arXiv subjects

Bowei Wu

Publications and source records attributed to Bowei Wu.

At least 19 recordsLinked to original sources

arXiv2026

Experimental Realization of Topological Surface Acoustic Wave Resonances under Surface Liquid Loading for Micro-volume sample Sensings

Surface acoustic wave (SAW) sensors, owing to their high operating frequencies, compatibility with planar micro-fabrication, and exceptional sensitivity to surface perturbations, are widely used in lab -on-a-chip and biomedical diagnostic applications. However, conventional SAW sensors operating in liquid environments suffer from substantial energy dissipation, which markedly reduces their quality factors (Q factors) and limits sensing reliability. Here, we design and fabricate a topological SAW resonant sensor for surface liquid loading by exploiting interference coupling between topological interface states and resonant cavities. The band structures are validated using a semi-analytical plane wave expansion-finite element method. The device requires only 0.04 uL of sample and enables concentration sensing of NaCl and glucose solutions, with sensitivities of up to 190 kHz/% for NaCl and 101.8 kHz% for glucose, respectively, and a concentration resolution of 0.01%. This work offers a potential technological route towards high-performance SAW biomedical chips for micro-volume sample analysis.

physics.app-ph↗

arXiv2026

Large area Waveguide Energy Harvesting Based on Fully Polarized Elastic Topological Metamaterials

To address the challenge that elastic wave energy can only transmit through narrow path waveguides in topological metamaterials, the proposal of large area waveguides effectively breaks through this technical bottleneck. Nevertheless, elastic waves are vector waves with complex multi component transmission characteristics. Realizing the cooperative transmission of in plane and out of plane fully polarized components poses substantial challenges for elastic wave energy transmission and trapping applications. To tackle the above mentioned problems, this paper proposes a fully polarized elastic topological heterostructure based on the quantum valley Hall effect. First, symmetric unit cell structures are designed to obtain unit cells with distinct topological properties for in plane and out of plane modes, and multiple types of supercell structures are fabricated to realize the simultaneous transmission of fully polarized elastic wave energy for both in plane and out of plane components. Furthermore, a gradient valley locked structure is designed using large area waveguide states to constrain and converge the transmitted energy, and its energy harvesting performance is analyzed. The results demonstrate that the proposed structure enables coupled transmission of fully polarized elastic wave components. Moreover, the energy harvesting capability of the gradient valley locked phononic crystal plate is approximately 4.79 times that of conventional single component transmission structures, which greatly improves the efficiency and transmission stability of acoustic energy harvesting. This work provides new insights for the engineering application of topological metamaterials in the field of energy harvesting.

physics.app-ph↗

arXiv2026

Topological Skyrmion-type microparticle manipulation based on surface acoustic wave phase modulations

Surface acoustic wave (SAW) micromanipulation enables the precise, non-contact handling of microscale particles and has attracted considerable interest in microfluidics and biomedicine. However, conventional SAW platforms generally rely on simple interference fields which are susceptible to fabrication imperfections and environmental perturbations, resulting in limited trapping stability. Here, we develop a SAW-based acoustofluidic platform that generates an acoustic skyrmion lattice through the coherent interference of three SAWs. The topologically structured field provides robust phase singularities and a stable gradient-force landscape, enabling microparticles to be localized at predefined lattice sites and supporting controllable rotational manipulation. Independent modulation of the amplitude and phase of the electrical inputs allows the field strength to be tuned for particles of different sizes. Numerical simulations and proof-of-concept experiments confirm particle trapping and ordered lattice assembly in the acoustic skyrmion field, demonstrating the feasibility of translating topological acoustic textures into practical on-chip manipulation functions. This reconfigurable strategy offers a route to robust SAW manipulation and may support applications in single-cell analysis, three-dimensional cell assembly, high-throughput screening, and microscale and nanoscale device assembly.

physics.app-ph↗

arXiv2026

Method of Fundamental Solutions for Maxwell's Equations in Bi-Periodic Multilayered Media

In this paper, we present an accurate numerical method for the time-harmonic Maxwell's equations for bi-periodic multilayered media with quasi-periodic incident waves using the Method of Fundamental Solutions in conjunction with a periodization scheme. Following an approach used in acoustic scattering problems, the electric and magnetic fields in each layer are expressed as a sum of near and distant interactions. The near interaction comprises interactions between the unit cell and its nearest neighboring copies, while the distant interaction is approximated by proxy source points placed on spheres surrounding the unit cell. Imposing continuity of tangential components at the layer interface, quasi-periodicity conditions on the walls of the unit cell, and Rayleigh-Bloch expansion for the radiation condition yields a system of equations for the unknown coefficients, which can be solved by Schur complement and a backward-stable solver. The scheme is verified with known solutions and exhibits exponential convergence close to $10^{-14}$ for both single and multiple interfaces. An example with 39 interfaces is presented to demonstrate the solver's performance. The paper provides promising results for extending this method to a fast and accurate boundary integral equation solver for many cutting-edge applications involving a large number of layers in electromagnetics and optics.

math.NA↗

arXiv2026

Non-Hermitian-induced higher-order topological phases in acoustic fractal lattices

For fractal (non-integer-dimension) geometries in Hermitian system, high-order topological phases were realized in the past few years, for which, it is difficult to tune the energy concentration degree of topological states flexibly and smoothly. Non-Hermiticity method is expected to solve this problem. However, in non-integer-dimension system, the non-Hermitian-fractal coupled topological mechanism is unclear and topological phases induced by non-Hermiticity remain unrealized. By introducing a loss contrast in a fractal lattice, this study proposes a non-Hermitian route to realize higher-order topological phases in acoustic fractal lattices with good tunability. Based on the tight-binding approximation, calculations on the Hamiltonian of the system yield the wave-function distribution of the zero-energy modes, revealing the formation mechanisms and conditions for the topological phase transitions induced by non-Hermiticity in acoustic fractal lattices. We numerically and experimentally realize non-Hermitian-induced topological edge and corner states in a fractal structure. Furthermore, a tunable acoustic energy concentrator has been realized, namely, the degree of acoustic energy localization can be tuned conveniently by merely adjusting the loss contrast, rather than redesigning the structure parameters. This work not only establishes an effective mechanism for manipulating higher-order topology in complex fractal geometries through non-Hermiticity but also provides a theoretical framework for exploring exotic topological states of matter in non-integer dimensions.

physics.app-ph↗

arXiv2026

A parametrix for the surface Stokes equation

We introduce an integral equation formulation of the surface Stokes equations, constructed using two-dimensional Stokeslets. The resulting integral equations are Fredholm integral equations of the second kind and can be discretized to high order using standard tools. Since the resulting discrete linear systems are dense, we describe and analyze a proxy shell method to construct fast direct solvers for these systems. The properties of our integral equation, and the performance of the resulting numerical scheme, are illustrated with several representative numerical examples.

math.NA↗

arXiv2025

Realization of Friedrich-Wintgen QBIC with high Q-factors based on acoustic-solid coupling and sensing applications

In recent years, bound states in the continuum (BICs) have attracted extensive attentions in the sensing field due to their theoretically ultra-high resonance quality factors (Q-factors). Among them, Friedrich-Wintgen (F-W) BICs, which arise from the interference between different coupled modes, are particularly promising for acoustic sensing applications owing to the easy realization. Most existing F-W BICs are realized in open systems through the interference between waveguides and resonant cavities. However, with increasing demands for higher resolution and sensitivity in modern chemical and biological sensing, the practically measured Q-factors of conventional open-system F-W BICs often fall short of expectations.In this work, we introduce F-P resonance via acoustic-solid coupling to explore the formation mechanism and realization method of high-Q F-W BICs in quasi-closed systems, and further investigate their application in gas sensing. A coupled resonator model combining elastic and acoustic waves in a quasi-closed cavity is first established. Coupled mode theory is employed to calculate the eigenmodes of both localized and radiative modes. Based on this, the Hamiltonian matrix of the coupled system is constructed, from which the acoustic transmission spectrum is derived. The results show that the Q-factor of the F-W BIC induced by acoustic-solid coupling is significantly higher than that of open systems, which is further validated by experiments.Based on this, a gas concentration sensing technique based on acoustic-solid coupled F-W BIC behavior is developed. A sensing device is fabricated accordingly, and gas concentration measurements are carried out. Experimental results demonstrate a pronounced response to gases with different concentrations, confirming the feasibility and reliability of this novel gas sensing approach.

physics.app-ph↗

arXiv2025

Corrected Trapezoidal Rules for Near-Singular Surface Integrals Applied to 3D Interfacial Stokes Flow

Interfacial Stokes flow can be efficiently computed using the Boundary Integral Equation method. In 3D, the fluid velocity at a target point is given by a 2D surface integral over all interfaces, thus reducing the dimension of the problem. A core challenge is that for target points near, but not on, an interface, the surface integral is near-singular and standard quadratures lose accuracy. This paper presents a method to accurately compute the near-singular integrals arising in elliptic boundary value problems in 3D. It is based on a local series approximation of the integrand about a base point on the surface, obtained by orthogonal projection of the target point onto the surface. The elementary functions in the resulting series approximation can be integrated to high accuracy in a neighborhood of the base point using a recursive algorithm. The remaining integral is evaluated numerically using a standard quadrature rule, chosen here to be the 4th order Trapezoidal rule. The method is reduced to the standard quadrature plus a correction, and is uniformly of 4th order. The method is applied to resolve Stokes flow past several ellipsoidal rigid bodies. We compare the error in the velocity near the bodies, and in the time and displacement of particles traveling around the bodies, computed with and without the corrections.

math.NA↗

arXiv2024

Tunable acoustic energy concentrations based on pseudo-spin locking waveguides and topological rainbow trappings

In this work, tunable acoustic energy concentrations are realized based on pseudo-spin locking waveguides and topological rainbow trappings. Firstly, a tunable pseudo-spin locking is proposed, and the broad acoustic energy transport and spin-locked one-way transport are verified. The results show that acoustic wave transports based on pseudo-spin locking waveguides are more robust to structure defects than conventional topological edge-state waveguides. Besides, topological rainbow trappings are realized by adjusting the distribution of liquid in tubes. Based on those, we investigate the coupling of the pseudo-spin locking waveguides and the topological rainbow trappings. The results show that high acoustic energy concentrations can be obtained conveniently by using the coupling energy concentrator based on the pseudo-spin locking waveguides and the topological rainbow trappings. The results present a novel method to concentrate acoustic wave energy, which is vital in the application field of acoustic sensings and microfludics. The according experimental verifications will be presented in the near future.

physics.app-ph↗

arXiv2024

Particle manipulations based on acoustic valley topological rainbow defect-state trapping

Acoustic microfluidic is an important technology in particle manipulations in biomedical analyses and detections. However, the particle-movement manipulations achieved by the standing surface acoustic wave is suitable for particles in a thin layer of fluids, however it is difficult to manipulate particles in deeper solutions due to the energy loss of surface acoustic waves. The traditional standing bulk wave method can realize the particle manipulation in deep solutions, but it cannot work properly for particle manipulation within a long distance due to the energy loss. In this work, the topological rainbow defect-state trapping is realized, the results show that an effect of point accumulation of acoustic pressure in the waveguide path exists, the position of maximum acoustic pressure can be adjusted flexibly by changing the frequency of the incident acoustic wave, based on which, long-distance movement and capture manipulations of particles in deep solution have been realized. The phenomenon presented in this work can provide a reliable method for manipulations of continuous long-distance particle movement and capture to meet the demand of multiple processing steps in biochemical analyses and detections. The experiment verification results will be presented in the near future.

physics.class-ph↗

arXiv2024

An Extension of the Euler-Maclaurin Summation Formula to Nearly Singular Functions

A extension of the Euler-Maclaurin (E-M) formula to near-singular functions is presented. This extension is derived based on earlier generalized E-M formulas for singular functions. The new E-M formulas consists of two components: a ``singular'' component that is a continuous extension of the earlier singular E-M formulas, and a ``jump'' component associated with the discontinuity of the integral with respect to a parameter that controls near singularity. The singular component of the new E-M formulas is an asymptotic series whose coefficients depend on the Hurwitz zeta function or the digamma function. Numerical examples of near-singular quadrature based on the extended E-M formula are presented, where accuracies of machine precision are achieved insensitive to the strength of the near singularity and with a very small number of quadrature nodes.

math.NA↗

arXiv2024

Topological resonance behaviors of surface acoustic waves under a surface liquid-layer loading and sensing applications

In this work, topological resonance behaviors of surface acoustic waves (SAW) under a surface liquid-layer loading are investigated. By revealing influences of the liquid-layer loading on wave velocity of SAW and topological indices (Berry curvature and Chern number) of topological interface-modes, a topological resonance peak with a high Q-factor is obtained based on couplings of a topological interface-mode waveguide and a resonant cavity under a surface liquid-layer loading. The results show that the degree of spatial-inversion-symmetry breaking resulting from structure parameters has an obvious influences on the topological resonance Q-factor, while the influences of the thickness of the liquid-layer loading on that is weak. It is worth noting that the topological resonance frequency is significantly sensitive to the liquid parameters. Based on that, a novel topological-resonance SAW liquid-phase sensor is proposed. Furthermore, sensing performances of this kind of sensor are simulated, which are used to sensing the concentration of hemoglobin, albumin, NaCl and NaI in aqueous solutions, and high sensitivities and Q-factors are obtained. The results presented in this paper can provide an important basis for the realization of highly sensitive and stable SAW micro-liquid-sample biomedical sensors in the future.

physics.app-ph↗

arXiv2024

Large-scale Outdoor Cell-free mMIMO Channel Measurement in an Urban Scenario at 3.5 GHz

The design of cell-free massive MIMO (CF-mMIMO) systems requires accurate, measurement-based channel models. This paper provides the first results from the by far most extensive outdoor measurement campaign for CF-mMIMO channels in an urban environment. We measured impulse responses between over 20,000 potential access point (AP) locations and 80 user equipments (UEs) at 3.5 GHz with 350 MHz bandwidth (BW). Measurements use a "virtual array" approach at the AP and a hybrid switched/virtual approach at the UE. This paper describes the sounder design, measurement environment, data processing, and sample results, particularly the evolution of the power-delay profiles (PDPs) as a function of the AP locations, and its relation to the propagation environment.

eess.SP↗

arXiv2023

Anomalous size effects with fixed criticality in bistable flexible mechanical metamaterials

When the structure deformation is dominated by the low-energy deformation mode, the structure hardens with the increase in the size (number of units) at small sizes. This anomalous behavior will eventually disappear with the decay length of the finite structure converging to a size-independent characteristic quantity, but the specific critical point at which the anomalous behavior disappears still cannot be accurately and concisely described. Here, under two steady states of the bistable chain, we observed anomalous size effects with constant and oscillating criticality (the proportion of inhomogeneous deformation), two criticalities exactly separate the increasing and decreasing intervals of stiffness variation. They are interrelated due to the implied symmetries between the two steady states. On the other hand, they are distinguished because of the opposite superposition modes under the two steady states. Specifically, the constant criticality corresponds to the anomalous size effect achieved by the competition mechanism, while the oscillating criticality reveals an anomalous size effect achieved by the new mechanism (cancellation mechanism). In the anomalous size effect achieved by the cancellation mechanism, the singular characteristics generated by the completely cancelled deformation make it very robust. This robustness reflects in that the anomalous effect is no longer limited to linear small deformation, but it can still be observed stably in nonlinear large deformation. Our study reinterprets the anomalous size effect at a quantitative level, and the proposed cancellation mechanism expands the possible application range of this anomalous effect.

physics.app-ph↗

arXiv2023

On quadrature for singular integral operators with complex symmetric quadratic forms

This paper describes a trapezoidal quadrature method for the discretization of weakly singular, singular and hypersingular boundary integral operators with complex symmetric quadratic forms. Such integral operators naturally arise when complex coordinate methods or complexified contour methods are used for the solution of time-harmonic acoustic and electromagnetic interface problems in three dimensions. The quadrature is an extension of a locally corrected punctured trapezoidal rule in parameter space wherein the correction weights are determined by fitting moments of error in the punctured trapezoidal rule, which is known analytically in terms of the Epstein zeta function. In this work, we analyze the analytic continuation of the Epstein zeta function and the generalized Wigner limits to complex quadratic forms; this analysis is essential to apply the fitting procedure for computing the correction weights. We illustrate the high-order convergence of this approach through several numerical examples.

math.NA↗

arXiv2023

Elastic fractal higher-order topological states

Fractal is an intriguing geometry with self-similarity and non-integer dimensions, the elastic-wave topological phase based on fractal structures has not been revealed up to now. In this work, elastic-wave higher-order topological states in fractal structures are investigated. Elastic real-space quantized quadrupole moment is calculated and used to characterize the topology of elastic fractal metamaterials, and formation conditions of topological phase transitions in elastic fractal systems are revealed. The topological edge and corner states of elastic waves in fractal structures are realized theoretically and experimentally. It is found that different from the acoustic fractal system, the topological outer and inner edge states can emerge separately in elastic fractal systems, which is important for the integrated sensing and particle manipulation in microfluidics. Besides, the results show that the robustness of the topological corner states in rhombus fractal structures is obviously stronger than that in Sierpinski fractal structures, and the physical mechanism is clarified. Compared with traditional elastic-wave topological insulators based on periodic structures, the richness of topological states in elastic fractal structures is much higher (for the Sierpinski fractal structure, the number of topological states is 156, much greater than that of the periodic structure (only 28)), which is vital in integrated sensing and energy-location applications. The topological phenomena of elastic fractal systems revealed in this work, provides an unprecedented way of controlling elastic waves, enriches the topological physics of elastic systems and breaks the limitation of that relying on periodic elastic structures. The results have great application prospects in high-Q resonators, high-resolution elastic-wave energy locations, energy harvester, and high-sensitivity sensors.

physics.app-ph↗

arXiv2022

Robust fast direct integral equation solver for three-dimensional quasi-periodic scattering problems with a large number of layers

A boundary integral equation method for the 3-D Helmholtz equation in multilayered media with many quasi-periodic layers is presented. Compared with conventional quasi-periodic Green's function method, the new method is robust at all scattering parameters. A periodizing scheme is used to decompose the solution into near- and far-field contributions. The near-field contribution uses the free-space Green's function in an integral equation on the interface in the unit cell and its immediate eight neighbors; the far-field contribution uses proxy point sources that enclose the unit cell. A specialized high-order quadrature is developed to discretize the underlying surface integral operators to keep the number of unknowns per layer small. We achieve overall linear computational complexity in the number of layers by reducing the linear system into block tridiagonal form and then solving the system directly via block LU decomposition. The new solver is capable of handling a 100-interface structure with 961.3k unknowns to $10^{-5}$ accuracy in less than 2 hours on a desktop workstation.

math.NA↗

arXiv2022

A Unified Trapezoidal Quadrature Method for Singular and Hypersingular Boundary Integral Operators on Curved Surfaces

This paper describes a trapezoidal quadrature method for the discretization of singular and hypersingular boundary integral operators (BIOs) that arise in solving boundary value problems for elliptic partial differential equations. The quadrature is based on a uniform grid in parameter space coupled with the standard punctured Trapezoidal rule. A key observation is that the error incurred by the singularity in the kernel can be expressed exactly using generalized Euler-Maclaurin formulae that involve the Riemann zeta function in 2D and the Epstein zeta functions in 3D. These expansions are exploited to correct the errors via local stencils at the singular point using a novel systematic moment-fitting approach. This new method provides a unified treatment of all common BIOs (Laplace, Helmholtz, Stokes, etc.). We present numerical examples that show convergence of up to 32nd-order in 2D and 9th-order in 3D with respect to the mesh size.

math.NA↗