Can’t Touch This
Wireless power transmission
A few years ago, a colleague and I enjoined a group of undergraduates on an old-fashioned field trip to the Edison National Historic Site in West Orange, NJ. We took the public tour and visited the storied laboratories that witnessed the development of the incandescent light bulb and motion picture technology. However, I was most impressed by two additional features of the complex.
The first was the research library outfitted with a complete collection of the publications of the U.S. Patent office at the time. The scientists and engineers were concerned with the creation of new technology that could be leveraged into marketable products. Universities are great places for following scientific discoveries for the sake of the science, but the Edison laboratories existed as a business. Not having Internet connectivity in the late 1800s, the library served as the laboratory’s information repository. Much like today, when a researcher needed information concerning a chemical reaction, a mathematical formula or cutting edge engineering solution they consulted the current literature, albeit via paper.
The second impressive thing was the complexity of the production and machining facilities. Creating tools to make new tools catalyzes the development of technology, and the Edison laboratories are an early representative example of the process of innovation. This process is further streamlined through the rapid adoption of standards. Since a majority of the tools and equipment was developed on site, the facility created its own standards that could be deployed throughout the multi-acre campus.
One such standard was the method of power distribution. Ultimately known for the development of electrical grids to power the famous Edison light bulb, the early machine tools used by the Edison laboratories were powered by a universal line shaft. Consisting of a long rotating shaft similar to the drive shaft of a rear-wheel drive automobile or the propeller shaft of an ocean vessel, the mechanical energy produced by the factory boiler was distributed throughout the factory in the form of rotational momentum. Individual machines were connected to the line shaft via a belt and simple clutch system that tightened the belt around the shaft through the use of a lever. Over time, the belt would wear out due to considerable friction, but this technology provided a less complicated method of power distribution when compared to early high-pressure steam and hydraulic systems.
Over time, the development of electrical and electronic devices necessitated the distribution of high-pressure electrons throughout our manufacturing plants, offices and homes and additional standards soon followed. In the U.S., electrical power is generated at 60 Hz and is ultimately delivered in standard nominal voltages of 120, 240 and 480 volts. Typical electrical outlets are limited to 15 amps and accommodate plugs having the familiar three prongs, consisting of two vertical paddles and a u-shaped grounding prong. Higher amperage outlets sport differing standard prong shapes and orientations to prevent the accidental connection of incompatible devices. Apart from not having enough electrical outlets, plug strips or extension cords, the standard three-prong power cord is a ubiquitous way to “plug” devices into the power distribution system.
As technology continued to develop, our present menagerie of mobile, hand held devices flourished, and so too did the utility of battery power. Physically connecting these miniature devices to the power grid would seriously interfere with their function, and it is for this reason that they incorporate their own local source of power in the form of single use or rechargeable batteries. Battery manufacturers quickly developed standard form factors for their industry including “AA” and “C” size cells to ease consumer confusion when they needed to be replaced.
While popular for use by early transistor radios, sensors and toys, single-use chemical batteries cannot supply the large amount of current required by sophisticated computational devices such as laptop computers, smartphones and personal entertainment equipment. Their rechargeable batteries are incorporated into the interior of the device and rarely require user replacement. This allows the device manufacturers to select battery form factors based on features such as size, battery life and the internal configuration of device components. Increased numbers of battery form factors grant industrial designers additional freedom to sculpt and differentiate the look and feel of their products.
But the downside of rechargeable batteries is that they eventually need to be recharged. Connecting the battery to the power grid through a standard AC/DC power adapter is easy. The difficult part is connecting the adapter or “charger” to the battery since each battery manufacturer is free to design the form factor of this connection. What? After this lovely century-old narrative of “innovate and standardize,” this step does not follow the pattern.
A conspiratorial theory may suggest that portable device manufacturers recognize battery chargers as a lucrative revenue channel. Similar to bubble-jet printer manufacturers relying on the sale of ink over the life of the device to offset the below-cost price of the machine, paying $25 to $100 to replace a broken or lost power adapter offsets the true cost of a “free” phone with service plan or low-cost laptop. An innocent non-conspiratorial theory may be in line with the Year 2000 (Y2K) problem. Programmers did not envision the future difficulties created by a two-digit year field, and few portable device designers may have predicted the number of consumers simultaneously carrying laptops, cell phones, mp3 players and digital video cameras. These capabilities may eventually be provided by a single “uber-smartphone” but, at the moment, the number of individual chargers is quite inconvenient. Chargers also are incompatible among similar devices that users may swap due to upgrades or lost equipment. If you are currently using your fifth cell phone, there is a high probability that you have four obsolete chargers on your garage workbench.
This past February, the Groupe Speciale Mobile Association (GSMA) formed by the Confederation of European Posts and Telecommunications (CEPT) and later endorsed by the European Union (EU) mandated the development of a standard mobile phone charger utilizing the micro-USB interface by 2012. Apart from increasing user convenience, this effort is being applied to stem the tide of discarded adapters entering the waste stream. While not addressing the adapter standardization problem between different mobile devices, it looks to be a good start.
But, what if the AC/DC adapter could be eliminated entirely? This is the goal of wireless energy transfer, an effect first demonstrated by Nikola Tesla in 1893. Utilized inside the very adapters the wireless technology may replace, inductively-coupled transformers rectify the AC electricity available at the power outlet into the DC voltage required to charge the battery though the utilization of two induction coils. Unfortunately, the induction effect decreases rapidly as the distance between transmitter and receiver increases and often suffers from interference. Among other recent developments to overcome these limitations, Professor Marin Soljacic and his colleagues at MIT have recently developed the use of inductively-coupled coils that can be tuned to a specific resonance frequency. This increases the efficiency of the power coupling and reduces the amount of interference from extraneous objects located near or between the coils. MIT has dubbed their development “Witricity” and it is being commercialized by Fulton Innovation of Ada, MI, in a product called eCoupled Technology.
While exploiting the high efficiency of the Witricity resonant induction, the eCoupled system includes data communication services between senders and receivers that negotiate and optimize the appropriate resonance frequency. Much like the identification friend or foe (IFF) radio-frequency identification (RFID) system, incompatible metallic devices that do not contain an IFF chip are sensed by the transmitter and the device is switched into sleep mode. Additional data services communicate the heath and status of the rechargeable battery and also switch power transmission off when the battery is fully charged. Multiple devices can be charged simultaneously though the use of separate resonance frequencies.
If widely adopted, wireless power transmission could find itself incorporated into common objects. Imagine a thin eCoupled transmitter taking the form of a hotel night stand, an airline tray table, a library reference desk, a laboratory workbench, an automobile cup holder or a college study pillow. When it comes to new standards there are usually two main methods used to spur their adoption. The first is to mandate forceful regulations. The second is to invent a technology that is so widely popular that manufacturers race to imitate it. Both methods are powerful, but I prefer the latter hands-off approach.
1. Electricity in the American Economy: Agent of Technological Progress, S.H. Schurr, C.C. Burwell, W.D. Devine and S. Sonenblum. (Greenwood Press, 1990) ISBN 0313275122.
2. On the Development and Transmission of Power from Central Stations, William Cawthorne Unwin, F.R.S. (Longmans, Green, and Co. 1894). Available at books.google.com.
William L. Weaver is an associate professor, Department of Integrated Science, Business and Technology, La Salle University. He may be contacted at editor@ScientificComputing.com.
eCoupled Technology www.ecoupled.com/index.html
Edison National Historic Site www.nps.gov/edis
Groupe Speciale Mobile Association www.gsmworld.com
Proffesor Marin Soljacic www.mit.edu/~soljacic
Wireless Energy Transfer History en.wikipedia.org/wiki/wireless_energy_transfer
Witricity Wireless Power Transfer witricitynet.com
CEPT Confederation of European Posts and Telecommunications | EU European Union | GSMA Groupe Speciale Mobile Association | IFF Friend or Foe | RFID Radio-frequency Identification | Y2K Year 2000