Capacitive-type Pressure Sensor Research Articles

Capacitive-Type Pressure Sensor for Classification of the Activities of Daily Living

In order to operate a gait rehabilitation device, it is necessary to accurately classify the states appearing in activities of daily living (ADLs). In the case of force sensing resistors (FSRs), which are often used as pressure sensors in gait analysis, it is desirable to replace them with other sensors because of their low durability. In the present study, capacitive-type pressure sensors, as an alternative to FSRs, were developed, and their performance was evaluated. In addition, the timed up and go test was performed to measure the ground reaction force in healthy individuals, and a machine learning technique was applied to the calculated biosignal parameters for the classification of five types of ADLs. The performance evaluation results showed that a sensor with thermoplastic polyurethane (substrate and dielectric layer material) and multiwall carbon nanotubes (conductive layer) has sufficient sensitivity and durability for use as a gait analysis pressure sensor. Moreover, when an overlapping filter was applied to the four-layer long short-term memory (LSTM) or the five-layer LSTM model developed for motion classification, the precision was greater or equal to 95%, and unstable errors did not occur. Therefore, when the pressure sensor and ADLs classification algorithm developed in this study are applied, it is expected that motion classification can be completed within a time range that does not affect the control of the gait rehabilitation device.

Design and Implementation of Vertically Integrated Deformable Hermetic Chambers for the Sensitivity Enhancement of CMOS-MEMS Capacitive Pressure Sensor

This study presents the design and implementation of a capacitive type pressure sensor with vertically integrated deformable hermetic chambers based on the standard commercial processes (the Taiwan Semiconductor Manufacturing Company (TSMC) 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> 1P6M complementary metal-oxide-semiconductor (CMOS) process) and the in-house post CMOS processes. The proposed pressure sensor features the realization of two vertically integrated hermetic chambers consisting of two deformable diaphragms with embedded sensing electrodes and one diaphragm with reference electrodes. Thus, the sensitivity of the pressure sensor can be improved for near twofold within the same footprint. Moreover, the stepped structure is designed to reduce the stiffness of the deformable diaphragms to further enhance the sensitivity of the proposed sensor. The feasibility of the proposed design has been evaluated through both finite element method (FEM) simulations and experiments. Measurement results indicate, as compared with the reference design with only one deformable hermetic chamber, the proposed pressure sensor with vertically integrated deformable hermetic chambers has a near twofold enhancement in sensitivity within the pressure range of 20–120 kPa. Additionally, the proposed design with the deformable stepped-diaphragm can enhance the sensitivity by about 5.1-fold within the same pressure range.

Capacitive Pressure Sensors Containing Reliefs on Solution-Processable Hydrogel Electrodes.

Highly sensitive capacitive-type pressure sensor has been achieved by fabricating reliefs on solution-processable hydrogel electrodes. Hybrid PVA/PANI hydrogels (PVA, poly(vinyl alcohol); PANI, polyaniline) with a fully physically cross-linked binary network are selected as the electrodes of the pressure sensors. On the basis of the solution processability, reliefs are fabricated on the surface of PVA/PANI hydrogel electrodes by a template method. The gauge factor (GF) is enhanced by introducing reliefs and regulated by controlling the composition and relief dimension of hydrogel electrodes. The optimized pressure sensor containing reliefs achieves the highest GF of 7.70 kPa-1 and a sensing range of 0-7.4 kPa. Furthermore, the freezing and drying problems of the hydrogel sensors are overcome by introducing a binary solvent of water/glycerol and the pressure sensing ability at -18 °C has been achieved. Finally, monitoring of various pressures in daily life, such as joint bending, blowing, and brush writing, is demonstrated using such pressure sensors.

Robust and sensitive pressure/strain sensors from solution processable composite hydrogels enhanced by hollow-structured conducting polymers

Flexible sensors based on conductive hydrogels have found potential applications in many emerging electronic devices, but they often suffer from poor mechanical properties, single response mode and low sensitivity. Herein, robust and sensitive pressure/strain sensors are designed and fabricated utilizing novel composite hydrogels composed of hollow polyaniline spheres (HPS), poly(vinyl alcohol) (PVA) and phytic acid (PA). By taking advantages of structure-derived elasticity of hollow spheres, conductivity of doped conducting polymers, flexibility of polymer matrix and physically cross-linked structure, the composite hydrogels exhibit outstanding mechanical properties, strain sensitivity, piezoresistivity and solution processability. The optimized composite hydrogel possesses high tensile strength (9.3 MPa), stretchability (>493%) and toughness (2.6 MJ/m3). Resistive-type strain sensors assembled from the composite hydrogel can achieve a gauge factor (GF) of 2.9 in the strain range of 0%~300%, a GF of 7.4 in the strain range of 300%–450%, a response time of 0.22 s and high reliability (1000 cycles). Capacitive-type pressure sensor with ultrahigh sensitivity of GF = 3.6 kPa−1 is fabricated by sandwiching a dielectric layer between two composite hydrogel films. Interestingly, piezoresistivity of such composite hydrogels makes them promising materials for piezoresistive-type pressure sensors and visualization of pressure. On the basis of their high performances, flexible sensors of the composite hydrogels are applied in monitoring various human motions, physiological activities and bending/vibration deformations in daily life.

Unveiling Viscoelastic Response of Capacitive-type Pressure Sensor by Controlling Cross-Linking Density and Surface Structure of Elastomer

Research on pressure sensors using elastic materials is actively underway to develop next-generation devices for applications in healthcare monitoring, haptic sensors, and electronic skin. Capaciti...

A new scheme for reducing breathing trouble through MEMS based capacitive pressure sensor

In this paper, a treatment of respiratory disorders with brushless DC motor (BLDC) driven positive airway pressure (PAP) respirator is developed. The proposed schema of the system consists of a BLDC motor driven blower fan aided by a MEMS capacitive type pressure sensor to measure respiration rate (RR). To measure the respiration rate, the array of such sensors are mounted below right nostril (RN) and left nostril (LN), in such a way that the nasal airflow during inspiration and expiration impinge on the sensor diaphragms directly. Due to irregularities in nasal airflow in some respiratory diseases, the RR varies from the normal rate (12---20). Thus, a supporting airflow regulatory system has been designed to reduce abnormalities in RR. The supporting system consists of a positive airway pressure (PAP) respirator with a blower fan to relieve patients breathing abnormalities. The MEMS based RR sensors help to monitor patients breathing rate continuously and finally maintain the required air pressure/flow by regulating the rpm of the blower fan through BLDC motor drive. In order to implement such a control action, we have chosen the sensorless drive of BLDC motor to construct a transportable as well as noise immune system. An algorithm has been developed to sustain normal RR for both bradypnea (RR 20), which puts into operation through ATmega 328 to facilitate high level precision controlled action. The control system alongwith the sensory part occupies limited space in few centimeters with light weight. As a result, the electronics of the whole system can be easily mounted at the outer surface of the tube connected with the nasal mask. The scheme of such a portable and cost effective system is described in this present work.

Silver nanowire-embedded PDMS with a multiscale structure for a highly sensitive and robust flexible pressure sensor.

The development of highly sensitive pressure sensors with a low-cost and facile fabrication technique is desirable for electronic skins and wearable sensing devices. Here a low-cost and facile fabrication strategy to obtain multiscale-structured elastomeric electrodes and a highly sensitive and robust flexible pressure sensor is presented. The principles of spontaneous buckle formation of the PDMS surface and the embedding of silver nanowires are used to fabricate the multiscale-structured elastomeric electrode. By laminating the multiscale-structured elastomeric electrode onto the dielectric layer/bottom electrode template, the pressure sensor can be obtained. The pressure sensor is based on the capacitive sensing mechanism and shows high sensitivity (>3.8 kPa(-1)), fast response and relaxation time (<150 ms), high bending stability and high cycle stability. The fabrication process can be easily scaled up to produce pressure sensor arrays and they can detect the spatial distribution of the applied pressure. It is also demonstrated that the fingertip pressure sensing device can sense the pressure distribution of each finger, when grabbing an object.

A Study of Pressure Sensor for Environmental Monitoring

In this study, capacitive type pressure sensors based on low temperature co-fired ceramics (LTCC) technology for environmental monitoring were demonstrated. The LTCC is one of promising technology than is based one since it has many advantages (e.g., low cost production, high manufacturing yields and easy realizing 3D structure etc.) for sensor application. Especially, it has good mechanical and chemical properties for robust environmental application. The 3D LTCC diaphragm with thickness of 400 were fabricated by laminating 4 green sheets using commercial powder (NEG, MLS 22C). To evaluate the sensing properties of the different cavity areas, two types of diaphragm which had different cavity areas with 25, 49 respectively, were fabricated. To realize capacitive type pressure sensor, the Au top electrode was fabricated using thermal evaporator and the bottome electrode was compressed using aluminium foil. The sensing properties of the fabricated sensors showed linear characteristic under different pressure (0~30 psi) using pressure measurement system.

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

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

CAD tools in mechanical sensor design

Optimization of advanced mechanical sensor structures can hardly be achieved on an intuitive basis. Therefore, extensive use was made of computer-aided design (CAD) tools in the design stage of a recently developed capacitive-type pressure sensor. The mechanical behaviour of the micro-machined membrane structures is evaluated using powerful commercial finite-element software. A dedicated software-extension, ‘CAPSIM’, has been developed to yield the output response of the capacitive pressure sensors as a function of applied pressure and design parameters. Feature include trapped-gas effects and evaluation of stress-concentrations due to anisotropic etching. A novel diaphragm structure, with a rigid centre part, is shown to increase both sensitivity and linearity substantially.