Innovative Acoustic Radiometer Spins with Sound Pressure

A new approach to building radiometers has emerged, showcasing the power of sound. Inventor Ben Krasnow has successfully created an acoustic radiometer that spins due to differences in sound pressure, rather than the traditional method of light radiation. This innovative device highlights the potential of acoustic radiation in scientific applications.

Instead of relying on light to generate movement, Krasnow constructed a set of vanes from laser-cut aluminium, affixed with sound-absorbing foam on one side. These vanes were mounted around a jewel bearing sourced from an analog voltmeter. Positioned above four speakers in an acoustically sealed chamber, Krasnow played a continuous stream of 130-decibel white noise. The vanes spun as the aluminium side, which reflects more sound, experienced greater pressure than the foam side, demonstrating the principle of sound pressure differences in action.

In testing, Krasnow discovered that when the foam was mounted on opposite sides of the vanes, they spun in opposite directions. This outcome confirmed that the spinning was a direct result of the pressure difference rather than an unintended acoustic streaming effect. The creation of such intense sound levels did present challenges; the high volume caused several speakers to burn out. To mitigate this, Krasnow monitored the temperature of the speaker coils, noting that their resistance increased with heat. By measuring this resistance, he could effectively manage the coil’s temperature, preventing overheating.

Further experimentation involved testing the radiometer’s performance in a variety of gases, including hydrogen, helium, carbon dioxide, and sulfur hexafluoride. Surprisingly, none of these gases outperformed air, which is counterintuitive. The results can be explained by the design of speakers, which are optimized for transferring energy to air. Although this method is not the most efficient for converting electrical power into motion, it aligns with previous findings, where several engines have harnessed the power of acoustic resonance.

Krasnow’s work demonstrates an exciting intersection of sound and mechanics, paving the way for future innovations in the field. For those interested in the historical context, Krasnow has also elaborated on the original Crookes radiometers, further enriching the understanding of this fascinating subject.