arXiv subjects

Steven A. Cummer

Publications and source records attributed to Steven A. Cummer.

At least 19 recordsLinked to original sources

arXiv2026

Computationally-efficient synthesis of inversely-designed 3D-printable all-dielectric devices

We present a systematic, computationally efficient approach for synthesizing 3D-printable all-dielectric devices. Inverse-design optimization methods lead to devices of a continuous dielectric constant profile with complex and conformal shapes. However, stereolithography 3D printers have a limited range of materials; usually, only resin and air are available. As the size and complexity of the devices increase, performing simulations of the entire detailed manufacturable device becomes computationally challenging or even prohibitive. We introduce the LOCABINACONN methodology for transforming an optimized device of a continuous material profile to a manufacturable one while preserving performance as close as possible to the continuous case. The LOCABINACONN is a local and computationally efficient methodology where we identify suitable air/resin configurations that will substitute non-manufacturable material components without simulating the entire manufacturable device. This work paves the way for synthesizing optimized larger-scale 3D-printable devices in a computationally tractable manner.

physics.app-ph↗

arXiv2026

Broadband multilayer metasurface absorbers with MXene resonators and topology optimized substrates

We present the synthesis of broadband multilayer metamaterial absorbers (MMA) based on MXenes, which are novel two-dimensional conductive materials with higher ohmic losses than copper. MXene resonator of different conductivity can be implemented at each layer or across the same layer, offering increased design flexibility. We examine the possibility of utilizing topology-optimized stereolithography (SLA) 3D-printed substrates as a complementary means for enhancing absorption. Combining MXenes with topology optimized 3D-printable structures paves the way for realizing MMAs of enhanced absorption.

physics.app-ph↗

arXiv2023

Observation of Two-Dimensional Acoustic Bound States in the Continuum

The design of devices based on acoustic or optical fields requires the fabrication of cavities and structures capable of efficiently trapping these waves. A special type of cavity can be designed to support resonances with a theoretically infinite quality factor, named bound states in the continuum or BICs. The experimental measurement of such modes is still a challenging problem, as they are, by definition, not accessible from external perturbations. Therefore, current reported works rely on indirect measurements that are based on the traces left by these modes on external properties of one-dimensional systems. Here we report on the theoretical design and experimental realization of a two-dimensional, fully open acoustic resonator supporting BICs. This BIC, whose symmetry is chosen during design by properly tailoring the geometrical properties of the system, is completely accessible and allows for the direct measurement of the whole pressure field and properties. We experimentally demonstrate its existence with high quality factor and field enhancement properties.

physics.class-ph↗

arXiv2020

Achromatic metasurfaces with inversely customized dispersion for ultra-broadband acoustic beam engineering

Metasurfaces, the ultrathin media with extraordinary wavefront modulation ability, have shown versatile potential in manipulating waves. However, existing acoustic metasurfaces are limited by their narrow-band frequency-dependent capability, which severely hinders their real-world applications that usually require customized dispersion. To address this bottlenecking challenge, we report ultra-broadband achromatic metasurfaces that are capable of delivering arbitrary and frequency-independent wave properties by bottom-up topology optimization. We successively demonstrate three ultra-broadband functionalities, including acoustic beam steering, focusing and levitation, featuring record-breaking relative bandwidths of 93.3%, 120% and 118.9%, respectively. All metasurface elements show novel asymmetric geometries containing multiple scatters, curved air channels and local cavities. Moreover, we reveal that the inversely designed metasurfaces can support integrated internal resonances, bi-anisotropy and multiple scattering, which collectively form the mechanism underpinning the ultra-broadband customized dispersion. Our study opens new horizons for ultra-broadband high-efficiency achromatic functional devices on demand, with promising extension to the optical and elastic achromatic metamaterials.

cond-mat.mtrl-sci↗

arXiv2019

Transfer matrix method for the analysis of space-time modulated media and systems

Space-time modulation adds another powerful degree of freedom to the manipulation of classical wave systems. It opens the door for complex control of wave behavior beyond the reach of stationary systems, such as nonreciprocal wave transport and realization of gain media. Here we generalize the transfer matrix method and use it to create a general framework to solve wave propagation problems in time-varying acoustic, electromagnetic, and electric circuit systems. The proposed method provides a versatile approach for the study of general space-time varying systems, which allows any number of time-modulated elements with arbitrary modulation profile, facilities the investigation of high order modes, and provides an interface between space-time modulated systems and other systems.

physics.class-ph↗

arXiv2018

Non-reciprocal sound propagation in space-time modulated media

Realization of non-reciprocal devices, such as isolators and circulators, is of fundamental importance in microwave and photonic communication systems. This can be achieved by breaking time-reversal symmetry in the system or exploiting nonlinearity and topological effects. However, exploration of non-reciprocal devices remains scarce in acoustic systems. In this work, sound propagation in a space-time modulated medium is theoretically studied. Finite-difference time-domain (FDTD) simulations are carried out to verify the results. Functionalities such as mode conversion, parametric amplification and phase conjugation are demonstrated.

physics.app-ph↗

arXiv2018

GRIPP: an automated computer-aided design tool for generating 3D printable gradient index acoustic devices

Gradient index (GRIN) acoustic devices have spatially inhomogeneous refractive index profile and allow flexible control of the propagation of acoustic waves. Previous GRIN acoustic lenses are mostly inherently two-dimensional designs that are difficult to be extended to all three dimensions. Besides, manually designing the spatially inhomogeneous structure is both time-consuming and error-prone. In this work, we proposed and numerically verified an automated computer-aided design tool: GRadient Index Pick-and-Place (GRIPP) algorithm, for generating three-dimensional GRIN acoustic wave controlling devices with scalable and 3D printable structures. The algorithm receives as inputs a spatial distribution of refractive index and a pre-defined library of gradient index unit cells, and outputs a 3D model of GRIN device that is ready to be 3D printed. The tool enables rapid design and realization of a large variety of 3D GRIN acoustic devices, which can be useful in areas such as speaker system design, airborne ultrasonic sensing, as well as therapeutic ultrasound.

physics.app-ph↗

arXiv2018

A Surface Impedance-Based Three-Channel Acoustic Metasurface Retroreflector

We propose the design and measurement of an acoustic metasurface retroreflector that works at three discrete incident angles. An impedance model is developed such that for acoustic waves impinging at -60 degrees, the reflected wave is defined by the surface impedance of the metasurface, which is realized by a periodic grating. At 0 and 60 degrees, the retroreflection condition can be fulfilled by the diffraction of the surface. The thickness of the metasurface is about half of the operating wavelength and the retroreflector functions without parasitic diffraction associated with conventional gradient-index metasurfaces. Such highly efficient and compact retroreflectors open up possibilities in metamaterial-based acoustic sensing and communications.

physics.app-ph↗

arXiv2018

Compact Acoustic Retroreflector Based on A Mirrored Luneburg Lens

We propose and demonstrate a compact acoustic retroreflector that reroutes probing signals back towards the source with minimal scattering. Gradient refractive index (GRIN) acoustic metamaterials, based on Archimedean spiral structures, are designed to fulfill the required refractive index profile. The experiments show that the compact acoustic retroreflector, whose radius is only approximately one wavelength, works in an incident angular range up to 120 degrees over a relatively broad bandwidth of about 27% of the central frequency. Such compact acoustic retroreflectors can be potentially applied in pulse-echo based acoustic detection and communication, such as unmanned aerial vehicle (UAV) sonar systems, robotic ranging detectors, ultrasonic imaging systems.

cond-mat.mtrl-sci↗

arXiv2017

Coherent perfect absorption and laser modes in a cylindrical structure of conjugate metamaterials

In this work, we theoretically find that coherent perfect absorption (CPA) and laser modes can be realized in a two-dimensional cylindrical structure composed of conjugate metamaterials (CMs). The required phase factors of CMs for achieving CPA and laser modes are determined by the geometric size of the CM cylinder, which is a unique feature compared with other non-Hermitian optical systems. Based on this property, we also demonstrate that CPA and laser modes can exist simultaneously in a CM cylinder with an extremely large size, where the excitations of CPA and laser modes depend on the angular momentum of coherent incident light. Therefore, compared with the well known parity time symmetry, our work opens up a brand-new path to obtaining CPA and laser modes, and is a significant advance in non-Hermitian optical systems.

physics.optics↗

arXiv2017

Acoustic Metacages for Omnidirectional Sound Shielding

Conventional sound shielding structures typically prevent fluid transport between the exterior and interior. A design of a two-dimensional acoustic metacage with subwavelength thickness which can shield acoustic waves from all directions while allowing steady fluid flow is presented in this paper. The structure is designed based on acoustic gradient-index metasurfaces composed of open channels and shunted Helmholtz resonators. The strong parallel momentum on the metacage surface rejects in-plane sound at an arbitrary angle of incidence which leads to low sound transmission through the metacage. The performance of the proposed metacage is verified by numerical simulations and measurements on a three-dimensional printed prototype. The acoustic metacage has potential applications in sound insulation where steady fluid flow is necessary or advantageous.

physics.app-ph↗

arXiv2017

Coherent perfect absorber and laser in purely imaginary conjugate metamaterials

Conjugate metamaterials, in which the permittivity and the permeability are complex conjugates of each other, possess the elements of loss and gain simultaneously. By employing a conjugate metamaterial with a purely imaginary form, we propose a mechanism for realizing both coherent perfect absorber (CPA) and laser modes, which have been widely investigated in parity-time symmetric systems. Moreover, the general conditions for obtaining CPA and laser modes, including obtaining them simultaneously, are revealed by analyzing the wave scattering properties of a slab made of purely imaginary conjugate metamaterials. Specifically, in a purely imaginary conjugate metamaterial slab with a sub-unity effective refractive index, perfect absorption can be realized for the incident wave from air.

physics.optics↗

arXiv2016

Acoustic Holographic Rendering with Two-dimensional Metamaterial-based Passive Phased Array

Acoustic holographic rendering in complete analogy with optical holography are useful for various applications, ranging from multi-focal lensing, multiplexed sensing and synthesizing three-dimensional complex sound fields. Conventional approaches rely on a large number of active transducers and phase shifting circuits. In this paper we show that by using passive metamaterials as subwavelength pixels, holographic rendering can be achieved without cumbersome circuitry and with only a single transducer, thus significantly reducing system complexity. Such metamaterial-based holograms can serve as versatile platforms for various advanced acoustic wave manipulation and signal modulation, leading to new possibilities in acoustic sensing, energy deposition and medical diagnostic imaging.

cond-mat.mtrl-sci↗

arXiv2015

Broad-band acoustic hyperbolic metamaterial

Acoustic metamaterials (AMMs) are engineered materials, made from subwavelength structures, that exhibit useful or unusual constitutive properties. There has been intense research interest in AMMs since its first realization in 2000 by Liu et al. A number of functionalities and applications have been proposed and achieved using AMMs. Hyperbolic metamaterials are one of the most important types of metamaterials due to their extreme anisotropy and numerous possible applications, including negative refraction, backward waves, spatial filtering, and subwavelength imaging. Although the importance of acoustic hyperbolic metamaterials (AHMMs) as a tool for achieving full control of acoustic waves is substantial, the realization of a broad-band and truly hyperbolic AMM has not been reported so far. Here, we demonstrate the design and experimental characterization of a broadband AHMM that operates between 1.0 kHz and 2.5 kHz.

physics.class-ph↗

arXiv2015

Active acoustic metamaterials reconfigurable in real-time

A major limitation of current acoustic metamaterials is that their acoustic properties are either locked into place once fabricated or only modestly tunable, tying them to the particular application for which they are designed. We present in this paper a design approach that yields active metamaterials whose physical structure is fixed, yet their local acoustic response can be changed almost arbitrarily and in real-time by configuring the digital electronics that control the metamaterial acoustic properties. We demonstrate experimentally this approach by designing a metamaterial slab configured to act as a very thin acoustic lens that manipulates differently three identical, consecutive pulses incident on the lens. Moreover, we show that the slab can be configured to implement simultaneously various roles, such as that of a lens and beam steering device. Finally, we show that the metamaterial slab is suitable for efficient second harmonic acoustic imaging devices capable to overcome the diffraction limit of linear lenses. These advantages demonstrate the versatility of this active metamaterial and highlight its broad applicability, in particular to acoustic imaging.

physics.class-ph↗

arXiv2014

Wavefront Modulation and Subwavelength Diffractive Acoustics with an Acoustic Metasurface

Metasurfaces are a family of novel wavefront shaping devices with planar profile and subwavelength thickness. Acoustic metasurfaces with ultralow profile yet extraordinary wave manipulating properties would be highly desirable for improving the performance of many acoustic wave-based applications. However, designing acoustic metasurfaces with similar functionality as their electromagnetic counterparts remains challenging with traditional metamaterial design approaches. Here we present a design and realization of an acoustic metasurface based on tapered labyrinthine metamaterials. The demonstrated metasurface can not only can steer an acoustic beam as expected from the generalized Snell s law, but also exhibits various unique properties including surface wave conversion, extraordinary beam-steering and apparent negative refraction through higher-order diffraction. Such designer acoustic metasurfaces provide a new design methodology for acoustic signal modulation devices and may be useful for applications such as beam-steering, surface wave manipulation, high efficiency sound absorption, acoustic imaging and ultrasound lens design.

cond-mat.mtrl-sci↗

arXiv2012

Measurements of Broadband Negative Index in Space-Coiling Acoustic Metamaterials

We report the experimental demonstration of broadband negative refractive index obtained in a labyrinthine acoustic metamaterial structure. Two different approaches were employed to prove the metamaterial negative index nature: one-dimensional extractions of effective parameters from reflection and transmission measurements, and two-dimensional prism-based measurements that convincingly show the transmission angle corresponding to negative refraction. The transmission angles observed in the latter case also agree very well with the refractive index obtained in the one-dimensional measurements and numerical simulations. We expect this labyrinthine metamaterial to become the unit cell of choice for practical acoustic metamaterial devices that require broadband and significantly negative indexes of refraction.

cond-mat.mtrl-sci↗

arXiv2011

Generalized Transformation Optics of Linear Materials

We continue the development of a manifestly 4-dimensional, completely covariant, approach to transformation optics in linear dielectric materials begun in a previous paper. This approach, which generalizes the Plebanski based approach, is systematically applicable for all transformations and all general linear materials. Importantly, it enables useful applications such as arbitrary relative motion, transformations from arbitrary non-vacuum initial dielectric media, and arbitrary space-times. This approach is demonstrated for a resulting material that moves with uniform linear velocity. The inverse problem of this covariant approach is shown to generalize Gordon's "optical metric".

physics.optics↗