Applications of additive manufacturing for ambient RF energy harvesting and wireless power transfer systems
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Power cables are the last wires that prevent us from realizing truly “wireless” electronic devices, and wireless power transfer and ambient RF energy harvesting technologies are the key enablers to achieve the energy autonomous operation of these devices for wearable, mobile, and IoT applications. However, a low output voltage and a low power conversion efficiency associated with a low ambient RF energy density, and the degradation of wireless power transfer efficiency hinder the use of these technologies in practical situations. In the meanwhile, additive manufacturing technologies, especially inkjet and 3D printing technologies, which has been exploited to fabricate RF circuits, have drastically improved over the past few decades. The on-demand deposition of multidisciplinary inks enables low-cost flexible coils, wearable RF energy harvesters as well as other type of ambient energy transducers with the same platform. These unique characteristics of additive manufacturing techniques can be utilized to overcome the challenges in RF energy harvesting and wireless power transfer. This work first reviews the challenges in wireless power transfer/RF energy harvesting, and capability and limitation of additive manufacturing technologies, then shows the application of additive manufacturing technologies in the field of near-field wearable RF energy harvesting and ultra-low power far-field RF/solar hybrid energy harvesting. Also, an active matching circuit design and operation for near-field wireless power, which is caused in wearable and flexible electronics is discussed.