Practical Activity for 14-16
A microwave detector shows the standing wave pattern in the space between a microwave generator and a reflective metal barrier.
Apparatus and Materials
- Aluminium barrier, plane
- Microwave transmitter
- Microwave receiver
Health & Safety and Technical Notes
Modern equipment using a solid-state diode transmitter is safe.
Older equipment using a klystron tube uses hazardous voltages. The connectors on the leads between the transmitter and the power supply MUST be shielded types to minimize the risk of serious electric shock. The ventilation holes in the power supply may also give access to hazardous voltages, so its use MUST be closely supervised.
The transmitter should produce microwaves of about 3 cm.
The microwaves can be unmodulated, in which case the receiver is connected to a meter. If they are modulated, it is possible to detect them using an amplifier and loudspeaker. A narrow probe receiver will better discriminate between nodes and antinodes than a horn receiver will.
Manufacturers usually supply a full instruction book, including experiments, with their microwave kits.
- Set the microwave transmitter and receiver facing a metal barrier.
- Move the receiver back and forth in the space between the speaker and the wall to show amplitude maxima and minima. You may need to adjust the distances carefully to produce a standing wave pattern.
Students find microwaves intriguing because of their invisibility. You may want to discuss how this is similar to other phenomena with which students are familiar; e.g. radio reception interference or mobile phone signal strength, and the way these result from reflections from buildings or geographical contours.
This experiment was safety-tested in February 2006