Microwave diffraction by a large adjustable iris.

Microwave diffraction by a large adjustable iris. A 3 cm. microwave transmitter is placed 140 cm. from a large metal adjustable iris. On the other side of the iris, 140 cm. away, a microwave receiver is placed. A handle on the iris adjusts the iris opening from a minimum of 7 cm. diameter to 62 cm. When the transmitter is turned on, it sends microwaves through the iris opening, and the receiver emits an audible tone from its speaker. As the handle on the iris is moved, the tone gets louder, then softer, then louder, then softer. The changing size of the iris causes the microwave diffraction pattern to change so that the receiver is at a node, then an antinode, etc .