VLF technology in Metal Detector

[pal114525]

Hi,

In designing a metal detector with VLF technology,

1. why do we choose VLF technology as the best among other frequency e.g. HF, UHF etc.
2. What are the advantages of the VLF technology than the other frequency?

Thanks.

 

[D.A.(Tony)Stewart]

Lower the frequency , the less effect from dielectrics like water.

 

[pal114525]

Hi,
In what case water can be the dielectric?

Thanks.

 

[betwixt]

Dielectric meant in the sense of "something obstructing the path" and obsuring what's underneath.

VLF signals are absorbed less by the ground, especially if it is moist. As the water content increases, so does the absorbtion of the signal and hence the range it can reach for a given power. For some applications, for example ground penetrating radar, higher frequencies are used but the power levels are relatively high and the shorter wavelengths make it easier to use directional antennas. They work on a different principle though, one that is complicated and not really suited to metal detection.

Brian.

 

[pal114525]

Hi,

Can you please tell me the block diagram of a Single Zone Door Frame Metal Detector?

Thanks.

 

[pal114525]

Hi,

How to design the coil housing of walk-through metal detector using VLF technology?

Thanks.

 

[pal114525]

Hi,

I have seen the attached circuit in a metal detector.
Can you please explain me the functionality of transistor Q10 in this circuit?

Thanks.

- - - Updated - - -

Here is the circuit.

 

[Audioguru]

Hi,

I have seen the attached circuit in a metal detector.
Can you please explain me the functionality of transistor Q10 in this circuit?

Q11 and Q12 are an oscillator Q11 has base bias current from the current sink made with Q10 and its battery b1.

Maybe the current sink is used to provide the same current even when the main battery voltage is running down.

 

[ALERTLINKS]

https://paleofuture.gizmodo.com/walk-through-metal-detectors-were-invented-to-catch-thi-520336775

 

[pal114525]

Is Q10 acting as a pull down network and battery b1 is making Q10 ON?

 

[Audioguru]

Is Q10 acting as a pull down network and battery b1 is making Q10 ON?

The Q10 circuit is called a "constant current sink" (look at it in Google). B1 is shown as a battery when it is actually a regulated voltage reference. Then the voltage across the base-emitter junction plus the emitter resistor is constant which causes the collector to ground (pull down as you called it) current biasing Q11 to be constant even when the main supply voltage changes.