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

The MEMS four-leaf clover wideband vibration energy harvesting device: design concept and experimental verification

In this contribution, we discuss a novel design concept of a high-performance wideband MEMS vibration energy harvester (EH), named four-leaf clover (FLC EH-MEMS) after its circular shape featuring four petal-like mass-spring systems. The goal is to enable multiple resonant modes in the typical range of vibrations scattered in the environment (i.e., up to 4–5 kHz). This boosts the FLC conversion capability from mechanical into electrical energy exploiting the piezoelectric effect, thus overcoming the common limitation of cantilever-like EHs that exhibit good performance only in a very narrow band of vibration (i.e., fundamental resonant mode). The FLC concept is first discussed framing it into the current state of the art, highlighting its strengths. Then, after a brief theoretical introduction on mechanical resonators, the FLC EH-MEMS device is described in details. Finite Element Method (FEM) analyses are conducted in the ANSYS Workbench™ framework. A suitable 3D model is built up to perform modal simulations, aimed to identify mechanical resonant modes, as well as harmonic analyses, devoted to study the mechanical and electrical behaviour of the FLC EH-MEMS (coupled field analysis). The work reports on experimental activities, as well. Physical samples of the FLC EH-MEMS device are fabricated within a technology platform that combines surface and bulk micromachining. Thereafter, specimens are tested both with a laser doppler vibrometer measurement setup as well as with a dedicated shaker-based setup, and the results are compared with simulations for validation purposes. In conclusion, the FLC EH-MEMS exhibits a large number of resonant modes scattered in the tested range of vibrations (up to 15 kHz) already starting from frequencies as low as 200 Hz, and expected levels of converted power better than 10 µW