Some wireless and RFID updates:
- U.S. Baby monitors cause interference in Japan. (H/T Steven J. Crowley)
- Two different perspectives on the history of RFID from Michael L. Davis at DefCon 17 and from SoftwareHelpOnline.
- I’m sorry to learn that David Schmarder is retiring. His business provided a valuable service by making Litz wire available in smaller quantities for test and experimentation.
- The Virginia Court of Appeals rules that warrantless GPS surveillance of a vehicle is not a violation of the Fourth Amendment.
- Finally, the usually erudite and tech savvy folks at Wired offer an erroneous “explanation” of “Why Everything Wireless Is 2.4 GHz:”
At certain frequencies, such waves cause something call Dielectric Heating in water and fat, while passing straight through other materials, like plastic or glass, without exciting them much at all. (Metal, on the other hand, gets too excited.) For a full explanation of how dielectric heating works, click here, but for the purposes of this article, just know this: Only certain materials are susceptible, and only when bombarded with waves of a certain frequency and power. One of those frequencies is 915 MHz. Others fall at 5.8 GHz and 24 GHz. But the one that proved to be both effective and relatively cheap to achieve was 2.45 GHz. That’s the frequency emitted by your microwave, right there in the kitchen.
But there’s nothing magical or special about 2.45 GHz and water – the lowest actual water resonance is in the neighborhood of 20GHz. Microwave ovens are at 2.45 GHz, because that was a convenient frequency in the neighborhood where the original WWII era 10cm wavelength microwave radars operated. The microwave oven was invented by Percy Spencer in 1945 (U.S. Patent 2,495,429) who recommended “wavelengths of 10cm or shorter,” i.e. frequencies of 3GHz or higher.