# Phase relationships of points between two current sources using AC

• August 22nd, 2018, 10:50 PM
Curiosity
Phase relationships of points between two current sources using AC
Long time no see everyone. Still working on my PhD using alternating current electricity to affect brain activity.

A problem was posed to me the other day by another team working on this. The set up is using two current sources, with a 1mA peak to peak current, with anti-phase relationship, so that the current sums to 0.

The electricity flows over the skin, and some of it penetrates the skull and into the brain. The question is, what is the phase relationship between the two current sources, and the surrounding recording points?

If the current sources are completely anti-phase, and you measure the voltage levels and therefore the phase relationship of multiple recording points BETWEEN them, how do you determine which recording point is in-phase to what current source?
• August 26th, 2018, 11:07 PM
NoCoPilot
I'm not a PhD scientist -- nor do I play one on TV -- but I do believe electric current moves at a significant percentage of the speed of light, even through a crummy conductor like the skin. Since you're using alternating current, the phase should be almost instantaneous, from the source injection to the sensor pickup right? However I don't understand your statement that in an "anti-phase relationship the current sums to 0" -- if your current sources are out-of-phase with each other, and one source is, say, +1vdc at the same moment the other is -1vdc, won't you get maximum current flow across the skin? It won't FEEL like it sums to 0... :smile:

Possibly related:
According to Quora, the resistance of a human body varies from about 1k ohms to 100kΩ, depending on how far it has to travel and how wet the path is.

TENS (transcutaneous electrical nerve stimulation) devices for pain relief use DC pulses of 175-200uS of up to 350v in bursts of 2 to 120 Hz at 700mA.

ECT (electroconvulsive therapy) for psychiatric disorders uses pulses of 100-400vAC for 1/10th to 1 second at 900mA.

Huh, that must be why they don't recommend putting the TENS pads on your temples.
• August 29th, 2018, 02:50 PM
Smite
Very interesting question, but difficult (at least for me) to understand. Antiphase normally indicates a singe circuit with two signals which are 180 degrees out of phase. In this case, the resultant voltage would be zero, ergo the current would be zero.
Can you describe the circuitry? Are there two separate circuits?
• August 29th, 2018, 03:05 PM
Smite
Very interesting question, but difficult (at least for me) to understand. Antiphase normally indicates a singe circuit with two signals which are 180 degrees out of phase. In this case, the resultant voltage would be zero, ergo the current would be zero.
Can you describe the circuitry? Are there two separate circuits?
• August 29th, 2018, 03:06 PM
Smite
Sorry for the double post. There seems to be something wrong with the database. It showed an error after the first post, so I just went ahead and clicked Post again. I shall be more careful in the future.