This paper discusses the fundamentals and developments of miniaturized fuel cells, both biological and electrochemical. An overview of microfluidic fuel cells, miniaturized microbial fuel cells, enzymatic biofuel cells, and implanted biofuel cells in an attempt to provide green energy and to power implanted microdevices is provided. Also, the challenges and applications of each type of fuel cell are discussed in detail. Most recent developments in fuel cell technologies such as novel catalysts, compact designs, and fabrication methods are reviewed.

Microbial fuel cells have gained popularity as a viable, environmentally friendly alternative for the production of energy. However, the challenges in miniaturizing the system for application in smaller devices as well as the short duration of operation have limited the application of these devices. Here, the capillary motion was employed to design a self-pumped paper-based microbial fuel cell operating under continuous flow condition. A proof-of-concept experiment ran approximately 5 days with no outside power or human interference required for the duration of operation. Shewanella oneidensis MR-1 was used to create a maximum current of 52.25 µA in a 52.5 µL paper-based microfluidic device. SEM images of the anode following the experiment showed biofilm formation on the carbon cloth electrode. The results showed a power density of approximately 25 W/m3 and proved unique capabilities of the paper-based microbial fuel cells to produce energy for an extended period of time.

This paper presents data and analyses from which emerges a physical picture of microsecond-conduction-time plasma opening switch operation. During conduction, a broad current channel penetrates axially through the plasma, moving it toward the load. Opening occurs when the current channel reaches the load end of the plasma, far from the load. During conduction, the axial line density in the interelectrode region is reduced from its value with no current conduction as a result of radial hydrodynamic forces associated with the current channel. A factor of 20 reduction is observed at opening in a small, localized region between the electrodes. When open, the switch plasma behaves like a section of magnetically insulated transmission line with an effective gap of 2 to 3 mm. Increasing the magnetic field in this gap by 50% results in an improvement of 50% in the peak load voltage and load current rise time, to 1.2 MV and 20 nsec, respectively. An erosion opening mechanism explains the inferred gap growth rate using the reduced line density at opening. Improved switch performance results when the maximum gap size is increased by using a rising load impedance.

Microfluidic technology has provided innovative solutions to numerous problems, but the cost of designing and fabricating microfluidic channels is impeding its expansion. In this work, ShrinkyDink thermoplastic sheets are used to create multilayered complex templates for microfluidic channels. We used inkjet and laserjet printers to raise a predetermined microchannel geometry by depositing several layers of ink for each feature consecutively. We achieved feature heights over 100 µm, which were measured and compared with surface profilometry. Templates closest to the target geometry were then used to create microfluidic devices from soft-lithography with the molds as a template. These microfluidic devices were in turn used to fabricate polymer microfibers using the microfluidic focusing approach to demonstrate the potential that this process has for microfluidic applications. Finally, an economic analysis was conducted to compare the price of common microfluidic template manufacturing methods. We showed that multilayer microchannels can be created significantly quicker and cheaper than current methods for design prototyping and point-of-care applications in the biomedical area.

Plasma opening switch (POS) experiments performed on the Hawk generator [Commisso et al., Phys. Fluids B 4, 2368 (1992)] (750 kA, 1.2 μs) determine the dependence of the conduction current and conduction time on plasma density, electrode dimensions, and current rise rate. The experiments indicate that for a range of parameters, conduction is controlled by magnetohydrodynamic (MHD) distortion of the plasma, resulting in a low density region where opening can occur, possibly by erosion. The MHD distortion corresponds to an axial translation of the plasma center-of-mass by half the initial plasma length, leading to a simple scaling relation between the conduction current and time, and the injected plasma density and POS electrode dimensions that is applicable to a large number of POS experiments. For smaller currents and conduction times, the Hawk data suggest a non-MHD conduction limit that may correspond to electromagnetohydrodynamic (EMH) field penetration through the POS plasma.

The observation of enhanced plasma potentials, i.e. potentials greater than the Boltzmann values, in a mirror device is reported. The potential structure is driven by strong radio frequency heating near the ion cyclotron resonance and near the local electron bounce frequency. The potentials and their effect on losses from the central cell of a tandem mirror are discussed.

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The Hawk pulsed power generator is used in plasma opening tch (POS) experiments in the 1-1s conduction time regime to study g conduction time switch physics. Experiments reported here lude modiflmg the POS electrode geometry, injecting plasma into e-beam diode, using gas gun plasma sources (with H2, He, and Ar ,es), and using a helical cathode center conductor in the switch ion to increase the total insulating magnetic field. Tapering the hode center conductor over the 8 cm POS length from 10 cm to, ically, a 2.5 cm diam produced peak load powers of 0.7 TW with kJ delivered to the diode--20% energy efficiency--with carbonrted flashboards as the plasma source. Performance (voltage, Mer generated) with a straight 10 cm diam cathode deteriorated en the POS anode outer conductor just downstream of the switch s extended toward the load at the same radius as the switch. Load Mer was up to 70% higher with a plasma-filled diode (PFD) used in ljunction with the POS for short POS conduction times (400 ns and j). Use of a helical center conductor resulted in dramatically;faded switch performance for >350 ns conduction times. Switch formance with gas guns was generally comparable to that with ihboards in a given switcMoad configuration and was independent ;he gas (H2, He, and Ar) used.