silicon area of 4 mm × 5 mm and consumes a power of 19 mW when the supply voltage is 3.3 V.

Pressure dependent capacitive sensing circuit switch construction

Abstract: A user interface which includes a capacitive measurement circuit with a sense plate covered by an electrically conductive cover which is movable relative to the sense plate,wherein the circuit distinguishes between the following situations: an object in proximity to the cover, an object in contact with the cover, and the cover in contact with the sense plate.

PocketTouch: through-fabric capacitive touch input

Abstract: PocketTouch is a capacitive sensing prototype that enables eyes-free multitouch input on a handheld device without having to remove the device from the pocket of one's pants, shirt, bag, or purse. PocketTouch enables a rich set of gesture interactions, ranging from simple touch strokes to full alphanumeric text entry. Our prototype device consists of a custom multitouch capacitive sensor mounted on the back of a smartphone. Similar capabilities could be enabled on most existing capacitive touchscreens through low-level access to the capacitive sensor. We demonstrate how touch strokes can be used to initialize the device for interaction and how strokes can be processed to enable text recognition of characters written over the same physical area. We also contribute a comparative study that empirically measures how different fabrics attenuate touch inputs, providing insight for future investigations. Our results suggest that PocketTouch will work reliably with a wide variety of fabrics used in today's garments, and is a viable input method for quick eyes-free operation of devices in pockets.