When it came to the big players expected to get involved with the wireless charging sector, all eyes were on Apple, especially after Android started manufacturing wireless charging to their smartphones (and Apple didn’t). Industry experts speculated Apple was overlooking contact-based chargers, and gearing toward developing long-distance devices. Apple eventually came out with their own contact-based wireless chargers.

Contact-based and resonance chargers have limited benefits for smartphone users. At best, they can put their iPhone X down on a wireless charging dock and retrieve the device later, minus the fidgeting with a lightning cable. Having said that, the setup uses just as many cables, which are merely attached to the pad’s charging docks.

RF-based charging over long distances have more promising benefits, enabling devices to be powered anywhere in the same vicinity as the charger. It’s not like Apple didn’t make these decisions without specific reasons, and their figuring behind foregoing long-distance wireless charging ties into why the “anywhere in a room” concept probably won’t happen any time in the near future.

RF wireless power comes in two forms known as near- and far-field, while some companies have adopted the term “mid-field” to describe a three-foot range device approved by the Federal Communications Commission (FCC). Rival companies, however, have dismissed the concept as a “marketing term,” and that this form of wireless charging actually falls in the near-field range. When using parameters to determine near and far-field, the differences are distinct. Near-field charging would exceed a few feet from the dock at most, whereas far-field can theoretically reach distances up to 80 feet.

One of the FCC’s regulations, known as Part 15, imposes limits on the amount of power output from an RF transmitter to one watt. There are also referrals to utilizing three- or four-watt devices, since the one-watt limit applies to omnidirectional antennas. You can efficiently concentrate the available power by focusing the radio beam in a specific direction, and the FCC does allow four-fold antenna gains within a particular arc. A sample RF charger, for example, utilizes a directional antenna with a 70-degree arc.

Since nothing is ever 100 percent efficient, the maximal power capable of being harnessed is less, even when it’s right next to the transmitter (which is realistically only half a watt). Radio waves face what’s known as the inverse-square law, which proclaims that intensity is inversely proportional to the square of the distance from a source. If you get .5 W one inch from a transmitter for example, you’ll be down .125 W two inches away, whereas at four inches, you’ll be down to .03 W. Simply put, the numbers reveal why reaching the point of powering a MacBook across the room from a transmitter are currently far from coming to fruition.

According to Dr. Charles Greene regarding the ability to charge a device anywhere in a room, the technology exists and is functional, but has no technical feasibility. The concept ultimately boils down to what is technically possible, along with what is both safe and legal. An iPhone could technically be charged anywhere in a room, although it wouldn’t be in a legal or safe manner. If you place a human in the crosshairs of a powerful RF field, the individual’s tissues would start heating up as if they were in a microwave oven.

This is primarily why the one-watt power limit factors into the equation, since the amount of deliverable power on any distance is very small. The maximal amount of available power next to the transmitter is about half a watt, and that figure drops to tens of milli-watts when moved within just inches from the power source. At three feet, the amount of available power falls to single-digit milli-watts, and drops to micro-watts at distances around ten feet.

The limits imposed by Part 15 regulations can be bypassed, however, by instead adhering to a different set of rules called Part 18, which have no specific limit regarding power, as long as other FCC safety and exposure requirements are met. This doesn’t change the fact that following these rules doesn’t get you significantly further regarding deliverable power. This is yet another reason why we’re unlikely to see long-distance wireless charging powering our laptops and smartphones any time soon.