An electric wire for improving the adhesion force between the adjacent winding wires of a coil is described. The electric wire of the present invention may include a conductive wire with a substantially quadrilateral cross-sectional shape. The electric wire further includes a first groove and a second groove positioned diagonally at two opposite corners of the quadrilateral along a longitudinal direction of the conductive wire. An adhesive pocket filled with an adhesive is sized to fit within each of the first and second grooves at diagonally arranged opposite corners.