| MadSci Network: Physics |
Hi Birol, Those are interesting questions. In general, different wire geometries exhibit different field patterns. This leads to different inductances and radiation patterns when used as antennas. There are also capacitance effects, but these tend to be significant for frequencies where the wavelength is on the order of the length of the wire. I'll address each of your questions in order: 1- What are the differences of the physical properties between a flat spiral Bifilar coil and solenoidal shaped Bifilar coil ? The inductance computations are different. Here's an online calculator for flat spirals: http://deepfriedneon.com/tesla_f_calcspiral.html Here is one for a solenoid: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/indsol.html Marc T. Thompson offers an interesting way of estimating the inductance of any geometry in this article titled "Guesstimating Inductance of Wire Loops": http://members.aol.com/marctt/CV/Abstracts/inductance.htm 2- According to question (1) which type of Bifilar coil is better to use ? That depends on what you mean by "better" ;-) Solenoids are easy to manufacture, so they are the most common geometry for low and medium frequencies. Higher inductances can be achieved for a given linear dimension with solenoids, so flat spirals are usually found in microwave circuits. 3- Is it possible to use a Tesla type bifilar winding in a LC (tank) circuit, which interesting results do you expect to get if used in two different styles ? Certainly! As mentioned above, flat spirals are common in microwave circuits. They are often printed on circuit boards or even integrated circuits. 4- Is it possible to use Tesla type bifilar winding in an RF antenna, which interesting results do you expect to get if used in two different styles ? Yes, just about any geometry can be used as an antenna. The difference is primarily radiation pattern, directional gain, and usable bandwidth. This can be calculated, but often it's easier to build an antenna and measure the characteristics. Solenoid antennas are commonly in AM radios. Here's article about that: http://www.mindspring.com/~loop_antenna/ Here's an article on spiral antennas for telemetry: http://gltrs.grc.nasa.gov/reports/2004/TM-2004-213217.pdf 5- What happens if a Tesla type bifilar winding is used in a transformer ? Not very good coupling, I'm afraid. Flat spirals don't confine magnetic field very well. This is one of the reasons solenoids are the work horse of the industry. Of course, there are applications where loose coupling is preferred, Telsa coils for example. I hope that answers all your quesions! Madhu - http://www.madhu.com
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