An unbalanced microstrip bandpass filter (BPF) in dual-extended doublet topology with source-load (S-L) coupling is first presented and researched based on dual-layer capacitive-loaded dual-mode loop ...resonators. The input and output ports are located on the upper substrate layer. The lower dual-mode loop resonator is coupled to the upper loop resonator using four coupling apertures in the middle metal layer. Single- and dual-band responses with four controllable finite-transmission zeros (FTZs) are analysed. Then, a balanced BPF in dual-extended doublet topology without S-L coupling on the basics of the proposed unbalanced filter is presented and researched. Single- and dual-band differential mode responses with three controllable FTZs can be realised with good common mode suppression. Some design examples are provided to illustrate the performances of the realised single- and dual-band unbalanced and balanced filters with controllable FTZs. The measured results agree well with simulated ones.
To prevent interference problems due to existing nearby communication systems within an ultrawideband (UWB) operating frequency, the significance of an efficient band-notched design is increased. ...Here, the band-notches are realized by adding independent controllable strips in terms of the notch frequency and the width of the band-notches to the fork shape of the UWB antenna. The size of the flat type band-notched UWB antenna is etched on 24 times 36 mm 2 substrate. Two novel antennas are presented. One antenna is designed for single band-notch with a separated strip to cover the 5.15-5.825 GHz band. The second antenna is designed for dual band-notches using two separated strips to cover the 5.15-5.35 GHz band and 5.725-5.825 GHz band. The simulation and measurement show that the proposed antenna achieves a wide bandwidth from 3 to 12 GHz with the dual band-notches successfully.
•Topology optimization strategy is proposed to design PnCs with the specified number of band gaps.•The number of topological design variables is rather small with the MFSE model.•The optimization ...problem is effectively solved with the Kriging-based gradient-free algorithm.•PnC unit cells with multiband gaps are used to obtain multifrequency PnC resonators.•The energy band structure and localization effects of PnC resonators are investigated.•PnC resonators are characterized by many flat defect bands within multiple forbidden bands.
Most existing phononic crystals (PnCs) are characterized by a single band gap, and for crystal systems that require multiple band gaps, the method of assembling multiple configurations with different gaps can seriously complicate the manufacture procedure, which hinders their potential applications. In this work, a multiple band gap topological optimization strategy is proposed to design a two-dimensional PnC with the objective of maximizing the specified number of relative band gaps in the in-plane or out-of-plane modes. The topology optimization problem is formulated based on the material-field series-expansion model and solved using a gradient-free algorithm. Calculations of the transmission curves and amplitude fields at typical frequencies confirm the validity of the optimized designs. In addition, PnC unit cells with multiband gaps are used to obtain PnC resonators, and their energy band structure and localization effects are investigated. It is found that these PnC resonators introduce many flat defect bands within each complete forbidden band, which give rises to multifrequency localization effects and promotes their facilitation in energy harvesting technologies.
In this study, the authors present three different metamaterial absorbers (MMAs) namely, T, split-I (SI) and split-Jerusalem cross (SJC) with different dimensions and geometrical configurations. The ...absorption rates of T-, SI- and SJC-shaped absorbers are studied at microwave frequencies. T-shaped absorber demonstrates perfect absorption at 10.19 GHz, making it suitable for single band operation, whereas SI-shaped absorber exhibits two perfect absorption peaks at 9.32 and 10.75 GHz finding its application in dual band operation. However, novel SJC-shaped absorber demonstrates multiple absorption peaks at 9.92, 10.42, 10.93, 11.75 and 13.25 GHz with absorption of 99.5, 91, 99.9, 91.8 and 99.6%, respectively, making it suitable for X- and Ku-band operations. The proposed MMAs have a thickness of around 0.8 mm (i.e. <λ/37) with respect to the lowest frequency of operation. Furthermore, the absorbers are analysed for different angles of polarisation and incidence for transverse electric polarised wave with a step size of 15°. The proposed absorbers have been fabricated and experimentally demonstrated at X-band verifying the results obtained from simulations and implementing an equivalent circuit method. Further, SJC-shaped absorber is demonstrated for multi-and wide-band terahertz applications exhibiting four perfect absorption peaks at 2.76, 2.89, 3.02 and 3.31 THz.
By 2009, reverberations of economic crisis spread from the United States around the globe. As corporations across the United States folded, however, small businesses on the Qualla Boundary of the ...Eastern Band of Cherokee Indians (EBCI) continued to thrive. In this rich ethnographic study, Courtney Lewis reveals the critical roles small businesses such as these play for Indigenous nations. The EBCI has an especially long history of incorporated, citizen-owned businesses located on their lands. When many people think of Indigenous-owned businesses, they stop with prominent casino gaming operations or natural-resource intensive enterprises. But on the Qualla Boundary today, Indigenous entrepreneurship and economic independence extends to art galleries, restaurants, a bookstore, a funeral parlor, and more.Lewis's fieldwork followed these businesses through the Great Recession and against the backdrop of a rapidly expanding EBCI-owned casino. Lewis's keen observations reveal how Eastern Band small business owners have contributed to an economic sovereignty that empowers and sustains their nation both culturally and politically.
In this paper, a multiple stubs loaded ring resonator (MSLRR) is proposed to design directly coupled multi-band bandpass filters (BPFs) with mixed electric and magnetic coupling (MEMC). The proposed ...MSLRR exhibits multiple-mode resonant behavior. The increased number of loaded stubs excite many more useful resonant modes, but these resonant modes can be still independently controlled. As examples, a dual-band BPF, a tri-band BPF, a quad-band BPF, and a quint-band BPF using different types of MSLRRs are designed and fabricated. The passband frequencies and return losses (RLs) of these multi-band BPFs can be independently controlled. A dual-mode open loop resonator is then introduced in the quint-band BPF to enhance the sixth resonant mode of the MSLRR to produce the sixth passband so that a sext-band BPF is also presented. Multiple transmission zeros due to the cancelling effect of MEMC and virtual grounds in the MSLRR can be observed around the passbands resulting in sharp passband selectivity and high band-to-band isolation. Moreover, all of the fabricated multi-band BPFs have compact sizes, good RLs, and low insertion losses. Good agreements are observed between the simulated and measured results.
This paper presents a new method for designing multiband bandpass filters (BPFs). The filter consists of low-pass filter and two open stub-loaded shorted stubs. Multiple transmission zeros (TZs) are ...produced by the open stub-loaded shorted stub, and multiple passbands can be realized. For the first time, different numbers of open stubs are used to realize multiband BPFs with two to seven passbands. The center frequencies and the last passband bandwidth can be tuned in a certain range by adjusting the TZs and transmission poles. First, a wideband BPF is presented to introduce the design concept. Theoretical analysis is done to illustrate the design principle. Then, a wide single-band BPF and a dual-band BPF are designed to demonstrate the design method. The design procedure is summarized to guide the design process. Finally, tri-/quad-/quint-/sext-/sept-band BPFs are designed according to the design principle. All the BPFs are manufactured. Measured results show good agreement with simulated ones.
Transition metal‐based electrocatalysts will undergo surface reconstruction to form active oxyhydroxide‐based hybrids, which are regarded as the “true‐catalysts” for the oxygen evolution reaction ...(OER). Much effort has been devoted to understanding the surface reconstruction, but little on identifying the origin of the enhanced performance derived from the substrate effect. Herein, we report the electrochemical synthesis of amorphous CoOOH layers on the surface of various cobalt sulfides (CoSα), and identify that the reduced intermolecular energy gap (Δinter) between the valence band maximum (VBM) of CoOOH and the conduction band minimum (CBM) of CoSα can accelerate the formation of OER‐active high‐valent Co4+ species. The combination of electrochemical and in situ spectroscopic approaches, including cyclic voltammetry (CV), operando electron paramagnetic resonance (EPR) and Raman, reveals that Co species in the CoOOH/Co9S8 are more readily oxidized to CoO2/Co9S8 than in CoOOH and other CoOOH/CoSα. This work provides a new design principle for transition metal‐based OER electrocatalysts.
The reduced intermolecular energy gap between the valence band maximum of CoOOH and the conduction band minimum of Co precursors can promote the formation of oxygen evolution reaction (OER)‐active high‐valent Co4+ species, and enhance the OER performance. This finding provides a new design principle for transition metal‐based OER electrocatalysts.
A new band selection (BS), called progressive BS (PBS) of spectral unmixing for hyperspectral imagery is being presented. It is quite different from the traditional BS in the sense that the former ...adapts the number of selected bands, p to various endmembers used for spectral unmixing, while the latter fixes the value of p at a constant for all endmembers. Due to the fact that different endmembers post various levels of difficulty in discrimination, each endmember should have its own custom-selected bands to specify its spectral characteristics. In order to address this issue, p is composed of two values, one value determined by virtual dimensionality to accommodate each of endmembers and the other is determined by a new concept of band dimensionality allocation to account for discrminability among endmembers. In order to find appropriate bands to be used for PBS, band prioritization and band de-correlation are included to rank bands according to significance of band information and to remove interband redundancy, respectively. As a result, spectral unmixing can be performed progressively by selecting different bands for various endmembers, a task that the traditional BS cannot accomplish. The effectiveness and advantages of using PBS over BS are also demonstrated by experiments.
In spatially periodic Hermitian systems, such as electronic systems in crystals, the band structure is described by the band theory in terms of the Bloch wave functions, which reproduce energy levels ...for large systems with open boundaries. In this paper, we establish a generalized Bloch band theory in one-dimensional spatially periodic tight-binding models. We show how to define the Brillouin zone in non-Hermitian systems. From this Brillouin zone, one can calculate continuum bands, which reproduce the band structure in an open chain. As an example, we apply our theory to the non-Hermitian Su-Schrieffer-Heeger model. We also show the bulk-edge correspondence between the winding number and existence of the topological edge states.
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