a) My microwave oven operates at 2.45 GHz and has a mesh screen behind its window.
b) My smartphone receives both WiFi connections as well as standard cellular calls.
c) I put my phone in the oven, closed the door and tried to make a WiFi connection. It would not connect. Not surprising because my modem runs at 2.4 GHz, which is almost the same frequency as the microwave oven. I opened the door and was able to connect WiFi. I tried the experiment several times with the same result. No mystery here.
d) I then put my phone in the oven, closed the door and called my phone from another phone. The phone rang with the door shut! But the carrier frequency of my phone is 800-900 GHz, which is a third of the microwave oven. That means the cellular carrier wavelength is 3 times longer than my WiFi wavelength, and yet the longer wavelength gets into the oven. I tried dialing the phone out to call a phone outside the oven, and quickly closed the door. The phone rang. So I established that the effect is a reciprocal one.
e) I then went to a friend's house and repeated the whole experiment again. However, my phone could not receive calls while in the oven, but it could dial out to an external phone successfully.
e) Question #1: Why does the longer wavelength get in, and yet the microwave oven does not leak microwaves?
f) Question #2: Why did the longer wavelength not get in, in the case of my friend's microwave oven and yet the signal dialed out successfully?
Derek the answer is that microwave shielding is imperfect, many microwaves leak radiation. The FDA (in the US) says that it can leak 5 milliwatts of microwave radiation per square centimeter at approximately 2 inches from the oven surface (at the operating frequency). Ovens in other countries may have even less shielding. Thus a good digital phone could receive a weak signal and still operate (even in the WiFi band), but certainly at longer wavelengths which are not measured for radiation protection, nor designed for in the shielding. Receiving and transmitting require different signal strengths, 3 watts (or 0.6 Watts) depending on need for transmitting, while it can receive much less, just look at how many bars it has while in the oven. Assuming your phone is CDMA (800 MHz in the US) you will be using a wide spectrum as well (824.04 – 893.7 MHZ), and longer wavelength so shielding is less effective. If it is GSM (1900 MHz in the US, 1800 and 900 elsewhere), then you are also using TDMA and the spectrum is split temporally as well, also reducing shielding, as it transmits in 6.7 ms bursts at various small bandwidths. Remember lower frequencies travel farther, and shorter signals are harder to shield (as are those longer wavelenghts). Think AM vs. FM.
Now, why you are putting your phone in the oven is another questions. Try turning on the microwave (1000 Watts) briefly. Your phone will be dead due to EMP in less than 100 ms ! :-)
Here is a nice primer…
http://www.mat.ucsb.edu/~g.legrady/academic/courses/03w200a/projects/wireless/cell_technology.htm
In the movie Snowden, he puts the reporter's cell phones in his microwave in the hotel room. So they can't be used to reveal his location?
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