Yifan Zhu

• PhD of Acoustics
• Professor at Southeast University

Encrypted acoustic meta‐holograms have potential applications in confidential acoustic information communication, noise control, acoustic cloaking, acoustic illusion, etc. Conventional encrypted optical and acoustic meta‐holograms only focus on the encrypted hologram in a single channel, viz. modulating spatial amplitude to project a holographic im...

Recent rapid developments in machine learning (ML) models have revolutionized the generation of images and texts. Simultaneously, generative models are beginning to permeate other fields, where they are being applied to the effective design of various structures. In the field of metamaterials, in particular, machine learning has enabled the creatio...

Recently, the concept of bound states in the continuum (BICs) has been extended to topological physics, inspiring investigations into higher-order topological BICs (TBICs) and related ultra-strong wave localization, which not only enriches the realm of topological physics but also bestows the BICs with inherent topological protection. However, prev...

classified higher‐order topological insulators (HOTIs) with chiral‐symmetric higher‐order topological phases protected by multipole chiral numbers (MCNs) have attracted extensive interest recently. However, how to design artificial ℤ‐classified HOTIs with multiple topological phases remains an unresolved issue. Here, multiorbital degrees of freedom...

Tunable ferroelectric film capacitors play an important role in tunable microwave devices and filter systems due to their high dielectric constant, low loss, and high dielectric tunability. However, there is a trade-off between low loss and high tunability, which limits further enhancement of dielectric performance. Here, we propose an ultra-tunabl...

We have developed an underwater acoustic meta-absorber that exhibits ultra-broadband absorption, with most of absorption coefficients exceeding 0.9 across the frequency range of 1 kHz−20 kHz. This performance is achieved through the localized trapping of acoustic waves and efficient energy dissipation, facilitated by local resonances within meticul...

We numerically and experimentally report the acoustic analogue of the super-Klein tunneling in a heterojunction of phononic crystals formed with Willis scatterers that exhibit pseudospin-1 Dirac cones. Pseudospin-1 Dirac cones are characterized by a triple states degeneracy in the band structure where two linear bands intersect with a flatband. The...

A R T I C L E I N F O Keywords: Acoustic-mechanical metamaterial Acoustic-mechanical metasurface Nonlocal coupling effect Sound absorption and vibration reduction A B S T R A C T We propose an acoustic-mechanical metasurface with simultaneous sound absorption and vibration reduction functionalities. This acoustic-mechanical feature results from a n...

In this paper, we present an alternative design for an acoustic metasurface with sparse units featuring open-ended pipes located on both sides of a central cavity, which can be tuned by designing the widths and length sizes. Band-stop and band-pass transmission control can be easily attained by alternating these units’ periodic arrangements with an...

In this paper, we propose a broadband tunable acoustic matching layer (BTAML) comprising an array of piezoelectric elements with non-uniform gradient shunt circuits (NGSCs). The effective impedance of the BTAML can be controlled in real time by regulating the parameters of NGSCs. The theoretical results demonstrate that BTAML is capable of adjustin...

With the development of flexible electronics, flexible tunable capacitors with high dielectric constant, high tunability, and low loss become important components in modern communication. A tunable Ba0.6Sr0.4TiO3 capacitor for radio frequency devices is prepared on a flexible substrate. The capacitor has a dielectric constant greater than 1000, cap...

We report on the theoretical, numerical, and experimental investigation of secure acoustic holography. This secure holography is achieved via an encoded hologram generated by a transducer array decoded by a transmissive acoustic metakey. An unreadable image is received if directly using the encoded hologram, while the desired image can be obtained...

We numerically and experimentally report the acoustic analogue of the super-Klein tunneling in a heterojunction of phononic crystals formed with Willis scatterers that exhibit pseudospin-1 Dirac cones. By comparing with the pseudospin-1/2 Dirac cones, pseudospin-1 ones require in the band structure an additional flatband across the Dirac points. Th...

We investigate the transverse trapping force acting on a small particle on or off the central axis of zero-order finite Bessel beams. Combining the simulated fields with the Gorkov force potential, the transverse trapping behaviors for small objects are analyzed, and the reversal of the trapping behaviors is recovered when varying the paraxiality p...

Passive acoustic wave manipulations are severely constrained by the narrow frequency bandwidth of acoustic metastructures. In this research, an unprecedented type of reconfigurable acoustic metascreen is proposed for broadband manipulations of transmitted acoustic waves. The conceived structure is composed of uniquely designed unit cells producing...

Skyrmions with topologically stable configuration have shown a promising route toward high-density magnetic and photonic information processing due to their defect-immune and low-driven energy. Here, we experimentally report and observe the existence of phononic skyrmions as new topological structures formed by the three-dimensional hybrid spin of...

Conventional acoustic metamaterial barriers are usually used to realize sound insulation for a continuous broad bandwidth. In some practical scenes, however, the noise signal from complex noise sources, such as gearboxes and motors, are usually complicated spectra with discrete peaks or valleys, instead of perfect continuous ones. In this case, the...

Elastic metamaterial, an engineered artificial material, has received much attention in physics and engineering communities due to its functional properties unavailable in natural materials. However, most elastic metamaterials, especially for their two-dimensional structures, belong to the Hermitian category, making them difficult to adapt to real...

Ventilated acoustic insulators can block sound whereas simultaneously allowing airflow, which has potential applications for noise control in ventilation structures. In this paper, we propose a highly sparse acoustic meta-insulator array consisting of multiple tunable units. The meta-insulator unit with a minimum deep subwavelength thickness of 0.0...

Skyrmions with topologically stable configurations have shown a promising route toward magnetic and photonic materials for information processing due to their defect-immune and low-driven energy. However, the practical application of magnetic skyrmions is severely hindered by their harsh cryogenic environment and complex carriers. In addition, the...

The advent of the acoustic metasurfaces offered an unprecedented expansion of our ability to manipulate and structure sound waves for many exotic functionalities. However, the metasurface designs require deep expertise in acoustics and highly intensive iterative computations using Finite Element Method. In this work, we use a two-dimensional convol...

Acoustic insulation in ventilated structures is an important problem in acoustic engineering with many potential practical applications, such as the noise control for ventilating ducts of buildings, vehicles, or air conditioners. Acoustic metamaterial is a good candidate for the design of acoustic insulation for ventilated channel (AIVC) because th...

In this work, we demonstrate nonreciprocal acoustic wave transmission in two-cascaded Fabry-Perot-like slab resonators undergoing time modulation of their effective density. A phase difference is introduced into the time modulation between the two coupled resonators to produce spatial bias to access unidirectional wave propagation. A theoretical mo...

In this research, we propose and design an acoustic metamuffler (AMM) by coupling a microperforatedplate and a composite waveguide formed by a main waveguide and a Helmholtz resonator. The pro-posed mechanism and deliberately designed structure are conducive to generating multimode resonancesthat help to improve the coupling absorption effect and l...

Integrating different reliable functionalities in metastructures and metasurfaces has become of remarkable importance to create innovative multifunctional compact acoustic, optic or mechanical metadevices. In particular, implementing different wave manipulations in one unique material platform opens an appealing route for developing integrated meta...

Classical designs of acoustic meta-absorber usually have a trade-off between bandwidth, efficiency and thickness. Here, we introduce the concept of nonlocal acoustic metasurface absorber by using a bridge structure connecting resonating unit cells to improve the performances of the meta-absorber. By utilizing the coupling effect between the adjacen...

Semi-infinite elastic metamaterials and metasurfaces on homogeneous elastic half-spaces have attracted significant attention in the past two decades as efficient artificial structures to control and mitigate surface waves. In this research, the first two attenuation zones of an elastic metasurface composed of different arrangements of pillars on a...

Acoustic metasurface has become one of the most promising platforms for manipulating acoustic waves with the advantage of ultra-thin geometry. The conventional design method of acoustic metasurface relies on numerical, trial-and-error methods to retrieve effective properties of the locally resonant unit cells. It is often inefficient and requires s...

Seismic metamaterials (SMs) are expected to assist or replace traditional isolation systems owing to their strong attenuation of seismic waves. In this work, a one-dimensional inverted T-shaped SM (1D ITSM) composed of arrays of inverted T-shaped structures on a half space is proposed, which have an ultra-wide first bandgap (FBG) from 6.7 to 17.2 H...

As shown in Experiment Video 1, in the test area of the beam, the incident wave is a perfect traveling wave, which confirms the elastic meta-absorber indeed, perfectly absorbs flexural waves. The displacement deformations inside the whole sub-beams are greatly enhanced, which is consistent with the theory.

For comparison, we also test the dynamic full wavefield at 3.2 kHz (away from the central frequency), as shown in Experiment Video 2. The intuitive evidence is the incident wave is a standing wave and the displacement deformations inside the sub-beams are not enhanced.

The partial or complete confinement of waves in an open system is omnipresent in nature and in wave-based materials and technology. Here, we theoretically analyze and experimentally observe the formation of a trapped mode with perfect mode conversion (TMPC) between flexural waves and longitudinal waves, by achieving a quasi-bound state in the conti...

Conventional vibration absorber is challenging to use in the extreme environment of high (low) temperature, due to the low tolerance of its additional damping material to temperature. To adapt to the extreme environment, here we propose an elastic meta-absorber (EMA) based on the quasi-bound states of the continuum (BICs) physical approach. The pro...

Acoustic holograms have promising applications in sound‐field reconstruction, particle manipulation, ultrasonic haptics, and therapy. This study reports on the theoretical, numerical, and experimental investigation of multiplexed acoustic holograms at both audio and ultrasonic frequencies via a rationally designed transmission‐type acoustic metamat...

The partial or complete confinement of waves in an open system is omnipresent in nature and in wave-based materials and technology. Here, we theoretically analyze and experimentally observe the formation of a trapped mode with perfect mode conversion (TMPC) between flexural waves and longitudinal waves, by achieving a quasi-bound state in the conti...

Classical meta-absorber designs usually have a tradeoff between bandwidth, efficiency, and thickness. Here, we introduce the concept of a nonlocal acoustic metasurface absorber by using a bridge structure connecting resonating unit cells to improve the performances of the meta-absorber. By utilizing the coupling effect between the adjacent unit cel...

Acoustic holograms have promising applications in sound-field reconstruction, particle manipulation, ultrasonic haptics and therapy. This paper reports on the theoretical, numerical, and experimental investigation of multiplexed acoustic holograms at both audio and ultrasonic frequencies via a rationally designed transmission-type acoustic metamate...

In engineering, plate structures are one type of the main load-bearing structures. However, most of the designed plate-like metamaterials/metasurfaces need to be heavily grooved or drilled on the original plate surface, which will inevitably cause some destruction to the strength and stiffness of the host plate structures. To overcome this weakness...

Seismic metamaterials (SMs) are expected to assist or replace traditional isolation systems owing to their strong attenuation of seismic waves. In this paper, a one-dimensional inverted T-shaped SM (1D ITSM) with an ultra-wide first bandgap (FBG) is proposed. The complex band structures are calculated to analyze the wave characteristics of the surf...

Metasurface-based acoustic hologram projectors fabricated with fixed microstructures can only generate the predesigned images at a single or few discrete frequencies. Here, a variety of acoustic holographic applications can be realized in broadband by a matched helical design of the tunable lossy acoustic metasurface (TLAM). The proposed TLAM unit...

We propose the design of an ultrathin planar acoustic metasurface with wavelength-dependent manipulation of a reflected wave. The metasurface comprises meta-atoms composed of multiple resonant elements working collectively to produce desired phase responses at different frequencies. We numerically demonstrate the performance of the proposed device...

Acoustic equalization is the process of adjusting the frequency response of a broadband sound signal, which is widely used in communication-system and audio acoustics. Here we introduce the concept of an acoustic meta-equalizer, viz., a passive acoustic metamaterial-based filter that has a tunable frequency response within an ultrabroadband range (...

Broadband acoustic absorbers with thin thickness are highly desired in practical situations such as architectural acoustics, yet it is still challenging to achieve high absorption by using structure with limited thickness. Here we report the theoretical optimal design, numerical simulation and experimental demonstration of a planar acoustic absorbe...

Superfocusing of acoustic and elastic waves is generally achieved by the combination of negative refraction and the enhancement of the evanescent waves. Here, we numerically and experimentally demonstrate the bifunctionality of a superlens that can simultaneously focus acoustic and flexural waves beyond the diffraction limit. The designed structure...

Metasurface-based acoustic vortex generators formed by fixed microstructures can only transfer the first-order orbital angular momentum (OAM) at a single frequency in a waveguide. Here, the multiple order acoustic vortices are realized through a helical metasurface design that is geometrically compact, broadband, and tunable. The proposed metasurfa...

The discovery of the disorder effect in traditional metamaterials has opened up possibilities in the search for disordered metasurfaces. Photonic, dielectric, and elastic metamaterials that exhibit added value of the disorder effect on wave-propagation physics are reported. Despite this extensive attention and progress in disordered metamaterials,...

A severe limitation of current acoustic metasurfaces remains in their modest tunability to meet multifrequency requirements and alterable functionalities on demand. Here, a reconfigurable curved acoustic metasurface for acoustic cloaking and illusion is reported. The structure is composed of an array of tunable helical units to break this limitatio...

We introduce a multicoiled acoustic metasurface providing quasiperfect absorption (reaching 99.99% in experiments) at an extremely low-frequency of 50 Hz, simultaneously featuring an ultrathin thickness down to λ/527 (1.3 cm). In contrast to the state of the art, this original conceived multicoiled metasurface offers additional degrees of freedom c...

We theoretically and experimentally propose two designs of broadband low-frequency acoustic metasurface coiled absorbers (Sample I/Sample II) for the frequency ranges of 460 Hz–972 Hz and 232 Hz–494 Hz (larger than 1 octave), with absorption larger than 0.8 (average is 0.87), and having the ultra-thin thickness of 4.5 cm and 9 cm respectively (λ/17...

No PDF available ABSTRACT Nonreciprocal acoustic systems, in which the reciprocity obeyed by wave motion in conventional propagation media, offer the possibility to achieve asymmetric transmission and contain rich physics. The emergence of “acoustic rectifier” for the first time realized both theoretically and experimentally the non-reciprocal wave...

Creating complex spatial objects from a flat sheet of material using origami folding techniques has attracted attention in science and engineering. We design, model, and fabricate reconfigurable origami-inspired metamaterials whose unit cells can be easily tailored into numerous specific shapes. Via combinations of different shapes of the unit cell...

Invisibility or unhearability cloaks have been made possible by using metamaterials enabling light or sound to flow around obstacle without the trace of reflections or shadows. Metamaterials are known for being flexible building units that can mimic a host of unusual and extreme material responses, which are essential when engineering artificial ma...

We introduce a multi-coiled acoustic metasurface providing a quasi-perfect absorption (reaching 99.99% in experiments) at extremely low-frequency of 50 Hz, and simultaneously featuring an ultrathin thickness down to {\lambda}/527 (1.3 cm). In contrast to the state of the art, this original conceived multi-coiled metasurface offers additional degree...

We introduce a multi-coiled acoustic metasurface providing a quasi-perfect absorption (reaching 99.99% in experiments) at extremely low-frequency of 50 Hz, and simultaneously featuring an ultrathin thickness down to λ/527 (1.3 cm). In contrast to the state of the art, this original conceived multi-coiled metasurface offers additional degrees of fre...

We theoretically and experimentally propose two designs of broadband low-frequency acoustic metasurface absorbers (Sample I/Sample II) for the frequency ranges of 458Hz~968Hz and 231Hz~491Hz (larger than 1 octave), with absorption larger than 0.8, and having the ultra-thin thickness of 5.2cm and 10.4cm respectively ({\lambda}/15 for the lowest work...

We theoretically and experimentally propose two designs of broadband low-frequency acoustic metasurface absorbers (Sample I/Sample II) for the frequency ranges of 458Hz~968Hz and 231Hz~491Hz (larger than 1 octave), with absorption larger than 0.8, and having the ultra-thin thickness of 5.2cm and 10.4cm respectively (λ/15 for the lowest working freq...

We demonstrate multifunctional acoustic metasurfaces that can simultaneously realize the same functionality or multiple different functionalities at multiple tunable frequencies. The fundamental physical mechanism is based on designing a supercell of Helmholtz resonators with multiple resonances operating at different frequencies. We theoretically,...

We propose a multiplexed-acoustic-metasurface hologram that can project multiple predesigned images at different frequencies. We demonstrate the generation of fourfold acoustic holographic images by one metasurface at 3500, 4500, 5500, and 6500 Hz, respectively, and discuss their fundamental physics. We uncover the design of this acoustic hologram...

We report the experimental realization of an acoustic Chern insulator (ACI), by using an angularmomentum- biased resonator array with the broken Lorentz reciprocity. High Q-factor resonance of the constituent rotors is leveraged to reduce the required rotation speed. ACI is a new topological acoustic system analogous to the electronic quantum Hall...

Invisibility or unhearability cloaks have been made possible by using metamaterials making light or sound flow around obstacle without the trace of reflections or shadows. Metamaterials are known for being flexible building units that can mimic a host of unusual and extreme material responses, which are essential when engineering artificial materia...

As a key component of various acoustic systems, acoustic beam splitter (BS) finds important application in many scenarios, yet are conventionally based on the assumption that the acoustic waves propagate as easily when incident from either input or output side. It would therefore be intriguing, from the viewpoints of both science and technology, to...

The fine manipulation of sound fields is critical in acoustics yet is restricted by the coupled amplitude and phase modulations in existing wave-steering metamaterials. Commonly, unavoidable losses make it difficult to control coupling, thereby limiting device performance. Here we show the possibility of tailoring the loss in metamaterials to reali...

High-efficiency emission of multipoles is unachievable by a source much smaller than the wavelength, preventing compact acoustic devices for generating directional sound beams. Here, we present a primary scheme towards solving this problem by numerically and experimentally enclosing a monopole sound source in a structure with a dimension of around...

Acoustic metasurfaces provide a way to manipulate wavefronts at anomalous reflection or refraction angles through subwavelength structures. Here, based on the generalized Snell's refraction law for acoustic metasurfaces and the classical acoustic phased array (PA) theory, a broadband acoustic PA with a subwavelength active tube array has been propo...

Topological insulators are new states of matter in which the topological phase originates from symmetry breaking. Recently, time-reversal invariant topological insulators were demonstrated for classical wave systems, such as acoustic systems, but limited by inter-pseudo-spin or inter-valley backscattering. This challenge can be effectively overcome...

As an important problem in acoustics, sound insulation finds applications in a great variety of situations. In the existing schemes, however, there has always been a tradeoff between the thinness of sound-insulating devices and their ventilating capabilities, limiting their potentials in the control of low-frequency sound in high ventilation enviro...

As an important problem in acoustics, sound insulation finds applications in a great variety of situations. In the existing schemes, however, there has always been a tradeoff between the thinness of sound-insulating devices and their ventilating capabilities, limiting their potentials in the control of low-frequency sound in high ventilation enviro...

Schroeder diffusers, as a classical design of acoustic diffusers proposed over 40 years ago, play key roles in many practical scenarios ranging from architectural acoustics to noise control to particle manipulation. Despite the great success of conventional acoustic diffusers, it is still worth pursuing ideal acoustic diffusers that are essentially...

“Schroeder diffuser” is a classical design, proposed over 40 years ago, for artificially creating optimal and predictable sound diffuse reflection. It has been widely adopted in architectural acoustics, and it has also shown substantial potential in noise control, ultrasound imaging, microparticle manipulation et al. The conventional Schroeder diff...

Suppression of the transmission of undesired sound in ducts is a fundamental issue with wide applications in a great variety of scenarios. Yet the conventional ways of duct noise control have to rely on mismatched impedance or viscous dissipation, leading the ducts to have ventilation capability weakened by inserted absorbers or a thick shell to ac...

We propose and experimentally achieve a directional dipole field radiated by an omnidirectional monopole source enclosed in a subwavelength structure of acoustically hybrid resonances. The whole structure in every dimension is an order smaller than the sound wavelength. The significance is that the radiation efficiency is up to 2.3 of the radiation...

Non-blind invisibility cloaks allowing the concealed object to sense the outside world have great application potentials such as in high-precision sensing or underwater camouflage. However the existing designs based on coordinate transformation techniques need complicated spatially-varying negative index or intricate multi-layered configurations, s...

Schroeder diffuser is a classical design, proposed over 40 years ago, for artificially creating optimal and predictable sound diffuse reflection. It has been widely adopted in architectural acoustics and it has also shown substantial potential in noise control, ultrasound imaging, microparticle manipulation, among others. The conventional Schroeder...

We propose to produce efficient three-dimensional sound converging in broadband with binary reflected phases on a planar surface with unit cells consisting of only two kinds of elements. The mechanism is experimentally demonstrated by focusing airborne sound and by forming an “acoustic needle,” with handmade arrays of commercial test tubes with/wit...

We theoretically and numerically present the design of multi-frequency acoustic metasurfaces (MFAMs) with simple structure that can work not only at fundamental frequency, but also at their harmonic frequencies, which breaks the single frequency limitation in conventional resonance-based acoustic metasurfaces. The phase matched condition for achrom...

We report the theoretical design, numerical simulation, and experimental demonstration of a flat mirror capable to efficiently focus the reflected sound in three-dimensional space within an ultra-broad band. The proposed mirror is implemented with a textured rigid surface, enabling simple design and easy fabrication. We analytically derive the dist...

Spatial modulation of acoustic wave has demonstrated theoretical and experimental importance in the field of acoustics, with wide applications such as in medical ultrasound and particle manipulation. However, the existing means for acoustic modulation have to rely on the acoustic metasurfaces providing only pure phase modulation or active element a...