Jake Bobowski

PERMITTIVITY MEASUREMENTS OF BIOLOGICAL SAMPLES BY AN OPEN-ENDED COAXIAL LINE

We previously reported on the complex permittivity and dc conductivity of waste-activated sludge. The measurements, spanning a frequency range of 3MHz to 40GHz, were made using an open-ended coaxial transmission line. Although this technique is well established in the literature, we found that it was necessary to combine methods from several papers to use the open-ended coaxial probe to reliably characterize biological samples having a high dc conductivity. Here, we provide a set of detailed and practical guidelines that can be used to determine the permittivity and conductivity of biological samples over a broad frequency range. Due to the electrode polarization efiect, low frequency measurements of conducting samples require corrections to extract the intrinsic electrical properties. We describe one practical correction scheme and verify its reliability using a control sample.

Conductive heating and microwave hydrolysis under identical heating profiles for advanced anaerobic digestion of municipal sludge

Microwave (2.45 GHz, 1200 W) and conventional heating (custom pressure vessel) pretreatments were applied to dewatered municipal waste sludge (18% total solids) using identical heating profiles that span a wide range of temperatures (80-160 °C). Fourteen lab-scale semi-continuous digesters were set up to optimize the energy (methane) output and sludge retention time (SRT) requirements of untreated (control) and thermally pretreated anaerobic digesters operated under mesophilic and thermophilic temperatures. Both pretreatment methods indicated that in the pretreatment range of 80-160 °C, temperature was a statistically significant factor (p-value < 0.05) for increasing solubilization of chemical oxygen demand and biopolymers (proteins, sugars, humic acids) of the waste sludge. However, the type of pretreatment method, i.e. microwave versus conventional heating, had no statistically significant effect (p-value >0.05) on sludge solubilization. With the exception of the control digesters at a 5-d SRT, all control and pretreated digesters achieved steady state at all three SRTs, corresponding to volumetric organic loading rates of 1.74-6.96 g chemical oxygen demand/L/d. At an SRT of 5 d, both mesophilic and thermophilic controls stopped producing biogas after 20 d of operation with total volatile fatty acids concentrations exceeding 1818 mg/L at pH <5.64 for mesophilic and 2853 mg/L at pH <7.02 for thermophilic controls, while the pretreated digesters continued producing biogas. Furthermore, relative (to control) organic removal efficiencies dramatically increased as SRT was shortened from 20 to 10 and then 5 d, indicating that the control digesters were challenged as the organic loading rate was increased. Energy analysis showed that, at an elevated temperature of 160 °C, the amount of methane recovered was not enough to compensate for the energy input. Among the digesters with positive net energy productions, control and pretreated digesters at 80 °C were more favorable at an SRT of 10 d.

Precision microwave electrodynamic measurements of K- and Co-dopedBaFe2As2

Ba0:72K0:28Fe2As2 (hole-doped, Tc � 30 K) and Ba(Fe0:95Co0:05)2As2 (electron-doped, Tc �20 K), by cavity perturbation and broadband spectroscopy. SQUID magnetometry was used to confirm the quality and homogeneity of the samples under study. Through cavity perturbation techniques, the temperature dependence of the in-plane London penetration depth ��(T), and therefore the superfluid phase stiffness � 2 (0)/� 2 (T) was measured. Down to 0.4 K, the data do not show the exponential saturation at low temperatures expected from a singly-, fully-gapped superconductor. Rather, both the electron- and the hole-doped systems seem to be best described by a power law behavior, with � 2 (0)/� 2 (T) � T n and n � 2.5. In the three samples we studied, a weak feature near the sensitivity limit of our measurements appears near T/Tc = 0.04, hinting at a corresponding low energy feature in the superconducting density of states. The data can also be relatively well-described by a simple two-gap s-wave model of the order parameter, but this yields parameters which seem unrealistic and dependent on the fit range. Broadband surface resistance measurements reveal a sample dependent residual loss whose origin is unclear. The data from the Ba0:72K0:28Fe2As2 samples can be made to scale as ! 2 if the extrinsic loss is treated as an additive component, indicating large scattering rates. Finally, the temperature dependence of the surface resistance at 13 GHz obeys a power law very similar to those observed for ��(T).

PERMITTIVITY OF WASTE-ACTIVATED SLUDGE BY AN OPEN-ENDED COAXIAL LINE

The complex permittivity of thickened waste activated sludge (WAS) was measured from 3MHz to 40GHz. The solid content of the thickened WAS sample was varied from 4.5% to 18% by weight. The permittivity spectra exhibit features typical of biological tissues that have a high water content. At high frequencies, a Debye-type dispersion is observed with a relaxation rate of 19GHz characteristic of the bulk water in the sample (∞-dispersion). At lower frequencies, the solid content of the samples determines the properties of the permittivity. The onset of the so-called fl-dispersion, attributed to the charging of cell membranes, occurs between 10{100MHz. For samples with higher solid concentrations, a weak dispersion of the real part of the permittivity, characteristic of bound water, was observed at intermediate frequencies (--dispersion).

Calibrated Single-Contact Voltage Sensor for High-Voltage Monitoring Applications

A single-contact voltage sensor designed for accurate measurements of ac voltages across a pair of conductors is described. The sensor design is motivated by remote monitoring applications where accurate voltage measurement of high-voltage transmission lines is required. The body of the sensor is electrically and mechanically attached to a single conductor: either the neutral or high-voltage conductor. A capacitive sensing plate attached to the sensor creates a capacitive voltage divider by using the stray capacitance to the noncontacted line. A very high-impedance buffer is used to measure the voltage across the divider output and estimate the line voltage. An important part of this paper includes a method of calibrating the sensor such that blind voltage measurements can be made without knowing the exact geometry of the conductors. Other important aspects of the design include a two-stage voltage divider for retaining accuracy and increasing the voltage range of the sensor. The work is supported by extensive numerical simulation models which were used to determine the optimum design for the sensing plate and to evaluate the sensitivity to different configurations including conductor spacing and the height above ground. For calibration values which are accurate to 1%, the line voltage can be measured with an accuracy of 10%. The paper describes the theory, design, and experimental verification of the sensor up to a line voltage of 7.5 kVrms.

Oxygen chain disorder as the weak scattering source in YBa2Cu3O6.50

The microwave conductivity of an ultra-pure single crystal of YBa

Probing Split-Ring Resonator Permeabilities with Loop-Gap Resonators

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Permittivity and Conductivity Measured Using a Novel Toroidal Split-Ring Resonator

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A voltage sensing unit for sensing voltage of high-power lines using a single-contact point and method of use thereof

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Oxygen chain disorder as a weak-limit scatterer in YBa2Cu3O6.50

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