Showing papers on "Capacitive sensing published in 2000"

Capacitive sensor and array

Abstract: Proximity of a body, which may be a user's finger, to an electrode pair (100, 104) is sensed by a charge transfer capacitive measurement approach. The electrode pair (100, 104) thus act as a key (10) that can be arrayed with other electrode pairs to form a keypad, keyboard, linear slider control, or liquid level sensor. In one embodiment of the invention, each key is associated with an alternating voltage source (101) and a pair of electrodes (100, 104) mounted on or within a solid dielectric substrate (103) or panel so as to be separated from each other by a gap. The voltage source (101) is connected to a driven electrode (100), a sampling charge detector (402) is connected to a second, receiving, electrode (104), and the output of the charge detector is, in turn, fed into an amplifier (403) and a charge measurement means (407). Disturbances in coupling between the two electrodes (100, 104) are detected through the solid substrate or panel material (103) when a substance or object approaches or contacts the panel. The receiving electrode (104) is a low-impedance node during the sampling phase of the process, which aids in keeping the sensor from being affected by wiring length or extraneous objects near an output lead.

A flexible transparent touch sensing system for electronic devices

Abstract: A transparent, capacitive sensing system particularly well suited for input to electronic devices is described. The sensing system can be used to emulate physical buttons or slider switches that are either displayed on an active display device or printed on an underlying surface. The capacitive sensor can further be used as an input device for a graphical user interface, especially if overlaid on top of an active display device like an LCD screen to sense finger position (X/Y position) and contact area (Z) over the display. In addition, the sensor can be made with flexible material for touch sensing on a three-dimensional surface. Because the sensor is substantially transparent, the underlying surface can be viewed through the sensor. This allows the underlying area to be used for alternative applications that may not necessarily be related to the sensing system. Examples include advertising, an additional user interface display, or apparatus such as a camera or a biometric security device.

Micro Mechanical Transducers: Pressure Sensors, Accelerometers and Gyroscopes

Abstract: Preface. Chapter 1 - Introduction to micro mechanical transducers. Chapter 2 - Basic mechanics of beam and diaphragm structures. Chapter 3 - Air damping. Chapter 4 - Electrostatic driving and capacitive sensing. Chapter 5 - Piezoresistive sensing. Chapter 6 - Piezoresistive pressure transducers. Chapter 7 - Piezoresistive accelerometers. Chapter 8 - Capacitive pressure transducers and accelerometers. Chapter 9 - Resonant sensors and vibratory gyroscopes. Subject Index.

Projective capacitive touchscreen

Abstract: A capacitive touchscreen using two sets of electrodes fabricated in a single plane. Individual electrodes of each set of electrodes are formed of a continuous length of conductive material such as fine wire or conductive coatings. The overall electrode pattern is such that there is no overlap thus eliminating the need for insulating layers and/or coatings. Preferably the pattern comprises a plurality of approximately triangular electrodes, formed such that the base of one triangularly shaped electrode is adjacent to the apex of the next. A touchscreen sensor employing the disclosed sensing electrodes can use any of a variety of readout systems such as a frequency domain approach, a time domain approach or by detecting frequency shifts of LC oscillators. Preferably, prior to calculating position, a subset of electrodes localised around the touch position is determined. Once a set of localised electrodes has been determined the touch coordinates are calculated.

Doubling Exponent Models for the Analysis of Porous Film Electrodes by Impedance. Relaxation of TiO2 Nanoporous in Aqueous Solution

Abstract: The paper is concerned with the small signal ac impedance of porous film electrodes in contact with solution. An overview is presented of the standard transmission line model with two transport channels and a crosswise element. The simplest configurations are discussed: a single resistance in one of the channels, and either an interfacial capacitor or a RC transfer circuit at the pore's wall. The resulting relaxation functions are classified in terms of two characteristic frequencies: one for coupled transport and interfacial polarization and another one for the interfacial reaction. Subsequently, these models are extended in order to describe porous electrodes where the interfacial polarization displays complex properties, i.e., frequency dispersion. The capacitive element is described by a constant-phase element (CPE), and it is shown that the fractionary exponent provides an additional and measurable degree of freedom in the parameter space of the relaxation function, whose determination can be explo...

Capacitive closure obstruction sensor

Abstract: A system for preventing the pinching or trapping of a human body part or foreign object by a closing panel, which may be a window, door, sunroof, hood or trunk lid, or other closure part of a transport vehicle operates by capacitively sensing the human body part, either before contact with a sensing electrode or plate, or at the time of contact with the plate. The sensing electrode may be a metal strip or wire, which can be embedded in a plastic or rubber molding strip, placed behind a piece of fascia or other trim part, or may simply be a metal element on top of the trim parts. Sensing electrodes of this sort can be prepared from conductive ink, made of adhesive backed metal foil, formed from a metal mesh strip, or simply be a wire or serpentine-laid wire. The capacitive sensing technology that follows the “charge transfer” approach and provides immunity from environmental effects, such as moisture and humidity.

Method and apparatus for monitoring and controlling tissue temperature and lesion formation in radio-frequency ablation procedures

Abstract: Impedance and capacitance-related parameters are monitored in the electrical circuit of a tissue-ablation apparatus wherein RF electrical power is administered at predetermined frequencies Tissue temperature has been found to correlate well with low-frequency impedance, or with the resistive component of impedance at any frequency Therefore, one or both of these parameters are calculated and tracked during the ablation procedure to estimate tissue temperature Similarly, tissue lesion formation has been found to correlate well with changes in the capacitive component of tissue impedance Thus, this parameter can be used to track tissue lesion formation during the ablation procedure The ratio of tissue-to-blood interface with the ablation electrode is estimated by measuring impedance at a very low frequency and a very high frequency The difference between these two values divided by the high-frequency value is taken to be a measure of such ratio Alternatively, other electrical parameters indicative of changes in the capacitive component of the system may be measured and the ratio is calculated as a function of these changes with respect to a baseline value

A high-speed capacitive humidity sensor with on-chip thermal reset

Abstract: This paper reports a high-speed capacitive humidity sensor integrated on a polysilicon heater. A response time of 1.0 s and a sensitivity of 30.0 fF/%RH have been obtained. High speed is achieved using multiple polyimide columns having diameters of a few microns and allowing moisture to diffuse into them circumferentially. Using structures that eliminate the air-gap capacitance between the columns, the simulated sensor output drifts by only 1% when the relative dielectric constant in the air region changes from 1 to 10. A polysilicon heater is used to measure relative humidity levels >80% RH. An accuracy of /spl plusmn/3% RH has been obtained using this method, with measurement errors of /spl plusmn/0.5/spl deg/C and /spl plusmn/2% RH in temperature and relative humidity, respectively. The heater also reduces the recovery time after wetting, enables the sensor to recover from contamination and aging, and allows the sensing film to be reset on demand during self-test protocols.

Dual band wideband adjustable antenna assembly

Abstract: A dual frequency wideband antenna assembly for use in a wireless communication device (22). The antenna assembly having a first resonator element (52) disposed away from the ground plane element (28), said first resonator element being operatively coupled at a first location (40) to the ground plane and being operatively coupled at a second location (42) to the RF signal port; a second resonator element (54) disposed away from the ground plane. The first and second resonator elements are coupled via a bridge conductor (56) and a capacitive tuning network (71). The capacitive tuning network may include a discrete capacitor or an adjustable capacitor which varies in response to a signal.

A novel surface-micromachined capacitive porous silicon humidity sensor

Abstract: The design, fabrication and characterisation of a novel humidity sensor are presented. The device consists of a capacitor with a porous silicon dielectric, two thermoresistors and a refresh resistor. The porous silicon is formed with a back-end process underneath a meshed metal electrode, which is fabricated in the same layer as the thermo- and refresh resistors. Due to this concept, very thin porous silicon could be formed with reproducible and stable metal contacts. At the same time, both the response time and the overall fabrication yield of the devices could be improved. The properties of the sensor are modelled and demonstrated with several experimental results.

Capacitive displacement encoder

Abstract: A capacitive motion encoder, for sensing the position of a moving object relative to a stationary object, includes at least one stationary element, coupled to the stationary object and a moving element, coupled to the moving object and in proximity to the stationary element. A field transmitter generates an electrostatic field, which is modulated by a change in capacitance between the stationary and moving elements responsive to relative motion of the elements. A conductive shield, is electrically decoupled from both the moving and the stationary objects, and encloses the moving and stationary elements so as to shield the elements from external electrical interference. Processing circuitry is coupled to sense the modulated electrostatic field and to determine responsive thereto a measure of the position of the moving object.

Capacitive microphone with low-stress polysilicon membrane and high-stress polysilicon backplate

Abstract: A capacitive single-chip silicon microphone with very low-stress polysilicon membrane was fabricated. A mechanism for stress-releasing due to the high stress of the perforated membrane was introduced. With the achieved stress level of 2 MPa, a microphone with the membrane area of 1 mm 2 can be optimally designed, although the measured components did not show the optimal resolution due to excessive acoustic resistance. With a membrane area of 1 mm 2 , the acoustical sensitivity was 4 mV/Pa (at 1 kHz) and the noise equivalent sound level was 33.5 dB (A), which are adequate values for many applications. The packaged components were tested with a thermal cycle between −40°C and +60°C, and due to low packaging-related stresses, no buckling of the membranes was observed.

Enhanced fingerprint detection

Abstract: An enhanced fingerprint sensing circuit in which a voltage change is applied to the body during sensing. When the person's fingerprint is being sensed, the person's body is in contact with an electrical terminal. When the sensing occurs, the voltage on the electrical terminal changes, which changes the voltage on the person's body. The pattern of the fingerprint performs two functions in the sensing circuit. In addition to being a plate of a capacitor whose distance is being sensed, it is now a source of input charge as well. The electrical effect on the cell of a voltage change on a person's finger is different at a ridge than at a valley in the fingerprint sensing circuit. Thus, the input capacitance to the sensing circuit is variable, depending upon whether a ridge or a valley is present. The sensing circuit also detects a change in its own capacitance based on the presence of a ridge or a valley. In summary, the person's body acts as the input capacitor to provide a variable charge transfer for the input capacitance and at the same time performs the function of being a variable sensing capacitor value for the capacitive sensor. The fingerprint sensor is thus very sensitive and can detect a person's fingerprint even if a protective layer, such as plastic, wax paper or the like is over the sensor. In addition, if the person is wearing a thin glove, such as a latex glove, the fingerprint patterns can still be sensed.

Magnetic stimulation coil and circuit design

Abstract: A detailed analysis of the membrane voltage rise commensurate with the electrical charging circuit of a typical magnetic stimulator is presented. The analysis shows how the membrane voltage is linked to the energy, reluctance, and resonant frequency of the electrical charging circuit. There is an optimum resonant frequency for any nerve membrane depending on its capacitive time constant. The analysis also shows why a larger membrane voltage will be registered on the second phase of a biphasic pulse excitation. Typical constraints on three key quantities voltage, current, and silicone controlled rectifier (SCR) switching time dictate key components such as capacitance, inductance, and choice of turns.

A miniature pressure system with a capacitive sensor and a passive telemetry link for use in implantable applications

Abstract: A miniature telemetric pressure-measuring system is presented in this paper. The system uses passive telemetry to transfer power to the transponder and pressure data to the remote base unit. Such telemetric systems are becoming ever more important in the biomedical field as the interest for in-vivo measurements of different biological parameters both of humans and animals is increasing. A novel capacitive-type pressure sensor based on an SiGeB diaphragm is used as a sensing element. The merits of combining a capacitive pressure sensor and passive telemetry lies in the inherent low-power consumption of the sensor and the continuous availability of power through induction. The pressure sensor is connected to an integrated interface circuit, which includes a capacitance to frequency converter and an internal voltage regulator to suppress supply voltage fluctuations on the transponder side. In addition, the sensor and accompanying interface circuit take up very little space so as to be suitable for implantation.

Electric field sensor

Abstract: An electric field sensor employs a capacitive pick-up electrode in a voltage divider network connected to a body emanating an electric field. The system is relatively insensitive to variations in the separation gap between electrode and body, reducing sensor motion artifacts in the output signal and stabilizing its low frequency response. The pick-up electrode may be positioned at a “stand off” location, spaced from intimate contact with the surface of the body. This is equivalent to providing low level capacitive values for the capacitive coupling between the pick-up electrode and the body whose electric field is to be monitored. Or a series limiting capacitor may be provided in the input stage. Human body-generated electrical signals may be acquired without use of conductive gels and suction-based electrodes, without direct electrical contact to the body, and even through thin layers of clothing.

A capacitive Frisch grid structure for CdZnTe detectors

Abstract: Recent results with CdZnTe (CZT) gamma spectrometers have shown that Frisch grid structures yield an excellent performance. Hole trapping problems have been solved by this means. However, some difficulties persist concerning optimization of performance in terms of electronic noise and response uniformity. Also, the complexity of Frisch grid structures makes them hard to manufacture on an industrial scale. This paper presents some results obtained using a new Frisch grid structure based on capacitive coupling. Extremely easy to produce, it allows highly efficient detector screening without leakage current increase.

Parametric resonance in microelectromechanical structures

Abstract: MEM structures which may be driven at parametric frequencies to provide stable operation and to permit precise switching between stable and unstable operations by very small changes in the drive frequency or by very small changes in the characteristics of the structure itself so as to provide improved control and sensing are disclosed. The techniques of the present invention are applicable to a wide variety of microstructures, including parallel plate linear actuators, reduction and augmentation actuators, linear force comb actuators, and in particular to torsional scanning probe z-actuators having an integrated tip. These devices incorporate capacitive actuators, or drivers, for producing mechanical motion, and more particularly comb-type actuator structures which consist of high aspect ratio MEM beams fabricated as interleaved fixed and movable capacitor fingers. The capacitive actuator structures can be used either for sensing displacements or inducing motion, the capacitive plates of the fixed and movable fingers allowing a wide range of motion and high amplitudes without failure. Such micromechanical torsional resonators obey the Mathieu equation, and are driven by a suitable driving force such as an AC driver to resonate at frequencies other than their natural frequencies of resonance with a sharp transition between stable and unstable operation. The devices may be switched between stable and unstable operation by very small changes in the physical characteristics, or parameters, of the devices and/or by small changes in the frequency or amplitude of the driving force.

High bandwidth passive integrated circuit tester probe card assembly

Abstract: Described herein is a probe card assembly providing signal paths for conveying high frequency signals between bond pads of an integrated circuit (IC) and an IC tester. The frequency response of the probe card assembly is optimized by appropriately distributing, adjusting and impedance matching resistive, capacitive and inductive impedance values along the signal paths so that the interconnect system behaves as an appropriately tuned Butterworth or Chebyshev filter.

Electrostatic capacitive touch sensor

Abstract: An electrostatic capacitive touch sensor including a substrate having a group of fixed electrodes formed thereon; and a movable electrode plate that is integrally molded by using rubber or resin having an elastic property as a whole and that has at least a face which opposes the group of fixed electrodes and is made of a conductive rubber or a conductive resin. The group of fixed electrodes and the movable electrode plate form a plurality of variable electrostatic capacitive sections, and in response to the magnitude and the direction of a force applied onto the movable electrode plate, the electrostatic capacitances of the respective variable electrostatic capacitive sections are allowed to change.

Principles of substrate crosstalk generation in CMOS circuits

Abstract: Substrate noise injection is evaluated for a 0.25-/spl mu/m CMOS technology, to determine the mechanisms that contribute to substrate crosstalk. At the transistor level, we find that impact ionization current and capacitive coupling from the junctions are the most significant contributors to substrate current injection. An investigation of substrate fluctuations at a circuit level included switching transients, capacitive damping, and separate substrate biasing. This investigation revealed that voltage transients on power-supply lines can be the dominant source of substrate fluctuations. Finally, a statistical analysis of signal cancellation in an integrated circuit was performed. The results indicate that more cancellation will take place for the high-frequency noise components than for the average and low-frequency components. As a consequence, the dc and low-frequency components of the transient that result from an individual switching event can not be neglected even if they are a relatively small fraction of the single transient.

Bias charge regulator for capacitive micromachined ultrasonic transducers

Abstract: An ultrasonic transducer is formed by a plurality of cMUT cells, each comprising a charged diaphragm plate capacitively opposing an oppositely charged base plate. A feedback controlled bias charge regulator controls the bias charge of the capacitive plates. The cMUT cells can be fabricated by conventional semiconductor processes and hence integrated with ancillary transducer circuitry such as the bias charge regulator.

MEMS devices for high isolation switching and tunable filtering

Abstract: This paper presents resonant capacitive microelectromechanical switches and their possible applications in tunable filtering. Single switches with a down capacitance of 2.9 pF and inductive sections of 3 to 50 pH are demonstrated, resulting in resonant frequencies from 13 to 54 GHz. Designs of resonant switches connected in parallel are also implemented with major advantages in isolation and bandwidth. Finally, tunable filters using these switches are discussed.

Plasma reactor with dynamic RF inductive and capacitive coupling control

Abstract: The invention provides a system and a method for dynamic RF inductive and capacitive coupling control to improve plasma substrate processing, as well as for achieving contamination and defect reduction. A plasma reactor includes a substrate support disposed in a chamber. An RF coil is disposed adjacent the chamber for inductively coupling RF energy into the chamber. An electrode is disposed adjacent the chamber and has a voltage for capacitively coupling energy into the chamber. The electrode is spaced from the substrate support and the RF coil. An electrode adjusting member is coupled with the electrode for dynamically adjusting the voltage in the electrode to vary the capacitive coupling for improved plasma ignition and plasma stability. A Faraday shield may be placed between the RF coil and the plasma process region in the chamber to suppress capacitive coupling of the RF coil. Sensors may be provided to monitor the amounts of inductive coupling and capacitive coupling to provide feedback to a controller which is used to adjust the inductive coupling and capacitive coupling in real time to stabilize the plasma and achieve improved processing.

A CMOS z-axis capacitive accelerometer with comb-finger sensing

Abstract: This paper reports the first design and experimental results of a z-axis accelerometer that utilizes the sidewall capacitance change of multi-conductor comb fingers. The accelerometer has a fully differential capacitive bridge interface and its fabrication is compatible with standard CMOS processes. The frequency response of the accelerometer is characterized both electrically and optically and about 9.3 kHz resonant frequency is measured, which matches MEMCAD simulation within 15%. Measured sensitivity is 0.5 mV/g with less than -40 dB cross-axis sensitivity, noise floor 6 mg/rtHz, and linear range from -27 g to 27 g.

Position sensing with variable capacitance transducers

Abstract: For enabling precise operation of an oscillating device, such as a galvanometric optical scanner, a capacitive position transducer is provided with strategically located internal capacitive fiducial features that interact with the armature of the transducer beyond the central range of excursion of the transducer, typically beyond the normal operating range of the device. Electric pulses obtained at instants of interaction with the fiducials enable determination of position drift caused e.g. by change in environmental conditions. The pulses can be detected by simple circuits to produce recalibration of the amplitude and null position of the instrument on an automatic or elective basis.

Design, fabrication, and real-time neural network control of a three-degrees-of-freedom nanopositioner

Abstract: A nanometric precision three-degrees-of-freedom positioner is designed and fabricated. Actuation is based on piezoelectric stacks. Capacitive gap sensors with less than 1.0-nm resolution are used for position feedback. In order to design a proper closed-loop controller, the open-loop characteristics of the nanopositioner (static stiffness, hysteresis, drift, frequency response, and the coupling effects) are experimentally investigated. A cerebellar model articulation controller neural network control algorithm was applied in order to provide real-time learning and better tracking capability compared to a standard proportional-integral-derivative control algorithm.

Coriolis mass flow controller

Abstract: A capacitive pick off sensor for a mass flow measurement device is disclosed. The mass flow measurement device includes a flow sensor tube and a drive device for vibrating the flow sensor tube. The capacitive pick off sensor includes at least one conductive plate connectable to a first voltage potential and adapted to be situated adjacent the flow sensor tube which is connected to a second voltage potential. The conductive plate is positioned relative to the flow sensor tube so as to define a gap therebetween. The capacitance between the conductive plate and the flow sensor tube varies due to the relative motion of the conductive plate and the flow sensor tube when the flow sensor tube is vibrated. In other aspects of the present invention, the flow sensor tube is situated in a housing and the drive device is positioned outside the housing for vibrating the flow sensor tube.