I have been reading that faraday cages need to be built with holes that are sufficiently smaller than the wavelength of these different emissions. We've noticed something strange, and need some help understanding what is going on.
The frequency is related to wavelength by the following equation:
f = c/γ
Where f = frequency in Hz, c is light velocity, and γ represents wavelength in meters.
One rule of thumb often used for Faraday cages to prevent transmission is that the holes need to be no larger than 1/10 of the wavelength of the signal.
So for a 3G cell phone that operates at a frequency of 2.1 GHz (2.1 * 109 Hz), the wavelength = (3 * 108 m/sec) / (2.1 * 109 Hz) = .14 meters. Thus, for a Faraday cage to prevent this noise from entering, the holes in the cage should be smaller than .014 meters (or 1.4 cm).
Also, 60Hz line noise will have a wavelength of (3 * 108 m/sec) / 60 Hz = 5.4 meters or ~17.5 feet. This would mean that 1 foot holes would block 60Hz EM waves, but that is not the case when I build a faraday cage.
When we surround our electronics with a metal screen mesh from Home Depot, as seen below:
This does a wonderful job of blocking 60 Hz noise, but does not effect the 3G cell phones signal when I place it inside the cage! That seems to be the opposite of what that equation is stating. What is my confusion?
I should note that I ground our electronics to the Faraday cage, but I'm not sure where to ground the cell phone to the cage. Is this what is making the difference? I am wondering why?
Thanks!
The frequency is related to wavelength by the following equation:
f = c/γ
Where f = frequency in Hz, c is light velocity, and γ represents wavelength in meters.
One rule of thumb often used for Faraday cages to prevent transmission is that the holes need to be no larger than 1/10 of the wavelength of the signal.
So for a 3G cell phone that operates at a frequency of 2.1 GHz (2.1 * 109 Hz), the wavelength = (3 * 108 m/sec) / (2.1 * 109 Hz) = .14 meters. Thus, for a Faraday cage to prevent this noise from entering, the holes in the cage should be smaller than .014 meters (or 1.4 cm).
Also, 60Hz line noise will have a wavelength of (3 * 108 m/sec) / 60 Hz = 5.4 meters or ~17.5 feet. This would mean that 1 foot holes would block 60Hz EM waves, but that is not the case when I build a faraday cage.
When we surround our electronics with a metal screen mesh from Home Depot, as seen below:
This does a wonderful job of blocking 60 Hz noise, but does not effect the 3G cell phones signal when I place it inside the cage! That seems to be the opposite of what that equation is stating. What is my confusion?
I should note that I ground our electronics to the Faraday cage, but I'm not sure where to ground the cell phone to the cage. Is this what is making the difference? I am wondering why?
Thanks!