All Charged Up – Convenience Costs!
RF Interference, Meet Wireless Power Transfer
Strap in, folks; we’re about to launch once again. The “Next Great Thing” is just coming into view, with lots of forthcoming fanfare and hype, now sailing into port just behind the “New Apple Wristwatch!” Consumers are about to receive yet another “wallet-ectomy”; from wireless charging. We’ll take a look at this new development first, and then broaden out to look more generally at “technology and society.”
Wireless Power for the Masses
The “hot consumer item” for this year could well be a “new” technique which was formally called “wireless power transfer” (WPT). In simpler terms, WPT is recharging your portable, belt-clip, digital tchotchkes on the go, without having to plug them into a battery charger. Emphasis here on “not plug them in.”
Good growth potential is predicted for the new WPT industry, bolstered by a lot of promotion of the “amazing new technology that frees you forever from the drudgery of locating and using tiny power or USB cables for charging your portable device(s).” A new era of labor-saving gadgets begins!
Tesla demonstrating WPT in an 1891 lecture at Columbia College, New York.
As usual, there are both less and more here than meets the untrained eye. “Less,” in that WPT is not an astounding new technology in any sense; 100 years ago Nikola Tesla demonstrated wireless power transfer, and various individual WPT applications have been introduced since then. But, of course, wireless charging has never before been promoted as a “Next Great Thing” consumer technology. There is also “More” here than meets the eye, in that WPT has unrecognized potential to become the next major RF spectrum polluter. Hence the alarm bell.
Before starting into spectrum pollution, first here is a mini-introduction to the WPT technology (a redundant explanation for engineers, of course). Rechargeable batteries are energy storage systems which both accumulate electrical charge and later dispense it via a direct current (DC) power circuit. Typically, power flows into the battery from a DC charging source via a pair of metallic conductors and later, in use, operating power is supplied from the battery to a load also through a pair of conductors. Nothing new here.
The two main methods of WPT device powering
What is new with WPT is the elimination of the charging cable. Recharging power is to be supplied through “free space” from the charging power supply to the battery-powered device without any cords or cables. “Just locate the battery-powered unit somewhere near the charger, and the battery will begin storing electrical energy sent through the air!” (“Somewhere near” means “very close to” or “on top of;” it doesn’t work if one just stands in the middle of a room containing a charger.)
DC power for recharging batteries travels very well through metallic conductors, but unfortunately it doesn’t flow at all through free space. But alternating current (AC) power can move through space, under the proper conditions. Thus, an alternating current flowing through a wire will develop both electrical and magnetic fields (each with constantly alternating polarity) surrounding the wire and each field will propagate itself through free space.
So the simplest conceivable system design for WPT, trying to send DC power across free space, won’t work. For WPT, the DC recharging power must first be converted to alternating current (AC). The AC-produced fields can, under controlled conditions, transfer electrical energy from a charging power source across a gap to a battery. Don’t worry about the details here; they’re somewhat complicated.
So, if we want to do WPT, we need a power source which naturally produces AC or, if the source produces DC, one which can first convert DC to AC power. Then we need an “AC power into free space launcher” on the power source, a “AC power from free space collector” at the battery (both are essentially “antennas”), and finally a rectifier for changing the received AC power back to DC to charge the battery. None of this is especially difficult to do.
Now that we have entered the realm of AC power, we have to consider the frequency at which the AC power charging system operates. The usual “60 cycles per second” household AC power will work for WPT, but it’s far from optimum. At this frequency, efficient “antennas” are huge, impractical structures. However, if we then increase the WPT’s AC operating frequency, the antennas shrink in size and the WPT efficiency improves considerably. And if we take the operating frequency up to about 500,000 cycles per second, the antenna size starts becoming practical, and good things begin to happen.
But Nature never provides a benefit without a corresponding cost or limitation. In the case of WPT, the major limitation is that the battery-containing device must be kept very close to the energy supplying device, in order to transfer useful amounts of energy across the gap. Move the two units too far apart, and little energy is transferred. Or, in other words, the power transfer efficiency will drop considerably if the gap becomes too large. [Power transfer efficiency for a metallic cable is >99%; this is a benchmark figure for WPT]
So the WPT developers strive to keep the transfer efficiency as high as possible, since a low efficiency means that some power purchased by the consumer is not beneficially used for charging. For very low powered devices, so little charging power is required that the actual efficiency figure isn’t all that important, but the transfer efficiency level of wireless charging devices could be critical for recharging a plug-in electric car’s batteries that require large amounts of power.
And that’s about the total amount of information about WPT that is provided to the general public. Save for the remaining need to adopt some industry-wide recharging system standards, the situation looks like a “done deal.” The manufacturers are ready to launch a new consumer industry.
The radio frequency spectrum
What, I’m a Radio Jammer?
But it’s not at all a “done deal” for us. Focus, if you will, on the alternating current power that is flowing through “free space” between the wireless battery charger and the battery-powered portable device. Let’s say that the power transfer efficiency is 90%. Of course, that means that 10% of the energy that has been launched into space is not collected and used. It’s still out there! And what is this energy? It’s a high frequency electromagnetic field that is moving outbound from the energy emitter. A more familiar name for such an AC field moving through space is…….radio! Furthermore, the fact that many of these WPT systems use pulsed RF transmissions means that the noise will be spread over a wide band of frequencies.
Well, we’ll need to be prepared for an entire new generation of unlicensed, low to medium power radio frequency noise producers! In the cited example, the “transmit frequency” is typically between 100 and 500 kHz. That spans international LF broadcasting, radio navigation, and is right at the bottom end of the AM radio broadcast band! Aside from obvious public safety dangers, broadcast AM radio gets another nail in its coffin; another few decibels of noise floor that will further mask purposeful radio communications. [To be fair to the manufacturers, many of the modern WPT systems do detect the presence of a device needing charging and will not launch their “radio jammers” if charging is not taking place. Thus the jamming then becomes a sporadic problem.]
However, if the only uses for WPT were for charging belt-clip tchotchkes such as low powered iPhones, the situation might remain at least tolerable into the future. But that’s not the end goal for the industry. There are bigger rechargeable batteries just waiting for WPT as well. For example, the Curmudgeon has a set of portable power tools energized by 18 volt, 1.5 Ampere-hour NiCad batteries. “And wouldn’t it be w o n d e r f u l if these tools could just be tossed onto a wireless charging table and picked up an hour later, fully charged and ready for work?”
Typical WPT device Architecture
But to accomplish that, the wireless charger must deliver an average of 1.5 Amperes of current during that hour, and probably significantly more than just that minimum amount. Now we’re into the realm of “high power” wireless power transfer, and two new “conditions” then occur. First, in order to keep power transfer efficiency high (we don’t want to waste significant amounts of purchased power!), the AC frequency has to go up, probably by another factor of ten. Thus we will be operating in the HF (“shortwave”) radio spectrum. This frequency change and the higher power in use raise whole new possibilities for noise production. Second, we now have significant amounts of power going “into the air.” While much of the radiated power will be captured and used to charge the battery, some will not. And that raises the possibility of (human) radio frequency exposure hazards around wireless chargers, an entirely new problem set. Again, not much of a problem with a single iPhone charger, but quite a different situation when there are many of these things scattered through residential and commercial districts or some huge batteries (automobile?) are being charged.
Of course, the manufacturers will “certify” that their devices will meet established FCC “Part 15″ unlicensed transmitter emission requirements, as well as OSHA and FCC OET 65-mandated human radiation exposure limits. But how successful has FCC Part 15 field enforcement been with the rackets created by the ubiquitous and ever-expanding numbers of “consumer digital devices?” What could – and would – the Commission do when there are fifteen hundred of these WPT “shrieking banshees” in every square mile of a metropolitan region? How could RF interference location and remediation even be accomplished?
Once the WPT devices are out there, their numbers do not decrease over time. And the new spectrum pollution becomes permanent.
All of this solely to allow consumers to avoid fifteen seconds of “hard labor” involved with plugging their devices into a conventional (non-radiating) battery charger using a cable? Sad! So sad!
So here’s a new technology that can be sold to willing, if not entirely knowledgeable, consumers. A technology which seems innocuous enough on the face of it – “Just trade a little loss in power transfer efficiency for an increase in convenience, and don’t give the matter a second thought.” But there’s more to it, as we’ve just seen. It’s another example of “embracing convenience today” at the cost of damaging our resources (i.e., the radio frequency spectrum) both now and in the future. Where’s the long-range thinking on this?
A Problem Which Is Never Solved
But this is not the first time that such a Faustian-like bargain has been made. A bargain which is promoted by today’s purported “need for convenience, novelty, and expanding sales” and paid for by the cost of a diminishment of our resources. We do this sort of thing repeatedly. So perhaps it’s time to look at some of the reasons why this occurs, and what engineers and the engineering profession might do to change this.
The prototypical conditions for this perpetual problem are fairly easy to present. A plain and hypothetical example will do this:
“My grandson wants to pee into the Hudson River; he’s “full” and just can’t wait until we get back to civilization. But his urinating into the river will introduce a slug of pollution into a pristine treasure. We know that we really shouldn’t do that. Nevertheless, my grandson is small, his need is urgent, and the river is very, very large! His one urination won’t even be noticed and certainly won’t do any damage. So I will let him relieve himself into the river, and life will continue onward.”
But a precedent has been set. It’s now just that much easier for the next person to do the same thing, all the while using exactly the same justification. We are considering a huge public resource here and a very small amount of pollution.
Gradually, through individual actions each done for a “personal need” and without consideration of the larger effect, cumulatively the river becomes polluted to the point where restoration activities are needed. No one person tipped the river into pollution. Each individual, considering only his needs and not the additive results of all the individual actions, created the pollution. And therefore no single individual is uniquely responsible.
This is known as “The Tragedy of the Commons,” and it is happening to all of our resources with increasing regularity. In regard to our society, and with particular regard to our common resource, the radio frequency spectrum, the individual culprit often is a single private company, sometimes an entire industry, who sense the opportunity to turn a profit today by “leveraging” the radio spectrum. The justification is much the same as the homely example given above:
“If I latch onto a frequency, channel, or band on which I can operate my novel new devices, I can sell 1,000,000 widgets a year for perhaps as long as ten years. I’ve been told that the operation of my devices will bollix up that part of the spectrum, but I can safely ignore that advice. It’s not in the least important to me if there are other ways of doing the same process that don’t require moving onto the RF spectrum. In fact, I don’t even want that fact made known. There’s almost no cost for using the spectrum, and certainly no major penalties if I create problems for others.
“The public will buy my devices because they are new and they create a nice time diversion for the buyers. I need to trade on the “novelty” and the ‘life is increasingly better with cutting-edge technology’ craze. Then I can sell my goods, make impressive profits today, and “disappear” at the right time, leaving a polluted spectrum behind. But then the spectrum becomes somebody else’s problem!”
It’s happening all the time, because “wireless” is the zeitgeist of the current culture. “Put it on the air, and it will have greatly increased sex appeal! The dollars are there, to be made today!”
Few people ever consider the fundamental question: what is the best use of the limited public resource known as the radio frequency spectrum? There’s really just a single, fundamental answer for that question, and it is never discussed or considered: radio frequencies should be used for creating channels or communications circuits only to locations and at times where wires and other conductors cannot reach. It’s just that simple and, equally, it’s just that complicated!
The Problem “Up Close and Personal”
Here’s a current and particularly nasty real example, one which makes the Curmudgeon’s bile rise! It illustrates just about everything described above (And a tip of the Curmudgeon’s derby to LBA’s Mike Britner for finding it!)
A manufacturing company wants to produce and to sell a new line of automated lawn mowers. Since the mower is, essentially, a mobile device, it could be controlled by radio, although non-radio means for control are also possible. But the manufacturer has chosen “wireless” as his control method, and he plans to furnish a control transmitter system with each mower. The radio links will operate at low power on a microwave frequency between 6240 and 6740 MHz. Using a discrete frequency and low power shouldn’t create any particular problem for anyone, and the product could well prove to be useful.
How the iRobot 6 GHz control system is configured
However, the manufacturer, in his haste to get to market, apparently failed to check out the “other” uses of the frequency that he chose. And it turns out that there are indeed other uses. One of them is in the field of radio astronomy, where it happens that the weak and distant signals from space on this frequency are a signature for the presence in interstellar space of the organic molecule methanol (“wood alcohol”). Knowing that methanol (along with over 100 other types of organic molecules, all containing both carbon and hydrogen atoms) is out there, and determining where it is located in space is an important guidepost to understanding how the universe originated and operates. And to perhaps unraveling an even more interesting question: “how did (carbon/hydrogen-based) life on earth originate?” So the radio astronomers have a very good “claim” on protecting the specific frequency in question from contamination by terrestrial communications!
That necessary protection of a frequency is a manageable problem. The radio telescopes that do this kind of observation are located at a very few spots on the surface of the earth. One of them is at the National Radio Astronomy Observatory in West Virginia. The site sits in a deep valley to protect the telescopes from incident terrestrial radio signals, and to further protect the ongoing observations the FCC has created a radio “quiet zone” surrounding the facility. Within the zone terrestrial radio transmitters, including cell phones, are banned and the radio noise background is kept as quiet as possible. These radio telescopes are operating with state-of-the-art low-noise receiver front ends, so frequency protection is highly important. The FCC transmitter ban is no surprise to anyone; it’s been around for decades and the local population has learned to live with it despite the “inconveniences.” And even with this there are yet no outstanding problems to be solved for the remotely-controlled mower company. They just need to avoid selling products that will be used within the small protected area.
NRAO radiotelescope, Green Bank, WV
NRAO “quiet area” by Federal Communications Commission rule
But they won’t agree to this. If there are potential customers within the protected area, this company apparently wants to sell to them! No matter that they will likely spoil the astronomers’ observations! In conflicts about spectrum rights, scientific projects don’t have the financial resources that private manufacturing corporations have. And who does speak for the spectrum anyway?
The astronomers proposed a workable solution: equip the mower systems with a GPS receiver card and a small amount of microprocessor power, and self-control the transmitters not to operate if the mower is located within the latitude and longitude borders of restricted zones. The cost of the electronics is minor and the geographical exclusion will affect only a small number of potential users, who should have been advised about the restriction prior to purchase anyway.
But the manufacturer reportedly won’t accept the idea, and instead has proposed one of its own: just place the “no operation in the quiet zone” notice within the mower’s owner’s manual. Presumably it would go in the “safety precautions” chapter, which very few purchasers ever read. And if, by chance, consumers should find it— well, they have already bought the product! This is an almost certain way to circumvent the intent of the quiet zone provisions, merely to sell a few more mowers!
Once again, the Tragedy of the Commons repeats itself. One manufacturer, intent only on maximizing his own next quarter’s “bottom line,” is apparently more than willing to consider solely his own needs and to decide to pollute at no cost to him; never caring about the larger picture.
Engineers and Social Responsibility
What can be done about this? How can we, as engineers and in combination as the engineering profession, try to create some awareness and change? This is a tough assignment. It involves the area of “social change” and, since social change can’t be characterized by a just few differential equations, we as a group don’t handle it well. We are not used to taking a few spare private moments and projecting out the future the consequences of our present directions as a society. But we, as a profession, have the kind of knowledge to do just this, and it’s a kind of knowledge that often the general public will never develop. If not us, then who?
This direction has already begun; you don’t necessarily have to originate this kind of thing “from scratch.” In his Spectral Lines columns in the IEEE magazine Spectrum, Robert W. Lucky has been toiling at this from time to time over the course of several years. And, curiously, the one parallel group which does do this fairly well and consistently, and which can serve as a model, is the natural scientists. They have been into “consequences and social responsibility” at least since Los Alamos days during the Second World War. So, what scientists can do, engineers also can do! Or am I wrong about this?
First, let’s break away from the notion that “if technology can support it, then we’ll automatically do it!” Technology, moving without internal examination, can develop exquisitely efficient methods for mass murder. But is that what we really want to do?
Before the population or an individual company or industry makes a decision to proceed in a new technology direction, we as professionals should conduct (or help conduct) a kind of “technological environmental impact” study. It doesn’t have to be formal, legalistic, expensive, time-consuming, etc. Only thoughtful! And it should contain a relatively small list of questions to be pondered: What are the future impacts on society if it adopts and uses this new system/device/method? What are the intangible “adoption costs” to our culture, our societal organization, and, of course, to our irreplaceable natural resources? Can this goal be achieved with our present tools and devices, without having to “re-invent” the already-existing? Will this new system/device/method increase personal freedom and enhance the possibilities for individual growth, or will it just consume more of an individual’s personal time with distractions? You, dear readers, should be easily able to expand the list of questions.
If the final answer to the study is solely, “The only mission for this proposed system/device/method is to produce short-term profits,” then there should be some serious discussion about whether the proposed new direction needs to be followed. The ability of a society to say “no” is a very fundamental right.
The intent of this topic has not been solely to “bash the private free enterprise system and its accomplishments.” All of us can think of numerous private enterprises that have remained in existence over periods greater than a human lifetime and that, during their existence, have done much good for themselves, their customers, and our society. But, sadly, today these companies are not as prominent and prevalent as they once were. Private businesses whose “game plan” is to exploit The Commons for quick profit are increasing in number. And our common resources, especially the radio frequency spectrum, are being pillaged. If we, the engineering professionals, do not stand up and say “enough!” then who will?
Certainly not our grandchildren, who will have nothing left to defend.
What do you think?
“Let’s keep the universe safe for RF!”
The Old RF Curmudgeon
Read some of the Curmudgeon’s earlier blogs on radio and noise: