Quote from: Grumage on November 14, 2013, 03:58:51 PM
As requested.
https://www.youtube.com/watch?v=2TTM414t_zI
Your views, as always, gratefully received. 

Well, your transmitting pulse on the scope has a short rise time in this video and that's good.
I did not see that low value sink resistor across the Tx piezo.  Did you have it connected?

Anyway, your receiving piezo is crap. However, if you don't have what you like then you like what you have.
...anyway, even such inferior piezo is not useless.
We can still use it to determine the propagation delay and the speed of sound in the ferrite, by doing the frequency sweep that you had done with the long rod, but this time with a 50% duty cycle square pulses (or sinewave - better), and noting at what frequency each transmitting pulse corresponds to only one received pulse as shown on the scopeshot below from 1:54. 
Once you have the 1:1 Tx/Rx pulse frequency ratio, fine tune the Tx frequency to obtain maximum Rx amplitude and write the frequency down.

For the double C core, remember to use both halves for this measurement.

This measurement will reveal the exact the fundamental standing wave frequency and that together with the length of the ferrite will allow us to calculate the exact acoustic propagation delay and the speed of sound in this ferrite, which is useful in characterizing its chemical composition.

After that, we can go back to playing with magnetic stimulation again.

Quote from: verpies on November 14, 2013, 09:14:09 PM
Well, your transmitting pulse on the scope has a short rise time in this video and that's good.
I did not see that low value sink resistor across the Tx piezo.  Did you have it connected?

Anyway, your receiving piezo is crap. However, if you don't have what you like then you like what you have.
...anyway, even such inferior piezo is not useless.
We can still use it to determine the propagation delay and the speed of sound in the ferrite, by doing the frequency sweep that you had done with the long rod, but this time with a 50% duty cycle square pulses (or sinewave - better), and noting at what frequency each transmitting pulse corresponds to only one received pulse as shown on the scopeshot below from 1:54. 
Once you have the 1:1 Tx/Rx pulse frequency ratio, fine tune the Tx frequency to obtain maximum Rx amplitude and write the frequency down.

For the double C core, remember to use both halves for this measurement.

This measurement will reveal the exact the fundamental standing wave frequency and that together with the length of the ferrite will allow us to calculate the exact acoustic propagation delay and the speed of sound in this ferrite, which is useful in characterizing its chemical composition.

After that, we can go back to playing with magnetic stimulation again.

Dear Verpies.

"I did not see that low value sink resistor across the Tx piezo.  Did you have it connected?"

Yes 50 ohms as suggested.

"Anyway, your receiving piezo is crap."

Oh dear!!      "After that, we can go back to playing with magnetic stimulation again."  I am looking forward to that!! 

I will have a look at your remaining suggestions over the weekend!!

Cheers Grum.

Hello dear Verpies, what about my schematics-test?

Cheers.

http://en.wikipedia.org/wiki/Magnon
The concept of a magnon was introduced in 1930 by Felix Bloch in order to explain the reduction of the spontaneous magnetization in a ferromagnet.






http://en.wikipedia.org/wiki/Magnonics
Magnonics is an emerging field of modern magnetism, which can be considered a sub-field of modern solid state physics.(1)
Magnonics combines waves and magnetism, its main aim is to investigate the behaviour of spin waves in nano-structure elements. In essence, spin waves are a propagating re-ordering of the magnetisation in a material and arise from the precession of magnetic moments. Magnetic moments arise from the orbital and spin moments of the electron, most often it is this spin moment that contributes to the net magnetic moment.


Spin waves themselves have group velocities on the order of a few km per second. The damping of spin waves in a magnetic material also causes the amplitude of the spin wave to decay with distance, meaning the distance freely propagating spin waves can travel is usually only several 10's of µm.


http://en.wikipedia.org/wiki/Magnetism
Magnetism, at its root, arises from two sources:

• Electric current (see electron magnetic dipole moment).
• Nuclear magnetic moments of atomic nuclei. These moments are typically thousands of times smaller than the electrons' magnetic moments, so they are negligible in the context of the magnetization of materials. Nuclear magnetic moments are very important in other contexts, particularly in nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI).

so thousands of amps more to get a field dense enough to reach them?  (thousands of volts, and therefore lots of amps in a short time)


magnetic fields do not rely on voltage; except where voltage translates to more current.  It's Amp-Meters...


http://en.wikipedia.org/wiki/Tesla_(unit)
The tesla (symbol T) is the SI derived unit of magnetic field strength or magnetic flux density  *Well Which IS it?*
V*s/m^2   (Volt, second, meter)

http://en.wikipedia.org/wiki/Henry_(unit)
n physics, and electronics, the henry (symbol H) is the SI derived unit of inductance. 
V*s/A   (volt, second, amp)

.... (Hmm lots of things about magnets, units relevant to magnetic fields PDF attached)


------------
Sorry where was I going with that? 
Magnonic fields are very small, although fairly slow, amounting to a few mm/uSec, and even at that, are limited to micrometer propagations.

should probably use a very long inverval pulse... you crossed the point that it was 2:1 result to signal  and then there was 4...  should just ping it to see the seperation...

that's closer then acoustic resonance