Soft lithography is an alternative to silicon-based micromachining that uses replica molding of nontraditional elastomeric materials to fabricate stamps and microfluidic channels. We describe here an extension to the soft lithography paradigm, multilayer soft lithography, with which devices consisting of multiple layers may be fabricated from soft materials. We used this technique to build active microfluidic systems containing on-off valves, switching valves, and pumps entirely out of elastomer. The softness of these materials allows the device areas to be reduced by more than two orders of magnitude compared with silicon-based devices. The other advantages of soft lithography, such as rapid prototyping, ease of fabrication, and biocompatibility, are retained.

http://science.sciencemag.org/content/sci/288/5463/113.full.pdf

Monolithic microfabricated valves and pumps by multilayer soft lithography

High-density microfluidic chips contain plumbing networks with thousands of micromechanical valves and hundreds of individually addressable chambers. These fluidic devices are analogous to electronic integrated circuits fabricated using large scale integration (LSI). A component of these networks is the fluidic multiplexor, which is a combinatorial array of binary valve patterns that exponentially increases the processing power of a network by allowing complex fluid manipulations with a minimal number of inputs. These integrated microfluidic networks can be used to construct a variety of highly complex microfluidic devices, for example the microfluidic analog of a comparator array, and a microfluidic memory storage device resembling electronic random access memories.

https://science.sciencemag.org/content/sci/298/5593/580.full.pdf

Microfluidic large scale integration

This paper presents a review of silicon micromachined accelerometers and gyroscopes. Following a brief introduction to their operating principles and specifications, various device structures, fabrication, technologies, device designs, packaging, and interface electronics issues, along with the present status in the commercialization of micromachined inertial sensors, are discussed. Inertial sensors have seen a steady improvement in their performance, and today, microaccelerometers can resolve accelerations in the micro-g range, while the performance of gyroscopes has improved by a factor of 10/spl times/ every two years during the past eight years. This impressive drive to higher performance, lower cost, greater functionality, higher levels of integration, and higher volume will continue as new fabrication, circuit, and packaging techniques are developed to meet the ever increasing demand for inertial sensors.

/pdf/micromachined-inertial-sensors-esf6197vdc.pdf

Micromachined inertial sensors

Sensor networks consist of a set of sensor nodes, each equipped with one or more sensors, communication subsystems, storage and processing resources, and in some cases actuators. The sensors in a node observe phenomena such as thermal, optic, acoustic, seismic, and acceleration events, while the processing and other components analyze the raw data and formulate answers to specific user requests. Recent advances in technology have paved the way for the design and implementation of new generations of sensor network nodes, packaged in very small and inexpensive form factors with sophisticated computation and wireless communication abilities. Although still at infancy, these new classes of sensor networks, generally referred to as wireless sensor networks (WSN), show great promise and potential with applications ranging in areas that have already been addressed, to domains never before imagined. In this article we provide an overview of this new and exciting field and a brief discussion on the factors pushing the recent flurry of sensor network related research and commercial undertakings. We also provide overview discussions on architectural design characteristics of such networks including physical components, software layers, and higher level services. At each step, we highlight special characteristics of WSNs and discuss why existing approaches and results from wireless communication networks are not necessarily suitable in WSN domains. We conclude by briefly summarizing the state of the art and the future research directions.

Wireless Sensor Networks

An adaptive interface for a programmable system, for predicting a desired user function, based on user history, as well as machine internal status and context. The apparatus receives an input from the user and other data. A predicted input is presented for confirmation by the user, and the predictive mechanism is updated based on this feedback. Also provided is a pattern recognition system for a multimedia device, wherein a user input is matched to a video stream on a conceptual basis, allowing inexact programming of a multimedia device. The system analyzes a data stream for correspondence with a data pattern for processing and storage. The data stream is subjected to adaptive pattern recognition to extract features of interest to provide a highly compressed representation that may be efficiently processed to determine correspondence. Applications of the interface and system include a video cassette recorder (VCR), medical device, vehicle control system, audio device, environmental control system, securities trading terminal, and smart house. The system optionally includes an actuator for effecting the environment of operation, allowing closed-loop feedback operation and automated learning.

Adaptive pattern recognition based control system and method

This paper reports the design and analysis of a generic thermal isolation platform that can support a variety of MEMS devices and isolate them from the environment. The platform provides high thermal isolation from the environment by employing long meandering and hollow support metal beams. This isolation is needed for low power (<10mW) micro oven controlled constant temperature operation over a -50/spl sim/70 /spl deg/C temperature range. These beams also provide mechanical support. Optimal selection of the thermal and mechanical characteristics of these beams depends on many factors including beam materials, shape and structure, and the number of electrical signals. Metal only, meandering and hollow beams provide the highest thermal isolation and mechanical stiffness. The combination of the isolation platform batch fabrication process and wafer level instrument transfer/assembly onto the platform enables its broad and cost effective application.

Low-power thermal isolation for environmentally resistant microinstruments

This paper presents an overview of high precision robust digital control of MEMS nonlinear actuators, in particular torsional electrostatic actuators, using sliding-mode control [N. Yazdi et al. (2003), H. Sane et al. (2004)]. Sliding-mode control enables compact realization of a robust controller tolerant of device characteristic variations, nonlinearities and many types of inherent instabilities. Application of 1/sup st/ order SMC to the control of dual-axis torsional actuators beyond their pull-in limit is demonstrated. Also a modified SMC scheme which uses adaptive switching of the sliding-mode variable differential gain to improve control precision is presented. The modified scheme has resulted in average reduction of 44-56% in output chatter and 70-91% when used for control of several 2-axis gimbaled beam steering micromirrors with a wide range of mechanical characteristics.

Robust digital control of nonlinear microelectro-mechanical actuators using sliding-mode control

The performance features of MEMS transducers allow the development of a new class of small, low-power sensor microsystems which utilize a suite of sensors to support a wide range of applications. This paper presents a system-level framework for constructing such microsystems where system modularity for application adaptability is a primary design consideration. System architecture, communication protocols, modular packaging, and interface electronics are discussed in general terms, and an implementation of these concepts is presented. Key requirements for microsystem modularity, such as a communication bus and a universal microsensor interface circuit which support plug-n-play operation for online reconfiguration, are developed and presented in this paper.

/pdf/a-modular-sensor-microsystem-utilizing-a-universal-interface-4pu7ps6jny.pdf

N. Yazdi

Papers

Low-power thermal isolation for environmentally resistant microinstruments

Robust digital control of nonlinear microelectro-mechanical actuators using sliding-mode control

A modular sensor microsystem utilizing a universal interface circuit

Spacecraft Microaccelerometer Microsystem