Periodic Structures Research Articles

Advanced Laser Techniques for the Development of Nature-Inspired Biomimetic Surfaces Applied in the Medical Field

This review focuses on the innovative use of laser techniques in developing and functionalizing biomimetic surfaces, emphasizing their potential applications in the medical and biological fields. Drawing inspiration from the remarkable properties of various natural systems, such as the water-repellent lotus leaf, the adhesive gecko foot, the strong yet lightweight spider silk, and the unique optical structures of insect wings, we explore the potential for replicating these features through advanced laser surface modifications. Depending on the nature and architecture of the surface, particular techniques have been designed and developed. We present an in-depth analysis of various methodologies, including laser ablation/evaporation techniques, such as Pulsed Laser Deposition and Matrix-Assisted Pulsed Laser Evaporation, and approaches for laser surface structuring, including two-photon lithography, direct laser interference patterning, laser-induced periodic surface structures, direct laser writing, laser-induced forward transfer, and femtosecond laser ablation of metals in organic solvents. Additionally, specific applications are highlighted with the aim of synthesizing this knowledge and outlining future directions for research that further explore the intersection of laser techniques and biomimetic surfaces, paving the way for advancements in biomedical applications.

Generation of bessel-like beam by a binary ultrasonic lens

Bessel beams have already been used in acoustic tweezers, ultrasonic medical imaging, and Doppler velocity estimation due to their non-diffractive and self-healing properties. We proposed a binary ultrasonic lens, with ultra-thin planar periodic structures for efficient conversion of the plane wave into a Bessel-like beam. The effectiveness of long-axis focusing has been demonstrated through simulations and experiments with FWHM of 8.5 mm and 9.5 mm around 10 mm. By varying the operating frequency of the incident wave from 1.9 MHz to 2.2 MHz, the position of the long-axis focusing point can be adjusted experimentally from 23.05 mm to 28.95 mm. Additionally, the beam generated by the binary ultrasonic lens can form a focused sound field when passing through multi-layered tissues and the self-healing capability of the Bessel-like beam has been numerically validated, showing strong robustness. This binary ultrasonic lens for a Bessel-like beam would conform better to ergonomic and miniaturization requirements, and expand versatile applications in clinical diagnosis and therapy.

3D Printing of Hierarchical Structures Made of Inorganic Silicon-Rich Glass Featuring Self-Forming Nanogratings.

Hierarchical structures are abundant in nature, such as in the superhydrophobic surfaces of lotus leaves and the structural coloration of butterfly wings. They consist of ordered features across multiple size scales, and their advantageous properties have attracted enormous interest in wide-ranging fields including energy storage, nanofluidics, and nanophotonics. Femtosecond lasers, which are capable of inducing various material modifications, have shown promise for manufacturing tailored hierarchical structures. However, existing methods, such as multiphoton lithography and three-dimensional (3D) printing using nanoparticle-filled inks, typically involve polymers and suffer from high process complexity. Here, we demonstrate the 3D printing of hierarchical structures in inorganic silicon-rich glass featuring self-forming nanogratings. This approach takes advantage of our finding that femtosecond laser pulses can induce simultaneous multiphoton cross-linking and self-formation of nanogratings in hydrogen silsesquioxane. The 3D printing process combines the 3D patterning capability of multiphoton lithography and the efficient generation of periodic structures by the self-formation of nanogratings. We 3D-printed micro-supercapacitors with large surface areas and a high areal capacitance of 1 mF/cm2 at an ultrahigh scan rate of 50 V/s, thereby demonstrating the utility of our 3D printing approach for device applications in emerging fields such as energy storage.

MHD simulations of astrophysical and laboratory jets under different magnetic field configurations

This paper presents the results of MHD simulations of astrophysical and laboratory supersonic jets under a superposition of poloidal (Br, Bz) and toroidal (Bϕ) magnetic fields. It is shown that the escaping matter is quickly collimated by the magnetic field. A shock wave of an elongated shape is formed, which moves from the target to the boundary of the chamber, leaving behind a stable flow. A periodic shock wave structure is observed inside the main conical expanding shock wave. It is shown that the toroidal component of the magnetic field remains in the region throughout the entire calculation and plays a role in the collimation of the flow. The poloidal magnetic field decreases in the region of the jet cone, but remains in the simulation region throughout the calculation and also participates in flow collimation. Thus, both components Bz and Bϕ take part in the collimation of the flow by the magnetic field. The width of the jet and the opening angle of the cone Ɵ depend on the magnitude of the magnetic field induction. As the field increases, the jet becomes narrower and the cone angle decreases. Initially, we do not specify the rotation of the jet Ω. However, due to the presence of the Bϕ field, the substance acquires angular velocity and twists along the z axis. The simulation results are in agreement with laboratory jets arising in the experiment at the Neodymium laser installation, and with the previously obtained results of MHD modeling of jet formation separately, in poloidal or toroidal magnetic field.

An enzymatic reaction-based SERS saliva analysis microporous array chip for chiral differentiation and high-throughput detection of D-amino acids.

ARaman-active boronate modified surface-enhanced Raman scattering (SERS) microporous array chip based on the enzymatic reaction was constructed for reliable, sensitive, and quantitative monitoring of D-Proline (D-Pro) and D-Alanine (D-Ala) in saliva. Initially, 3-mercaptophenylboronic acid (3-MPBA) was bonded to Au-coated Si nanocrown arrays (Au/SiNCA) via Au-S bonding. Following this, H2O2 obtained from D-amino acid oxidase (DAAO)-specific catalyzed D-amino acids (D-AAs) further reduced 3-MPBA to 3-hydroxythiophenol (3-HTP) with a new Raman peak at 882cm-1. Meanwhile, the original characteristic peak at 998cm-1 remained unchanged. Therefore, the I882/I998 ratio increased with increasing content ofD-AAs in the sample to be tested, allowing D-AAs to be quantitatively detected. TheAu/SiNCA with large-area periodic crown structure prepared provided numerous, uniform "hot spots," and the microporous array chip with 16 detection units was employed as the platform for SERS analysis, realizing high-throughput, high sensitivity, high specificity and high-reliability quantitative detection of D-AAs (D-Pro and D-Ala). The limits of detection (LOD) were down to 10.1µM and 13.7µM throughout the linear range of 20-500µM. The good results of the saliva detection suggested that this SERS sensor could rapidly differentiate between early-stage gastric cancer patients and healthy individuals.

Multi-functional periodically heterogeneous structures for energy harvesting and vibration attenuation-effects of piezoelectricity and shunting circuits

Abstract We explore a kind of metamaterial plate structures intended for simultaneous energy harvesting and vibration control. These structures are designed using a periodically perforated piezoelectric plate (the matrix) with elastic inclusions situated in the holes and serving for the resonators. The design options comprise two- and three-phase configurations related to the mechanical connection between the matrix and inclusions. By introducing a singularity—the focal spot created as a defect in the perfectly periodic structure and using the theory of super-cell, an enhanced piezoelectric energy harvester is obtained. It is observed that such a meta-structure serves as a dual-purpose system: efficiently capturing vibrational energy at a focal spot while maintaining the overall vibration attenuation throughout the structure. The band gap analysis based on the Bloch’s wave decomposition theory shows that by concentrating energy and halting vibration propagation, approximately 10 times energy harvesting enhancement and a remarkable 100 dB reduction in vibrations are achieved simultaneously. Besides the passive response of these meta-structures, we consider its extension by an external electric circuit (EC). Such modified configurations enable to exploit ‘actively’ the piezoelectric plate property to transmit the mechanical response between two, or more distant locations. Due to nonlocal interactions introduced by means the controllable EC, we consider optimization of the EC impedance to reduce the vibrations at a selected location of the whole structure without any external energy supply. The computational study discovers perspectives and benefits of designing such active self-powered meta-structures.

Pulse Duration Dependent Formation of Laser‐Induced Periodic Surface Structures in Atomic Layer Deposited MoS2

AbstractIn this paper, the formation of laser‐induced periodic surface structures (LIPSS) on atomic‐layer deposited MoS2 layers are studied experimentally. The process parameters (laser fluence and the pulse overlap) corresponding to formation of low‐ and high‐spatial frequency LIPSS as well as ablation and modification of the layers are identified for different pulse durations in the range from 0.2 to 10 ps. The role of the temperature accumulation is evaluated by changing the repetition rate from 0.2 to 2 MHz. The negative accumulation effect, i.e., the ablation of the layers becomes more difficult at higher laser pulse overlaps, is also observed. A simple model explaining the transition between different types of the LIPSS and the decrease of the ablation efficiency with the pulse overlap is suggested.

Multi-scale topology optimization of periodic structures with orthotropic multiple materials using the element-free Galerkin method

ABSTRACT A multi-scale topology optimization model is proposed for orthotropic multi-material periodic structures using the element-free Galerkin method. The macro multi-material distribution is optimized with the alternating active-phase algorithm, and the effective elastic tensor of multi-type microstructures is determined by energy-based homogenization. The feasibility of the model is verified and the effects of the quantities of material types and design subdomains, the Poisson's ratio factor and the multi-material off-angle on topological configuration and compliance are studied. The results indicate that the quantity of material types affects the mechanical properties of the periodic structure, and different microstructure configurations can be obtained under different numbers of design subdomains. The increase in the Poisson's ratio factor and decrease in the off-angle can enhance the effective elastic properties of the microstructure and reduce the compliance. Reasonable values of the Poisson's ratio factor and multi-material off-angle are suggested to be 2–4 and 0–45°.

Improving piezoelectric performance in PMN-0.26 PT single crystal via low frequency AC poling

In this experiment, the alternating current poling (ACP) was applied to the 0.74 Pb(Mg1/3Nb2/3)O3-0.26PbTiO3 (PMN-0.26 PT) single crystal to explore the impact of low frequency (0.1 Hz) ACP on electrical performance. When the poling condition is loading 5 cycles at 14 kV/cm, high piezoelectric coefficient d33 of 1780 pC/N and giant dielectric constant of 5881 are obtained for the ACP treatment sample, enhanced 42.4 % and 14.3 % by contrast with the conventional direct current poling (DCP), respectively. The values of coercive field, maximum strain, and converse piezoelectric constant d33∗ vary considerably around the ferroelectric phase transition detected by polarization-electric field, as well as bipolar and unipolar electric field-induced strain hysteresis loops. In addition, the domain configuration of the ACP sample presents a more periodic stripe-like structure with narrower width and relatively more uniformity after three months aging as compared with the DCP sample, showing the importance of domain engineering in enhancing electrical performance of ferroelectric single crystals.

Band structures based phononic crystals in quasi-Sierpinski fractals with defects

This study presents a detailed analysis of the effects of geometric defects in phononic crystals, focusing on the use of a distribution of Sierpinski fractals for the strategic placement of inclusions. Using theoretical and computational approaches, we investigate the influence of these defects on the material's band structure. Phononic crystals, designed based on fractal geometry inspired by the Sierpinski pattern, are particularly sensitive to the introduction of inclusions, resulting in disorder in the periodic structure. Our study examines in detail how different defect configurations affect the formation of localized modes and the energy distribution in the material's band structure. The results obtained provide valuable insights into how the presence of geometric defects can be exploited or minimized in the design of phononic crystals for practical applications, including acoustic isolation, vibration control, and the development of advanced acoustic devices. These results contribute to the understanding and advancement of fractal phononic crystals, paving the way for future research and promising technological applications, both in terms of frequency and attenuation, depending on the complexity and hierarchy of the fractal structures used.

Computation of the sound transmission loss of heterogeneous periodic structure using the wave finite element-based methodology

In the present study, a Wave Finite Element-based method is introduced to estimate the Sound Transmission Loss (STL) of periodic structures with contrasting properties. This method addresses the precision and computational speed limitations of existing methodologies. It calculates the wave STL by applying a plane wave excitation from the ambient medium to a Unit Cell (UC), which is representative of the periodic structure. The STL under Diffuse Acoustic Field (DAF) is then computed by integrating the wave STL over all possible incidence angle ranges. The advantages of this methodology are demonstrated through various configurations, ranging from simple plates to complex laminated structures. Additionally, the study investigates the Mass Law of STL.

Effect of scatterer shape, opening angle and periodicity on sound attenuation by local resonating sonic crystal

Noise Control has become critical and demanding task for acoustic engineers due to continuous Technological developments in construction, transportation, and industries. These developments have raised the level of low frequency noise in densely populated areas. Unfortunately, there cannot be sufficient noise reduction with traditional acoustic materials. However, new research has shown that the manipulation of sound waves and drastic reduction in sound transmission can be possible using periodic structure known as Sonic Crystals (SnC). This study describes the eigenfrequency analysis to investigate the effect of different shapes, periodicities, and opening angles of scatterers in a Local resonating Sonic Crystal (LRSnC). The Block-Floquet boundary condition is applied to the unit cell of the LRSnC, using the Finite Element Method to study the complex acoustic wave interactions throughout the structure. An acoustic module has been applied to find the band gap and to simulate transmission loss spectra in COMSOL Multiphysics. Results show that shape, opening angle and periodicity effect the band gap and transmission loss significantly. Based on these results, it is possible to develop advanced SnC with a wider band gap and higher sound attenuation in the lower sound frequency range by carefully considering these factors.

From filler to structure: Designing 3D-printable silicone elastomers with broadband electromagnetic interference shielding

Material extrusion has revolutionized the fabrication of silicone elastomers with intricate and customized structures. However, the trade-off between the ink printability and functional filler compounding impedes the advancement of 3D-printed silicone elastomers for applications such as electromagnetic interference (EMI) shielding and thermal management. In this study, we present a novel approach to fabricating functional silicone elastomers, focusing on the design of fillers, inks and structures. Ink printability was achieved by modified nanosheets, which conferred the thixotropy and self-support capacity to inks by constructing dynamic interfacial interactions within the silicone matrix. Additionally, modified nanosheets exhibited a “lubricating” effect under high shear rates owing to their layered structure, thereby facilitating a smooth extrusion process. Utilizing EMI shielding simulations of periodic porous structures as a guide, we successfully printed broadband EMI shielding silicone elastomers. Furthermore, the versatility of our approach was demonstrated through the creation of customized 3D-printed shielding boxes and wearable thermal management films, showcasing the diverse potential applications of the 3D-printed silicone elastomers. We anticipate that our innovative design approach will bridge the gap between functional elastomers and 3D printing technology, opening up new avenues for their applications in various fields.

Noise-insulating structures based on supercells and chirped lattices enhanced via tuning of local coupling

Acoustic metamaterials and phononic crystals have proven themselves to be highly promising for the development of next-level noise-mitigation systems. One of the main challenges limiting the implementation of such structures is a typically narrow operational frequency range. In this work, we consider a periodic system consisting of locally coupled Helmholtz resonators and demonstrate that positions and widths of stop-bands can be adjusted via tuning of the coupling strength. Several approaches are developed, including the introduction of the chirped structures, supercells, or resonators with enhanced intrinsic losses. We numerically and experimentally demonstrate that tuning of local coupling leads to a merging of stop-bands, resulting in broadband noise-insulation within the operational range covering about 3.5 octaves. This property is linked to band structures of the associated infinitely periodic structures and discussed in terms of band-gap engineering. The low filling factor of the unit cells also suggests that the considered structures can be ventilated, which is demonstrated numerically.

Machine learning for locally periodic structure transmission modelling

This research aims to obtain an analytical transmission model for locally periodic structures with the approach of data-driven physics. So far, this task has been done mainly numerically for non-trivial geometries. From a dataset of Bloch phases generated for given frequency band and structure geometry parameters, it is possible to learn equations relating dispersion relation to axis-symmetric geometry. The dataset is transformed into a lower-dimensional space by applying Principal Component Analysis (PCA) to reduce the complexity of the problem. In the newly obtained coordinate system, the lower-dimensional patterns are extracted via symbolic regression. The resulting model is interpretable in terms of underlying physics and can be used, e.g., to propose an optimized design for a desired band gap width. Note that this has been so far possible only with numerical optimization repeatedly going back and forth from geometry to the dispersion relation, and hence, it significantly contributes to the overall readability of the system features.

Computing the dynamic response of a periodic structure coupled with a nonlinear junction using the harmonic balance method and Floquet-Bloch modelling

Structures constituted of assembled sub-components are often subject to nonlinear effects due to the presence of joints or contacts, which can induce higher-order harmonics of the source excitation. In the context of periodic structures, these nonlinearities cannot be tackled using the Floquet-Bloch theory in its usual harmonic formulation. This study hence presents an adaptation of the classical Floquet-Bloch theory to address multi-harmonic systems arising from a finite number of localized nonlinearities in periodic waveguides. We adopt the Harmonic Balance Method to recast the governing equations into a nonlinear algebraic system, which can then be solved using numerical continuation algorithms. To demonstrate the validity and benefit of this approach, the predictions derived from the proposed methodology are compared to results obtained through conventional Finite Element analysis. Excellent agreement and a notable reduction in computational cost are observed. This efficient procedure for analysing the nonlinear dynamic response of periodic waveguides opens up new possibilities in the study of damaged composite structures.

Using wave based SEA methods to model noise and vibration in underwater structures across a broad frequency range

Modelling noise and vibration transmission in underwater structures is often challenging due to the large size of the structures and the need for analysis across a broad frequency range. Finite Element and Boundary Element methods are useful at lower frequencies but are typically not computationally tractable for system level models at mid and high frequencies. Statistical Energy Analysis (SEA) methods are widely used for modeling structures in air at mid and high frequencies. However, traditional SEA methods often do not contain enough detail to describe wave propagation in heavy fluid loaded structures in underwater applications. This paper discusses the use of a more general 'wave based' SEA method that uses periodic structure theory to accurately calculate the wavetypes of typical underwater structures. The paper illustrates the method by initially considering simple structural sections and showing the effects of: curvature, heavy fluid-loading, panel stiffeners/ribs. The method is then applied to a simplified full scale submarine model and comparisons are made with a nodal finite element model. The domain of validity and the hypotheses of the method are then discussed.

A basic study on sound insulation characteristics of Triply Periodic Minimal Surface by using the finite element method

Triply periodic minimal surfaces (TPMS) have garnered attention in the field of natural science. For example, these structures are observed in insect wing scales, where their intricate periodic structures create structural colors via the reflection and interference of certain wavelengths of light. The objective of this study is to utilize the acoustic analogy of such photonic properties for sound insulation. In a previous report, it was found that the bandgap of G-surface, which is one of TPMS, enabled us to insulate sound effectively at specific frequencies. Furthermore, it was suggested that sound insulation performance can be improved by compressing the structure along the incident direction while maintaining its thickness. In this paper, we focus on the P-surface, which is a typical TPMS other than the G-surface. The sound insulation properties were calculated by numerical analysis and compared with those of the G-surface. As a result, it is found that P- and G-surfaces are effective structures for different frequency bands. In addition, compression of the P-surface along the incident direction in the same manner as in the previous study improves the sound insulation performance without increasing the thickness, as well as G-surface.

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.

Point defect distributions in ultrafast laser-induced periodic surface structures on β-Ga2O3

β-Ga2O3 has received widespread attention due to its ultrawide bandgap, which potentially permits applications in extreme conditions. Ultrafast laser irradiation of β-Ga2O3 provides a means for exploring the response of the material under such conditions, which could result in the generation of point defects as well as a localized modification of structural features that could yield properties that differ from the pristine surface. However, an understanding of defects generated by femtosecond laser irradiation in the vicinity of laser-induced periodic surface structures (LIPSS) remains to be explored. We correlate topographic features with optical and electronic properties by combining near-nm scale resolution cathodoluminescence with Kelvin probe force microscopy. Defects are found to correlate with crystalline order and near-surface morphology, as well as changes in work function. They are also suggested to be closely related to the formation of high spatial frequency LIPSS. These results suggest a need for precise tuning of laser irradiation conditions as well as possible post-processing to control defects in future Ga2O3 devices.