Bashar B. Alzuwayer

Self-powered sensor nodes need vibration harvesters that work over a band of frequencies, but the arrays and graded metamaterials that provide such bandwidth need many separately clamped resonators. This numerical study presents a kirigami-graded metabeam in which U-shaped slits in one 250 × 16 × 0.5 mm aluminum sheet release four tabs of graded length (44–62 mm); the sheet is folded and clamped at both ends, and a PZT-5A patch straddling each root feeds its own resistive load. A distributed-parameter cell model is verified against a three-dimensional coupled-field finite-element model within 1% in frequency and 2% in power. In the finite-element model, each cell mode is confined to one tab (off-diagonal amplitudes ≤ 0.09) and the cells deliver 0.59–1.44 µW per (m s⁻²)² at 130–274 Hz; their band-mean power is 3.6 times that of a single clamped tab and 0.9 times that of four separately clamped tabs, with two clamps instead of four. Interleaving the cells so that frequency-adjacent cells are not spatial neighbors keeps the modes localized on an 18 Hz grid and gives a continuous 212–284 Hz band with 1.1 times the four-tab power. One root-compliance parameter places 18 cell frequencies within 2–3%, and the sensitivity of the results to the assumed damping is quantified. No measurement is reported; the experimental characterization of the prototype is left to a separate study.

Nonlinear elements in vibration energy harvesters conventionally act on coordinates that every structural mode shares, so added functionality detunes the power-carrying resonance. We analyse a different placement: a permanent-magnet pair mounted inside the slit of a monolithic slitted piezoelectric cantilever, acting only on the difference in the prong deflections. Because this coordinate is odd under the device mirror symmetry, an exact selectivity theorem holds: at equal tip masses, the element is invisible to the symmetric mode family at every order in amplitude, while a rank-one lever places the antisymmetric resonance across 33–60 Hz. Deliberate mass mistuning μ then opens a gated 2:1 internal resonance (coupling asymptotically ∝ μ², activation threshold ∝ μ⁻³), verified against direct integration of the full cubic model to 0.1–2% and cross-checked by an independent finite element model. The two regimes trade off: at the mistuned design point, the first resonance shifts by 5.9%, and thresholdless transfer syphons 38% of its matched-load power at 0.05 g. The device serves a 43.3 Hz line at 16.6–20.1 μW, where the symmetric platform delivers 0.15–0.21 μW, integrates 448 vs. 354 μW⋅Hz over the band (1.27×), with unloaded/matched activation thresholds 0.017 g/0.079 g and an optimal load fraction ρ^⋆ ≈ 0.34.

Cellular and perforated substrate roots are stated to improve the output of piezoelectric cantilever energy harvesters, which serve as the primary vibration power source for self-powered wireless sensor nodes. The present work applies stricter control: a uniformly thinned root of equal substrate compliance. A single geometric family, defined by hole–footprint fractions and depth, contains through-cuts, skin-closed pockets and the thinned band. The family is analyzed with closed-form section mechanics, a validated segmented distributed-parameter model with active-coverage bounds for electrodes bridging holes, and coupled-field finite element analysis, and it is optimized in footprint, depth, thickness profile, and load in matched and frequency-free frames. At matched compliance and equal assumed damping, 1 m/s² and 1 MΩ, the band delivers 27.8 µW against 20.7 (through-cut) and 25.8 µW (pocket), a 62% gain over the solid reference at equal footprint, at the lowest peak substrate stress of the three, and optimization terminates at the no-hole boundary. The through-cut’s +20% gain over the solid baseline reproduces the literature and is traced to root compliance. Sensitivity studies bound the claim. The power ordering holds for all patch thicknesses and coverages in the weak-coupling regime and at equal modal damping, reversing only if the band’s damping exceeds that of the pocket’s thinner skin and slender ribs. It flips in favor of the pocket under strong coupling at optimal load. The stress ordering reverses only with a damping contrast of 24–62%, an order of magnitude larger. Coupled finite element checks at three optimized designs confirm the model-frame conclusions: the best real-hole design at matched compliance delivers 16% less power than the plain band, while for a front-loaded thickness profile, a thinned root still delivers 9% more at 1.6-times the peak stress. Within this envelope, the benefits belong to thinning, not preformation.

A piezoelectric cantilever with a longitudinal slit splits one bending resonance into two closely spaced peaks. This is attractive for two-frequency sources. However, existing models fit, rather than predict, the resonances. We develop a predictive branched-beam model where the harvester consists of a full-width root splitting into two prongs with independent tip masses. The two resonances are the roots of a closed-form characteristic equation without fitted parameters, the anti-resonance is the transmission zero of the same branched model, and the formulation reduces to the classical cantilever in the no-slit limit. The second (anti-symmetric) mode is weakly tunable and is located near 45 Hz; the inversion leaves the first resonance free and pins the second effectively. It is predictive and inverted to size the tip masses. Three-dimensional finite-element analysis, which tracks 27.2 → 22.3 Hz (against a finite-element 28.9 → 23.5 Hz as the mass doubles) within about 6%, and the prong kinematics, confirm the tip-mass trend. The anti-resonance is called the charge cancellation effect and can be controlled by wiring the electrodes. For a two-line source (25/45 Hz), the design, tuned to the two lines, yields up to about 1.9× the power of a size-matched single-peak beam with two matched lines (1.6× when the second dominates, ≈1× for broadband), with the second peak being intrinsically smaller. A Monte-Carlo study shows a power coefficient of variation of about 72% with manufacturing and damping scatter, the two layer thicknesses accounting for about 83% of the variance, motivating post-fabrication tip-mass trimming. The model is rigorously validated against three-dimensional electromechanical finite-element analysis; experimental validation on a physical prototype is identified as the essential next step. This work transforms the slitted harvester into a designable monolithic dual-frequency device.

This research investigates how slitted beams fitted with piezoelectric transducers (PZTs) behave when generating energy from environmental vibrations. By changing slit widths, slit lengths, and tip masses, we investigated the frequency response of these beams using analytical methods and finite element analysis (FEA). The obtained results demonstrate that resonance peaks are brought closer together, and coupling between vibrational modes is enhanced by larger slit spacing, whether or not anti-resonance dips are present, though the magnitudes of these peaks are affected by the width of the slits. The possibility of energy harvesting can be enhanced when resonance peaks are shifted and amplified by heavier tip masses. The FEA results support the analytical model, showing other characteristics such as sharp dips or anti-resonance troughs. This work provides valuable information for future design improvements by highlighting the significance of optimizing slit parameters and tip masses to enhance the efficiency of piezoelectric energy harvesters. This study demonstrates the benefits of using slitted beams with piezoelectric energy harvesting and provides recommendations for their efficient design.

The Supercritical Carbon Dioxide Brayton Cycle (sCO₂-BC) is a highly efficient and eco-friendly alternative for marine propulsion. The adoption of sCO₂-BC aligns with the industry’s focus on sustainability and can help meet emission regulations. In this context, the current study introduces a cascade system that harnesses the exhaust gases from a marine Gas Turbine Propulsion System to serve as a heat source for a bottoming Supercritical Carbon Dioxide Brayton Cycle (sCO₂-BC), which facilitates an onboard heat recovery system. The investigation primarily focuses on the recompression cycle layouts of the sCO₂-BC. To assess the performance of the bottoming cycle layouts and the overall cascade system, various parameters of the recompression sCO₂-BC are analyzed. These parameters include the mass flow rate of CO₂ in the bottoming cycle and the effectiveness of both the low-temperature recuperator (LTR) and the high-temperature recuperator (HTR). For conducting the cycle simulations, two codes are built and integrated; this first code models the thermodynamic cycle, while the second code models the recuperators. The research shows that incorporating the sCO₂ Brayton Cycle as a bottoming cycle has the potential to greatly improve the efficiency of the entire system, increasing it from 54% to 59%. Therefore, it provides a useful framework for advancing energy-efficient gas turbine systems and future research.

Over the past decade, various researchers have shown the practicality of extracting electrical energy from vibrating structures. The primary objective of this research was to optimize the parameters of a basic cantilever harvester to maximize the energy production of electricity from surrounding mechanical energy. A distributed parameter model and its modal solution were utilized to determine the design variables via a parametric investigation. It is important to ensure sufficient power generation when there is a wide range of frequencies being excited, without any specific frequency being emphasized. The cost function for the optimization problem was defined as the average power within a specific frequency range, considering geometric and physical restrictions. It was discovered that different parameters’ values can be utilized to generate varying maximum power levels for different frequency ranges. Furthermore, a comparative analysis was performed between the finite element method (FEM) using ANSYS and the current harvesting model. The comparison demonstrated a high level of concordance, enabling the utilization of the finite element method (FEM) for subsequent investigation.

The results obtained from the exergoeconomic and exergy analysis of a model of a generic air conditioning (A/C) system without and with an air membrane exchanger using three commercially available refrigerants: R410A, R407C, and R134a, are reported. The model used specialized software that was validated against recently published data and showed good agreement. A/C systems are energy intensive and consume a significant portion of global electricity. Improving their efficiency by even a small amount will produce considerable savings, reduce running costs, and lower pollution emissions. The efficiency of the same A/c system without and with a membrane was investigated for different ambient temperatures, relative humidities (RHs), and pressure ratios of the compressor. It was shown that the inclusion of a membrane improved the efficiency of the system for all three refrigerants tested, particularly at higher ambient temperature. Both the coefficient of performance and exergetic efficiency reduced with the increase in the pressure ratio due to increasing fuel exergy and losses. In all system components except one, it was found that the source of the cost is inefficiencies; hence, increasing the efficiency at the expense of the non-exergy cost will improve the cost effectiveness of the entire system.