## 1 Introduction  
In the past, vibration energy harvesting (VEH) had been utilized to power small-scale devices such as sensors and instruments. Many studies have been conducted throughout the years to improve the efficiency and capacity of current vibration harvesting systems, the ultimate goal of which has been to the remove the power source or battery required for small usage. Transducers are used to convert ambient vibration energy sources into electrical energy. The most common transducers are electrostatic, electromagnetic and piezoelectric. Electromagnetic transducers use electromotive force that is createdthrough change in magnetic flux when vibrational force is induced [1]. Piezoelectric harvesters convert mechanical strain into electrical energy. Efforts had been put into increasing the efficiency and output of a piezoelectric system--some research fine tunes the resonant frequencies while some combines both electromagnetic and piezoelectric systems into a hybrid system which effectively increases the bandwidth of the optimum operating frequencies [2]. In this research relating to flow induced vibration, piezoelectric harvesting is the go-to method of VEH and thus this investigation is aimed at improving performance through the amplification of force while fine tuning the vortex frequency towards the natural frequency of the model. Flow induced motion (FIM) is a physical phenomenon that occurs when a body is placed in a transverse flow. Vortex induced vibration (VIV) is the most common occurrence of FIM mainly caused by periodic lift forces induced by the flow shedding of bluff bodies [3]. VIV exists through a wide range of velocities whereby the vortex frequency synchronizes with the oscillating frequency of the vibrating object. Extensive studies on VIV and its effects have been carried out throughout the years and the phenomenon is well explained in many comprehensive reviews published in [4; 5; 6; 7]. [PERSON] and [PERSON] identified the 3 types of VIV excitation: movement-induced excitation (MIE), extraneously-induced excitation (EIE) and instability-induced excitation (IIE). MIEVV arises from the movement of structures exciting the flow in contact. EIEVIV is caused by fluctuating velocities and pressures independent of flow instabilities such as flow turbulence, machine vibrations and earthquake. IEEVIV is caused by flow instabilities due to the presence of bluff body in a transverse flow. VIV was once considered a threat to structural designs such as bridges, buildings, stacks, cables, pipelines and many more [8], but as technology advances in recent years the VIV phenomenon is utilized as a new form of renewable energy source. Wind turbines have been exhaustively researched throughout the years and nowadays VIV energy harvesting is seen as a new form of a smaller and more robust energy harvesting method related to fluid flow. MIEVIV and ITEVIV energy harvesting concepts were usually the main focus of research with MIE harvesters discussed exhaustively. Vortex induced vibration aquatic clean energy (VIVACE) was the first MIEVIV based harvester developed by [PERSON] et al., which involves a cylinder connected to a generator through the installation of a spring [9]. [PERSON] et al., [PERSON] et al., [PERSON] et al. and [PERSON] et al. show that optimizing fluid flow speed, mass ratio, aspect ratio, damping ratio and surface roughness were contributing to improvement of the VIVACE system [10; 11; 12; 13; 14]. [PERSON] et al. proved that a cylindrical and trapezoidal shaped MIEVIV harvester system was the better performing out of all shapes designed [15]. [PERSON] et al. studied the flow effects of a step cylinder where different sizes of cylinder produced different vortex frequencies [16]. [PERSON] et al. developed an airfoil shaped MIEVIV harvesting system that involves both the heaving and pitching motions of airfoil, improving VIV motion through structure and flow instability [17; 18]. [PERSON] et al. studied the bending and torsion vibration effect of a VIV energy harvester [19].