Michael J. Leamy

Abstract It is my pleasure to announce the winner of the 2025 Journal of Vibration and Acoustics Best Paper Award. Based on a selection process that included nominations open to all Associate Editors on the Editorial Board, followed by careful consideration and voting open to the same, the winner of the award was determined to be Edmundo F. Lavia, Juan D. Gonzalez, and Guadalupe Cascallares for their paper entitled “Tetrascatt Model: Born Approximation for the Estimation of Acoustic Dispersion of Fluid-Like Objects of Arbitrary Geometries,” J. Vib. Acoust., Feb 2025, 147(1): 011004, https://doi.org/10.1115/1.4067286. The authors will receive a $1,500 honorarium and a Best Paper plaque.

We explore topological properties of one-dimensional (1D) bilayered elastic rods (i.e., phononic crystals) using the phason as a virtual dimension and subsequently analyze topological interface modes. Following adoption of the phason, we use a two-dimensional (2D) topological invariant---the Chern number---and show that its differences for various crystals predict the number of gapless interface states in $(1+1)\mathrm{D}$ systems. The latter constitutes a manifestation of the bulk-boundary correspondence principle. We develop equations of periodic systems that depend explicitly on the phason, hence facilitate understanding and bring new insight into wave propagation and dynamics of topological states in these media. For the design and analysis of interface modes in systems with two virtual parameters, we introduce the phason-phason space. We find that the interface states mark strips in this space, separated by linear functions with slopes related to the Chern numbers. Consequently, this space can be used to directly predict the Chern numbers of both adjoined phononic crystals as well as the number of gapless interface modes for different phason changes.

We experimentally demonstrate the tunability of a topological defect mode and its spectral flow within the bandgap of a periodic structure made of beams and cylindrical masses and hosting a topological bandgap in its frequency spectrum. A defect is introduced by incorporating a pair of piezoelectric plates into a single unit cell of the lattice, giving rise to a localized mode inside the bandgap. We experimentally observe this mode and its spectral flow in the bandgap by altering the elastic modulus of the piezoelectric plates using negative capacitance shunt circuits. Further, through finite element simulations and experiments, we show that the spectral flow can be tuned by modulating the mass of the defect cell alone. This work introduces additional degrees of freedom in the design of elastic wave-based devices for applications in acoustic logic, waveguiding, and energy harvesting.

Abstract We present a cyclically-arranged split-ring resonator metamaterial design that is capable of simultaneously attenuating P, SH, and SV-waves. The design targets tonal vibration frequencies in electric vehicles (EVs) caused by inverters and electric machines. The metamaterial’s plate-like nature facilitates straight-forward integration with unibody sheet metal structures commonly found in automotive applications. The basis for the unit cell is a sub-cell with nearly-coincident in-plane and out-of-plane resonant frequencies. This sub-cell effectively blocks SV-waves and P or SH-waves in a single polarization direction dependent on the resonator orientation. To achieve a total bandgap in all propagation directions, we cyclically rotate and replicate the sub-cell to form a unit cell containing 2×2 sub-cells. We then compute the unit cell’s band structure using a finite element model, documenting the expected bandgaps. To validate the numerical predictions, we fabricate a square polylactic acid plate embedded with 25 unit cells and subject it to P, SH, and SV-wave excitation on one edge using an electrodynamic shaker. We measure the displacement of the structure on the opposite edge using a laser Doppler vibrometer and compute the response transfer function. Results demonstrate significant attenuation of P, SH, SV-waves within the targeted frequency range of at least 35 dB, with SV-waves exhibiting the highest attenuation. This enhanced suppression of SV-waves is attributed to a greater number of sub-cells per unit cell participating in resonance compared to P and SH-waves. The measured performance demonstrates the strong potential for the proposed metamaterial to attenuate tonal frequencies in EV applications, potentially without additional mass.

Abstract We present optimized phononic crystals for tailoring wave propagation and damage in one-dimensional media under plastic amplitude excitation. We first adapt an optimization procedure, coupled to the semi-analytical treatment of elastic-plastic wave propagation, to assist in configuring phononic crystals of variable cross-section. A scenario-specific objective function, with elastic-plastic wave propagation predictions, quantifies a performance metric for a phononic crystal with a dogbone-like unit cell. As such, starting with an initial phononic crystal design and the objective function, the optimization approach yields phononic crystals exhibiting enhanced wave propagation characteristics in comparison to a uniform rod. Specifically, we apply the approach to three idealized one-dimensional problems involving elastic-plastic wave propagation: (i) vibration and damage mitigation, (ii) pulse shaping, and (iii) occupant protection. Through these scenarios, we demonstrate the ability of optimized phononic crystals to mitigate damage by suppressing select plastic wave frequency content, manipulating a time-domain pulse by extending its duration, and localizing damage as a protective measure. Furthermore, the optimized designs subtract material from a uniform sample, producing lightweight and easily manufactured structures. Ultimately, the research results support the use of optimized phononic structures as a means to extend the design space associated with elastic-plastic damage mitigation, pulse shaping, and impact protection.

Electrification of the transportation sector will bring about significant reductions in greenhouse gas emissions. However, with increasing penetration of electric vehicles (EVs) and overnight charging patterns, evening surges in power demand will stress power distribution infrastructure and degrade power quality. To address this, we present a two-stage smart charging (SC) algorithm for an EV fleet and a depot equipped with solar power generation and energy storage to minimize electricity costs and negative grid effects. We use real data from an Iowa feeder model to study the result of placing the fleet at various commercial nodes. We present a fleet-operator cost analysis under a time-of-use rate plan, and a grid-operator impact analysis considering transformer overloads and voltage sensitivity changes. The proposed two-stage SC algorithm reduces operator costs by <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${1 9. 6 \% - 4 9. 3 \%}$</tex>, and mitigates transformer overload events and voltage sensitivity changes caused by rapid charging and rule-based BESS operation.

We pose and solve a two-stage smart charging (SC) problem for a single residence equipped with an electric vehicle (EV), battery energy storage system (BESS), and solar photovoltaic panels. We study the differences between an example rule-based operation of BESS and our SC problem, seeking to minimize homeowner costs and perform peak-shaving. Furthermore, we compare unregulated EV charging and our two-stage SC algorithm. We apply our models to a single residence in the Southern US with historical home demand and solar generation data under a time-of-use (TOU) rate plan to study cost changes alongside aggregate demand for one year. We determined our two-stage SC solution to be more effective at minimizing electricity costs and demand spikes under a TOU rate plan when compared to the rule-based operation of BESS and unregulated EV charging.

We experimentally demonstrate a topologically protected electroacoustic transistor. We construct a reconfigurable phononic analog of the quantum valley-Hall insulator composed of electrically shunted piezoelectric disks bonded to a patterned plate forming a monolithic structure. The device can be dynamically reconfigured to host one or more topological interface states via breaking inversion symmetry through selective powering of shunt circuits. Above a threshold, the amplitude of wave energy at a chosen location in one topological interface creates a second interface by dynamically switching power between two groups of shunts using relays. This enables the flow of wave energy between two locations in the reconfigured interface analogous to the voltage-controlled electron flow in a field effect transistor. The amplitude of wave energy in the second interface is used for bit abstraction to implement acoustic logic. We illustrate the various states of the transistor and experimentally demonstrate wave-based switching. The proposed electroacoustic transistor is envisioned to find applications in wave-based devices and edge computing in extreme environments and inspire novel technologies leveraging acoustic logic.

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;We propose a novel Split Ring Resonator (SRR) metamaterial capable of achieving a total (or complete) bandgap in the material’s band structure, thereby reflecting airborne and structure-borne noise in a targeted frequency range. Electric Vehicles (EVs) experience tonal excitation arising from switching frequencies associated with motors and inverters, which can significantly affect occupant perception of vehicle quality. Recently proposed metamaterial designs reflect airborne noise and structure-borne transverse waves over a band of frequencies, but do not address structure-borne longitudinal waves in the same band. To achieve isolation of acoustic, transverse, and longitudinal elastic waves associated with tonal frequencies, we propose a metamaterial super cell with transverse and longitudinal resonant frequencies falling in a total bandgap. We calculate the resonant frequencies and corresponding mode shapes using finite element (FE) modal analysis. We obtain the unit cell band structure by applying Floquet-Bloch boundary conditions to a single cell and subsequently solve the associated eigenvalue problem. We compute the out-of-plane polarization of the eigenmodes to further distinguish between in-plane and flexural bandgaps. The resonant frequencies depend on the material used and the physical dimensions of the unit cell features. Using aluminum, we design the super cell to exhibit resonant frequencies and a total bandgap near 10 kHz, which is typically observed in the frequency content of inverter noise. Scaling the unit cell size also offers a predictable shift in the resonant frequencies, and thereby bandgap, offering adaptability for regulating various frequency emissions under consideration. Further, we assess the frequency response functions of the structure-borne vibration transmission using FE analysis and evaluate the sound transmission loss (STL) of the metamaterial using simulations accounting for coupled acoustic-structure interactions. Our proposed metamaterial is based on plate-like and shell-like structures commonly employed in automotive design, and thus can serve as a cost-effective and lightweight alternative to traditional sound-deadening materials.&lt;/div&gt;&lt;/div&gt;

We review the notion of “phase bit” or “phi-bit” in externally driven nonlinear acoustic metamaterials. Phi-bits are classical analogues of quantum bits, which open pathways to promising and validated modes of initializing, operating, and measuring information. Acoustic metamaterials offer ways to compute information using phase that should compare favorably with state-of-the-art quantum systems without suffering from quantum fragility.

Topological insulators (TIs), exhibiting topologically protected edge and interface waves, have recently emerged in phononic systems. Reconfigurabilty is essential for enabling TI-based applications. One potential means for achieving reconfigurability employs shunted piezoelectric (PZT) disks in which a unit cell’s mechanical impedance is altered using negative capacitance circuits. Dynamic reconfigurability and programmability of such material platforms can then be obtained through simple on/off switching. In this vein, we propose and experimentally verify an electroacoustic TI which exhibits programmable topologically protected edge states useful for acoustic multiplexers, demultiplexers, and transistors. This reconfigurable structure is composed of an elastic hexagonal lattice whose unit cell contains two shunted PZT disks, each connected to a negative capacitance circuit by an on/off switch. Closing one or the other circuit results in the breaking of mirror symmetry and yields mechanical behavior analogous to the quantum valley Hall effect. By interfacing two topologically distinct materials, a domain wall is introduced exhibiting a localized interface state topologically protected from backscattering at defects and sharp edges. Through the use of programmable time-division, in which domain walls appear and disappear in time, we demonstrate multiplexing and demultiplexing. We also demonstrate an acoustic transistor using the same programmable platform, before closing with a discussion on future research directions.

Abstract We investigate the spectral properties of one-dimensional spatially modulated nonlinear phononic lattices, and their evolution as a function of amplitude. In the linear regime, the stiffness modulations define a family of periodic and quasiperiodic lattices whose bandgaps host topological edge states localized at the boundaries of finite domains. With cubic nonlinearities, we show that edge states whose eigenvalue branch remains within the gap as amplitude increases remain localized, and therefore appear to be robust with respect to amplitude. In contrast, edge states whose corresponding branch approaches the bulk bands experience de-localization transitions. These transitions are predicted through continuation studies on the linear eigenmodes as a function of amplitude, and are confirmed by direct time domain simulations on finite lattices. Through our predictions, we also observe a series of amplitude-induced localization transitions as the bulk modes detach from the nonlinear bulk bands and become discrete breathers that are localized in one or more regions of the domain. Remarkably, the predicted transitions are independent of the size of the finite lattice, and exist for both periodic and quasiperiodic lattices. These results highlight the co-existence of topological edge states and discrete breathers in nonlinear modulated lattices. Their interplay may be exploited for amplitude-induced eigenstate transitions, for the assessment of the robustness of localized states, and as a strategy to induce discrete breathers through amplitude tuning.

Using analytical and numerical means, we document a geometry-enabled phenomenon, termed herein dispersion morphing, in which lattice stretching in rotator structures modifies the real and imaginary dispersion characteristics of the system. We then demonstrate diverse functionality derived from dispersion morphing under adiabatic (static) and nonadiabatic (dynamic) lattice deformation, to include dramatic changes in group velocity, refractive index, directivity, and amplification. The proposed rotator lattices consist of in-plane rotators coupled by angled elastic linkages the location and spacing of which can be easily reconfigured, allowing significant changes in the dispersion characteristics of the lattices. Under adiabatic lattice deformation, we reconfigure the directivity and refractive index of the periodic structure and present a closed-form solution to achieve flat bands across the entire wave-number domain. We also incorporate chirality in the unit-cell design to counteract pass-band shifting in the process of dispersion morphing, such that a real-time wave manipulation becomes possible. For dynamic lattice deformation, we model the lattice constant as (i) a step function of time and (ii) a harmonic function of time. In the former scenario, we employ the concept of temporal interfaces and achieve on-demand time delay of the propagation. In the latter scenario, we demonstrate a parametric amplification effect with stretching-informed amplification parameters. We report strong agreement between our theoretical analysis and numerical simulations, verifying the aforementioned findings. We believe that the versatile adaptations of such rotator lattices and their rich dynamics may inspire next-generation reconfigurable and multifunctional metamaterial devices.

In this paper we conceptualize electroacoustic transistors based on topologically protected interface states in a reconfigurable valley-Hall topological insulator. Using piezoelectric media and active shunt circuits, we numerically model the spatial inversion symmetry breaking in a unit cell to produce topological bandgaps. These gaps are known to host robust modes for wave propagation along an interface. We use two such modes to design a transistor where the wave propagation in one topological channel switches on or off a second topological channel between a source and receiver elsewhere in the structure. Multiple such transistors may be combined to develop logic gates. Further, we develop and simulate the behavior of an electronic circuit which enables the transistor action. Our design opens a pathway to novel wave-based devices which may find applications in structure-based computing, as hybrid multiplexers in communication devices, and as structural switches or embedded sensors in robotics and internet of things.

Unrestricted charging of electric vehicles (EVs) can result in violations of the grid’s operating limits, and/or equipment damage or failure. To address this, we propose a two-stage smart charging (SC) algorithm for EVs in single-family residences. In the first stage, we pose an SC optimization problem considering only the EV owner’s interests. In the second stage, we leverage the existence of multiple optimal (or near-optimal) solutions to this optimization problem to reduce the grid impact of EV charging at no (or negligible) cost to the EV owner. We then assess the grid impact of our SC strategy in a residential area, where all EVs are controlled in a decentralized manner (i.e., independently of one another). For comparison, we also assess the grid impact of rapid charging and other known SC strategies. Our assessment utilizes Monte-Carlo simulation techniques and a physics-based distribution feeder model. Focusing only on the price-minimization SC problem, we show that (i) if existing SC strategies are employed, then SC can have the same undesirable effects as unrestricted, rapid charging, and (ii) if our proposed SC strategies are employed, then SC can significantly lower the grid impact of EV adoption at no additional cost to the EV owner.

Abstract We propose an electroacoustic transistor enabled by reconfigurable topological insulators (TIs). The underlying structure of the device is a hexagonal lattice with a unit cell consisting of piezoelectric disks bonded to an aluminum substrate. First, we study the dispersion of flexural waves in the reconfigurable TI to identify Dirac cones in the band structure of a unit cell possessing C6v-symmetry. A topological bandgap can be opened by breaking inversion symmetry in the unit cell. This is achieved by altering the elastic response of one of the affixed piezoelectric disks using a negative impedance shunt circuit. Next, we analyze various topological states formed by interfacing mirror-symmetric unit cells. Sublattices with interface states are then combined to construct a transistor supercell which hosts at least two topologically protected channels for wave propagation. The amplitude of an incoming acoustic signal propagating in one of the topological channels, referred to as the ‘Gate’, is used to switch on or off a second topological channel between a wave source and receiver, mimicking the behavior of a field effect transistor in electronics. We employ finite element analysis to study the harmonic response of the transistor structure demonstrating the OFF and ON states of the device. Further, we present a mock-up of an electrical circuit which enables the switching of the topological channel between a wave source and receiver. The design of the proposed wave-based transistor promises the advantage of topological protection and may find applications in wearable devices, edge computing, and sensing in harsh environments.

This paper describes the development and demon-stration of a smart charging system for a plug-in electric vehicle (EV) that can help manage grid impacts. Our vehicle-external smart charging system supports charging Levels 1 and 2 defined in the SAE J1772 standard, and interfaces with the EV through (i) a standard charging cable, and (ii) a third-party telematics API (compatible with a wide range of EV manufacturers). The smart charging system interacts with the EV owner via a smartphone application to obtain charging requirements and preferences. User preferences inform an optimization objective function which captures multiple interests of the EV owner via a user-weighted sum of three performance metrics: cost of electricity, usage of renewable energy, and time-to-charge. An optimization-based feedback control algorithm determines an optimal set of time intervals, during which to charge the EV at a pre-defined, constant power level. Power flow to the EV is subsequently (dis)allowed accordingly by controlling a relay placed between the EV and the mains connection. Experimental results demonstrate minimum-cost charging of a 2021 Volvo XC90 Recharge using our prototype smart charging system.