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This paper addresses an issue in energy harvesting that has plagued the potential use of harvesting through the piezoelectric effect at the micro-electro-mechanical systems (MEMS) scale. Effective energy harvesting devices typically consist of a cantilever beam substrate coated with a thin layer of piezoceramic material and fixed with a tip mass tuned to resonant at the dominant frequency of the ambient vibration. The fundamental natural frequency of a beam increases as its length decreases, so that at the MEMS scale the resonance condition occurs orders of magnitude higher than ambient vibration frequencies, rendering the harvester ineffective. Here, we propose a new geometry for MEMS scale cantilever harvesters with low fundamental frequencies. A “zigzag” geometry is proposed, modeled, and solved to show that such a structure would be able to vibrate near resonance at the MEMS scale. An analytical solution is presented and verified against Rayleigh’s method and is validated against a macroscale experiment. The analysis is used to provide design guidelines and parametric studies for constructing an effective MEMS scale energy harvesting device in the frequency range common to low frequency ambient vibrations, removing a current barrier.

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Continuous monitoring of drinking water quality is essential in terms of heavy metals and toxic substances. The general objective of this study were to determine the concentration of heavy metals in drinking water of Khorramabad city and to determine the water quality indices (The heavy metal pollution index and heavy metal evaluation index). According to the city map, 45 points were selected for drinking water sampling through the city distribution system. The results of this study showed that the average concentration of heavy metals such as Zn, Pb, Cd, Cr, and Cu were 47.01 μg/l, 3.2 μg/l, 0.42 μg/l, 5.08 μg/l, and 6.79 μg/l, respectively. The HPI and HEI (water quality indices) for Zn, Pb, Cd, Cr, and Cu were 46.58, 46.58, respectively. According to the indices, the city drinking water quality is good in terms of heavy metals.

An analytical electromechanical model is proposed to predict the deflection, voltage, and the power output of a proposed low-frequency micro-harvesting structure. The high natural frequencies of the existing designs of micro-scale vibrational energy harvesters are serious drawbacks. A zigzag design is proposed to overcome this limitation. First, the natural frequencies and the mode shapes of the zigzag structure are calculated. The piezoelectric direct and reverse effect equations, together with the electrical equations, are used to relate the voltage output of the structure to the base vibrations magnitude and frequency. The closed-form solution of the continuous electromechanical vibrations gives the power output as a function of base acceleration spectrum. The usefulness of the design is proved by the significant increase of the power output from the same base accelerations, providing a method of designing a micro-scale harvester with low natural frequency. The optimal mechanical and electrical conditions for power generation are investigated through the case studies.

This paper studies energy harvesting from heartbeat vibrations for powering leadless pacemakers. Unlike traditional pacemakers, leadless pacemakers are implanted inside the heart and the pacemaker is in direct contact with the myocardium. A leadless pacemaker is in the shape of a cylinder. Thus, in order to utilize the available 3-dimensional space for the energy harvester, we choose a fan-folded 3D energy harvester. The proposed device consists of several piezoelectric beams stacked on top of each other. The volume of the energy harvester is 1 cm3 and its dimensions are 2 cm × 0.5 cm × 1 cm. Although high natural frequency is generally a major concern with micro-scale energy harvesters, by utilizing the fan-folded geometry and adding tip mass and link mass to the configuration, we reduced the natural frequency to the desired range. This fan-folded design makes it possible to generate more than  10 μW of power per cubic centimeter. The proposed device is compatible with Magnetic Resonance Imaging. Although the proposed device is a linear energy harvester, it is relatively insensitive to the heart rate. The natural frequencies and the mode shapes of the device are calculated analytically. The accuracy of the analytical model is verified by experimental investigations. We use a closed loop shaker system to precisely replicate heartbeat vibrations in vitro.