Directional sound using ultrasound

Create a device capable of directing sound like a flashlight, creating the ability to whisper into someone's ear from a distance of 20+ meters (similar to the LRAD: http://en.wikipedia.org/wiki/LRAD).

Create a device capable of directing sound like a flashlight, creating the ability to whisper into someone's ear from a distance of 20+ meters (similar to the LRAD: http://en.wikipedia.org/wiki/LRAD).

Conceptual ideas:

- Use a large emitting surface to bundle ultrasound waves (for example an old satellite dish).

- Use an ultrasonic power transducer (UPT) originally meant for use in ultrasound cleaning devices.

- Original audio signal is demodulated by the physical properties of air.

- Modulate carrier frequency with audio signal (FM modulation).

To discuss:

- What's the best way to use a UPT:

- mount it on a larger surface

- mount it in front of a satellite dish (in place of the receiver)

- Is it possible to modulate the carrier frequency with a UPT? Is it still efficient? (a UPT has a very large Q: >500)

- If a UPT is not suitable: How to create an affordable HF transducer?

- Electronics!