Described embodiments include an apparatus that includes anexpandable structure, configured for insertion into a body of asubject, and a plurality of conducting elements coupled to theexpandable structure. Each of the conducting elements comprisesa respective coil and has an insulated portion that iselectrically insulated from tissue of the subject, and anuninsulated portion configured to exchange signals with thetissue, while in contact with the tissue. Other embodiments arealso described.
