New PI technology proposals.

radiated

The energy is radiated as Electromagnetic Energy.

Of course the Electromagnetic Spectrum includes

Infrared Radiation (heat) and Radio Frequency Spectrum.

Some energy would make the targets heat up by virtue of

eddy currents, some would make the coil heat a bit, the rest

radiates into the surroundings and into space, where the aliens

could receive it on their super sensitive receivers.

[Aziz]

Hi Eric,

Hi Aziz,

So where does the energy go?

Eric.

this is really a very very interesting question. At the end, the magnetic field energy must be converted to heat in the matter of the surrounding coil and/or an electro magnetic field emission will occur.

Is this correct? I don't know, what exactly happens.
Aziz

[KingJL]

Not necessarily. As I stated before, provided the downward current (field) ramp takes place in 1/10 of the target time constant, ...

Ferric Toes
On that note... Is there a published set of general TC ranges for different target types? What little information that I have come across varies greatly depending on the source. I have a suspicion (and some data from experiments that suggest this) that the TC is dependent on more than target composition (e.g. size, shape). What I am looking for is something that gives a reasonable range of TC's for the types of targets typically sought by hobbyist metal detectors. I have a 14K gold band that appears to have a TC of ~6-9usec (I am working from memory at the moment). What TC ranges do we need to be concerned with?

[Ferric Toes]

Hi Aziz,

So where does the energy go?

Eric.

[Aziz]

Hi Eric,

Not necessarily. As I stated before, provided the downward current (field) ramp takes place in 1/10 of the target time constant, then the object is fully stimulated. Designing for a higher flyback voltage and faster switch off will not get you any more signal. Very high flyback voltages have their own problems. i.e very high peak currents in the RX input clipping diodes, and input resistors working outside their voltage ranges. I had an input resistor fail on an early Goldscan for this reason. It didn't fail completely, it just went horribly noisy.

Basic PI theory can be considered by just examining one step in a magnetic field. If a field has been set up for an infinitely long time and then reduced to zero in a infinitely short time, we can see what happens in a conductive object within that field. All the time the field is static, then nothing happens within the object. As soon as the field starts to change, then eddy currents will be generated which try to maintain the field within the object at its pre-switch off value. These eddy currents first flow on the objects surface, and then gradually diffuse inwards, until for times after one time constant, they become exponential. This diffusion is caused by the object's resistance that cause the eddy currents to lose energy (heat loss). Eventually, there is no internal emf and hence no current and the field and object become static again. In this theoretical consideration the initial field could be generated by means other than a coil of wire carrying a current. Something to ponder on during the upcoming holiday period - if a long standing magnetic field (not coil generated) is instantaneously switched off in free space with no conductive objects nearby, is there a flyback voltage?

Eric.

a higher target stimulation with higher flyback voltage or fast damping will not necessarily cause more RX signals. My recent simulation models showing really interesting results, which will be presented soon.
They might very likely be simple, but they contain very useful informations. Your practical experiences will help to understand the process. I appreciate that. Pity, that I haven't the means for some practical experiments at the moment.


"if a long standing magnetic field (not coil generated) is instantaneously switched off in free space with no conductive objects nearby, is there a flyback voltage?"

Of course not. Why?
Free moving electrons in the conductur will see a force (EMF) when there is magnetic field change. So electrons in the conductor will start moving and building an electrical potential (voltage induction).
Non conducting objects haven't free moving electrons. So no flyback voltage can be induced.

Regards,
Aziz

[Aziz]

Hi JC1,

Hi Aziz,

Nice simulation, which shows everything that is

been talked about.

Thanks. I have still many many interesting "rubbish" thoughts, that might surprise you all at the end. It will take several weeks to present all them. So you all will be well entertained. Step by step.

Now an interesting question to be proofed next:
Has the coil a different time constant during transmit on and off?
(My rubbish statement was: NO).

You mentioned this very interesting related question. Why the flyback damping is faster than charging the coil during transmit on?

But I want let the people to think for oneself this question. (I have the "rubbish" proof already.)

Aziz

[Ferric Toes]

"So clipping the flyback voltage will decrease the target stimulation."

Sorry for my bad english.
It should be:
"So clipping the flyback voltage will limit the target stimulation."

Not necessarily. As I stated before, provided the downward current (field) ramp takes place in 1/10 of the target time constant, then the object is fully stimulated. Designing for a higher flyback voltage and faster switch off will not get you any more signal. Very high flyback voltages have their own problems. i.e very high peak currents in the RX input clipping diodes, and input resistors working outside their voltage ranges. I had an input resistor fail on an early Goldscan for this reason. It didn't fail completely, it just went horribly noisy.

Basic PI theory can be considered by just examining one step in a magnetic field. If a field has been set up for an infinitely long time and then reduced to zero in a infinitely short time, we can see what happens in a conductive object within that field. All the time the field is static, then nothing happens within the object. As soon as the field starts to change, then eddy currents will be generated which try to maintain the field within the object at its pre-switch off value. These eddy currents first flow on the objects surface, and then gradually diffuse inwards, until for times after one time constant, they become exponential. This diffusion is caused by the object's resistance that cause the eddy currents to lose energy (heat loss). Eventually, there is no internal emf and hence no current and the field and object become static again. In this theoretical consideration the initial field could be generated by means other than a coil of wire carrying a current. Something to ponder on during the upcoming holiday period - if a long standing magnetic field (not coil generated) is instantaneously switched off in free space with no conductive objects nearby, is there a flyback voltage?

Eric.

Nice !!!

Hi Aziz,

Nice simulation, which shows everything that is

been talked about.

[Aziz]

Hi gwzd,

if you have something PI related, then let us know now. We are very interested on your contribution.

Aziz

[gwzd]

Hi gwzd,



Have you something about PI related so we all can profit from your excellent knowledge?

Yes

I know, you never do any mistakes. Don't you?

I do make mistakes, I just don't call them "engineering process", but plain stupidity and ignorance from my side.

Please, stop your way of discrediting people.

I'm not discrediting anyone, certainly not you, you manage pretty well yourself. I was answering to your question, remember?

This is not efficient for our purpose.

Aziz

On the contrary, it prevents other people following your "many mistakes" and thinking that not working efficiently is the "correct way".

As always, stay calm and please note that I don't call you names or anything like that, but do not expect me to agree with whatever rubbish comes out of your keyboard.
My best regards,

[Aziz]

"So clipping the flyback voltage will decrease the target stimulation."

Sorry for my bad english.
It should be:
"So clipping the flyback voltage will limit the target stimulation."

[Aziz]

Hi all,

Eric described exactly the flyback process of what is happening during the avalanche breakdown voltage of the MOSFET. Thanks Eric.

You can see the SPICE simulation results, which exactly confirms this. The second picture shows the target induction voltage (target eddy current has same behaviour). So clipping the flyback voltage will decrease the target stimulation. The target voltage induction is not instantly high. You can not see the rise of this in the picture below.

Aziz

[Aziz]

Hi gwzd,

No, it aint. Only if you want to get fired...
Normal engineering process as opposed to researching process involves a solid knowledge of the technology being used in order to apply it to the solution of an specific problem in a traditional or novel way.
"doing many mistakes" is a rather costly way of working, for your employer that can be devastating.

Do you know how much your employer would pay in social fees if you would actually work in Germany?
Do you think a real engineering office could afford that way of thinking?
Do you think your eventual customer would patiently wait until you are done with Spice and finally start producing things that actually work?

Get real, as a hobby yes, do as many mistakes as you wish, as a part of "engineering process", dream about it!

Regards,

Have you something about PI related so we all can profit from your excellent knowledge? I know, you never do any mistakes. Don't you?
Please, stop your way of discrediting people. This is not efficient for our purpose.

Aziz

[gwzd]

Different way of thinking and of course by doing many mistakes. This is a normal engineering process. Isn't it?


Aziz

No, it aint. Only if you want to get fired...
Normal engineering process as opposed to researching process involves a solid knowledge of the technology being used in order to apply it to the solution of an specific problem in a traditional or novel way.
"doing many mistakes" is a rather costly way of working, for your employer that can be devastating.

Do you know how much your employer would pay in social fees if you would actually work in Germany?
Do you think a real engineering office could afford that way of thinking?
Do you think your eventual customer would patiently wait until you are done with Spice and finally start producing things that actually work?

Get real, as a hobby yes, do as many mistakes as you wish, as a part of "engineering process", dream about it!

Regards,

[Carl-NC]

Thank you Carl,
I would rather believe the comments of one of the most respected and clever electronic engineers in the USA and those of a legend in the Pi world, Eric Foster rather than somebody totally unknown and with no credentials or evidence whatsoever to support his assertions!

Sorry, but I'm still learning! And that means being willing to say, "I could be wrong." I am leaving tonight for 3 weeks of travel, so my work on PI is suspended until I return. One area I will research more is the effect of turn-on time. But to do that, I want to use my USB-PIC board, so I need to get it running first.

- Carl