I have an iron rod supported by a coil spring that vibrates vertically within a solenoid coil. The solenoid has a 5 ohm dc resistance. There is no physical contact between the coil and rod.
As I increase the current through the solenoid, the natural (mechanical) frequency of the system changes - this is desired. Unfortunately mechanical damping also appears to increase with current.
I understand this damping may be related to two phenomena: eddy current losses and back-emf.
For the eddy current component I understand I may be able to reduce this by using a ferrite (non conductive) rod in place of iron. Please correct me if this is wrong.
For the back-emf component, what are my options? Some advice I was given was that adding a large resistance (100 to 1000ohms) in series with the coil would reduce it. Is this true? If it would work then the problem with the solution is the massive increase in power consumption of my system in order to achieve the same current through the solenoid coil. Are there more power efficient solutions?
I attempted a comparison with the system powered via a lab bench supply set to be a voltage source versus set to be a current source and the damping was identical with both settings.
Is this bench supply inappropriate for this purpose or does this result suggest the dominant factor is eddy currents instead of back-emf?