What size of piezocrystal required to depolarize a single nerve?

[Next223]

If you were to use the highest performing synthetic piezocrystal what dimensions would be required to stimulate a typical nerve? Experiments have been done to use ultrasound to compress the crystal and store the charge in a capacitor, if I'm understanding correctly. How much volume is required, or how could I calculate that answer for my own personal interest. Thank you.

 

[berkeman]

Please always post links to your reading to help us answer your questions. Thanks.

 

[jrmichler]

There is more to it than merely sizing a crystal. Here's how I would start working on this problem.

Step 1: If you are stimulating a nerve with electricity, then you start by defining what it takes to stimulate a nerve. The required stimulation will be some combination of current, voltage, time, and possibly charge.

Step 2: Knowing what it takes to stimulate a nerve, you can calculate a capacitor to store the necessary charge at the appropriate voltage. There will be a circuit to control the electricity from the capacitor to the nerve. You need to allow for the energy loss in that circuit (oversize the capacitor).

Step 3: Given a capacitor, and the peak capacitor voltage, find an energy harvesting (search the term) chip/circuit/system to connect the piezoelectric generator to the capacitor. Keep in mind that energy harvesting is not 100% efficient, and that the energy losses can be a significant portion of the energy generated by the piezoelectric crystal.

Step 4: Search piezoelectricity, piezoelectric constant, and electromechanical coupling factor to learn about the types of piezoelectric crystals, and their electrical response to mechanical stress. Steps 3 and 4 are not linear - you need to iterate until you converge on a solution.

 

[Next223]

There is more to it than merely sizing a crystal. Here's how I would start working on this problem.

Step 1: If you are stimulating a nerve with electricity, then you start by defining what it takes to stimulate a nerve. The required stimulation will be some combination of current, voltage, time, and possibly charge.

Step 2: Knowing what it takes to stimulate a nerve, you can calculate a capacitor to store the necessary charge at the appropriate voltage. There will be a circuit to control the electricity from the capacitor to the nerve. You need to allow for the energy loss in that circuit (oversize the capacitor).

Step 3: Given a capacitor, and the peak capacitor voltage, find an energy harvesting (search the term) chip/circuit/system to connect the piezoelectric generator to the capacitor. Keep in mind that energy harvesting is not 100% efficient, and that the energy losses can be a significant portion of the energy generated by the piezoelectric crystal.

Step 4: Search piezoelectricity, piezoelectric constant, and electromechanical coupling factor to learn about the types of piezoelectric crystals, and their electrical response to mechanical stress. Steps 3 and 4 are not linear - you need to iterate until you converge on a solution.

I'm a biology major so I'm more familiar with the generation of action potentials than I am the physics and piezocrystals. Here is an attach image of a compressed piezocrystal. In order to generate an action potential, typically excitatory neurotransmitters exit one synapse and land on the next nerve in the chain. Ligand gated ion channels then open allowing sodium to flood in and propagate positive charge down the axon, with insulation and voltage gated ion channels. Essentially sodium enters the cell body to a sufficient point to trigger the voltage gate sodium channels to open and the charge fires down the axon to the next synaptic terminal.

With that background info, would we put the positive electrode (top wire of the graphic) inside the cell body in order to depolarize the cell body(make it more positive opening the voltage gated sodium channels) and leave the negative electrode outside? Or is it the other way around? It is positive charge that is required to stimulate the nerve so I'm not sure exactly how to make that work if it is the electrons that get compressed and flow. Is that where the capacitor comes in? thank you for your reply.

 

[Next223]

mV action potential