What’s A Faraday Cage? Hear No RF Evil - See No RF Evil

Posted: 22 Oct 2012 10:36 AM PDT

Ben and His Kite – Don't Try This At Home!

A Faraday cage (sometimes called a Faraday shield, RF cage or EMF cage) is a shielded enclosure formed by conducting material or by a mesh of such material. The enclosure is like a sealed tin can; it keeps the electromagnetic fields inside, and blocks the entry of external electric fields and radiofrequency waves. Faraday cages are named after English scientist Michael Faraday, who is credited with their invention in 1836.

Quick history: Although the development of the faraday cage shielding effect has been attributed to Michael Faraday, it was actually Benjamin Franklin in 1755 who observed the effect by lowering an uncharged cork ball suspended on a silk thread through an opening into a metal container. He noted that the cork was not attracted to the inside of the enclosure as it would have been to the outside and although it touched the bottom, when pulled out it was not found to be "charged" by the touch. Thus, Franklin actually discovered the behavior of what we now refer to as a Faraday cage or shield.

Faraday's famous ice pail experiments duplicated Franklin's cork and can trial. He conclusively demonstrated the electrostatic shielding effect when he built the first formal Faraday cage in 1836. With it, he observed and documented that the charge on a charged conductor remained only on its exterior with no influence on the interior. His Faraday enclosure was a room coated with metal foil. Faraday made high voltage discharges from an electrostatic generator to strike the outside of the room. Using an electroscope, he demonstrated that the discharges caused no deflection when located inside the room. Since it did so outside, no response meant absence of an electric charge on the inside of the walls.

Quick physics: The operation of a Faraday shield is best understood considering a hollow conductor. Externally applied electric fields produce forces on the charge carriers (usually electrons) within the conductor, generating a current that rearranges the charges. The rearranged charges cancel the applied field within and the current stops. There are additional factors to consider when applying an alternating current, particularly one in the radio frequency (RF) domain. The walls of a Faraday box or enclosure only shield the interior from external electromagnetic (RF) radiation if the walls are thick enough to reduce skin effect penetration and any holes are much smaller than the radiation's wavelength.

Applications: The usefulness of the RF Faraday cage is its ability to protect personnel, operating systems, sensitive test equipment, volatile materials, and other things from radio frequency waves. For instance, in the hospital environment sensitive operating room instruments are protected by RF shields from the bombardment of environmental RF energy. In research and test labs and industrial shops similar protection is often afforded by faraday enclosures similar to the LBA EMFaraCage® (http://www.lbagroup.com/technology/faraday-cages.php).

Technicians Applying LBA Room Shielding Systems

The security of wireless communications is often protected using the Faraday principle by shielding building areas and forensic test facilities with architectural materials such as LBA's SM-10 shielding fabric or CPC-54 conductive paint (http://www.lbagroup.com/technology/emi-rf-shielding-materials-fabric-paint.php). Coaxial cable such as used for cable television, actually includes a continuous Faraday shield to protect the internal conductors from electrical noise and to limit external radiation of the enclosed RF. Finally, the military uses this Faraday cage technology for protection of defense equipment for both RF protection, and protection from electromagnetic pulse attacks.

Ironically, the technology can also be used for illicit purposes. A shopping bag lined with aluminum foil acts as a Faraday cage assisting shoplifters to steal RFID tagged merchandise. Hackers can set up Faraday cage test cells for "black" development of wireless LAN intrusion tools, for instance. On the other hand, university researchers use faraday cages to study anti-hacking in a secure RF environment. An excellent example is the program at East Carolina University that utilizes a custom LBA EMFaraCage® Faraday box as discussed in Technical Note 127: Keeping Black Hat In The Box.

University "Black Hat" Test in an LBA FC-10 EMFaraCage® Faraday Cage

LBA Faraday cage solutions: The EMFaraCage® shown above is one of a line of innovative portable desktop Faraday cages developed by LBA for production testing, laboratories, and other applications. Many other RF shielding requirements may be accomplished through LBA designed Faraday cages of architectural shielding materials. We design and furnish RF cages integrated into room or building construction using the most effective RF fabrics and RF conductive paints. We can also furnish architectural shielding solutions against EMF effects of nearby power lines, such as found in utility telecommunications sites.

For assistance on shielding system design, or to purchase EMFaraCages® or shielding materials, contact Byron Johnson at byron.johnson@lbagroup.com or at 252-757-0279.

The post What's A Faraday Cage? appeared first on LBA Blogs.

GOOD TECHNOLOGY, BAD TECHNOLOGY: Part 1

Posted: 22 Oct 2012 08:37 AM PDT

The Curmudgeon recently read an influential article in the August, 2012, issue of IEEE's Spectrum magazine. The piece is titled, "Our Tools Are Using Us," and was written by William K. Davidow. The man has well earned his chops in the field of the "uses of technology," and the Curmudgeon will not try to paraphrase his thoughts here. But the article did kindle great internal thought storms plus a re-examination of some of the Curmudgeon's own interactions with technology, and even some practical changes therein.

It also initiated thinking about which items of current general popularity are "good" technology, and which are "bad" technology. Not necessarily good and bad in a moral sense, but rather which kinds of technology make performance of everyday tasks more efficient and improve the enjoyment of daily living, and which other ones sap time and effort and present their own additional problems to be solved, problems that didn't exist before the item of technology arrived. Or, in other words, which technologies are "pleasing" to use and which are "annoying," and why.

The results of the examinations of the devices and applications that the Curmudgeon currently uses were a little surprising. Almost all of the "good" class of technologies had somewhat similar properties, as did almost all of the "bad" technologies (the properties of the two classes are very different, of course). Let's first look at some examples of technologies that were rated "good", in a list that is not exhaustive (and your similar kind of list might be quite different from this one), and then at some examples of "bad" technology.

The "Good" Technology:

1. An automatic home blood pressure cuff. Used nightly to measure and record blood pressures and pulse rates (isn't that what you, valued reader, also do?). The cuff is battery operated, installs in just seconds, runs its test with the push of a single button, and presents the results instantly. The tests are complete in a matter of a few minutes, with no fuss or bother.

Antenna Farm and Coverage Map for WWVB 60 kHz Transmissions

2. "Atomic clock." The Curmudgeon has inexpensive Chinese-made, WWVB radio-controlled, battery powered wall clocks stashed unobtrusively in almost every room in his house, plus a Casio digital wrist watch that also has a 60 kHz receiver on board. Being the most automated possible time keeper, the synchronized clocks (almost) never need to be touched. No guessing about the correct time either, because NIST, the operating agency for WWVB, itself "manufactures" primary standard time (with some assists from other agencies), and one can't quibble with NIST accuracy! The wrist watch is even better, as it has a miniature solar PV cell on board that charges a small internal battery. It never needs to be fooled with!

3. Personal pedometer (a device which measures the number of steps and the amount of energy expended in walking or jogging). This device has a one-time set-up process, does its counting automatically, and presents several measured and calculated values with the push of a button. It even has the smarts to know when a new day begins at midnight, at which point it automatically stores the previous day's results into memory and opens a new blank page. All that is necessary for its use is to place it in a pants pocket while dressing and then to forget about it.

4. Telephone network "automatic number identification" function. This ANI technology has finally tamed the detestable abuses of the telephone sales industry. Out-of-area calls from "TV Survey" and "Jackpot Administrator" display their caller ID and calling telephone number instantly on the receiving telephone, and these unwanted calls receive swift introductions to "Mr. Voice Mail!" As do other calls that display no calling party data. Of course we all certainly could use the identical technology applied to door bells!

EO Lawrence Behr Holds An HP-35 Bought In 1973 For $495, Still Used At LBA!

5. Scientific/engineering pocket calculator. The Curmudgeon owns about a dozen of these, representing the entire chronological span of the technology. With these, there are no limitations in doing numerical calculations. They are always at hand, always ready to work in a blink of an eye, accurate in their calculations far beyond any practical requirements, and able to handle problems ranging from checkbook balancing to evaluation of hyperbolic functions in engineering.

6. Small, desk-top, "re-purposed" broadcast radio. The Curmudgeon recently took an OEM automotive solid-state AM/FM/tape deck radio that he had pulled out of his vehicle during a past upgrade and he reworked it into a desk radio. It is delightful. Automobile radios (generally) are solidly built, with good RF front ends, plenty of audio output power, and good sound quality. This radio is always at hand on the desk, powers up instantly, and, best of all, has pre-set tuning buttons for preferred stations. It is much more satisfying than the typical consumer products.

The Bad Technology:

1. Current-production consumer entertainment electronic equipment. A long time ago in the Curmudgeon's youth, all consumer electronic devices used vacuum tubes. And an inherent feature of that class of device was a warm-up time delay after power was first applied, as the tube filaments brought the cathodes up to operating temperature. One switched on the radio or TV, and about ten to fifteen seconds later the program appeared. Later, with the advent of "instant on" solid state circuits and products, the warm up delay disappeared.

But now it's back again! It seems as though many current-day receivers and players do not function for the first fifteen to thirty seconds after power up. A plausible explanation for this is that on-board timer-switches disable user control and output circuit operation until internal microprocessors can boot and phase-locked loops have time to lock-up and stabilize. The use of these pesky delay timers certainly eases circuit design requirements, but is this annoyance what consumers deserve? There's certainly little justification for the reappearance of the warm-up delay in these modern times.

The "Cloud" As Visioned By cloud-computing-network.com

2. "Cloud computing." Back in the mists of digital history, we used to call this practice "time share" computing, complete with dumb CRT user terminals (remember the VT-100?). The terminals were remotely connected by dedicated wire or dial-up modems to a big, shared mini-computer located somewhere in the bowels of a building. The arrival of the personal computer liberated us from that, and it was a "one giant leap for mankind." But now "time share" is back, in the guise of cloud computing, retaining most of the problems from the "time share" era plus adding a few new ones also.

3. Hugely complex, vastly-scaled computer applications. In historical times, when UNIX (the precursor of Linux) was an up-and-coming computer operating system, no self-respecting UNIX programmer would write a new basic command (i.e., "edit," "search," "copy," etc.) without simultaneously publishing at least fifty different appended "switches" to modify the main command (i.e., as a hypothetical example, "copy \-a, \-b,\ -z, \-qf" etc.) It was of no importance whether these modifiers did anything useful or would ever be used. "For the sake of completeness," they just had to be there.

Today's large personal computer applications carry forward the tradition. Huge and bloated packages, they are almost useless for doing simple, basic tasks. The amount of time needed to bring the applications onto the screen and then to wrestle them into accepting and processing simple jobs almost negates the value of having them available. And, analogous to Amateur radio hardware, they also succumb to "creeping featuritis," packing in functions and options that few users would ever need. They also, however, present an even further liability: with their complex, bloated code, they break down and require continuing software "patches." The user is inserted into the never-ending chase for "updates," thus adding one more chore to a complex environment.

Feature-Rich 200 Watt ICOM-7800 Amateur Radio Transceiver

4. Feature-stuffed Amateur radio gear. It's necessary to walk a fine line here. Many of the auxiliary functions which, in the decades past, used to be provided for transmitters/receivers by add-on accessories (antenna tuners, speech processors, CW keyers, SWR bridges, etc) now have been built into modern transceivers, made possible today by use of large scale integrated circuits. If these functions were necessary back then, there's every reason to believe they are still useful.

But there is much also built into the current gear that amounts to little more than "creeping featuritis," whose intent is mainly to stimulate desire and to increase sales while adding little if anything to performance. In general, in the Curmudgeon's opinion, if a circuit doesn't directly contribute to producing spectrally-clean, properly-modulated, powerful transmitted signals and to received signals that remain copy-able under difficult conditions, there's not much reason to have it on board. These little-used features tie up buttons and knobs on the radio front panel and slots in the radio's menu structure. They contribute to increasingly complex and expensive equipment while not doing much to aid the overall mission.

5. Smart phones. The "darlings" of the current technology world, they probably could be the subject of entire college courses in the Sociology or Anthropology departments, in addition to the Engineering department. These devices are not "telephones;" rather they are fully-portable, "multi-technology," microprocessor-driven applications platforms

Of all the modern electronic technologies, smart phones are the most likely to be misused, most likely to divert human attention away from human matters. They "accumulate" increasing user involvement with the devices because smart phones are forever proximate to the user, and not because they solve long-standing needs to accomplish tasks that have never before been realizable with a portable device. They can be well criticized for "burning up" huge portions of the endangered RF spectrum for arguably "frivolous purposes" (and the Curmudgeon has made this criticism previously). But they also provide a "one-way trapdoor" leading out of the real world toward permanent residence in the virtual world. (Not just the Curmudgeon's opinion either; see Mr. Davidov's article referenced above.)

In Part 2 we'll take a closer look at the properties of both the "good" and the "bad" technologies, and try to understand what makes them such.

What do you think?

"Let's save the universe for RF!"

The Old RF Curmudgeon

Since 1963, LBA has been providing RF equipment and engineering consulting services for radio and television broadcast and wireless communications.

The post GOOD TECHNOLOGY, BAD TECHNOLOGY: Part 1 appeared first on LBA Blogs.

SPECTRUM TECHNOLOGY TREND BUZZLES

Monday, October 22, 2012