Equivalent Transmission Line Model Research Articles

A Design Method and Application of Meta-Surface-Based Arbitrary Passband Filter for Terahertz Communication.

A meta-surface-based arbitrary bandwidth filter realization method for terahertz (THz) future communications is presented. The approach involves integrating a meta-surface-based bandstop filter into an ultra-wideband (UWB) bandpass filter and adjusting the operating frequency range of the meta-surface bandstop filter to realize the design of arbitrary bandwidth filters. It effectively addresses the complexity of designing traditional arbitrary bandwidth filters and the challenges in achieving impedance matching. To underscore its practicality, the paper employs silicon substrate integrated gap waveguide (SSIGW) and this method to craft a THz filter. To begin, design equations for electromagnetic band gap (EBG) structures were developed in accordance with the requirements of through-silicon via (TSV) and applied to the design of the SSIGW. Subsequently, this article employs equivalent transmission line models and equivalent circuits to conduct theoretical analyses for both the UWB passband and the meta-surface stopband portions. The proposed THz filter boasts a center frequency of 0.151 THz, a relative bandwidth of 6.9%, insertion loss below 0.68 dB, and stopbands exceeding 20 GHz in both upper and lower ranges. The in-band group delay is 0.119 ± 0.048 ns. Compared to reported THz filters, the SSIGW filter boasts advantages such as low loss and minimal delay, making it even more suitable for future wireless communication.

Multi-objective Agent Model for XGBoost Controlled VFTO Simulator Based on Bayesian Optimization Algorithm

VFTO generated from GIS may cause interference and damage to terminal equipment on the primary and secondary sides, but experimental measures to evaluate the affected equipment and electromagnetic effects of the equipment through actual measurements are quite limited, so it is desired to build a VFTO simulator in the laboratory for experimental research and laboratory testing. Most of the current researches are conducted by building a true-type experimental platform for VFTO simulation, but this method has the disadvantages of large footprint, high cost and the scope of application can only simulate VFTO in a certain situation. Therefore, this paper establishes a broadband circuit model considering the pulse generator and the frequency domain equivalent transmission line model, and introduces the machine learning algorithm XGBoost to fit the agent model of the functional relationship between the design target and the structural parameters by establishing the sample data of the input circuit parameters and the output frequency waveform characteristics of the simulator, which is capable of dynamically adjusting the input parameters based on the waveform characteristics according to the changes of the target waveform, and ensures that a controllable waveform is obtained accurately in the laboratory the accuracy of obtaining controllable waveforms, thus realizing the output of controllable analog VFTO waveforms by changing the parameters of circuit components. Finally, the Bayesian optimization process is used for the hyper-parameter optimization of the XGBoost model, which has a fast convergence speed, and the characteristics of the output model are compared and analyzed, which verifies the feasibility and superiority of the proposed agent model as well as the multi-objective optimization method.

Design and theoretical analysis of a tunable bifunctional metasurface absorber based on vanadium dioxide and photoconductive silicon.

A tunable bifunctional metasurface absorber based on vanadium dioxide (VO2) and photoconductive silicon (PSi) is proposed in a terahertz (THz) band. When the conductivities of VO2 (σvo2) and PSi (σPSi) are 10 S m-1 and 1 × 105 S m-1, the designed absorber has a function of dual-broadband absorption. The absorptivity rate of over 90% is in the dual-broadband of 2.47-3.71 THz and 8.90-10.62 THz, corresponding to relative bandwidths (RBs) of 40.13% and 17.62%, respectively. When σvo2 and σPSi are equal to 2 × 105 S m-1 and 1 × 105 S m-1, the proposed design has a function of single-broadband absorption. More than 90% absorptivity is achieved in 4.69-7.72 THz (RB = 48.83%). Furthermore, the absorptivity under the dual- and single-broadbands is manipulated by changing σPSi. An impedance matching theory, equivalent transmission-line (TL) model and electric field distribution are used to reveal the tunable bifunctional absorption mechanism. The influences of structure parameters, polarization mode and incidence angle on the dual- and single-broadband absorption are investigated. The dual- and single-broadband absorption performances are maintained within the incident angles of 55° and 60°, which also possess polarization insensitivity. The proposed absorber has a potential application value in multifunctional devices such as modulation, sensing and electromagnetic (EM) stealth.

Equivalent transmission line characterization and multi‐layer material measurement analysis of the signal conversion process in the pulsed electro‐acoustic method

AbstractThis paper studies the equivalent transmission line model of the pulsed electro‐acoustic (PEA) method with its applications. Based on the consistency of acoustic wave behaviour inside lossy acoustic materials and voltage wave propagation in transmission line, an equivalent simulation model of the PEA system is developed, whose reliability is verified by the output from the transducer and amplifier models and the comparison with measured waveforms. For the problem of acoustic impedance mismatch between different modules, simulation indicates that the unequal impedances of semiconducting electrode and sample can affect the amplitude of the measured signal at the upper electrode side, and the reflected acoustic waves caused by the transducer can affect the charge waveform. Further simulation for multi‐layer materials finds that the reflected acoustic waves of different samples and sound absorbing module can superimpose on the charge signal. Accordingly, a selection criterion is proposed to avoid the effect of the reflected waves at the interface. As for the acoustic reflection caused by internal charge, it needs to be dealt with sequentially in calibration process, starting from the result inside the sample near ground electrode. The research can provide a foundation for analyzing the acoustic properties of the PEA method.

A Performance-Enhanced Antenna for Microwave Biomedical Applications by Using Metasurfaces

In this article, we introduce a novel antenna employing specifically designed metasurfaces to improve the radiating performance in close proximity to the human body, as required in microwave biomedical applications. We first present design guidelines to realize a thin metasurface acting as an impedance matching layer between the radiating element and the biological tissue, based on the transmission line equivalent model. Additionally, for the first time to the best of our knowledge, we combine an artificial magnetic conductor (AMC) as the backing element of the antenna, to improve the gain and reduce the undesired back radiation. To validate the proposed approach, we conceived a numerical test-case consisting of a bow-tie antenna operating close to a biological phantom at 2.56 GHz. Numerical simulations demonstrated the performance enhancement in terms of higher field penetration within tissues and better radiating behavior when the bow-tie antenna is working in the presence of both the metasurfaces. Furthermore, measurements carried out over fabricated prototypes confirmed the numerical results, validating the overall design procedure. The herein presented methodology can be helpful in several applications when the radiating elements operate in close proximity to biological tissues, as in medical imaging, on- body communication, mobile phones, and consumer devices.

Analysis and design of weak coupling coupler based on the half mode substrate integrated waveguide

AbstractSubstrate integrated waveguide (SIW) technology represents a good solution for the design of couplers. Coupler structures proposed in most relevant reports cannot achieve excellent performance in the case of weak coupling. This work proposes a new weak coupling coupler architecture, similar to the branch line coupler. The metal via arrays is used to reshape the electric field distribution of the SIW structure, making the overall structure achieve weak coupling characteristics. The even-odd mode decomposition method analyzes this structure's equivalent transmission line model. For this purpose, a systematic design procedure is deployed to achieve several coupling values over a wide frequency bandwidth. A novel half-mode substrate integrated waveguide (HMSIW) coupler with a 29 dB coupling is designed and fabricated for verification based on the proposed method. Good agreements between the calculated and simulated results are observed. The proposed coupler has the advantage of high directivity within the broadband and can be used for SIW-based circuits and power detection in the Ku-band.

Nonuniform Transmission Line Model for Electromagnetic Radiation in Free Space

An equivalent nonuniform transmission line model for electromagnetic radiation in free space is developed. By properly defining a voltage and a current associated with the transverse component of the mode fields, a kind of telegrapher’s equation is derived for each spherical harmonic mode in frequency domain. Based on the equivalent distribution inductance and capacitance, the local characteristic impedance and phase velocity are derived. For each spherical mode, a cutoff spherical surface and an associated cutoff radius are introduced to separate the space into an evanescent region and a propagating region. A spherical mode field decays approximately exponentially in the evanescent region and experience local reflection in the propagating region. The proposed model may provide an intuitive illustration for the radiation process in free space.

Trilayered Gires-Tournois Resonator with Ultrasensitive Slow-Light Condition for Colorimetric Detection of Bioparticles.

Over the past few decades, advances in various nanophotonic structures to enhance light-matter interactions have opened numerous opportunities for biosensing applications. Beyond the successful development of label-free nanophotonic biosensors that utilize plasmon resonances in metals and Mie resonances in dielectrics, simpler structures are required to achieve improved sensor performance and multifunctionality, while enabling cost-effective fabrication. Here, we present a simple and effectual approach to colorimetric biosensing utilizing a trilayered Gires-Tournois (GT) resonator, which provides a sensitive slow-light effect in response to low refractive index (RI) substances and thus enables to distinguish low RI bioparticles from the background with spatially distinct color differences. For low RI sensitivity, by impedance matching based on the transmission line model, trilayer configuration enables the derivation of optimal designs to achieve the unity absorption condition in a low RI medium, which is difficult to obtain with the conventional GT configuration. Compared to conventional bilayered GT resonators, the trilayered GT resonator shows significant sensing performance with linear sensitivity in various situations with low RI substances. For extended applications, several proposed designs of trilayered GT resonators are presented in various material combinations by impedance matching using equivalent transmission line models. Further, comparing the color change of different substrates with low RI NPs using finite-difference time-domain (FDTD) simulations, the proposed GT structure shows surpassing colorimetric detection.

Ultra-Wideband 3-D Microwave Absorbers With Composite Slotlines and Microstrip Lines: Synthetic Design and Implementation

This article proposes a class of ultra-wideband 3-D microwave absorbers with composite slotlines and microstrip lines from synthetic design to practical implementation. Firstly, the general equivalent transmission line (TL) model of the proposed 3-D absorber element is formed based on two sets of shunt short-ended stubs and an i-section nonuniform connecting line. Then, the synthetic procedure is theoretically investigated using the equivalent TL model, aiming to construct an ultra-wide absorption band with the Chebyshev equal-ripple response. According to the prescribed absorptive performance, such as maximum reflection coefficient (C) and fractional bandwidth (FBW), the relevant parameters of the TL model can be directly calculated by the established synthesis approach. To validate the proposed concept, two prototypes, namely, absorber-I (i=1) and absorber-II (i=2), are designed, fabricated, and measured. Each prototype element applies a simple 3-D structure composed of slotlines, microstrip lines, and only one absorptive load, which are all etched on a single-layered substrate. Measured results agree well with synthetizations and simulations. For absorber-I, the measured bandwidth of 95.5% in a frequency range from 5.08 to 14.44GHz is successfully realized. Absorber-II obtains a measured FBW of 111.1% in a range from 4.48 to 15.68GHz. Average absorption ratios within the operating band are higher than 95.5% and 93.8% for absorber-I and absorber-II, respectively. Besides, the proposed 3-D absorbers are angularly stable within 600 oblique incidence. Therefore, such ultra-wideband 3-D microwave absorbers with simple structures possess the attractive potential for effectively absorbing electromagnetic waves.

Analysis of High Gain Wideband 2 × 2 Printed Slot Array With AMC Surface by Presenting Equivalent Transmission Line Model for C and X-Band Applications

Analysis of High Gain Wideband 2 × 2 Printed Slot Array With AMC Surface by Presenting Equivalent Transmission Line Model for C and X-Band Applications

AMC-Loaded Low-Profile Broadband Printed 2×2 Array With Gain and Isolation Enhancement Using Equivalent Circuit Model for Wireless Systems

A 2×2 array of printed antenna loaded by planar Giuseppe Peano artificial magnetic conductor (AMC) is presented for vehicular wireless systems. The four-element of the proposed array by utilizing diverse polarized directions of the printed dipoles with a 5×5 AMC reflector achieves a wideband antenna with enhanced properties. It shows the measured S-parameters of the wide bandwidths from 3.30 to 6.02 GHz with increased stable gains and efficiencies (more than 90%) for all elements. Moreover, the appropriate isolation of greater than 30 dB between the elements is achieved. The proposed design of the printed dipoles includes T-shaped microstrip dipoles and a feedline system as a T-shape to broaden the bandwidth in 4.7-6.02 GHz (S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> ≤ -10 dB). By utilizing the 3×3 Giuseppe Peano AMC reflector into the one element of the printed dipole, enhanced radiation efficiency and -10 dB measured bandwidth from 3.26 to 6.02 GHz (60%) is achieved for vehicular wireless systems. The proposed design with AMC with respect to the antenna without AMC indicates a reduced size of 70%, increased gain up to 8.4 dBi, and uni-directional radiation patterns. The new AMC unit cell is configured by the Giuseppe Peano design to resonate at 5.36 GHz in 4.27-6.34 GHz (39%). Finally, the suggested equivalent transmission line model of the 2×2 array with AMC surface is introduced with a suitable agreement between the results of reflection coefficients.

Spatial domain communication technique for future chipless ID sensors based on vortex terahertz beams generated by metasurfaces

As future communication systems move toward the terahertz (THz) spectrum with a much higher speed and more densification, enhanced security utilizing the novel concepts will be inevitable, particularly in automated identification systems. This paper proposes a novel spatial domain technique based on vortex beams generated by metasurface structures for efficient chipless identification (ID) sensors where the information is saved in the vortex modes. This approach using the vortex concept offers the high security strength in the automated systems compared to existing solutions, including time-based and frequency-based sensors. Furthermore, combining these vortex-based sensors and conventional ones results in substantially increasing the stored information capacity. To verify the idea, here, we present an uneven dielectric metasurface (UDM) to generate distinct vortex modes to identify different information. The proposed sensor is designed by using an equivalent transmission line (TL) model, and the extracted results exhibited a good agreement between simulation and theoretical approaches. Furthermore, it is demonstrated that the transmitted information capacity can be notably enhanced by using a sensor tag with simultaneous multiple modes and also using more than one tag simultaneously.

Port Impedance Measurement and Current Injection Response Analysis for PLCs

Programmable logic controllers (PLCs) are used to control devices throughout the power system since they have fast control capabilities and can utilize multiple types of communication interfaces. Therefore, studying and mitigating their vulnerabilities to electromagnetic pulse is important for the reliability of PLC operations. In this article, an effective impedance measurement scheme is proposed and demonstrated for three PLCs to estimate their susceptibility to an electromagnetic pulse. The equivalent nonuniform transmission line model is established to eliminate the impact of the fixture in the de-embedding process. Then, different parameters of the impedance measurement setup are explored. Based on the measured impedance, the equivalent circuit is established to calculate the response of the device when subjected to the electromagnetic pulse. The voltage and current responses of different interfaces are compared utilizing the developed pulsed current injection (CI) method. Finally, the impedance measurement scheme is verified through testing using three measuring instruments. And the CI simulation experiments reveal the characteristics and susceptibilities of different PLCs interfaces, indicating that some protection measures are required for the reliable operation of the PLC.

3-D Pattern Modulation Surfaces Using Short-Circuited Slotline Structure: Proposal, Design, and Implementation

This article presents the proposal, design, and implementation of 3-D pattern modulation surfaces (PMSs) using short-circuited slotline structure. First, the reflection coefficient of short-circuited slotline with a certain length is studied using the equivalent transmission line model. Since the magnitude of its reflection coefficient nearly equals 1, the TE-polarized incident plane wave can be almost fully reflected at the input terminal of each short-circuited slotline. Most importantly, the phase of its reflection coefficient can be freely changed and adjusted by only varying the length of short-circuited slotline. Then, the short-circuited slotline structure is used as the key element of the proposed PMS. In this way, the functionality of pattern modulation is obtained by unequally selecting the lengths of a row of short-circuited slotlines. Finally, three prototypes with modulated angles of 15°, 30°, and 45° are fabricated and tested to validate our design concept. The measured results agree well with the calculations, showing that the predicted reflection angles are realized using short-circuited slotlines. Therefore, the proposed 3-D PMS is evidently verified to be a promising candidate for future wireless networks to achieve pattern modulation in a smart radio environment.

Analysis of 2 × 2 MIMO array loaded by artificial magnetic conductor with improved gain, isolation, and bandwidth using equivalent transmission line model for indoor wireless base station

A low profile printed dipole antenna (PDA) backed by broadband Giuseppe Peano fractal artificial magnetic conductor (AMC) is introduced for wireless communications. First, a suggested PDA with a pair of microstrip dipoles excited by an E-shaped microstrip feedline is used to expand the bandwidth in the range of 5.96–7.04 GHz (S11 ≤ −10 dB). Then, the suggested Giuseppe Peano fractal AMC surface as a reflector of the antenna is inserted into the PDA to gain improved radiation efficiency. The PDA with the 6 × 6 Giuseppe Peano AMC array exhibits −10 dB measured impedance bandwidth of 4.95–7.05 GHz (35%) for wireless local area network (WLAN) and worldwide interoperability for microwave access (WiMAX) applications. The suggested PDA with AMC compared to the PDA without AMC exhibits a size reduction of 38%, enhanced gain up to 8.2 dBi, and excellent impedance matching (at least −20 dB) with directional radiation patterns. The novel AMC unit cell is realized based on the Giuseppe Peano fractal patch to operate at 6.10 GHz with an AMC bandwidth of 5.15–7.10 GHz (32%). Besides, by loading 12 × 12 AMC reflector into the four-element array of PDA, low profile wideband structure with enhanced radiation properties are achieved. The measured results show the broad bandwidths of 5–7 GHz for all elements with enhanced gains and good isolations between the elements (more than 24 dB) for multiple-input multiple-output (MIMO) systems.

A modified implementation of the Folded Line Equivalent transmission line model in the Alternative Transient Program

This paper proposes a modified implementation of the Folded Line Equivalent transmission line model to represent three-phase transmission lines. The Folded line equivalent decomposes a line into its open circuit and short circuit contributions. We propose an alternative orthogonal matrix to transform single-phase transmission line parameters, voltages, and currents to the Folded Line Equivalent domain. Because the proposed matrix is orthogonal, it can directly represent bidirectional transformations using circuit components in simulation software, such as the ATP-EMTP. First, the circuit implementation of Clarke’s matrix decouples a three-phase transmission line into its modes. Then, the circuit implementation of the proposed matrix decouples each mode into its open circuit and short circuit contributions. This paper proves that the proposed approach outputs similar results as those obtained by the Universal Line Model and the JMarti model in the simulation of transmission lines under open-circuit, energization, and fault conditions. However, because the proposed model does not derive from the method of characteristics, it can run with simulation times greater than the propagation delay of the transmission line. It is shown that the proposed approach outputs accurate results for time steps that are 10%, 100%, 200%, and 400% of the propagation delay of the transmission line. Thus, one major advantage of the proposed approach is that it can be used to reduce runtimes in the representation of short transmission lines in large complex networks by increasing time steps without compromising accuracy.

Multilayer graphene-based radiation modulator for adaptive infrared camouflage with thermal management

Graphene film is a promising thermal camouflage and thermal management material because of its thin, light, flexible structural characteristics and controllable broad-spectrum electromagnetic radiation modulation properties. In this study, a thermal radiation modulator (TRM) based on multilayer graphene (MLG) was studied by simulation and an equivalent transmission line model. The physical mechanism underlying the spectral characteristics and the sensitivity of infrared (IR) radiation modulation to the number of graphene layers is revealed. Furthermore, to solve the problem of thermal instability in the MLG-based TRM, a design scheme integrating a TRM and a meta-absorber is proposed. By electrical control of the MLG, the improved modulator can achieve dynamic emissivity modulation in the wavelength ranges of 3–5 µm and 8–14 µm for adaptive thermal camouflage while maintaining a high emissivity at 5–8 µm for radiative cooling. The compatibility of tunable IR emission and radiative heat dissipation enables graphene to be used for thermal camouflage in complex environments and at high temperatures. The results not only promote the exploration of advanced thermal camouflage materials or devices but also provide inspiration for the application of graphene in thermal management, thermophotovoltaics, IR displays and communications.

Microwaves as Diagnostic Tool for Pituitary Tumors: Preliminary Investigations

To date, tumors, the second cause of death worldwide, are a modern medicine plight. The development of rapid, cost-effective and reliable prevention and diagnostics tools is mandatory to support clinicians and ensure patients’ adequate intervention. Pituitary tumors are a class of neoplasm, which calls for suitable and ad hoc diagnostic tools. Recently, microwaves have gained interest as a non-ionizing, non-invasive valuable diagnostic approach for identifying pathologic tissues according to their dielectric properties. This work deals with the preliminary investigation of the feasibility of using microwaves to diagnose pituitary tumors. In particular, it focuses on benign tumors of the adenohypophysis, e.g., the pituitary adenomas. It is assumed to access the region of interest of the pituitary region by following a trans-sphenoidal approach. The problem was modeled by developing an equivalent transmission line model of the multi-layered, lossy tissues (front bone of sphenoid sinuses, air in the sinuses, posterior bone of sphenoid sinuses, the pituitary gland and the tumor). The forward problem was developed to investigate the transmission coefficient for identifying the most favorable propagation conditions. Then, it was analyzed if, by the solution of an inverse problem, it is possible to reconstruct the permittivity and electrical conductivity profiles and identify the tumor presence. The results are promising since a maximum reconstruction error of 8% is found, in the worst case, thus paving the way for the use of microwaves for the diagnosis of pituitary tumors.

Reactive Impedance Surface-Loaded Wideband Wide-Scanning Phased Array in Triangular Lattice

A phased array loaded with a reactive impedance surface (RIS) is proposed for wideband wide-scanning performance. The mushroom-like RIS structure, etched on the same printed circuit board (PCB) of the antenna, is introduced as a superstrate over the antenna aperture. The reactance of the RIS structure compensates for the scan impedance variation of the antenna during the beam scanning, explained by the equivalent transmission-line model. A superior scanning performance in all azimuth planes is achieved, and the scan blindness in the H-plane is alleviated, especially. The total compact design is capable of operating over a 2.3:1 (6 –14 GHz) bandwidth in broadside and over a 1.8:1 bandwidth in ±60° E-plane, ±70° D-plane, and ±65° H-plane scanning. The array is implemented in a triangular lattice, and edge elements in the E-plane are connected to metal walls for edge effect elimination. A 45-element ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5\times 9$ </tex-math></inline-formula> ) array prototype is fabricated and measured. Active reflection coefficients are calculated, and scanning patterns are synthesized.

Antenna Current Calculation Based on Equivalent Transmission Line Model.

This paper provides a new way for spatial current/field profiles for frequency-selective surface analytical approximation. It confirms that the per unit length radiation resistance of an equivalent transmission line model for line antenna has little influence on the normalized current distribution. The two-wire equivalent transmission line model (typically used for transmitting line antenna) is applied to the receiving line antenna. In this case, the corresponding incident field is decomposed into odd and even mode for asymmetric distribution. A one-wire equivalent transmission line model is then introduced for any antenna composed of relative narrow strips. The incident field does not need to be decomposed. According to the simulation, the transmission line loss has little influence on the current distribution.