Douglas R. Adkins

Mass-Sensitive Microfabricated Chemical Preconcentrator

This paper describes a mass-sensitive microfabricated preconcentrator for use in chemical detection microsystems. The device combines mass sensing and preconcentration to create a smart preconcentrator (SPC) that determines when it has collected sufficient analyte for analysis by a downstream chemical microsystem. The SPC is constructed from a Lorentz-force-actuated pivot-plate resonator with an integrated heater. Subsequent to microfabrication, the SPC is coated with an adsorbent for collection of chemical analytes. The frequency of operation varies inversely with the mass of collected analyte. Such shifts can be measured by a back-EMF in the SPCs drive/transducer line. By using a calibrated vapor system, the limit of detection of the SPC was determined to be less than 50 ppb for dimethyl-methyl-phosphonate (DMMP) (actual limits of detection are omitted due to export control limitations). At 1 ppm of DMMP, 1-s collection was sufficient to trigger analysis in a downstream microsystem; other micropreconcentrators would require an arbitrary collection time, normally set at 1 min or longer. This paper describes the theory of operation, design, fabrication, coating, vapor system testing, and integration of the SPC into microanalytical systems. The theory of operation, which is applicable to other torsional oscillators, is used to predict a shear modulus of silicon (100) of G = 57.0 GPa plusmn2.2 GPa.

Solar heat pipe testing of the Stirling Thermal Motors 4-120 Stirling engine

Stirling-cycle engines have been identified as a promising technology for the conversion of concentrated solar energy into usable electrical power. A 25 kW electric system takes advantage of existing Stirling-cycle engines and existing parabolic concentrator designs. In previous work, the concentrated sunlight impinged directly on the heater head tubes of the Stirling Thermal Motors (STM) 4-120 engine. A Sandia-designed felt-metal-wick heat pipe receiver was fitted to the STM 4-120 engine for on-sun testing on Sandias Test Bed Solar Concentrator. The heat pipe uses sodium metal as an intermediate two-phase heat transfer fluid. The receiver replaces the directly-illuminated heater head previously tested. The heat pipe receiver provides heat isothermally to the engine, and the heater head tube length is reduced, both resulting in improved engine performance. The receiver also has less thermal losses than the tube receiver. The heat pipe receiver design is based on Sandias second-generation felt-wick heat pipe receiver. This paper presents the interface design, and compares the heat pipe/engine test results to those of the directly-illuminated receiver/engine package.

Micro acoustic spectrum analyzer

A micro acoustic spectrum analyzer for determining the frequency components of a fluctuating sound signal comprises a microphone to pick up the fluctuating sound signal and produce an alternating current electrical signal; at least one microfabricated resonator, each resonator having a different resonant frequency, that vibrate in response to the alternating current electrical signal; and at least one detector to detect the vibration of the microfabricated resonators. The micro acoustic spectrum analyzer can further comprise a mixer to mix a reference signal with the alternating current electrical signal from the microphone to shift the frequency spectrum to a frequency range that is a better matched to the resonant frequencies of the microfabricated resonators. The micro acoustic spectrum analyzer can be designed specifically for portability, size, cost, accuracy, speed, power requirements, and use in a harsh environment. The micro acoustic spectrum analyzer is particularly suited for applications where size, accessibility, and power requirements are limited, such as the monitoring of industrial equipment and processes, detection of security intrusions, or evaluation of military threats.

Micro heat spreader enhanced heat transfer in MCMs

The peak thermal power generated in microelectronics assemblies has risen from less than 1 W/cm/sup 2/ in 1980 to greater than 40 W/cm/sup 2/ today, due primarily to increasing densities at both the IC and packaging levels. We have demonstrated enhanced heat transfer in a prototype Si substrate with a backside micro heat channel structure. Unlike conventional micro heat pipes, these channels are biaxial with a greater capacity for fluid transfer. Thermal modeling and preliminary experiments have shown an equivalent increase in substrate thermal conductivity to over 500 W/m.K, or a four times improvement. Optimization of the structure and alternative liquids will further increase the thermal conductivity of the micro heat channel substrate with the objective being polycrystalline diamond, or about 1200 W/m.K. The crucial design parameters for the micro heat channel system and the thermal characteristics of the system are covered.

Recent advancements in the gas-phase MicroChemLab

Sandias hand-held MicroChemLabTM system uses a micromachined preconcentrator (PC), a gas chromatography channel (GC) and a quartz surface acoustic wave array (SAW) detector for sensitive/selective detection of gas-phase chemical analytes. Requisite system size, performance, power budget and time response mandate microfabrication of the key analytical system components. In the fielded system hybrid integration has been employed, permitting optimization of the individual components. Recent improvements in the hybrid-integrated system, using plastic, metal or silicon/glass manifolds, is described, as is system performance against semivolatile compounds and toxic industrial chemicals. The design and performance of a new three-dimensional micropreconcentrator is also introduced. To further reduce system dead volume, eliminate unheated transfer lines and simplify assembly, there is an effort to monolithically integrate the silicon PC and GC with a suitable silicon-based detector, such as a magnetically-actuated flexural plate wave sensor (magFPW) or a magnetically-actuated pivot plate resonator (PPR).

Evaluation of Mini/Micro-Pumps for Micro-Chem-Lab™

The performance of a selective group of mini and micro-pumps has been evaluated for use in gas phase detection for the Micro-Chem-Lab™. Our major assessment criteria are: flow rate, pressure drop across the pump, and electrical current drawn by the pump. Two pumping configurations have been investigated: (1) upstream pumping to build up pressure head and (2) downstream pumping to draw vacuum. Four mini-pumps (T-Square, SP 250 EC, SP 135 FZ-4, and KNF Neuberger) have been studied. Each of these pumps has been tested to determine whether they meet our requirements of high head pressure, high flow rate, and low power consumption. We have also assessed different mechanisms for pumping gas in micro-domains — specifically, a valveless diffuser/nozzle micro-pump, a LIGA diaphragm micro-pump and a micro drag pump. However our preliminary findings reveal that these micro-pumps do not meet our minimal requirements for use in the μChemLab™.Copyright

Testing of the STM4-120 kinematic Stirling engine for solar thermal electric systems

The STM4 120 is being bench-tested at Sandias engine test facility and will be combined later with a solar receiver for on-sun evaluation. The test system layout, instrumentation, controls, testing parameters, and preliminary performance results for the STM4-120 are presented. Ten hours of operation have been carried out and used to check out the facility. These preliminary results indicate that the engine is performing to specifications.<<ETX>>

Compact low-power gas detector for chemical alarms

Through an internally funded research program, Defiant Technologies has developed a compact chemical detector that can be tailored for a range of target analytes. The system uses a preconcentrator (PC) to collect and screen samples from the air, and a surface acoustic wave (SAW) microbalance to detect analytes when they are released from the PC. This PC-SAW system serves as a trigger for a secondary analysis channel that uses a micro-gas chromatographic (micro-GC) column to perform a more detailed analysis of the air. This combined approach provides high-confidence results while conserving power and minimizing response time. By properly selecting coatings on the PC, micro-GC and SAW, the unit can be designed for optimum performance in detecting specific target gases while ignoring interferents. This paper presents test results from our research and discusses some of the applications for this type of system.

Real-time discriminatory sensors for water contamination events :LDRD 52595 final report.

The gas-phase {mu}ChemLab{trademark} developed by Sandia can detect volatile organics and semi-volatiles organics via gas phase sampling . The goal of this three year Laboratory Directed Research and Development (LDRD) project was to adapt the components and concepts used by the {mu}ChemLab{trademark} system towards the analysis of water-borne chemicals of current concern. In essence, interfacing the gas-phase {mu}ChemLab{trademark} with water to bring the significant prior investment of Sandia and the advantages of microfabrication and portable analysis to a whole new world of important analytes. These include both chemical weapons agents and their hydrolysis products and disinfection by-products such as Trihalomethanes (THMs) and haloacetic acids (HAAs). THMs and HAAs are currently regulated by EPA due to health issues, yet water utilities do not have rapid on-site methods of detection that would allow them to adjust their processes quickly; protecting consumers, meeting water quality standards, and obeying regulations more easily and with greater confidence. This report documents the results, unique hardware and devices, and methods designed during the project toward the goal stated above. It also presents and discusses the portable field system to measure THMs developed in the course of this project.

Mass transport, corrosion, plugging, and their reduction in solar dish/Stirling heat pipe receivers

Solar dish/Stirling systems using sodium heat pipe receivers are being developed by industry and government laboratories in the US and abroad. The unique demands of this application lead to heat pipe wicks with very large surface areas and complex three-dimensional flow patterns. These characteristics can enhance the mass transport and concentration of constituents of the wick material, resulting in wick corrosion and plugging. As the test times for heat pipe receivers lengthen, we are beginning to see these effects both indirectly, as they affect performance, and directly, in post-test examinations. We are also beginning to develop corrective measures. In this paper, we report on our test experiences, our post-test examinations, and on our initial effort to ameliorate various problems.