MEMS-based gas flow sensors

Micro-electro-mechanical system (MEMS) devices integrate various mechanical elements, sensors, actuators, and electronics on a single silicon substrate in order to accomplish a multitude of different tasks in a diverse range of fields. The potential for device miniaturization made possible by MEMS micro-fabrication techniques has facilitated the development of many new applications, such as highly compact, non-invasive pressure sensors, accelerometers, gas sensors, etc. Besides their small physical footprint, such devices possess many other advantages compared to their macro-scale counterparts, including greater precision, lower power consumption, more rapid response, and the potential for low-cost batch production. One area in which MEMS technology has attracted particular attention is that of flow measurement. Broadly speaking, existing micro-flow sensors can be categorized as either thermal or non-thermal, depending upon their mode of operation. This paper commences by providing a high level overview of the MEMS field and then describes some of the fundamental thermal and non-thermal micro-flow sensors presented in the literature over the past 30 years or so.     

Design and fabrication of novel micro electromagnetic actuator

This study designs, fabricates, and characterizes a novel micro electromagnetic actuator comprising a PDMS diaphragm, a polyimide-coated copper micro coil, and a permanent magnet. When an electrical current is passed through the micro coil, a magnetic force is induced between the coil and the magnet which causes the diaphragm to deflect, thereby creating an actuation effect. The experimental results demonstrate that the diaphragm deflection can be accurately controlled by regulating the current passed through the micro coil. It is shown that the maximum diaphragm deflection within elastic limits is 150 μm; obtained by passing a current of 0.6 A through a micro coil with a line width of 100 μm. The micro actuator proposed in this study is easily fabricated and is readily integrated with existing bio-medical chips due to its planar structure.     

Multimedia augmented reality information system for museum guidance

This paper introduces the design and implementation of an augmented reality-based guidance system used for museum guidance. The objective of this study is to deliver the new museum guidance with intuitive and user-friendly interactions between man and machine based on computer vision technique in ubiquitous computing environment. In our design, a camera is used to capture hand motions and images of a printed guide, which are analyzed instantaneously to parse the designated actions the guidance system promptly responds with. The system can display and illustrate contextual information about 3D models of museum artifacts and multimedia materials to users in real time to compliment the museum experience. Moreover, the performance of the approach we proposed herein has been compared with that of the other alternatives with which the guidance system has also been installed for similar exhibitions. As a result, our proposed approach outperforms the other applications. The advantage of the proposed approach includes the exclusion of common tactile peripheral devices, for example, keyboard and mouse, which accordingly reduces hardware-related costs and reduces the risk of contamination in a public environment.     

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.

     

Effects of Impact Inertia and Surface Characteristics on Deposited Polymer Droplets in Microcavities

Microflow visualization and computational fluid dynamics (CFD) are complementarity performed to study the evolution of a single poly(ethylenedioxythiophene) (PEDOT) droplet ejected from a piezoelectric ink-jet printhead and the equilibrium film characteristic of the droplet deposition in a microfabricated cavity. The verified CFD code is further applied to investigate the influences of contact angles thetas_s of the PEDOT droplet/air interface and the PEDOT droplet/cavity sidewall interface as well as droplet impact velocity Vd on the transient deposition process in the micro cavity. Impact inertia was studied by varying the droplet Weber number from 30.3 to 42.6. The surface characteristics are explored by choosing thetas_s of 10deg, 30deg, 50deg, 70deg, 90deg, and 110deg. The influences of impact inertia are also examined by increasing Vd from 2.0 to 12.0 m/s at 2.0 m/s interval. The computed results are found in good agreement with the experimental ones. For the first time, critical Weber numbers have been found relating to the ability of the droplet to wet the side walls and fill a microcavity with a uniform film. The results are also new in terms of the identifications of the critical contact angle (thetas_s)_C and critical impact velocity (Vd)_c. At (thetas_s)_C and at and beyond (Vd)_c, the formation of an intact flat film in the cavity is fulfilled.     

Fabrication and characterization of MEMS-based flow sensors based on hot films

The purpose of this paper is to propose two types of airflow velocity measurement modules, double-chip and single-chip, of MEMS-based flow sensors that consisting of heating resistors and sensing resistors on alumina substrates. In this study, MEMS techniques are used to deposit platinum films on the substrate to form resistors which are to regard as heaters and sensing elements. As air flows through the heater and the sensor, the temperature of the sensing resistor on the hot film decreases and the changes of the local temperature determine the airflow rate. The experimental results show the resistance linearly varies as airflow velocity changes from 5 to 28 ms⁻¹. Finally the experimental data indicate that sensing performance of the single-chip type is better than that of the double-chip type with its higher sensitivity (0.7479 Ω/ms⁻¹) due to the more rapid heat conduction from the heating resistor to the sensing resistor.     

Electrophoretically deposited manganese oxide coatings for supercapacitor application

In the present study, manganese oxide electrodes with promising pseudo-capacitive properties were prepared by electrophoretic deposition (EPD) using needle-like manganese dioxide powders. As-deposited coating exhibited a porous microstructure where the size and shape of the starting powders can be observed. The electrochemical performance of the as-deposited coating was then evaluated by cyclic voltammetry (CV) up to 300 times. The initial specific capacitance was 236 F/g which dropped to 200 F/g after 25 CV tests, and decreased gradually to 190 F/g thereafter. The electrochemical behaviors during EPD and CV were examined by synchrotron X-ray absorption spectroscopy techniques from which it was deciphered that a reduction reaction from Mn⁴⁺ to Mn³⁺ occurred during EPD concomitant with re-oxidization during repetitive CV cycles.     

Micro-controlled design of portable cattle mastitis detection system

Microsystem Technologies - This work presents a novel handheld mastitis detection device for detecting mastitis in dairy cattle, as well as a cattle management information system for managing...     

Enhanced sensing characteristics in MEMS-based formaldehyde gas sensors

This paper presents a novel micro fabrication for formaldehyde gas sensors to enhance sensitivity and detection resolution capabilities. Therefore, two different types of fabrication sequences of gas sensors were considered, different positions of micro heaters and sensing layers to compare the effects of different areas of the sensing layers contact with the surrounding gas. The MEMS-based formaldehyde gas sensor consists of a quartz substrate, a thin-film NiO/Al₂O₃ sensing layer, an integrated Pt micro-hotplate, and Pt inter-digitized electrodes (IDEs) to measure the resistance variation of sensing layers caused by formaldehyde oxidation at the oxide surface. This abstract offers comparisons of the characteristics of sensors in different areas of the sensing layers contacting the surrounding gas as well as those to decrease the thickness of the sensing layer and deposits of the sensing layer using co-sputtering technology with NiO/Al₂O₃ to improve the sensitivity limits of the sensors. The experimental data indicated that increasing the area of the sensing layer that contacts with the surrounding gas and decreasing the thickness of the sensing layer in the sputtering process and then co-sputtered NiO/Al₂O₃ sensing layers, significantly enhanced the sensing characteristics of the developed formaldehyde sensor.