There is an increased awareness nowadays regarding the potential shortage of fuel sources for electricity generation in the future, where various studies have been conducted about the usage alternative sources. Currently, the renewable energy has been prioritized for instance, through ambient energy scavenging. To achieve this goal, sound, being the most abundant energy in the environment, is likely the best candidate to fill the slot. The existing rectifying technique that has been used for energy transfer in energy harvesting is ‘switch-only’ and ‘bias-flip’ techniques which is utilize an additional switches or switched inductors for speedy voltage rectification. However, such techniques depend on the timing accuracy and synchronization of the pulses of the switch whenever the changes in the currents' polarity generated by the piezoelectric harvester. The existing acoustics-based energy harvesting systems utilized a self powered active rectifying diode circuitry technique to converts alternating current signal to direct current. The active MOSFET rectifier circuit has extra components and required an external DC supply to powering the rectifying circuit. Thus it is not a good option for small scale harvester system and suffered some drawbacks in the implementation of the circuit. Although synchronous switch harvesting on the inductor(SSHI) and synchronous electric charge extraction (SECE) rectifiers possess high efficiency to extract and harvest the energy available from system, they have drawbacksof SSHI circuits such as the complexity of the circuit which is can contribute to additional losses of power, threshold voltages, frequency selectivity and parasitic bandwidth filters. In this study, the developments of passive circuit including voltage multipliers (Dickson and Villard circuits) and step-up transformer were proposed and designed to rectify the low voltage acoustic voltage. The simulation of the proposed harvesting circuit was performed using Multisim and Portus simulator. For verification purpose, the PZT-5A piezoelectric transducer model has been chosen as the harvester due to the consistency. During the experiment, the resonance frequency of the harvestersystem was at 68 Hz with the 95 dB of acoustic pressure. The experimental results showed that the output closed-circuit voltage and the output power harvester can reach up to 3.894Vrmsand 1.556mW respectively. The passive AC-DC harvesting circuits can probably achieve the overall energy conversion efficiency by 78.9% (Dickson circuit) (1.228mW), 70.5% (Villard circuit) (1.097mW), and 10.1% (step-up transformer) (0.1564mW) respectively. Based on the results presented above, the proposed energy harvesting systems seem to be promising and possess a good potential to be used in low power sensors such as wireless sensor networks.
