# Electrical resistance of a nut

Discussion in 'General Electronics Chat' started by speekergeek, Mar 6, 2013.

1. ### speekergeek Thread Starter New Member

Mar 6, 2013
2
0
Hi, everyone.

First post here, sorry if it is in the wrong section.

I am doing some research for work, my task is to find the electrical resistance of an Almond.

I tried a megger and got no joy.

I figured because of the high oil content it is a good insulator.

We heat these nuts in an RF field, 27.12 Mhz to be exact, to roast or dry them.

So my question if it is answerable, is how do I gauge the resistance of the almond in an RF field?

The circuit is a free oscillator vacuum tube type, 50Kw with several RF transformer type points so it is very difficult to gauge the potential on the electrodes.

I am at a loss and would be thankful for any help in the matter.

Any free oscillating RF experts out there?

Preferably with either wood glue drying, or textile drying experience.

Although the principles should be the same.

Thanks!

Mike

EDIT:
The almonds, wood, textiles, etc.. in my understanding make the circuit "work" by providing a high ESR capacitor as the load. The Series resistance being the nuts. there has to be a way.....

Last edited: Mar 6, 2013
2. ### ErnieM AAC Fanatic!

Apr 24, 2011
7,957
1,827
During the 80's several million dollars went down the drain researching various nut harvesting methods. No matter what was tried it was impossible to accurately detect the targets. Because... sometimes you feel like a nut, sometimes you don't.

3. ### MrChips Moderator

Oct 2, 2009
17,560
5,450
See how many kilovolts you can apply between his arms before he punches you in the face.

4. ### tubeguy Well-Known Member

Nov 3, 2012
1,157
198
Are these almonds in the shell or nut ??

5. ### Ron H AAC Fanatic!

Apr 14, 2005
7,049
675
Measuring the resistance of something at RF frequencies is similar to measuring the equivalent series resistance of a capacitor. You can't do it with DC, because the impedance of the capacitance is infinite at DC.
In principle, you could use a network analyzer, but a network analyzer makes point contact to two terminals. You are subjecting the almond to a non-contacting field.
You might find an RF engineer, or even a good radio amateur (ham), who could tell you how to measure the effective resistance.

6. ### bance Member

Aug 11, 2012
315
34
I believe the "HANDBOOK OF TORTURE" states something like the resistance of nuts is futile......

7. ### DenzilPenberthy New Member

May 28, 2012
20
7
Hi there,

I used to design RF heating stuff for a living a while ago..

As mentioned above, what you want to measure is not the DC resistance of the nut but its Loss Tangent. In basic terms, your nut forms part of the dielectric of a capacitor when it is in the electric field of the RF cavity. Contunually reversing this E field is a lossy process (like how a squash ball isn't a lossless so it gets warm). The effect of this is that the electric permittivity is a complex number with a reactive and resistive component.

http://en.wikipedia.org/wiki/Loss_tangent

An excellent book that covers loads of stuff on dielectric heating is 'Foundations of Electroheat' by A.C.Metaxas. I'd highly recommend it.

Alternatively, someone has already done the hard work for you..

http://www.sciencedirect.com/science/article/pii/S1537511003000424

This paper shows how the dielectric properties of almonds and other products can be measured and has a table of results. I'm sure with some searching you could find other papers with results for dielectric properties of almonds and compare them.

Be careful with that machine, RF burns hurt!

8. ### MrChips Moderator

Oct 2, 2009
17,560
5,450
Check out Electrical Impedance Tomography (EIT). I have done EIT on tree trunks. We do scans at different frequencies and measure both amplitude and phase in order to determine impedance.