Non-resonant Energy Harvester Research Articles

A nonresonant triboelectric-electromagnetic energy harvester via a vibro-impact mechanism for low-frequency multi-directional excitations

A majority of current studies about non-resonant energy harvesters for low-frequency energy are based on pure experiment without theoretical modeling. In this work, a novel hybrid triboelectric-electromagnetic harvester in form of a rolling magnet inside a casing is proposed for scavenging low-frequency energy from multi-directional excitations, which includes a number of sub triboelectric energy harvesters (sub-TEHs) and two sub electromagnetic energy harvesters (sub-EEHs). Both the mechanical model and electrical model are established for a horizontal excitation, a rocking excitation and a vertical excitation. A velocity-dependent coefficient of restitution for impact and an impact-velocity-dependent charge density are obtained via experiment, which improve the theoretical model and result in better agreement between theoretical and experimental results. Structural response and electric outputs under different types of external excitations are investigated theoretically. It is found that the harvester has a good sensitivity to small-angle ultra-low-frequency rocking excitations, which is beneficial to low-frequency energy harvesting. When tested on a shake table at 4 Hz, a sub-TEH and a sub-EEH can generate peak powers of 212.1 µW and 57.8 mW, respectively. An electronic clock is able to work continuously when powered by the harvester shaken by hand. The harvester is also tested inside a handbag carried by a walking human for biomechanical energy and on a floating structure for wave energy, which exhibits good performance. This work presents a novel design with a capability of harvesting low-frequency energy under different external excitations, which contributes to the development and applications of triboelectric and electromagnetic energy harvesting.

Textured, lead-free piezoelectric ceramics with high figure of merit for energy harvesting

Piezoelectrics are key materials for energy conversion, for example in ultrasound transducers and energy harvesters. This work presents the synthesis and characterization of the lead-free piezoelectric composition (Li0.06(K0.52Na0.48)0.94)(Nb0.71Ta0.29)O3 doped with 0.25 mol% Mn (KNNLTM) as textured ceramics. Templated grain growth from NaNbO3 platelet templates aligned by tape casting was used to introduce texture, and after sintering for 14 h at 1100 °C this produced up to 84% (100)pc grain orientation. After high temperature poling, the textured samples exhibit reasonable piezoelectric response with d 33 values up to 171 pC N−1, and k t values of 0.35, which is 71% of the response obtained in a single crystal of the same composition. The low relative dielectric permittivity of the textured and high temperature-poled KNNLTM (ϵ 33 T/ϵ 0 down to 182) resulted in record-high piezoelectric voltage constants (g 33 up to 101 mV m N−1), higher than previously reported for lead-free piezoelectric ceramics, as well as very high figure of merit (d 33 g 33 up to 16 × 10−12 m3 J−1) for non-resonant energy harvesting in compression. These numbers make the textured KNNLTM materials of this work highly promising for use in thickness mode, non-resonant piezoelectric energy harvesters.

Non-resonant energy harvester with elastic constraints for low rotating frequencies

This paper presents a non-resonant piezoelectric energy harvester (PEH) which is designed to capture energy from low frequency rotational vibration. The proposed device works out of the plane of rotation where the motion of a mass-spring system is transferred to a piezoelectric layer with the intention to generate energy to power wireless structural monitoring systems or sensors. The mechanical structure is formed by two beams with rigid and elastic boundary conditions at the clamped end. On the free boundaries, heavy masses connected by a spring are placed in order to increase voltage generation and diminish the natural frequency. A mathematical framework and the equations governing the energy-harvesting system are presented. Numerical simulations and experimental verifications are performed for different rotation speeds ranging from 0.7 to 2.5 Hz. An output power of 125 μW is obtained for maximum rotating frequency demonstrating that the proposed design can collect enough energy for the suggested application.

Non-Resonant Electromagnetic Broad-Band Vibration-Energy Harvester Based on Self-Assembled Ferrofluid Liquid Bearing

This paper reports a non-resonant, broadband electromagnetic vibration-energy harvester based on self-assembled ferrofluid liquid bearing. Magnet array is suspended by the liquid bearing over a microfabricated multi-layer coil plate such that the energy harvester does not rely on any mechanical resonance, and can harvest vibration energy over a broad frequency range. An analytical model of the non-resonant energy harvester with liquid bearing is developed to predict the frequency responses under various external accelerations. Experimental results show that the electromagnetic energy harvester occupying 1.1 cm3 and weighing 2.5 gram generates an induced electromotive force of $\text{V}_{\mathrm {rms}} =61$ to 93.7 mV (delivering 11.6– $27.5~\mu \text{W}$ power into 80- $\Omega $ load) from 2-g acceleration at 2–4 Hz. When the energy harvester is placed on the back of a human walking at various speeds, the power output is increased as the walking speed is increased from 0.44 m/s (walking) to 3.56 m/s (running), and reaches $18.1~\mu \text{W}$ at 3.56 m/s. [2016-0167]

Non-resonant energy harvesting via an adaptive bistable potential

Narrow bandwidth and easy detuning, inefficiency in broadband and non-stationary excitations, and difficulties in matching a linear harvester’s resonance frequency to low-frequency excitations at small scales, have convinced researchers to investigate nonlinear, and in particular bistable, energy harvesters in recent years. However, bistable harvesters suffer from co-existing low and high energy orbits, and sensitivity to initial conditions, and have recently been proven inefficient when subjected to many real-world random and non-stationary excitations. Here, we propose a novel non-resonant buy-low-sell-high strategy that can significantly improve the harvester’s effectiveness at low frequencies in a much more robust fashion. This strategy could be realized by a passive adaptive bistable system. Simulation results confirm the high effectiveness of the adaptive bistable system following a buy-low-sell-high logic when subjected to harmonic and random non-stationary walking excitations compared to its conventional bistable and linear counterparts.

Non-resonant electromechanical energy harvesting using inter-ferroelectric phase transitions

Non-resonant electromechanical energy harvesting is demonstrated under low frequency excitation (<50 Hz) using [110]C-poled lead indium niobate-lead magnesium niobate-lead titanate relaxor ferroelectric single crystals with compositions near the morphotropic phase boundary. The efficiency of power generation at the stress-induced phase transition between domain-engineered rhombohedral and orthorhombic ferroelectric states is as much as four times greater than is obtained in the linear piezoelectric regime under identical measurement conditions but during loading below the coercive stress of the phase change. The phase transition mode of electromechanical transduction holds potential for non-resonant energy harvesting from low-frequency vibrations and does not require mechanical frequency up-conversion.

Non-resonant electromagnetic wideband energy harvesting mechanism for low frequency vibrations

A novel non-resonant energy harvesting mechanism with wide operation frequency band is investigated for collecting energy from low frequency ambient vibration. A free-standing magnet is packaged inside a sealed hole which is created by stacking five pieces of printed circuit board substrates embedded with multi-layer copper coils. This device was tested under various acceleration conditions. Considering the air damping effect, two types of device structures with different covered plates are investigated. For type I, one covered acrylic plate with drilled air holes and another plate with no holes are used to package the moving magnet. For type II, the middle hole is sealed by two acrylic plates with drilled air holes. The output voltage of type II is better than the one of type I at the same acceleration. When the energy harvester of type II is shook at 1.9 g acceleration along longitudinal direction of the hole, the 9 mV output voltage with 40 Hz bandwidth, i.e., from 40 to 80 Hz, is generated. The maximum output power within the ranges of 40–80 Hz, i.e., operation bandwidth, is measured as 0.4 μW under matched loading resistance of 50 Ω. Experimental results show that type I device has wider frequency bandwidth, higher center frequency and smaller output voltage than type II device because type I device experiences severe damping influence.