A QUANTUM OF SCIENCE
Nanoscale metals in paint block WiFi signals - with big implications for mobile users
WiFi is everywhere these days, but less than a decade ago it was rare - and less than two decades ago it did not exist at all. Wireless technology was invented in 1991 by AT&T/Lucent (now Agere) but the current standard technology was not patented until 1996 by an Australian company called CSIRO. The Wi-Fi Alliance, a loose affiliation of over 300 companies manufacturing wireless products or services, was formed in 2000 to ensure standardization of WiFi technologies. The first fully-wireless campus was Carnegie-Mellon in 1994 and the first free-WiFi airport was Pittsburgh International in 2003. In 2005 an undergraduate communications class at the University of Washington mapped all the wireless networks in the Seattle area (5,225 at that time). But what is WiFi?
Though the term suggests "Wireless Fidelity" by analogy to Hi-Fi, the WiFi Alliance (who owns the term) officially states that the term is just a brand name and means nothing. In practice, WiFi is a short-range radio signal, an electromagnetic wave that propagates through space in all directions over a distance that decreases quadratically from its source. Depending on the power of the signal it could travel as little as 120 feet (the average home router) and as much as several kilometers using outdoor line-of-sight directional antennas. The power of the signal is limited by the FCC and is generally up to 1 Watt (compare this with an AM radio station at around 50,000 watts for a sense of scale). The frequency is set by industry standard: 2.4 gigahertz (2.4 billion waves per second) is the current standard. As a consequence, the wavelength of WiFi is in the low millimeter range.
Despite the fantastic growth in WiFi hardware and accessibility over the last decade, little attention has been given to controlling WiFi broadcasting. Some information should not be shared freely, such as for businesses who use WiFi internally but which would rather not share their internal emails with the world. This is especially true for businesses who handle confidential information, such as banks and hospitals. Governmental WiFi networks are obvious targets for WiFi hacking as well, and increasing home WiFi network prevalence makes identity theft from unsecured routers a growing concern for millions of consumers.
While many software security solutions exist to protect networks from illicit access, no system is hack-proof, so methods of preventing the propagation of wireless signals beyond a certain boundary are increasingly important. WiFi "jammers" are devices that function by transmitting a signal in the same wavelength range as WiFi (millimeter) but with opposite sign, creating destructive interference with the WiFi signal. They are illegal in many countries (including the US) nominally because they interfere with emergency-response but more likely because they could theoretically prevent law enforcement communications.
Recently, researchers at the University of Tokyo published a paper detailing their work at blocking wireless transmissions with nanoscale magnets – tiny metallic crystals that can be suspended in an oil/latex matrix (AKA paint) and coated onto walls or other surfaces. These tiny magnetic particles absorb electromagnetic energy in the millimeter wavelength (the same range as wireless signals) and a process called gyromagnetic resonance (or "natural" resonance) results, effectively dissipating the wireless signal into tiny, random magnetic resonances that block further propagation of the electromagnetic wave through space. In this case the nanoscale magnets are composed of aluminum-doped iron oxide crystals, which are unique in that they have the highest gyromagnetic coefficient recorded to date. The researchers also noted that both iron oxide and aluminum were inexpensive, non-toxic materials and thus eminently suitable for this application. Additionally, this nanomagnetic paint will block cell phone signals as well, since those operate at a lower frequency than WiFi.
One area that is not affected by this innovation is human health. The World Health Organization did a study on the impact of radiofrequency emanations on human health in 2007, with the finding that normal levels of RF permitted by most industrialized nations have no measurable impact on health or development - so don’t order a few gallons of anti-WiFi paint thinking it will protect you from cancer. Still, while movie theatres, restaurants and museums might hail this "quiet" technology as a welcome breakthrough, consumers’ ever-increasing use of wireless devices is unlikely to wane any time soon – even if some Wi-Fi hotspots will soon become No-Fi coldspots.
For more information:
Anti-Wi-Fi paint keeps your wireless signal to yourself (Yahoo Tech)
University of Washington WiFi map of Seattle (2005)
Synthesis of an Electromagnetic Wave Absorber for High-Speed Wireless Communication (Namai et al)
A Millimeter-Wave Absorber Based on Gallium-Substituted -Iron Oxide Nanomagnets (Ohkoshi et al)
World Health Organization report on Health Consequences of Wireless Networks
WiFi (Wikipedia article)
Electromagnetic interference in the 2.4GHz range (Wikipedia)
The Physics of WiFi (WiFi Forum)
© AQOS / P. Smalley (2009)
Reproduction with attribution is appreciation