Micro and Nano Systems Letters最新文献

The extraordinary enhancement in heat transfer efficiency of nanofluids at extremely low volume fractions has attracted a lot of attention in identifying the governing mechanisms. The nanoscale effects, Brownian motion (random motion of particles inside the base fluid) and thermophoresis (diffusion of particles due to temperature gradient) are found to be important slip mechanisms in nanofluids. Based on these findings, a set of partial differential equations for conservation laws for nanofluids was formed. Since then, a large number of mathematical studies on convective heat transfer in nanofluids became feasible. The present paper summarizes the studies pertaining to instability of a horizontal nanofluid layer under the impact of various parameters such as rotation, magnetic field, Hall currents and LTNE effects in both porous and non-porous medium. Initially, investigations were made using the model considering fixed initial and boundary conditions on the layer, gradually the model was revised in the light of more practical boundary conditions and recently it has been modified to get new and more interesting results. The exhaustive analysis of instability problems is presented in the paper and prospects for future research are also identified.

This paper proposes a new design of bimorph-type electrothermal actuators based on flexible Ni-Co substrates and describes the results of the finite element method (FEM) simulation and performance evaluation of the actuators. In the design of the actuators, a multilayer structure consisting of an adhesion layer, two insulation layers, and a Pt (platinum) heater layer was formed on the Ni-Co flexible substrate that was patterned in an individual shape. The thin-film actuators proposed in this study could be detached from a Si carrier wafer and adhered to other micro or macrostructural elements. To investigate the temperature distribution and mechanical behavior of the actuators, multiphysics FEM simulations combining electrothermal and static structural analyses were carried out. The actuators were fabricated using conventional microfabrication and electroplating technologies on Si carrier wafer; then, the actuators were peeled off from the carrier wafer using the release process proposed in this paper. After fabricating the actuators, the deflection of their tips was evaluated and compared with that obtained from the FEM simulations.

We present a method to fabricate planar metal layers to be used as micromachined mirrors. Released mirrors of pure metal involve severe stress and reveal specific challenges to obtain planar mirror structures. Introducing sub-structures generating corrugated patterns, the metal mirror layers can be mechanically stabilized and undesired mirror bending can be reduced. For our investigations we used different arrangements of line structures on our metal mirrors, such as a group of straight or curved lines oriented differently. Comparing all the implemented different designs, planar micromirrors were achieved via sub-structures with a combination of straight lines arranged orthogonally to a single line. These planar micromirrors allow steering of the incident light by reflection and adjustment of the window transmittance. The presented low-cost method is suitable for large area fabrication of micromirror arrays, but also can be customized for other applications, where planar free-standing metal layers are required.

A comparative study of elastic properties and mode I fracture energy has been presented between conventional carbon fibre (CF)/epoxy and advanced carbon nanotube (CNT)/epoxy laminated composite materials. The volume fraction of CNT fibres has been considered as 15%, 30%, and 60% whereas; the volume fraction of CF has been kept constant at 60%. Three stacking sequences of the laminates viz.[0/0/0/0], [0/90/0/90] and [0/30/–30/90] have been considered in the present analysis. Periodic microstructure model has been used to calculate the elastic properties of the laminated composites. It has been observed analytically that the addition of only 15% CNT in epoxy will give almost the same value of longitudinal Young’s modulus as compared to the addition of 60% CF in epoxy. Finite element (FE) analysis of double cantilever beam specimens made from laminated composite has also been performed. It has been observed from FE analysis that the addition of 15% CNT in epoxy will also give almost the same value of mode I fracture energy as compared to the addition of 60% CF in epoxy. The value of mode I fracture energy for [0/0/0/0] laminated composite is two times higher than the other two types of laminated composites.

Preterm infants are prone to have higher risks of morbidity, disability and developmental delay compared to term infants. The primitive reflexes, inborn behaviors found in early life development, are shown to be a good tool to assess the integrity of the central nervous system of infants and to predict potential malfunctions. Among these reflexes, the non-nutritive sucking reflex plays an important role in indicating congenital abnormalities in brain development and feeding readiness, especially for premature infants. Conventionally, pediatricians evaluate the oral sucking power qualitatively based on their experiences, by using a gloved finger put inside the infant’s mouth. Thus, more quantitative solutions to assess the sucking power of preterm infants are necessary to support healthcare professionals in their evaluation procedures. Here, we developed a silver nanowire (AgNW)-based flexible pressure sensor to measure the non-nutritive sucking power of infants. The flexible sensor was fabricated using silver nanowires deposited on polydimethylsiloxane (PDMS) in a sandwich-like structure. The sensor based on the principle of strain gauge was attached to a ring-shaped connecting module, and then to a pacifier. The negative sucking pressure exerted by the infant deformed the sensor membrane, causing its electrical resistance to change without any contact between the infant’s mouth and the sensing element. The fabricated sensor was characterized and optimized to achieve both the suitable sensitivity and stability. Thanks to the excellent long-term electro-mechanical stability and high sensitivity, the developed sensor is expected to provide the means to quantitatively assess the non-nutritive sucking of infants, with a portable, low-cost, non-invasive and light-weight solution.

Recently, as the concentration of fine dust in the atmosphere has increased due to an increase in the use of fossil fuel power plants, automobiles, and factories, it has been increasingly important to measure fine dust in the atmosphere. This is because exposure to fine dust is closely related to the incidence of respiratory and cardiovascular diseases and eventually affects mortality. In this paper, we introduce a MEMS particle sensor based on the resonance frequency shift according to added particle mass. The actuation is driven by Aluminum nitride (AlN), and the total thickness is 2.8?μm. A laser doppler vibrometer (LDV), an optical measuring instrument, was used to measure the resonance frequency of the sensor. Airborne particles naturally were deposited on the sensor. To show the frequency shift according to the particle mass, the frequency shift was measured by dividing the case where the deposited particle mass was small and large. In each case, the frequency shift according to the deposited particle mass was predicted and compared with the frequency shift measured by LDV. It was shown that the deposited particle mass and frequency shift are proportional. The deposition of particulate mass was estimated by image analysis. The frequency shift caused by the particle mass deposited on the sensor was defined as the sensitivity of the sensor. The estimated sensitivity of the sensor is 0.219 to 0.354?kHz/pg.

Rapid diagnosis and treatment are required when blood clots build up in a blood vessel and clog up the vessel. This study proposes novel smart catheters that can simultaneously diagnose and treat blood vessel disease. This quick treatment increases survival probability and can prevent various complications. In the design of the smart catheters, Pt strain gauges can be used to measure the inside diameter of the vessel. This paper proposes a new fabrication process of the Pt strain gauges based on metal substrates made of Ni and Co alloy (referred to as “Ni-Co” in this paper). In the fabrication process, a Ni-Co thin film was deposited onto a silicon carrier wafer by electroplating and patterned into individual shapes by a liftoff process. Then, a multilayered Pt strain gauge consisting of insulation, adhesive layers, and Pt metallization was formed on the Ni-Co flexible substrate. Subsequently, the Pt strain gauges were peeled off from the carrier wafer by a new release process. To evaluate the performance of the strain gauges in terms of gauge factor and nonlinearity, tensile and compression tests were conducted by attaching Pt strain gauges to the constant stress beam.

Deep reactive-ion etching (DRIE) is commonly used for high aspect ratio silicon micromachining. However, scalloping, which is the result of the alternating Bosch process of DRIE, can cause many problems in the subsequent process and degrade device performance. In this work, we propose a simple and effective method to smoothen the scalloping of DRIE trenches. The proposed method utilizes sidewall dry etching by reactive-ion etching (RIE) based sulfur hexafluoride (SF₆) plasmas, following the DRIE process. To investigate the effect of the etch parameter on the scallop smoothing effect, the radio frequency (RF) power and gas flow are controlled. After the RIE treatment, the scallop smoothing effects were evaluated by measuring the average scallop depth under each condition. The scallop depth was reduced by 91% after implementing the scallop smoothing technique using RIE. Thus, our smoothening method based on SF₆ plasmas would provide broad availabilities and applicability in silicon micromachining with the simple low-temperature process.