Short-Pulse Laser-Assisted Fabrication of a Si-SiO2 Microcooling Device.

Thermal management is one of the main challenges in the most demanding detector technologies and for the future of microelectronics. Microfluidic cooling has been proposed as a fully integrated solution to the heat dissipation problem in modern high-power microelectronics. Traditional manufacturing of silicon-based microfluidic devices involves advanced, mask-based lithography techniques for surface patterning. The limited availability of such facilities prevents widespread development and use. We demonstrate the relevance of maskless laser writing to advantageously replace lithographic steps and provide a more prototype-friendly process flow. We use a 20 W infrared laser with a pulse duration of 50 ps to engrave and drill a 525 µm-thick silicon wafer. Anodic bonding to a SiO2 wafer is used to encapsulate the patterned surface. Mechanically clamped inlet/outlet connectors complete the fully operational microcooling device. The functionality of the device has been validated by thermofluidic measurements. Our approach constitutes a modular microfabrication solution that should facilitate prototyping studies of new concepts for co-designed electronics and microfluidics.

Real-Time Measurement of Xenon Concentration in a Binary Gas Mixture Using a Modified Ultrasonic Time-of-Flight Anesthesia Gas Flowmeter: A Technical Feasibility Study.

BACKGROUND: Xenon (Xe) is an anesthetic gas licensed for use in some countries. Fractional concentrations (%) of gases in a Xe:oxygen (O2) mixture are typically measured using a thermal conductivity meter and fuel cell, respectively. Speed of sound in such a binary gas mixture is related to fractional concentration, temperature, pressure, and molar masses of the component gases. We therefore performed a study to assess the feasibility of developing a novel single sterilizable device that uses ultrasound time-of-flight to measure both real-time flowmetry and fractional gas concentration of Xe in O2. METHODS: For the purposes of the feasibility study, we adapted an ultrasonic time-of-flight flowmeter from a conventional anesthetic machine to additionally measure real-time fractional concentration of Xe in O2. A total of 5095 readings of Xe % were taken in the range 5%-95%, and compared with simultaneous measurements from the gold standard of a commercially available thermal conductivity Xe analyzer. RESULTS: Ultrasonic measurements of Xe (%) showed agreement with thermal conductivity meter measurements, but there was marked discontinuity in the middle of the measurement range. Bland-Altman analysis (95% confidence interval in parentheses) yielded: mean difference (bias) 3.1% (2.9%-3.2%); lower 95% limit of agreement -4.6% (-4.8% to -4.4%); and upper 95% limit of agreement 10.8% (10.5%-11.0%). CONCLUSIONS: The adapted ultrasonic flowmeter estimated Xe (%), but the level of accuracy is insufficient for clinical use. With further work, it may be possible to develop a device to perform both flowmetry and binary gas concentration measurement to a clinically acceptable degree of accuracy.

Implementation of ultrasonic sensing for high resolution measurement of binary gas mixture fractions.

We describe an ultrasonic instrument for continuous real-time analysis of the fractional mixture of a binary gas system. The instrument is particularly well suited to measurement of leaks of a high molecular weight gas into a system that is nominally composed of a single gas. Sensitivity < 5 × 10(-5) is demonstrated to leaks of octaflouropropane (C3F8) coolant into nitrogen during a long duration (18 month) continuous study. The sensitivity of the described measurement system is shown to depend on the difference in molecular masses of the two gases in the mixture. The impact of temperature and pressure variances on the accuracy of the measurement is analysed. Practical considerations for the implementation and deployment of long term, in situ ultrasonic leak detection systems are also described. Although development of the described systems was motivated by the requirements of an evaporative fluorocarbon cooling system, the instrument is applicable to the detection of leaks of many other gases and to processes requiring continuous knowledge of particular binary gas mixture fractions.