radiation shield project

[=BlackDog=]

I need help with a science fair project.

 

I will tell u briefly what i am trying to do. In a Science Fair, i need to prove

that sound, radio, and light waves can be affected by destructive interference.

I already have used my computer to lower the dB of a given sound wave by about

85%. I have taken one speaker from the computer and angled it about 10 degrees

toward the other, and let one speaker play the opposite continuous tone as the

other (at 350Hz). This works fine. Radio and light waves are much more difficult to do a demonstration for, so i hope that i can JUST prove the possibility of canceling them out using just math. I read that light waves are known to spike randomly quite a bit, so it will be difficult in a real life situation to use a computer to cancel them. I also wanted to suggest to people that this may be practical when used as a shield or dampening field for radiation.

 

My question is, can someone help me prove mathematically that destructive interference works with radio waves and light waves?

 

and does anyone have any suggestions to make the project more interesting to judges

 

thank you for your time everyone

[insane_alien]

get yourself a laser(a laser pointer will work, consult a teacher to make sure it's okay) and a diffraction grating. shine the laser intothe grating and it will make a cool pattern that shows both constructive interference and destructive interference by bright and dark patches.

 

maths and more info can be found on wikipedia.

[=BlackDog=]

anyone have actual math they can give me?

[waitforufo]

For radio waves you could create a cardioid antenna array. See:

 

http://personal.ee.surrey.ac.uk/Personal/D.Jefferies/antarray.html

 

Since reciprocity applies in radio propagation and reception, showing that there is a receiving null in an antenna proves also that there would be and cancelling transmission null. You could create an antenna of hand held size if you pick a high enough frequency. Then you need to find a signal source and a tuned receiver. Perhaps a cell tower and a cell phone (with coaxial input) could be used.

 

Perhaps you could also show standing waves on a short circuited transmission line. Ladder line is open and you could measure the electric field with a probe.

 

http://www.microwaves101.com/encyclopedia/vswr.cfm

[xptoast]

Perhaps make a receiver that isolates the frequencies you wish to cancel and then broadcasts back over them with a mimicked but more more intense signal thus overriding the signal. Just an idea. Most waves can be caught by a grate or mesh of sorts. This is especially true of emp waves as well as microwaves. Its called a Faraday cage. You can see them everyday. Just go look at a microwave door. The clear portion on the door that has the tiny holes is actually a special sized Faraday cage that catches the radiation before it escapes through the window portion of the door.

[=BlackDog=]

i demonstrated light waves canceling eachother when opposite, and sound waves with high efficiency, but apparently the judges didnt like the project because it was to "original" and "not useful enough for modern society"