Rhonda R. Franklin

Linking spectral and electrochemical analysis to monitor c-type cytochrome redox status in living geobacter sulfurreducens biofilms

When transferring electrons to insoluble Fe oxyhydroxide particles, the bacterium Geobacter sulfurreducens must utilize a chain of redox proteins to relay electrons from cytoplasmic electron carriers to external electron acceptors. In the presence of an electrode poised at an oxidizing potential, not only can cells in contact with the electrode respire directly to the surface, but 10 to 20 cell layers can stack upon each other, and each layer is also electrically connected to the electrode. Thus, G. sulfurrueducens naturally self-assembles a three-dimensional network of proteins capable of oxidizing complex fuels, relaying electrons out of the cytoplasm and across their membranes, and through a biofilm as thick as 40 mm, to sustain current densities on the order of 1 mA cm . 5] Such rates of simultaneous enzymatic oxidation and long-range current transfer rival those achieved by pure enzymes embedded in advanced redox hydrogels. The adaptation of electrochemical techniques to study and control this complex microbial electron-transfer process has opened a window into the physiology of these bacteria. 2, 5, 7–9] However, challenges remain in correlating voltammetry data with specific proteins, and understanding the molecular mechanism of long-distance electron relay between living cells. Mutant analyses, immunogold labeling, and proteomic studies 14–18] have suggested roles for many different multiheme ctype cytochromes, as well as pili and multicopper proteins, 14, 16, 18–24] but less is known about their kinetics or activity in vivo. The use of spectroscopic methods during potentiometric analysis of redox enzymes offers a tool to directly measure the redox status of multiple cofactors. When proteins are immobilized on transparent conductive electrodes, potential-dependent changes can be linked to specific redox centers. 26] Two recent reports extended spectral and electrochemical techniques to the study of whole cells capable of electron transfer to electrodes. Busalmen et al. detected signatures characterisic of c-type cytochromes at a Geobacter cell–electrode interface using surface-enhanced infrared absorption, while Nakamura et al. were able to detect redox-dependent changes in the Soret-band characteristic of c-type cytochromes in Shewanella suspensions, using evanscent wave spectroscopy. These previous studies primarily examined concentrated cell suspensions for short periods of time. However, it is well known that biofilm growth requires disctrete attachment, biosynthesis, and secretion events to construct the external network of delicate proteins that transports electrons from cells. 29–33] Thus, the goal of this work was was to design a system able to support growth of metal-reducing bacteria on transparent conductive electrodes to link potential-dependent changes with real-time measurements of spectral signatures in an undamaged biofilm network (Figure 1). Extensive physiological, proteomic, mRNA expression, and imaging data already exists describing Geobacter biofilm growth on graphitic carbon and gold electrodes. To investigate whether data from this well-understood model could be com-

Conducting Polymer Material Characterization Using High Frequency Planar Transmission Line Measurement

A conducting polymer, poly 3-hexylthiophene (P3HT) is characterized with the metal-insulator-semiconductor (MIS) measurement method and the high frequency planar circuit method. From the MIS measurement method, the relative dielectric constant of the P3HT film is estimated to be 4.4. For the high frequency planar circuit method, a coplanar waveguide is fabricated on the P3HT film. When applying +20 V to the CPW on P3HT film, the P3HT film is in accumulation mode and becomes lossy. The CPW on P3HT film is 1.5 dB lossier than the CPW on SiO2 film without P3HT film at 50 GHz.

Independently Tunable Annular Slot Antenna Resonant Frequencies Using Fluids

An annular slot antenna with surface integrated fluidic channels is presented. The fluidic channels provide independent, tunable control of the first and second resonant frequencies. Simulation and measurement results for channels filled with air, acetone, or deionized (DI) water are investigated. A tunable range from 3.3 to 4.2 GHz for the first resonance and 5.2 to 8 GHz for the second resonance is demonstrated. The loss tangent effects are also assessed for the fluids in terms of peak realized gain degradation.

Frequency tunable fluidic annular slot antenna

A coplanar waveguide fed annular slot antenna with fluidic housing is investigated. The channels of the housing are filled either with air, acetone, or de-ionized (DI) water to dynamically change the resonant frequency of the antenna. Two channels are fabricated perpendicular to the feedline on the half of the annular slot opposite the feed. The outer channel is shown to control the first resonance of the antenna with a tunable frequency range from 3 GHz to 4.2 GHz. The second channel, which is closer to the center of the antenna, is shown to control the second resonance of the antenna with a tunable range of 4.4 to 7.9 GHz.

Comparative analysis of frequency selective surface geometry effect in Fabry-Perot Cavity antenna design

Fabry-Perot Cavity (FPC) antenna using a single radiating element with different frequency selective surface (FSS) is presented. The FSS designs are rectangular and square unit cells with rectangular and circular openings, respectively. A slot antenna is used as a primary source in the FPC antenna and the system is designed to operate in X-band. The effect of each FSS geometry on the radiation pattern of the source is investigated.

Characteristics of planar monopole antenna on high impedance electromagnetic surface

This paper presents for the first time measured characteristics of a planar monopole antenna placed directly on a high impedance electromagnetic surface or artificial magnetic conductor (AMC). The return loss and radiation patterns are compared between the antenna in free space, and when placed directly on a perfect electrical conductor (PEC), and on the AMC. The antenna measured in free space has a wide pass band from 3 to 10 GHz. The return loss for the antenna on the PEC is nearly all reflected back and the return loss for the antenna on the AMC has a 10 dB bandwidth from 7.5 to 9.5 GHz. The gain of the antenna in free space, on PEC and on AMC is 1, −12 and 10 dBi, respectively. This indicates that the AMC is working properly, sending all the radiation outward with little loss.

Mini workshop — MUSE — Multi-University Systems Education

This mini-workshop will thoroughly explore the MUSE instructional method that emphasizes systems thinking and that creates a learner-centric environment appropriate for todays engineering students. By tapping unique expertise at multiple institutions in the timely area of wireless sensor networks, implementing an inverted classroom instructional method, and involving open-ended, hands-on experiences, the MUSE approach has been shown to provide a unique pedagogical experience. The mini-workshop will not only present the MUSE approach and results to date but also is designed to encourage participants to develop new MUSE collaborations based on other complex-engineered systems.

Microfluidic Near-Field Beam-Splitting Frequency Selective Surface for Fabry-Perot Cavity Antenna System

A microfluidic Fabry-Perot Cavity (FPC) antenna system is presented with split beam in the near-field. For this purpose, fluidic housing, which is made of polydimethylsilone (PDMS), is used and integrated into the FPC system. The FPC system consists of a slot antenna and frequency selective surface (FSS). Two FSS designs with rectangular apertures are considered: augmented and microfluidic FSS arrays. Each is designed, modeled, and tested for comparison in the FPC system.

Parametric study of near- and far-field performance of the Fabry-Perot cavity antenna system

This paper discusses the effects of varying the design parameters of the cavity or rectangular aperture in the frequency selective surface (FSS) of a Fabry-Perot Cavity (FPC) antenna system. The FPC system is excited by a coplanar-waveguide (CPW)-fed slot antenna. Theoretical results of the near-field distribution and far-field radiation pattern for each variation are shown to investigate the impact of the cavity height and FSS design parameters on the system.

Fabry-Perot Cavity antenna system with beam-splitting of near-field radiation

This paper describes the design and behavior of a Fabry-Perot Cavity (FPC) antenna system with split beam in the near-field and decreased beamwidth of the far-field pattern. The FPC antenna system is a coplanar waveguide (CPW)-fed slot antenna with 9 × 27 rectangular aperture unit cells in the frequency selective surface (FSS) oriented in horizontal and vertical directions. The far-field response has 3dB beamwidth of 21° and gain of 12.84 dBi at 11.2 GHz.