Scalable microwave waste-to-fuel conversion

[EN] This paper presents an efficiency study for scalable microwave waste management. When waste with carbon content is subjected to volume power densities on the order of 0.25W/cm3 at GHz frequencies, it converts to solid coke fuel with oil and gas bi-products that can further be processed for fuel, leaving no trace. For an efficient process, a well-controlled uniform RF field should be maintained in a non-uniform and time-variable material. We are developing a 2.45-GHz active microwave cavity with solid-state (GaN) spatially power combined sources for lower volumes, Fig.1. In the energy balance calculations, the input energy into the system consists of the waste chemical energy and the DC electrical energy used to obtain the RF power with an efficiency that can reach 70% for kW power levels. The efficiency of RF power conversion to heat in the waste mass is calculated from full-wave simulations for typical waste mixtures and ranges from 10 to 90% depending on the material and cavity filling. The output energy estimates are collected from various pyrolysis process descriptions, e.g. [1], with the total energy being that of the solid fuel (35MJ/kg) and oil caloric values, e.g. 40MJ/kg for plastics and about 10-15MJ/kg for nonplastics [2]. A byproduct is flue gas which can be converted to Syngas [3]. The total worse-case carbon footprint balance (0.3-3) calculations will be presented. Fig. 1. Block diagram of active microwave cavity for waste to fuel conversion. References D. Czajczyńska, “Potential of pyrolysis processes in the waste management sector,” Thermal Science and Engineering Progress, vol. 3, p. 171. Sept., 2017. J.A. Onwudili, “Composition of products from the pyrolysis of polyethylene and polystyrene in a closed batch reactor: effects of temperature and residence time,” Journal of Analytical and Applied Pyrolysis, vol. 86 p. 293–303. Nov., 2009. S. Chunshan, "Tri-reforming of methane: a novel concept for synthesis of industrially useful synthesis gas with desired H2/CO ratios using CO2 in flue gas of power plants without CO2 separation." Prepr. Pap.-Am. Chem. Soc., Div. Fuel Chem 49, no. 1 (2004): 128.This work was funded by DARPA under contract W911NF-18-1-0073.Robinson, M.; Popovic, Z. (2019). Scalable microwave waste-to-fuel conversion. En AMPERE 2019. 17th International Conference on Microwave and High Frequency Heating. Editorial Universitat Politècnica de València. 210-216. https://doi.org/10.4995/AMPERE2019.2019.9839OCS21021

Bandwidth control of forbidden transmission gaps in compound structures with subwavelength slits

Phase resonances in transmission compound structures with subwavelength slits produce sharp dips in the transmission response. For all equal slits, the wavelengths of these sharp transmission minima can be varied by changing the width or the length of all the slits. In this paper we show that the width of the dip, i.e., the frequency range of minimum transmittance, can be controlled by making at least one slit different from the rest within a compound unit cell. In particular, we investigate the effect that a change in the dielectric filling, or in the length of a single slit produces in the transmission response. We also analyze the scan angle behavior of these structures by means of band diagrams, and compare them with previous results for all-equal slit structures.Comment: 16 pages, 5 figures, submitted to Phys. Rev.

Class-E rectifiers and power converters

This paper reviews the use of the class-E topology for RF-to-DC and DC-to-DC power conversion. After covering its early history, the class-E rectifier is introduced in the context of the time-reversal duality principle, to be then integrated with an inverter in a class-E2 DC/DC converter. Recent examples and applications at UHF and microwave bands are finally presented. A review of RF rectifiers based on Schottky diodes or FET transistors, is followed by a discussion of synchronous and self-synchronous implementations of the double class-E DC/DC converter, using advanced GaN HEMT transistors.This work was supported in part by the Spanish Ministry of Economy and Competitiveness (MINECO) under project TEC2014-58341-C4-1-R, co-funded with FEDER, and in part by the Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy, under Award Number DEAR0000216 and the DARPA MPC program, ONR award N00014-11-1-0931

Microwave class-E power amplifiers

This paper reviews circuit architectures and demonstrated class-E power amplifiers in the UHF and microwave frequency range. Scaling class-E soft-switching operation to high frequencies presents a number of challenges, particularly in the control of parasitic reactances of the device and the circuit. Different approaches have been taken, from using parasitics of lumped elements to provide the correct fundamental and harmonic impedances in the UHF range, to transmission-line implementations at frequencies above 10GHz

Microwave class-E power amplifiers: a brief review of essential concepts in high-frequency class-E PAs and related circuits

Since Nathan Sokal's invention of the class-E power amplifier (PA), the vast majority of class-E results have been reported at kilohertz and millihertz frequencies, but the concept is increasingly applied in the ultrahigh-frequency (UHF) [1]-[13], microwave [14]-[20], and even millimeter-wave range [21]. The goal of this article is to briefly review some interesting concepts concerning high-frequency class-E PAs and related circuits. (The article on page 26 of this issue, "A History of Switching-Mode Class-E Techniques" by Andrei Grebennikov and Frederick H. Raab, provides a historical overview of class-E amplifier development.)We acknowledge support, in part, by a Lockheed Martin Endowed Chair at the University of Colorado and in part by the Spanish Ministry of Economy, Industry, and Competitiveness (MINECO) through TEC2014-58341-C4-1-R and TEC2017-83343-C4-1-R projects, cofunded with FEDER

Class-E rectifiers and power converters: the operation of the class-E topology as a power amplifier and a rectifier with very high conversion efficiencies

In the late 70’s, the interest in reducing the value and size of reactive components moved power supply specialists to operate dc-to-dc converters at hundreds of kHz or even MHz frequencies. Passive energy storage (mainly magnetics) dominates the size of power electronics, limiting also its cost, reliability and dynamic response. Motivated by miniaturization and improved control bandwidth, they had to face the frequency-dependent turn-on and turn-off losses associated with the use of rectangular waveforms in the hard-switched topologies of that time. Similar to approaches for RF/microwave power amplifiers (PAs), the introduction of resonant circuits allowed shaping either a sinusoidal voltage or current, with parasitic reactive elements absorbed by the topology in the neighborhood of the switching frequency. The resulting resonant power converters, obtained by cascading a dc-to-ac resonant inverter with a high-frequency ac-to-dc rectifier, first transform the dc input power into controlled ac power, and then convert it back into the desired dc output [1]. This paper provides some historic notes on the operation of the class-E topology, introduced worldwide to the RF/microwave community by Nathan O. Sokal [2], as a power inverter and as a rectifier, with very high conversion efficiencies up to microwave frequencies. Recent research advances and implementations of class-E rectifiers and dc-to-dc converters at UHF and beyond are included. Offering competitive performance in terms of efficiency for RF power recovery, together with a wide bandwidth for low-loss power conversion, their potential for some modern applications is highlighted.The authors would like to acknowledge support in part by the Spanish Ministry of Economy, Industry and Competitiveness (MINECO) through TEC2014-58341-C4-1-R and TEC2017-83343-C4-1-R projects, co-funded with FEDER, and in part by Lockheed Martin Endowed Chair at the University of Colorado

Grid oscillators

In the microwave and millimeter-wave frequency range, solid-state oscillators have limited output power levels. The alternative high-power sources are tubes, which are expensive, bulky, have a limited lifetime and require high-voltage power supplies. Combining a large number of low-power solid-state negative resistance devices becomes attractive. In this work a coherent oscillator that can combine thousands of solid-state devices is presented. The feasibility of a reliable high-power, monolithically integrated microwave and millimeter-wave source is demonstrated. In this approach, the active devices load a two-dimensional metal grid that radiates, and the power combining is done in free-space. Several MESFET grid oscillator designs are presented in this thesis, ranging from a 5 by 5 to a 10 by 10 grid in size. The 100-MESFET hybrid grid oscillator is a planar structure suitable for wafer-scale monolithic integration. This grid locks at 5 GHz, with an ERP of 24 Watts and a conversion efficiency of 20%. An equivalent embedding circuit for the devices in the grid predicts the oscillation frequency. The devices in the grid self-lock with no external locking signal present, but the grid can also be externally injection-locked. Measurements and analysis are presented for the injection-locked planar grid oscillator