Adaptive moving mesh level set method for structure topology optimization

The level set method is a promising approach to provide flexibility in dealing with topological changes during structural optimization. Normally, the level set surface, which depicts a structure's topology by a level contour set of a continuous scalar function embedded in space, is interpolated on a fixed mesh. The accuracy of the boundary positions is therefore largely dependent on the mesh density, a characteristic of any Eulerian expression when using a fixed mesh. This article combines the adaptive moving mesh method with a level set structure topology optimization method. The finite element mesh automatically maintains a high nodal density around the structural boundaries of the material domain, whereas the mesh topology remains unchanged. Numerical experiments demonstrate the effect of the combination of a Lagrangian expression for a moving mesh and a Eulerian expression for capturing the moving boundaries.     

Miniaturization limits of field-effect based MEMS accelerometers

Accelerometers are increasingly gaining in importance in the consumer electronics sector. To estimate whether field-effect based accelerometers have an advantage over sensor types common today, we analyze their scaling performance in this paper. Within the scope of this research, firstly we create an analytical model and subsequently verify it by numerical simulation. Based thereon, a numerical–analytical study of the scaling performance follows. The requirements are based on a commercially available capacitive accelerometer. We identify the main miniaturization limits of field-effect based accelerometers, which are total noise and pull-in effect. Those limits lead to a total area estimation for a triaxial MEMS accelerometer core of only 410 μm × 300 μm.     

Microfluidic Chips for Life Sciences—A Comparison of Low Entry Manufacturing Technologies

Microfluidic water‐in‐oil droplets are a versatile tool for biological and biochemical applications due to the advantages of extremely small monodisperse reaction vessels in the pL–nL range. A key factor for the successful dissemination of this technology to life science laboratory users is the ability to produce microfluidic droplet generators and related accessories by low‐entry barrier methods, which enable rapid prototyping and manufacturing of devices with low instrument and material costs. The direct, experimental side‐by‐side comparison of three commonly used additive manufacturing (AM) methods, namely fused deposition modeling (FDM), inkjet printing (InkJ), and stereolithography (SLA), is reported. As a benchmark, micromilling (MM) is used as an established method. To demonstrate which of these methods can be easily applied by the non‐expert to realize applications in topical fields of biochemistry and microbiology, the methods are evaluated with regard to their limits for the minimum structure resolution in all three spatial directions. The suitability of functional SLA and MM chips to replace classic SU‐8 prototypes is demonstrated on the basis of representative application cases.     

Miniaturization limits of piezoresistive MEMS accelerometers

We present the miniaturization limits of axially loaded piezoresistive MEMS accelerometers. Therefore we identify limiting factors on the basis of FEM-verified analytical models. To ensure a broad discussion we compare two different axially loaded topologies: first a conventional topology, which can be manufactured already today, and second a future-oriented topology utilizing nanowires. To enable a realistic comparison of the different topologies we shrink the sensor while maintaining a specific performance (e.g. sensitivity and noise) considering design limitations such as fracture of silicon and buckling. To find the minimum total sensor area under certain constraints and therefore the optimal geometric and material parameters we apply optimization techniques to our analytical models. It will be seen that the piezoresistive transducer principle for MEMS accelerometers has a promising shrink potential with minimum total sensor dimensions as low as 150 × 150 × 10 μm³ achievable by use of currently available manufacturing processes.     

Modeling, Design, and Verification for the Analog Front-End of a MEMS-Based Parallel Scanning-Probe Storage Device

We present an integrated analog front-end (AFE) for the read-channel of a parallel scanning-probe storage device. The read/write element is based on an array of microfabricated silicon cantilevers equipped with heating elements to form nanometer-sized indentations in a polymer surface using integral atomic-force microscope (AFM) tips. An accurate cantilever model based on the combination of a thermal/electrical lumped-element model and a behavioral model of the electrostatic/mechanical part are introduced. The behavioral model of the electrostatic/mechanical part is automatically generated from a full finite-element model (FEM). The model is completely implemented in Verilog-A and was used to co-develop the integrated analog front-end circuitry together with the read/write cantilever. The cantilever model and the analog front-end were simulated together and the results were experimentally verified. The approach chosen is well suited for system-level simulation and verification/extraction in a design environment based on standard EDA tools.     

Validation of X-ray lithography and development simulation system for moving mask deep X-ray lithography

This paper presents a newly developed 3-Dimensional (3-D) simulation system for Moving Mask Deep X-ray Lithography (M/sup 2/DXL) technique, and its validation. The simulation system named X-ray Lithography Simulation System for 3-Dimensional Fabrication (X3D) is tailored to simulate a fabrication process of 3-D microstructures by M/sup 2/DXL. X3D consists of three modules: mask generation, exposure and resist development (hereafter development). The exposure module calculates a dose distribution in resist using an X-ray mask pattern and its movement trajectory. The dose is then converted to a resist dissolution rate. The development module adopted the "Fast Marching Method" technique to calculate the 3-D dissolution process and resultant 3-D microstructures. This technique takes into account resist dissolution direction that is required by 3-D X-ray lithography simulation. The comparison between simulation results and measurements of "stairs-like" dose deposition pattern by M/sup 2/DXL showed that X3D correctly predicts the 3-D dissolution process of exposed PMMA.     

Advanced Numerical Methodology to Analyze High-Temperature Wire-Net Compact Heat Exchangers For a Micro-Combined Heat and Power System Application

Abstract

The objective of this paper is to predict compact heat exchanger (CHE) performance for a miniaturized combined heat and power system by a detailed modeling of the complex microchannels and assessing the collector performance using a new reduced order modeling (ROM). The ROM was introduced to decrease the computational size and predict the collector performance with a reasonable accuracy. The CHE is assembled as a stack of counter-flow passages with optimized thickness and an isotropic wire-net (to provide required stiffness and enhance the mixing) which separates the thin partition foils. Computational fluid dynamics (CFD) methodology comprises of conjugate heat transfer (CHT) analysis for a microchannel section and ROM to analyze the entire CHE performance based on the collector performance. The porous medium model, based on the Darcy-Forchheimer law, is modified (constant integration method) to account for the temperature evolution and localized turbulence effects. The resulting microchannel characteristics from a series of three-dimensional CFD-CHT analysis are used to calculate the inertial and viscous coefficients using the constant integration method. These characteristics have been implemented and verified numerically as well as experimentally. The best-revised methodology allows obtaining pressure drop with less than three percent error with respect to the CHT model.