http://www.eecs.ucf.edu/~dcm/Teaching/COT4810-Spring2011/Literature/SensorNetworksSurvey.pdf

Wireless sensor networks: a survey

The advancement in wireless communications and electronics has enabled the development of low-cost sensor networks. The sensor networks can be used for various application areas (e.g., health, military, home). For different application areas, there are different technical issues that researchers are currently resolving. The current state of the art of sensor networks is captured in this article, where solutions are discussed under their related protocol stack layer sections. This article also points out the open research issues and intends to spark new interests and developments in this field.

/pdf/a-survey-on-sensor-networks-5beav0ez6k.pdf

A survey on sensor networks

基礎講座 電気泳動(Electrophoresis)

Electrowetting has become one of the most widely used tools for manipulating tiny amounts of liquids on surfaces. Applications range from 'lab-on-a-chip' devices to adjustable lenses and new kinds of electronic displays. In the present article, we review the recent progress in this rapidly growing field including both fundamental and applied aspects. We compare the various approaches used to derive the basic electrowetting equation, which has been shown to be very reliable as long as the applied voltage is not too high. We discuss in detail the origin of the electrostatic forces that induce both contact angle reduction and the motion of entire droplets. We examine the limitations of the electrowetting equation and present a variety of recent extensions to the theory that account for distortions of the liquid surface due to local electric fields, for the finite penetration depth of electric fields into the liquid, as well as for finite conductivity effects in the presence of AC voltage. The most prominent failure of the electrowetting equation, namely the saturation of the contact angle at high voltage, is discussed in a separate section. Recent work in this direction indicates that a variety of distinct physical effects?rather than a unique one?are responsible for the saturation phenomenon, depending on experimental details. In the presence of suitable electrode patterns or topographic structures on the substrate surface, variations of the contact angle can give rise not only to continuous changes of the droplet shape, but also to discontinuous morphological transitions between distinct liquid morphologies. The dynamics of electrowetting are discussed briefly. Finally, we give an overview of recent work aimed at commercial applications, in particular in the fields of adjustable lenses, display technology, fibre optics, and biotechnology-related microfluidic devices.

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Electrowetting: from basics to applications

Micromachining technology was used to prepare chemical analysis systems on glass chips (1 centimeter by 2 centimeters or larger) that utilize electroosmotic pumping to drive fluid flow and electrophoretic separation to distinguish sample components. Capillaries 1 to 10 centimeters long etched in the glass (cross section, 10 micrometers by 30 micrometers) allow for capillary electrophoresis-based separations of amino acids with up to 75,000 theoretical plates in about 15 seconds, and separations of about 600 plates can be effected within 4 seconds. Sample treatment steps within a manifold of intersecting capillaries were demonstrated for a simple sample dilution process. Manipulation of the applied voltages controlled the directions of fluid flow within the manifold. The principles demonstrated in this study can be used to develop a miniaturized system for sample handling and separation with no moving parts.

Micromachining a miniaturized capillary electrophoresis-based chemical analysis system on a chip

Droplet-based programmable processors promise to offer solutions to a wide range of applications in which chemical and biological analysis and/or small-scale synthesis are required, suggesting they will become the microfluidic equivalents of microprocessors by offering off-the-shelf solutions for almost any fluid based analysis or small scale synthesis problem. A general purpose droplet processor should be able to manipulate droplets of different compositions (including those that are electrically conductive or insulating and those of polar or non-polar nature), to control reagent titrations accurately, and to remain free of contamination and carry over on its reaction surfaces. In this article we discuss the application of dielectrophoresis to droplet based processors and demonstrate that it can provide the means for accurately titrating, moving and mixing polar or non-polar droplets whether they are electrically conductive or not. DEP does not require contact with control surfaces and several strategies for minimizing surface contact are presented. As an example of a DEP actuated general purpose droplet processor, we show an embodiment based on a scaleable CMOS architecture that uses DEP manipulation on a 32 × 32 electrode array having built-in control and switching circuitry. Lastly, we demonstrate the concept of a general-purpose programming environment that facilitates droplet software development for any type of droplet processor.

Dielectrophoresis-based programmable fluidic processors.

This research utilizes the levitation effect of electrostatic comb fingers to design vertical-to-the-substrate actuation for optical phase shifting interferometry applications. For typical polysilicon comb drives with 2 /spl mu/m gaps between the stationary and moving fingers, as well as between the microstructures and the substrate, the equilibrium position is nominally 1-2 /spl mu/m above the stationary comb fingers. This distance is ideal for most phase shifting interferometric applications. A parallel plate capacitor between the suspended mass and the substrate provides in situ position sensing to control the vertical movement, providing a total feedback-controlled system. The travel range of the designed vertical microactuator is 1.2 /spl mu/m. Since the levitation force is not linear to the input voltage, a lock-in amplifier capacitive sensing circuit combined with a digital signal processor enables a linearized travel trajectory with 1.5 nm position control accuracy. A completely packaged micro phase shifter is described in this paper. One application for this microactuator is to provide linear phase shifting in the phase shifting diffraction interferometer (PSDI) developed at LLNL which can perform optical metrology down to 2 /spl Aring/ accuracy.

Vertical-actuated electrostatic comb drive with in situ capacitive position correction for application in phase shifting diffraction interferometry

A DC-to-200MHz, CCD-based transient data recorder is currently under development. Multiple recorders will be operated via a conventional computer interface. Each recorder is designed to acquire 512 samples of data at intervals as small as one nanosecond (±25ps) and to an amplitude accuracy of eight bits (±0.2%). Developmental data is presented.

A One Gigasample per Second Transient Recorder

This article introduces a new type of transducer that combines capacitive pressure sensing techniques with biosensitive hydrogels, using an adaptable MEMS fabrication platform. Hydrogel swelling in response to analyte concentration exerts contact pressure on a deformable conducting diaphragm, producing a capacitance change. Initial results are reported for testing device feasibility. Uncrosslinked PHEMA hydrogel was tested for swelling pressure in response to calcium nitrate tetrahydrate. Diaphragm deflection due to applied air pressure was measured on NiTi-based diaphragms and compared with hydrogel-actuated deflections of the same diaphragms to determine the pressure generating characteristics of the hydrogel. The PHEMA sample exhibited greatest sensitivity in the concentration range 0–0.5 M, generating an average of 110 mN/M/μl. The device was incorporated into a passive LC resonant circuit. Resonance frequency was measured as a function of applied air pressure, in the range of pressures generated by hydrogel swelling. Resonance frequency shifted from 66 MHz to 33 MHz over the pressure range 0–32 kPa, corresponding to an estimated average sensitivity of 66 Hz per μmol of calcium nitrate tetrahydrate over the range 0–0.5 M.

Hydrogel-Actuated Capacitive Transducer for Wireless Biosensors

Emerging CMOS and MEMS technologies enable the implementation of a large number of wireless distributed microsensors that can be easily and rapidly deployed to form highly redundant, self-configuring, and ad hoc sensor networks. To facilitate ease of deployment, these sensors should operate on battery for extended periods of time. A particular challenge in maintaining extended battery lifetime lies in achieving communications with low power. This paper presents a direct-sequence spread-spectrum modem architecture that provides robust communications for wireless sensor networks while dissipating very low power. The modem architecture has been verified in an FPGA implementation that dissipates only 33 mW for both transmission and reception. The implementation can be easily mapped to an ASIC technology with an estimated power performance of less than 1 row.

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C. McConaghy

Papers

Dielectrophoresis-based programmable fluidic processors.

Vertical-actuated electrostatic comb drive with in situ capacitive position correction for application in phase shifting diffraction interferometry

A One Gigasample per Second Transient Recorder

Hydrogel-Actuated Capacitive Transducer for Wireless Biosensors

Low-power direct-sequence spread-spectrum modem architecture for distributed wireless sensor networks