CAUTION: This apparatus is not meant to operate at very low frequencies. When setting the frequency range of your scan, do not start below 100 Hz. And note that there is a peak at 370 Hz that has to do with the equipment and not with the resonances in the apparatus, so don’t analyze that one!

SAVE ALL YOUR DATA. Make sure you are saving text files of your data and not just a picture of the nice plot that the UI generates.

DON’T RUSH! Take your time and think about ho/why your data has changed after you’ve changed the apparatus.

4.1 Oscilloscope Practice

1. Add a BNC tee to the microphone and speaker inputs of the control box
2. Use the extra BNC cables to connect the speaker to channel and the microphone to channel 2.
3. Set the scope to trigger off of channel 1, since that’s the variable we are controlling. The signal is going to be an oscillation around 0, so set the trigger level somewhere close to zero.
4. Start the software to scan the frequency. You should see the speaker output with a constantly growing frequency and the microphone output that periodically increases in amplitude at the resonant frequencies.
5. Do the increases in microphone signal correspond to resonances displayed in the software?

4.2 Taking Data

1. Start with a 400 mm column (8×50 mm tubes). As you sweep the frequency up to 12 kHz, you should see resonance peaks at regular intervals. Save your data (not just the image, the data points).
2. Now introduce lattice sites by placing a 16-mm inner-diameter iris after each piece of tube. Scan over the same frequency range. Note the band gaps that have formed!
3. Add another unit cell (tube+iris) and repeat the frequency scan. Do this step several times. You should notice a pattern forming. HINT: Count the resonances in the Brillouin zones.
4. Go back to using eight 50-mm tubes and 16-mm iris’s and take an initial data set. Now vary the length of the tubes and do frequency scans. Again, be on the lookout for patterns that develop.
5. Go back to using eight 50-mm tubes and 16-mm iris’s and take an initial data set. Now vary the iris diameter and do frequency scans. As always, be on the lookout for patterns that develop.