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Fabrication of high aspect ratio microelectromechanical systems (MEMS) like comb drive structures are mostly done by DRIE (Deep Reactive Ion Etching) process. Bosch process is a type of DRIE which involves alternate repetition of plasma etching and side wall passivation to achieve deep vertical structures. A continued plasma etching may lead to tapered wall due to some lateral etching. Although, a straight and smooth wall is expected due to combined alternate processes of etching and passivation, very often the resulting walls are having surface undulations called as scalloping. So, due to slanting, scalloping and combined slanting and scalloping defects the working and performance of a MEMS device get affected. MEMS gyrocope is one such widely comercialized device, which is required to measure angular rotation wth certain accuracy. We take a simple single-axis MEMS vibratory gyroscope to study the effect on these defects on its dynamics performance. The study presented in the paper may be useful for including undesirable effects in designing MEMS vibratory gyroscopes. [ABSTRACT FROM AUTHOR]

Wet anisotropic etching is extensively employed in silicon bulk micromachining to fabricate microstructures for various applications in the field of microelectromechanical systems (MEMS). In addition, it is most widely used for surface texturing to minimize the reflectance of light to improve the efficiency of crystalline silicon solar cells. In wet bulk micromachining, the etch rate is a major factor that affects the throughput. Slower etch rate increases the fabrication time and therefore is of great concern in MEMS industry where wet anisotropic etching is employed to perform the silicon bulk micromachining, especially to fabricate deep cavities and freestanding microstructures by removal of underneath material through undercutting process. Several methods have been proposed to increase the etch rate of silicon in wet anisotropic etchants either by physical means (e.g. agitation, microwave irradiation) or chemically by incorporation of additives. The ultrasonic agitation during etching and microwave irradiation on the etchants increase the etch rate. However, ultrasonic method may rupture the fragile structures and microwave irradiation causes irradiation damage to the structures. Another method is to increase the etching temperature towards the boiling point of the etchant. The etching characteristics of pure potassium hydroxide solution (KOH) is studied near the boiling point of KOH, while surfactant added tetramethylammonium hydroxide (TMAH) is investigated at higher temperature to increase the etch rate. Both these studies have shown a potential way of increasing the etch rate by elevating the temperature of the etchants to its boiling point, which is a function of concentration of etch solution. The effect of various kinds of additives on the etch rate of silicon is investigated in TMAH and KOH. In this paper, the additives which improve the etch rate have been discussed. Recently the effect of hydroxylamine (NH2OH) on the etching characteristics of TMAH and KOH is investigated in detail. The concentration of NH2OH in TMAH/KOH is varied to optimize the etchant composition to obtain improved etching characteristics especially the etch rate and undercutting which are important parameters for increasing throughput. In this article, different methods explored to improve the etch rate of silicon have been discussed so that the researchers/scientists/engineers can get the details of these methods in a single reference. [ABSTRACT FROM AUTHOR]

Objective: To estimate effectiveness of presumptive doxycycline or azithromycin treatment in preventing progression of Acute Febrile Illness to Acute Encephalitis Syndrome in Gorakhpur. Study Design: Prospective cohort study. Study Setting: Primary healthcare centers and Community healthcare centers of Gorakhpur district, Uttar Pradesh. Participants: Children aged 1 year to less than 15 years with fever of 3 days to less than 15 days duration attending three selected peripheral health facilities in Gorakhpur during August to October, 2018. Procedure: 35 medical officers in three selected Primary Healthcare Centers/Community Healthcare centers were sensitized on the treatment strategy. After sensitization, study participants were enrolled and information about prescription of doxycycline or azithromycin was collected. Participants were telephonically followed-up to know their progression status from AFI to AES. Main outcome measure: Incidence of acute encephalitis syndrome among acute failure illness patients who received presumptive doxycycline or azithromycin treatment and those who did not receive this treatment. Results: Of the enrolled 930 AFI patients, 801 (86%) were prescribed doxycycline or azithromycin and 725 (78%) could be telephonically followed-up. Progression to acute encephalitis syndrome was seen in 6 of the 621 patients who received presumptive treatment, and 5 of the 104 who did not receive the treatment. The relative risk of developing acute encephalitis syndrome among acute febrile illness patients who were prescribed presumptive treatment with doxycycline or azithromycin was 0.20 (95% Cl: 0.06–0.65). The effectiveness of presumptive treatment with doxycycline or azithromycin strategy was 79.9% (95% CI: 35.4–94). Conclusion: PDA treatment to children presenting with fever in peripheral health facilities of the study blocks in Gorakhpur during August-November, 2018 had good effectiveness in preventing progression of acute febrile illness to acute encephalitis syndrome. [ABSTRACT FROM AUTHOR]

In this work, we present the design and analysis of microcantilever beams based on arrow shape. Effect of rectangular step length and width as well as free end width of beam have been investigated on various characteristics of proposed microcantilever beams. The proposed microcantilever beams were fabricated from silicon dioxide material using wet bulk micromachining in 25 wt.% TMAH at 75 °C. Vibration analysis of the microcantilever beams was carried out using a laser vibrometer. A FEM software, ANSYS, was used primarily for numerical analysis of resonance frequency, and to examine the effect of rectangular step length as well as free end width of microcantilever beam on its resonance frequency. Furthermore, ANSYS was employed to determine the maximum deflection, torsional end rotation and quality factor of proposed microcantilever beams. Additionally, effects of bottom gap and rectangular step length on quality factor of proposed microcantilever beams at lower and higher bottom gaps have also been investigated. The fundamental transverse bending mode frequency for a proposed microcantilever beam comprising rectangular step length of 50 μm and free end width 0 μm is approximately 48% higher than that of the conventional rectangular profile microcantilever beam of width 40 μm. Furthermore, maximum deflection and torsional end rotation obtained for a proposed microcantilever beam having rectangular step length 190 μm and beam free end width 40 μm are found as 680% and 800%, respectively, higher than that of the rectangular beam of length 200 μm and thickness 40 μm. [ABSTRACT FROM AUTHOR]

Bamboo shoots being low in fat, high in dietary fiber and rich in mineral content, like an ideal vegetable have been used traditionally. Besides nutrients, bamboo shoots also contain lethal concentration of the anti-nutrient (cyanogen) that need to be removed before human consumption. Therefore an attempt has been made to find out the best processing method for confiscation of cyanogens. B. bambos, B. tulda, D. strictus and D.asper were selected for the study. Fresh and processed bamboo shoots were analyzed for their various nutritional and anti-nutritional contents. Carbohydrate content in fresh shoots of studied species ranged from 2.39%–3.6%, proteins from 1.65%–2.08%, phenols from 0.36%–0.63%, cyanogens from 0.011%–0.018%, minerals did not vary significantly among the species except potassium which ranged from 0.32%–0.52%. The shoots were processed by boiling in water and different concentrations of NaCl (1%, 5% and 10%) for different intervals (10, 15, 20 and 25 min) to achieve maximum removal of cyanogens with minimum loss of nutrients. Boiling shoots in 5% NaCl for 15 min was found to be the best method for B. bamboos, 10 min boiling in 1% NaCl for B. tulda, 15 min boiling in 1% NaCl for D. strictus and 10 min boiling in 5% NaCl for D. asper. These processing methods will be very useful in utilization of bamboo shoots as these are very simple and can be used by the local inhabitants and shoot processing industries. [ABSTRACT FROM AUTHOR]

MEMS resonators are designed for a fixed resonant frequency. Therefore, any shift in the resonant frequency of the final fabricated structure can be a denting factor for its suitability towards a desired application. There are numerous factors which alter the designed resonant frequency of the fabricated resonator such as the metal layer deposited on top of the beam and the residual stresses present in the fabricated structure. While the metal coating, which acts as electrode, increases the stiffness and the effective mass of the composite structure, the residual stress increases or decreases the net stiffness if it is a tensile or compressive type respectively. In this paper, we investigate both these cases by taking two different structures, namely, the micro cantilever beam with gold layer deposited on its top surface and the MEMS gyroscope with residual stresses. First, we carry out experiments to characterize both these structures to find their resonant frequencies. Later, we analytically model those effects and compare them with the experimentally obtained values. Finally, it is found that the analytical models give an error of less than 10% with respect to the experimental results in both the cases. [ABSTRACT FROM AUTHOR]

In this paper, we present the design and characterization of a vibratory yaw rate MEMS sensor that uses in-plane motion for both actuation and sensing. The design criterion for the rate sensor is based on a high sensitivity and low bandwidth. The required sensitivity of the yawrate sensor is attained by using the inplane motion in which the dominant damping mechanism is the fluid loss due to slide film damping i.e. two-three orders of magnitude less than the squeeze-film damping in other rate sensors with out-of-plane motion. The low bandwidth is achieved by matching the drive and the sense mode frequencies. Based on these factors, the yaw rate sensor is designed and finally realized using surface micromachining. The inplane motion of the sensor is experimentally characterized to determine the sense and the drive mode frequencies, and corresponding damping ratios. It is found that the experimental results match well with the numerical and the analytical models with less than 5% error in frequencies measurements. The measured quality factor of the sensor is approximately 467, which is two orders of magnitude higher than that for a similar rate sensor with out-of-plane sense direction. [ABSTRACT FROM AUTHOR]

A base of gas hydrate stability zone was established after coring and drilling under the National Gas Hydrate Program (NGHP) Expedition-01 in the Mahanadi basin. At two sites, logging-while-drilling log data, and, at one site, wireline log data, were acquired during the NGHP Expedition-01. Gas hydrate reservoirs modelling can be performed in two different ways. One way is isotropic (load bearing) and, on the other hand, anisotropic media (fracture filling with gas hydrate). Here, we have performed anisotropic modelling and estimated gas hydrate saturation using P-wave velocity, assuming an incidence angle of 75 ∘ represents the vertical fracture. The estimated gas hydrate saturation at sites NGHP-01-08 and NGHP-01-09, assuming anisotropic media, reduces the estimate by half compared to the saturation estimation by assuming isotropic media. The saturation at site NGHP-01-19 estimated from the isotropic and anisotropic P-wave velocity models are more or less similar except in the zone (175–210 m) just above the bottom simulating reflector depth, and this zone shows similar reduction in saturation as estimated at sites NGHP-01-08 and NGHP-01-09. Observations show that average gas hydrate saturations are relatively low (up to 5% of the pore space). The saturation of a gas hydrate estimated from an isotropic P-wave model varies from 5% to 20%. However, the saturation estimated from the anisotropic P-wave model shows a variation up to 10% of the pore spaces at three sites. [ABSTRACT FROM AUTHOR]

Silicon wet anisotropic etching based bulk micromachining technique is widely used for the fabrication of microelectromechanical systems components. In this technique of microfabrication, alignment of mask edges with crystallographic directions plays a crucial role to avoid unwanted undercutting to control the dimensions of fabricated structures. Various kinds of pre-etched designs have been reported to identify the crystallographic directions (e.g. 〈110〉 and 〈100〉) on Si{100} and Si{110} wafer surfaces. To the best of our knowledge, no pre-etched design has been reported to identify crystal directions on Si{111} wafer. In this work, a self-aligning technique based on pre-etched patterns has been investigated to precisely determine the 〈110〉 direction on Si{111} wafer surface. In this technique, a set of circular shape mask patterns close to wafer edge are etched for the identification of 〈110〉 direction. On wet anisotropic etching these patterns transform to hexagonal shapes. The notches of hexagonal patterns align precisely along a straight line only when they lie on exact 〈110〉 direction. The self-aligned notches can easily be identified by visual inspection using an optical microscope. The major advantages of this technique are simplicity, precision, and self-alignment. In addition, the pre-etched patterns at the wafer periphery occupy very less place. [ABSTRACT FROM AUTHOR]

Compliant mechanisms have been realized as a potential tool to enhance the sensitivity of MEMS accelerometers through displacement amplification. In this article, optimization of a compound lever-based compliant mechanism has been carried out for the inclusion in MEMS accelerometer. The compliant displacement amplifier has been studied using the pseudo-rigid body approach and expressions for the displacement and fundamental natural frequency have been derived for the MEMS accelerometer. Further, for a range of values of the selected parameters, a detailed comparison has been made between the outcomes of the considered pseudo-rigid body-based approach and FEA simulations. Based on the derived mathematical model, optimization has been carried out for the best performance of the MEMS accelerometer. Using switched capacitor-based signal conditioning, output voltage has been calculated for the given input signal. Performance of displacement amplifier based MEMS accelerometer has been compared with the conventional one for sensitivity and nonlinearity. In this work, using a comparatively smaller size of proof mass, the higher figure of merits has been achieved in terms of natural frequency and amplified displacement of sense comb fingers. [ABSTRACT FROM AUTHOR]