Because the physics of sound creation is so different than any traditional loudspeaker, Holosonics had to make substantial advancements in several areas to bring this technology to successful fruition. Each advancement independently doesn't create success - all of the elements must be present for a high-performance, useful technology.
MATHEMATICS AND ALGORITHMS
The mathematics of nonlinear wave physics is quite complex, and the specific governing equations addressing the conversion of ultrasound to audible sound are not solvable in closed-form. Solving these equations is essential for knowing how to synthesize the correct ultrasound signal, in real time, such that the desired audio signal is reproduced accurately. Beginning with the pioneering work by Dr. Pompei at MIT, Holosonics has successfully developed the proper mathematical basis for the ultrasound-to-audio effect, as well as realtime signal processing algorithms necessary for practical implementation. In addition, Holosonics has pioneered several processing techniques for enhancing the conversion efficiency, and ensure that only the absolute minimum of ultrasound is needed for reproducing the desired audio output, and for developing fast, efficient computational techniques to implement these algorithms on inexpensive DSP's.
Even when armed with the correct mathematical formula for synthesizing the ultrasonic signal, the ultrasound still needs to be reproduced accurately. High-fidelity audio requires high-fidelity ultrasound.
This presented a formidable challenge to Holosonics, as the only transducers commercially available were the common sonar-style piezoelectric devices, used in the prototypes of the earlier researchers in this field. While these can create ultrasound, and can be used to generate audio, the bandwidth is quite limited, and fidelity of ultrasound - and therefore audio - is abysmally poor. This was one major reason that no other company has ever had a successful product in this market.
Holosonics developed its own custom, proprietary transducer technology to address these difficulties. Based on a thin moving film, rather than piezoelectric ceramics, the transducer is light, inexpensive, extremely efficient, and has unmatched ultrasonic bandwidth and fidelity. With over 10 years in continuous development, it is an important part of Audio Spotlight technology.
Traditional architectures for audio amplifiers do not have nearly enough high-frequency bandwidth to properly recreate ultrasound. Further, the electrical load (impedance) of the Holosonics transducer is vastly different than that of a traditional loudspeaker. Therefore, existing audio amplifier technology and design techniques could not be applied to Audio Spotlight technology. Starting from first principles, Holosonics developed its proprietary, digital, high-efficiency ultrasound amplifier specifically to create high-power ultrasonic signals extremely accurately, and drive its transducer technology efficiently. The amplifier is so efficient, no heatsinks are needed, and very little energy is wasted.
Covering the above major innovations, and several others, Holosonics has over 25 issued patents in the USA and Internationally, with many others pending.