Showing papers on "Capacitive sensing published in 2012"

Energy Scavenging for Wireless Sensor Networks: with Special Focus on Vibrations

Abstract: 1 Introduction.- 1. Energy Storage.- 2. Power Distribution.- 3. Power scavenging.- 4. Summary of potential power sources.- 5. Overview of Vibration-to-Electricity Conversion Research.- 2 Vibration Sources and Conversion Model.- 1. Types of Vibrations Considered.- 2. Characteristics of Vibrations Measured.- 3. Generic Vibration-to-Electricity Conversion Model.- 4. Efficiency of Vibration-to-Electricity Conversion.- 3 Comparison of Methods.- 1. Electromagnetic (Inductive) Power Conversion.- 2. Electrostatic (Capacitive) Power Conversion.- 3. Piezoelectric Power Conversion.- 4. Comparison of Energy Density of Converters.- 5. Summary of Conversion Mechanisms.- 4 Piezoelectric Converter Design.- 1. Basic Design Configuration.- 2. Material Selection.- 3. Analytical Model for Piezoelectric Generators.- 4. Discussion of Analytical Model for Piezoelectric Generators.- 5. Initial Prototype and Model Verification.- 6. Design Optimization.- 7. Analytical Model Adjusted for a Capacitive Load.- 8. Discussion of Analytical Model Changes for Capacitive Load.- 9. Optimization for a Capacitive Load.- 10. Conclusions.- 5 Piezoelectric Converter Test Results.- 1. Implementation of Optimized Converters.- 2. Resistive load tests.- 3. Discussion of resistive load tests.- 4. Capacitive load tests.- 5. Discussion of capacitive load test.- 6. Results from testing with a custom designed RF transceiver.- 7. Discussion of results from custom RF transceiver test.- 8. Results from test of complete wireless sensor node.- 9. Discussion of results from complete wireless sensor node.- 10. Conclusions.- 6 Electrostatic Converter Design.- 1. Explanation of concept and principle of operation.- 2. Electrostatic Conversion Model.- 3. Exploration of design concepts and device specific models.- 4. Comparison of design concepts.- 5. Design Optimization.- 6. Flexure design.- 7. Discussion of design and conclusions.- 7 Fabrication of Electrostatic Converters.- 1. Choice of process and wafer technology.- 2. Basic process flow.- 3. Specific processes used.- 4. Conclusions.- 8 Electrostatic Converter Test Results.- 1. Macro-scale prototype and results.- 2. Results from fluidic self-assembly process prototypes.- 3. Results from integrated process prototypes.- 4. Results from simplified custom process prototypes.- 5. Discussion of Results and Conclusions.- 9 Conclusions.- 1. Justification for focus on vibrations as a power source.- 2. Piezoelectric vibration to electricity converters.- 3. Design considerations for piezoelectric converters.- 4. Electrostatic vibration to electricity converters.- 5. Design considerations for electrostatic converters.- 6. Summary of conclusions.- 7. Recommendations for future work.- Acknowledgments.- Appendix A: Analytical Model of a Piezoelectric Generator.- 1. Geometric terms for bimorph mounted as a cantilever.- 2. Basic dynamic model of piezoelectric generator.- 3. Expressions of interest from basic dynamic model.- 4. Alterations to the basic dynamic model.- Appendix B: Analytical Model of an Electrostatic Generator.- 1. Derivation of electrical and geometric expressions.- 2. Derivation of mechanical dynamics and electrostatic forces.- 3. Simulation of the in-plane gap closing converter.- References.

A highly elastic, capacitive strain gauge based on percolating nanotube networks.

Abstract: We present a highly elastic strain gauge based on capacitive sensing of parallel, carbon nanotube-based percolation electrodes separated by a dielectric elastomer. The fabrication, relying on vacuum filtration of single-walled carbon nanotubes and hydrophobic patterning of silicone, is both rapid and inexpensive. We demonstrate reliable, linear performance over thousands of cycles at up to 100% strain with less than 3% variability and the highest reported gauge factor for a device of this class (0.99). We further demonstrate use of this sensor in a robotics context to transduce joint angles.

A wireless wearable ECG sensor for long-term applications

Abstract: Ubiquitous vital signs sensing using wireless medical sensors are promising alternatives to conventional, in-hospital healthcare systems. In this work, a wearable ECG sensor is proposed. This sensor system combined an appropriate wireless protocol for data communication with capacitive ECG signal sensing and processing. The ANT protocol was used as a low-data-rate wireless module to reduce the power consumption and size of the sensor. Furthermore, capacitive ECG sensing is a simple technique that avoids direct contact with the skin and provides maximum convenience to the user. In our work, small capacitive electrodes were integrated into a cotton T-shirt together with a signal processing and transmitting board on a two-layer standard printed circuit board design technology. The entire system has small size, is thin, and has low power consumption compared to recent ECG monitoring systems. In addition, appropriate signal conditioning and processing were implemented to remove motion artifacts. The acquired ECG signals are comparable to ones obtained using conventional glued-on electrodes, and are easily read and interpreted by a cardiologist.

Flexible microfluidic normal force sensor skin for tactile feedback

Abstract: Robotic applications often require robust tactile sensing capabilities on curved surfaces, such as artificial fingertips. Flexible tactile sensors could be conformally wrapped around curved digits and could enhance grip by cushioning impacts and increasing the effective contact area during grasp. Flexible microfabricated devices that use thin film or solid electrical components are susceptible to failure due to cracking and fatigue. Conductive fluids have been used as transduction media, electrical connections, and in resistance-based pressure and bend sensors. In this work, a flexible and multilayer capacitive microfluidic normal force sensor is developed with a 5 × 5 taxel array. The sensor uses liquid metal-filled microfluidic channels as the capacitive plates and conductive interconnects. The sensor is microfabricated using soft lithography microfabrication techniques and consists of multiple layers of PDMS microchannels filled with the liquid metal alloy Galinstan and air pockets that modify the mechanical and electrical properties of the sensor. A single taxel is calibrated for normal forces ranging from 0 to 2.5 N, is shown to provide repeatable measurements of static uniaxial loads, and follows the loading and unloading phases of low-frequency dynamic loads (0.4–4 Hz). The sensor prototype has a spatial resolution on the order of 0.5 mm, performs reliably when wrapped around a surface having a curvature similar to that of a human finger (1.575 cm−1), and has been shown to tolerate curvatures as high as 6.289 cm−1. The deformable liquid capacitive plates and heterogeneous PDMS-air dielectric medium can be designed to tune the sensor's sensitivity and range. The sensor prototype provides greater sensitivity at low loads, a feature which can be exploited for robotic applications in which light touch is important.

Effective Capacitive Power Transfer

Abstract: Capacitive power transfer (CPT) systems have up to date been used for very low power delivery due to a number of limitations. A fundamental treatment of the problem is carried out and a CPT system is presented that achieves many times higher power throughput into low-impedance loads than traditional systems with the same interface capacitance and frequency of operation and with reasonable ratings for the switching devices. The development and analysis of the system is based well on the parameters of the capacitive interface and a design procedure is provided. The validity of the concept has been verified by an experimental CPT system that delivered more than 25W through a combined interface capacitance of 100 pF, at an operating frequency of only 1 MHz, with efficiency exceeding 80%.

Touchpad with Capacitive Force Sensing

Abstract: Described herein are techniques related to a touchpad with capacitive force sensing. The described techniques may determine the point or region of a user-engagement surface contacted by a user. In addition, the described techniques may also determine a force of the user's finger press on the user-engagement surface using one or more capacitance force-sensors. Furthermore, the described techniques may offer active tactile feedback (i.e., haptics) to the user's finger touching the user-engagement surface. This Abstract is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Piezopotential-Driven Redox Reactions at the Surface of Piezoelectric Materials

Abstract: Themanipulation of charge-carrier conduction characteristics is a critical attribute governing the operation and efficiency of photovoltaic, catalytic, and other energy-converting systems that are based on electrochemical principles. This manipulation is often accomplished through the application of electrical-potential gradients by an external power supply and/or the creation of electronic-state discontinuities by heterojunction-interface engineering. For example, in electrochemical systems, the transport of charge across chemical phases is governed by the energy and density of electronic states within the disparate phases as well as any existing bias between said phases. Piezoelectric materials have long been used as a source of bias and mechanical displacement, relying on their mechanical to electrical coupling character for applications in sensors, actuators, and energy harvesters. In contrast to this historical precedent, contemporary integration of piezoelectric materials in semiconductor heterostructures capitalizes on the capability of the piezoelectric potential to manipulate charge carriers (i.e., piezotronics). For instance, the straining of a piezoelectric element in order to change its semiconducting properties has recently been investigated in zinc oxide nanomaterials, which have opened the doors to strain-gated logic operations and new possibilities for microelectronic circuitry elements. Straining effects in piezoelectric photoelectrochemical cells have also been shown to result in performance enhancements through manipulation of interface energetics. In principle, the piezoelectric modulation of charge carrier energetics should extend beyond the bounds of the buried electronic interfaces explored to date, thus allowing the direct enhancement or suppression of electrochemical processes that occur at the interface of a piezoelectric material and a solution (i.e., piezocatalysis). Preliminary experiments have shown an evolution of H2 and O2 from mechanically agitated piezoelectric BaTiO3 and ZnO microstructures in an aqueous sonication bath. In order to elucidate the intriguing piezocatalytic phenomenon, we report a systematic study of the piezoelectric-potentialdriven electrochemical H2 evolution process that takes place at the electrodes located on the surface of the material. The results compliment the general trends expected from the combinatorial assemblage of piezoelectricity and electrochemistry. The H2 evolution rates were dependent upon the oscillation frequency and amplitude of the piezoelectric material, in accordance with the combination of the direct piezoelectric effect and electrochemical reactions. A study of the piezocatalytic effect was conducted on a single-crystalline ferroelectric Pb(Mg1/3Nb2/3)O3-32PbTiO3 (PMN-PT) cantilever in a sealed chamber (see Figure S1 in the Supporting Information). The voltage output of the PMN-PT slab was first characterized in air (Figure 1a). The cantilever was mechanically oscillated with a fixed frequency and amplitude. When the piezoelectric cantilever was transitioned to the deionized water environment, the voltage amplitude decreased while the mechanical oscillation frequency and amplitude remained constant. In order to encompass the entire piezocatalytic system into a cohesive entity, an analogous circuit was constructed (Figure 1b). In this circuit, opposite and iteratively alternating sides of the piezoelectric material serve as both the working and counter electrodes, respectively. A strained piezoelectric material can be considered a charged capacitor, and thus the change in measured voltage is correlated with a change in piezoelectricity-induced surface charge (DQp). When a strained piezoelectric material is placed within an aqueous medium of finite conductivity and polarizability, its piezoelectricity-induced surface charge can be depleted through two primary pathways: Faradic (If) and capacitive (Ic=dCdVd/dt, in which Cd and Vd are the double layer capacitance and voltage drop across the double layer, respectively) currents:

Capacitive Power Transfer for Rotor Field Current in Synchronous Machines

Abstract: Permanent magnet (PM) synchronous machines are utilized in a wide variety of applications due to their many desirable characteristics, including high torque density capability and high efficiency. In the near future, however, the demand for the PM rare earth materials is projected to exceed world production. As a result, electric machines that do not rely on rare earth materials, such as wound field synchronous machines (WFSMs), are receiving renewed attention for use in traction and wind energy applications. However, WFSMs require a current delivery mechanism to the rotor such as mechanical slip rings whose components require periodic replacement and generate adverse debris within the machine enclosure. Rotary transformers may replace slip rings but also introduce rotor speed dependences and magnetic coupling difficulties. This paper proposes a capacitive noncontact power transfer technique to eliminate the need for mechanical slip rings while also avoiding the pitfalls of rotating transformer technologies. The capacitive power transfer system is compared to traditional rotor power coupling techniques and its performance is validated with experimental results.

Large-Signal Stabilization of a DC-Link Supplying a Constant Power Load Using a Virtual Capacitor: Impact on the Domain of Attraction

Abstract: It is known that the interaction between poorly damped LC input filters and constant power loads (CPLs) leads to degradation of dynamic performance or system instability. This paper addresses a large-signal stability study and stabilization of an electrical system containing a dc power supply, an LC filter, and a CPL. This latter is realized here by a voltage source inverter supplying a motor drive. To stabilize the system, the control structure is slightly modified to implement a nonlinear stabilization block that virtually increases the dc-link capacitance and, hence, the damping of the system. The main idea consists in adding a capacitive power component to the CPL power reference. This allows reducing the real dc-link capacitance value and volume, which is, for weight and size reasons, an important issue in aerospace applications. The impact on the large-signal stability will be analyzed by estimating the domain of attraction of the operating point. An illustrative example consisted of an LC input filter connected to an inverter-permanent-magnet synchronous motor designed for aircraft applications treated by simulations and experimentation, which confirm the validity of the proposed approach.

A review of technologies for sensing contact location on the surface of a display

Abstract: Touchscreen interactive devices have become increasingly important in both consumer and commercial applications. This paper provides a broad overview of all touchscreen technologies in use today, organized into 13 categories with 38 variations. The 13 categories are projected capacitive, analog resistive, surface capacitive, surface acoustic wave, infrared, camera-based optical, liquid crystal display in-cell, bending wave, force sensing, planar scatter detection, vision-based, electromagnetic resonance, and combinations of technologies. The information provided on each touchscreen technology includes a little history, some basic theory of operation, the most common applications, the key advantages and disadvantages, a few current issues or trends, and the author's opinion of the future outlook for the technology. Because of its dominance, this paper begins with projected capacitive; more information is provided on this technology than on any of the other touch technologies that are discussed. This paper covers only technologies that operate by contact with a display screen; this excludes technologies such as 3D gesture recognition, touch on opaque devices such as interactive whiteboards, and proximity sensing. This is not a highly technical paper; it sacrifices depth of information on any one technology for breadth of information on multiple technologies.

Capacitive bioanodes enable renewable energy storage in microbial fuel cells.

Abstract: We developed an integrated system for storage of renewable electricity in a microbial fuel cell (MFC). The system contained a capacitive electrode that was inserted into the anodic compartment of an MFC to form a capacitive bioanode. This capacitive bioanode was compared with a noncapacitive bioanode on the basis of performance and storage capacity. The performance and storage capacity were investigated during polarization curves and charge–discharge experiments. During polarization curves the capacitive electrode reached a maximum current density of 1.02 ± 0.04 A/m2, whereas the noncapacitive electrode reached a current density output of only 0.79 ± 0.03 A/m2. During the charge–discharge experiment with 5 min of charging and 20 min of discharging, the capacitive electrode was able to store a total of 22 831 C/m2, whereas the noncapacitive electrode was only able to store 12 195 C/m2. Regarding the charge recovery of each electrode, the capacitive electrode was able to recover 52.9% more charge during eac...

Beam Steering Transmitarray Using Tunable Frequency Selective Surface With Integrated Ferroelectric Varactors

Abstract: A tunable frequency selective surface (FSS) with beam steering capability is presented. The FSS is used as a transmitarray with a bandpass characteristic in Ku-band. The periodic sub-wavelength (λ0/25) unit-cells are composed of capacitive and inductive structures creating a bandpass for an incident wave. By patterning the capacitive elements on a screen-printed barium-strontium-titanate (BST) thick-film ceramic, the resonant frequency of the FSS can be tuned. This technology offers a simple and cost effective way for integrating varactors into the FSS and is particularly attractive for microwave circuits with a high varactor density. A prototype is fabricated including two capacitive layers with an overall size of 40 mm × 40 mm. Each layer includes a total of 1600 integrated BST varactors that are fabricated by using a patterning and metallization process. A transmitted wave passing through the FSS will experience a phase shift, which can be tuned by tuning the passband. This allows steering the transmitted wave to a certain direction by applying a phase gradient along the FSS interface. A phase shift range of 360° can be covered by cascading several FSS panels. The prototyped tunable FSS demonstrates the feasibility of the proposed technology and its potential for beam steering.

Droplet-based interfacial capacitive sensing.

Abstract: This paper presented a novel droplet-based pressure sensor using elastic and capacitive electrode-electrolyte interfaces to achieve ultrahigh mechanical-to-electrical sensitivity (1.58 μF kPa(-1)) and resolution (1.8 Pa) with a simple device architecture. The miniature transparent droplet sensors, fabricated by one-step laser micromachining, consisted of two flexible polymer membranes with conductive coating and a separation layer hosting a sensing chamber for an electrolyte droplet. The sensing principle primarily relied on high elasticity of the sensing droplet and large capacitance presented at the electrode-electrolyte interface. A simple surface modification scheme was introduced to the conductive coating, which reduced hysteresis of the droplet deformation without substantially compromising the interfacial capacitance. Moreover, the major concern of liquid evaporation was addressed by a mixture of glycerol and electrolyte with long-term stability in a laboratory environment. Theoretical analyses and experimental investigations on several design parameters (i.e., the dimensions of the sensing chamber and the droplet size) were thoroughly conducted to characterize and optimize the overall sensitivity of the device. Moreover, the environmental influences (e.g., temperature and humidity) on the capacitive measurement were further investigated. Finally, the simply constructed and mechanically flexible droplet sensor was successfully applied to detect minute blood pressure variations on the skin surface (with the maximum value less than 100 Pa) throughout cardiovascular cycles.

Capacitance sensor for determining a distance between a head and a magnetic storage medium

Abstract: A proximity sensor is described including a capacitor formed by a first conductive element and a second conductive element. The first conductive element and the second conductive element are situated at a magnetic head, a slider that connects to the magnetic head, a reader of the magnetic head, a writer of the magnetic head, a reader shield of the magnetic head, or a writer shield of the magnetic head. A capacitance and a fringing electric field are formed by the capacitor when there is a voltage difference between the first conductive element and the second conductive element. The capacitor is situated such that the fringing electric field changes with a positioning change of a magnetic storage medium with respect to at least one of the first conductive element and the second conductive element. The capacitor is also situated such that the capacitance changes with the fringing electric field change.

Distinguishing users with capacitive touch communication

Abstract: As we are surrounded by an ever-larger variety of post-PC devices, the traditional methods for identifying and authenticating users have become cumbersome and time-consuming. In this paper, we present a capacitive communication method through which a device can recognize who is interacting with it. This method exploits the capacitive touchscreens, which are now used in laptops, phones, and tablets, as a signal receiver. The signal that identifies the user can be generated by a small transmitter embedded into a ring, watch, or other artifact carried on the human body. We explore two example system designs with a low-power continuous transmitter that communicates through the skin and a signet ring that needs to be touched to the screen. Experiments with our prototype transmitter and tablet receiver show that capacitive communication through a touchscreen is possible, even without hardware or firmware modifications on a receiver. This latter approach imposes severe limits on the data rate, but the rate is sufficient for differentiating users in multiplayer tablet games or parental control applications. Controlled experiments with a signal generator also indicate that future designs may be able to achieve datarates that are useful for providing less obtrusive authentication with similar assurance as PIN codes or swipe patterns commonly used on smartphones today.

Generation of Propagating Bessel Beams Using Leaky-Wave Modes: Experimental Validation

Abstract: We present the experimental generation of Bessel beams using a leaky radial waveguide. The radial waveguide consists of a capacitive sheet over a ground plane. The capacitive sheet is composed of patch elements printed on both sides of a dielectric substrate. The radial waveguide is coaxially fed and supports an azimuthally invariant leaky-wave mode whose normal electric-field component is a truncated, zeroth-order Bessel function. Two prototypes are presented with the same propagation constant and lateral extent, but different attenuation constants. 2D electric field measurements and their respective Fourier transforms validate the operation of the prototypes as Bessel-beam launchers at two frequency bands. Cleaner patterns are achieved by the prototype with lower attenuation constant. The dual-band capability and associated frequency dependent resolution can be useful in near-field planar focusing systems. The proposed structure can be used for generating arbitrary zeroth-order propagating Bessel beams at microwave and millimeter-wave frequencies.

Fundamental investigations of capacitive radio frequency plasmas: simulations and experiments

Abstract: Capacitive radio frequency (RF) discharge plasmas have been serving hi-tech industry (eg chip and solar cell manufacturing, realization of biocompatible surfaces) for several years Nonetheless, their complex modes of operation are not fully understood and represent topics of high interest The understanding of these phenomena is aided by modern diagnostic techniques and computer simulations From the industrial point of view the control of ion properties is of particular interest; possibilities of independent control of the ion flux and the ion energy have been utilized via excitation of the discharges with multiple frequencies ‘Classical’ dual-frequency (DF) discharges (where two significantly different driving frequencies are used), as well as discharges driven by a base frequency and its higher harmonic(s) have been analyzed thoroughly It has been recognized that the second solution results in an electrically induced asymmetry (electrical asymmetry effect), which provides the basis for the control of the mean ion energy This paper reviews recent advances on studies of the different electron heating mechanisms, on the possibilities of the separate control of ion energy and ion flux in DF discharges, on the effects of secondary electrons, as well as on the non-linear behavior (self-generated resonant current oscillations) of capacitive RF plasmas The work is based on a synergistic approach of theoretical modeling, experiments and kinetic simulations based on the particle-in-cell approach

Capacitive RF MEMS switch dielectric charging and reliability: a critical review with recommendations

Abstract: This paper presents a comprehensive review of the reliability issues hampering capacitive RF MEMS switches in their development toward commercialization. Dielectric charging and its effects on device behavior are extensively addressed, as well as the application of different dielectric materials, improvements in the mechanical design and the use of advanced actuation waveforms. It is concluded that viable capacitive RF MEMS switches with a great chance of market acceptance preferably have no actuation voltage across a dielectric at all, contrary to the ‘standard’ geometry. This is substantiated by the reliability data of a number of dielectric-less MEMS switch designs. However, a dielectric can be used for the signal itself, resulting in a higher Con/Coff ratio than that one would be able to achieve in a switch without any dielectric. The other reliability issues of these devices are also covered, such as creep, RF-power-related failures and packaging reliability. This paper concludes with a recipe for a conceptual ‘ideal’ switch from a reliability point of view, based on the lessons learned.

A Capacitive Fringing Field Sensor Design for Moisture Measurement Based on Printed Circuit Board Technology

Abstract: Interdigitated electrode capacitive fringing field sensors have been utilized in numerous applications. Although various technologies are used to realize these types of sensors, printed circuit board technology is particularly advantageous for realizing this type of sensor through fabricating the interdigitated electrode structures in the patterned Cu foil. Additionally, the solder mask coating can insulate the electrodes to prevent shorting in the presence of water. Using this approach, prototype sensors were designed, simulated, fabricated, and successfully evaluated. Applications include water detection and quantity measurement and soil moisture content measurement.

A capacitance-to-digital converter for displacement sensing with 17b resolution and 20μs conversion time

Abstract: In precision mechatronic systems, such as wafer steppers, the position of critical mechanical components must be dynamically stabilized with sub-nanometer precision. This can be achieved by a servo loop consisting of a displacement sensor and an actuator. Compared to optical interferometers, capacitive displacement sensors offer smaller size and lower cost. However, mechanical tolerances limit their electrode spacing to about 10μm [1], while the targeted resolution is below 100pm rms . This requires a capacitance-to-digital converter (CDC) with more than 17b resolution. Furthermore, its latency must be low enough (20μs) to avoid compromising servo-loop stability. Lastly, it should be stable enough to maintain measurement accuracy during the intervals between system calibrations.

Capacitive field sensor with sigma-delta modulator

Abstract: A capacitive sensor includes a switching capacitor circuit, a comparator, and a charge dissipation circuit. The switching capacitor circuit reciprocally couples a sensing capacitor in series with a modulation capacitor during a first switching phase and discharges the sensing capacitor during a second switching phase. The comparator is coupled to compare a voltage potential on the modulation capacitor to a reference and to generate a modulation signal in response. The charge dissipation circuit is coupled to the modulation capacitor to selectively discharge the modulation capacitor in response to the modulation signal.

Wearable monitoring and treatment device

Abstract: A wearable therapeutic device to facilitate care of a subject is provided. The wearable therapeutic device can include a garment having a sensing electrode. The garment includes at least one of an inductive element and a capacitive element, and a controller identifies an inductance of the inductive element or a capacitance of the capacitive element, and determines a confidence level of information received from the sensing electrode based on the inductance or the capacitance. The wearable therapeutic device also includes an alarm module coupled with the controller and configured to provide a notification to a subject based on the confidence level.

Capacitive touch panel with force sensing

Abstract: A capacitive type touch sensing device includes a first electrode array including a plurality of drive electrodes and a plurality of sense electrodes, and a second electrode array spaced apart from the first electrode array and including a plurality of discrete, electrically floating conductive regions. At least part of the second electrode array positionally overlaps with at least part of the first electrode array to define a separation distance therebetween, the separation distance varying with a force applied to a surface of the touch sensing device. Further, each conductive region is positioned relative to a respective drive electrode and sense electrode of the first electrode array so that a capacitance between certain pairs of drive and sense electrodes is more sensitive to a variation in the separation distance than a capacitance between other pairs of drive and sense electrodes.

Thermodynamic relation between voltage-concentration dependence and salt adsorption in electrochemical cells.

Abstract: Electrochemical cells containing two electrodes dipped in an ionic solution are widely used as charge accumulators, either with polarizable (supercapacitor) or nonpolarizable (battery) electrodes Recent applications include desalination ("capacitive deionization") and energy extraction from salinity differences ("capacitive mixing") In this Letter, we analyze a general relation between the variation of the electric potential as a function of the concentration and the salt adsorption This relation comes from the evaluation of the electrical and mechanical energy exchange along a reversible cycle, which involves salt adsorption and release by the electrodes The obtained relation thus describes a connection between capacitive deionization and capacitive mixing We check this relation with experimental data already reported in the literature, and moreover by some classical physical models for electrodes, including polarizable and nonpolarizable electrodes The generality of the relation makes it very useful in the study of the properties of the electric double layer

An improved lumped element nonlinear circuit model for a circular CMUT cell

Abstract: This paper describes a correction and an extension in the previously published large signal equivalent circuit model for a circular capacitive micromachined ultrasonic transducer (CMUT) cell The force model is rederived so that the energy and power is preserved in the equivalent circuit model The model is able to predict the entire behavior of CMUT until the membrane touches the substrate Many intrinsic properties of the CMUT cell, such as the collapse condition, collapse voltage, the voltage–displacement interrelation and the force equilibrium before and after collapse voltage in the presence of external static force, are obtained as a direct consequence of the model The small signal equivalent circuit for any bias condition is obtained from the large signal model The model can be implemented in circuit simulation tools and model predictions are in excellent agreement with finite element method simulations

Flexible polyimide-based force sensor

Abstract: We have realized a flexible force sensor, composed of four redundant capacitors, the operation of which is based on the measurement of a load-induced capacitance change. We use polyimide both as flexible substrate and as elastic dielectric between two levels of finger-shaped aluminum electrodes. In particular we have developed a technology for realization of two-level polyimide microstructures with gentle slopes to facilitate subsequent metallization processes. Thereby, we could improve step coverage and electrical contacting between the two metallization levels, as well as the mechanical stability of the sensor. The smooth polyimide slopes were obtained by combining lithographic resist-reflow techniques with dry etching procedures. We have analytically modeled the sensor's capacitance and its force sensitivity. We have electrically characterized the capacitors using an impedance analyzer and obtained capacitances in the range of 130 pF and a typical force sensitivity of 0.5–1 fF/N, in excellent agreement with our model.

A compact and miniaturized high resolution capacitance dilatometer for measuring thermal expansion and magnetostriction

Abstract: We describe the design, construction, calibration, and two different applications of a miniature capacitance dilatometer. The device is suitable for thermal expansion and magnetostriction measurements from 300 K down to about 25 mK, with a resolution of 0.02 A at low temperatures. The main body of the dilatometer is fabricated from a single block of a Be-Cu alloy by electrical discharge milling. This creates an extremely compact high-resolution measuring cell. We have successfully tested and operated dilatometers of this new type with the commonly used physical property measurement system by quantum design, as well as with several other cryogenic refrigeration systems down to 25 mK and in magnetic fields up to 20 T. Here, the capacitance is measured with a commercially available capacitance bridge. Using a piezoelectric rotator from Attocube Systems, the cell can be rotated at T = 25 mK inside of an inner vacuum chamber of 40 mm diameter. The miniaturized design for the one-axis rotation setup allows a rotation of 360°.