I'm currently doing a project on magnetic haptic feedback using DC electromagnet. The principle of my haptic feedback system is very simple (figure shown below):
A permanent magnet is stuck to the user's finger (It doesn't necessarily have to be one permanent magnet, here can be multiple permanent magnets stuck to different positions on one finger or even the entire hand). An array of electromagnets surround the permanent magnet and exert electromagnetic force on the permanent magnet in arbitrary magnitude (by changing the magnitude of the current) or direction (by changing the direction of the current). The presumed working space of this system is around 60mm * 60mm * 60mm~150mm * 150mm * 150mm, depending on the performance of the electromagnets. The maximum force exerted should be around 0.5-1N. The electromagnet consists of an iron core and multiple turns of copper wire.
I've currently done some experiments, namely, I tested the magnitude of electromagnetic force on a permanent magnet from one electromagnet by passing an adequate amount of current through its coil. The problem I'm having now, as is expected from electromagnetic theory, is that the magnitude of electormagnetic force decreases way too fast as the distance between the permanent magnet and the electromagnet increases and by the time the permanent magnet reaches the range of the "working space" of this system, there's barely any force left.
Therefore, I'm hoping to increase the magnetic field intensity in the "working space" so that the magnetic force also increases. However, since it's an academic project, I'm trying to explore some more fancy, more novel ways to realize that goal other than the more common, more straightforward ways, namely, increasing the current, increasing the number of turns, increasing the size of the electromagnet...
Therefore I'm hoping you guys can give me some hints or keywords with regard to these potentially fancy methods to increase the magnetic field intensity from a DC electromagnet. DC magnets are preferrable simply it's easier to control but if adopting AC magnets in a certain way can do a better job in this application, the option is still welcomed! I'll be more grateful if you can give me a detailed description about the method you propose!
