Experimental and Analytical Study of Micro-Serrations on Surgical Blades

This paper reports on a study and application of laser ablation for machining of micro-serrations on surgical blades. The proposed concept is inspired by nature and mimics a mosquito’s maxilla, which is characterized by a number of serrations along its edge in order to painlessly penetrate human skin and tissue. The focus of this study is to investigate the maxilla’s penetration mechanisms and its application to commercial surgical blades. The fundamental objective is to understand the friction and cutting behavior between a serrated hard surface and soft materials, as well as to identify serration patterns that would minimize the cutting force and the friction of the blade during tissue cutting. Micro-serrations characterized by different patterns and sizes ranging from 200 μm to 400 μm were designed and manufactured on surgical blades. As supported by finite element methods (FEM), a reduction of 20∼30% in the force during blade cutting has been achieved, which encourages further studies and their applications to biomedical devices.

RFIC Transformer With 12x Size Reduction and 15x Performance Enhancement by Self-Rolled-Up Membrane Nanotechnology

Two types of on-chip RFIC transformers based on CMOS compatible strain-induced self-rolled-up membrane (S-RuM) nanotechnology, with extremely small footprint, are demonstrated. The rolled-up transformers, with their 3D tubular form factors, dramatically reduce the substrate parasitic effects and push the maximum working frequency into millimeter wave bands with a coupling coefficient, k, as high as 0.92. The 3D stand-up nature also allows the tube transformers to be less susceptible to residue stress in the substrate and thus compatible with flexible platforms for wearable RF applications. The demonstrated samples with a turn ratio, n, of 5.5:1 only occupies 805 μm2 on-chip area (s) which is 12x smaller than that of the best planar transformer with the same turn ratio, and its figure of merit n·k/s, is therefore ∼ 6046/mm2, enhanced by 15x.

Analyzing Temperature Changes in Powered LEDs by Combining Thermal and Radiometric Characterization With Computational Fluid Dynamics

This paper describes the workflow and improved accuracy of a combined characterization and simulation of an LED luminaire. The achieved measurement results of the thermal and radiometric characterization, the process of implementing these results into a thermal simulation, and the benefit for the luminaire designer are presented.

High Heat Flux Subcooled Flow Boiling of Methanol in Microtubes

As the proper cooling of the electronic devices leads to significant increase in the performance, two-phase heat transfer to dielectric liquids can be of an interest especially for thermal management solutions for high power density devices with extremely high heat fluxes. In this paper, the pressure drop and critical heat flux (CHF) for subcooled flow boiling of methanol at high heat fluxes exceeding 1 kW/cm2 is investigated. Methanol was propelled into microtubes (ID = 265 and 150 μm) at flow rates up to 40 ml/min (mass fluxes approaching 10000 kg/m2-s), boiled in a portion of the microtube by passing DC current through the walls, and the two-phase pressure drop and CHF were measured for a range of operating parameters. The two-phase pressure drop for subcooled flow boiling was found to be significantly lower than the saturated flow boiling case, which can lead to lower pumping powers and more stability in the cooling systems. CHF was found to be increasing almost linearly with Re and inverse of inner diameter (1/ID), while for a given inner diameter, it decreases with increasing heated length.

Embedded Two-Phase Cooling of High Flux Electronics via Micro-Enabled Surfaces and Fluid Delivery Systems (FEEDS)

This work presents the experimental design and testing of a two-phase, embedded manifold-microchannel cooler for cooling of high flux electronics. The ultimate goal of this work is to achieve 0.025 cm2-K/W thermal resistance at 1 kW/cm2 heat flux and evaporator exit vapor qualities at or exceeding 90% at less than 10% absolute pressure drop. While the ultimate goal is to obtain a working two-phase embedded cooler, the system was first tested in single-phase mode to validate system performance via comparison of experimentally measured heat transfer coefficient and pressure drop to the values predicted by CFD simulations. Upon validation, the system was tested in two phase mode using R245fa at 30°C saturation temperature and achieved in excess of 1 kW/cm2 heat flux at 45% vapor quality. Future work will focus on increasing the exit vapor quality as well as use of SiC for the heat transfer surface upon completion of current experiments with Si.

A Study on Flow Boiling in Microchannel With Piranha Pin Fin

In this paper we reported an advanced structure, the Piranha Pin Fin (PPF), for microchannel flow boiling. Fluid flow and heat transfer performance were evaluated in detail with HFE7000 as working fluid. Surface temperature, pressure drop, heat transfer coefficient and critical heat flux (CHF) were experimentally obtained and discussed. Furthermore, microchannels with different PPF geometrical configurations were investigated. At the same time, tests for different flow conditions were conducted and analyzed. It turned out that microchannel with PPF can realize high-heat flux dissipation with reasonable pressure drop. Both flow conditions and PPF configuration played important roles for both fluid flow and heat transfer performance. This study provided useful reference for further PPF design in microchannel for flow boiling.

Design Considerations of Packaging a High Voltage Current Switch

In this paper an attempt has been made to demonstrate various package design considerations to accommodate series connection of high voltage Si-IGBT (6500V/25A die) and SiC-Diode (6500V/25A die). The effects of connecting the cathode of the series diode to the collector of the IGBT versus connecting the emitter of the IGBT to the anode of the series diode has been analyzed in regards to gate terminal operation and the parasitic line inductance of the structure. ANSYS Q3D/MAXWELL software have been used to analyze and extract parasitic inductance and capacitances in the package along with electromagnetic fields, electric potentials, and current density distributions throughout the package for variable parameters. SIMPLIS-SIMETRIX is used to simulate typical switch behavior for different parasitic parameters under hard switched conditions. Various simulation results have then been used to redesign and justify the optimized package structure for the final current switch design. The thermal behavior of such a package is also conducted in COMSOL in order to ensure that the thermal ratings of the power devices is not exceeded, and to understand where potentially harmful hotspots could arise and estimate the maximum attainable frequency of operation. The main motivation of this work is to enumerate detailed design considerations for packing a high voltage current switch package.

Novel Dynamic Numerical Microchannel Evaporator Model to Investigate Parallel Channel Instabilities

A novel fully dynamic model of a microchannel evaporator is presented. The aim of the model is to study the highly dynamic parallel channel instabilities that occur in these evaporators in more detail. The numerical solver for the model is custom-built and the majority of the paper is focused on detailing the various aspects of this solver. The one-dimensional homogeneous two-phase flow conservation equations are solved to simulate the flow. The full three-dimensional conduction domain of the evaporator is also dynamically resolved. This allows for the correct simulation of the complex hydraulic and thermal interactions between the microchannels that give rise to the parallel channel instabilities. The model uses state-of-the-art correlations to calculate the frictional pressure losses and heat transfer in the microchannels. In addition, a model for inlet restrictions is also included to simulate the stabilizing effect of these components. In the final part of the paper, initial validation results of the model are presented, in which stability results of the model are compared to existing experimental data from literature. Finally, some representative dynamic results are also given to demonstrate some of the unique capabilities of the model.

A Microfluidic-Based Tactile Sensor for 3-DOF Force/Torque Detection

This paper reports on a microfluidic-based tactile sensor capable of detecting forces along two directions and torque about one direction. The 3-Degree-Of-Freedom (3-DOF) force/torque sensor encompasses a symmetric three-dimensional (3D) microstructure embedded with two sets of electrolyte-enabled distributed resistive transducers underneath. The 3D microstructure is built into a rectangular block with a loading-bump on its top and two microchannels at its bottom. Together with electrode pairs distributed along the microchannel length, electrolyte in each microchannel functions as a set of three resistive transducers. While a normal force results in a resistance increase in the two sets of transducers, a shear force causes opposite resistance changes in the two sets of transducers. Conversely, a torque leads to the opposite resistance changes in the two side transducers in each set. Soft lithography and CNC molding are combined to fabricate a prototype tactile sensor. The experimental results validate the feasibility of using this microfluidic-based tactile sensor for 3-DOF force/torque detection.

Thermal Performance Enhancement of Glass Interposer

As demands on performance for mobile electronics continue to increase, traditional packaging technology is facing its limit in number of input/outputs (I/Os) and thermal challenges. Glass interposers offer many advantages over previous packaging technology for mobile electronics, including ultra-high electrical resistivity, low loss, and lower cost at processed interposer levels. However, it has two fundamental limitations; brittleness and relatively low thermal conductivity (∼1 W/mK), compared to Si (∼150 W/mK). This paper presents a study on thermal performance enhancement of glass interposer based on thermal modeling, and compares it with silicon interposer. The model captures in-plane and out-of-plane thermal performance enhancement with copper structures incorporated in the interposer. To further study the effect of advanced cooling schemes on interposer technology, an integrated vapor chamber design is evaluated through computational modeling.