This works presents the design of wireless power transfer systems that can transfer power through materials such as stainless steel, aluminum, carbon fiber, and fiberglass. Wireless power transfer research has been limited to through-air applications, focusing on short distances and high efficiencies. However, complex scenarios require specific design criteria to provide the advantages of wireless power transfer for critical applications. Taking this into consideration, this work presents the extensive research towards enabling wireless power transfer systems for unconventional barriers. In the first chapter a new approach is taken towards the design of compact and embedded wireless power transfer solutions. A miniature coil is designed to transfer power through a 1 mm thick aluminum metal plate. The results are unprecedented, P_rx=100 mW, considering that through metal power transfer had only being demonstrated using large diameter coils. In addition to that, the metal barrier used is aluminum, a high conductivity material. This is important because traditional research focused on less conductive material such as stainless steel or tin. In the next chapter, we demonstrated a wireless power and data transfer system that uses a miniature coil with a size of 15 mm × 13 mm × 6 mm. Our system demonstrated that not only power but data could be transferred through an aluminum barrier using the same coil for power and data transmission. The maximum coil-to-coil power transfer efficiency is 2.4%, and the maximum harvested power is 440 mW operating at 2 kHz. Additionally, our system demonstrated that power can be harvested in variety of materials of different thicknesses. The next chapter presents a breakthrough in the field of wireless power transfer through metal by enabling long distance wireless power transfer. A large portion of the technologies for wireless power transfer are limited to short operation distances, distances around 1-10 millimeters to less than 20 cm. The operation distances are even shorter for the ...