Multimodal Energy Harvesting Skin Using Piezoelectric Unimorph Shell Structure

1 Introduction Energy harvesting (EH) research area has been emerged to build self-powered wireless electrical devices such as wireless sensors by collecting ambient or wasted energy. This EH technology is highly demanding because wireless sensors are increasingly used in the areas of structural health monitoring (SHM), building automation, and so on. The battery, a current power source for wireless sensors, can be troublesome due to their limited lifespan and replacement cost. This issue has motivated the rapid growth of the EH field. Among various EH technology the studies of piezoelectric EH to utilize machine vibration have been focused on designing EH devices including shape [1-3] and electric circuit [4, 5], or both. Even though most piezoelectric EH devices take a form of cantilever, this form has some drawbacks from a practical point of view: (i) it requires an extra space because of a bulky proof mass and additional clamping part, (ii) it must be protected from dirt, moisture, and other environmental harms, and (ii) a great deal of vibration energy can be lost when clamping conditions become loosened after a long-time vibration. The disadvantages of the cantilever design motivated the proposition of an innovative and practical EH design entitled "energy harvesting skin (EHS) [6, 7]." In the EHS, thin piezoelectric patches were directly attached onto a vibrating shell structure to harvest electric power while attempting to overcome the drawbacks of the cantilever EH device. This paper proposes an advanced EHS design concept, entitled multimodal EHS, which utilizes multimodal vibration and enhances the energy harvesting capability.