unipolar

Concise Oxford English Dictionary © 2008 Oxford University Press:
unipolar/juːnɪˈpəʊlə/

▶adjective

• 1 having or relating to a single pole or extremity.

  ■ Electronics (of a transistor or other device) using either negative or positive charge carriers but not both.

• 2 (of psychiatric illness) characterized by either depressive or manic episodes but not both.

• 3 (of a nerve cell) having one axon.

– derivatives
unipolarity /-ˈlarɪti/ noun.