Microwave Tunneling

This demonstration illustrates the principle of quantum tunneling using microwaves and wax prisms. First, microwaves are sent across a space to a detector. The detector registers a reading. Then, a wax prism is inserted between the generator and detector. The detector now reads zero. If the detector is moved to the other side of the prism is will show a reading again. This shows total internal reflection. If the detector is returned to its original position and a second prism is placed on the other side of the first, the detector will show a reading if the gap between the prisms is small enough. At this point, the photons are able to tunnel under the gap into the second prism and continue on to the detector. This phenomenon of photons traveling through the gap is known as quantum tunneling.

* Equipment seen in the video may vary from equipment used in ND Demonstrations. See information below and images above for ND equipment and setup.

Setup:

Place the microwave transmitter on a flat surface.

Place a microwave receiver directly across from the microwave transmitter. If the height of the receiver is not aligned with the height of the transmitter, then place some object beneath the receiver until is is perfectly level. Turn on the receiver.

Turn on the transmitter by plugging it in and rotating the dial.

Adjust the power dials as needed until the desired signal strength is reached.

The receiver will register a reading. Depending on the strength of the signal, turn the receiver to the appropriate multiplier (where the signal reads between the maximum and minimum).

Place a wax prism between the transmitter and receiver. The receiver should read zero. Rotate the receiver around the prism. You should get a reading at the point of total internal reflection.

Return the detector to its original position. Turn on and place the other receiver at the point of total internal reflection that was previously observed. Make the second receiver level with the transmitter's signal. The detector will register a reading if the gap is small enough. As the gap narrows, the detector reading should increase.

Notes:

While the receivers can be used in a more qualitative, observational manner, precise quantitative data can be collected. Simply use banana plugs to attach the transmitters to the current sensors and connect the current sensor to a device equipped with PASCO Capstone software. If using this method of observation, the multipliers on the receivers become even more important. ND Demos primarily used a multiplier of 10.

The volume dial has no effect on the microwave emissions. It is only on the transmitter to serve as an auditory signal that the transmitter is operating correctly. If unsure of the strength of the microwave emissions, use the volume as a tool. The volume can get very loud quite quickly, so be sensitive with any volume adjustments.

The microwave transmitter has many dials and attachments that impact the emitted signal. To make the signal at its strongest, rotate the attenuator so that it hits the leftmost boundary (as seen in the above image).

Courses Used In:

• PHYS 10342

Discussion and Polling Questions:

Coming Soon

Equipment Needed:

• Microwave transmitter

• Microwave receivers (x2)

• Receiver stands (x2)

• Plug-in transformer

• Belz microwave emitter attachment

• Budd-Stanley curved waveguide

• Circular waveguide

• Dielectric waveguide

• Wax prisms (x2) (may not be kept with kit)

• Grid

• Small plastic screws (x7)

• Reflective metal plate

• Banana plugs (x4) (optional)

• PASCO current sensor (x2) (optional)