Nanotechnology for wireless gas sensor

Gas sensor are increasingly being employed, not only in industrial settings and also in every aspect of human life, where they are telling something about their environment by bridging them with the electronic world. Sensors are used to gather a wealth of information from the process that can improve operational efficiency and product quality which involving a mass of data that need to be analysis especially with the merging of the Internet of Things (IoT). They included with new features such as communication capability and on-board diagnostics. Meanwhile, leading edge research in sensors has been propelled by the advancements made in fabrication, signal processing and nanotechnology in the last decade. With these the scientific world is now on the verge of delivering sensors with radically new capabilities for the human societies. This talk deals with the future trend in sensor technology especially for wireless gas sensor and several researches works in Universiti Putra Malaysia related with them

Theoretical formulation to evaluate capacitance for before and after touch point MEMS capacitive pressure sensors

Micro-electromechanical systems (MEMS) have received a great deal of attention in recent years. This is due to the great promise of increased miniaturization and Performance of MEMS devices over conventional devices. MEMS pressure sensors currently dominate the market for greater than atmospheric pressure sensors. In this paper, a theoretical and finite elements analysis (FEA) solution for Micro-electromechanical systems (MEMS) pressure sensor to evaluate capacitance for before and after touch point is proposed. By looking at MEMS devices, when the diaphragm starts touching the fixed electrode by applying loads, it will have a major effect on the overall of the capacitance. Therefore, one should consider the effect of touch mode capacitance value in the system to evaluate good linearity, large operating pressure range and large overload protection at output. As of so far the evaluation for capacitance value of touch point and after touch point has not been evaluated in the literatures. This paper presents the new analytical formula to approach for including the touch-down effect capacitance value of Microsystems. The proposed MEMS capacitive pressure sensor demonstrated diaphragm with radius of , the gap depth of and the sensor exhibit linear response with pressure from 0.01 Mpa to 1.7 Mpa

Reactive ion etching of 4H-SiC using SF6/O2 for MEMS application

Deep Reactive Ion Etching (DRIE) of 4H-SiC performed using SF6/O2 plasma. The etching rates investigated as a function of the ratio of the O2 flow rate to total gas flow rate under different etching conditions such as the effect of power density, temperature, and the combination of chemistries on etching. The investigation was proven that the contribution and effect of the direct role of Oxygen to deep etching of SiC. An optimum value of O2 fraction of 60% to 40% Sulfur Hexafluoride (SF6) used to give high etching rate of 1.2μm/min. for maximum etching

Hydrogen gas sensor using double SAW resonator system

This paper presents a hydrogen gas sensor based on Double Surface Acoustic Wave Resonator (DSAWR) system configuration. Two commercial SAW resonators were employed to develop the DSAWR system. The sensing layer was prepared using functionalized Carbon Nanotubes (CNT) with polyaniline nanofibers. The sensing layer was integrated into the DSAWR system and measurements were carried out for hydrogen gas between 1% to 2% concentrations. Results obtained showed response of the sensor to hydrogen gas with a minimum detection limit of 1% and good response and recovery time

Sensing Materials for Surface Acoustic Wave Chemical Sensors

Online real‐time monitoring of gases requires a miniaturized, passive, and accurate gas sensor. Surface acoustic wave (SAW) devices possess these properties which make them suitable for gas‐sensing applications. They have shown remarkable results in sensing of different gases in terms of sensitivity, selectivity, response, and recovery times. One of the important prerequisites a designer should know is to have knowledge on the different types of sensing material suitable for gas‐sensing applications, prior to design and fabrication of the sensor. Different sensing materials, including metal oxides, polymers, carbon nanotubes, graphene, nanocomposites, etc. have been used for SAW gas sensors. In this article, different sensing materials for SAW gas sensors will be discussed

Artificial olfactory system with fault-tolerant sensor array

Numerous applications of artificial olfaction resulting from research in many branches of sciences have caused considerable interest in the enhancement of these systems. In this paper, we offer an architecture which is suitable for critical applications, such as medical diagnosis, where reliability and precision are deemed important. The proposed architecture is able to tolerate failures in the sensors of the array. In this study, the discriminating ability of the proposed architecture in detecting complex odors, as well as the performance of the proposed architecture in encountering sensor failure, were investigated and compared with the generic architecture. The results demonstrated that by applying the proposed architecture in the artificial olfactory system, the performance of system in the healthy mode was identical to the classic structure. However, in the faulty situation, the proposed architecture implied high identification ability of odor samples, while the generic architecture showed very poor performance in the same situation. Based on the results, it was possible to achieve high odor identification through the developed artificial olfactory system using the proposed architecture

Pressure sensors based on MEMS, operating in harsh environments (touch-mode)

In this paper, Poly-crystalline silicon carbide (poly-sic) Micro-electromechanical systems (MEMS) capacitive pressure sensor operating in harsh environment in touch mode is proposed, The principle of the paper is to design, obtain analytical solution and compare the results with the simulation for a circular diaphragm deflection before and after touch point. The sensor demonstrated a high temperature sensing capability up to 400°C, the device achieves a linear characteristic response and consists of a circular clamped-edges poly-sic diaphragm suspended over sealed cavity on a silicon carbide substrate. The sensor is operating in touch mode capacitive pressure sensor, The advantages of a touch mode are the robust structure that make the sensor to withstand harsh environment, near linear output, and large over-range protection, operating in wide range of pressure, higher sensitivity than the near linear operation in normal mode, The material is considered to be used for harsh environment is SiC (Silicon Carbide), Because of SiC owing excellent electrical stability, mechanical robustness, and chemical inertness properties and the application of pressure sensors in harsh environments are, such as automotive industries, aerospace, oil/logging equipments, nuclear station, and power station. We are simulating MEMS capacitive pressure sensor to optimize the design, improve the performance and reduce the time of fabricating process of the device. The proposed touch mode MEMS capacitive pressure sensor demonstrated diaphragm ranging from 150 μm to 360 μm in diameter, with the gap depth from 0.5 μm to 7.5 μm and the sensor exhibit a linear response with pressure from 0.05 Mpa to 10 Mpa

Transistor sizing methodology for low noise charge sensitive amplifier with input transistor working in moderate inversion

In this paper noise contribution of current source transistors and sizing methodology in charge sensitive amplifier for application in the front-end readout electronics is presented. In modern deep-submicron technologies, MOS transistor operating region tends to shift from strong inversion to moderate inversion, this makes traditional square-law MOS device modeling not applicable anymore. Thus a simplified EKV model, which is quite successful in all CMOS operating regions, has been adopted to develop a new analytical methodology to optimize geometry of current source transistors so that the noise contribution from these transistors is only a fraction of input transistor noise. A charge sensitive amplifier based on dual PMOS cascode structure is designed by adopting this current source transistor sizing methodology, and has been simulated using 130nm CMOS technology. The proposed methodology and noise contribution from current source transistors have been found in good agreement with simulation results using deep-submicron CMOS technology

Identification of initial drift in semiconductor gas sensors caused by temperature variation

Metal-oxide (MOX) gas sensors are well-known with their high sensitivity in detecting gases. Despite of this quality, the responses of gas sensor are inclined to substantial drift effects caused by the environmental variable of the surrounding atmosphere such as temperature. The variation of temperature introduced shifts in the dynamic features of sensor resistance, and nonlinearly modified the original unique patterns of acquired response. In this paper, the initial drift in MOX gas sensors were identified from the responses of gas sensors that shifted over temperature variation. This initial drift identification is important for further analyses on drift compensation

Relation of parallel resistance to the passive double SAW resonator

This paper presents the relationship of parallel resistor to the frequency response of the passive remote acoustic wave resonators (SAWRs) sensor system in 433.42MHz and 433.92MHz. Impedance matching is achieved with the connection of L-network to the parallel SAW resonator. The main objective of this finding is to improve the sensor of narrow bandwidth application. Circuit with high quality factor (Q factor) has better suppression for narrow band application. Parallel resistor improves the system by increasing the Q factor. Increasing the parallel resistance will decreased the bandwidth of the resonant frequency. Simulation results of the system are presented and discussed