||Because portable electronic devices are popular, a durable electrical power for these devices is necessary. However, there is a problem of electrical exhaust during a prolonged use. So as to provide sufficient and continuous electrical power, interest in developing portable energy harvesters with a spring-mass system is raising.
As can be seen, application of the cantilever-beam electrical generator is limited to small vibrations at a higher frequency and is used within small systems such as the MEMS. A structure with a spring-mass system is often used to extract energy from a vibration system of lower frequencies and larger displacement.
In order to find an optimal mechanism for the one-mass energy harvester that produces maximal electrical power, the assessment of optimal electrical power with ten design factors is presented. Concerning the geometric allocation, four parameters ( : the magnet diameter; : the magnet height; : the system damping ratio; and : the coil’s revolution number) are adopted for maximization of electrical power. Also, considering the buckling effect for a spring that will consume the vibrational energy and damage the spring, a critical deflection is included in the optimization using a penalty factor of PN1. Similarly, concerning the influence of fatigue induced by fluctuating stress, the safety factor will be rechecked using a penalty factor PN2 in the SA optimization.
Considering the portable energy harvester which can be easily carried put inside a backpack and generates great electricity while walking, three kinds of one-mass portable energy harvesters with swinging type (prototype I, prototype II, and prototype III) are also developed and experimentally tested. Results reveal that the electrical energy reaching 0.25 W is generated from the energy harvester (prototype III) by extracting kinetic energy produced by walking.
Moreover, because only a resonating vibration will be induced for a one-mass vibrating system, the energy extracted from the one-mass vibrational system was limited to vibration with one forcing frequency. Therefore, in order to extract more vibrational energy from equipment having multi-tone forcing vibration, the development of a multi-mass energy harvester used to extract the vibrational energy at the multi-tone resonating frequencies is essential. In order to improve output electricity, a vibration-based energy harvester with a two-mass vibrational system is also proposed. To maximize the extracted energy, two resonant frequencies of the two-mass vibrational system will be simultaneously tuned as two external vibrating frequencies emitted from the vibrational source. Eight kinds of design parameters used in tuning the system’s natural frequencies are adopted. The optimization of above one-mass and two-mass electromagnetic energy harvesters is performed by using the simulated annealing (SA) method. Results reveal that the electrical power is optimally extracted at the two primary forcing frequencies of the vibrational equipment. Furthermore, it is obvious that the induced electrical power of the two-mass energy harvester will be superior to that of the one-mass energy harvester.