Phonon Structure Research Articles

Research on Fabrication of Phononic Crystal Soft-Supported Graphene Resonator.

In aviation, aerospace, and other fields, nanomechanical resonators could offer excellent sensing performance. Among these, graphene resonators, as a new sensitive unit, are expected to offer very high mass and force sensitivity due to their extremely thin thickness. However, at present, the quality factor of graphene resonators at room temperature is generally low, which limits the performance improvement and further application of graphene resonators. Enhancing the quality factor of graphene resonators has emerged as a pressing research concern. In a previous study, we have proposed a new mechanism to reduce the energy dissipation of graphene resonators by utilizing phononic crystal soft-supported structures. We verified its feasibility through theoretical analysis and simulations. This article focuses on the fabrication of a phononic crystal soft-supported graphene resonator. In order to address the issues of easy fracture, deformation, and low success rate in the fabrication of phononic crystal soft-supported graphene resonators, we have studied key processes for graphene suspension release and focused ion beam etching. Through parameter optimization, finally, we have obtained phononic crystal soft-supported graphene resonators with varying cycles and pore sizes. Finally, we designed an optical excitation and detection platform based on Fabry-Pérot interference principle and explored the impact of laser power and spot size on phononic crystal soft-supported graphene resonators.

High-performance Ethyl lactate sensor via phononic crystal-based T-shape structure

High-performance Ethyl lactate sensor via phononic crystal-based T-shape structure

Profiling Electronic and Phononic Band Structures of Semiconductors at Finite Temperatures: Methods and Applications

Semiconductor devices are often operated at elevated temperatures that are well above zero Kelvin, which is the temperature in most first-principles density functional calculations. Computational approaches to computing and understanding the properties of semiconductors at finite temperatures are thus in critical demand. In this review, we discuss the recent progress in computationally assessing the electronic and phononic band structures of semiconductors at finite temperatures. As an emerging semiconductor with particularly strong temperature-induced renormalization of the electronic and phononic band structures, halide perovskites are used as a representative example to demonstrate how computational advances may help to understand the band structures at elevated temperatures. Finally, we briefly illustrate the remaining computational challenges and outlook promising research directions that may help to guide future research in this field.

Intelligent optimization design of large-scale three-dimensional ultrasonic vibration system

Large-scale three-dimensional ultrasonic vibration systems are susceptible to the influence of coupled vibration, resulting in a series of problems such as increased energy loss, small longitudinal displacement amplitude of the radiation surface, and uneven distribution of longitudinal displacement amplitude, which can seriously affect the working efficiency of ultrasonic processing system. How to effectively control the coupled vibration of large-scale three-dimensional ultrasonic transducer systems and optimize their performance has become an urgent problem in the field of power ultrasound. The research has found that some phononic crystal slots and point defect structures can suppress the lateral vibration of large-scale transducer systems, improve the uniformity of system amplitude distribution, and artificially regulate the performance of large-scale three-dimensional ultrasonic vibration systems by changing the configuration parameters of phononic crystal structures. However, excessive design parameters will inevitably increase the complexity of system design, and, currently, the optimization design of large-scale three-dimensional ultrasonic transducer systems relies on empirical trial and error methods which has low design efficiency and low success rate, and cannot guarantee the system performance. Therefore, in the study, homogeneous dislocations and point defect structures are introduced to optimize the design of large-scale three-dimensional ultrasonic vibration systems. Data analysis techniques are used to evaluate the influences of the configuration of homogeneous dislocations and point defect structures on the longitudinal displacement amplitude, amplitude distribution uniformity, radiated sound power, working bandwidth of the system’s radiation surface. And a predictive model for the performance of large-scale ultrasonic transducer system with homogeneous dislocation structure and near periodic defect structure is established, which can achieve intelligent design of large-scale power ultrasonic transducer system, improve design efficiency and success rate, and reduce the design cost.

Unveiling the complex phonon nature and phonon cascades in 1L to 5L WSe2 using multiwavelength excitation Raman scattering.

Tungsten diselenide (WSe2) is a 2D semiconducting material, promising for novel optoelectronic and phononic applications. WSe2 has complex lattice dynamics and phonon structure. Numerous discrepancies in the literature exist regarding the interpretation and identification of phonon modes. This work presents a complete investigation of the vibrational properties of 1L to 5L flakes and bulk WSe2 using multi-wavelength Raman spectroscopy. We especially highlight measurements using 785 nm excitation, which have not been performed before. These allow us to solve inconsistences in the literature in terms of defect-activated non-Γ point single phonon modes and Breit-Wigner-Fano type resonance. We identify 35 Raman peaks per flake thickness, which we attribute to either one-phonon or multi-phonon modes, including two-phonon scattering due to a van Hove singularity (vHs). The measurements are in excellent agreement with the theoretical predictions. Using photoluminescence measurements, we identify photon-exciton coupling leading to resonant Raman scattering, suggesting wavelength laser excitations best suited for further investigations of specific WSe2 flake thicknesses. Finally, we report the observation of phonon-cascades for all WSe2 flake thicknesses, indicating strong phonon-electron interactions during early carrier relaxation processes in WSe2. This research provides a solid foundation and reference for future investigations of the vibrational properties of WSe2, paving the way for further development of this material towards applications.

Optimization Design of Phononic Crystals Based on BPNN‐MPA in Applied Mathematical Analysis

Traditional finite element analysis methods have the problem of expensive and unstable band structure diagram calculation when generating phononic crystals. Therefore, this study combines back propagation neural networks with ocean predator algorithms to optimize the geometric structure of phononic crystals. The results show that the coefficient of determination for the predicted bandgap width and lower bound of Model 3 is 1.00, which is better than the comparison model. However, Models 2 and 5 have poor predictive performance for bandgap width due to overfitting during actual training. Therefore, after using the ocean predator algorithm for hyperparameter adjustment, it is found that the maximum number of failures in the validation set of Model 5 is 30, the number of hidden layer nodes is 30, and after 500 experiments, the average error of the bandgap width is 5.26%, and the average error of the lower bound of the bandgap is 1.33%. The average error of the bandgap width after hyperparameter adjustment is 4.89%, and the average error of the lower bound of the bandgap is 1.21%, both of which are effectively reduced and better than the comparison model. Overall, the combination model has high computational efficiency and stability in phononic crystal optimization and can be practically applied in the design and optimization of phononic crystal geometric structures.

Phononic band calculations and experimental imaging of topological boundary modes in a hexagonal flexural wave machine

We construct a two-dimensional mechanical wave machine based on a hexagonal lattice to investigate low-frequency flexural plate waves whose propagation mimicks a topological quantum valley Hall system. We thereby demonstrate “mechanical graphene” by extension of the one-dimensional Shive wave machine to two dimensions. Imaging experiments, backed up by simulations, reveal the presence of boundary modes along a topological interface. This work provides an alternative route for the investigation of topological phononic crystals, and should lead to new insights into the design and observation of artificial phononic structures.

Multi-Material Radial Phononic Crystals to Improve the Quality Factor of Piezoelectric MEMS Resonators.

In this paper, a multi-material radial phononic crystal (M-RPC) structure is proposed to reduce the anchor-point loss of piezoelectric micro-electro-mechanical system (MEMS) resonators and improve their quality factor. Compared with single-material phononic crystal structures, an M-RPC structure can reduce the strength damage at the anchor point of a resonator due to the etching of the substrate. The dispersion curve and frequency transmission response of the M-RPC structure were calculated by applying the finite element method, and it was shown that the M-RPC structure was more likely to produce a band-gap range with strong attenuation compared with a single-material radial phononic crystal (S-RPC) structure. Then, the effects of different metal-silicon combinations on the band gap of the M-RPC structures were studied, and we found that the largest band-gap range was produced by a Pt and Si combination, and the range was 84.1-118.3 MHz. Finally, the M-RPC structure was applied to a piezoelectric MEMS resonator. The results showed that the anchor quality factor of the M-RPC resonator was increased by 33.5 times compared with a conventional resonator, and the insertion loss was reduced by 53.6%. In addition, the loaded and unloaded quality factors of the M-RPC resonator were improved by 75.7% and 235.0%, respectively, and at the same time, there was no effect on the electromechanical coupling coefficient.

A review of methods of achieving the optimal band gap in two-dimensional phononic crystal structures

A review of methods of achieving the optimal band gap in two-dimensional phononic crystal structures

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.

Coupled Resonator Acoustic Waveguides‐Based Acoustic Interferometers Designed within 2D Phononic Crystals: Experiment and Theory

AbstractThe acoustic response of defect‐based acoustic interferometer‐like designs, known as Coupled Resonator Acoustic Waveguides (CRAWs), in 2D phononic crystals (PnCs) is reported. The PnC is composed of steel cylinders arranged in a square lattice within a water matrix with defects induced by selectively removing cylinders to create Mach‐Zehnder‐like (MZ) defect‐based interferometers. Two defect‐based acoustic interferometers of MZ‐type are fabricated, one with arms oriented horizontally and another one with arms oriented diagonally, and their transmission features are experimentally characterized using ultrasonic spectroscopy. The experimental data are compared with finite element method (FEM) simulations and with tight‐binding (TB) calculations in which each defect is treated as a resonator coupled to its neighboring ones. Significantly, the results exhibit excellent agreement indicating the reliability of the proposed approach. This comprehensive match is of paramount importance for accurately predicting and optimizing resonant modes supported by defect arrays, thus enabling the tailoring of phononic structures and defect‐based waveguides to meet specific requirements. This successful implementation of FEM and TB calculations in investigating CRAWs systems within PnCs paves the way for designing advanced acoustic devices with desired functionalities for various practical applications, demonstrating the application of solid‐state electronics principles to underwater acoustic devices description.

Acoustic valley Hall topological insulators with controllable band gap

In recent years, numerous studies have investigated the impact of imperfections on topological insulators, and certain defects have been observed. Former topological insulators have a limited range of topological transport bands and an irregular lattice structure, which hampers their usefulness in technological applications. Here, it’s implemented the topological transport of sonic waves in a phononic crystal array structure. This paper has shown that changing the rotating scatterer's angle can alter the topological phase, resulting in lattice band inversion. This establishes a topological channel that enables acoustic conduction. It is feasible to create multifarious channel structures and devise acoustic transmission systems with varying positions. The introduction of rotating scatterers enables the regulation of the influx of acoustic waves into targeted channels. And the robustness of its edge states was verified by using the finite element method. These outcomes furnish the sound wave control mechanism with a novel formation and urge the development of programmable sound wave regulation. Based on these properties, the technique of regulating topological wave propagation through the use of a topological insulator can also be extended to other systems, including filters and acoustic devices.

Bandgap and its defect band analysis of flexoelectric effect in phononic crystal plates

The wave equations of a novel model for the electro-elastic Kirchhoff plate containing the flexoelectric effect are constructed using a variational formulation. Through an Improved Plane Wave Expansion (IPWE) approach, the proposed wave equations are then applied to examine the elastic wave bandgap and defect band in a phononic crystal plate structure without or with a defect. The results demonstrate that the flexoelectric effect on the bandgap is apparent when the structure is at the submicron scale and fades as the scale increases. Moreover, at all length scales, the magnitude of the bandgap varies dramatically with lattice length and inclusion volume ratio. This suggests that the frequency and broadness of the bandgap can be tuned by modifying the volume percentage of inclusion, plate size parameters and lattice length. The dispersion curves of the defect model and corresponding mode shape at the defect band are also studied, which can indicate the applicability of the current model incorporating flexoelectric effect in energy harvesting and wave focusing. The novel model and these findings would help the design of MEMS/NEMS devices for enhanced wave guiding when flexoelectric-based electro-elastic fields are involved.

Alterferroicity with seesaw-type magnetoelectricity.

Primary ferroicities like ferroelectricity and ferromagnetism are essential physical properties of matter. Multiferroics, with coexisting multiple ferroic orders in a single phase, provide a convenient route to magnetoelectricity. Even so, the general trade-off between magnetism and polarity remains inevitable, which prevents practicable magnetoelectric cross-control in the multiferroic framework. Here, an alternative strategy, i.e., the so-called alterferroicity, is proposed to circumvent the magnetoelectric exclusiveness, which exhibits multiple but noncoexisting ferroic orders. The natural exclusion between magnetism and polarity, as an insurmountable weakness of multiferroicity, becomes a distinct advantage in alterferroicity, making it an inborn rich ore for intrinsic strong magnetoelectricity. The general design rules for alterferroic materials rely on the competition between the instabilities of phononic and electronic structures in covalent systems. Based on primary density functional theory calculations, Ti-based trichalcogenides are predicted to be alterferroic candidates, which exhibit unique seesaw-type magnetoelectricity. This alterferroicity, as an emerging branch of the ferroic family, reshapes the framework of magnetoelectricity, going beyond the established scenario based on multiferroicity.

Influence of Meta-Atom Geometry on the Occurrence of Local Resonance Regions in Two-Dimensional Finite Phononic Structures

Influence of Meta-Atom Geometry on the Occurrence of Local Resonance Regions in Two-Dimensional Finite Phononic Structures

The Influence of the Shape of Acoustic Impedance Change on the Propagation of a Mechanical Wave in Multilayer Phononic Structures

The Influence of the Shape of Acoustic Impedance Change on the Propagation of a Mechanical Wave in Multilayer Phononic Structures

Sound insulation prediction and band gap characteristics of four vibrators acoustic metamaterial with composite phononic crystal structure

Acoustic Metamaterial have been widely concerned because of their strong sound insulation characteristics for specific low-frequency bands. However, further optimization is still needed in terms of broadband sound insulation characteristics, and phononic crystals can generate multiple sound insulation bandwidths due to their unique bandgap characteristics. Therefore, a four vibrators acoustic Metamaterial structure with phononic crystals is proposed to broaden the sound insulation performance at medium and high frequencies while retaining the advantages of sound insulation at low frequencies. Firstly, a semi analytical method combining finite element analysis was proposed for the sound insulation performance of the structure. Afterwards, a bandgap theory based on the equivalent medium method was proposed to reveal the reasons for its characteristics. Finally, a cylindrical sleeve structure was designed for a certain rolling rotor compressor, and its sound insulation performance in the cylindrical state was verified through finite element simulation.

Acoustic 4 × 2 encoder based on linear waveguides in two-dimensional solid-solid phononic crystals

The paper proposes a design for an acoustic 4 × 2 encoder that incorporates acoustic waveguides within a two-dimensional square lattice phononic crystal structure. The encoder's structure comprises of a nylon matrix embedded with a 33 × 30 molybdenum rod array, featuring four input ports and two output ports. The simulation results demonstrate that the proposed structure can effectively achieve the acoustic 4 × 2 encoder functionality. To evaluate the performance of the acoustic 4 × 2 encoder, we analyzed the transmission spectrum using the finite element method (FEM).

Broadband acoustic signal enhancement via gradient metamaterials coupled to crystals

In this work, a phononic crystal gradient metamaterial structure (PCGMs) is proposed based on the strong wave compression effect coupled with equivalent medium theory to achieve enhancement and directional sensing of weak target acoustic signals. Compared with the conventional gradient structure, PCGMs exhibit superior acoustic enhancement performance and wider range of acoustic response capability. Numerical analysis and experimental validation consistently demonstrate that PCGMs can effectively enhance the target frequency signals in harmonic signals. This study breaks through the detection limit of acoustic sensing systems and provides a great method for engineering applications of weak acoustic signal perception.

Four-input acoustic XOR logic gate based on solid-solid phononic crystals

The paper introduces a 2D square lattice phononic crystal structure, with a nylon matrix and molybdenum rods as inclusions. Initially, a new type of resonator, called a triangle resonator, was designed, each of which acts as a two-input acoustic XOR logic gate. Then, a four-input acoustic XOR logic gate is presented by combining these resonators. Simulation results indicate that the realization of two-input and four-input acoustic XOR logic gates is possible using the structures we have proposed. In order to analyze the proposed acoustic XOR logic gates, the transmission spectrum is calculated using the finite element method (FEM).