Physics Textbook that would apply to metal detectors

[Wirechief]

Hi Mr. Foster and everyone else here on the forum. I am a new fellow to this forum. My question is for Mr. Foster. I know that the field of physics is quite broad but do you know of or can you recommend any particular physics textbook or any publication that would be related to the art of building or designing metal detectors? I am greatly interested in the theory and electronics of metal detectors. Thank you Mr. Foster and God Bless you and the forum. Wirechief.

 

[Eric Foster]

Hi Wirechief,

There are few books available that go deeply into the physics of metal detection. There are several books that deal with the general principles e.g. The Electronic Metal Detector Handbook by E. S. LeGaye. Published in 1969, it's rather dated now, but still a good read. Garrett Electronics has brought out some useful books over the years - Modern Metal Detectors, being one.

If it is greater theoretical detail you require, the best source is the geophysical literature, or do a search on mine detectors and humanitarian demining. Searching Time Domain Electromagnetics, or TDEM, will bring up a lot of information related to pulse induction detectors. After all, most metal detectors are just scaled down and simplified versions of equipment used for geophysical prospecting. The Canadian company, Geonics, have a series of technical leaflets relating to their TDEM/PI equipment.

Hope this helps.

Eric.

 

[bbsailor]

Another alternative to a physics book related to PI metal detectors is to study the generic circuits that most PI detectors use. Here are a few to start you off in the right direction. Get the data sheets for these devices. Read the PI-1 Article on the following web page:http://www.thunting.com/cgi-bin/geotech/pages/common/index.pl?page=metdet/projects/pi1&file=index.dat. This will give you a very good explaination of how a PI machine works and how to build one for yourself. A circuit board is even available from Carl, who runs that web site.

-Master clock timer (555)

-Clock dividers (74HC221 or equivalent)

-RX preamplifier (NE 5534 or NE5534A)

-TX MOSFET Coil Driver (IRF740 or low output capacitance equivalent)

-Integrator circuits (TL072 or equivalnet) Go the the following web site for some good information about lock-in amplifiers. http://www.cpm.uncc.edu/lock_in_1.htm The integrator, along with the master clock and clock dividers actually functions like a very simple lock-in amplifier.


Lock-in amplifiers need to be synchronized with the PI master clock pulse. Then the signal is integrated over what ever time period is appropriate for target types and hunting sweep speed.
Lock-in amplifiers can extract very minute signals even in the presence of noise. The only trade off is how much time you must wait for the integrator to accumulate enough samples to overcome the noise.

I have purchased a couple of lock-in amplifiers off e-bay for less than $100 including shipping. If you build the Hammerhead circuit, you can substitute the Lock-in amplifier, using the differential inputs, in place of the integrator circuit and see how much more sensitivity you can squeeze out the Hammerhead design by trading off speed (meaning integration time) for gain vs. noise. This should be a good bench-top learning experience as you begin to appreciate the design tradeoffs that are built into any good, sensitive PI machine.

I hope this stimulates your interest in understanding PI machines.

bbsailor

 

[Wirechief]

Ok thank you bb and I appreciate your suggestions. Yes I have printed out the paper work on the Hammerhead project and I am going to order the boards from Carl. I am super fascinated with the PI instruments and am trying to learn all I can about them. Don't get me wrong because I'm just a regular guy not a physicist. I work with Instrumentation used in the radiation field. I'm also interested in the physics of mineralization and geology. Ok bb you take care and God Bless. Wirechief.

 

[Wirechief]

Hi Eric and Nice to meet you. I really like the forum and many thanks for the info on the various books and publications. As I told bb I am extremely interested in PI metal detectors but would also like to find any physics books that deal with the effects of electromagnetism on mineralized grounds. I'm not a whiz by any means but want to learn as much as possible. Ok Eric I hope to talk to you again soon. Take care, God Bless and 73's. Wirechief. John's Detectors.