I. Introduction
Resonant Electromagnetic Vibration Energy Harvesters (REVEHs) represent one of the available options for supplying Wireless Sensor Nodes (WSNs) [1]–[8]. A REVEH can be represented, as shown in Fig. 1, by means of its equivalent electric circuit [9]. In particular, is the coil inductance, is the coil resistance, is the base acceleration. Moreover: is the viscous damping coefficient and is the electromechanical coupling coefficient), is the stiffness coefficient), is the vibrating mass). As shown in Fig. 1, the output voltage of the REVEH is usually rectified by means of a diode bridge rectifier [10]–[14]. Typically, the rectified output voltage of the REVEH needs to be varied (boosted) from to by means of an active DC/DC converter [15]. Indeed, also other single or double-stage active AC/DC topologies have been proposed in the literature [16]–[18]. They allow to carry out the emulation of the optimal impedance of the REVEH and therefore to maximize the extracted power [5]–[9]. However, they are also characterized by increases of the complexity and of the power losses that are often not consistent with most low-power REVEH applications. In this paper, the attention will be focused on the architecture of Fig. 1 that is by far the most widespread architecture in REVEH applications. In particular, an important Figure Of Merit (FOM) will be proposed and analyzed: the REVEH Ideal Utilization Factor (IUF). The REVEH IUF is very useful in order to quantify how close to the ideal case the REVEH can be at most exploited in presence of the architecture of Fig. 1. Two relevant powers need to be investigated: and . is the ideal (highest) average power that can be provided by the REVEH when its load is equal to the complex conjugate of the REVEH output impedance (maximum power transfer theorem [19]). Instead, is the power that is provided by the REVEH when its load is an optimal resistance. As discussed in Section II, . The REVEH IUF is formally defined in Section II as a function of and . Moreover, in this paper, the great usefulness of the IUF for designing REVEH optimizations is also evidenced. In particular, in Section III, it is proved that, depending on the value of the REVEH IUF, significant optimizations of the actual performances of a REVEH system can be possible. Conclusions end the paper.
REVEH system.