AC Solenoid Resonance Problem

Jesse__S

AC Solenoid Resonance Problem [Copy link]

 

I would like to ask you a question about AC solenoids. When I measure the magnetic field of a wound solenoid, I find that resonance occurs at high frequencies, which is manifested as an increase in the magnetic field and a 180° phase reversal between the magnetic field signal and the AC source signal. What is the reason for this resonance? Thank you very much The sudden decrease in magnetic field at higher frequencies is due to the power limitation of the AC source meter, which can be ignored for now.

Jesse__S

The method for measuring magnetic field is as follows https://www.bb.ustc.edu.cn/jpkc/ ... rade1/solenoid.html

Jesse__S

This picture may be clearer

maychang

The magnetic field is strictly proportional to the current. The peak of the magnetic field must be the peak of the current. The peak of the current is mostly caused by the resonance of the solenoid inductance and the distributed capacitance of the winding.

maychang

The vertical axis in the first post is labeled as B (Oe), which may be wrong. Magnetic flux density (magnetic induction intensity) has never used Oersted as a unit. The centimeter-gram-second system uses Oersted as the unit of magnetic field intensity.

Jesse__S

maychang posted on 2018-11-8 16:32 The magnetic field is strictly proportional to the current. The peak of the magnetic field must be the peak of the current. The peak of the current is mostly due to the distributed capacitance of the solenoid inductance and the winding...

Thank you very much for your reply. I am also considering the issue of distributed capacitance. Is there a way to measure the distributed capacitance? Or how to reduce this capacitance?

maychang

Jesse__S posted on 2018-11-9 00:40 Thank you very much for your reply. I am also considering the issue of distributed capacitance. Is there a way to measure distributed capacitance? Or how to reduce this capacitance?

To measure distributed capacitance, the resonance method is usually used, which is to drive the coil with an approximate current source and observe at which frequency the voltage across the coil is the largest.

maychang

Jesse__S posted on 2018-11-9 00:40 Thank you very much for your reply. I am also considering the issue of distributed capacitance. Is there a way to measure the distributed capacitance? Or how to reduce this capacitance?

To reduce the distributed capacitance, we mainly rely on improving the winding method of the coil. For cylindrical multi-layer coils, the distributed capacitance of the simple flat winding method (winding from one end of the coil to the other end, and then the second layer is wound back to the beginning from the other end) is the largest. The pull-back winding method (winding from one end of the coil to the other end, and then pulling the wire back to the beginning to wind the second layer) is a little smaller. You can also use the segmented winding method, that is, dividing the coil into several sections, each section is very narrow, winding one section and then winding the next section, and each section is shaped like a pancake.

maychang

Jesse__S posted on 2018-11-9 00:40 Thank you very much for your reply. I am also considering the issue of distributed capacitance. Is there a way to measure distributed capacitance? Or how to reduce this capacitance?

The ultimate goal of reducing distributed capacitance is to increase the resonant frequency. The use of a magnetic core in the coil can increase the inductance with the same number of turns. Of course, the number of turns can also be reduced while keeping the inductance unchanged. Reducing the number of turns can also reduce the distributed capacitance. This increases the resonant frequency.

chunyang

The best way to reduce the distributed capacitance of the coil is the segmented honeycomb winding method. This is the ultimate means, but it requires a honeycomb winding machine. It would be very difficult to wind it by hand, so it is better to find a manufacturer to customize it.

Jesse__S

chunyang posted on 2018-11-9 12:08 The best way to reduce the distributed capacitance of the coil is the segmented honeycomb winding method, which is considered the ultimate means, but it requires a honeycomb winding machine. It would be very difficult to wind it manually. ...

Thank you, senior. Do you have any reliable manufacturers to recommend? We are a scientific research unit and we don’t wind too much each time. Thank you!

Jesse__S

maychang posted on 2018-11-9 09:26 The ultimate goal of reducing distributed capacitance is to increase the resonant frequency. The use of a magnetic core in the coil can increase the inductance under the same number of turns, and of course it can also reduce it...

Thank you for your advice, I will try it according to your method and let you know the result!

chunyang

Jesse__S posted on 2018-11-15 17:47 Thank you, senior. Do you have any reliable manufacturers to recommend? We are a scientific research unit, and we don’t wind too much each time. Thank you!

Search online, but if the quantity is not large, it is a problem whether the manufacturer is willing to accept it.