Acoustic Radiometer Demonstrates Unique Energy Conversion Method

Engineers and physicists continue to explore innovative ways to harness sound energy, as demonstrated by a recent project involving the construction of an acoustic radiometer. This device, built by inventor Ben Krasnow, operates on the principle of acoustic radiation rather than the commonly misunderstood radiation pressure used in traditional Crookes radiometers.

The Crookes radiometer, often misattributed to radiation pressure, actually works by heating vanes inside a near-vacuum chamber. When light strikes these vanes, they gain energy, which then affects gas molecules that come into contact with them. In contrast, Krasnow’s radiometer utilizes sound waves to generate movement, presenting a fresh approach to energy conversion.

Innovative Design and Testing

Krasnow crafted two sets of vanes from laser-cut aluminium, attaching sound-absorbing foam to one side. He mounted these vanes around a jewel bearing sourced from an analog voltmeter, positioning the rotor above four speakers within an acoustically sealed chamber. By playing a sound level of 130 decibels of white noise through the speakers, he created a significant difference in pressure between the two sides of the vanes. The aluminium side, designed to reflect sound more effectively, experienced greater pressure, causing the vanes to spin.

Testing revealed that the vanes spun in opposite directions when the foam was mounted on alternate sides. This outcome demonstrated that the pressure difference caused by the sound waves was indeed responsible for the rotation, rather than an acoustic streaming effect, as initially speculated.

Challenges and Efficiency

Throughout the experimentation, Krasnow faced challenges, particularly with speaker durability. The high volume often led to speaker burnout. To mitigate this, he monitored the temperature of the speaker coil at varying power levels. By observing the increase in resistance as the coil heated, he established a method for calculating its temperature, allowing him to prevent overheating.

Additionally, Krasnow tested the performance of the radiometer with various gases, including hydrogen, helium, carbon dioxide, and sulfur hexafluoride. Surprisingly, none of these gases outperformed air, which is counterintuitive given their differing properties. The results suggest that speakers are optimized for transferring energy to air, making it the most effective medium for this application.

While the acoustic radiometer represents a novel approach to converting electrical power into motion, it is not yet a practical solution for efficient energy conversion. Nevertheless, the exploration of acoustic resonance has previously led to various engines powered by sound, indicating potential for future developments in this area.

For those interested in the intricacies of the original Crookes radiometers, Krasnow has previously provided insightful explanations that delve into their workings, adding context to the advances being made with acoustic technologies. As research in this field progresses, it highlights the creative potential of sound as an energy source.