Three-dimensional Piezoelectric Vibration Energy Harvester With Triple Motion Modals

With the fast development of the new technology, our daily life has entered the time of the Internet of Things(IoT), which interconnected the things via the internet. The wireless sensor networks are one of the essential parts of the IoT, which includes the wireless networks and the wireless sensor nodes. The wireless sensor nodes play the role of sampling information from the ambient environment, and the wireless networks interconnect and share the information. However, the traditional battery technology, which is characterized by short lifespan, high cost and environment pollution, restricts them large-scaled used. On the other hand, the development of the low-power consumption technology makes it possible to achieve the self-powered wireless sensor device which converts the ambient energy into the electrical energy.Energy harvesting technology means scavenging the physical energy from the nature, such as the light, sound, heat, and vibration, and converting them into the electrical energy to power the wireless sensor device via the energy harvester. Particularly, the vibration energy attracts a large amount of attention of the researchers due to its high density and widespread existing. In recent years, the researchers have designed numbers of the vibration energy harvesters. Most of the vibration energy harvesters are capable of scavenging the vibration energy only when the frequency and the direction of the vibration energy source closely matching the resonant frequency and the motion of the harvester. However, the vibration energy sources are varied. Their frequencies are distributed in a wide range, and their vibration directions are time-variant and multi-directional, which makes the traditional energy harvester are impractical.Addressing those disadvantages, this paper proposed a three-dimensional piezoelectric vibration energy harvester with triple operating frequencies. In this harvester, a spiral-shaped elastic thin beam instead of the traditional thin cantilever beam was adopted to absorb the external vibration with arbitrary direction in three-dimensional(3D) spaces owing to its ability to bend and stretch flexibly and its three motion modes. The differential motion equations of the spiral elastic thin beam was deduced and the theory formula was presented. The 3D prototype of the harvester was designed with the Solidworks software. The COMSOL software was used to study the motion behaviors. The simulation results demonstrate that the spiral-shaped elastic thin beam has the character of the triple motion modes and the ability of absorbing the multi-direction vibration energy. Moreover, the width and thickness parameters of the beam determin the eigenfrequencies and the space between them. A prototype was fabricated and used in the experiment to validate the theory and simulation. The experiment results shows that the output voltage has three peaks, which are at 16 Hz,21 Hz and 28 Hz, respectively. When the direction of the vibration source is 0°,30°,60°,90°,120°,150°, the maximum output voltages in X-Y plane are 37.8 V, 33.2 V, 32 V, 30 V, 21.6 V, and 19.6 V, respectively, while the maximum output voltages in X-Z plane are 30.4 V, 33.2 V, 30 V, 6.8 V, 22 V, and 27.2 V, respectively. Moreover, when the direction of the vibration source is 0° in X-Y plane, the maximum output power of the harvester are 30.07 W/3, 28.5 W/3 and 0.59 W/3u across the optimal resistances of 1.8 M?,950 K?, and 1.2 M?, respectively.In addition, two demos were fabricated based on the three-dimensional piezoelectric vibration energy harvester to scavenge the human walking and water wave vibration, which successfully proved that this harvester was practical to scavenge the time-variant or multi-directional energy in our daily life.