Abstract: Electromagnetic radiation is converted to usable power in the form of electrical current by means of a plurality of transducing cavities having a wall structure that is inclined inwardly to receive impinging radiation and includes potential barrier strips each having different conduction electron densities which are also different from the conduction electron density of the material constituting the wall structure of each cavity; each potential barrier strip extends from the mouth of the cavity to the base thereof and, at the mouth, is connected to a conductor having a preselected conduction electron density whereby radiation impinging on a cavity will induce current flow which will be rectified across the potential barriers; the cavities are connected in parallel so that current can be delivered to a load connected across the conductors.