1. Ch.S. Roumenin and P.T. Kostov, “Planar Hall effect device”, Bulg. Patent N 37208, Dec. 26, 1983.
2. Ch.S. Roumenin, “Solid State Magnetic Sensors”, Elsevier, Amsterdam, 1994.
3. Ch.S. Roumenin and P.T. Kostov, “Hall effect sensor”, Bulg. Patent N 41974, May 6, 1986.
4. Ch.S. Roumenin, “Parallel-field Hall microsensor”, Compt. rendus Acad. Bulg. Sci., 40(11), pp. 59–62, 1987.
5. R.S. Popovic, “The vertical Hall-effect device”, IEEE Electron Dev. Lett., EDL-5(9), pp. 357–358, 1984.