Self Test

Here are two experiments you could try out for yourself, one with a permeant magnet and a floppy the other with a bulk cassette tape eraser. Not everyone will have a bulk cassette tape eraser.

• The easiest test is to use a readable formatted floppy with some files coped to it. Find a large strong enough permeant magnet, so as to make the floppy un-readable when doing a preliminary air test. Place a piece of cardboard the same thickness as your steel, or copper plate (or best conductor being tested) between the floppy, and the magnet. This will insure a constant distance. Move the magnet around at between 1-10 cycles/second. Check for readability, if you can still read it, go find a stronger magnet. Once you have a strong enough magnet, then, test each shielding maternal checking the readability of the floppy after each test. This test can be done by anyone wanting to test the effectiveness of their shielding.

• The bulk tape eraser test gives a shielding comparison of different materials at one test ELF of 60 cycles/sec. This indicates a trend that says Iron-steel is many times better than Aluminum at this frequency. A Fourier series analysis of any given "asymmetric pulse" to find the amplitude and frequency of all of the harmonic components that make up the pulse would give the fact that: The lowest frequency component would have the highest amplitude. If we shield for that low frequency, then the other higher frequency components with the much lower amplitudes will not be an issue, being easily shielded using the same material.

Offered by Mike.