"most switching power supplies really don't care if their input is AC or DC" They do care if they have Power Factor Correction.

Update to my own post:

Should have been: But it's easier to just give them a game console so they DO NOT ask for even more parent's attention :-(

I told the kid (about 10 yo at that time) of friends about the can-string-can phone and we made one. I didn't expect that he would play with it for more than a few minutes. But to my surprise I noticed on later visits that the string phone was used when playing with friends. I've even noticed that it got repaired or even rebuild at some time. However, I think that he would never have learned about it if I didn't told him. Many parents are not enough involved with their kids to tell them about (or point them to the right books, web sites, ...) about these easy to try experiments. Most kids would love to do these kind of experiments, but they need some guidance to get started. But it's easier to just give them a game console so they ask for even more parent's attention :-(

Or replace the water with potatoes and get French fries at the same time.

I once ran into a website with pictures of (adult) girls wearing headphones. Just (adult) girls wearing headphones, not even in sexual explicit poses. At least for me there was nothing erotic or pornographic about it... But on their forum there was a heavy discussion going on at that time because someone posted pictures of a younger girl wearing headphones. That was a big issue because (it seems that) some people get turned on by pictures of girls wearing headphones. So yeah, very subjective...

I got depressed too and I noticed that the more depressed I get the more time I spend on slashdot, watch youtubes and try to chat more. Untill I read the study I thought slasdot was making me depressed :-) Still not at 18 hours a day, I hope I can change the situation before I hit the 18 hours.

They say that it are 2 square grids seperated by at thin film, with the grids rotated over 45 degrees. That would make it a cage in a cage. Difracting the signals will only bend the path of the signal. So the signals just end up in another place and that also depends on the incoming path of the signal. To 'absorb' this signal they have to be able to bend al signals, regardless of ther original path/direction, to a known absorber. The 'diffraction grid' has to be so tight that there are no gaps bigger than the wavelength they want to filter or there will be leaks. But they still needs some gaps somehow that are big enough to allow the longerwanted wavelength signals to get through the grid.

Neither will this magic snake oil paper filter only wifi signals. The frequency (actually wavelength) of signals that can penetrate (or exit) a faraday cage are determined by the size of the holes in the cage. Holes will let wavelengts through that are shorter than the hole's size. Or to put it in another way: everthing up from the lowest frequency that can fit through the hole will pass the holes. Wifi happens to use a higher frequency (shorter wavelength) than GSM (and most mobile phone frequencies). If a GSM signal fits the hole, a wifi signal will have enough room left. Oh, and those holes don't know the difference between regular and emergency calls...