Design and Analysis of a Preconcentrator for the ChemLab

Preconcentration is a critical analytical procedure when designing a microsystem for trace chemical detection, because it can purify a sample mixture and boost the small analyte concentration to a much higher level allowing a better analysis. This paper describes the development of a micro-fabricated planar preconcentrator for the {mu}ChemLab{trademark} at Sandia. To guide the design, an analytical model to predict the analyte transport, adsorption and resorption process in the preconcentrator has been developed. Experiments have also been conducted to analyze the adsorption and resorption process and to validate the model. This combined effort of modeling, simulation, and testing has led us to build a reliable, efficient preconcentrator with good performance

Investigation of gas flow in long and narrow channels

To minimize the viscous flow losses in a microsystem for chemical analysis, the authors have investigated gas flow in long capillary tubes and microchannels to characterize the flow behavior. Both experimental results and theoretical predictions indicate that gas flow in long and narrow channels, as in capillary tubes or rectangular channels, compressibility effect is very important. This leads to a higher mass flow rate than predicted by the incompressible flow model. Different computational fluid dynamics (CFD) codes have been applied to simulate this flow problem. While some existing CFD codes have difficulties to model this problem, other codes, such as MPSalsa, predict a converged and reasonably accurate solution. This difficulty may be caused by numerical solution technique in these computer codes being optimized for incompressible flow problems rather than for compressible low-speed flow problems

Microfabricated planar preconcentrator

Front-end sampling or preconcentration is an important analytical technique and will be crucial to the success of many microanalytical detector systems. This paper describes a microfabricated planar preconcentrator ideal for integration with microanalytical systems. The device incorporates a surfactant templated sol gel adsorbent layer deposited on a microhotplate to achieve efficient analyte collection, and rapid, efficient thermal desorption. Concentration factors of 100--500 for dimethyl methyl phosphonate (DMMP) have been achieved with this device, while selectivities to interfering compounds greater than a factor of 25 have been demonstrated. Device performance will be compared with conventional preconcentrators, and the effects of system flow rate, flow channel geometry and collection time will be presented. A physical model of adsorption/desorption from the device will be reviewed and compared with experiment, while numerical simulation of flow over the device will be described

Microscale Modeling and Simulation

The Microsystems Subgrid Physics project is intended to address gaps between developing high-performance modeling and simulation capabilities and microdomain specific physics. The initial effort has focused on incorporating electrostatic excitations, adhesive surface interactions, and scale dependent material and thermal properties into existing modeling capabilities. Developments related to each of these efforts are summarized, and sample applications are presented. While detailed models of the relevant physics are still being developed, a general modeling framework is emerging that can be extended to incorporate evolving material and surface interaction modules

Materials Issues for Micromachines Development - ASCI Program Plan

This report summarizes materials issues associated with advanced micromachines development at Sandia. The intent of this report is to provide a perspective on the scope of the issues and suggest future technical directions, with a focus on computational materials science. Materials issues in surface micromachining (SMM), Lithographic-Galvanoformung-Abformung (LIGA: lithography, electrodeposition, and molding), and meso-machining technologies were identified. Each individual issue was assessed in four categories: degree of basic understanding; amount of existing experimental data capability of existing models; and, based on the perspective of component developers, the importance of the issue to be resolved. Three broad requirements for micromachines emerged from this process. They are: (1) tribological behavior, including stiction, friction, wear, and the use of surface treatments to control these, (2) mechanical behavior at microscale, including elasticity, plasticity, and the effect of microstructural features on mechanical strength, and (3) degradation of tribological and mechanical properties in normal (including aging), abnormal and hostile environments. Resolving all the identified critical issues requires a significant cooperative and complementary effort between computational and experimental programs. The breadth of this work is greater than any single program is likely to support. This report should serve as a guide to plan micromachines development at Sandia