Description:
Approximately 20 years ago, I observed an acoustic phenomenon that could have been chaos. Not understanding what I was observing, I found that I could maintain experimental conditions to prevent it from occurring. I did so in order to complete the task at hand. The study involved understanding what conditions subharmonics were generated in an ultrasonic standing wave cavity. Two air-backed quartz transducers were placed in a Fabry-Perot configuration with water; one transducer having a resonant frequency of about 1 MHz; the other always being at lower frequency. Their separation was adjustable to be between 5 to 10 cm apart. The 1-MHz transducer was driven with a variable frequency oscillator. At sufficient power and at some driving frequencies, subharmonics were observed both optically and with a piezoelectric transducer. Upon the onset of subharmonics, an optical diffraction pattern displayed lines in between the lines normally observed. A frequency analyzer connected to the piezoelectric transducer showed subharmonics and the corresponding idlers. Under some higher power conditions, the optical pattern became a smear and the frequency analyzer display became uninterpretable. In retrospect, I now believe what I was observing was chaos.