  This paper is on tilings of polygons by rectangles. A celebrated physical
interpretation of such tilings due to R.L. Brooks, C.A.B. Smith, A.H. Stone and
W.T. Tutte uses direct-current circuits. The new approach of the paper is an
application of alternating-current circuits.
  The following results are obtained:
  - a necessary condition for a rectangle to be tilable by rectangles of given
shapes;
  - a criterion for a rectangle to be tilable by rectangles similar to it but
not all homothetic to it;
  - a criterion for a generic polygon to be tilable by squares.
  These results generalize the ones of C. Freiling, R. Kenyon, M. Laczkovich,
D. Rinne and G. Szekeres.
