Membrane-based Pressure Sensor Research Articles

Polyaniline-nanospines engineered nanofibrous membrane based piezoresistive sensor for high-performance electronic skins

The development of a highly sensitive pressure sensor with a wide linear range is an emerging technological goal in the area of electronic skin (e-skin). Several studies have focused on imitating tactile perception closer to natural skin, however, there remains a great challenge in developing a complete artificial tactile sensory system with high sensitivity over a broad pressure range. Herein, a highly sensitive hybridized nanofibrous membrane-based pressure sensor is newly proposed to overcome the limitation of the existing piezoresistive pressure sensor by improving the sensitivity and working range. As a primary sensing material, polyaniline (PANI)-nanospines are uniformly deposited throughout the hybrid hierarchical nanofibers to achieve a high sensitivity (179.1 kPa−1) with a low detection limit (1.2 Pa). Additionally, the highly deformable hierarchical nanofibrous membranes enables linear response over a broad pressure range (0 − 50 kPa) with a high durability (10,000 cycles). These results indicate that the fabricated pressure sensor has a broad application perspective, particularly in e-skins and wearable electronic devices.

Modeling of magnetic shape memory alloy plates for pressure sensor application

This article investigates the basis for pressure sensor application based on the magnetic shape memory effect in membranes. Von Karmans nonlinear terms are considered in strain–displacement relationships of thin films, and a new method is presented for solution of large deflections of thin films with arbitrary boundary condition. In this study, the equations of motion of magnetic shape memory alloys are extended. In pressurized membranes, the complex distribution of mechanical stress can cause the martensitic reorientation, which is the underlying mechanism for sensing applications in magnetic shape memory alloys. To examine the obtained model, the governing equations of magnetic shape memory alloys are solved for clamped thin films and results are compared with experimental data. Demonstrating good agreement with experimental data, the presented model can be used for analysis of magnetic shape memory alloy–based smart structures. In this article, the deflection profile of the uniformly loaded thin films is determined with different boundary conditions. Furthermore, the center deflection of magnetic shape memory alloy membrane under different magnetic bias field is simulated. The results of simulation can be used for designing a membrane-based pressure sensor using magnetic shape memory alloys.

Facilely prepared layer-by-layer graphene membrane-based pressure sensor with high sensitivity and stability for smart wearable devices

With the prosperous development of artificial intelligence, medical diagnosis and electronic skins, wearable electronic devices have drawn much attention in our daily life. Flexible pressure sensors based on carbon materials with ultrahigh sensitivity, especially in a large pressure range regime are highly required in wearable applications. In this work, graphene membrane with a layer-by-layer structure has been successfully fabricated via a facile self-assembly and air-drying (SAAD) method. In the SAAD process, air-drying the self-assembled graphene hydrogels contributes to the uniform and compact layer structure in the obtained membranes. Owing to the excellent mechanical and electrical properties of graphene, the pressure sensor constructed by several layers of membranes exhibits high sensitivity (52.36 kPa−1) and repeatability (short response and recovery time) in the loading pressure range of 0–50 kPa. Compared with most reported graphene-related pressure sensors, our device shows better sensitivity and wider applied pressure range. What’s more, we demonstrate it shows desired results in wearable applications for pulse monitoring, breathing detection as well as different intense motion recording such as walk, run and squat. It’s hoped that the facilely prepared layer-by-layer graphene membrane-based pressure sensors will have more potential to be used for smart wearable devices in the future.

MEMS piezoresistive flow sensors for sleep apnea therapy

A MEMS liquid crystal polymer (LCP), used in the membrane-based pressure sensor, has been found highly useful as a flow sensor. Here we conducted a set of elaborate experiments using an air flow generator to investigate the potential of our LCP flow sensor for sleep apnea therapy. Critical properties of the LCP flow sensor, including flow range, resolution (sensitivity), accuracy, and response time, have been systematically characterized. As a result, LCP flow sensor achieves a limit of detection of 8 LPM to measure flow rate, better than the commercial flow sensor (>10 LPM). Our LCP flow sensor shows a favourable response in a large flow range (8–160 LPM) with a sensitivity of detecting a linear voltage response of 0.004 V per 1 LPM flow rate. With minimum detectable flow, high sensitivity and resolution, we further demonstrated our LCP flow sensor for detecting human respiration. Moreover, using a two- dimensional simulation in COMSOL Multiphysics, we demonstrated the deformation of LCP membrane in response to different flow velocities which leads to resistance change in sensor’s strain gauge.

Highly Sensitive Membrane-Based Pressure Sensors (MePS) for Real-Time Monitoring of Catalytic Reactions.

Functional, flexible, and integrated lab-on-chips, based on elastic membranes, are capable of fine response to external stimuli, so to pave the way for many applications as multiplexed sensors for a wide range of chemical, physical and biomedical processes. Here, we report on the use of elastic thin membranes (TMs), integrated with a reaction chamber, to fabricate a membrane-based pressure sensor (MePS) for reaction monitoring. In particular, the TM becomes the key-element in the design of a highly sensitive MePS capable to monitor gaseous species production in dynamic and temporally fast processes with high resolution and reproducibility. Indeed, we demonstrate the use of a functional MePS integrating a 2 μm thick polydimethylsiloxane TM by monitoring the dioxygen evolution resulting from catalytic hydrogen peroxide dismutation. The operation of the membrane, explained using a diffusion-dominated model, is demonstrated on two similar catalytic systems with catalase-like activity, assembled into polyelectrolyte multilayers capsules. The MePS, tested in a range between 2 and 50 Pa, allows detecting a dioxygen variation of the μmol L-1 s-1 order. Due to their structural features, flexibility of integration, and biocompatibility, the MePSs are amenable of future development within advanced lab-on-chips.

Pressure sensors based on suspended graphene membranes

A novel pressure sensor based on a suspended graphene membrane is proposed. The sensing mechanism is explained based on tight binding calculations of strain-induced changes in the band structure. A CMOS compatible fabrication process is proposed and used to fabricate prototypes. Electrical measurement data demonstrates the feasibility of the approach, which has the advantage of not requiring a separate strain gauge, i.e. the strain gauge is integral part of the pressure sensor membrane. Hence, graphene membrane based pressure sensors can in principle be scaled quite aggressively in size.

A liquid crystal polymer membrane MEMS sensor for flow rate and flow direction sensing applications

The paper reports the design, fabrication and experimental results of a liquid crystal polymer (LCP) membrane-based pressure sensor for flow rate and flow direction sensing applications. Elaborate experimental testing results demonstrating the sensors' performance as an airflow sensor have been illustrated and validated with theory. MEMS sensors using LCP as a membrane structural material show higher sensitivity and reliability over silicon counterparts. The developed device is highly robust for harsh environment applications such as atmospheric wind flow monitoring and underwater flow sensing. A simple, low-cost and repeatable fabrication scheme has been developed employing low temperatures. The main features of the sensor developed in this work are a LCP membrane with integrated thin film gold piezoresistors deposited on it. The sensor developed demonstrates a good sensitivity of 3.695 mV (ms−1)−1, large operating range (0.1 to >10 ms−1) and good accuracy in measuring airflow with an average error of only 3.6% full-scale in comparison with theory. Various feasible applications of the developed sensor have been demonstrated with experimental results. The sensor was tested for two other applications—in clinical diagnosis for breath rate, breath velocity monitoring, and in underwater applications for object detection by sensing near-field spatial flow pressure.

Electrically insulating Al2O3 and SiO2 films for sensor and photovoltaic applications deposited by reactive pulse magnetron sputtering, hollow cathode arc activated deposition and magnetron-PECVD

Electrically insulating films find wide applications in electronics, sensor and medical technology as well as in photovoltaics. This paper describes the deposition of Al2O3 and SiO2 films using reactive pulse magnetron sputtering, hollow cathode arc activated deposition and Magnetron-PECVD. The deposition rate of these processes ranges between 1 and 4 nm/s in stationary mode and between 80 and 1000 nm m/min in dynamic mode. Breakdown field strength values between 1 and 9 MV/cm were achieved for the as-deposited Al2O3 and SiO2 films. The resistivity of the sputtered films is between 10+15 and 10+17 Ω cm. In the case of SiO2 films, considerably higher resistivity and breakdown field strength were obtained for process conditions with high plasma density and hence increased energetic substrate bombardment. Example applications of the SiO2 and Al2O3 films are metal membrane based pressure sensors and CIS/CIGS photovoltaics on metal strips.

Demonstration of Alternative Fabrication Techniques for Robust MEMS Device

This work describes efforts in the fabrication and testing of robust microelectromechanical systems (MEMS). Robustness is typically achieved by investigating non-silicon substrates and materials for MEMS fabrication. Some of the traditional MEMS fabrication techniques are applicable to robust MEMS, while other techniques are drawn from other technology areas, such as electronic packaging. The fabrication technologies appropriate for robust MEMS are illustrated through laminated polymer membrane based pressure sensor arrays. Each array uses a stainless steel substrate, a laminated polymer film as a suspended movable plate, and a fixed, surface micromachined back electrode of electroplated nickel. Over an applied pressure range from 0 to 34 kPa, the net capacitance change was approximately 0.14 pF. An important attribute of this design is that only the steel substrate and the pressure sensor inlet is exposed to the flow; i.e., the sensor is self-packaged.