New detecting method?

[g-sani]

http://iospress.metapress.com/content/q767074h6n070577/

I found this page accidently and I thought lets have a look because it is something coming from a University and I tried to read the concept but I couldn't.
Do you have to pay for it? This is what I understood.
May be I am wrong.

[Seden]

New Detecting method

By typing in the title on Google, I found enough of the article here via Google Books that explains the tests with a schematic and graphs of the results. Wow, very interesting and nice to have a new idea for our hobby.

SWR take this very seriously.

Randy

[epitopios]

to g-sani
the article says:
A new type of magnetic field detection system, which can operate at a frequency below 1 kHz, is proposed and developed. The system consists of a 40-turn-coil to generate the magnetic field and a magneto resistive sensor to detect both the amplitude and the phase signal of the magnetic field induced by eddy-current and magnetization of the samples. The magnetic field detection of ferro- and non-magnetic samples using the system is demonstrated and discussed.

accidentaly , last days I made a receiver 100Hz-11Khz
if you find a operator uder 1Khz , maybe I say maybe ....or if someone can give us a design????
να τα παντρέψουμε , τι λές Γιώργο ?
friendly , epitopios
σε Π.Μ.

[J_Player]

to g-sani
the article says:
A new type of magnetic field detection system, which can operate at a frequency below 1 kHz, is proposed and developed. The system consists of a 40-turn-coil to generate the magnetic field and a magneto resistive sensor to detect both the amplitude and the phase signal of the magnetic field induced by eddy-current and magnetization of the samples. The magnetic field detection of ferro- and non-magnetic samples using the system is demonstrated and discussed.

accidentaly , last days I made a receiver 100Hz-11Khz
if you find a operator uder 1Khz , maybe I say maybe ....or if someone can give us a design????
να τα παντρέψουμε , τι λές Γιώργο ?
friendly , epitopios
σε Π.Μ.

Hi epitopios.

There is no circuit shematic showing components or values.
The designers from the Okayama University gave this vital information that explains the technique to discriminate metals:

[g-sani]

to g-sani
the article says:
A new type of magnetic field detection system, which can operate at a frequency below 1 kHz, is proposed and developed. The system consists of a 40-turn-coil to generate the magnetic field and a magneto resistive sensor to detect both the amplitude and the phase signal of the magnetic field induced by eddy-current and magnetization of the samples. The magnetic field detection of ferro- and non-magnetic samples using the system is demonstrated and discussed.

accidentaly , last days I made a receiver 100Hz-11Khz
if you find a operator uder 1Khz , maybe I say maybe ....or if someone can give us a design????
να τα παντρέψουμε , τι λές Γιώργο ?
friendly , epitopios
σε Π.Μ.

Well epitopios something like gold gun comes up to my mind.
I don't know, people involved in electronics can tell us more.
In Greece they say that 20Khz is allright for a receiver to be used for treasure hunting since there is transmition over here in this frequency.
The thing is you have to know what the meter is reading plus learning to read the audio signal is important as well.
VLF transmitters are not an easy subject when to be used for treasure hunting.
Many years back I used a AL718 and I was suprised to see that it was
responding in a known target(50kilos) of copper wire from 50mts away.
Then it was many VLF stations in use for Navy but now there are not.
I have it always in my mind as a problem to be solved in order to use my AL707 properly but I always hold back until I can see something serious as a solution.Okm sells 10Watts VLF Txs for big money.
I believe that 50W is a must for long range detection when using a receiver.
Any possible help in that is welcome.

[WM6]

I believe that 50W is a must for long range detection when using a receiver.


.

50W? Do you intend to sense gold from home on other hemisphere?

0.3W can be here far enough to reach way deeper than signals from former navy stations.

Secret is not in Tx electronic and its Watts but in proper build Tx antenna for ULF/VLF band.

[Fred]

Secret is not in Tx electronic and its Watts but in proper build Tx antenna for ULF/VLF band.

Maybe this is why you need more power with inefficient antennas (ferrite), or gigantic military stations far away

[Seden]

New detecting method?

WM6 is right. If you used a large ferrtie bar antenna and mounted it on a tripod with a 1 watt transmitter you would have all you need to use your AL707. So easy at 20 khz to make a simple OP-AMP signal generator and feed it into a audio power amp IC. Couldn't cost more than $25USD.

Randy

[J_Player]

WM6 is right. If you used a large ferrtie bar antenna and mounted it on a tripod with a 1 watt transmitter you would have all you need to use your AL707. So easy at 20 khz to make a simple OP-AMP signal generator and feed it into a audio power amp IC. Couldn't cost more than $25USD.

Randy

Hi Randy,
What kind of ferrite, and what size do you recommend?
what size wire, and how many turns?

I am sure the oscillator can be adjusted to whatever inductance and response the coil assembly would produce.

Best wishes,
J_P

[mikebg]

TX of Geonics

Low power transmitter in catalog of Geonics Ltd.
The TX27 is a portable VLF transmitter supplying a VLF field for surveying with either the EM16
or the EM16/16R if remote broadcasts are weak, intermittent or poorly coupled with the target.
For EM16 surveys, the TX27 antenna consists of a long (typically 1 km) grounded wire.
PRIMARY FIELD SOURCE: Grounded wire or 500 x 500 m loop, current adjustable, 0 to 2 A
OPERATING FREQUENCY: 18.6 kHz
POWER SUPPLY: 120/220 V, 350 W motor generator
DIMENSIONS: Transmitter and loop; Shipping: 89 x 29 x 39 cm
Generator; Shipping: 50 x 27 x 36 cm
WEIGHTS: Transmitter and loop; Shipping: 32.5 kg
Generator; Shipping: 17 kg

[epitopios]

WM6 is right. If you used a large ferrtie bar antenna and mounted it on a tripod with a 1 watt transmitter you would have all you need to use your AL707. So easy at 20 khz to make a simple OP-AMP signal generator and feed it into a audio power amp IC. Couldn't cost more than $25USD.

Randy

οκ , but we will have a signal distortion or not ??

[J_Player]

Low power transmitter in catalog of Geonics Ltd.
The TX27 is a portable VLF transmitter supplying a VLF field for surveying with either the EM16
or the EM16/16R if remote broadcasts are weak, intermittent or poorly coupled with the target.
For EM16 surveys, the TX27 antenna consists of a long (typically 1 km) grounded wire.
PRIMARY FIELD SOURCE: Grounded wire or 500 x 500 m loop, current adjustable, 0 to 2 A
OPERATING FREQUENCY: 18.6 kHz
POWER SUPPLY: 120/220 V, 350 W motor generator
DIMENSIONS: Transmitter and loop; Shipping: 89 x 29 x 39 cm
Generator; Shipping: 50 x 27 x 36 cm
WEIGHTS: Transmitter and loop; Shipping: 32.5 kg
Generator; Shipping: 17 kg

Hi mikebg,
Geonics Ltd. has some very nice geophysical testing instruments in their catalog along with their logging systems. These could be very useful for mapping both shallow data and data from much deeper in the ground. I like the products they show. They have a particularly interesting arrangement of their PI metal detectors that use a focusing coil and digital data loggers that log multiple sample readings taken at various delays along the decay curve. These look like good tools to use for geological surveys.

I think epitopios is looking for a hand-held transmitter that tells him the direction where a metal object is buried at some distance, rather than a large loop placed on the ground. He is probably interested only in locating shallow metallic items (less than 5 m deep) without performing a survey, by simply holding a detector that will indicate which direction the metal is located.

Best wishes,
J_P

[g-sani]

50W? Do you intend to sense gold from home on other hemisphere?

0.3W can be here far enough to reach way deeper than signals from former navy stations.

Secret is not in Tx electronic and its Watts but in proper build Tx antenna for ULF/VLF band.

0.3W?
Why nobody did it then?
What I know is high power and very long aerials because of the longer wavelength.
If low power could be used then they would do it.Well as far as I know.
The thing is which one would be best for treasure hunting whith a receiver to go on target?
1. Sending the frequency into the ground using a probe?
2. Air transmision using a special aerial? What type of?

[g-sani]

Hi J_P
Don't you think that 5m depth is enough?
I think it is.
The best for me is a handheld device for a radius of 200 meters.
I know I am asking too much.

[WM6]

οκ , but we will have a signal distortion or not ??

Probably yes, but nothing bad if you use as TX very simple and cheap so called self-modulated transmitter. Find one schematic on web and as previous say you do not need more than 0.3W of power output signal to cover your actually search field and much much more. Simple try and you will see.

Antenna have to be resonate on selected VLF/ULF frequency and adjusted by impedance to transmitter output or on feeding cable (if you use cable to feed antenna it have to be adjusted by impedance on both side - at minimum reflected standing wave).

g-sani mentioned here good enough schematic for receiver, so called "gold gun" and Qiaozhi posted somewhere on forum. Basically it only have to be adapted to our TX frequency or vice versa and maybe need some mods. And again antenna is crucial part here too.

Main thing here, if electronic Tx and Rx stages was correctly build, come antenna. Antenna implementation can be different, regarding one needs and tendency, wound on ferrite rod too - even not so effective. Best solution for sure are wire antenna as pointed mikebg, but we need such gigantic antenna only for communication with other earth hemisphere and not for our limited search field. To cover our limited search field even ferrite antenna can be fully sufficient.

Practically two main type of antennas are applicable. Vertical stacked and circular radiated 1/4 wavelength antenna and directed frame (quad, triangle or circular) antenna. Vertical antenna can be put in the middle of our search field while directive antenna is usually placed on the edge of search field (higher-better, but especially vertical antenna have to be grounded).

Building of directive antenna on quad (circle or triangle) shape (1.5x1.5m) is well known from coil winding. We use coil calculator to determine Nr. of turns and inductance for given frequency and wire diameter. After about 100 windings we tighten coil, remove a bit of isolation from wire, measure inductance and recalculate coil data again. At the end antenna must resonate at Tx frequency. Then we need only to adjust antenna input to Tx output. Check this by put antenna at the virtually same position (nonmetallic carrier, radiating orientation and height) as it will be placed latter in search field.

Vertical stacked antenna can be build in such way: We use about 1.5m length rigid plastic tube with outer diameter of about 10cm and about 1.5m Alu tube OD 1cm. Then we use coil calculator and calculate coil for 4th upper harmonic of our Tx frequency (with coil inner diameter of 10 cm an length of 15cm). Mean if our Tx is working on 10kHz we calculate coil for 40kHz. Calculated Nr. of turns we divide per 15 which give our data of turns for each of 15 section windings. Then we wind 15 section of turns on plastic tube of about 9cm apart each other. One end of windings we connect to Alu tube which is stacked as extension of plastic tube other end to hot wire of Tx output. First (mean lower) of 15 winding sections have to be wounded with about 15 inter-windings connections for latter antenna tuning. This antenna is needed to be re-tuned on every search field cause of different grounding soil characteristic. Although once fitted on location comfortable for hunting, this antenna not suit best for less experienced.