Narrow Stopband Research Articles

Multi-functional metasurface as a transmissive/reflective FSS and an on-air frequency mixer

In this paper, a multi-functional metasurface is proposed, which can work as a narrowband transmissive/reflective frequency selective surface (FSS) and an on-air frequency mixer based on its switching response. The metasurface is made up of unit cells with square and circular metallic loops connected by PIN diodes controlled by a bias source. In contrast to typical wideband FSSs, the structure provides 0.55 GHz of narrow stopband (a fractional bandwidth of 22%) at 2 GHz in the OFF state bias. The bandstop response can be adjusted by varying the reverse bias voltage. The metasurface alternates between its functionalities when in forward bias by providing a passband at the operational frequency. The structure is compact and operates as a transmissive/reflective surface under two different bias conditions (ON and OFF). The design is angularly stable and polarization-insensitive for both TE and TM polarisation. A prototype of the designed structure is developed and the measured results correlate well with the simulated responses from the finite-difference time-domain (FDTD) method-based simulation of the circuit model. On-air frequency mixing for a wave propagating through the metasurface is demonstrated and the effects of different parameters affecting the mixing are parametrically studied through FDTD simulations and experiments.

A new technique for improving performance of conventional CRLH resonators using IDC/UISs with enhanced harmonic suppression in balanced dual-band BPFs

Abstract The design of balanced filters based on composite right/left hand (CRLH) structure is well developed. Among those, few designs exist which although they provide some good responses, suffer from narrow stopbands and interdependent passbands. This paper proposes a new technique for improving the characteristics of dual-band balanced bandpass filters (B-BPFs) based on planar CRLH. Using unequal inductive stubs (UISs) attached to the interdigital capacitor (IDC) unit cell, we were able to achieve outstanding harmonic suppression and passband controllability. This structure offers higher degrees of freedom compared to conventional designs and provides better control over the filter specifications. Mathematical modeling, analysis, simulation, fabrication, and performance measurement of the proposed technique in a dual-band B-BPF are also provided. Our work resulted in an independent and controllable dual-band B-BPF with ultra-wide upper differential-mode (DM) stopband of 5.9f 1 and common-mode (CM) suppression of 40.4 and 32.6 dB for the first and second bands, respectively.

A Wide Stopband Dual-notched Bands UWB Filter Based on A Novel Composite Right/left Handed Transmission Line

Background:: As one of the key components of ultra-wideband (UWB) system, UWB filter has important research significance. However, the current UWB filter still has the problem of a narrow stopband and cannot suppress the interference signals in the passband Objective:: In this paper, a novel UWB bandpass filter is proposed, which has wide stopband characteristics and good out-of-band rejection performance and implements a notch function for the WLAN band and the X satellite communication band in the passband to improve the antiinterference performance. Method:: The filter adopts a novel composite right/left handed transmission line (CRLH-TL) structure to realize the passband characteristics with low insertion loss (< 0.8dB). The anticoupled line structures generate two transmission zeros (TZs) in the upper stopband, which improves the upper stopband performance of the filter. The short circuit step impedance resonators (SIRs) and the asymmetric coupling structure generate a notched band in the passband respectively. Results:: The simulated and measured results show that the 3dB passband range is 3.4-11.0 GHz, the out-of-band rejection is more than 20 dB in the stopband range of 12.8-28 GHz, and the dualnotched bands are located at 5.86 GHz and 8.0 GHz respectively. The measured results are basically consistent with the simulated results. Conclusion:: Compared with the existing filters, the proposed filter has outstanding advantages and has a wide range of application prospects in the field of indoor UWB positioning system.

A thin-walled cavity structure with double-layer tapered scatterer locally resonant metamaterial plates for extreme low-frequency attenuation

Locally resonant acoustic metamaterials (LRAMs) are effective spatial frequency filters due to their local resonance system. However, they own narrow stopbands, charge additional weight on the primary system, and operate only at the adjusted frequency range. In this paper, a novel dual-target LRAM is proposed based on coupling the cavity and convex mechanisms, utilizing the benefits of both sound-barrier and sound-absorbing types of acoustic metamaterials. A combination of the cavity and convex structures is presented and investigated for the first time, which exploits both the reflection and absorption theories simultaneously to improve the sound attenuation performance of acoustic metamaterials. By arranging two-layer finite periodic of 5×5 proposed convex unit cells along x and y directions and separating them by an air cavity, a supercell named hybrid locally resonant acoustic metamaterials (HLRAM) baffle is designed. The band structures, transmission spectrum, and displacement vector fields are calculated employing the finite element method (FEM). In addition, vibration modes at the edges of stopbands are computed and carefully analyzed to determine the formation mechanism, mechanics/dynamic response, and dispersion features of stopbands. Meanwhile, sensitivity analyses have been conducted on the model to investigate the influence of material and geometry parameters on dispersion characteristics. Equivalent spring-mass analytic models are used to direct the modifications of structure and the adjustment of structural and material parameters in order to achieve a wide stopband with a low opening frequency. Thereby, the effective stiffness and mass values influencing the starting and cutoff frequencies are adjusted in a desirable manner. The results show that the structure can generate a wide stopband that covers the frequency range of 64.9-805.6Hz, allowing the structure to block incoming acoustic waves with 35.42dB root mean square of noise attenuation (RMSNA) the given frequency range (0-1kHz). This study indicates that the HLRAM has a preponderance among conventional techniques as we can manipulate dispersion characteristics and the sound transmission loss (STL) based on the desired sound reduction level and shift stopbands to the intended frequency range. This can be achieved by altering cavity size, material, or geometry parameters.

Design and analysis of quasi‐lumped notch filter with extended upper pass band

AbstractThis paper presents a hybrid technique‐based compact narrow band stop filter design for broadband applications. It provides the rejection of 60 dB at the centre frequency of 2.25 GHz without any stop band harmonics over the required frequency band of operation, i.e. 1–10 GHz. This filter is highly appropriated for the rejection of undesired bands for RADAR, electronic warfare, and military communications.

Tailoring Tamm Plasmon Resonances in Dielectric Nanoporous Photonic Crystals.

The fields of plasmonics and photonic crystals (PCs) have been combined to generate model light-confining Tamm plasmon (TMM) cavities. This approach effectively overcomes the intrinsic limit of diffraction faced by dielectric cavities and mitigates losses associated with the inherent properties of plasmonic materials. In this study, nanoporous anodic alumina PCs, produced by two-step sinusoidal pulse anodization, are used as a model dielectric platform to establish the methodology for tailoring light confinement through TMM resonances. These model dielectric mirrors feature highly organized nanopores and narrow bandwidth photonic stopbands (PSBs) across different positions of the spectrum. Different types of metallic films (gold, silver, and aluminum) were coated on the top of these model dielectric mirrors. By structuring the features of the plasmonic and photonic components of these hybrid structures, the characteristics of TMM resonances were studied to elucidate effective approaches to optimize the light-confining capability of this hybrid TMM model system. Our findings indicate that the coupling of photonic and plasmonic modes is maximized when the PSB of the model dielectric mirror is broad and located within the midvisible region. It was also found that thicker metal films enhance the quality of the confined light. Gas sensing experiments were performed on optimized TMM systems, and their sensitivity was assessed in real time to demonstrate their applicability. Ag films provide superior performance in achieving the highest sensitivity (S = 0.038 ± 0.001 nm ppm-1) based on specific binding interactions between thiol-containing molecules and metal films.

A dual‐band complementary frequency selective surface combining structures that provides narrow and wide stop‐band frequency responses

AbstractIn this paper, we proposed a dual‐band complementary frequency selective surface (CFSS) with narrow stop band and large stop band. The proposed CFSS combines two simple geometries, the square loop with grid and the crossed dipole. The resonant frequencies are 2.53 and 5.38 GHz. The bandwidths of 280 MHz and 1.77 GHz were obtained, at –10 dB level, for the first and second bands, respectively. These frequencies and bands show that the structure can be applied in Wi‐Fi (2.4–2.5 GHz) and C‐band (4–6 GHz) frequencies. The simulated and measured results show that the chosen geometry has angular stability and polarization independence up to 45°. We can observe a good agreement between simulated and measured results.

A Metamaterial-Based Cross-Polarization Converter Characterized by Wideband and High Efficiency

Metamaterial-based polarization converters, which have all kinds of polarizations realizable via adjusting metamaterial parameters, have been springing up at an increasing rate. However, the reported metamaterial-based polarization converters suffer from either limited bandwidth or low polarization conversion ratios. In this study, a metamaterial-based polarization converter consisting of multilayer copper split-ring resonators and a copper ground separated by dielectrics was demonstrated and was characterized by the cross-polarization with wideband and high-efficiency. For normal incidence, the simulated results illustrated that the expanded bandwidth benefited from the superposition of cross-polarization electromagnetic resonances around 2.78, 3.09, 3.68, and 4.54 GHz, and the polarization conversion ratio was higher than 99% in the frequency range of 2.73 and 4.63 GHz. For oblique incidence, the design can provide larger angle tolerance in the investigated band, except for a very narrow stopband. Moreover, the experimental results agreed well with the simulations, which verified the reliability of the performance.

Modeling of surface grating-loaded VCSEL with slowing light

We propose single-mode vertical cavity surface-emitting lasers (VCSEL) based on the surface grating with various cavity lengths ranging from 10 μm to 1 cm. We present the modeling of surface grating-loaded VCSEL based on the coupled-mode theory with slowing light. Thanks to the low effective index caused by the slow-wave propagation, a shallow surface grating of a few tens nm provides large optical feedback. A narrow stop band in the surface grating-loaded VCSEL waveguide appears because of the large waveguide dispersion of slow-waves. The numerical results on coupling coefficient, mode selectivity and threshold gain are given for single-mode, long-cavity and short-cavity grating-loaded VCSELs with different grating parameters. A wide range of grating coupling strength enables a short cavity of 10 μm and a long cavity of 1 cm with a single-mode operation. The proposed VCSEL structure may open up new VCSEL platforms for low-power consumption and high-power applications.

Electromagnetically induced transparency, narrow absorption and transient response in a three-photon excitation process

The probe absorption characteristic of a four-level ladder-type system, in presence of two strong coherent radiation fields, is investigated analytically by following the density operator method. The parameters of 85Rb 5S1/2→5P3/2→5D5/2→63P3/2 transition are used in the simulation. In addition to the control field acting between the first excited state and the second excited state, if a switching field is applied to couple the second excited state to a Rydberg state, two-photon electromagnetically induced transparency (EIT) is converted into double EIT (DEIT) window having a strong central absorption peak. In a thermal vapor, the double EIT window is transformed into three transparency windows depending on the values of the control and switching Rabi frequencies. These multiple transparency windows vanish for certain combinations of the Rabi frequencies of the control and switching fields and the probe absorption is enhanced. It is also demonstrated how a very narrow optical band stop filter can be conceptualized by using three-photon excitation scheme. The transient optical response of the medium under three-photon transition is also investigated under both Doppler free and Doppler broadened conditions.

Mid-infrared spectral reconstruction with dielectric metasurfaces and dictionary learning.

Mid-infrared (MIR) spectroscopy has numerous industrial applications and is usually performed with Fourier-transform infrared (FTIR) spectrometers. While these work well for many purposes, there is currently much interest in alternative approaches that are smaller and lighter, i.e., MIR microspectrometers. Here we investigate all-dielectric metasurfaces as spectral filters for MIR microspectrometers. Two metasurface types are studied. For the first, we design, fabricate, and test a metasurface with a narrow and angularly tunable transmission stop band. We use it to reconstruct the transmission spectra of various materials. The second metasurface, investigated theoretically, possesses narrow passband features via symmetry-protected bound states in the continuum.

An Approach to Successful Power-line Interference Suppression in ECG Signals

The ECG signals acquisition is usually corrupted by presence of Power-Line Interference (PLI) induced by the electromagnetic field around us. Many methods for PLI suppression/elimination have been developed over the years. The easy to apply traditional notch filters suppress unacceptably the ECG spectrum around the rated PL frequencies of 50 or 60 Hz and their deviations, which are restricted by the standards within the range of ± 0.5 Hz. The changes are very slow but the current PL frequency has to be continuously checked to allow start and performance of adequate PLI suppression during any ECG recordings including the 24 hours Holter monitoring. According to the proposed approach, the corrupted ECG recording is bi-directional band-pass (BP) filtered. The resulting sinusoidal BP waves differ in amplitude from the PLI but their zero crossing points remain identical. The two out-sample distances located at both ends of each current sinusoidal curve are calculated and aided to the inter-sample distances. The obtained fractal wave period is converted into current PL frequency and used for bi-directional notch filtration with narrow stop-band. The results obtained demonstrate a very successful PLI suppression in ECG signals. The errors committed are within a few μV, except for the edges of the recordings due to the transition processes.

A Compact Wide Stopband Band Pass SIW Filter For K-Band Applications

Direct coupled filters have narrow stopband due to higher order modes passband. A compact dual layer band pass filter is proposed with wide stop band. The proposed filter provides the return loss of 16.87db and insertion loss of 2.5dB at the passband frequency 20.9 GHz. The filter size is half of the conventional direct coupled filters. The stop band covers up to 40 GHz with insertion loss below 35dB. The filter has no slot which makes it immune to the EMI/EMC problems.

Design and analysis of UWB antenna with quintuple band-notched and wide-band rejection characteristics

AbstractIn this study, a compact ultra-wideband (UWB) antenna with quintuple band-notched and wide-band rejection characteristics is studied. The proposed antenna mainly consists of a rectangular radiating patch, a microstrip feeding line, and a modified rectangular ground plane. The quintuple band-notched functions with narrow stop bands are achieved at WiMAX (3.3–3.7 GHz), WLAN (5.15–5.35 GHz and 5.725–5.825 GHz), C-band IEEE INSAT/super-extended (6.7–7.1 GHz) by using three modified inverted U-shaped slots and two symmetrical rectangular slots on the radiating path. Each stop band formed in the UWB antenna can be adjusted independently, and deep reflection zeros are formed between the adjacent stop bands. The formation of reflection zeros improves the band-edge selectivity of the stop band, and the notch characteristics are more prominent. To further study the wide stop band (C-band and X-band) with good selectivity characteristics, a pair of L-shaped open slot is added to the edges of two rectangular slots. Additionally, a pair of modified Rho-shaped resonators is located near the feeding line to realize band-notched characteristic at ITU service bands (8.025–8.4 GHz), thus a quintuple band-notched UWB antenna is achieved. The shape factor (ratio of the −3 dB bandwidth to the −10 dB bandwidth) of the wide stop band is 0.56, which indicates that the antenna has excellent band-edge selectivity. To verify the performance of the proposed design, both the time-domain and the frequency-domain characteristics of the antenna have been studied and analyzed. The simulated and measured results verify the design as a good candidate for various portable UWB applications.

Theory and design of narrowband band-stop filters using slotted ground resonators

This paper reports the demonstration of design and implementation of narrow band band-stop filters using slotted ground resonators. Using coupled-mode resonator theory, the systematic implementation of BSFs are performed to achieve narrow stopband (<25% FBW) with desired stopband isolation. By exchanging the band-pass transfer function polynomials, the BSF design has become straight-forward with these band-stop resonators. Designed and optimized BSFs are fabricated, characterized and analysed as a detailed report. Slotted ground resonators yield compact and scalable BSFs which are potential alternatives for the development of future microwave systems.

Band gap manipulation on P-wave propagating in functionally graded phononic crystal by periodical thermal field

Phononic crystals and acoustic metamaterials have attracted many researchers by reason of unconventional acoustic behaviors which can be applied to achieve wave propagation control. To enhance the application value of acoustic behaviors, period structures with adaptive control ability have been an investigation focus. In the present paper, an innovative manipulation method based on inhomogeneous and periodic thermal field for longitudinal wave (P-wave) band gap control is proposed and investigated. A three-dimensional solid model, consist of homogeneous thermal sensitive material, can be transferred into functionally graded phononic crystals by a series of metallic films which are periodically embedded in structure and play the role of heat sources. Based on laminated model and transfer matrix method, propagation characteristics of both normal incident and oblique incident P-wave in functionally graded crystals are investigated. Numerical band structure results from analytical method, validated by simulation result via COMSOL Multiphysics software and transmission spectra result, reveal that period thermal field owns the ability to affectively tune the band gap properties including band width and band gap location. Also, transmission spectra result indicates that the attenuation of wave propagation may be inconspicuous even there exists obvious but relatively narrow stop band gaps. The present research proposes a band gap tuning method on P-wave according to the application of period thermal field and may lay theoretical and simulation foundation for designing and fabrication of tunable vibration isolators and acoustic filters.

Filtering line waves at the impedance-interface using metamaterials in the millimeter-wave band

Edge waves have been one of the hot spots of research in electromagnetic fields in recent years. They exist between different interfaces such as impedance interfaces which are capacitive and inductive. Different kinds of edge wave components have been invented, including transmission lines, antennas and splitters. In this work, we design an impedance interface waveguide using metamaterial unit cells. The dispersion properties of the unit cells and the impedance interface are investigated. A Vivaldi antenna is used as the transition section between the traditional microstrip line and the impedance interface waveguide to convert the transverse electromagnetic mode to edge waves. We use split ring resonators to design different filters with narrow and broad stopbands. The filters are fabricated and measured, and are consistent with simulation results. The filters have good transmission and filtering properties at high frequency. The proposed mode-matching technique and component integration method will be helpful for the development of diverse microwave components.

All-Optical Graphene Oxide Modulator Based on Phase-Shifted FBG

An all-optical graphene oxide modulator based on phase-shifted FBG is proposed and experimentally proved to overcome the electronic bottleneck. The phase-shifted FBG is formed by tapering and the surface of nanofiber is covered with graphene oxide film to adjust the phase-shift. In order to reduce the complexity of production and improve the practicability, graphene oxide aqueous solution is used to produce the film on the surface of nanofiber. Experimental results show that the graphene oxide can obtain different phase shifts in phase-shifted FBG by changing the pump intensity. The extinction ratio of the proposed modulator can reach up to 1.1 dB. Besides, the experimental result of transmission spectrum is consistent with the simulated result. With its narrow band-stop characteristics, multiple modulators can be cascaded to achieve the wavelength division, which takes full advantage of low-loss. Due to the ultra-fast and broadband response of graphene, the theoretical rate of the modulator can reach 200 GHz. Therefore, the modulator has broad applications in ultra-high-speed all-optical networks.

A 14-Pole Dual-Band High Temperature Superconducting Filter Including Narrow Bandstop Notches

A 14-Pole Dual-Band High Temperature Superconducting Filter Including Narrow Bandstop Notches

High-Gain On-Chip Antenna Design on Silicon Layer With Aperture Excitation for Terahertz Applications

This letter investigates the feasibility of designing a high gain on-chip antenna on silicon technology for subterahertz applications over a wide-frequency range. High gain is achieved by exciting the antenna using an aperture fed mechanism to couple electromagnetics energy from a metal slot line, which is sandwiched between the silicon and polycarbonate substrates, to a 15-element array comprising circular and rectangular radiation patches fabricated on the top surface of the polycarbonate layer. An open ended microstrip line, which is orthogonal to the metal slot-line, is implemented on the underside of the silicon substrate. When the open ended microstrip line is excited it couples the signal to the metal slot-line which is subsequently coupled and radiated by the patch array. Measured results show the proposed on-chip antenna exhibits a reflection coefficient of less than −10 dB across 0.290–0.316 THz with a highest gain and radiation efficiency of 11.71 dBi and 70.8%, respectively, occurred at 0.3 THz. The antenna has a narrow stopband between 0.292 and 0.294 THz. The physical size of the presented subterahertz on-chip antenna is 20 × 3.5 × 0.126 mm3.