Capacitive Detector

[Anonymous]

This is no joke. Go to http://www.delphion.com/ and look up US patent number 5,617,031. The patent is thinly disguised as being a buried pipe locator. The assignee is The United States of America as represented by the Secretary of the Army, Washington, DC. To put it into North Carolina English (or pidgeon) "This Ain't No Pipe Locator" Sure, the embodiment shown is designed to find pipes. You can rest assured though that the rest of the story is something quite different. This is a mine detector. As described, the invention is capable of finding both metallic and non metallic targets. This could easily include a plastic land mine. A combination of this technology and a regular detector to find the metallic firing mechanism will I am sure be quite obvious to the group here. The question is, does the technology have any value to what we are doing? I will leave this up for discussion. Is there a use for a capacitive detector for our interests? My first thought was that the method would not go deep enough to a target. Applying a little thought, I considered the old BFO. The frequency of the tuned search-coil was altered due to the change in inductance of the coil due to a metal target. What one may ask is the difference between this and a change in capacitance? Maybe we can use a similar method to develop a new kind of detector? The patent describes the use of a tunable oscillator to drive the capacitive transducer. Different kinds of targets appear to peak at different frequencies. This is even more interesting!!! it is amusing that the pipe location embodiment is illustrated looking just like a goat cart. Why they were trying to hide the true function of the invention is a mystery to me, Dave. * * *

 

[Anonymous]

Hi Dave,
That must be one of the clearest and understandable patents I've ever read! Looks interesting and worth doing a few experiments. I still have to look through it in detail but, from past experience in related methods, the big problem comes in distinguishing rocks, tree roots voids etc from good targets. Combining it with a metal detector would be useful, particularly for mines. If you get a capacitive anomaly with a small metal object in the middle, start to tread carefully.
B.f.o.'s certainly respond to capacitance. That is why good ones had a well shielded coil to keep the capacitance the coil sees, constant and independant of its surroundings. Sweeping an unshielded b.f.o. would be very frustrating as not only ground anomalies but height variations would have an effect. I suspect that is why the sensor in the patent is mounted on a cart; to keep the thing at as constant a height as possible.
Eric.

 

[Anonymous]

Eric, One of the main points of interest to me was that the different targets peaked at different frequencies. This part is truly worth a few experiments. A roll of foil and a funtion generator is a small cost to try it! Dave. * * *