Capacitor Design Questions
Capacitor Design Questions
(OP)
I am developing a large scale capacitor to determine the effect of electric fields on tissue samples. The capacitor is a formed by two parallel plates (made of stainless steel), using an overlaping method to reduce edge effects. I am using a high permittivity material (foamglas) in between the plates that will increase the total capacitance of the system, and allow us to use smaller applied voltages to obtain electrical field requirements.
What are some considerations I should take into effect on this?
I feel that heat might be as issue, but without a current I don't know how heat would be generated?
Any incite on this would be very helpful.
Thanks!
What are some considerations I should take into effect on this?
I feel that heat might be as issue, but without a current I don't know how heat would be generated?
Any incite on this would be very helpful.
Thanks!





RE: Capacitor Design Questions
frequency?
voltage?
capacitance?
RE: Capacitor Design Questions
RE: Capacitor Design Questions
There are standard power capacitors available, but these use aluminum foil for the plates and have a dielectric fluid between the plates for medium voltages. For low voltages, the standard is now a metalized film, where the metal is deposited on the PPE film. It's a fairly compact design to get high amounts of capacitance in a fairly small can.
Why the special design?
RE: Capacitor Design Questions
I assume the samples will be going between the plates. If so, then why use the other materials between the plates? Or am I misinterpreting what you're trying to do?
RE: Capacitor Design Questions
The design is unique because we are placing petri dishes between the capacitor plates, that must have an air supply and cannot be subject to contaminants. The stainless steel was chosen because the last iteration of the project used stainless steel plates (which I was not on the design team), I believe this is the case because the system must be sterilyzed and the stainless steel wont rust. I chose stainless steel because of it's relatively inexpensive nature and ease of machinability. And I chose foamglas because the dielectric constant was relatively high at the frequency which our system was running, and it is available locally.
geekEE:
I am placing the other materials between the plates so that I can maximize my capacitance. According to the formulas I have come across if I have a large dielectric constant (with all other things being held constant) I should also yield a large capacitance. Essentially I want to get my capacitance as high as I can so that I can use the readily available power supplies that I have.
All:
As you can tell my background is in mechanical engineering, and the knowledge that I have expressed is that of limited research and introductory level courses in circuits. So if I have said anything that is incorrect, or if my thinking is wrong please correct me. Thanks.
RE: Capacitor Design Questions
The distance between the plates is going to be around 1inch to 1.75inches. The overall plate area is going to be maximized but is limited to the dimensions of the incubator which the system must fit into. Currently I am designing the system to have plate areas of approximately 144in^2.
RE: Capacitor Design Questions
RE: Capacitor Design Questions
RE: Capacitor Design Questions
Thanks.
RE: Capacitor Design Questions
I'd say you should put the plates as close as possible. I don't see the need for the foamglass if all you're trying to do is maximize your electric field. It sounds like you'll be able to get many times your required electric field.
RE: Capacitor Design Questions
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Capacitor Design Questions
Also, if not foamglas dielectric and stainless steel plate electrodes, what materials do you guys recommend?
RE: Capacitor Design Questions
The field is going to be nonuniform where you ripped out the foamglas, so you might as well just metallize the top and bottom of the petri dish and apply the 20 V directly. That's the absolute highest field that you can achieve with your power supply.
A typical Petri dish is only about 0.75" thick, so that would given you a field of 20V/0.75in = 10V/cm. You're never going to do better than the voltage applied divided by the thickness of the air gap in the Petri dish.
Putting your voltage across a 1.75 in gap drops your field down to 4.5 V/cm. I doubt that there's a usable dielectric with a sufficiently high enough dielectric constant to make up for the decrease field strength. Seems like you'd need a dielectric constant on the order of 10 to do anything useful in terms of reducing the effect of the larger gap.
TTFN
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RE: Capacitor Design Questions
RE: Capacitor Design Questions
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RE: Capacitor Design Questions