This article presents a novel broadband common-mode (CM) absorptive balun developed through an optimization strategy. Different from the conventional Marchand balun that reflects CM waves, the ...proposed balun excels in mitigating the radio frequency interference issues stemming from the reflected CM noise in high-speed circuits by effectively absorbing these unwanted signals. Meanwhile, by simply adding two slotlines and two resistors on the ground plane of a conventional two-layer Marchand-balun structure, a wide absorbing band is achieved. An equivalent circuit model of the proposed balun is also introduced, and a closed-form CM reflection coefficient is further derived. The equivalent circuit facilitates efficient optimization of key design parameters of the balun structure, negating the need for time-consuming full-wave simulation while ensuring broadband CM-absorptive performance. The proposed balun structure can consistently deliver a wideband CM absorption exceeding 10 dB spanning from 1.3 GHz to 4.2 GHz, which is validated by a full-wave simulation and measurement.
A broadband low-profile L-probe fed metasurface antenna is proposed by well exciting both transverse magnetic (TM) leaky wave and transverse electric (TE) surface wave resonances. The metasurface is ...composed of an array of rectangular metallic patch cells. An L-shaped probe positioned underneath the finite metasurface is utilized to excite a TM leaky wave resonance and a TE surface wave resonance simultaneously for broadband operation. The dispersion properties of the TM leaky wave and TE surface wave are used to analyze the dual resonance modes. The proposed L-probe fed metasurface antenna achieves a broad −10 dB impedance bandwidth of 34.5% with the peak gain of 10.3 dBi and the front-to-back ratio larger than 18 dB with a low profile of <inline-formula> <tex-math notation="LaTeX">0.06\lambda _{0} </tex-math></inline-formula>, where <inline-formula> <tex-math notation="LaTeX">\lambda _{0} </tex-math></inline-formula> is the free-space wavelength at the center operating frequency.
For the analysis of performance limiting processes in various electrochemical systems like lithium ion batteries, polymer electrolyte membrane fuel cells or solid oxide cells, impedance spectroscopy ...is a powerful tool. The distribution of relaxation times (DRT) enables the deconvolution of the polarization processes in the spectrum. The simple approach, to correlate each peak in the DRT with a single polarization process fails for multiphase electrodes as the complex coupling of electronic, ionic and transport of different species by spatially distributed charge transfer reactions leads to a number of correlated peaks in the DRT.
In this contribution such coupling of transport and reaction is analyzed for ceria based fuel electrodes applied in solid oxide cells. A physicochemically meaningful two-channel transmission line model is developed. Due to the ambiguity of impedance spectra and DRT, the straightforward approach of fitting this model to measured spectra does not allow an unambiguous model parameterization. Additional methods as conductivity measurements and focused ion beam-tomography are indispensable to obtain physicochemically meaningful parameters to be applied in the fitting procedure. With this parameterization approach DRT based modeling becomes feasible and ionic/electronic transport resistances and area specific charge transfer resistance of the ceria surface can be quantified.
•Identification of loss processes by distribution of relaxation times.•Physicochemically meaningful impedance model for a single phase GDC fuel electrode.•Impedance model enables access to charge transfer resistance at the GDC-surface.
The metal resistance in the transmission line model (TLM) structures creates a serious obstacle to determine precisely the intrinsic contact resistivity. To tackle this problem, we propose a new ...model, the lump model, to evaluate the metal resistance influence in both TLM and circular TLM (CTLM) test structures. In this letter, we demonstrate the high simplicity, great robustness, and flexibility of the lump model. The previous reported contact resistivity values extracted with CTLM are usually above 1 χ 10 -7 Ω · cm 2 because the metal resistance impact is commonly neglected. This is the first time that the role of the metal in CTLM is appropriately analyzed. Low contact resistivity, 3.6χ10 -8 Ω · cm 2 , of standard NiSi/n-Si contact has been extracted and this shows the high sensitivity of this method.
•Design of the ultra-broadband Terahertz absorber is based on Circuit Model.•This absorber is based on Periodic Arrays of Graphene Ribbons.•The bandwidth of the absorber can be adjusted by the ...chemical potential.•Two various dielectrics have been used in the configuration of the device.
In this paper, a novel configuration of a tunable ultra-broadband terahertz (THz) absorber based on two layers of graphene ribbons and two different kinds of substrate materials has been proposed. The recently suggested equivalent circuit theory of Periodic Arrays of Graphene Ribbons (PAGRs) with a developed transmission line model is utilized to design the structure of the THz absorber. Also, an equivalent series RLC branch is considered for each layer of PAGRs. By adopting the impedance matching approach, the real part of the input impedance of the proposed structure is tuned to be approximately matched to the free-space impedance in a wideband THz region. Then, the imaginary part of the input impedance is adjusted to near zero around the central frequency for increasing the proposed absorber's bandwidth. As a result, the normalized bandwidth of 70% absorption has reached up to 118% with only just two layers of graphene ribbons. Based on the purpose of this paper, the bandwidth of the proposed absorber has been controlled by the chemical potentials of the graphene ribbons.
•A porous electrode model analysis method by a circuit simulator is established.•LIB porous electrode is modeled with a transmission line model.•LiCoO2 positive electrode performance is measured with ...a three-electrode cell.•The discharge performance of a LiCoO2 porous electrode is simulated.•Reaction distribution inside the pore space of the porous electrode is visualized.
Improving the performance of secondary batteries is indispensable for promoting the proliferation of electric vehicles, and many researchers are working toward further sophistication of lithium-ion batteries (LIBs). In general, the electrode of a battery has a three-dimensional structure, and a reaction distribution occurs inside the electrode because of changes in the load current. In particular, because LIBs require high output, a thin porous material with a thickness of several tens of micrometers is used as an electrode material; the electrolyte permeates into the spaces of the pores constituting this electrode, and the electrochemical reaction proceeds. From the perspective of an electric circuit, this pore space can be modeled by a transmission line model using a distributed-constant circuit as a frame. Here, this equivalent circuit was analyzed using a circuit simulator, which is an electrical engineering tool. We then developed a new method to analyze the distribution of the electrode reaction at each position by dividing the pore space of the positive electrode into N points. That is, the transmission line model of the current, potential, and resistance distribution in the pore space was analyzed by the circuit simulator and a new algorithm coupled with electrochemical reaction analysis (Butler–Volmer equation/diffusion equation) was constructed. In addition, to characterize the LiCoO2 positive electrode itself, we measured the discharge performance under a constant current from 1C to 10C using the three-electrode cell method and reproduced the discharge characteristics using the aforementioned simulation method. On the basis of the results, the distribution of electrochemical reactions occurring in the electrolyte-filled pore space of the porous electrode (positive electrode) was widely analyzed.
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Supercapacitors are electricity storage systems with high power performances. Their short charge/discharge times are due to fast adsorption/desorption rates for the ions of the electrolyte on the ...electrode surface. Nanoporous carbon electrodes, which give larger capacitances than simpler geometries, might be expected to show poorer power performances because of the longer times taken by the ions to access the electrode interior. Experiments do not show such trends, however, and this remains to be explained at the molecular scale. Here we show that carbide-derived carbons exhibit heterogeneous and fast charging dynamics. We perform molecular dynamics simulations, with realistically modeled nanoporous electrodes and an ionic liquid electrolyte, in which the system, originally at equilibrium in the uncharged state, is suddenly perturbed by the application of an electric potential difference between the electrodes. The electrodes respond by charging progressively from the interface to the bulk as ions are exchanged between the nanopores and the electrolyte region. The simulation results are then injected into an equivalent circuit model, which allows us to calculate charging times for macroscopic-scale devices.
Recently, super-harmonic ultrasound imaging technology has caused much attention due to its capability of distinguishing microvessels from the tissues surrounding them. However, the fabrication of a ...dual-frequency confocal transducer is still a challenge. In this work, 270-<inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula> PMN-PT single crystal 1-3 composite and 28-<inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula> PVDF thick film, acting as transmission layer and receiving layer, respectively, are integrated in a novel co-focusing structure. To realize delicate wave propagation control, microwave transmission line theory is introduced to design such structure. Two acoustic filter layers, 13-<inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula> copper layer and 39-<inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula> Epoxy 301 layer, are indispensable and should be added between two piezoelectric layers. Therefore, an acoustic issue can be overcome via an electrical method and the successful achievement of a dual-frequency (5 MHz/30 MHz) ultrasound transducer with a confocal distance of 8 mm can be realized. The super-harmonic ultrasound imaging experiment is conducted using this kind of device. The 3-D image of 110-<inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula>-diameter phantom tube injected with microbubbles can be obtained. These promising results demonstrate that this novel dual-frequency (5 MHz/30 MHz) confocal ultrasound transducer is potentially usable for microvascular medical imaging application in the future.
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