Abstract Radial resonances of electric motor housings can induce significant structural vibration and radiated noise in electric drive systems. To achieve frequency-targeted and reconfigurable vibration attenuation without modifying the mechanical structure, this study proposes a circuit-tunable piezoelectric bimorph cantilever phononic crystal (PB-PC). An electromechanical model of the PB-PC unit cell is established by coupling Euler–Bernoulli beam theory with the frequency-dependent impedance of an external shunt circuit. The proposed model is validated through finite-element simulations and hammer-impact experiments on a single PB-PC unit, showing good agreement between the predicted and measured electromechanical resonance frequencies, with a maximum relative error below 2%. Based on the validated model, the effects of shunt parameters, connection configurations, and shunted-cell position within finite periodic structures are systematically investigated. The results demonstrate that the attenuation frequency can be effectively reconfigured by adjusting the external circuit parameters while maintaining the same mechanical configuration. Specifically, resistance mainly affects the attenuation depth and response robustness, whereas inductance and capacitance primarily determine the frequency location of the shunt-induced attenuation feature. Furthermore, introducing a shunted unit into a finite periodic chain creates a localized transmission response through the dynamic-stiffness mismatch between shunted and open-circuit cells, with its output characteristics governed by the shunted-cell position and the number of downstream unit cells. Finally, the proposed PB-PC strategy is evaluated through finite-element analysis of a cast-iron motor housing with target radial resonances at 918 Hz and 931 Hz. Adjusting only the external shunt inductance, while keeping the geometric and material parameters unchanged, shifts the attenuation intervals to cover the respective target frequencies. These results demonstrate frequency-selective vibration attenuation through electrical retuning, highlighting the potential of the PB-PC for reconfigurable vibration control in engineering structures.
Abstract Bio-inspired structural architectures can extend the performance envelope of conventional lightweight designs when their topology is explicitly tailored to loading conditions, boundary constraints, and structural objectives. This work introduces stochastic spider webs, a parametric class of radial/spiral metamaterial plates in which controlled geometric perturbations break strict periodicity, enabling non-periodic topologies that expand the achievable design space beyond classical lattice architectures. A novel algorithm governs member count, thickness distribution, spiral spacing, and stiffness distribution through physically interpretable variables, with a randomness parameter that transitions between periodic and stochastic designs. These architectures are compared against honeycomb metamaterial plates, an established periodic benchmark in structural design, and both are optimized via Bayesian search over mixed discrete-continuous design spaces with respect to three objectives: minimization of maximum von Mises stress, total elastic strain energy density, and maximum elastic strain energy density. Results demonstrate that structural efficiency is governed by the interaction between the optimization objectives, boundary conditions, and load distributions. Under simply supported uniform loading, stochastic spider webs outperform honeycombs by 28-54% in stress and strain energy metrics depending on the performance objective. Moreover, under clamped conditions, spider webs reduce total elastic strain energy by up to 73%. Honeycombs retain advantages where suppression of localized curvature peaks is critical. The design framework is experimentally validated via uniaxial compression and three-point bending testing of additively manufactured specimens of both architectures, with the flexural tests confirming the topological advantage of the spider web architecture in the bending dominated regime.
Abstract Self-sensing cementitious composites containing conductive fillers have attracted considerable attention; however, the influence of seawater and sea sand on the electromechanical response of hybrid CNT–stainless steel fiber (SSF) systems remains insufficiently understood.. Therefore, this study investigates the effects of seawater and sea sand on the mechanical performances, electrical conductivity, and self-sensing property of CNT-SSF sulphoaluminate cement-based composites (CSSCC). Four mixtures incorporating freshwater or seawater and river sand or sea sand were comparatively evaluated, while the CNT and SSF contents were maintained at 0.3 wt.% of binder and 2.0 vol.%, respectively. The results showed that the use of seawater and sea sand reduced the mechanical strengths but enhanced the electrical and self-sensing properties of the composites. The electrical resistivity decreased by up to 36.2%, while the maximum fractional change in resistivity (FCR) under compressive/flexural/splitting tensile loading increased by 95.8%/712.2%/320.6%. Meanwhile, their corresponding stress sensitivity and strain sensitivity were increased of 166.7%/1200%/341.4% and 116.5%/673.2%/178.8%, respectively. The enhanced electrical response is interpreted in terms of the coexistence of ionic-mediated conduction and conductive pathways associated with nanoscale CNTs and microscale SSFs. The results demonstrate that seawater and sea sand can substantially modify the conductive and electromechanical behavior of CNT-SSF sulphoaluminate cementitious composites, providing insight into the design of self-sensing cement-based composites incorporating marine resources.
Abstract Very-low-frequency vibration energy harvesters are constrained simultaneously by resonance detuning, finite electromechanical coupling, allowable stroke and retuning energy. This study asks how much structural stiffness programming adds once the electrical load is optimized under the same physical limits. Delivered power to a low-inductance electromagnetic load is used throughout, and the displacement limit is enforced directly in the steady-state dynamics; no post-hoc response clipping is used. For an arbitrary fixed stiffness state, an analytical optimum for non-negative external load resistance is derived together with a finite-coupling no-impact feasibility condition. Finite-state stiffness programming is then compared with fixed tuning, load programming, a resource-normalized passive resonator-array proxy and ideal continuous stiffness/load programming. In a high-resolution 0.5–4 Hz moderate benchmark, worst-case constrained coverage is 0.486 for fixed-stiffness load programming, 0.872 for two stiffness states with load programming and 0.934 for three states. In a tighter-stroke regime, load programming alone reaches 0.875 and two stiffness states reach 0.926, showing that the incremental value of stiffness programming is regime-dependent. Physical QZS uncertainty is propagated through the positive and negative stiffness components rather than through their small difference; under the stated 1000-sample uncertainty scenario, the three-state design gives median and fifth-percentile worst-case coverage of 0.867 and 0.681. The retuning study uses an explicit five-cycle neighbour-search algorithm, charges every probe and return, and is repeated over 200 independent 1% measurement-noise realizations. Median time within 90% of the instantaneous finite-state oracle is 88.5%, median time-averaged power ratio is 96.8%, and median net/oracle energy ratio is 95.6%. The results separate the roles of electrical damping and structural retuning and identify regimes in which stiffness programming adds material benefit beyond load programming.
Abstract This work studies the operating principles and performance limits of magnetoelectric transducers, which are promising compact receiver alternatives for wireless powering of biomedical implantable devices. We develop an analytical framework to investigate the maximum power that can be transferred to an electrical load. Although an electrically lossless model is widely used to explore the magnetoelectric transducer capability, we find that in this idealization, allowing a complex-valued load impedance enables the delivered power to attain the physical bound at an arbitrary operating frequency and with any electromechanical coupling strength. This behavior may not be feasible in practice. To reflect a more realistic potential of a magnetoelectric wireless power transfer system, the inevitable electrical losses are taken into account. We derive closed-form expressions for the maximum output power under a general complex load, in both series and parallel configurations, and determine the corresponding optimal conditions. The results show that the optimal power is achieved uniquely at mechanical resonance and increases monotonically with an effective figure of merit, yielding a physically attainable maximum power strictly below the theoretical bound and a finite operating bandwidth. Motivated by implant-size limitations, we formulate a power optimization subject to volume constraints. We establish an analytical condition for the optimal thickness ratio, defined as the ratio between the piezoelectric thickness and the total thickness of the composite. The conventional magnetoelectric voltage coefficient is also considered. It is shown that there exist scenarios in which reducing the thickness ratio can maximize both the power delivered and the voltage coefficient, unifying an optimal setting for wireless power transfer and sensing. These findings provide a comprehensive understanding and a general framework for realizing an efficient magnetoelectric-based system for biomedical implants.
