Complete Band Research Articles

Complex band structure of two-dimensional thermal wave crystals

We investigate the complex band structure of temperature oscillations in a two-dimensional thermal wave crystal. We use the Cattaneo-Vernotte heat model to describe the thermal properties. We apply the plane wave method to calculate the complex band structure of a square lattice composed of an infinite array of square bars. We find that a complete band gap exists across the whole Brillouin zone, where temperature oscillations are forbidden. This has potential applications in thermal management, thermal cloaking, and other areas.

Design of a high-gain, low-ECC 2x2 MIMO antenna for 28 GHz 5G wireless communication system

In this paper, a 2 × 2 MIMO antenna with inset feed is designed for the frequency Range 2 (FR2) millimeter wave frequencies such as n257 (26-29.5 GHz), n258 (24.25-27.5 GHz), and n261 (27.5-28.35 GHz). The MIMO antenna is designed and fabricated using low loss Rogers RT/duroid 5880 substrate having dimension of 1.4λ 0×2.8λ 0×0.073λ 0, where λ 0 is the free-space wavelength operating at 28 GHz.The defected ground structure (DGS) minimized the surface waves current. Thus DGS are used to increased the gain and the isolation of the proposed MIMO antenna design. The gain of the MIMO antenna reported is 10.3 dBi with 97.01% radiation efficiency at 28 GHz resonant frequency. The -10 dB impedance bandwidth lies between 26.95-29.50 GHz, which covers the 5G frequency bands. The isolation is ≥28 dB and envelope correlation coefficient (ECC) is 10 −5, respectively, in the complete operating band.

Designed honeycomb lattice for improving vibration control

Honeycombs represent common cellular structures characterised by two-dimensional arrays of unit cells arranged in-plane and stacked parallelly in the out-of-plane direction, exhibiting a periodic structure. Due to the interconnected network of these unit cells, honeycombs possess higher porosity and lower mass density than their matrix materials, resulting in superior specific stiffness/strength and specific energy absorption. The arrangement of repeating unit cells profoundly impacts the mechanical properties of these lightweight materials. This study explores a 2D metamaterial cellular system inspired by the lightweight characteristics of honeycombs. In this system, squared honeycomb cells with additional lumped masses can influence vibrating modes. Unlike conventional methods employing discrete mass-spring resonators, this approach intentionally adds masses to create complete or incomplete stop bands wherein wave propagation is either wholly or partially suppressed along specific directions. The dispersion curves of wave bands and the sensitivity of bandgaps concerning design parameters are estimated using the finite element method and Block's theorem. Numerical simulations demonstrate the stop band behaviour, providing insights for optimisation strategies and a deeper comprehension of these remarkable cellular material systems and improvements in the design with enhanced vibro-acoustics performance and control.

A three-dimensional rubber-steel phononic crystal for broad and low-frequency vibration attenuation

Elastic metamaterials and phononic crystals have the potential for vibration isolation applications due to wave band gaps where elastic waves cannot propagate. However, their real-life application may be compromised by the narrow band gaps of the former and the high frequencies of the latter. In the current study, we present a three-dimensional frame structure made of steel and rubber elements that presents a wide complete band bag at low frequency. The structure provides extreme vibration isolation because it combines band gaps with high impedance mismatch between steel and rubber damping. The manufacturing process of the proposed frame structure is widely used in mounting pads, and its cost is relatively low. It provides reasonable structural strength, which makes its application in real life possible. The dynamic behavior predicted with spectral and finite element models is validated with experimental results.

Composite metastructure with tunable ultra-wide low-frequency three-dimensional band gaps for vibration and noise control

Low-frequency vibration and noise control present enduring engineering challenges that garner extensive research attention. Despite numerous active and passive control solutions, achieving multiple ultra-wide attenuation regions remains elusive. Addressing vibration and noise control across a multidirectional broad low-frequency spectrum, three-dimensional metastructures have emerged as innovative solutions. This study introduces a novel three-dimensional composite metastructure featuring multiple ultra-wide three-dimensional complete band gaps. The research emphasizes the design strategy of elastic ligaments to achieve multiple ultra-wide attenuation regions spanning from 0.7 to 40 kHz. The band structures are elucidated through modal analysis and further substantiated by an analytical model based on a spring-mass chain with an additional resonator. The underlying physical mechanism for the formation of multiple ultra-wide band gaps is revealed through novel vibration modes from finite element analyses. Furthermore, we demonstrate that the distribution and the relative width of the ultra-wide band gaps can be tuned by modifying the geometric parameters of the metastructure. Utilizing additive manufacturing, prototypes are fabricated, and low-amplitude vibration tests are conducted to evaluate real-time vibration attenuation properties. Consistency is observed among theoretical, numerical, and experimental results. The proposed structure shows significant potential for high-performance meta-devices aimed at controlling noise and vibration across an extremely wide low-frequency spectrum.

Durability of annuloplasty in patients with atrial functional mitral regurgitation associated with atrial fibrillation

ObjectiveTo determine the durability of mitral valve repair (MVr) with complete ring or flexible band annuloplasty in patients with atrial functional mitral regurgitation (AFMR) due to atrial fibrillation (AF) and identify risk factors associated with postoperative recurrence of mitral regurgitation. MethodsBetween January 1, 2000, and January 1, 2023, 194 adults with a history of AF underwent MVr with annuloplasty alone for moderate/severe AFMR. Exclusion criteria were prior cardiac surgery, additional repair techniques, ejection fraction <45%, ischemic heart disease, aortic valve disease, mitral annular calcification, and concomitant procedures other than surgical ablation or tricuspid repair/replacement. The durability of annuloplasty was assessed using longitudinal analysis of postoperative echocardiographic data. ResultsComplete ring annuloplasty was performed in 126 of 194 patients (65%); partial ring (posterior band) in the other 68 (35%). Concomitantly, 124 of the 194 patients underwent tricuspid valve surgery, and 173 (89%) had a procedure for AF, including biatrial Cox-Maze III/IV lesion set in 152 (88%) and pulmonary vein isolation in 21 (12%). All patients were discharged with no/trace MR. Freedom from moderate/severe MR after repair with annuloplasty alone was 89% at 10 years, and no significant differences were noted between complete and partial ring annuloplasty (early, P = .41; late, P = .92). Forty-eight percent of patients developed AF at 3 months or longer after surgery, and the presence of postoperative AF was not associated with a greater likelihood of recurrence of MR (P = .15). Freedom from mitral reintervention was 96% at 10 years. ConclusionsIn appropriate patients with AFMR, the long-term durability of annuloplasty is excellent with complete ring and posterior band annuloplasty techniques.

Observation of photonic chiral edge states in penrose quasicrystals

Photonic chiral edge states with one-way propagation and robust topological protection are hallmark features of photonic Chern insulators. To date, photonic chiral edge states have been observed in two-dimensional (2D) periodic and amorphous gyromagnetic photonic crystals. Recent theoretical studies reveal that photonic chiral edge states can also exist in 2D Penrose quasicrystals with long-range order but lack translational symmetry. Here, we report the first experimental observation of photonic chiral edge states in a 2D Penrose-tiled gyromagnetic photonic quasicrystal. By using microwave measurements, we observe a complete photonic band gap in the Penrose photonic quasicrystal despite the absence of bulk Bloch bands in momentum space. Moreover, we directly observe unidirectional backscattering-immune photonic chiral edge states within the photonic bandgap of the 2D Penrose quasicrystal. These results broaden our understanding of photonic chiral edge states and provide a new platform for exploring the intriguing properties of topological photonic quasicrystals.

Identifying epileptogenic abnormality by decomposing intracranial EEG and MEG power spectra

BackgroundAccurate identification of abnormal electroencephalographic (EEG) activity is pivotal for diagnosing and treating epilepsy. Recent studies indicate that decomposing brain activity into periodic (oscillatory) and aperiodic (trend across all frequencies) components can illuminate the drivers of spectral activity changes. New methodsWe analysed intracranial EEG (iEEG) data from 234 subjects, creating a normative map. This map was compared to a cohort of 63 patients with refractory focal epilepsy under consideration for neurosurgery. The normative map was computed using three approaches: (i) relative complete band power, (ii) relative band power with the aperiodic component removed, and (iii) the aperiodic exponent. Abnormalities were calculated for each approach in the patient cohort. We evaluated the spatial profiles, assessed their ability to localize abnormalities, and replicated the findings using magnetoencephalography (MEG). ResultsNormative maps of relative complete band power and relative periodic band power exhibited similar spatial profiles, while the aperiodic normative map revealed higher exponent values in the temporal lobe. Abnormalities estimated through complete band power effectively distinguished between good and bad outcome patients. Combining periodic and aperiodic abnormalities enhanced performance, like the complete band power approach. Comparison with existing methods and conclusionsSparing cerebral tissue with abnormalities in both periodic and aperiodic activity may result in poor surgical outcomes. Both periodic and aperiodic components do not carry sufficient information in isolation. The relative complete band power solution proved to be the most reliable method for this purpose. Future studies could investigate how cerebral location or pathology influences periodic or aperiodic abnormalities.

A study on poly(indene)

Indene was polymerized to polyindene (PI) through a cationic mechanism using TiCl4•2THF complex as initiator. The cationic mechanism was investigated through electronic absorption spectroscopy and either the indanyl cation as well as the polyindenyl cation absorption bands were distinguished and assigned. The PI structure was investigated through the indane model compound and the indene reference compound electronic absorption spectra. Furthermore, the Raman spectrum of PI was recorded for the first time and the complete Raman and FT-IR absorption bands of PI are reported with the assignment of the main bands. The glass transition (Tg) of cationic, radiation-induced and thermally initiated PI were measured through DSC and the corresponding molecular weight estimated. DSC and TGA-FTIR analysis were used to study the thermal decomposition of PI. It was assessed that PI is pyrolyzed back into indene monomer in almost theoretical yield with an activation enthalpy of E# = 164 kJ/mol while the decomposition enthalpy of PI was determined at 101.6 kJ/mol a value very close to the theoretical value of 108.9 kJ/mol. It was assessed that PI is a fully recyclable polymer which could be decomposed back to the monomer and re-polymerized at will.

Complete zero-energy flat bands of surface states in fully gapped chiral noncentrosymmetric superconductors

Complete zero-energy flat bands of surface states in fully gapped chiral noncentrosymmetric superconductors

Nacre-like block lattice metamaterials with targeted phononic band gap and mechanical properties

The extraordinary quasi-static mechanical properties of nacre-like composite metamaterials, such as high specific strength, stiffness, and toughness, are due to the periodic arrangement of two distinct phases in a “brick and mortar” structure. It is also theorized that the hierarchical periodic structure of nacre structures can provide wider band gaps at different frequency scales. However, the function of hierarchy in the dynamic behavior of metamaterials is largely unknown, and most current investigations are focused on a single objective and specialized applications. Nature, on the other hand, appears to develop systems that represent a trade-off between multiple objectives, such as stiffness, fatigue resistance, and wave attenuation. Given the wide range of design options available to these systems, a multidisciplinary strategy combining diverse objectives may be a useful opportunity provided by bioinspired artificial systems. This paper describes a class of hierarchically-architected block lattice metamaterials with simultaneous wave filtering and enhanced mechanical properties, using deep learning based on artificial neural networks (ANN), to overcome the shortcomings of traditional design methods for forward prediction, parameter design, and topology design of block lattice metamaterial. Our approach uses ANN to efficiently describe the complicated interactions between nacre geometry and its attributes, and then use the Bayesian optimization technique to determine the optimal geometry constants that match the given fitness requirements. We numerically demonstrate that complete band gaps, that is attributed to the coupling effects of local resonances and Bragg scattering, exist. The coupling effects are naturally influenced by the topological arrangements of the continuous structures and the mechanical characteristics of the component phases. We also demonstrate how we can tune the frequency of the complete band gap by modifying the geometrical configurations and volume fraction distribution of the metamaterials. This research contributes to the development of mechanically robust block lattice metamaterials and lenses capable of controlling acoustic and elastic waves in hostile settings.

Gaussian-process-regression-based method for the localization of exceptional points in complex resonance spectra

Resonances in open quantum systems depending on at least two controllable parameters can show the phenomenon of exceptional points (EPs), where not only the eigenvalues but also the eigenvectors of two or more resonances coalesce. Their exact localization in the parameter space is challenging, in particular in systems, where the computation of the quantum spectra and resonances is numerically very expensive. We introduce an efficient machine learning algorithm to find EPs based on Gaussian process regression (GPR). The GPR-model is trained with an initial set of eigenvalue pairs belonging to an EP and used for a first estimation of the EP position via a numerically cheap root search. The estimate is then improved iteratively by adding selected exact eigenvalue pairs as training points to the GPR-model. The GPR-based method is developed and tested on a simple low-dimensional matrix model and then applied to a challenging real physical system, viz., the localization of EPs in the resonance spectra of excitons in cuprous oxide in external electric and magnetic fields. The precise computation of EPs, by taking into account the complete valence band structure and central-cell corrections of the crystal, can be the basis for the experimental observation of EPs in this system.

Terahertz MIMO antenna array for future generation of wireless applications

Abstract The paper proposes a high gain, low ECC, and high isolation THz MIMO antenna array for future generation wireless applications to accommodate a growing population of mobile users. A THz MIMO antenna array is designed with dimensions of 1200 × 2200 × 191.29 µm3. It employs the array of double-slit complementary split-ring resonators (D-CSRRs) on the bottom layer to improve the gain, return loss, and isolation. The gain of the proposed antenna array is 11.3 dBi with 66.45 % radiating efficiency at 0.65 THz. The −10 dB impedance bandwidth lies from 0.62–0.66 THz. The parameters of the MIMO antenna are evaluated such as isolation, envelope correlation coefficient (ECC), diversity gain (DG), and channel capacity loss. The ECC and DG value observed are 2.84 × 10−6 and 9.98 dB, respectively, at 0.65 THz. The channel capacity loss and isolation of the proposed MIMO antenna array are below 0.4 bps/Hz and (|S 21| &gt; 25 dB), respectively, in the complete operating band. The suggested THz MIMO antenna array can be utilised for THz high-speed wireless communication, video-rate imaging systems, sensing, the medical field for cancer imaging, security scanning, and the detection of illicit goods.

Function phononic crystals

We propose a novel type of phononic crystal for which the materials parameters are continuous functions of space coordinates without discontinuities corresponding to a seamless fusion of the constituent materials within the crystal lattice. With the help of an adaptation of this fundamental approach, we extend the well-established concept of phononic crystals, allowing an investigation of the transition from conventional phononic crystals with a regulated step-like parameter function to the realm of so-called function phononic crystals. Our study is based on a first-principle theory assisted by high-performance computer simulations and focuses on an understanding of the effects of a deviation from the typical parameter step function on the phononic density of states (DOS). Our exploration of the DOS reveals a characteristic rapid convergence: even a slight deviation from an ideal step function has the potential to induce radical changes in the band structure leading to the emergence of desirable features, especially multiple complete phononic band gaps.

Quality Factor Improvement of a Thin-Film Piezoelectric-on-Silicon Resonator Using a Radial Alternating Material Phononic Crystal.

This paper studies the radial alternating material phononic crystal (RAM-PnC). By simulating the band gap structure of the phononic crystal, a complete acoustic band gap was verified at the resonant frequency of 175.14 MHz, which can prevent the propagation of elastic waves in a specific direction. The proposed alternately arranged radial phononic crystal structure is applied to the thin-film piezoelectric-on-silicon (TPOS) MEMS resonator. The finite element simulation method increases the anchor quality factor (Qanchor) from 60,596 to 659,536,011 at the operating frequency of 175.14 MHz, which is about 10,000 times higher. The motion resistance of the RAM-PnC resonator is reduced from 156.25 Ω to 48.31 Ω compared with the traditional resonator. At the same time, the insertion loss of the RAM-PnC resonator is reduced by 1.1 dB compared with the traditional resonator.

Experimental evidence of isotropic transparency and complete band gap formation for ultrasound propagation in stealthy hyperuniform media.

Following on recent experimental characterization of the transport properties of stealthy hyperuniform media for electromagnetic and acoustic waves, we report here measurements at ultrasonic frequencies of the multiple scattering of waves by 2D hyperuniform distributions of steel rods immersed in water. The transparency, for which the effective attenuation of the medium is canceled, is first evidenced by measuring the transmission of a plane wave propagating in a highly correlated and relatively dense medium. It is shown that a band gap occurs in the vicinity of the first Bragg frequency. The isotropy of both transparency and band gap are also evidenced for the case of waves generated by a point source in differently ordered and circular-shaped distributions. In other words, we thus obtain a representation of the Green's function. Our results demonstrate the huge potential of hyperuniform, as well as highly correlated, media for the design of functional materials.

Multi-band topological valley modes of flexural waves in micro-perforated phononic plates

To develop phononic topological insulators (PTIs) with time reversal invariance, phononic crystals (PCs) are elaborately configurated to ensure the lattice symmetry and meanwhile to open the complete band gap. Particularly, a multi-band PTI requires more complex architecture than its single-band counterpart, leading to extra difficulty in implementation and poor manufacturability of PCs. Here, we present a straightforward and generic design strategy, to realize multi-band PTIs in micro-perforated phononic plates. Rather than using complex surface-mounted or embedded scatterers, the novel phononic plate is micro-perforated with a type of fan-shaped split-ring resonators (SRRs), the multi-modal resonances of which under constrained lattice symmetry induce multiple Dirac degeneracies in flexural-wave dispersions at different frequency scales. The multi-band topological phase transitions are observed, and triple topological band gaps are caused when rotating micro-perforated slots properly. Experimental results agree well with numerical simulation results, both demonstrating triband valley edge-state propagation of flexural waves. In addition, we also prove that the developed valley PTIs enable the second-order corner modes of flexural waves within the corresponding topological band gaps. Parametric studies further reveal that the emergence of the valley-shaped Dirac degeneracy bands in the developed PTI is insensitive to the plate thickness and slots parameters, and more than three Dirac cones exist in flexural-wave dispersions. The developed micro-perforated plates with SRRs provides a convenient platform for enabling multi-band PTIs with various symmetries, facilitating applications of multi-frequency topological effects of elastic waves in a cost-effective way.

Controlling Thermal Radiation in Photonic Quasicrystals Containing Epsilon-Negative Metamaterials

The transfer matrix approach is used to study the optical characteristics of thermal radiation in a one-dimensional photonic crystal (1DPC) with metamaterial. In this method, every layer within the multilayer structure is associated with its specific transfer matrix. Subsequently, it links the incident beam to the next layer from the previous layer. The proposed structure is composed of three types of materials, namely InSb, ZrO2, and Teflon, and one type of epsilon-negative (ENG) metamaterial and is organized in accordance with the laws of sequencing. The semiconductor InSb has the capability to adjust bandgaps by utilizing its thermally responsive permittivity, allowing for tunability with temperature changes, while the metamaterial modifies the bandgaps according to its negative permittivity. Using quasi-periodic shows that, in contrast to employing absolute periodic arrangements, it produces more diverse results in modifying the structure’s band-gaps. Using a new sequence arrangement mixed-quasi-periodic (MQP) structure, which is a combination of two quasi periodic structures, provides more freedom of action for modifying the properties of the medium than periodic arrangements do. The ability to control thermal radiation is crucial in a range of optical applications since it is frequently unpolarized and incoherent in both space and time. These configurations allow for the suppression and emission of thermal radiation in a certain frequency range due to their fundamental nature as photonic band-gaps (PBGs). So, we are able to control the thermal radiation by changing the structure arrangement. Here, the We use an indirect method based on the second Kirchoff law for thermal radiation to investigate the emittance of black bodies based on a well-known transfer matrix technique. We can measure the transmission and reflection coefficients with associated transmittance and reflectance, T and R, respectively. Here, the effects of several parameters, including the input beam’s angle, polarization, and period on tailoring the thermal radiation spectrum of the proposed structure, are studied. The results show that in some frequency bands, thermal radiation exceeded the black body limit. There were also good results in terms of complete stop bands for both TE and TM polarization at different incident angles and frequencies. This study produces encouraging results for the creation of Terahertz (THz) filters and selective thermal emitters. The tunability of our media is a crucial factor that influences the efficiency and function of our desired photonic outcome. Therefore, exploiting MQP sequences or arrangements is a promising strategy, as it allows us to rearrange our media more flexibly than quasi-periodic sequences and thus achieve our optimal result.

A GRAPHENE-BASED MONOPOLE MICROSTRIP ANTENNA WITH TUNEABLE BANDGAP FOR UWB IMPLEMENTATIONS

Monopole Microstrip Antennas (M-MSAs) are widely used because of their price, ease of manufacturing, and compact size, making them ideal for portable applications. Nowadays, Ultrawide Band (UWB) technology, used in wireless applications, relies on this antenna. The UWB frequency range is 3.1 to 10.6 GHz, allowing low-power wireless applications such as wireless music, personal localization, radio frequency recognition, radar, and HD video dissemination. However, this frequency band's broadness increases interference. This contribution research formulates simulates, and optimises a modified small-square M-MSA that meets UWB technology's huge bandwidth requirements. A square radiated patch, a dielectric material with a thickness of 1 mm and 4.7 relative permittivity, a partly ground plane printed on the patch's face, and a coplanar waveguide feed make up the M-MSA design. The M-MSA design is modified to reduce the patch's bottom corners and change its proportions to enable compatibility with the UWB complete band. A U-shaped aperture on the patch should be etched to produce a bandgap in UWB frequencies, reducing interference. Filling the aperture with graphene allows bandgap tunability. The graphene's bandgap dissipates with DC voltage, but without biassing, its high impedance restricts aperture current flow. The bandgap's effect is seen at 3.87-4.85 GHz. After simulation and tweaking, gain and efficiency improved significantly. The bandgap region, which was chosen to reduce interference from military fixed communications, mobile communications, unmanned aerial vehicles, short-range radio links, satellite communications, and the low band of 5G, also exhibits a significant increase in attenuation and gain degradation.

Complex band structure in viscoelastic thin plate phononic crystals

Phononic crystals (PnCs) are artificial composites designed by a periodic arrangement of two or more materials with different properties and/or geometry, in order to tailor the propagation of mechanical waves. The complex band structures of PnC thin plates, consisting of a hard matrix material reinforced by inclusions of soft viscoelastic material (HS-PnC), and vice-versa (SHPnC), are investigated. In general, elastic plate structures can be modelled using the Kirchhoff- Love theory, which is suitable for thin plates in low frequencies. However, there is a lack of knowledge concerning the effects of viscoelastic constituents on the complex band structure of flexural Bloch waves in PnC thin plates. In this study, an extended plane wave expansion (EPWE) method is used to compute the complex band structures of VPnC thin plates. The evanescent behaviour of periodic plates for the cases HS-PnC and SH-PnC is calculated, and the results show that the first creates flat bands for wave localization and the second opens up complete and partial Bragg scaterring band gaps.