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 case of through metal wireless power transfer. For through metal wireless power transfer, the high losses from the metal barrier require short operation distances less than 1 mm, in order to transfer some energy through the metal barrier. On the contrary, our system uses a custom designed coil to transfer energy to a receiving coil enclosed in a 1-mm thick aluminum metal box up to a distance of 1m. The maximum AC harvested power was 231 μW when the transmitted power is only 6.16 W. The next chapter presents a long range through metal wireless power transfer and communication system. The system demonstrated that power can be harvested inside a metal box, and that data can be transferred bidirectionally between the nodes. Operating at 103 kHz, a maximum harvested power of 408 μW AC and 96 μW DC is achieved, with bidirectional communication at a rate of 1.2 kbps. The last chapter presents the design of a wireless power transfer systems that can operate through composite materials. The work analyses the effect of different materials and presents a system that can operate wirelessly through carbon fiber and fiberglass. Finally, conclusions present the results of this research and the future perspectives in the field.