Modeling and Tuning of Energy Harvesting Device Using Piezoelectric Cantilever Array

Piezoelectric devices have been increasingly investigated as a means of converting ambient vibrations into electrical energy that can be stored and used to power other devices, such as the sensors/actuators, micro-electro-mechanical systems (MEMS) devices, and microprocessor units etc. The objective of this work was to design, fabricate, and test a piezoelectric device to harvest as much power as possible from vibration sources and effectively store the power in a battery.;The main factors determining the amount of collectable power of a single piezoelectric cantilever are its resonant frequency, operation mode and resistive load in the charging circuit. A proof mass was used to adjust the resonant frequency and operation mode of a piezoelectric cantilever by moving the mass along the cantilever. Due to the tiny amount of collected power, a capacitor was suggested in the charging circuit as an intermediate station. To harvest sufficient energy, a piezoelectric cantilever array, which integrates multiple cantilevers in parallel connection, was investigated.;In the past, most prior research has focused on the theoretical analysis of power generation instead of storing generated power in a physical device. In this research, a commercial solid-state battery was used to store the power collected by the proposed piezoelectric cantilever array. The time required to charge the battery up to 80% capacity using a constant power supply was 970 s. It took about 2400 s for the piezoelectric array to complete the same task. Other than harvesting energy from sinusoidal waveforms, a vibration source that emulates a real environment was also studied. In this research the response of a bridge-vehicle system was used as the vibration sources such a scenario is much closer to a real environment compared with typical lab setups

Multigraphic degree sequences and supereulerian graphs, disjoint spanning trees

AbstractA sequence d=(d1,d2,…,dn) is multigraphic if there is a multigraph G with degree sequence d, and such a graph G is called a realization of d. In this paper, we prove that a nonincreasing multigraphic sequence d=(d1,d2,…,dn) has a realization with a spanning eulerian subgraph if and only if either n=1 and d1=0, or n≥2 and dn≥2, and that d has a realization G such that L(G) is hamiltonian if and only if either d1≥n−1, or ∑di=1di≤∑dj≥2(dj−2). Also, we prove that, for a positive integer k, d has a realization with k edge-disjoint spanning trees if and only if either both n=1 and d1=0, or n≥2 and both dn≥k and ∑i=1ndi≥2k(n−1)