## 2 Background and Related Work  
The power transmission performance of inductive coupling and magnetic resonant coupling, which are the two most widely studied WPT technologies, is optimal within a range of 1 m [7]; thus, these technologies cannot be applied to EVs without modifying the existing road infrastructure. The magnetic induction method has been introduced to charging smartphones which resulted in a reduced price of the products and increased spread of charging devices. Similarly, in the case of an EV, a magnetic resonance method in which energy is transmitted using a magnetic field generated from a coil is commercialized and used to transmit power at a distance of up to several meters. The magnetic induction method is the most efficient WPT method and a PTE of 95% or more is possible over a distance of several millimeters. The magnetic induction method is mainly used for non-contact types, such as transportation cars, because the power transmission distance is short. The magnetic resonance method is capable of WPT over a distance of several meters, and power transmission efficiency of about 70% is possible. However, due to the influence of the transmission/reception coil's size and location, it is not easy to commercialize it for EVs. EV wireless charging methods using WPT currently apply magnetic resonance technology operating in a short distance. This method has high PTE; however, it is essential to embed a PTX on the road for constant charging because it operates in a short distance. For high-speed wireless charging of EV, it is necessary to transmit multiple wireless powers simultaneously. In the magnetic induction and the magnetic resonance methods, for WPT coils are widely used to transmit power to several PRXs using one power transmitter. Despite that, using several PTXs to transmit power to one PRX is very challenging. When using a coil, a pair of coils matching the coil of the PTX must exist, and when there are multiple coils in a narrow space, mutual interference occurs between the coils, making it difficult to find an appropriate match. In EVs, increasing the transmission power is pursued by making multiple transmission/reception pairs using multiple coils. The long-distance WPT technology that can transmit power over several tens of kilo-watts over a distance of several kilometers is still in the early research stage, and a method using microwaves and lasers is used. Microwave and laser-based WPT technologies with far fields greater than or equal to several kilometers used in drones and satellites may be more easily applicable to EVs because the existing road infrastructure can be used without any modifications [9; 10; 11; 12]. The microwave method is a technology that transmits high-power energy over a long-distance using a high frequency of several gigahertz. This method requires a very large transmit/receive antenna and has the disadvantage of being harmful to the human body and radio wave interference. HILPB is applied to fields requiring medium and long-distance power transmission, such as unmanned aerial vehicles. The basic process is the same as that of solar power generation, where the solar panel converts sunlight into electricity. The key difference is that the WPT system uses a highly concentrated laser beam, rather than sunlight and aims at a specialized solar panel that converts the laser beam into electricity. Additionally, the laser beam can have higher energy than the sunlight and it can be directed at any point in the line-of-sight of the transmitter. While WPT technologies using microwaves have several constraints owing to radio frequency interference, those using laser beams have advantages of zero interference and simultaneous power delivery from multiple power sources [17]. However, WPT technologies for EVs require high electrical power, which poses significant safety concerns [18; 19], such as the risk of exposure to high electromagnetic energy. The inherent ability of lasers to produce a focused and directed energy beam makes the laser-based WPT system hazardous [20; 21].