Differential C<Superscript>4</Superscript>D sensor for conductive and non-conductive fluidic channel

This paper presents a novel design of a differential C⁴D (DC⁴D) sensor based on three electrodes for both conductive and non-conductive fluidic channel. This structure consists of two single C⁴D with an applied carrier sinusoidal signal to the center electrode as the excitation electrode. The electrodes are directly bonded on the PCB with built-in differential amplifier and signal processing circuit in order to reduce the parasitic component and common noise. In the non-conductive fluidic channel, the output voltage and capacitance changes 214.39 mV and 14 fF, respectively when a 3.83 μl tin particle crosses an oil channel. In conductive fluidic channel, the output voltage and admittance change up to 300 mV and 0.07 μS for the movement of a 4.88 μl plastic particle through channel. Moreover, the voltage change of this sensor is linear relation with the volume of investigated particle. This sensor also allows measuring velocity of particle inside fluidic channel and resistivity of the conductive fluidic.     

Capacitive flexible pressure sensor: microfabrication process and experimental characterization

Kapton-based flexible pressure sensor arrays are fabricated using a new technology of film transfer. The sensors are dedicated to the non-invasive measurement of pressure/force in robotic, sport and medical applications. The sensors are of a capacitive type, and composed of two millimetric copper electrodes, separated by a polydimethylsiloxane (PDMS) deformable dielectric layer. On the flexible arrays, a very small curvature radius is possible without any damage to the sensors. The realized sensors are characterized in terms of fabrication quality. The inhomogeneity of the load free capacitances obtained in the same array is ±7 %. The fabrication process, which requires 14 fabrication steps, is accurate and reproducible: a 100 % transfer yield was obtained for the fabrication of 5 wafers gathering 4 sensor arrays each (215 elementary sensors). In the preliminary electro-mechanical characterization, a sensor (with a PDMS dielectric layer of 660 μm thickness and a free load capacitance of 480 fF) undergoes a capacitance change of 17 % under a 300 kPa normal stress.     

Meter-scale large area LED-embedded light fabric for the application of fabric ceilings in rooms

We have developed a meter-scale light emitting diode (LED)-embedded light fabric and its weaving machine for application to a light device for fabric ceilings, which have recently become desired for lightweight safe ceilings in Japan and other countries with frequent earthquakes. The LED fabric structure is 1.2-m-wide woven fabric that has 5-mm-wide LED chip-mounted printed circuit board (PCB) tapes as wefts. LEDs are mounted on the tape of PCBs with a reel-to-reel chip mounting system. Then, the LED-mounted tapes are woven with a developed automatic looming machine that aligns the weft with an accuracy of 0.9 mm, which is suitable for precise arrangement of LEDs and wiring to power supply. A 1.2 × 1.2 m LED-embedded light fabric weighing 320 g/m² was woven. The luminance of the LED fabric is 353 lx at a distance of 1 m, which is the luminance of conventional office lighting. The temperature increase of LEDs without a rigid cooling aluminum plate is only 5.8 °C, and the LED fabric is flexible enough to sustain 1,000 bends down to a radius of 3 mm. This LED fabric and its weaving technology will lead to light devices that have lightweight, large area, and high flexibility for fabric ceilings, walls, and other large areas in homes and offices.     

A flexible PDMS capacitive tactile sensor with adjustable measurement range for plantar pressure measurement

A flexible capacitive tactile sensor with adjustable characteristics, i.e., measurement range and sensitivity, has been developed. The proposed sensor is designed for large pressure measurement; therefore, polydimethylsiloxane (PDMS) material is selected as the material of the dielectric layer between the parallel plate electrodes of the sensor. Since the elasticity of the PDMS material can be adjusted by the mixing ratio of PDMS pre-polymer and curing agent during formation, sensors in different measurement ranges, i.e., 240–1,000 and 400–3,000 kPa, and corresponding sensitivities, i.e., 2.24 and 0.28 %/MPa, were respectively constructed and demonstrated. These measurement ranges are suitable for most of the biomechanical applications, especially for plantar pressure measurement. Moreover, because the output of the sensor, i.e., capacitance, is highly influenced by the dimension of the sensor structure, each sensor consists of four independent capacitance elements. The output of each sensor is averaged by four capacitances for single force measurement. This could improve the measurement accuracy in practical situation. Also, linearity of the measurement response could be enhanced and it was shown by the R-squared values in two measurement ranges, i.e., 0.9751 and 0.9881, respectively. The proposed sensor is flexible and miniaturized and has the potential to be applied to biomechanical applications.     

Liquid film thickness measurement underneath a gas slug with miniaturized sensor matrix in a microchannel

Measurement of liquid film thickness is essential for understanding the dynamics of two-phase flow in microchannels. In this work, a miniaturized sensor matrix with impedance measurement and MEMS technology to measure the thin liquid film underneath a bubble in the air–water flow in a horizontal microchannel has been developed. This miniaturized sensor matrix consists of 5 × 5 sensors where each sensor is comprised of a transmitter and a receiver electrode concentrically. The dimension and performance of the sensor electrodes were optimized with simulation results. The maximum diameter of the sensor ring is 310 µm, allowing a measurable range of liquid film thickness up to 83 µm. These sensors were distributed on the surface of a wafer with photolithography technology, covering a total length of 8 mm and a width of 2 mm. A spatial resolution of 0.5 × 2.0 mm² and a temporal resolution of 5 kHz were achieved for this sensor matrix with a measurement accuracy of 0.5 µm. A series of microchannels with different heights were used in the calibration in order to achieve the signal-to-thickness characteristics of each sensor. This delicate sensor matrix can provide detailed information on the variation of film thickness underneath gas–water slug directly, accurately and dynamically.     

Fabrication of micro-capacitive inclination sensor by resin molding

Capacitive inclination sensors have the advantage that they can easily provide a linear analog output with respect to inclination. Although inclination sensors featuring this advantages are already commercially available, they are generally too large. We fabricated a micro-capacitive inclination sensor by a combination of a resin forming method and a mold. Electrodes of the sensor are 40 μm in a gap and 12 mm² in area. The sensor detects difference of capacitance, which varies with movement of silicone oil accompanying with inclination of the sensor. Since the dimensions of the sensing region are 5 × 5 × 3 mm³ this inclination sensor is expected to be widely used in fields where efficient and reliable position control is a primary factor to be considered. The use of resins is also expected to contribute to a reduction in the costs of materials. We successfully fabricated a micro inclination sensor as a molded product. In future, we will wire up the device to complete this inclination sensor, and will then conduct performance evaluations. If techniques using resin-molded parts are introduced to the low-cost mass-production of Micro Electro Mechanical Systems devices, the range of applications will further expand to new areas of technology and industry.     

A printed circuit board capacitive sensor for air bubble inside fluidic flow detection

This paper presents a three-electrode capacitive fluidic sensor for detecting an air bubble inside a fluidic channel such as blood vessels, oil or medical liquid channels. The capacitor is designed and fabricated based on a printed circuit board (PCB). The electrodes are fabricated by using copper via structure through top to bottom surface of the PCB. A plastic pipe is layout through the capacitive sensor and perpendicular to the PCB surface. Capacitance of sensor changes when an air bubble inside fluidic flow cross the sensor. The capacitance change can be monitored by using a differential capacitive amplifier, a lock-in amplifier, filter and an NI acquisition card. Signal is processed and calculated on a computer. Air bubble inside the liquid flow are detected by monitor the unbalance signal between the three electrode potential voltages. Output voltage depends on the volume of the air bubble due to dielectric change between capacitor’s electrodes. Output voltage is up to 53 mV when an 2.28 mm³ air bubble crosses the sensing channel. Air bubble velocity can be estimated based on the output pulse signal. This proposed fluidic sensor can be used for void fraction detection in medical devices and systems; fluidic characterization; and water–gas, oil–water and oil–water–gas multiphase flows in petroleum technology. That structure also can apply to the micro-size for detecting in microfluidic to monitor and control changes in microfluidic channels.     

A novel high sensitive MEMS intraocular capacitive pressure sensor

This paper presents a novel high sensitive MEMS capacitive pressure sensor that can be used as a part of LC tank implant circuit for biomedical applications. The pressure sensor has been designed to measure pressures in the range of 0–60 mmHg that is in the range of intraocular pressure sensors. Intraocular pressure sensors are important in detection and treatment of an incurable disease called glaucoma. In this paper two methods are presented to improve the sensitivity of the capacitive pressure sensor. First low stress doped polysilicon material is used as a biocompatible material instead of p++silicon in previous work (Gu in Microfabrication of an intraocular pressure sensor, M.Sc Thesis, Michigan State University, Department of Electrical and Computer Engineering, 2005) and then some slots are added to the poly Si diaphragm. The novelty of this research relies on adding some slots on the sensor diaphragm to reduce the effect of residual stress and stiffness of diaphragm. The slotted diaphragm makes capacitive pressure sensor more sensitive that is more suitable for measuring intraocular pressure. The results yield a sensor sensitivity of 1.811 × 10^?5 for p++silicon clamped, 2.464 × 10^?5 1/Pa for polysilicon clamped and 1.13 × 10^?4 1/Pa for polysilicon slotted diaphragm. It can be seen that the sensitivity of the sensor with slotted poly Si diaphragm increased 6.2 times compared with previous work (clamped p++silicon diaphragm).     

A micro PDMS flow sensor based on time-of-flight measurement for conductive liquid

Transdermal extraction of interstitial fluid (ISF) offers an attractive method for non-invasive blood glucose monitoring. In order to calculate blood glucose concentration accurately, precise volume measurement of transdermally extracted ISF is required due to human skin’s varying permeability. In this paper, we presented a novel flow sensor fabricated from polydimethylsiloxane (PDMS), designed to measure the volume of conductive liquid. The flow sensor consists of two pairs of metal electrodes, which are fabricated in the PDMS channel. The volume of liquid is measured utilizing the time-of-flight of the two electrode pairs’ resistance while the liquid is flowing through the flow sensor. 1–14 μL normal saline solution was measured, the flow sensor measured volumes correlate very well (R ² = 0.9996 and R ² = 0.9975 for vacuum pump and syringe pump situations respectively) with the actual volumes. And the coefficient of variation for 10 times 10 μL normal saline solution measurement is 0.0077 (vacuum pump) and 0.0381 (syringe pump), respectively. The demonstrated flow sensor provides excellent functionality for conductive liquid.     

A high-shear, low Reynolds number microfluidic rheometer

We present a microfluidic rheometer that uses in situ pressure sensors to measure the viscosity of liquids at low Reynolds number. Viscosity is measured in a long, straight channel using a PDMS-based microfluidic device that consists of a channel layer and a sensing membrane integrated with an array of piezoresistive pressure sensors via plasma surface treatment. The micro-pressure sensor is fabricated using conductive particles/PDMS composites. The sensing membrane maps pressure differences at various locations within the channel in order to measure the fluid shear stress in situ at a prescribed shear rate to estimate the fluid viscosity. We find that the device is capable to measure the viscosity of both Newtonian and non-Newtonian fluids for shear rates up to 10⁴ s^?1 while keeping the Reynolds number well below 1.     

Fabrication of high precision microstructure using ICP etching for capacitive inclination sensor

Capacitive inclination sensors have the advantage because it could easily provide a linear analog output with respect to inclination. Since the dimensions of the sensing region are very small, then this sensor is expected to be widely used in fields where efficient and reliable position control is a primary factor to be considered if this sensor could be mass produced at low cost. Therefore, we proposed fabrication process based on transfer to resin using mold. We successfully fabricated a micro capacitive inclination sensor by a combination of a resin forming method and a mold. The sensor consists of a gap distance of 80 μm between its electrodes. The sensor detects difference of capacitance, which varied with movement of silicone oil accompanying with inclination. When the sensor was inclined, linear analog output was obtained within the range of ?45 to +45°     

Polyisoprene-nanostructured carbon composite – A soft alternative for pressure sensor application

Latest related research shows natural polyisoprene-nanostructured carbon composite (PNCC) as a promising piezoresistive material for soft pressure sensors. The main advantages of PNCC over conventional sensors are exceptional sensitivity in pressure range from 0.1 to 10 bar and possibility to be embedded into completely soft (hyper-elastic) structures.In this work we have elaborated a completely soft (hyper-elastic) PNCC pressure sensor prototype, made using functional multi-layer approach, when elementary layers of PNCC with different conductive filler concentration are cured together and form a uniform sensor body with integrated soft (hyper-elastic) electrodes. We proposed also a theoretical model to explain the observed positive piezoresistivity and used it for fitting of our experimental results.The prototype system elaborated could be used for counting interface events between sensor and external environmental factor. The achieved result could be a step towards the artificial skin, capable to sense non-destructive interaction with the external influence.     

目标导体对近感电容传感器电极电容影响研究

电容传感器是利用探测电极间电容的变化来实现目标近感探测的.对两电极电容传感器,分别探讨了探测大目标导体和小目标导体时电极的自电容、互电容以及等效电容的变化趋势,结果表明,电容传感器在遇目标后,其电极间的自电容均会增大,而互电容则减少.大目标导体会导致电极间等效结构电容增大,而小目标导体的介入不会影响电极间的等效结构电容.     

A novel capacitive pressure sensor based on sandwich structures

This paper presents a sandwich structure for a capacitive pressure sensor. The sensor was fabricated by a simple three-mask process and sealed in vacuum by anodic bonding. The sensor, which utilizes a combined SiO/sub 2//Si/sub 3/N/sub 4/ layers as the elastic dielectric layers, exhibits high sensitivity. Mechanical characteristics of the sensor are theoretically analyzed based on a composite membrane theory and evaluated by use of finite element analysis (FEA). Square membrane sensors with side lengths of 800 /spl mu/m, 1000 /spl mu/m, 1200 /spl mu/m, and 1500 /spl mu/m were fabricated, providing a measured sensitivity of 0.08 pF/kPa, 0.12 pF/kPa, 0.15 pF/kPa, and 0.2 pF/kPa, respectively. The nonlinearity of the sensor is less than 1.2% over a dynamic range 80-106 kPa and the maximum hysteresis is about 3.3% to the full scale capacitance change. The TCO at 101 kPa is 1923 ppm//spl deg/C. All the electrodes of the sensor are leaded from the top side of the chip. Residual pressure in the sealed cavity at room temperature is evaluated by a pressure scanning test, indicating about 8 kPa. Comparison of experimental results with theoretical analysis shows that change of capacitance for the sandwich structure under pressure is mainly due to variation of the dielectric constant while geometric variations such as the area change of electrodes and the thickness change of dielectric layers is about two orders less than the variation of the dielectric constant. Sensitivity enhancements for the sensor are qualitatively discussed based on the physical effects of strained dielectrics, including electrostriction and flexoelectricity. [1551].     

Effect of piezoresistor configuration on output characteristics of piezoresistive pressure sensor: an experimental study

Piezoresistive sensing is one of the most frequently used transduction mechanism in pressure sensors. The piezoresistor placement on the diaphragm and the piezoresistor configuration play a pivotal role in determining the output characteristics of a pressure sensor. In this work, two different pressure sensors with different transverse piezoresistor configurations are studied to determine the effect of piezoresistor configuration on the sensitivity and non-linearity of the pressure sensors. A sensor structure with a square diaphragm size of 1,480 µm edge length and diaphragm thickness of 50 µm is chosen for the study. The design considerations for piezoresistor placement and the piezoresistor shapes are discussed in detail. The sensors are fabricated with bulk micromachined diaphragm and polysilicon piezoresistors. The sensor characteristics are determined for three temperatures, namely, ?5, 25 and 55 °C and for a pressure range of 0–30 Bar. The characterization results indicate that the design with two piezoresistor arms in transverse piezoresistor configuration (2 × 2 Design) has higher sensitivity than the single arm configuration (2 × 1 Design) by about 25 % at 25 °C but it also has a higher non-linearity. The study shows the importance of selecting the proper piezoresistor configuration in the design of pressure sensors.     

A novel capacitive pressure sensor and interface circuitry

A novel capacitive pressure sensor with the island-notch structure is introduced. Its theory model is established based on the structure theory of the plate capacitive pressure sensor. The relationships between the external pressure and capacitance of the capacitive pressure sensor with the island-notch structure are studied by using the method of the finite element analysis (FEA). The results show that the linearity of the capacitive pressure sensor with island-notch structure reached up 0.9941 in the linear measurement zone, the sensitivity reached up 0.0019 pF/kPa, and the measurement range of the capacitive pressure sensor is enlarged. Thus, the contradictory among measure sensitivity, linearity and measure range is effectively relieved in the capacitive pressure sensors with island-notch. In addition, the interface circuitry of the charge transfer is designed, and the performance of the interface circuitry is analyzed.     

Design and analysis of a z-axis tuning fork gyroscope with guided-mechanical coupling

This paper presents design and analysis of a z-axis tuning fork gyroscope. The sensor is designed to reduce noises and improve the sensitivity by using a drive coupling spring in the lozenge shape. The in-phase sensing mode is suppressed by using a self-rotation ring. The designed sensor prioritizes anti-phase driving and sensing modes. The frequencies of anti-phase driving and sensing modes are far from those of parasitic ones. The design also enables the sensing mode to decouple from the driving one, which is considered to decrease vibration-induced error. The proposed sensor structure is analyzed by finite element method. The simulated frequencies of the driving and sensing modes are 9.9 and 10.0 kHz, respectively, which show the bandwidth of sensor of 100 Hz. The frequency difference between the driving and sensing modes and the parasitic ones is obtained to be 50 %. The optimized gap between electrodes leads to the determination of the number of the sensing capacitor fingers and consequently the suitable dimension parameters of the whole device. The sensor performance in the time domain and the frequency domain having the transient response to a given rotation rate is also simulated showing the linear dependence of capacitance change on angular velocity. As a result, the sensitivity of the sensor is evaluated to be 11 fF/°/s.     

电容式传感器探测电极设计

为提高电容式传感器的探测灵敏度,对传感器的探测电极进行了设计,当两电极面积之和为一定值,且与目标等距离接近时,为获得最大的电容变化,应使两电极的表面积尽量相等,同时,进行了具有隔离极的探测电极结构设计,经实验证明:当满足隔离极宽度大于2倍探测极宽度时,该结构的探测电极能够显著提高电容式传感器的探测灵敏度,从而提高电容引信的探测距离.     

A flexible encapsulated MEMS pressure sensor system for biomechanical applications

 The use of pressure sensors made of conductive polymers is common in biomechanical applications. Unfortunately, hysteresis, nonlinearity, non-repeatability and creep have a significant effect on the pressure readings when such conductive polymers are used. The objective of this paper is to explore the potential of a new flexible encapsulated micro electromechanical system (MEMS) pressure sensor system as an alternative for human interface pressure measurement. A prototype has been designed, fabricated, and characterized. Testing has shown that the proposed packaging approach shows very little degradation in the performance characteristics of the original MEMS pressure sensor. The much-needed characteristics of repeatability, linearity, low hysteresis, temperature independency are preserved. Thus the flexible encapsulated MEMS pressure sensor system is very promising and shows superiority over the commercially available conductive polymer film sensors for pressure measurement in biomechanical applications. Received: 1 December 1999/Accepted: 17 August 2000     

MEMS-based formaldehyde gas sensor integrated with a micro-hotplate

This paper presents a novel micro-fabricated formaldehyde gas sensor with enhanced sensitivity and detection resolution capabilities. The device comprises a quartz substrate with Pt heaters as a micro-hotplate and deposited formaldehyde-sensing layer on it. A sputtered NiO thin film is used as the formaldehyde-sensing layer. A specific orientation of NiO becomes more apparent as the substrate temperature increases in the sputtering process, which helps the formation of NiO material with a correct stoichiometric ratio. The gas sensor incorporates Pt heating resistors integrated with a micro-hotplate to provide a heating function and utilizes Au inter-digitated electrodes. When formaldehyde is present in the atmosphere, oxydation happens near the sensing layer with a high temperature caused by the micro-hotplate and causes a change in the electrical conductivity of the NiO film. Therefore, the measured resistance between the inter-digitated electrodes changes correspondingly. The application of a voltage to the Pt heaters causes the temperature of the micro-hotplate to increase, which in turn enhances the sensitivity of the sensor. The nanometer scale grain size of the sputtered oxide thin film is conducive to improving the sensitivity of the gas sensor. The experimental results indicate that the developed device has a high stability (0.23%), a low hysteresis value (0.18%), a quick response time (13.0 s), a high degree of sensitivity (0.14 Ω ppm^?1), and a detection capability of less than 1.2 ppm.