Thursday, December 16, 2010

Steph’s Science Corner: Wireless Charging Devices and The Scheme of “Cool”

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powermat wireless chargerI would like to pose a question to my readers, and please direct your answers to the comments section. How many of you own, or know someone who owns, one of these hot-new wireless charging stations? The most prominent brands on the market are the Powermat and the Duracell myGrid, though there are other manufacturers that have devices designed specifically for their product (i.e. for a cell phone, a hand-held video game system, or game controllers).

When I first saw commercials for these toys shortly after they became commercially available in 2008, I raised my hand and studiously chimed, “Electromagnetic induction!” Having confused the TV momentarily for a physics professor, I was disappointed to find that it did not reward me by heaping praise over my identification of a relatively simple and well-understood physical phenomenon like I was hoping. Naturally, I responded vengefully by vowing that I would never own one, though I might have been motivated by the simple fact that they seemed unnecessary, inefficient, and over-indulgent. Why should I spend money on these things when I was already guaranteed a free wired charger with every device I purchased? Was the dreaded “tangle” so overwhelming? I usually found that a rubber band or a twist-tie did the trick for neatness, and those only cost a couple of cents. Was it simply for sex-appeal and sleekness, or just a general appreciation of how cool it was?

I can honestly say that in the two years that these devices have been available, I have never personally seen one used, nor have I known of anyone who owns one. As I am only human, I naturally take my limited personal experience as proof of a sweeping generalization: these devices haven’t had a storm of commercial success. I assume they’ve had enough to be worth their production value. But then again, I’m being rather facetious, and clearly I haven’t conducted any semblance of market research on the matter. What I do understand is that these devices are relatively straightforward, and they’ve actually been around much longer than most of us might have realized.

The Electromagnetic Force

Electromagnets...but you know, less literally Electricity and Magnetism fascinate everyone. We can all admit to being mesmerized by toy magnets as children, and we’ve all gotten secret delight out of statically shocking the cat. These forces have been observed and studied for thousands of years, but it wasn’t until the 19th century that we started to understand their link. This discovery came to a climax in 1865 when James Maxwell published a monumental paper showing that the two phenomena were complementary aspects of one force -- The Electromagnetic Force, or force experienced between two or more charged entities-- and he pulled all the important knowledge of the field into four equations. Today, Maxwell’s Equations still stand elegantly as some of the most important and useful laws of physics, parenting the derivations of nearly every important relationship that applies to our modern technological world, which is rich in electromagnetic devices.

Electromagnetic force is one of four fundamental forces in the universe along with Gravity, the Strong Nuclear Force, and the Weak Force. It is second in strength only to the Strong Force, but it surpasses it in significance with sheer range. The strong force is only felt within the nuclei of atoms, giving it a range of about 10-15 meters, while the attraction and repulsion between charges has an infinite range. Note, however, that distance does play a role in strength, tapering off as you separate charges by larger distances.

What are magnetic and electric fields?

Maxwell was guided to his theories by the work of several other notable scientists from the 19th century. Early on, one of these individuals observed that a magnetic compass needle would be deflected from polar north when nearby electric devices were turned on or off. Specifically, it was the act of actually turning the device on or off that deflected the needle, not the state of being on or off. It was known at the time that charged particles created electric fields, but it was André-Marie Ampère ( you might know him for the “Amp,” the unit we use to measure electrical current) who famously noticed that moving electrical charges are responsible for creating magnetic fields.

Magnetic and electric fields are very different beasts. Electric fields -- created by charged particles -- act on other charged particles, pushing away or pulling towards. Magnetic fields -- created by moving charged particles -- only act on other moving charged particles. But instead of just simply pushing out or pulling in, they change the path of the particle by acting perpendicularly to it.

some common shapes of coils in industrial use We can create many different types of magnetic fields just by wire magnetic fieldconstructing shapes with winding wires. A hollow cylindrical coil, for example, creates a magnetic field (B) that  points straight through the middle of it (right). A single straight wire creates a magnetic field of concentric circles around itself, radiating outward (left).

Induction, Faraday’s, and Lentz’s Law

About ten years after Ampère, an English scientist named Michael Faraday discovered something game-changing. He took two coils of wire and wrapped them each around a large iron ring. He bolted both of these coils down near to each other, but not touching, and then passed an electric current through one of them. As he did so, he observed a momentary electric current that simply appeared in the other coil, even though it wasn’t connected to anything. He then followed that up moving a bar magnet through a loop of wire and finding the same thing - an electric current simply appeared in the wire. The same thing happened when it was the loop that was moving and the magnet that was held still.

Faraday had discovered Electromagnetic Induction. A changing magnetic field will generate, or induce, an electric field. Similarly, any changing electric field will generate a magnetic field. That change can originate from fluctuating size, position, shape, or field strength. This induction can occur in another nearby conductor, and it can be induced in the original apparatus, which is called Self Induction. If the change is occurring repeatedly, the current is maintained.

A couple of years later, Heinrich Lenz pointed out that this induction opposes the original change that produced it. The generated current flows in a direction that attempts to keep the original magnetic field the same. In other words, nature opposes a deviation from its balance.

Where you’ve seen them before

When we push current through a wire, that moving electricity generates a magnetic field. If this current were to be constantly changed (say, by using Alternating Current, or AC power coming from your wall after it is passed through an adaptor), the magnetic field it generates would constantly change. This constantly changing magnetic field could induce a current in another nearby wire. If this wire was attached to a small battery, the battery would charge. Voila. Your wireless charging mat.

electric toothbrushThis technology isn’t new. We’ve seen it for years in electric toothbrushes and razors. When you’re  placing these devices on their charger, you wont see any metal contacts. That’s because contact-conduction would be dangerous if the device were to become wet. Instead, specially designed coils in the charging base induce a current in the specially designed coils at the bottom of your device. In electric generators, mechanical energy (a crank) spins a magnet through a coil to generate electricity. This technology has been possible and very well understood for a long time. 

The cons: extra pieces, extra conversions, and range

Part of what holds these devices back is the absence of that special coil imbedded in your standard Smartphone or Nintendo DS. That means that most devices have to be fitted with some kind of attachment, which translates to extra pieces and extra cost.

Additionally, it is a fundamental law of the universe that nothing is perfectly efficient, and every time energy undergoes a conversion from one form to another, some of it is lost. These mats pull electricity from the wall, generate a magnetic field with it, and then use that to generate electricity in a nearby device, which seems much less efficient than a single wire connecting wall to gadget.

Lastly, induction has a small range, practically implying direct contact. So this isn’t something that we can use to keep our devices on hand while they charge. You still have to put them down and walk away, and there are times when I would want the advantage of a few feet of mobility over the inconvenience of tripping hazards.

Resonance: a peak at some interesting developments

resonance induction charging There is some value here, however. In 2006, researchers at MIT claiming that they had found a way to increase the range of electromagnetic induction by taking advantage of resonance, a property of things with wave forms. In music, an instrument’s shape and size determines the frequencies at which it naturally vibrates, which is what produces notes. If you hold one trumpet up to another, the second one will vibrate with that same frequency. This group asserted that it was possible to increase the range of inductance by tuning coils to resonate at the same frequency just like instruments, which could increase their range to several meters. They call this resonant induction charging, and in 2007 they used this method to power a light bulb over a distance of about seven feet.

Concluding thoughts

I will likely never buy one of these charging mats unless I’m forced to, but not because they’re poorly designed, and certainly not because they’re not fascinating. Induction is a strange thing to witness when you first understand it, and I remember having some very [yes, sober] mind-bending thoughts about the nature of the universe after I first learned about it. It is almost hard evidence of some underlying rule that nature wants to maintain balance, observably opposing your attempts to mess with it. I don’t know, maybe it’s just me, but I think that’s pretty amazing.

Nevertheless, the device itself isn’t really all that innovative or necessary. It’s not much of an improvement over wired charging, just a different way to do it. If I were to buy one of these, it would just be because I like science.

On the other hand, just because this isn’t world-altering doesn’t mean that improvements in technology such as this one aren’t important steps forward. Improving the range of these devices would be quite handy if this resonance idea continues to develop. And if it does, companies like Powermat and Duracell will be armed with the precursors and the infrastructure to develop the recharging methods of the future.

In the meantime, however, I’m not swayed by hip, sexy advertising campaigns just yet. Anyone else care to disagree?

See you back again next Thursday. Email suggestions or requests to!