eBow Groove Box

Description

I have seen couple of recommendations about induction coils (prefered with 50 ohms resistance for the sensor and with 8 Ohms for the second coil which would be the driver) you could try finding such coils in old telephone pickups or tiny PC speakers or maybe locate them at alibaba
http://www.alibaba.com

Here is a description from an ebow like patent
The coil magnet assembly is shown in detail in FIG. 10. The metallic string 321 is passed through coils 33 and 34 of coil magnet assembly 320. Coils 33 and 34 are comprised of 28-36 gauge copper enameled wire with an inner diameter of three-sixteenths to one-fourth peg side and nine thirty-seconds at the bridge side in the preferred embodiment of the present invention. It will be understood, however, that other types of wire and coil configurations can be utilized without departing from the scope or spirit of the present invention. In the preferred embodiment, a coil having a resistance of a minimum of 8 ohms has been found to be advantageous. The inner diameter of the coil should be such that the field generated can affect the metallic violin string 321. However, the diameter should not be so small that the metallic string contacts the coil, deadening its motion.

Source:
http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITO…