235 results found
Sun J, Dawood A, Otter W, et al., Microwave Characterization of Low-loss FDM 3-D Printed ABS with Dielectric-filled Metal-pipe Rectangular Waveguide Spectroscopy, IEEE Access, Vol: 7, ISSN: 2169-3536
Over time the accuracy and speed by which a material can be characterized should improve. Today, the Nicolson-Ross-Weir (NRW) methodology represents a well-established method for extracting complex dielectric properties at microwave frequencies, with the use of a modern vector network analyzer. However, as will be seen, this approach suffers from three fundamental limitations to accuracy. Challenging NRW methods requires a methodical and robust investigation. To this end, using a dielectric-filled metal-pipe rectangular waveguide, five independent approaches are employed to accurately characterize the sample at the Fabry-Pérot resonance frequency (non-frequency dispersive modeling). In addition, manual Graphical and automated Renormalization spectroscopic approaches are introduced for the first time in waveguide. The results from these various modeling strategies are then compared and contrasted to NRW approaches. As a timely exemplar, 3-D printed acrylonitrile-butadiene-styrene (ABS) samples are characterized and the results compared with existing data available in the open literature. It is found that the various Fabry-Pérot resonance model results all agree with one another and validate the two new spectroscopic approaches; in so doing, exposing three limitations of the NRW methods. It is also shown that extracted dielectric properties for ABS differ from previously reported results and reasons for this are discussed. From measurement noise resilience analysis, a methodology is presented for determining the upper-bound signal-to-noise ratio for the vector network analyzer (not normally associated with such instrumentation). Finally, fused deposition modeling (FDM) 3-D printing results in a non-homogeneous sample that excites open-box mode resonances. This phenomenon is investigated for the first time, analytically and with various modeling strategies.
Lim YP, Toh YL, Cheab S, et al., 2019, Coupling matrix synthesis and design of a chained-function waveguide filter, Asia-Pacific Microwave Conference 2018, Publisher: IEEE, Pages: 103-105
This paper presents, for the first time, the coupling matrix synthesis for the application of a chained-function to waveguide filters. The realization of this filter is carried out by successively adding one resonator at a time by comparing the simulated responses of each stage with those obtained using the coupling matrix synthesized from the chained-function. A sixth-order chained-function waveguide bandpass filter centered at 28 GHz with a fractional bandwidth of 2% is demonstrated. The simulated S-parameter responses and the sensitivity analysis pertaining to the manufacturing errors is included. The chained-function waveguide has the lowest percentage changes in terms of the return loss performance given the same amount of distortion as compared with those of the Chebyshev response filters. This results in a lower sensitivity rate with respect to the manufacturing errors, leading to achieving a high-performance filter implementation with a minimum tuning effort.
AL-JUBOORI B, ZHOU J, HUANG Y, et al., 2018, Lightweight and low-loss 3-D printed millimeter-wave bandpass filter based on gap-waveguide, IEEE Access, Vol: 7, Pages: 2624-2632, ISSN: 2169-3536
This paper presents a comprehensive study of a groove gap waveguide (also known as a waffle-iron) bandpass filter at Ka-band (26.5-40 GHz), fabricated using a high resolution polymer jetting (Polyjet) 3-D printing technology. The same filter was previously fabricated using brass CNC milling technology. The metalized Polyjet 3-D printed filter has lower loss, is lighter in weight and more cost-effective, when compared to the solid metal case. The filter operates at a center frequency of 35.65 GHz, has a 500 MHz bandwidth (1.4% fractional bandwidth), and has a transmission zero below and above the passband. Without any design iterations, the measured S-parameters for the Polyjet 3-D printed filter are presented and compared with simulated results, showing excellent agreement. A comparison is then made between the measured results and that of its brass machined counterpart. The new Polyjet 3-D printed filter is 85% lighter than the conventional machined version. All these features prove the important potential of 3-D printing technology for millimeter-wave applications, which includes aerospace.
Lucyszyn S, Shang X, Otter W, et al., Polymer-based 3D printed millimeter-wave components for spacecraft payloads, International Microwave Workshop Series on Advanced Materials and Processes (IMWS-AMP), Publisher: IEEE MTT-S
This paper summarizes the current state of research & development within the U.K. for polymer-based 3D printed guided-wave and quasi-optical components for spacecraft payloads. Preliminary measured results look promising and show that this emerging technology may well overtake existing machined technologies in the not too distant future for general aerospace applications.
Hanham S, Watts C, Ahmad M, et al., Photonic crystal resonators for terahertz sensing applications, Progress in Electromagnetics Research Symposium, Publisher: IEICE, Pages: 803-803
Sun J, Lucyszyn S, 2018, Extracting complex dielectric properties from reflection-transmission mode spectroscopy, IEEE Access, Vol: 6, Pages: 8302-8321, ISSN: 2169-3536
Material characterization of homogeneous dielectric slabs using reflection-transmission mode spectroscopy can be problematic due to the ambiguity from a phasor term. A comprehensive analytical review of methods for calculating the normalized power spectra, to extract the effective complex dielectric properties of a sample, is undertaken. Three generic power response models (zero-order, power propagation and electric field propagation) are derived; these models act as a common mathematical framework for the whole paper. With our unified engineering approach, the voltage-wave propagation, transmission line and telegrapher’s equation transmission line models are then independently derived; the first two giving the same mathematical solutions, while the third generates the same numerical results, as the exact electric field propagation model. Mathematically traceable simulation results from the various models are compared and contrasted using an arbitrarily chosen dataset (window glass) from 1 to 100 THz. We show how to extract the approximate effective complex dielectric properties using time-gated time-domain spectroscopy and also the exact values with our graphical techniques from the first-order reflectance and transmittance. Our approach is then taken further by considering all the Fabry-Perot reflections with frequency- and space-domain spectroscopy. With scalar reflection-transmission mode infrared spectroscopy, we model the threshold conditions between the solution space that gives the single (exact) solution for the complex refractive index and that which gives multiple mathematical solutions. By knowing threshold conditions, it is possible to gain a much deeper insight, in terms of sample constraints and metrology techniques that can be adopted, to determine the single solution. Finally, we propose a simple additional measurement/simulation step to resolve the ambiguity within the multiple solution space. Here, sample thickness is arbitrary and no initia
Otter W, Ridler NM, Lucyszyn S, 2017, 3D printed waveguides: A revolution in low volume manufacturing for the 21st century, ARMMS RF & Microwave Society Conference, Publisher: ARMMS RF & Microwave Society, Pages: 1-6
3D printing is a disruptive technology, offering the inherent capabilities for creating truly arbitrary 3D structures, with low manufacturing costs associated with low volume production runs. This paper provides an overview of the current progress in 3D printing of metal-pipe rectangular waveguide (MPRWG) components, from 10 GHz to 1 THz, at Imperial College London. First, measurements performed at the UK National Physical Laboratory demonstrate that 3D printed MPRWG performance is comparable to standard commercial waveguides at X-band and W-band. Then, a fully 3D printed X-band dielectric flap tuneable phase shifter and W-band 6th-order inductive iris bandpass filter are demonstrated experimentally. Finally, an optically-controlled 500 GHz IQ vector modulator will also be presented; packaged laser diodes and high resistivity silicon implants are integrated within a hybrid 3D printed split-block module, representing a paradigm shift in additive manufacturing for realizing tuneable THz applications.
Otter WJ, Lucyszyn S, 2017, Printing: the future of THz, Electronics Letters, Vol: 53, Pages: 443-443, ISSN: 0013-5194
3D printing allows for record-breaking, low-cost waveguides operating at 1.1 THz
Abstract:For the first time, 3D printed metal-pipe rectangular waveguides (MPRWGs) have been demonstrated in the WM-380 (500-750 GHz) and WM-250 (750 GHz-1.1 THz) waveguide bands. The ultra-high spatial resolution offered by the new RECILS additive manufacturing technology enables the precision fabrication of these prototype MPRWGs at such high frequencies. This enabling technology avoids the need for access to expensive microfabrication resources and, thus, opens up the terahertz spectrum to the low-cost manufacture of passive components.
Muller AA, Sanabria-Codesal E, Moldoveanu A, et al., 2017, Extended Capabilities of the 3-D Smith Chart with Group Delay and Resonator Quality Factor, IEEE Transactions on Microwave Theory and Techniques, Vol: 65, Pages: 10-19, ISSN: 0018-9480
This paper extends the capabilities of the 3D Smith chart for representing positive and negative differential-phase group delay and the associated loaded resonator quality factor, displayed simultaneously with scattering (S)-parameters. Here, mathematical concepts, inspired from elementary differential geometry and topology, are used to implement 3D projections. It is shown that a condition for a circuit to exploit negative differential-phase group delay is that its S-parameter winding number should be ≥ 0 (relative to its origin). Finally, exemplar network responses that exhibit both positive and negative differential-phase group delay and loaded resonator quality factor are shown with the 3D Smith chart. The convenience of being able to simultaneously display a wider range of parameters on one visualization platform, with the 3D Smith chart, may help to speed-up the design and analysis of microwave circuits by the user.
Hanham SM, Ahmad MM, Lucyszyn S, et al., 2017, LED-switchable High-Q Packaged THz Microbeam Resonators, IEEE Transactions on Terahertz Science and Technology, Vol: 7, Pages: 199-208, ISSN: 2156-342X
This paper describes the design, fabrication and experimental characterization of photonic crystal microbeam cavity resonators for the terahertz band implemented using suspended dielectric rectangular waveguide (DRW) in high resistivity silicon. Electrical quality factors of up to 11,900, combined with small modal volumes of 0.28 mm3 and 0.077 mm3, are demonstrated for devices operating at 100 and 200 GHz, respectively. The devices are found to be extremely light-sensitive, opening up new opportunities for light-controlled switching devices at terahertz frequencies. It is shown that the quality factor of the resonator can be tuned and the resonance extinguished through photo-illumination with an infrared light-emitting diode (IR LED). Additionally, the questions of thermal tunability and thermal stability of the resonators are examined. The demonstrated resonators are inherently suited to integration with DRW and by silicon bulk micromachining represent an attractive approach for realizing microphotonic integrated circuits for terahertz systems-on-a-substrate.
Science and technologies based on terahertz frequency electromagnetic radiation (100 GHz–30 THz) have developed rapidly over the last 30 years. For most of the 20th Century, terahertz radiation, then referred to as sub-millimeter wave or far-infrared radiation, was mainly utilized by astronomers and some spectroscopists. Following the development of laser based terahertz time-domain spectroscopy in the 1980s and 1990s the field of THz science and technology expanded rapidly, to the extent that it now touches many areas from fundamental science to 'real world' applications. For example THz radiation is being used to optimize materials for new solar cells, and may also be a key technology for the next generation of airport security scanners. While the field was emerging it was possible to keep track of all new developments, however now the field has grown so much that it is increasingly difficult to follow the diverse range of new discoveries and applications that are appearing. At this point in time, when the field of THz science and technology is moving from an emerging to a more established and interdisciplinary field, it is apt to present a roadmap to help identify the breadth and future directions of the field. The aim of this roadmap is to present a snapshot of the present state of THz science and technology in 2017, and provide an opinion on the challenges and opportunities that the future holds. To be able to achieve this aim, we have invited a group of international experts to write 18 sections that cover most of the key areas of THz science and technology. We hope that The 2017 Roadmap on THz science and technology will prove to be a useful resource by providing a wide ranging introduction to the capabilities of THz radiation for those outside or just entering the field as well as providing perspective and breadth for those who are well established. We also feel that this review should serve as a useful guide for government and funding agencies.
Otter W, Lucyszyn S, 2016, Hybrid 3-D-printing technology for tunable THz applications, Proceedings of the IEEE, Vol: 105, Pages: 756-767, ISSN: 0018-9219
In recent years, additive manufacturing has experienced rapid growth, due to its inherent capabilities for creating arbitrary 3-D structures, accessibility and associated low manufacturing costs. This paper first reviews the state of the art in 3-D printing for terahertz (THz) applications and identifies the critical features required for such applications. The future potential for this technology is demonstrated experimentally with the first 3-D printed, optically-controlled THz I-Q vector modulator. Here, miniature high-resistivity silicon implants are integrated into metal-pipe rectangular waveguides. The 3-D printed split-block assembly also includes two packaged infrared laser diodes and a heat sink. The measured performance of a proof-of-principle 4-QAM vector modulator that can operate up to 500 GHz is reported. This new hybrid 3-D printing THz technology, which combines semiconductor devices with potentially low cost, high performance passive guided-wave structures represents a paradigm shift and may prove to be an ideal solution for implementing affordable transceivers in future ubiquitous THz applications.
Muller A, Sanabria-Codesal E, Lucyszyn S, 2016, Computational cost reduction for N+2 order coupling matrix synthesis based on Desnanot-Jacobi identity, IEEE Access, Vol: 4, Pages: 10042-10050
Matrix inversion is routinely performed in computational engineering, with coupling matrix filter synthesis considered here as just one of many example applications. When calculating the elements of the inverse of a matrix, the determinants of the submatrices are evaluated. The recent mathematical proof of the Desnanot-Jacobi (also known as the “Lewis Carol”) identity shows how the determinant of an N+2 order square matrix can be directly computed from the determinants of the N+1 order principal submatrices and N order core submatrix. For the first time, this identity is applied directly to an electrical engineering problem, simplifying N+2 order coupled matrix filter synthesis (general case, which includes lossy and asymmetrical filters). With the general two-port network theory, we prove the simplification using the Desnanot-Jacobi identity and show that the N+2 coupling matrix can be directly extracted from the zeros of the admittance parameters (given by N+1 order determinants) and poles of the impedance parameters (given by the N order core matrix determinant). The results show that it is possible to decrease the computational complexity (by eliminating redundancy), reduce the associated cost function (by using less iterations), and under certain circumstances obtain different equivalent solutions. Nevertheless, the method also proves its practical usefulness under constrained optimizations when the user desires specific coupling matrix topologies and constrained coefficient values (e.g, purely real/imaginary/positive/negative). This can lead to a direct coupling matrix constrained configuration where other similar methods fail (using the same optimization algorithms).
Sun J, Hu F, Lucyszyn S, 2016, Predicting Atmospheric Attenuation under Pristine Conditions between 0.1 and 100 THz, IEEE Access, Vol: 4, Pages: 9377-9399, ISSN: 2169-3536
This multidisciplinary article reports on a research application-led study for predicting atmospheric attenuation, and tries to bridge the knowledge gap between applied engineering and atmospheric sciences. As a useful comparative baseline, the paper focuses specifically on atmospheric attenuation under pristine conditions, over the extended terahertz spectrum. Three well-known simulation software packages are compared and contrasted ('HITRAN on the Web', MODTRAN(RM)4 and LBLRTM). Techniques used for modeling atmospheric attenuation have been applied to investigate the resilience of (ultra-)wide fractional bandwidth applications ('THz Torch') to the effects of molecular absorption. Two extreme modeling scenarios are investigated: horizontal path links at sea level and Earth-space path links. It is shown by example that a basic software package ('HITRAN on the Web') can give good predictions with the former; whereas sophisticated simulation software (LBLRTM) is required for the latter. Finally, with molecular emission included, carrier-to-noise ratio fade margins can be calculated for the effects of line broadening due to changes in macroscopic atmospheric conditions with sub-1 THz ultra-narrow fractional bandwidth applications. Outdoors can be far from pristine, with additional atmospheric contributions only briefly introduced here; further discussion is beyond the scope of this study, but relevant references have been cited.
Otter WJ, Lucyszyn S, 2016, 3-D printing of microwave components for 21st century applications, IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications (IMWS-AMP 2016), Publisher: IEEE
Additive manufacturing using 3-D printing is anemerging technology for the production of high performancemicrowave and terahertz components. Traditionally, thesecomponents are made by (micro-)machining. However, recentadvances in rapid prototyping technology have led to its use increating high performance and low weight RF components. In thisreview paper ten state-of-the-art exemplars are described,covering a wide variety of applications (absorbers, waveguides,antennas and lenses) operating over a broad range of frequencies,from 8 to 330 GHz.
This letter presents the first fully 3-D printed microwave variable phase shifter. The design methodology for a 3-D printable dielectric flap metal-pipe rectangular waveguide variable phase shifter is described. The ABS building material was independently characterized, revealing a dielectric constant of 2.34 and loss tangent of only 0.0015 at 10 GHz. The predicted and measured performance is given, demonstrating a maximum relative phase shift of 142 degrees at 10 GHz, with a near uniform relative phase shift across the whole of X-band and a low variation in differential-phase group delay.
Klein N, Watts C, Hanham SM, et al., 2016, Microwave-to-terahertz dielectric resonators for liquid sensing in microfluidic systems, Conference on Terahertz Emitters, Receivers, and Applications VII, Publisher: Society of Photo-optical Instrumentation Engineer, ISSN: 0277-786X
The microwave-to-terahertz frequency range offers unique opportunities for the sensing of liquids based on the degree of molecular orientational and electronic polarization, Debye relaxation due to intermolecular forces between (semi-)polar molecules and collective vibrational modes within complex molecules. Methods for the fast dielectric characterization of (sub-)nanolitre volumes of mostly aqueous liquids and biological cell suspensions are discussed, with emphasis on labon- chip approaches aimed towards single-cell detection and label-free flow cytometry at microwave-to-terahertz frequencies. Among the most promising approaches, photonic crystal defect cavities made from high-resistivity silicon are compared with metallic split-ring resonant systems and high quality factor (Q-factor) whispering gallery-type resonances in dielectric resonators. Applications range from accurate haemoglobin measurements on nanolitre samples to label-free detection of circulating tumor cells. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Mitcheson PD, Lucyszyn S, Pinuela M, et al., 2016, RF energy harvester, US9837865B2
Disclosed herein is an antenna apparatus for use in harvesting ambient radio frequency, RF, energy. The apparatus comprises one or more RF antenna components arranged to receive RF energy for producing electricity. The one or more RF antenna components comprise a plurality of frequency filtering components, each frequency filtering component being arranged to filter a respective frequency band of the received RF energy. Also disclosed herein is an apparatus comprising a rectifying circuit arranged to convert a variable electrical signal received at an input from an associated antenna into a direct current electrical signal for supplying to an electrical energy storage unit, the antenna for use in harvesting ambient radio frequency, RF, energy. The apparatus also comprises a power management module having an input arranged to receive the direct current and control supply of the direct current to the electrical energy storage unit. The rectifying circuit comprises a plurality of transmission lines, wherein the input of the rectifying circuit and the input of the power management module are connected via the plurality of transmission lines. The power management module is arranged at least partially within a boundary defined by the plurality of transmission lines.
Hanham SM, Watts C, Otter WJ, et al., Probing the THz response of biological cells using photonic crystal resonators, Energy Materials Nanotechnology (EMN) Meeting on Terahertz
Hu F, Lucyszyn S, 2016, Advances in Front-end Enabling Technologies for Thermal Infrared ‘THz Torch’ Wireless Communications, Journal of Infrared, Millimeter, and Terahertz Waves, Vol: 37, Pages: 881-893, ISSN: 1866-6892
The thermal (emitted) infrared frequency bands (typically 20-40 THz and 60-100 THz)are best known for remote sensing applications that include temperature measurement (e.g., noncontactingthermometers and thermography), night vision and surveillance (e.g., ubiquitous motionsensing and target acquisition). This unregulated part of the electromagnetic spectrum also offerscommercial opportunities for the development of short-range secure communications. The ‘THzTorch’ concept, which fundamentally exploits engineered blackbody radiation by partitioningthermally-generated spectral radiance into pre-defined frequency channels, was recentlydemonstrated by the authors. The thermal radiation within each channel can be independently pulsemodulated,transmitted and detected, to create a robust form of short-range secure communicationswithin the thermal infrared. In this paper, recent progress in the front-end enabling technologiesassociated with the ‘THz Torch’ concept is reported. Fundamental limitations of this technology arediscussed; possible engineering solutions for further improving the performance of such thermalbasedwireless links are proposed and verified either experimentally or through numericalsimulations. By exploring a raft of enabling technologies, significant enhancements to both data rateand transmission range can be expected. With good engineering solutions, the ‘THz Torch’ conceptcan exploit 19th century physics with 20th century multiplexing schemes for low-cost 21st centuryubiquitous applications in security and defence.
Pavia JP, Otter WJ, Lucyszyn S, et al., Design of a THz-MEMS frequency selective surface for structural health monitoring, International Conference on Metamaterials, Photonic Crystals and Plasmonics
This paper characterizes the relationship between applied force and reflectance/transmittance of a terahertz frequency selective surface for use as a sensor in structural healthmonitoring. Numerical modelling of both the mechanical and electromagnetics, solving the elasticityequation and Maxwell’s equations, respectively, has been undertaken for a 3 layer device.The unit cell comprises of a metal cross wire embedded within a (hard) silicon substrate, interleavedwith stacks of (soft) low density polyethylene.
Otter W, Hu F, Hanham S, et al., Terahertz metamaterial devices, International Conference on Semiconductor Mid-IR and THz Materials and Optics (SMMO2016)
Otter WJ, Hanham SM, Klein N, et al., 2016, Millimeter-wave negative group delay network, URSI Asia-Pacific Radio Science Conference (URSI AP-RASC), Publisher: IEEE, Pages: 1205-1207
Muller AA, Lucyszyn S, 2015, Properties of purely reactive Foster and non-Foster passive networks, Electronics Letters, Vol: 51, Pages: 1882-1884, ISSN: 0013-5194
The mathematical concept of strongly real functions of positive and negative types is introduced to network theory for the first time. In this letter we show that the driving point reactance/susceptance of a pure Foster network, made up of only ideal positive inductance and capacitance element, is a strongly real function of real frequency of positive type. As a corollary, for a pure non-Foster network made up of only ideal negative inductance and capacitance elements, we show that the driving point reactance/susceptance is a strongly real function of real frequency of negative type. It is shown that a condition for a purely reactive passive network to exhibit a positive or negative reactance/susceptance-frequency gradient is that the driving point immittance should have alternating poles and zeros lying on the real frequency axis. Finally, it is shown that either purely Foster or non-Foster networks can be constructed by combining ideal Foster and non-Foster reactive elements.
D'Auria M, Otter WJ, Hazell J, et al., 2015, 3-D printed metal-pipe rectangular waveguides, IEEE Transactions on Components, Packaging and Manufacturing Technology, Vol: 5, Pages: 1339-1349, ISSN: 2156-3950
This paper first reviews manufacturing technologies for realizing air-filled metal-pipe rectangular waveguides (MPRWGs) and 3-D printing for microwave and millimeter-wave applications. Then, 3-D printed MPRWGs are investigated in detail. Two very different 3-D printing technologies have been considered: low-cost lower-resolution fused deposition modeling for microwave applications and higher-cost high-resolution stereolithography for millimeter-wave applications. Measurements against traceable standards in MPRWGs were performed by the U.K.'s National Physical Laboratory. It was found that the performance of the 3-D printed MPRWGs were comparable with those of standard waveguides. For example, across X-band (8-12 GHz), the dissipative attenuation ranges between 0.2 and 0.6 dB/m, with a worst case return loss of 32 dB; at W-band (75-110 GHz), the dissipative attenuation was 11 dB/m at the band edges, with a worst case return loss of 19 dB. Finally, a high-performance W-band sixth-order inductive iris bandpass filter, having a center frequency of 107.2 GHz and a 6.8-GHz bandwidth, was demonstrated. The measured insertion loss of the complete structure (filter, feed sections, and flanges) was only 0.95 dB at center frequency, giving an unloaded quality factor of 152--clearly demonstrating the potential of this low-cost manufacturing technology, offering the advantages of lightweight rapid prototyping/manufacturing and relatively very low cost when compared with traditional (micro)machining.
Mitcheson PD, Lucyszyn S, Pinuela M, et al., 2015, Inductive power transfer system, US9899877B2
An inductive power transfer system comprises a transmitter circuit comprising a transmitter coil and a receiver circuit comprising a receiver coil spaced from the transmitter coil. The transmitter circuit is in the form of a Class E amplifier with a first inductor and a transistor in series between the terminals of a power supply. A first transmitter capacitance is in parallel with the transistor between the first inductor and a power supply terminal, a primary tank circuit in parallel with the first transmitter capacitance, the primary tank circuit comprising the transmitter coil and a second transmitter capacitance arranged in parallel with the transmitter coil, and a third transmitter capacitance in series with the first inductor between the first transmitter capacitance and the primary tank circuit. The second transmitter capacitance is selected such that a resonant frequency of the primary tank circuit is not equal to the first frequency.
Hanham S, Watts C, Otter WJ, et al., 2015, Dielectric measurements of nanoliter liquids with a photonic crystal resonator at terahertz frequencies, Applied Physics Letters, Vol: 107, ISSN: 1077-3118
Papantonis S, Lucyszyn S, 2015, Lossy Spherical Cavity Resonators for Stress-testing Arbitrary 3D Eigenmode Solvers, Progress in Electromagnetics Research, Vol: 151, Pages: 151-167, ISSN: 1070-4698
A lossy metal-wall cavity resonator that extends well beyond perturbation theory limitsis studied. An exact analytical solution is employed for the spherical cavity resonator, having wallstransformed from being a perfect electrical conductor (PEC) to free space. This model then acts as anideal benchmark reference standard. A plane-wave approximation is then derived. Independent full-wavenumerical modeling of the spherical cavity resonator is undertaken using eigenmode solvers within twowell-known commercial, industry-standard, simulation software packages (HFSSTMand COMSOL). Ithas been found that the plane-wave approximation model accurately characterizes the results generatedby these solvers when equivalent ¯nite conductivity boundary (FCB) and layered impedance boundary(LIB) conditions are used. However, the impedance boundary (IB) condition is accurately characterizedby the exact model, but the precise value of complex wave impedance at the wall boundary for the specificresonance mode must first be known a priori. Our stress-testing results have profound implications onthe usefulness of these commercial solvers for accurately predicting eigenfrequencies of lossy arbitrary3D structures. For completeness, an exact series RLC equivalent circuit model is given specifcallyfor a spherical cavity resonator having arbitrary wall losses, resulting in the derivation of an extendedperturbation model.
Hu F, Otter W, Lucyszyn S, Optically tunable THz frequency metamaterial absorber, 40th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz)
In this paper, we propose a metamaterial-based terahertz (THz) absorber with optically tunable absorbance. The unit cell of the structure consists of a cross-shaped resonator, a dielectric spacing layer for wave impedance matching and a high-resistivity silicon (HRS) substrate. Without illumination, the structure acts as a capacitive metal mesh filter that has minimum transmittance and maximum reflectance at its resonance frequency. When the HRS substrate is optically illuminated, its conductivity increases, effectively blocking transmission through the structure. Therefore, this device will have a low reflectance if the impedance is matched. The optimized structure shows a high absorbance of 98% at 0.25 THz in simulations. This concept can be used for the realization of dynamic control of absorbance and emissivity for applications in the THz and infrared (IR) range.
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