Can Sound Be Direct Like a Laser Beam?
For many, the idea of directing sound much like a laser beam is an intriguing concept. Sound waves, unlike light waves, have long wavelengths and can be challenging to focus. In recent decades, however, advancements in technology have brought us closer to achieving this goal. Ultrasonic sound technology, in particular, shows promise in creating a more directional sound beam.
Ultrasonic Sound Directionality
The concept of directing sound was explored by researchers at Ultrasonic Focusing Technology Ltd. They noted that 'ultrasonic frequencies, although not exactly like a laser, can be directed with a high degree of precision.' The most significant development in this field was the creation of a device capable of focusing ultrasonic sound. This device is unique as it demonstrates the potential of focusing sound in ways similar to directed light.
A Case Study: Ultrasonic Kidney Stone Treatment
In the late 1980s, a particular company working on precision electroformed optical reflectors was approached by a medical device manufacturer. The manufacturer had developed a groundbreaking system for breaking kidney stones using ultrasonic radiation. The primary challenge was the need to focus the ultrasonic energy at a focal point, which was achieved using an ellipsoidal reflector with an aperture of approximately 3 inches.
The Ellipsoidal Reflector
An ellipsoidal reflector is a curved surface that focuses light or sound waves. The unique property of an ellipsoidal reflector is that all reflected rays, from any point on the reflecting surface, converge at a single point, known as the focal point. This property is crucial for the directed sound technology described, as it ensures that the ultrasonic beams are focused with a high degree of accuracy, similar to how a laser beam is directed.
Commercial Applications and Military Use
The commercial and military applications of focused ultrasonic sound are not limited to medical treatments. The Hypersonic Technologies Corporation, for instance, has developed and commercialized hypersonic speakers that can be used to beam sound and modulate sound messages, a technology previously used by the military. These systems rely on ultrasonic frequencies, which are significantly higher than audible frequencies, and exhibit minimal dispersion in air, allowing for precise sound directionality.
Limitations of Focused Sound
Despite the advancements, there are limitations to directed sound, primarily due to the nature of sound waves. For audible frequencies, which range from 20 Hz to 20 kHz, sound waves are significantly longer than light waves, making it difficult to focus them with precise technology. Even at ultrasonic frequencies, a sound panel would need to be exceptionally large to achieve the same level of directionality as a laser. For example, to achieve a laser-like focus with audible sound, a sound panel would need to be one kilometer by one kilometer.
Non-Linear Effects and Phased Array Technology
However, there are innovative techniques that can be used to achieve some level of directional sound focusing. Non-linear effects in the atmosphere and interference between two ultrasound waves can create more localized sound beams. These systems utilize phased array technology, which controls multiple small speakers to achieve synchronization and create a directionally focused sound beam. Such systems can effectively direct sound to a specific individual in an audience, making it less dependent on large panels and reducing the impact of reflections.
Conclusion
While the idea of directing sound like a laser beam remains captivating, current technologies offer promising solutions, particularly in the realm of ultrasonic sound. The advancements in focused ultrasonic sound, such as applications in medical treatments and military technologies, highlight the potential for further refinement and development in this area. Despite the challenges, the future of focused sound devices looks bright, promising more precise and controlled sound directionality in various applications.