Hyperovals in Knuth's binary semifield planes

In each of the three projective planes coordinatized by the Knuth's binary semifield Kn of order 2n and two of its Knuth derivatives, we exhibit a new infinite family of translation hyperovals. In particular, when n=5, we also present complete lists of all translation hyperovals in them. The properties of some designs associated with these hyperovals are also studied.