How would weather conditions affect the functionality and efficiency of an RFID interrogator—say, in heavy rain?
I have not heard that rain has a significant impact on RFID systems, but I reached out to the folks at Rush Tracking Systems, which has deployed both passive and active systems, to get input from the experts.
According to Rush Tracking's engineers, the impact of rain is dependent on the RFID system's frequency, as well as on how heavy the rain is, and the size of the rain drops. At 900 MHz, rain doesn't significantly impact signal propagation, unless it is a heavy rainfall. That's because the raindrops are small with respect to signal wavelength, so minimal scattering occurs. It takes a high density of scatterers—raindrops, in this case—to have any substantial impact. Where one would expect to see an impact is in difficult or long read-range environments. Since the size of an ultrahigh-frequency (UHF) tag is such a big factor in range, one can not really say exactly what long read range is. There are too many variables to play with to provide a definitive answer.
Active tags in the 400 MHz range and below would not see much attenuation. The impact of rain becomes more significant as frequency increases, since signal wavelength begins to approach the size of the raindrops. As this occurs, both scattering and absorption become significant. This tends to occurs at around 3 GHz.
The most obvious impact on an RFID system would be that the read distance for both active and passive tags would be reduced, due to the increased attenuation across the signal path. However, as most RFID technologies operate at frequencies lower than 3 GHz, this impact would likely be minor.
—Mark Roberti, Editor, RFID Journal
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