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

Harvesting traffic-induced bridge vibrations

This paper demonstrates the harvesting of low-frequency and low-amplitude vibration energy from a suspension bridge. The performance of a Parametric Frequency Increased Generator (PFIG) [1] is evaluated at different locations along the bridge. Bridge vibrations have very low acceleration 0.1-1 m/s2 and variable frequency characteristics (1-40 Hz), making them very challenging to harvest. Field test results show consistent operation along the length of the bridge, producing 0.46-0.72 W of continuous (average) power (peaks in the range of 30-100 W), independent of the location of the harvester on the bridge, and without any modifications or tuning. These results pave the way for installing a network of wireless structural health monitoring sensors throughout the bridge without regard to the specific characteristics of the vibration at each location. The fabricated device has a volume of 43 cm3 (68 cm3 including casing)

A hybrid piezoelectric and electrostatic vibration energy harvester

Micro Electro Mechanical Systems for vibration energy harvesting have become popular over recent years. At these small length scales electrostatic forces become significant, and this paper proposes a hybrid cantilever beam harvester with piezoelectric and electrostatic transducers for narrow band base excitation. One approach would be to just combine the output from the different transducers; however, this would require accurate tuning of the mechanical system to the excitation frequency to ensure the beam is resonant. In contrast, this paper uses the applied DC voltage to the electrostatic electrodes as a control parameter to change the resonant frequency of the harvester to ensure resonance as the excitation frequency varies. The electrostatic forces are highly non-linear, leading to multiple solutions and jump phenomena. Hence, this paper analyses the non-linear response and proposes control solutions to ensure the response remains on the higher amplitude solution. The approach is demonstrated by simulating the response of a typical device using Euler Bernoulli beam theory and a Galerkin solution procedure