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Capacitive proximity sensing arrays (CPSAs) have diverse applications in industrial and service fields. However, the trade-off between spatial resolution and detection range poses challenges for such sensors in flexible interactive environments. This paper presents a physical combination approach to address this key barrier by modulating the effective sensing area of electrodes. Using an 8-element CPSA, we demonstrate 800% adjustability in spatial resolution and 300% in detection range. Finally, implemented on a robotic hand, it realizes large-scale distance estimation and high-precision (>95%) feature classification in real grasping scenarios. The distinctive feature of this method is that the physically effective contact avoids a large number of parasitic capacitance and noise interference, and has a highly stable signal acquisition capability in different perception modes. This method paves a new way to enhance and flexibly tune existing CPSA performance. [Display omitted] • Propose a flexible electrode area adjustment method for capacitive sensing array. • Enable programmable spatial resolution and sensing range for proximity sensing. • Demonstrate wide-range distance estimation and high-precision shape recognition. • Optimize the sensing performance at different stages of the grasping task. [ABSTRACT FROM AUTHOR]

In this study, a flexible capacitive strain sensor based on a novel wavy-shaped structure for multiple deformations recognition was developed. Based on the simplified deformation of the wavy-shaped structure, the capacitive response of the sensor under both stretching and compressing deformations was analyzed. To evaluate the performance of the sensor, both stretch and compression for the sensor unit were calibrated and characterized, with results showing excellent sensitivity for both deformations. The sensor unit also exhibits super high resolution and dependable durability, which demonstrates its extraordinary sensing ability. Furthermore, by using active capacitive shielding layers, the wavy-shaped flexible strain sensor can also recognize stretching and bending deformations. Finally, the developed flexible sensor was integrated on a wearable elbow sleeve for sensing the bending angle of the elbow joint, which demonstrates its performance in rehabilitation. [Display omitted] • A wavy-shaped flexible strain sensor unit that exhibits bi-directional strain sensing ability is proposed in this paper. • Combining the unit and appropriate shielding technique, this sensor is capable of recognizing different deformations. • Integrating this sensor and a wearable device, this sensor is capable of sensing the bending angle of elbow joint. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A novel temperature sensor was fabricated with CuTsPc based electrolytic fluid. • TiO2 nanoparticles have been added to enhance the sensitivity of the device. • Combination of CuTsPc and TiO2 showed strong temperature dependence on the capacitance. • The hybrid electrolytic based device enhanced the performance of the sensor. Abstract This work demonstrates a highly efficient electrochemical cell based on the hybrid nanofluid of titanium dioxide (TiO 2) nanoparticles dispersed in a water-based copper (II) phthalocyanine-tetrasulfonic acid tetrasodium salt (CuTsPc) solution. A chemical cell of ITO/nanofluid/ITO has been fabricated to study the effect of temperature variations towards its capacitance and resistance. The resultant device showed capacitive sensing mechanism, and the synergistic hybridization of the two different sensing elements lead to the superior performance as compared to the single CuTsPc based device. The hybrid device outperformed the pristine CuTsPc based device in terms of sensitivity, stability, linearity, response/recovery and possessed narrow hysteresis loop. [ABSTRACT FROM AUTHOR]

In practical applications of collaborative robots, proximity and pressure sensing capabilities are crucial for ensuring the safety and effectiveness of interaction. This paper proposes a novel method of integrating a bimodal sensor that uses a piezoresistive membrane as a self-capacitive electrode, overcoming the current challenges in integration and signal independence. By optimizing the graphene dispersion concentration, the prepared piezoresistive membrane can meet the initial resistance requirements of the self-capacitive electrode and the high sensitivity requirements of piezoresistive sensing. Experimental trials conducted to characterize the sensor focus on its sensitivity (8.49 MPa−1 /2.75% cm−1), response time, and repeatability for both pressure and proximity sensing. Results indicate successful dual-mod e detection with crosstalk-free between the two sensing modalities, achieved by evaluating proximity performance under different pressure conditions. Furthermore, a practical application of a 6-array e-skin mounted on a robotic arm is demonstrated, enabling proximity pause and pressure-based servo position control. This innovative approach enhances the robot's sensing ability and promotes safer and more efficient collaboration between humans and machines. [Display omitted] • Bimodal Sensor Integration: Novel method integrating pressure/proximity sensing. • Graphene Optimization: Fine-tuned graphene dispersion for high sensitivity and initial resistance. • Robotic Arm Application: Demonstrated six-array sensor for robotic arm's closed-loop control. [ABSTRACT FROM AUTHOR]

This work focuses on the development of custom capacitive sensors for measuring vibration and small displacements of high-speed rotating machines. The main criteria for this development are to use cheap and available resources and to optimize these resources to achieve the best possible performance. The aim was to design a solution that could be implemented within an Active Vibration Control (AVC) system, where the focus is mainly on high measurement frequency. The paper also includes a theoretical description of the measurement methodology with capacitive sensors and the use of the FDC2214 capacitive-digital converter (CDC), which works on the principle of a resonant LC circuit. The last part of the paper is devoted to the comparison of different designs of sensitive parts and also the concepts themselves. In addition to the calibration, the static characteristics are also described, and a measurement range error analysis is performed. The result of this work is a solution with a maximum measurement frequency of 3.8 MHz, maximum relative error of about 0.7% and sensor resolution from about 700 nm to 14 µm. The work also includes the deployment of the resulting smart sensors on the high-speed rotating machine to prove the capability to use them in the already mentioned AVC system. [Display omitted] • Explanation of the principles of capacitive sensing. • Development of an efficient and low-cost solution for measuring small displacements in the range of 0–1000 micrometers. • Comparison of several developed sensor designs. • The maximum relative error of the sensor is approximately 0.7% over the measuring range. • Maximum measurement frequency reached up to 3.8 MHz. [ABSTRACT FROM AUTHOR]

Highlights • Fabrication of flexible Graphite/PDMS sensor patches using 3D printed molds. • Casting technique was used to develop the electrodes and substrate of the sensor patches. • Interdigitated electrodes were employed for the patches operating on capacitive principle. • The sensor patches were characterized for the change in responses with stress and iterative bending cycles. • The sensor patches were used for low-force sensing applications ranging from 3.5 mN to 17.5 mN. Abstract This paper concerns the design, fabrication and characterization of graphite/PDMS sensors for low-force sensing applications. Exploiting the design flexibility of 3D printing, moulds of specific dimensions were prepared onto which graphite powder and PDMS were cast, to develop sensor patches. The sensor patches were highly flexible with repeatable responses to iterative bending cycles. The patches were tested in terms of stretchability, strain and bending-cycle responses. The sensor patches had interdigitated electrodes operating on capacitive sensing, where the effective capacitance changes with an applied force because of changes in their dimensions. Forces ranging from 3.5 mN to 17.5 mN were applied to determine the capability of these sensor patches for low-force sensing applications. The sensor patches had a quick recovery having a sensitivity and SNR per unit force of 0.2542 pF mN−1 and 10.86 respectively. The patches were capable of differentiating the forces applied on them, when they were attached to different objects in daily use. [ABSTRACT FROM AUTHOR]

The relation between the pressure and the capacitance of the carbon black filled silicone rubber composite with the carbon black content ranging from 5 vol.% to 9 vol.% (this content range can ensure the reinforcement effect and the flexibility of the composite for sensor development) under the multi compression cycles is researched. The capacitance of the composite increases with the increase of the pressure. There are deviations between the thicknesses/capacitivities of the composite under the same pressure in the different compression cycles, which results in the repeatability error of the piezocapacitivity of the composite. The experimental results show that the repeatability can be improved by increasing the number of the compression cycles. Therefore, the piezocapacitive effect of the composite has the potential to be used to measure the compressive pressure by applying the multi pre-compression cycles on the composite. The further analyses show that the hysteresis error, the nonlinear error and the sensitivity decrease with the increase of the number of the compression cycles. [ABSTRACT FROM AUTHOR]

Endoscopic palpation is a developing technology that shows promise in identifying early stage small tumors located beneath the surface of an organ. This technology requires sensors to detect the stiffness difference between stiff tumors and soft healthy tissue. This paper proposes a three-axis ballpoint-pen-type force sensor that can scan the surface to measure both shear and reactive forces, which can be used to calculate the distribution of stiffness. The sensor design includes five capacitors, four of which are formed at the lateral side of the cylindrical silicone rubber body. Fabrication of the electrodes is achieved by filling the pockets of a molded polydimethylsiloxane structure with liquid metal. The manufactured sensor was capable of identifying the magnitude and orientation of an applied shear force at 1 N. Detection of a stiff region was also successfully demonstrated. [ABSTRACT FROM AUTHOR]

Electrowetting on dielectric (EWOD) based digital microfluidics (DMF) emerges as a modern paradigm for lab on a chip (LOC) application, as it offers advantages of portability, automation, higher sensitivity and high throughput in diagnosis applications. One of the challenges in designing of EWOD devices for such applications is managing many droplets on the single substrate. The controlling of the droplet traffic requires a feedback control system whose sensor can continuously monitor the droplet parameters like contact angle, position, size, and velocity. In this work, we have demonstrated a low-cost open EWOD based dynamic sensing system, which is capable of tracking multiple droplets on the single substrate in real time. Droplet parameters are measured by sensing the capacitance value between electrode pad and ground wire. This makes the systems scalable, portable, robust, highly sensitive and inexpensive. We have used printed circuit board (PCB) based open EWOD device, where polydimethylsiloxane (PDMS) is used as a dielectric as well as a hydrophobic layer. The analytical model for droplet velocity has been developed, which matches quite well with experimental results. The droplet sensing approach presented in this work, adds to the functionality of DMF by allowing measurement with top ground configuration. [ABSTRACT FROM AUTHOR]

Safety devices are essential for humans and robots to work alongside each other or together. This paper introduces a multi-functional safety sensor for physical Human–Robot Interaction (pHRI). We adapted dual-type capacitive and inductive measurements for the proposed sensor. It enables the sensor to detect the human body and the metal sensitively and distinguish whether an object is a human body. The tendency of the capacitance and the inductance depending on the thing is significant to recognize the objects. We introduce three practical techniques to enhance sensor performance. The conversion time control allows the sensor to adopt the dual-type measurement. The carbon micro-coils (CMC) and the active shield improve the sensitivity and the signal integrity. Three typical pHRI functions have been verified, from proximity range to contact interaction. Emergency stop, collision avoidance, and direct teaching are the representative functions. The sensor allows the robot to interact with the operator's body for emergency stop, collision avoidance, and even interact with conductive objects. However, only the operator's hand is allowed in the direct teaching function for safe human–robot collaborative work. Experimental results have shown that the sensor enables a robot to perform the various safety functions with a maximum of 300 mm of proximity and 11 N of force sensing capability. • The proposed sensor enables the robot to perform three typical physical Human–Robot Interactions (pHRI). • The dual-type capacitive and inductive measurement enables the sensor to detect both the human body and the metal sensitively. It distinguishes whether an object is a human body. It allows the robot to interact with only the operator's hand. • Experimental results have shown that the sensor enables a robot to perform the various safety functions with showing specific tendencies of the capacitance and the inductance. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper presents a technique to perform pose estimation of planar three degrees of freedom (DOF) motions using two-plate capacitive sensors. These sensors are commonly utilised to measure linear motion, however their capacitance response becomes nonlinear and errors can be introduced with the introduction of angular motions. This paper focusses on the development of a methodology to invert a nonlinear model which maps the pose of the end effector of a planar positioner to the capacitances of each sensor, in effect providing pose estimates from capacitance measurements. Strategies for the calibration of model parameters, for cases where full reference or only yaw sensor measurements are available, are extensively explored. The points evaluated through the proposed method are shown to outperform the best affine transformation when trained with a full reference, and improved performance is also observed when the single reference is employed. [ABSTRACT FROM AUTHOR]

A novel capacitive displacement sensor is proposed. The stator consists of a pair of interlocking comb-type electrodes, driven by two consistent high frequency voltage sources with opposite phase. The mover consists of double sensing channels with electrical orthogonal relationship. Through capacitive coupling, a relative displacement between the mover and the stator is converted to quasi sine/cosine signals, featured with direction identification and instantaneous displacement interpolation. Theoretical analysis indicates that the physical resolution of the studied sensor is the same as the electrode unit's width. And also, the interchannel's amplitude ratio and phase difference keep stable in a wide range of air gap size. Hence the performance of displacement detection can be enhanced by amplitude normalization and interpolation. Using a Printed Circuit Board (PCB) fabricated prototype, the proposed scheme was experimentally tested. Typical coupling statuses were captured. Main sensing characteristics and performance were investigated, such as the responding of air gap variation, the displacement sensitivity, and the measurement uncertainty. [ABSTRACT FROM AUTHOR]

This paper deals with the development and characterization of label-free microfluidic biosensors dedicated to the microwave dielectric spectroscopy of small volumes and flowing micro-scale particles. Especially, microwave dielectric spectroscopy offers unique capabilities to investigate intracellular properties of biological cells, which are informative on many biological processes. This paper presents two prototypes of high frequency biosensors able to operate in the microwave frequency range. Both are based on capacitive detection either in a broadband or resonant mode. Thick gold metal electrodes have been investigated to perform high sensitive analysis, while a microfluidic system was implemented over the RF circuit so that flowing liquid minimally impacts global losses of the system and has hence a limited effect on sensor sensitivity. Particles to be tested are manipulated to be accurately located in the detection area using dielectrophoresis techniques. To demonstrate the proposed approach and assess the detection capabilities of such sensors, HF measurements (up to 8 GHz) have been performed on calibrated size polystyrene beads (12 μm diameter) and compared with full-wave electromagnetic simulations. Measured capacitance contrasts are typically around 1 fF at 5 GHz. Preliminary experimentations were then achieved on cancerous cells. The presented results demonstrate the high potential of the proposed approach to develop new label-free analysis tools with a large application range, either in the diagnosis or treatment fields. [ABSTRACT FROM AUTHOR]

In a capacitive tactile sensor the dielectric layer plays an important role: both its electrical and mechanical properties affect the capacitance variation and the sensor response in terms of sensitivity, since the deformation ability of the dielectric layer allows for the detection of small pressures, and spatial resolution, since the dielectric layer acts as a low-pass spatial filter decreasing the spatial resolution. In this work we comparatively evaluate the effect of different elastomers on the performance of a capacitive sensor designed to cover large areas of a robot body. In particular, we compare the sensitivity, the spatial resolution and the durability of the sensor using foams, bulk elastomers and high permittivity composites. [ABSTRACT FROM AUTHOR]

Bi-axial or two-dimensional (2D) MEMS micro-scanning mirrors (or micro-scanners) are considered the key component for laser scanning projectors. Many studies have shown the mechanical characterization of fabricated devices driven by various mechanisms. This work presents an electrostatically driven bi-axial micro-scanner with capacitive position sensing for Lissajous scanning projection. With the added sensing capability, a PLL (phase-locked loop)-based oscillator loop is developed to sustain mechanical resonance and to provide mirror position information, which are equally important for practical applications. The micro-scanner and the required circuits are implemented using bulk micromachining SOI (silicon on insulator) and 0.35-μm CMOS (complementary metal oxide semiconductor) technologies, respectively. The measured resonant frequencies of the bi-axial micro-scanner for the slow and fast-axis scans are 1.4 and 21.9 kHz, and the associated optical scan angles are 22.5° and 40°, respectively, under pulse modulation of 48 and 115 V pp . The fabricated micro-scanner is adopted in a laser beam scanning projection system to achieve WVGA (852 × 480) display resolution. [ABSTRACT FROM AUTHOR]

The uniqueness of eyes, facial geometry, and gaze direction makes eye tracking a very challenging technological pursuit. Although camera-based eye-tracking systems are popular, the obtrusiveness of their bulky equipment along with their high computational cost and power consumption is considered problematic for wearable applications. Noncontact gaze monitoring using capacitive sensing technique has been attempted but failed due to low sensitivity and parasitic capacitance. Here, we study the interaction between a novel capacitive sensor and eye movement for wearable eye-tracking. The capacitive sensors are made of a pair of asymmetric electrodes; one comprising carbon nanotube-paper composite fibers (CPC) and the other being a rectangular metal electrode. The interaction between the asymmetric sensor and a spherical object mimicking an eyeball is analyzed numerically. Using a face simulator, both single- and differential capacitive measurements are characterized with respect to proximity, geometry, and human body charge. Using a prototype eye tracker, multiple sensor locations are studied to determine the optimal configurations. The capacitive responses to vertical and horizontal gaze directions are analyzed in comparison to those of a commercial eye tracking system. The performance is demonstrated for sensitive eye-movement tracking, closed-eye monitoring, and human-machine interface. This research has important implications for the development of capacitive, wearable eye trackers, which can facilitate fields of human-machine interface, cognitive monitoring, neuroscience research, and rehabilitation. [Display omitted] • Carbon nanotube paper composite (CPC) capacitive sensors were fabricated and used to create a wearable eye tracker. • A facial model was used to characterize the influence of facial geometry and human body charge on the CPC sensors. • Single- and differential capacitance modes enabled simultaneous detection of vertical and horizontal eye movements. • Eye tracker performance was shown for gaze tracking, closed-eye monitoring, and human-machine interface applications. [ABSTRACT FROM AUTHOR]

We developed a lightweight flexible keyboard with a touch sensor fabric that consists of conductive polymer-coated fibers. In our sensor fabric, the conductive polymer-coated fibers, which are sensing electrodes, are woven at a 2-cm pitch and the rest of the fabric is filled with pristine polyester fibers. The sensing principle for human touch detection is the measurement of the capacitance between the conductive polymer-coated sensing fibers and human fingers. The keyboard system consists of the touch sensor fabric, a capacitance measurement circuit, a signal processing circuit and software for entering characters into a personal computer (PC). The fabricated fabric has a large area, 20.5 cm × 12.5 cm, and weighs only 9 g, making it large enough for touch input and light enough to carry. In addition, the sensing electrode is bendable to a diameter of 1 mm because the sensor electrode is not inorganic material but rather polymer. When the sensor is touched, the capacitance between fiber and finger is increased by 2 pF, which is large enough to be detected with conventional capacitance measurement circuits. Finally, the keyboard input is demonstrated with our fabricated fabric sensors. This technology will lead to the development of keyboards that are especially well suited for wearable and portable electronic devices. [ABSTRACT FROM AUTHOR]

Air entrainment is among the key issues in solid-liquid mixing operations. In this paper, both analytical and finite element methods are employed to study the relationship between the volume of entrained air and the changes of capacitance. With a capacitance sensor installed at the bottom of the stirred tank, an experimental platform is established, which integrates a stirring system and a capacitive detection system. The pitched-blade turbines with four blades (PBT-4) are employed as the impellers in the experimental system and made of Plexiglas. Afterwards, the experiments are conducted with an empty tank to study the influences of propellers on capacitance. The capacitance values are measured at different stirring speeds in the single-phase (deionized water) and two-phase (deionized water and glass beads) stirring systems and applied in the assessment of air entrainment. The results are as follows. In the single-phase system, there is scarcely any air entrained in stirred tanks at low stirring speeds, and air entrainment occurs after the stirring speed (N) reaches a certain value. In the two-phase system, air entrainment is not observed obviously when the solid particles are at rest, but can be found after solid particles are mixed uniformly. Nevertheless, in the transition period between the two regions above, the capacitance becomes increasingly larger along with the growth of N due to the decrease of volume fraction of solid particles in the sensing area, which hinders the assessment of air entrainment. The discussions in this paper may serve as guidelines for solid-liquid mixing processes and can be further generalized for the assessment of air entrainment in solid-liquid mixing operations under other different parameters. [ABSTRACT FROM AUTHOR]

Highlights: [•] We propose an interdigital capacitive sensor for water level measurement. [•] This sensor has low-cost, low-energy, good repeatability, and high linearity. [•] This sensor can directly be applied to various types of water without recalibration. [•] This sensor can measure water level with 0.2cm resolution. [•] This sensor is also sensitive enough to trace the variability of water level. [ABSTRACT FROM AUTHOR]

Abstract: With the development of micro systems in recent years, the demands for ultraprecision measurement become more important in the field of dimensional metrology. In this paper, a tactile probing system based on capacitive sensor for precision metrology is presented. The capacitive sensor is fabricated by MEMS technique, and a commercial micro-probe and the capacitive sensor are integrated together to constitute the initial probing system. The signal processing circuit is designed to be based on AD7747 chip which is substantially a high resolution, Σ-Δ capacitance-to-digital converter (CDC). Then the experiment set-up is configured and experimental results indicate that when a 0.3mm probing head is used, the probing system has a resolution of better than 10nm along axial direction and better than 25nm along radial direction. With the low residual nonlinear error, the proposed system can therefore be used for submicron measurement of small structures with dimension larger than 0.3mm and depth down to 2.3mm. [Copyright &y& Elsevier]

Abstract: High-speed gap measurement in the nano/micrometer range presents unique engineering challenges. A signal conditioner is required for capacitive sensors to amplify, denoise, and restrict the bandwidth. In this work, a capacitive sensor was used in combination with a SAW device that serves as a signal conditioner. The proposed system provides 2.75MHz bandwidth through amplitude modulation using the center frequency of the SAW device as a carrier signal and has outstanding signal conditioning capabilities. Construction and characterization of a SAW-based capacitive gap sensor to measure a 200Hz gap frequency are described. [Copyright &y& Elsevier]

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 2.5N, is shown to provide repeatable measurements of static uniaxial loads, and follows the loading and unloading phases of low-frequency dynamic loads (0.4–4Hz). The sensor prototype has a spatial resolution on the order of 0.5mm, performs reliably when wrapped around a surface having a curvature similar to that of a human finger (1.575cm−1), and has been shown to tolerate curvatures as high as 6.289cm−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. [Copyright &y& Elsevier]

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 130pF and a typical force sensitivity of 0.5–1fF/N, in excellent agreement with our model. [Copyright &y& Elsevier]

Abstract: The experimental detection of capacitance variations with a resolution as low as few zeptoFarads (10−21 F) is presented. This is achieved by means of a CMOS ultra-low-noise and wide-bandwidth current sensing circuit, coupled to a lock-in amplifier to perform capacitance and conductance measurements in a frequency range from DC to 1MHz. The adoption of an integrated implementation, based on an original circuital topology, provides miniaturization and performance improvement. The mm-sized chip can be easily integrated in extremely compact sensing setups. Resolution limits are analyzed in detail and experimentally investigated by means of a mechanical fixture that converts micrometric linear displacement into sub-aF capacitance steps. The experimental results match the theoretical expectation down to a resolution of 5zFrms (6V at 100kHz, with a 100ms time constant). The achieved current resolution of 15fArms (at ∼ms time scale) and the tracking of 40zF capacitance steps demonstrate how the proposed read-out circuit can serve as a versatile tool for the development of nanosensors. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: In this study design and operation of invasive and non-invasive cylindrical capacitive sensor (CCS) designs for the electrical measurements of water, water solutions, and water mixtures are reported. Operation of the capacitance measurement module for such probes is based on the charge/discharge method. The measured capacitances and resistances for distilled water, mineral water, tap water and salt water samples are reported by using two sensor types and results are compared. The measured capacitance by invasive CCS for distilled water is about 2.28μF and by non-invasive CCS is 31.40pF, which shows a big difference for different probes. Such a difference is due to the electrical conductivity effects on the invasive CCS, which can be used for the conduction study of different liquids. In another study the capacitance values of a binary solution of water plus additive liquids such as antifreeze, petroleum, ethanol, methanol and mixtures of water with fresh and used motor oils are measured. The effects of the guard ring electrodes, and electrode–liquid interactions on the capacitance/resistance measurements for the invasive CCS filled with different water liquids are also investigated. [Copyright &y& Elsevier]

Abstract: Non-contact voltage sensors are designed to detect the voltage in a wire or piece of equipment without actually making direct contact with the conductor or energized part. Conventional single capacitive probe approach is not accurate and could easily be affected by environmental factors. In this paper, a capacitive probe with two sensor heads has been developed for the accurate sensing of AC voltage. Orthogonal least squares estimation algorithm has been implemented to identify the nonlinear relationship between the two sensor heads readings and the sensed AC voltage. With the added second sensor head, the sensed AC voltage will be less sensitive to the medium of the sensing environment and distance between the sensing surface and the probe. Experimental results are included to show the effectiveness of the proposed sensor system with the fitted model in sensing different AC voltages under different sensing environments. [Copyright &y& Elsevier]

Abstract: This paper presents the characterization of a novel tactile sensor designed to measure shear forces. The sensor design is targeted for use in robotic and prosthetic hands, where haptic feedback or ability to detect shear forces associated with slip are critical. The presented sensor utilizes the principle of differential capacitance to measure the mechanical deflection of the sensor element. The dynamic range of the sensor can be varied by encapsulating the sensor terminal within silicone of varying hardness. The design features ease of mass production, low per-unit-cost, novel overload protection and low wire count, while still preserving the ability to achieve reasonable spatial resolutions and array densities. Mathematical and COMSOL multiphysics models of the sensor are presented, in addition to results from practical experiments. Sensors with a full scale displacement range of ±0.525mm were produced and the differential capacitance was measured. Shear force transduction was characterized over the range of 0N–4N with the sense terminal encapsulated by silicone with a shore A hardness of 20. The effect of elastomer hardness on the sensor''s dynamic range was analyzed. The differential capacitance, when measured at each fixed interval, was found experimentally to have a maximum standard deviation of 4.28e−16 F over a ±2N range. A maximum standard deviation of 1.35e−15 F was measured across characterized full scale sensor range of ±4N. The sensor design has a sensitivity of 1.967fF/N of applied force and the sensor output was found to be approximately linear. The coefficient of determination, r 2, was found to be 0.941. [Copyright &y& Elsevier]

Abstract: This paper presents the development of a MEMS based capacitive tactile sensor intended to be incorporated into a tactile array as the core element of a biomimetic fingerpad. The use of standard microfabrication technologies in realising the device allowed a cost efficient fabrication involving only a few process steps. A low noise readout electronics system was developed for measuring the sensor response. The performance of both bare and packaged sensors was evaluated by direct probing of individual capacitive sensor units and characterising their response to load–unload indentation cycles. [Copyright &y& Elsevier]

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 2mm 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 30mm. The cell size is 1mm×1mm, and the initial capacitance of each cell is approximately 900fF. The tactile response of a cell is measured with a commercial force gauge having a resolution of 1mN. The sensitivity of a cell is 4%/mN within the full scale range of 0.3N. [Copyright &y& Elsevier]

Abstract: A sensor system for the study of oil–water flow in pipes is proposed. The purpose is to estimate the area fraction occupied by each fluid in a given section of the pipe, taking advantage of the difference in dielectric permittivity between the fluids. The estimation is done by capacitance measurements between electrodes flush-mounted on the external surface of a nonconductive section of the pipe. A key contribution of the present work is to propose a solution to the problem of capacitive sensing in presence of conductive water which introduces parasitic coupling to stray elements outside the measurement section of the pipe. To this purpose it is proposed a novel sensor configuration that employs guard electrodes, coupled to a tailored electronic interface to drive the guard electrodes and amplify the measurement signal at 2MHz. The sensor system has been designed, manufactured and tested in an experimental plant where flows of oil–tap water have been generated. The results obtained from the developed sensor system for different fluid fractions have been compared with those obtained by the Quick Closing Valve (QCV) technique adopted as a reference. Differences between the two methods below 3% have been found in the estimations of the normalized oil-area fraction. [ABSTRACT FROM AUTHOR]

Abstract: Nano-precision gap measurement in the sub-micron range presents its own unique engineering challenge. The popular capacitive sensor platform, for example, is susceptible to the erroneous effect of electrode tilting and high noise floor, both of which are exacerbated by the small form factor required of a nano-precision gap sensor. In this paper, a capacitive gap sensor with a hemispherical electrode, used in combination with a SAW filter is presented. The proposed system outperforms the existing ones on two fronts. First, the system is virtually immune to the effect of electrode tilting due to the improved capacitor geometry. Second, it benefits from the outstanding signal conditioning capability of the SAW filter. Construction and characterization of a SAW-based capacitive gap sensor having resolution as fine as 10nm are described. [ABSTRACT FROM AUTHOR]

Abstract: This paper introduces the BladderPill: an in vivo sensor system which is inserted into the bladder cavity through minimal invasive cystoscopy. It allows the autonomous monitoring and logging of the internal bladder pressure. Prototype circuits have been realized and tested in various layouts, to gradually approach the final pill-shaped form, measuring 40mm in length and 5mm in diameter. Constructed out of off-the-shelf components and embedded into silicone as a protective encapsulation, a low-cost flexible implant is created. The circuits fit on a double-sided flex measuring 4.2mm18mm and consume on average 350 A. Operation for over 24h is thus assured on a 13 mAh lithium cell with a diameter of 3mm. [ABSTRACT FROM AUTHOR]

Abstract: Due to an increasing need for devices with low power consumption, capacitive pressure sensors have become good substitutes for the well known piezoresistive pressure sensors. Mathematical models are necessary to design and characterize the device, preferably the model is analytical such that geometrical scalings are revealed. We show that, in the case of linear elastic behavior, a simple analytical model can be found for a touch mode capacitive pressure sensor (TMCPS). With this model it is possible to readily evaluate the main features of a TMCPS such as: sensitivity (both in normal and touch mode), touch point pressure and parasitic capacitance. Therefore, the desired device can be designed without using finite element modeling (FEM). This reduces the effort needed to design a micromachined TMCPS. Finally, the model has been compared with a micromachined TMCPS showing an excellent agreement with the experimental data. [Copyright &y& Elsevier]

Abstract: This paper reports on a sensor for the detection of microdroplets in flight. The presented sensor is based on a capacitive principle, which allows for non-contact monitoring of a complete droplet dispensing process. In the presented experiments the change in capacity caused by liquid droplets in the range of a few nanoliters passing through the electric field of the sensor is studied. From the capacitive change the droplet presence can be deduced with a reliability of 100%, which means that every single droplet dispensed within the experiments caused a significant signal change. In addition, the sensor signal is sensitive to the droplet''s volume V, dielectric constant ɛ r (epsilon) and velocity . It turns out that every specific droplet exhibits a characteristic “fingerprint” signal depending on these parameters. Especially the droplet volume correlates very well with the peak value of the extracted signal. Therefore, the calibrated sensor is able to determine the volume of dispensed droplets in the range from 20 to 65nl with a resolution of less than 2nl. Furthermore, the printed circuit board (PCB) technology applied for fabrication of the sensor enables a very cost efficient and flexible realisation of the whole sensor unit. The non-contact capacitive principle prevents contamination and loss of media. Therefore, the proposed approach is well suited for high precision droplet presence detection and low cost online monitoring of liquid volumes in microdispensing processes for various applications. [Copyright &y& Elsevier]

Abstract: The present paper reports the development of a capacitive ultrasonic sensor having Parylene diaphragm. Parylene diaphragm is flexible and non-brittle, allowing good sensitivity and durability. The resonant frequency under the tensile stress of Parylene and the influence of the number and the radius of acoustic holes on damping ratio are investigated by FEM (finite element method) simulation. Practical sensor devices are fabricated. They can receive an impulsive ultrasonic pulse transmitted by a spark discharge. The ranging system using this sensor can detect the distance up to 1m with the error less than 1mm. The developed sensor can be approximated to be non-directional. An arrayed sensor device comprising 5×5 developed sensors is fabricated, and its receiving performance is characterized. It is proven that the electric scanning of directivity based on delay-and-sum principle is possible. [Copyright &y& Elsevier]

Abstract: A sigma delta (ΣΔ) capacitive sensor is presented in this paper for highly integrated lab-on-chip (LoC) applications using charge based capacitance measurement method (CBCM). We put forward the design and implementation of sensor chip in 0.18μm CMOS process featuring an array of capacitive sensors, an offset cancellation (OC) circuitry and a DC input first-order ΣΔ analog to digital converter (ADC). This sensor chip is incorporated with a microfluidic channel using direct-write fabrication process. The design, construction and experimental results are demonstrated using chemical solvents with known dielectric constants and polyelectrolyte solutions in order to show the viability of the proposed capacitive sensor for LoCs. [Copyright &y& Elsevier]

Abstract: This paper proposes and analyses a direct interface circuit for capacitive humidity sensors. Such a circuit relies on directly connecting the sensor to a microcontroller without using either a signal conditioner or an analogue-to-digital converter, thus resulting in a simple, compact, low-cost and low-power interface circuit. In spite of its simplicity, the interface circuit performs satisfactorily when measuring commercial capacitive humidity sensors (Philips H1 and Humirel HS1101). The non-linearity error of the interface circuit itself (0.1% full scale span (FSS)) is much smaller than that of the sensor (5.6% FSS for the H1 and 2.1% FSS for the HS1101) and, therefore, the circuit does not limit the accuracy (in terms of linearity) of the measurement, as is to be expected from a well-designed interface circuit. Furthermore, the effective resolution equals 9 bits for a measuring time of 50ms, which are fully acceptable for humidity measurements. [Copyright &y& Elsevier]

Abstract: A monolithically packaged surface acoustic wave (SAW) radio transponder and pressure sensor are developed for the application to a tire pressure monitoring system (TPMS). The device contains the wireless transponder, which converts analog signal into digital one without any auxiliary electronic circuits and transmits the converted data wirelessly. No power sources are needed for wireless transponder and pressure sensor. The touch-mode pressure sensor converts externally applied pressure into capacitance, and the SAW radio transponder radiates sensor values with pulse train to the interrogation (measurement) unit. The realization of the mechanical A/D conversion is possible since the SAW radio transponder is connected to the touch-mode capacitive pressure sensor. The SAW radio transponder and touch-mode sensor are fabricated using a surface micromachining and a bulk micromachining technologies, respectively. The performance of the integrated, passive and wireless pressure sensor meets the design specifications such as linearity, sensitivity and noise figure. Finally, experimental results for the radio transponder and the sensor without power source are presented. [Copyright &y& Elsevier]

Abstract: In this paper, we put forward a capacitive sensor for Lab-on-Chip applications using a charge-based capacitance measurement (CBCM) method. This simple and highly sensitive capacitive sensor is implemented in the TSMC 0.18 CMOS process to which we incorporate microfluidic structures for chemical sensing. The post-layout simulation, fabrication and preliminary Lab-on-Chip testing results are also reported. [Copyright &y& Elsevier]

Abstract: This paper describes the design and implementation of a liquid-level measurement system based on a remote grounded capacitive sensor. The electrodes of the capacitive sensor are built with affordable materials: a rod of stainless steel and a PTFE-insulated wire. The interface circuit relies on a simple relaxation oscillator and a microcontroller. A cable with active shielding interconnects the sensor to the interface circuit. The stability of the active-shielding circuit is analysed by taking into account the parasitic components of both the interconnecting cable and the sensor. The system has been experimentally tested by measuring the level of tap water in a grounded metallic container. Over a level range of 70cm, the system has a non-linearity error smaller than 0.35mm and a resolution better than 0.10mm for a measuring time of 20ms. [Copyright &y& Elsevier]

Abstract: In this paper we examine with analytical and finite element modeling the influence of structural parameters on the performance of capacitive silicon pressure sensors. It is found that device behavior is dependant on the substrate deformation as well as the foundation of the sensor diaphragm. Accurate results may only be obtained when all parameters and residual stresses are included. [Copyright &y& Elsevier]

Abstract: In this paper, we propose a laboratory-on-chip (LOC) integration technique based on a novel electro-fluidic implementation and packaging procedures for blood-based diagnostics. LOC-based diagnostic tool is a complex, hybrid system consisting of various electrical, fluidic, and biochemical components, connected electrically and through fluidic channels on a single platform. The microfluidic fabrication technique is based on a direct-write fabrication process (DWFP) while the conventional wire bonding makes needed electrical connections. The microelectronic parts of proposed LOC put forward a high precision capacitive sensor carried out in TSMC''s 0.18μm CMOS process. Experimental results allow demonstrating the capability of the proposed DWFP to fabricate polymer-based microfluidics on top of CMOS chips for LOCs. In addition, the preliminary results of the proposed capacitive sensor show a sensitivity of 250mV/fF with a noise level equivalent to less than 10aF where the existing parasitic capacitances can be more than 150fF. [Copyright &y& Elsevier]

Abstract: This paper describes the design of a functional strain sensing module with large dynamic range (80dB), DC to 10kHz response, high resolution, and mini size for industrial applications, such as the rolling-element bearings research. The design of the MEMS capacitive strain sensor employs mechanical amplifications of package design and buckle beams as well as the linear differential comb capacitor. The sensor is interfaced with a low noise charge amplifier, mixer, and filter circuits to provide an analog output that demonstrated a resolution of 0.09 microstrains with a maximum range of ±1000 microstrains. The sensor and the electronic circuits, including a temperature sensor, can be integrated on a chip, and packaged as a small functional unit. Additional electronics were integrated with the interface circuit on the chip that provide A/D conversion, radio frequency power supply, and digital signal telemetry to a near-by control unit. Preliminary test results are compared with the design simulation. [Copyright &y& Elsevier]

Abstract: Air speed and flight attitude angles are fundamental parameters for manual of automatic control of flying bodies. Conventional measurement methods rely on probes (e.g. Pitot tubes or vanes) having a one-to-one correspondence with the physical quantities of interest and requiring specific placements. Here, a novel measurement approach is proposed, relying on indirect measurement and on a plurality of pressure readings made by thin capacitive sensors directly placed on the aircraft skin. A redundant number of probes relaxes the accuracy requirements posed on the individual units and helps achieving fault detection or fault tolerance. A strategy for efficiently processing/combining sensor data is herein presented together with an error propagation analysis, and experimental data. [Copyright &y& Elsevier]

Abstract: The localised flux density measurements are practically limited to two methods: search coil and needle probe technique. The search coil requires drilling holes in the sample under test; therefore it is a destructive method. Needle probe technique is classified as a non-destructive technique. However, removing the coating affects the magnetic properties of the sample sharp needles introduce micro-damages to the surface of the specimen. At certain conditions, the electrical contacts between the needles and the sample could be replaced by capacitors made as pads manufactured from self-adhesive conductive tape or directly painted with conductive paint on the insulated surface of the sample. The paper presents theoretical analysis of the concept of the capacitive sensor. The simulations suggest that the described capacitive sensor would be suitable for detecting localised flux density in laminated material, especially at higher frequencies. [Copyright &y& Elsevier]

Abstract: The paper describes a one-directional position-sensitive force transducer based on polypropylene electret film (EMFi). While the voltage amplifier had relatively low input impedance, the dynamic response of the transducer in the dilatation phase (recovering of micropores) was four times more intensive than during compression. Software tools for an application of the sensor for recording and comparing human touching patterns were designed. The preliminary test was done with eight subjects using the prototype of the pressure sensitive lock (PSL). Some individuals can use the high security level and could control touching behavior rapidly and accurately within as little as 1 week. The model of the position-sensitive force transducer and preliminary evaluation of the PSL are considered in detail. [Copyright &y& Elsevier]

Abstract: In the present work, a new monolithic capacitive pressure sensor is being introduced. The sensor is manufactured according to a custom, 15-step SOI process. The process primarily offers great flexibility as far as sensor design is concerned. Absolute or differential pressure sensing is possible by simply arranging proper sensor package. Measurement sensitivity and span are easily regulated over a wide range of values by setting one-single design parameter. Attention is paid to avoid p–n junction formation in order to improve the sensor robustness against temperature increase and allow high-temperature post-processing without doping profile degradation. The presented design allows the implementation of an ordinary p-well CMOS post-process. Sensitivity of 2mV/kPa, within a span of 180kPa (2%) and a bandwidth of 25kHz, is achievable by means of a CMOS switched-capacitor ASIC that is developed and presented here. Significant care has been taken for the ASIC performance to depend as less as possible on CMOS process and transistor-parameter variations that increase due to poor uniformity of the transistor substrate. Moreover, a state-of-the-art design is implemented for the circuit to provide robustness against parasitic capacitances connected in parallel with sensing capacitors. Implementation of additional analog signal processing improves the aforementioned accuracy at a significant extend. The sensors main applications include medical devices such as sphygmomanometers and respirators that require high reliability and biocompatibility. [Copyright &y& Elsevier]

Abstract: The combs of the comb capacitive inertial sensors fabricated by a deep reactive ion etching are usually not parallel. This non-ideal feature is greater in high aspect ratio structure and significantly affects the capacitance and electrostatic force. In this paper, the effects of non-parallel combs on the reliable operation range for step and pulse signals in three capacitive configurations are investigated when alternative electronic testing signals are applied on the sensors for detecting the variation of capacitance. Analytical expressions of the critical step acceleration and the critical time duration of pulse acceleration of the capacitive sensor whose comb electrodes have little angle of the decline are obtained. Results show that for a step inertial signal, even the angle of the decline is 0.5°, the reliable operation ranges of the sensor with single-sided structure, double-sided structure and double-sided structure with feedback voltage are diminished to 0.34, 0.44 and 0.54 of the ones whose comb electrodes are parallel, respectively, for pulse inertial signal, the reliable operation ranges with single-sided structure and double-sided structure are diminished to 0.45 and 0.56, respectively, and the ones of double-sided capacitive sensor with feedback voltage are diminished to 0.95 as the angle is changed from 0.1° to 0.15°, which show that the effects of the non-parallel can not also been ignored. Results also show that the reliable dynamic operation ranges of the sensor with double-sided comb capacitive structure are least affected by the effects of non-parallel plates and its merit is more evident as the angle of the decline of the comb electrodes increases. Compared to the effects of non-parallel comb electrodes on the reliable operation range for step inertial signal, the effects for pulse inertial signal are smaller. [Copyright &y& Elsevier]

Abstract: The equivalent circuit model of a capacitive type level sensor has been discussed in this paper. The effect of double layer in a polarizable liquid medium has been taken into account in the proposed model. It has been shown that the parameters of the equivalent circuit can be estimated through a combination of theoretical and experimental approaches. Finite element analysis (FEA) has been used to estimate the resistance and capacitance due to the polarizable medium. The performance of a novel capacitance sensor with the liquid medium surrounding the probe has been investigated using the proposed method. [Copyright &y& Elsevier]