PI metal detector for really small nuggets

[Detectorist#1]

Ferrite screen is widely used in wireless charging systems. The flat ferrite plate is situated on the one side of the flat coil and directed all energy in one direction.

[lucifer]

Yes and that's why the device being charged is put directly on top of the ferrite pad. The energy transfer distance is very small but charging efficiency is higher as the magnetic field is not spread in all directions around.

[Detectorist#1]

The device being charged is put directly on the top of TX coil - not on the ferrite pad! The ferrite pad is situated on the opposite side! This is the function of the ferrite pad - to direct the energy only on one direction.

[lucifer]

Yes, I am well aware how it works. Still the device being charged is very close to the TX coil and this is the point. The pad below limits the range of the TX magnetic field, and not just on the back side of the TX coil.

How would you explain that only half of the magnetic field is directed in the pad while the other half is unaffected? What law of physics is that?!

[Detectorist#1]

Detailed explanation that only half of the magnetic field is directed in the pad is done in attached paper.

[lucifer]

Detailed explanation that only half of the magnetic field is directed in the pad is done in attached paper.

Where did you read that in the article? If you read it carefully you will notice that the primary coil (TX) is without shield. The shield or magnetic material is placed under the RX coil. The reason is to capture as much of the TX magnetic field as possible and increase the coupling between the coils. This is confirmed by tables 2 and 3 (test case #5) where the RX inductance and mutual inductance is increased by the magnetic pad which acts as a magnetic core for the RX coil.

There's no point to argue. Just make a real world experiment: make a coil, get some ferrite sheets, drive the coil and measure the magnetic field at a fixed distance with and without ferrite.

Do you think coil and MD manufacturers won't use this idea if it works as you believe?

[Detectorist#1]

For your information, attached is the datasheet of some TX coils from TDK.

[Detectorist#1]

In my practice, I have been designing wireless charging systems for 3 years.

[Detectorist#1]

This idea is applicable only for short distances - like pinpointers. Remember the start of this conversation - you insisted that the ferrite screen is not capable to direct energy on only one side of the TX coil.

[Detectorist#1]

See your post #165

[pito]

for 3 years.

maybe you know how to turn on Tx without Rx module ?

[Detectorist#1]

Hi pito,
What you mean with "turn on" ? If you want to send max energy without Rx module, you have in mind that uP controls Tx power by changing the Tx frequency and PVM of the Tx signal automatically AFTER hand shaking with Rx module. This is done by software in control uP. If you will to use Tx coil only for sending of energy, you have to made your own electronics with generator of 100-125KHz with 50% PVM and power bridge with 4 pcs power transistors ( two N-ch and two P-ch) and suitable drivers. In this case, you will use only Tx coil and serial connected capacitors (they formed LC tank for 100-125KHz) from ready wireless module. Finally, set the Tx frequency at resonance frequency of the LC tank. Also you have to use some desoldered parts from ready module.

[pito]

What you mean with "turn on" ? = When you apply power to Tx module it is trying to communicate with Rx module sending short pulses 100kHz , when communication is established it is sending continuously 100kHz.

Can this be done without Rx module ?

[lucifer]

This idea is applicable only for short distances - like pinpointers. Remember the start of this conversation - you insisted that the ferrite screen is not capable to direct energy on only one side of the TX coil.

Exactly what I was telling you!
Why the short distance if ferrite doesn't affect the field on the other side?
The ferrite directs the magnetic field through itself, it creates the least 'resistance' for the magnetic field.
How does it select only half of the field? What law physics explains this? You didn't answer some basic questions. Instead you throw PDFs you haven't even read. This is my last post on the topic, it doesn't bring any benefits to metal detecting.

[Detectorist#1]

No. In handshaking they exchange more data - the type of Rx, max power for Rx .... It is not way to simple "enable on" sending of power from Tx module.