2. The following shows the existence of oscillating magnetic and electric fields in an electromagnetic wave The detection of the fields relies on the two properties: 1. Ed = V (electric field drives a current back and forth in the antenna) 2. ф B /t = V (driving a current back and forth around the loop)

3. The sensor is at right angles to the antenna. Little electric field is detected. Meter Diode Antenna SENSOR ANTENNA Diode dipole

4. The sensor antenna is parallel to the plane of the electric field. The electric field makes a larger current through the sensor antenna. Dipole Diode

5. wire As the electric field passes the wire it forces electrons up and down generating heat. The energy must come from the field and therefore the amplitude of the electric field and the magnetic field are reduced. The alternating magnetic field produces the alternating electric field. The alternating electric field produces an alternating magnetic field.

6. The plane of the magnetic field is horizontal and parallel to the plane of the sensor loop. Therefore no magnetic flux goes through the loop and the magnetic field of the electromagnetic wave is not sensed. B diode meter LOOP

7. diode The magnetic field now passes through the loop generating a larger current through the meter in the sensor circuit.

8. Click on the movie square and see what happens when this screen is lowered between the sensor and the antenna.

9. Click on the movie and watch what happens to the electromagnetic wave field…as measured by sampling the electric field… when horizontal rods are placed between the sensor and the generated field. Energy is not absorbed by the rods because the vertically polarized electric field only moves electrons across the diameter of the rods and therefore does not generate large currents and thermal energy and does not get absorbed.