Is Line-of-Sight required for Wireless Power technologies?

Jun. 2018

No, but it helps.

When considering far-field wireless power technologies, the question of “line of sight” sometimes comes up. Sometimes, a straight line free of obstacles exists between the transmitter and the receiver. This is referred to as “line of sight”. If a line of sight does not exist, energy from the transmitter needs to be reflected off at least one surface before it reaches the receiver.

Is line of sight a requirement?

A mirror can reflect light very well. In contrast, a piece of foam might absorb some of the light, scatter a portion of the light and reflect some small portion. Similarly, a highly polished piece of metal might reflect RF well while foam might not. Different materials reflect, absorb or scatter energy beams to a different degree. How much is reflected, absorbed and scattered depends on many factors. Some of these factors are type of material, shape, surface quality, thickness, orientation angle, etc.

Having said all that, the absolute best that someone could hope for is that the amount of energy reflect towards the receiver is the same amount that hits the reflecting surface. That’s the ideal case. The reflection does not increase the energy. In the real world, the amount reflected towards the receiver will be lower than the amount that hits the reflecting surface. As such, it is always preferable to have direct line of sight between transmitter and receiver. When a line of sight exists, the receiver can get more energy.

Additionally, the shortest distance between the receiver and the transmitter is a straight line. A path that includes a reflection is longer than a direct line. For some technologies, power significantly degrades with distance. This could be because the power beam spreads out or because energy is absorbed in air. For these technologies, it is particularly important to achieve transmission in a straight line between transmitter and receiver.

Energy going in a straight line from transmitter to receiver is always going to be better than a path that has reflections.

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