Sensitivity Of Capacitive Sensors Research Articles

Fabrication of 3D microstructures for flexible pressure sensors based on direct-writing printing

Microstructure plays an important role in improving the performance of flexible sensors. Changing the shape of the dielectric layer microstructure is an effective countermeasure to promote the sensitivity of capacitive sensors. Nevertheless, traditional microstructure fabrication methods have high manufacturing costs, cumbersome manufacturing processes, and single structure manufacturing, which restrict the development of flexible sensors. In this work, electro-hydro-dynamic (EHD) printing method and aerosol jet (AJ) printing method were applied to fabricate 3D microstructures, in a manner of printing the same pattern in multiple layers. The height and morphology of 3D microstructures, under different printing parameters, were compared by changing the number of printing layers and printing speed. Additionally, the printing effects of the two printing methods were compared. The results demonstrated that various shapes and highly controllable 3D microstructures could be fabricated by both methods. The EHD printing method had higher manufacturing precision, whereas the AJ printing method had higher stacking efficiency. The height and morphology of 3D microstructures could be effectively controlled by changing the number of printed layers and the printing speed of the microstructures. It is indicated that the EHD printing method and the AJ printing method both have great potential in the fabrication of 3D microstructures and that both methods had their own advantages.

A new strategy for the fabrication of a flexible and highly sensitive capacitive pressure sensor

The development of flexible capacitive pressure sensors has wide application prospects in the fields of electronic skin and intelligent wearable electronic devices, but it is still a great challenge to fabricate capacitive sensors with high sensitivity. Few reports have considered the use of interdigital electrode structures to improve the sensitivity of capacitive pressure sensors. In this work, a new strategy for the fabrication of a high-performance capacitive flexible pressure sensor based on MXene/polyvinylpyrrolidone (PVP) by an interdigital electrode is reported. By increasing the number of interdigital electrodes and selecting the appropriate dielectric layer, the sensitivity of the capacitive sensor can be improved. The capacitive sensor based on MXene/PVP here has a high sensitivity (~1.25 kPa−1), low detection limit (~0.6 Pa), wide sensing range (up to 294 kPa), fast response and recovery times (~30/15 ms) and mechanical stability of 10000 cycles. The presented sensor here can be used for various pressure detection applications, such as finger pressing, wrist pulse measuring, breathing, swallowing and speech recognition. This work provides a new method of using interdigital electrodes to fabricate a highly sensitive capacitive sensor with very promising application prospects in flexible sensors and wearable electronics.

Gradient Architecture-Enabled Capacitive Tactile Sensor with High Sensitivity and Ultrabroad Linearity Range.

The sensitivity and linearity are critical parameters that can preserve the high pressure-resolution across a wide range and simplify the signal processing process of flexible tactile sensors. Although extensive micro-structured dielectrics have been explored to improve the sensitivity of capacitive sensors, the attenuation of sensitivity with increasing pressure is yet to be fully resolved. Herein, a novel dielectric layer based on the gradient micro-dome architecture (GDA) is presented to simultaneously realize the high sensitivity and ultrabroad linearity range of capacitive sensors. The gradient micro-dome pixels with rationally collocated amount and height can effectively regulate the contact area and hence enable the linear variation in effective dielectric constant of the GDA dielectric layer under varying pressures. With systematical optimization, the sensor exhibits the high sensitivity of 0.065kPa-1 in an ultrabroad linearity range up to 1700kPa, which is first reported. Based on the excellent sensitivity and linearity, the high pressure-resolution can be preserved across the full scale of pressure spectrum. Therefore, potential applications such as all-round physiological signal detection in diverse scenarios, control instruction transmission with combinatorial force inputs, and convenient Morse code communication with non-overlapping capacitance signals are successfully demonstrated through a single sensor device.

Ultra-sensitive wide-range small capacitive pressure sensor based on porous CCTO-PDMS membrane

Dielectric elastomer is a very popular composite material used for different applications. Calcium copper titanate (CCTO) particles have a high dielectric constant, while polydimethylsiloxane (PDMS) is a commonly used flexible elastomer with good elastic property and durable chemical resistance, and their composite has shown an important and unique character for the fabrication of the pressure/force sensor. To improve the sensitivity of the capacitive sensor, various elastomers’ microstructures have been introduced; but the methods used to manufacture microstructures in PDMS have so far been more difficult, requiring special equipment or hazardous chemicals such as strong acids and alkalis, otherwise, the sponge-like structures produced are slightly larger and cannot be applied to very small scenes. In this report, the extraction method was used to manufacture porous microstructures of the PDMS with multiple porosities; the influence of different porosities and pore sizes on the sensitivity of capacitive pressure sensors, which can increase the sensitivity of capacitive pressure sensors, the measuring force range, and also applied to tiny scenes, were explored. Additionally, the current methodology for manufacturing porous PDMS composite membranes is also suitable for the manufacture of other thinner PDMS composite porous membranes.

Simulator of a Full Fetal Electrocardiogram Measurement Chain by Multichannel Capacitive Sensing

Long-term ambulatory monitoring of the fetal heart rate (fHR) can greatly increase insight into fetal well-being and reduce pregnancy risks. Unfortunately, the existing solutions using wet or dry electrodes are unsuitable for long-term fHR monitoring due to the use of a gel or direct skin contact. Capacitive electrodes can measure an electrocardiographic (ECG) signal through clothes and, therefore, are perfectly suitable for long-term monitoring of the fHR. However, capacitive fetal ECG (fECG) measurements are challenging due to the high sensitivity of capacitive sensors to motion artifacts (MAs) and the low amplitude of the fECG. This article aims at investigating the feasibility of fECG measurements using capacitive electrodes with dedicated postprocessing algorithms for signal-to-noise ratio (SNR) improvement and MA reduction. To this end, a novel simulator of the full measurement chain is realized that generates multichannel capacitive fECG data with artificial MAs and system noise. A dedicated blind source separation (BSS) algorithm is then employed for MA removal and fECG extraction. The extracted fECG is evaluated by SNR calculation and R-peak detection. Our results show that the BSS algorithm may extract the fECG signal from noisy capacitive data. In addition, lower system noise or higher number of channels may lead to better fECG extraction. A maximum increase of 0.5 dB in the SNR and decrease of 80.7 % in the R-peak detection error are observed with increased electrode number from 8 to 20. Our findings provide useful insights for the hardware design of a capacitive fECG measurement system.

Highly sensitive capacitive pressure sensor with elastic metallized sponge

This paper presents a novel capacitive pressure sensor that is capable of making highly accurate measurements at low pressure. Different from the method that many researchers have successfully used to improve the sensitivity of capacitive sensors by using a micro-structured dielectric layer (such as the micro-structured PDMS film), this paper creatively used an elastic metallized sponge (nickel-plated polyurethane sponge) as the elastic porous electrode of the capacitive sensor, so that it can detect very low pressure (such as a 0.2 g soybean). Compared with the traditional capacitive sensor using an insulative polyurethane sponge as the dielectric, the baseline capacitance of the sensor of the same size can increase by 10 times, and it has a better signal-to-noise ratio. In addition, the sensor has good robustness due to the good mechanical properties of the nickel-plated polyurethane sponge. The fabrication process of the sensor is extremely simple, the cost is low, and it can be made into any planar shape. In this paper, we describe the structure, principle and manufacture of the sensor, and present the application on robotic grasping.

Highly stretchable and transparent dielectric gels for high sensitivity tactile sensors

Soft tactile sensors have been widely used in wearable electronics and soft robotics. Among different sensing technologies, soft capacitive sensors receive much attention due to good signal repeatability, temperature insensitivity, relative simplicity of fabrication and adaptability of configuration. Many methods such as adding nano-fillers have been developed to increase the sensitivity of capacitive sensors. However, the existing methods usually sacrifice the transparency and reduces the flexibility. In this work, we propose to use dielectric gels to fabricate capacitive sensors for the first time. We synthesize dielectric gels by using ethylene carbonate and propylene carbonate as solvents and 2-Ethylhexyl acrylate and acryloyl morpholine as polymer networks. The synthesized dielectric gels are extremely soft, highly stretchable, and fully transparent to visible lights. The relative permittivity is as high as 30. We demonstrate that the sensitivity of the capacitive sensor made of the new dielectric gel increases about 6 times compared to the sensors made of VHB, PDMS, or Ecoflex. We design a touch sensor with the dielectric gel to control the LED, and also demonstrate the use of the dielectric gels as the transparent cover layer of a cell phone which may displace the traditional protective layer made of glass in future wearable electronics.

Modeling and Verification in Silicon Micro-Mechanical Structures

A design issue, dependent on mechanical and geometrical parameters, is described related to silicon micro-mechanical structures. A piezoresistive pressure sensor fabricated by deeply anisotropic etching from a silicon substrate is modeled and analyzed by involving the rim boundary effect, caused by a gently tapered shape around a thin diaphragm, and large deflection effect, causing a nonlinear response to a load. Experimental results indicate that the calculated values agree very well with measured ones. A doubly-supported beam having residual stress due to deep boron diffusion is also modeled, allowing a set of elastic coefficients different from that for an undoped silicon to be derived. Sensitivity in capacitive sensors based on the doubly-supported beam structures is indicated as being considerably largely decreased due to the residual stress. The calculated sensitivity agrees fairly well with measured one.