GUM WRAPPER DECAY

[Anonymous]

This test was done at the request of BBSailor (see post of 24th Dec.).
This was a standard Wrigley's wrapper, spread out flat and laid on a 11in coil connected to an earlier Deepstar electronics. The decay was longer than I expected, but was fully down in the noise level by 25uS. The trace was done on a storage scope and shows one waveform before the wrapper was laid on the coil, and the other after. The full scan width is 20uS, although if the scope was set to 5uS/cm and the sensitivity increased, a small signal was observed out to 25uS. Detectors with a sample delay of 10uS or 15uS will give strong responses on flat gum wrapper. However, I would imagine this is more of a problem on the dry sand. Once in the wet, and subject to wave action, I can't imagine it lasts very long. I have not detected, as far as I recall, any gum wrappers in the wet sand or water.
When I screwed the wrapper into a ball after the above test, it was almost undetectable.
For comparison, the signal from a US nickel extends to 70uS.
Eric.

 

[Anonymous]

As stated above, a gum wrapper, when laid flat, has a total decay time of 25uS. Fold it in half, and it is still 25uS. Fold in half again and continue to six times, measuring at each fold. The decay time is always 25uS, give or take a microsecond or two. If you can achieve a seventh fold, well done, as this is the maximum number of times a flat sheet can be folded.
Cut a gum wrapper in half, and the decay time reduces by 5uS. Cut in half again, and another 5uS is lopped off. Couldn't go beyond the next cut, as the recovery time on the test setup was 10uS.
Screw a gum wrapper up into a ball and it is hardly detectable at 10uS.
Eric.

 

[Anonymous]

Hi Eric,
Your foil has a longer decay time than what I tested over here. The decay curve extended out to about 12 to 13 usec's was about all I could see. I don't have a storage scope so I would have to post two pics to display a similar before and after.
Hopefully, I will have a used storage scope shortly which will help.
Reg

 

[Anonymous]

Ah! The old mass versus area issue!
The reason why I asked the question in the first place was to see if something as common and universal as a gum wrapper could be a useful "low tech" way to check the response speed of a PI machine. Once someone calibrates some basic sizes and responses, like Eric did, anyone can quickly see what their machine is doing using the same size gum wrapper samples.
Eric, thanks for answering my question and providing some points of reference to test against. I guess the gum foil wrapper materiel is still too thick to be a useful coil shield?
bbsailor