This is similar to a device called the "E-Bow" which was developed in
the 1970's.  It was a battery powered hand-held electromagnet that was
used to magnetically excite the strings of an electric guitar.  It
produced a sustained "bowed" tone from the strings.  The device is
still in production and has a website at  http://www.ebow.com/

Bob Godfried
Bronx, NYC