Pranay Podder

Combined Effect of Bistability and Mechanical Impact on the Performance of a Nonlinear Electromagnetic Vibration Energy Harvester

This paper presents the design, modeling, fabrication, and characterization of a nonlinear bistable electromagnetic vibrational energy harvesting device. A folded cantilever structure based on low Youngs modulus FR4 material reduces the operating frequency, while keeping the device footprint relatively small. The bistability is introduced into the system by a pair of repulsively oriented NdFeB permanent magnets. A second nonlinear mechanism, i.e., mechanical impact between the oscillator and the base, is also taken into account. Analytical expressions are derived to obtain the restoring force and potential energy for such a system. The model was further numerically simulated and validated with experimental results of the fabricated device. The device generated maximum power of 19.3 μW at 1.5-g acceleration across an optimum resistive load of 1 kΩ, which was further improved by almost 70% with an optimized prototype. Both the numerical simulation and experimental results show broadening of the operational frequency range of the nonlinear bistable device by up to 4.35 Hz at 0.6-g acceleration with respect to the linear counterpart. At higher input vibration, the harvester oscillates with large amplitude and collides with the base, which abruptly changes the system dynamics. At an acceleration of 1.5 g, this impact induced change in dynamics increases the peak power frequency and widens the bandwidth even further up to 8 Hz (22% of the peak power frequency). Thus, the effects of both bistability and mechanical impact are incorporated into a single device to obtain a fairly wideband operation.

Nonlinear Energy Harvesting Using Electromagnetic Transduction for Wide Bandwidth

We report the relative performances of monostable and bistable miniaturized electromagnetic energy harvesters (EMEHs) using micromachined fiberglass-epoxy spring structures. Monostable nonlinearity is realized in our device using the specially designed spring arms, whereas bistable nonlinearity is introduced through the interactions between repulsively oriented magnets. For devices of similar size, the monostable electromagnetic harvester generates larger output power compared to the bistable system under the same mechanical input. This is due to the additional damping provided by the strong bistable force, which also restricts the bandwidth widening of the bistable device compared to that of the monostable energy harvester. However, as the bistable force changes the linear stiffness of the system as well, the overall frequency response shifts toward the low-frequency region. Hence, low-frequency, wideband harvesting can be obtained in bistable devices compared to monostable devices of the same mechanical dimensions.

Influence of combined fundamental potentials in a nonlinear vibration energy harvester.

Ambient mechanical vibrations have emerged as a viable energy source for low-power wireless sensor nodes aiming the upcoming era of the ‘Internet of Things’. Recently, purposefully induced dynamical nonlinearities have been exploited to widen the frequency spectrum of vibration energy harvesters. Here we investigate some critical inconsistencies between the theoretical formulation and applications of the bistable Duffing nonlinearity in vibration energy harvesting. A novel nonlinear vibration energy harvesting device with the capability to switch amidst individually tunable bistable-quadratic, monostable-quartic and bistable-quartic potentials has been designed and characterized. Our study highlights the fundamentally different large deflection behaviors of the theoretical bistable-quartic Duffing oscillator and the experimentally adapted bistable-quadratic systems, and underlines their implications in the respective spectral responses. The results suggest enhanced performance in the bistable-quartic potential in comparison to others, primarily due to lower potential barrier and higher restoring forces facilitating large amplitude inter-well motion at relatively lower accelerations.

Silicon MEMS bistable electromagnetic vibration energy harvester using double-layer micro-coils

This work reports the development of a MEMS bistable electromagnetic vibrational energy harvester (EMVEH) consisting of a silicon-on-insulator (SOI) spiral spring, double layer micro-coils and miniaturized NdFeB magnets. Furthermore, with respect to the spiral silicon spring based VEH, four different square micro-coil topologies with different copper track width and number of turns have been investigated to determine the optimal coil dimensions. The micro-generator with the optimal micro-coil generated 0.68 micro-watt load power over an optimum resistive load at 0.1g acceleration, leading to normalized power density of 3.5 kg.s/m3. At higher accelerations the load power increased, and the vibrating magnet collides with the planar micro-coil producing wider bandwidth. Simulation results show that a substantially wider bandwidth could be achieved in the same device by introducing bistable nonlinearity through a repulsive configuration between the moving and fixed permanent magnets.

Bandwidth widening in nonlinear electromagnetic vibrational generator by combined effect of bistability and stretching

This work reports the novel concept of frequency response widening of vibrational energy harvesters exploiting the combined effects of bistable and monostable nonlinearities in a single device. The bistability is introduced into the system by repulsive arrangement of magnets, while monostable nonlinear force through the stretching is incorporated by large deformation of two-end-fixed cantilevers. The simulation results show wider bandwidth in the bistability and stretching combined configuration compared to the bistable only or the monostable stretching only configuration.

Magnetic Tuning of Nonlinear MEMS Electromagnetic Vibration Energy Harvester

Ambient mechanical vibrations are an untapped yet attractive energy source for powering wireless sensor nodes in the upcoming Internet-of-Things. Here we demonstrate the magnetically induced frequency tuning effect in a MEMS electromagnetic vibrational energy harvester. Spiral-shaped springs and double-layer copper micro-coils are fabricated on silicon substrate using MEMS fabrication processes. Numerical simulations and finite-element analysis exhibit substantial transformation in the potential energy and stiffness profiles due to controlled changes in the magnetic repulsion force between the transducing and tuning magnets, which effectively modifies the frequency response profile. Specifically, by increasing the repulsive interaction between the transducing and tuning magnets, both the linear and nonlinear frequency response profiles can be shifted toward higher frequencies. This experimentally validated magnetic tuning mechanism can potentially be implemented in MEMS vibrational energy harvesters with other transduction mechanisms and in other micro-mechanical oscillators for broader frequency response tunability. [2016-0123]

Wideband electromagnetic energy harvesting from ambient vibrations

Different bandwidth widening schemes of electromagnetic energy harvesters have been reported in this work. The devices are fabricated on FR4 substrate using laser micromachining techniques. The linear device operate in a narrow band around the resonance; in order to tune resonant frequency of the device electrically, two different types of complex load topologies are adopted. Using capacitive load, the resonant frequency is tuned in the low frequency direction whereas using inductive load, the resonant frequency is tuned in the high frequency direction. An overall tuning range of ∼2.4 Hz is obtained at 0.3g though the output power dropped significantly over the tuning range. In order to improve the off-resonance performance, nonlinear oscillation based systems are adopted. A specially designed spring arm with fixed-guided configuration produced single well nonlinear monostable configuration. With increasing input acceleration, wider bandwidth is obtained with such a system as large displacement, stretchin...