The investigation of the conversion of vibrational energy into electrical power has become a major field of research. In recent years, bistable energy harvesting devices have attracted significant attention due to some of their unique features. Through a snap-through action, bistable systems transition from one stable state to the other, which could cause large amplitude motion and dramatically increase power generation. Due to their nonlinear characteristics, such devices may be effective across a broad-frequency bandwidth. Consequently, a rapid engagement of research has been undertaken to understand bistable electromechanical dynamics and to utilize the insight for the development of improved designs. This paper reviews, consolidates, and reports on the major efforts and findings documented in the literature. A common analytical framework for bistable electromechanical dynamics is presented, the principal results are provided, the wide variety of bistable energy harvesters are described, and some remaining challenges and proposed solutions are summarized.

https://iopscience.iop.org/article/10.1088/0964-1726/22/2/023001/pdf

A review of the recent research on vibration energy harvesting via bistable systems

Carbon nanotubes possess unique properties that make them potentially useful in many applications in optoelectronics. This review describes the fundamental optical behaviour of carbon nanotubes as well as their opportunities for light generation and detection, and photovoltaic energy generation.

Carbon-nanotube photonics and optoelectronics

Micro- and nanoelectromechanical systems, including cantilevers and other small scale structures, have been studied for sensor applications. Accurate sensing of gaseous or aqueous environments, chemical vapors, and biomolecules have been demonstrated using a variety of these devices that undergo static deflections or shifts in resonant frequency upon analyte binding. In particular, biological detection of viruses, antigens, DNA, and other proteins is of great interest. While the majority of currently used detection schemes are reliant on biomarkers, such as fluorescent labels, time, effort, and chemical activity could be saved by developing an ultrasensitive method of label-free mass detection. Micro- and nanoscale sensors have been effectively applied as label-free detectors. In the following, we review the technologies and recent developments in the field of micro- and nanoelectromechanical sensors with particular emphasis on their application as biological sensors and recent work towards integrating these sensors in microfluidic systems.

http://cau.ac.kr/~jjang14/BioMEMS/Waggoner_LOC_Cantilever_Sensors_Bio_detection_Review_2007.pdf

Micro- and nanomechanical sensors for environmental, chemical, and biological detection

The last two decades have witnessed several advances in microfabrication technologies and electronics, leading to the development of small, low-power devices for wireless sensing, data transmission, actuation, and medical implants. Unfortunately, the actual implementation of such devices in their respective environment has been hindered by the lack of scalable energy sources that are necessary to power and maintain them. Batteries, which remain the most commonly used power sources, have not kept pace with the demands of these devices, especially in terms of energy density. In light of this challenge, the concept of vibratory energy harvesting has flourished in recent years as a possible alternative to provide a continuous power supply. While linear vibratory energy harvesters have received the majority of the literature’s attention, a significant body of the current research activity is focused on the concept of purposeful inclusion of nonlinearities for broadband transduction. When compared to their linear resonant counterparts, nonlinear energy harvesters have a wider steady-state frequency bandwidth, leading to a common belief that they can be utilized to improve performance in ambient environments. Through a review of the open literature, this paper highlights the role of nonlinearities in the transduction of energy harvesters under different types of excitations and investigates the conditions, in terms of excitation nature and potential shape, under which such nonlinearities can be beneficial for energy harvesting. [DOI: 10.1115/1.4026278]

On the Role of Nonlinearities in Vibratory Energy Harvesting: A Critical Review and Discussion

The dramatic reduction in power consumption of current integrated circuits has evoked great research interests in harvesting ambient energy, such as vibrations, as a potential power supply for electronic devices to avoid battery replacement. Currently, most vibration-based energy harvesters are designed as linear resonators to achieve optimal performance by matching their resonance frequencies with the ambient excitation frequencies a priori. However, a slight shift of the excitation frequency will cause a dramatic reduction in performance. Unfortunately, in the vast majority of practical cases, the ambient vibrations are frequency-varying or totally random with energy distributed over a wide frequency spectrum. Hence, developing techniques to increase the bandwidth of vibration-based energy harvesters has become the next important problem in energy harvesting. This article reviews the advances made in the past few years on this issue. The broadband vibration-based energy harvesting solutions, covering re...

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Toward Broadband Vibration-based Energy Harvesting

It is shown that the energy harvesting capabilities of a piezoelectric cantilever can be enhanced through coupling to a static magnetic field. A permanent magnet is fixed to the end of a piezoelectric cantilever, causing it to experience a non-linear force as it moves with respect to a stationary magnet. The magnetically coupled cantilever responds to vibration over a much broader frequency range than a standard cantilever, and exhibits non-periodic or chaotic motion. While the off-resonance response is substantially increased compared to that of a standard cantilever, no reduction in the response at the resonant frequency is observed, as long as a symmetric magnetic force is applied. The magnetically coupled cantilever motion is analyzed using a simple driven harmonic oscillator model with a non-linear magnetic force term. The results show that magnetic coupling can be used to increase the amount of power scavenged from environments containing multi-mode, or random vibration sources.

http://eri.louisville.edu/papers_pres/Alphenaar_Smart_Materials_2010.pdf

The magnetic coupling of a piezoelectric cantilever for enhanced energy harvesting efficiency

The damping effect of various gas environments on a silicon, lateral microresonator implemented with piezoresistive detection is investigated in this study. The resonant frequency of the cantilever shifts due to viscous damping by an amount that is directly determined by the molar mass of the gas, thereby providing a method to determine the composition of the gas environment. In addition, the microresonator demonstrates the ability to perform CO2 composition analysis using this nonreaction based detection method. The advantages of this gas analysis method are that it is simple, repeatable, reversible and not limited to reactive gases.

Viscous damping of microresonators for gas composition analysis

It is demonstrated experimentally that the energy harvested from a random noise source by a piezoelectric cantilever can be substantially enhanced by introducing a magnetic coupling force. The coupled cantilever responds to a 1/f vibration spectrum (‘pink noise’) with chaotic motion that on average has larger amplitude than the non-chaotic motion of an uncoupled cantilever. A 50% increase in output voltage was observed in the coupled cantilever compared to the uncoupled cantilever. Calculations show that the magnetic force transforms the quadratic spring potential of the cantilever into a double valley of two potential wells. Fluctuations between the two potential minima increase the amplitude of the cantilever motion over a range of vibration frequencies.

Enhancement of Energy Harvested from a Random Vibration Source by Magnetic Coupling of a Piezoelectric Cantilever

Excitonic and free-carrier transitions in single-wall carbon nanotubes are distinguished using field-enhanced photocurrent spectroscopy. Electric field dissociation allows for the detection of bound-exciton states that otherwise would not contribute to the photocurrent. Excitonic states associated with both the ground-state semiconductor and the ground-state metallic nanotube transitions are resolved. The observation of a metallic excitonic state corroborates recent predictions of a symmetry gap existing in metallic nanotubes.

Field-enhanced photocurrent spectroscopy of excitonic states in single-wall carbon nanotubes.

An embodiment of the invention provides a MEMS cantilever strain sensor. Capacitor plates in a MEMS device of the invention are carried on cantilevered opposing micro-scale plates separated by a micro-scale gap under an unstrained condition. At least one of the micro-scale plates may be attached to a substrate or forms a substrate, which may be part of a monitored system. When a load is applied to the substrate, distal ends of the opposing cantilevered micro-scale plates become further separated, resulting in a change of capacitance. The change of capacitance is proportional to a load and therefore is an indication of the strain. Electrodes may be integrated into the strain sensor to provide a connection to measurement circuitry, for example. Sensors of the invention also provide for telemetric communication using radio frequency (RF) energy and can be interrogated without a power supply to the sensor.

Ji-Tzuoh Lin

Papers

The magnetic coupling of a piezoelectric cantilever for enhanced energy harvesting efficiency

Viscous damping of microresonators for gas composition analysis

Enhancement of Energy Harvested from a Random Vibration Source by Magnetic Coupling of a Piezoelectric Cantilever

Field-enhanced photocurrent spectroscopy of excitonic states in single-wall carbon nanotubes.

MEMS capacitive cantilever strain sensor, devices, and formation methods