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Join Date: Feb 2014
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Measuring the Impedance of a Muscle?

05/08/2014 6:28 PM

i've made a constant current source using hawland circuit 5V P-P and 100KHz sinwave input , and the output is 1mA which enter the to the mussels by two electrods and the output voltage enter to instrumentation amplifier to amplifying the signal to (gain 10) the its enter to rms to DC converter (ad637) , what is exactly i should do next to measure the impedance of the muscle , and to measure the change on the impedance when the muscle in constriction and extraversion , what should i do to make my circuit complete???

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#1

Re: measuring the impedance of a muscle?

05/08/2014 6:35 PM

Does you tutor have any suggestions?

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#2

Re: measuring the impedance of a muscle?

05/08/2014 6:56 PM

From your first post:

"i want to build a constant current source to measure a high frequency bioimpedance with a current source as input work on (1MHz frequency) and the output (1mA). i need the circuit for this current source and the type of the amplifier????"

Now, "what should i do to make my circuit complete???"

I suggest trying it out on yourself.

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#3

Re: Measuring the Impedance of a Muscle?

05/08/2014 7:48 PM

Are you saying that you've built a circuit to measure muscle impedance without quite knowing how to measure muscle impedance?

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#8
In reply to #3

Re: Measuring the Impedance of a Muscle?

05/09/2014 12:45 PM

And, without quite know how to design and build the amp.

Worry, worry.................

The gene pool will benefit. ;>)

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#4

Re: Measuring the Impedance of a Muscle?

05/08/2014 9:18 PM

You have a fixed current, a voltage that you can measure and so an impedance you calculate from the two. Sounds like a good place to now start testing and see what results you get, preferably on something organic and similar to muscle First!). Safety and all.

I'm not quite sure the voltage is high enough for accurate measurements, but see what happens and let us know. How did you plan on accessing the muscle?

If you think you can just place electrodes on top of the skin over the muscle and take the measurement (for example) it won't work!

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#5

Re: Measuring the Impedance of a Muscle?

05/09/2014 7:16 AM

1 mA is much too large a current to use.

The only thing you really need to know is Ohms law: V = IR

As you can see if R is greater than 5 KΩ, which it will be, then you will not be able to get 1mA through that resistance at 5V.

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#6

Re: Measuring the Impedance of a Muscle?

05/09/2014 9:05 AM

You may need to study and familiarize yourself with anatomy and human physiology. Focus on their characteristics and normalized behaviors. Muscles do behave differently as well as reacts differently to different frequencies when stimulated electrically.

Thereafter you would have an idea what your next steps would be.. based on what expectations you may want to achieve or anticipated?

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#7

Re: Measuring the Impedance of a Muscle?

05/09/2014 11:30 AM

It sounds like your idea might be a little half baked. Bring it up to 3/4 baked and you will probably get better help here.

I don't know much about what you are doing but it sounds a little like what I hear when I asked people how the percentage of body fat meters work at the health club. I never did the research to determine the value of what I was being told but you might want to Google "body fat meters" (or similar words) and see if you find anything interesting. EEG and GSR meters are also different but learning about their terminals and circuits might be useful for your current project.

One of the times I was wired up they used Ten20 conductive paste from http://bio-medical.com/products/ten20-eeg-conductive-paste-4oz-tubes-3-pack.html to connect the metal terminals to me. It might be useful for you. I think they also used some sort of conductive pads from 3M.

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#9

Re: Measuring the Impedance of a Muscle?

05/09/2014 2:14 PM

Just to be on the safe side....in case your constant current source happens to run a little outside the desired output...remember:

'Only cross your heart, if you hope to die'.

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#10

Re: Measuring the Impedance of a Muscle?

05/09/2014 3:51 PM

Well, if you put a known value of resistance in series, you can compare the voltage drop across the resistor with the voltage drop across the muscle (both in amplitude and phase).

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#11

Re: Measuring the Impedance of a Muscle?

05/13/2014 4:14 PM

What should you do to make your circuit complete? You should seek the services of a competent Biomedical Engineer. If you were doing this on dead tissue there would be no need for the warnings that follow, but once I saw terms like constriction and extraversions I knew this is not the right forum for you.

Anytime that you inject current into, or impose a voltage onto, live tissue you need to ensure the complete isolation of the circuit from any unintentional source or ground. There are many rules and regulations regarding powered medical equipment, simply having a data sheet with a Howland circuit on it does not ensure your subject's safety.

Read this article on measuring muscle impedance, then start researching through the references for a better understanding of how to do this without endangering anything's life.

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