A
Anonymous
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This should liven up the posts on this forum amongst those who prefer to wield the soldering iron rather than the spade.
In all the electromagnetic metal detectors that I am aware of, the search coil has been driven by either a sine wave, a square wave or a pulse. This includes detectors where the transmit search coil forms part of a tuned circuit, as in an induction balance detector. There are many variations of these types, but is there as yet, an untried waveform than might have possibilities in a metal detector? I say untried, but as in many cases, technology is already in use in the field of geophysical prospecting that can be scaled down to detect small metallic objects rather than million ton orebodies.
A post on another forum suggested that hobby metal detectors are way behind the technology that is available to professionals in geophysics. I would tend to disagree with this bearing in mind the differences in scale between the two problems and the timescale allowed to analyse data. A geophysical PI (TEM in their terminology) may have a transmitter loop 2000ft square laid on the ground. The receiver coil is much smaller, often wound on a ferrite core and mounted on a tripod. The power supply may be a 1500W gasoline generator. The receiver coil is moved to different locations on a survey line and readings taken at several different sample windows along the decay curve. These readings are stored for future analysis when the survey is completed. The response time of such a system is very slow as multiple samples are averaged, or stacked, to eliminate noise and the repetition frequency of the transmitter is only a few tens of pulses per second. There is also some very sophisticated software that has been designed to process the data and extract the maximum amount of information from it in the days and weeks following the survey. Naturally, such equipment is very advanced and is in the tens of thousands of $ price bracket.
Scaling the equipment down and adjusting all the timing functions to the point where it will detect coin size metal objects is quite practical and has been done many times in custom built PI detectors for archaeological surveys. Such surveys often use many geophysical techniques such as IP, Resistivity, Magnetometry, GPR, Spontaneous Potential and Infra Red. Again you end up with vast amounts of data which need to be data logged and processed
In all the electromagnetic metal detectors that I am aware of, the search coil has been driven by either a sine wave, a square wave or a pulse. This includes detectors where the transmit search coil forms part of a tuned circuit, as in an induction balance detector. There are many variations of these types, but is there as yet, an untried waveform than might have possibilities in a metal detector? I say untried, but as in many cases, technology is already in use in the field of geophysical prospecting that can be scaled down to detect small metallic objects rather than million ton orebodies.
A post on another forum suggested that hobby metal detectors are way behind the technology that is available to professionals in geophysics. I would tend to disagree with this bearing in mind the differences in scale between the two problems and the timescale allowed to analyse data. A geophysical PI (TEM in their terminology) may have a transmitter loop 2000ft square laid on the ground. The receiver coil is much smaller, often wound on a ferrite core and mounted on a tripod. The power supply may be a 1500W gasoline generator. The receiver coil is moved to different locations on a survey line and readings taken at several different sample windows along the decay curve. These readings are stored for future analysis when the survey is completed. The response time of such a system is very slow as multiple samples are averaged, or stacked, to eliminate noise and the repetition frequency of the transmitter is only a few tens of pulses per second. There is also some very sophisticated software that has been designed to process the data and extract the maximum amount of information from it in the days and weeks following the survey. Naturally, such equipment is very advanced and is in the tens of thousands of $ price bracket.
Scaling the equipment down and adjusting all the timing functions to the point where it will detect coin size metal objects is quite practical and has been done many times in custom built PI detectors for archaeological surveys. Such surveys often use many geophysical techniques such as IP, Resistivity, Magnetometry, GPR, Spontaneous Potential and Infra Red. Again you end up with vast amounts of data which need to be data logged and processed