# An Improved Rectifier Circuit for Piezoelectric Energy Harvesting from Human Motion  
[PERSON]  
1 School of Environment, Science and Engineering, Southern Cross University,  
East Islamore, NSW 2480, Australia; [EMAIL_ADDRESS] (Y.Y.L. ); [PERSON].) [PERSON]  
1 School of Environment, Science and Engineering, Southern Cross University,  
East Islamore, NSW 2480, Australia; [EMAIL_ADDRESS] (Y.Y.L. ); [PERSON].) [PERSON]  
1 School of Environment, Science and Engineering, Southern Cross University,  
East Islamore, NSW 2480, Australia; [EMAIL_ADDRESS] (Y.Y.L. ); [PERSON]
eradicate the need of chemical batteries, thus exerting a positive impact on human life and environment. Piezoelectric materials received wide attention in this application because of their unique piezoelectric effect, which is capable of converting ME, in the form of vibration, into EE, in the form of alternating current (AC) voltage. A typical piezoelectric energy harvesting (PEH) system involves an electromechanical system [8] (such as a piezoelectric device (PD) attached to a cantilever beam), a source of mechanical vibration, electronic circuitry and a storage device/load. A flow chart illustrating a typical PEH system is demonstrated in Figure 1.  
When the PD is subjected to mechanical excitation, it generates AC. To power any electronic device, such as mobile phones, LED bulbs, charging batteries, or wristwatches, a stable direct current (DC) voltage is necessary. For this reason, the AC voltage generated by the PD needs to be converted into DC voltage with the use of an AC-DC rectifier circuit. In the literature, several adroit circuits have been presented [9; 10; 11; 12; 13; 14; 15]. Some widely used circuits are full-wave bridge rectifier (FBR) and voltage doubler (VD) [16; 17; 18]. In spite of their simplicity and popularity, these circuits suffer from several limitations:  
* They consist of diodes, which suffer from forward voltage (V\({}_{t}\)) loss. Thus, the output voltage and power are low. * The rectified voltage is unstable. To overcome these limitations, various strategies have been proposed by researchers in this field. One example is the Bridgeless AC-DC converter proposed by [14] to improve the power flow into the load capacitor and power efficiency. The Bridgeless split capacitor converter circuit is shown in Figure 2a. The MOSFET (Metal Oxide Silicon Field Effect Transistor) switches used in the circuit are operated by an external power supply in both positive and negative half-cycles. This eliminated the problem of losses across the diodes. However, the capacitors C1 and C2 have a large ripple and capacitor C3 has gained steady-state output. Thus, it makes these methods intricate because of the limitation of energy harvester size, losses, and cost [19]. Furthermore, the additional switches can cause switching losses during the switching process. On the other hand, the boost converter, as shown in Figure 2b, with additional switches, results in significant improvement in power conversion from the PD [20]. However, it is rather complex. Power consumption of switches is also higher than the power generated by the PD, rendering it impractical. A low power stand-alone adaptive circuit was proposed by [21] to maximise power extracted from the PD. It consists of a voltage doubler (VD) and a step-down switching converter. The controller adopted uses PD's voltage as a feedback signal to improve power extraction. The result shows that the proposed circuit controls the rectified voltage, output power, and efficiency. However, it requires a complex switching circuit and an additional controller circuit. Another approach to maximise output power from PD, namely, the complex conjugate method, has been used in [22]. In this method, the source generator, (i.e., the PD) has a large internal capacitance with a low resonant frequency [23; 24]. Therefore,  
Figure 1: A flow chart of illustrating a typical piezoelectric energy harvesting (PEH) system.