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Some topographies in plate structures can hide cracks and make it difficult to monitor damage growth. This is because topographical features convert homogeneous structures to heterogeneous one and complicate the wave propagation through such structures. At certain points destructive interference between incident, reflected and transmitted elastic waves can make those points insensitive to the damage growth when adopting acoustics based structural health monitoring (SHM) techniques. A newly developed nonlinear ultrasonic (NLU) technique called sideband peak count – index (or SPC-I) has shown its effectiveness and superiority compared to other techniques for nondestructive testing (NDT) and SHM applications and is adopted in this work for monitoring damage growth in plate structures with topographical features. The performance of SPC-I technique in heterogeneous specimens having different topographies is investigated using nonlocal peridynamics based peri-ultrasound modeling. Three types of topographies – “X” topography, “Y” topography and “XY” topography are investigated. It is observed that “X” and “XY” topographies can help to hide the crack growth, thus making cracks undetectable when the SPC-I based monitoring technique is adopted. In addition to the SPC-I technique, we also investigate the effectiveness of an emerging sensing technique based on topological acoustic sensing. This method monitors the changes in the geometric phase; a measure of the changes in the acoustic wave’s spatial behavior. The computed results show that changes in the geometric phase can be exploited to monitor the damage growth in plate structures for all three topographies considered here. The significant changes in geometric phase can be related to the crack growth even when these cracks remain hidden for some topographies during the SPC-I based single point inspection. Sensitivities of both the SPC-I and the topological acoustic sensing techniques are also investigated for sensing the topographical changes in the plate structures.more » « lessFree, publicly-accessible full text available May 22, 2025
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Rizzo, Piervincenzo ; Su, Zhongqing ; Ricci, Fabrizio ; Peters, Kara J (Ed.)A newly developed Nonlinear Ultrasonic (NLU) technique called sideband peak count-index (or SPC-I) measures the degree of nonlinearity in materials by counting the sideband peaks above a moving threshold line – larger the SPC-I value, higher is the material nonlinearity. In various published papers, the SPC-I technique has shown its effectiveness in Structural Health Monitoring (SHM) applications. However, the effects of different types of nonlinear phenomenon on the sideband peak generation is yet to be investigated in depth. This work addresses this knowledge gap and investigates the effects of different types of nonlinearity on the SPC-I technique. Three types of nonlinearities (material nonlinearity, structural nonlinearity and contact nonlinearity) are investigated separately through numerical modeling. Numerical modeling results show that the sideband peak values do not increase proportional to the input signal strength thus indicating nonlinear response, and different types of nonlinearities affect the SPC-I measurements differently. For the experimental verification a composite plate with impact-induced damage is considered for investigating the material nonlinearity and structural nonlinearity while a linear elastic aluminum plate is used to examine the contact nonlinearity between the transducers and the plate. The trends observed in the experimental observations matched the numerical model predictions. Monitoring damage growth in topographical structures – formed by inserting different materials in a matrix material is also investigated. In addition to the SPC-I technique an emerging acoustic parameter – “geometric phase change” based on the topological acoustics is also adopted for sensing damage growth in the topographical structures. The performance of SPC-I and topological acoustic sensing techniques as well as the Spectral Amplitude Difference (SAD) parameter for sensing the damage growth in topographical structures are compared and discussed.more » « lessFree, publicly-accessible full text available May 9, 2025
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Quantum computing utilizes superposition and entanglement to surpass classical computer capabilities. Central to this are qubits and their use to realize parallel quantum algorithms through circuits of simple one or two qubit gates. Controlling and measuring quantum systems is challenging. Here, we introduce a paradigm utilizing logical phi-bits, classical analogues of qubits using nonlinear acoustic waves, supported by an externally driven acoustic metastructure. These phi-bits bridge a low-dimensional linearly scaling physical space to a high-dimensional exponentially scaling Hilbert space in which parallel processing of information can be realized in the form of unitary operations. Here, we show the implementation of a nontrivial three-phi-bit unitary operation analogous to a quantum circuit but achieved via a single action on the metastructure, whereby the qubit-based equivalent requires sequences of qubit gates. A phi-bit-based approach might offer advantages over quantum systems, especially in tasks requiring large complex unitary operations. This breakthrough hints at a fascinating intersection of classical and quantum worlds, potentially redefining computational paradigms by harnessing nonlinear classical mechanical systems in quantum-analogous manners, blending the best of both domains.more » « lessFree, publicly-accessible full text available March 4, 2025
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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.
Free, publicly-accessible full text available March 1, 2025 -
We investigate a one-dimensional discrete binary elastic superlattice bridging continuous models of superlattices that showcase a one-way propagation character, as well as the discrete elastic Su–Schrieffer–Heeger model, which does not exhibit this character. By considering Bloch wave solutions of the superlattice wave equation, we demonstrate conditions supporting elastic eigenmodes that do not satisfy the translational invariance of Bloch waves over the entire Brillouin zone, unless their amplitude vanishes for a certain wave number. These modes are characterized by a pseudo-spin and occur only on one side of the Brillouin zone for a given spin, leading to spin-selective one-way wave propagation. We demonstrate how these features result from the interplay of the translational invariance of Bloch waves, pseudo-spins, and a Fabry–Pérot resonance condition in the superlattice unit cell.more » « lessFree, publicly-accessible full text available January 19, 2025
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Phi-bits, akin to the quantum concept of qubits but in a classical mechanical framework, play a critical role in the development of quantum-analogue computing, and hence, understanding the nonlinear dynamics governing their control and interactions is crucial. These phi-bits, represented by acoustic waves within nonlinearly coupled arrays of waveguides, can exist in coherent superpositions of states. Adjusting external drivers' frequency, amplitude, and phase allows precise control over the phi-bit states. We have devised a discrete element model to analyze and predict the nonlinear response of phi-bits to external drivers, considering various types, strengths, and orders of nonlinearity stemming from intrinsic medium coupling among waveguides and external factors like signal generators, transducers, and ultrasonic couplant assemblies. Notable findings include the influence of nonlinearity type, strength, and order on the complex amplitudes within the coherent superposition of phi-bit states. This investigation serves as a groundwork for controlling design parameters in phi-bit creation, facilitating the preparation and manipulation of state superpositions crucial for developing phi-bit-based quantum analogue information processing platforms.more » « lessFree, publicly-accessible full text available April 13, 2025
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Understanding the control of phi-bits, akin to qubits, is crucial for developing quantum-inspired computing. Phi-bits, or two states of an acoustic wave in coupled waveguides, can be in a superposition of states. Our experiments showed that external drivers' frequency, amplitude, and phase influence phi-bit states. We developed a discrete element model to predict phi-bit responses under varying nonlinear conditions, influenced by the intrinsic medium coupling the waveguides and external factors like signal generators and transducers. The study reveals that nonlinearity and damping significantly affect the amplitude and phase of phi-bit states, with a notable impact on their predictability and stability, particularly at high damping levels. These findings are crucial to manipulating phi-bits for quantum-inspired information processing, highlighting the importance of optimizing nonlinearity and damping to control phi-bit states.more » « lessFree, publicly-accessible full text available April 12, 2025
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Phi-bits are classical mechanical analogues of qubits. Comprehending the nonlinear phenomena that underlie the control and relationships between phi-bits is of utmost importance for advancing phi-bit-based quantum-analogue computing systems. Phi-bits are acoustic waves in externally driven nonlinearly coupled arrays of waveguides, that can exist in a coherent superposition of two states. Tuning the frequency, amplitude, and phase of external drivers is a means of controlling the phi-bit states. We have developed a discrete element model to analyze and predict the nonlinear phi-bit response to external drivers that may result from different types, strengths, and orders of nonlinearity due to the presence of (i) intrinsic medium (epoxy) coupling the waveguides and (ii) external factors such as signal generators/transducers/ultrasonic couplant assembly. Key findings include the impact of nonlinearity type, strength, and order as well as damping on the modulus and phases of the complex amplitudes of the phi-bit coherent superposition of states. This research serves as an exploration for control of design parameters in the creation of phi-bits, which will enable the preparation and manipulation of superpositions of states essential for developing phi-bit-based quantum analogue information processing platforms.more » « lessFree, publicly-accessible full text available March 6, 2025
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We present a sensing modality using the geometric phase of acoustic waves propagating in an underwater environment. We experimentally investigate the effect of scattering by a small subwavelength perturbation on a flat submerged surface. We represent the state of an acoustic field in the unperturbed and perturbed cases as multidimensional vectors. The change in geometric phase is obtained by calculating the angle between those vectors. This angle represents a rotation of the state vector of the wave due to scattering by the perturbation. We perform statistical analysis to define a signal-to-noise ratio to quantify the sensitivity of the geometric phase measurement and compare it to magnitude based measurements. This geometric phase sensing modality is shown to have higher sensitivity than the magnitude based sensing approach.more » « less
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Bone mineralization is critical to maintaining tissue mechanical function. The application of mechanical stress via exercise promotes bone mineralization via cellular mechanotransduction and increased fluid transport through the collagen matrix. However, due to its complex composition and ability to exchange ions with the surrounding body fluids, bone mineral composition and crystallization is also expected to respond to stress. Here, a combination of data from materials simulations, namely density functional theory and molecular dynamics, and experimental studies were input into an equilibrium thermodynamic model of bone apatite under stress in an aqueous solution based on the theory of thermochemical equilibrium of stressed solids. The model indicated that increasing uniaxial stress induced mineral crystallization. This was accompanied by a decrease in calcium and carbonate integration into the apatite solid. These results suggest that weight-bearing exercises can increase tissue mineralization via interactions between bone mineral and body fluid independent of cell and matrix behaviours, thus providing another mechanism by which exercise can improve bone health. This article is part of a discussion meeting issue ‘Supercomputing simulations of advanced materials’.more » « less