Nuclear Magnetic Resonance (NMR)

[Smudge]

Hi Conrad,
Thank you for your interest in this.

The papers you quoted are very interesting but they show that it needs sophisticated electronic circuits to do the measurements. The fine tuning of the frequencies is tricky and the circuit boards need a certain layout to avoid cross-disturbances.

Don't get carried away by those magnetometer papers.  As magnetometers they are used to measure very small changes in the earth's field and we are not doing that.  We don't need the sophistication used there.

I have a function generator, but it then needs a pretty good circuit to reach the necessary power (Voltage and Amperage) to drive the pancake coils.

If you need a power amplifier then maybe someone on this forum could help with this.

Also the measuring of the output is not trivial because of the calibration. Does a scope suffice?

Since we are dealing with sine waves a scope should suffice.

How big is the difference in the output coil with and without water in the circular tube? The difference could be only in the dielectric properties and not in the magnetic resonance?

With no water present there should be no output, as input and output coils are at 90 degrees to each other.  It is the gyratory property of the protons in the water that couple the input to the output.

Smudge

[conradelektro]

@Smudge: Thank you for your answers, it clarified a lot.

About the power amplifier:

As I recall, one wants several hundred Volts in the pancake coils, so, an audio speaker amplifier will not do it?

The frequency required for the pancake coils would be 4.25 MHz, which an audio speaker amplifier also can not do.

A power amplifier to several hundred Volts at 4.25 MHz is therefore not that easy. Should the pancake coils get short pulses or a sine wave?

My function generator can do up to 20 MHz sine waves and up to 5 MHz square waves (pulses). I do not want to over complicate the experiment, just wanting to understand the requirements for a possible build in relation to my meager skills.

RF power amplifiers are quite expensive (5000.-- and more):

https://www.bellnw.com/manufacturer/Electronics-and-Innovation/210L.htm
https://www.bellnw.com/manufacturer/Electronics-and-Innovation/1020L.htm

Greetings, Conrad

[conradelektro]

Would this RF amplifier be good for the experiment?

https://www.ebay.com/itm/100KHz-60MHz-RF-Power-Amplifier-5W-Liner-Amplifier-RF-Broadband-HF-Amp/383126732260

100KHz-60MHz RF Power Amplifier 5W Liner Amplifier RF Broadband HF Amp  (about $ 90.--)

Description: The RF amplifier is a linear power amplifier with low distortion and wide frequency range, which can be used for various forms of signal amplification. Worked as a final stage power amplifier, it can be applied to TPMS transmission, wireless charging and other communications or remote control, enhancing the transmission power and prolonging the transmission distance. And it also can act as a driver amplifier to promote a final stage high power amplifier. This medium-, long- and high- wave frequency amplifier is suitable for universities, research institutes and radio lovers.

Parameters:
- Frequency: 100 KHz-60 MHz
- Single Power Supply: 12-15V, 0.9A
- Gain: the default is 37dB. (If you need other gains, please contact with our customer service staff.)
- Input Power: 1mW (0dBm); Output Power: 4W
- Working Voltage: 12V (Output Power reaches 6W when the operating voltage comes to 15V)
- Resistance: 50Ω
- THD: - 18dBc Typical Value (Max. output power)
- Input & Output Connector: SMA Female
- Size: 103 x 90 x 50mm (Excludes the size of the input & output connector and the power connector)

Package Included:
- 1 x Radio Frequency Amplifier

This shows that a good RF power amplifier is not easily built at home.


There are 2.5 Watt Chinese RF amplifiers (1 - 1000 MHZ) for about $ 50.-- available.

Greetings, Conrad

[Smudge]

@Smudge: Thank you for your answers, it clarified a lot.

About the power amplifier:

As I recall, one wants several hundred Volts in the pancake coils, so, an audio speaker amplifier will not do it?

The frequency required for the pancake coils would be 4.25 MHz, which an audio speaker amplifier also can not do.

A power amplifier to several hundred Volts at 4.25 MHz is therefore not that easy.

It is quite standard practice to drive from a low voltage low impedance source into a series resonant LC circuit where the inductance obtains a much higher voltage.  If your resonant circuit has a Q of 100 then the several hundred volts needed comes from a source of just several volts.  Audio speaker amplifiers have output impedance of just a few ohms but of course may only cover the audio spectrum.  Others may have an output impedance of 50 ohms.  This value must be taken into account when calculating the Q.

Should the pancake coils get short pulses or a sine wave?

Sine waves, the CW system applies sine waves.  The pulse NMR system is more complex and not recommended at this stage.

My function generator can do up to 20 MHz sine waves and up to 5 MHz square waves (pulses). I do not want to over complicate the experiment, just wanting to understand the requirements for a possible build in relation to my meager skills.

That should be quite adequate.

Smudge

[Smudge]

Would this RF amplifier be good for the experiment?

https://www.ebay.com/itm/100KHz-60MHz-RF-Power-Amplifier-5W-Liner-Amplifier-RF-Broadband-HF-Amp/383126732260

100KHz-60MHz RF Power Amplifier 5W Liner Amplifier RF Broadband HF Amp  (about $ 90.--)

I would say that would do nicely.  The Chinese ones you mentioned could also be used.

Regards
Smudge