Optimal Parameters Selection for Novel Low-Voltage Vibration Energy Harvesters

Energy harvesting from vibration sources is emerging as interesting alternative power source for micro and nano devices. Therefore, reducing the device’s size implies also a reduction of the harvester. As consequence, a lower output voltage/power will be obtained. Obviously in order to store the energy provided by the transducer (e.g. piezoelectric), a particular electrical interface is required in order to rectify the alternate piezoelectric voltage. Unfortunately often its amplitude is under diode threshold; for this reason, standard solutions, based on classical diode-bridge rectifiers, cannot be used. Several approaches have been proposed in literature focusing the attention on innovative interface and novel conversion principles. Moreover these existing solutions (synchronized approach) present several limitations such as they work efficiently only under the hypothesis of a sinusoidal input and an accurate driving of electrical switches. It is worth noting that in many real situations, the input is random, low amplitude and broadband. In this paper, authors discuss about an innovative solution to overcome the previously highlighted problems. A new system is presented and here, in particular, the characterization of the system performance with respect to two crucial construction parameters has been highlighted. The system is composed of a piezoelectric transducer, a storage circuit and a mechanical switch driven by the same input vibrations, in which the mutual position of the electrical terminals is tunable (to evaluate the best performance). An analytical model, a simulation software and an experimental prototype have been implemented in order to verify the working principle and test the validity of the proposed approach.