Energy Scavenging From Low Frequency Vibrations.

The development of three energy conversion devices that are able to transform vibrations in their surroundings to electrical energy is discussed in this thesis. These energy harvesters are based upon a newly invented architecture called the Parametric Frequency Increased Generator (PFIG). The PFIG structure is designed to efficiently convert low frequency and non-periodic vibrations into electrical power. The three PFIG devices have a combined operating range covering two orders of magnitude in acceleration (0.54-19.6m/s2) and a frequency range spanning up to 60Hz; making them some of the most versatile generators in existence. The PFIG utilizes a bi-stable mechanical structure to initiate high-frequency mechanical oscillations in an electromechanical scavenger. By up-converting the ambient vibration frequency to a higher internal operation frequency, the PFIG achieves better electromechanical coupling. The fixed internal displacement and dynamics of the PFIG allow it to operate more efficiently than resonant generators when the ambient vibration amplitude is higher than the internal displacement limit of the device. The PFIG structure is capable of efficiently converting mechanical vibrations with variable characteristics including amplitude and frequency, into electrical power. The first electromagnetic harvester can generate a peak power of 163μW and an average power of 13.6μW from an input acceleration of 9.8m/s2 at 10Hz, and it can operate up to 60Hz. The internal volume of the generator is 2.12cm3 (3.75 including casing). It sets the state-of-the-art in efficiency in the <20Hz range. The volume figure of merit is 0.068%, which is a 10x improvement over other published works. It has a record high bandwidth figure of merit (0.375%). A second piezoelectric implementation generates 3.25μW of average power under the same excitation conditions, while the volume of the generator is halved (1.2cm3). A third PFIG was developed for critical infrastructure monitoring applications. It is used to harvest the very low-amplitude, low-frequency, and non-periodic vibrations present on bridges. The device generates 2.3μW of average power from an input acceleration of 0.54m/s2 at only 2Hz. The internal volume of the generator is 43cm3. It can operate over an unprecedentedly large acceleration (0.54-9.8m/s2) and frequency range (up to 30Hz) without any modifications or tuning.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/78812/1/tgalchev_1.pd

Harvesting traffic-induced vibrations for structural health monitoring of bridges

This paper discusses the development and testing of a renewable energy source for powering wireless sensors used to monitor the structural health of bridges. Traditional power cables or battery replacement are excessively expensive or infeasible in this type of application. An inertial power generator has been developed that can harvest traffic-induced bridge vibrations. Vibrations on bridges have very low acceleration (0.1–0.5 m s _2 ), low frequency (2–30 Hz), and they are non-periodic. A novel parametric frequency-increased generator (PFIG) is developed to address these challenges. The fabricated device can generate a peak power of 57 µW and an average power of 2.3 µW from an input acceleration of 0.54 m s _2 at only 2 Hz. The generator is capable of operating over an unprecedentedly large acceleration (0.54–9.8 m s _2 ) and frequency range (up to 30 Hz) without any modifications or tuning. Its performance was tested along the length of a suspension bridge and it generated 0.5–0.75 µW of average power without manipulation during installation or tuning at each bridge location. A preliminary power conversion system has also been developed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90794/1/0960-1317_21_10_104005.pd

A new low-temperature high-aspect-ratio MEMS process using plasma activated wafer bonding

This paper presents the development and characterization of a new high-aspect-ratio MEMS process. The silicon-on-silicon (SOS) process utilizes dielectric barrier discharge surface activated low-temperature wafer bonding and deep reactive ion etching to achieve a high aspect ratio (feature width reduction-to-depth ratio of 1:31), while allowing for the fabrication of devices with a very high anchor-to-anchor thermal impedance (>0.19 _ 10 6 K W _1 ). The SOS process technology is based on bonding two silicon wafers with an intermediate silicon dioxide layer at 400 °C. This SOS process requires three masks and provided numerous advantages in fabricating several MEMS devices, as compared with silicon-on-glass (SOG) and silicon-on-insulator (SOI) technology, including better dimensional and etch profile control of narrow and slender MEMS structures. Additionally, by patterning the intermediate SiO 2 insulation layer before bonding, footing is reduced without any extra processing, as compared to both SOG and SOI. All SOS process steps are CMOS compatible.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90799/1/0960-1317_21_4_045020.pd