Features of airborne ultrasonic fields

A transducer array having known relative positions and orientations comprising:

• an acoustic array;
• at least one control point wherein each control point:
• (a) has a known spatial relationship relative to the transducer array which is used to define a corresponding focal point basis function belonging to a first set of focal point basis functions;
• and (b) has a control point amplitude;
• computing potentially estimated transducer activations required to produce an acoustic field corresponding to a control point set with the first set of focal point basis functions comprised of transducer coefficients to produce a first set of potentially estimated transducer activation amplitudes;
• an adjuster for adjusting each transducer coefficient of the first set of focal point basis functions using the potentially estimated transducer activation amplitude for the transducer in combination with statistical properties of the potentially estimated transducer activation amplitudes to produce a second set of focal point basis functions;
• a computer for computing transducer activations required to produce the acoustic field with the second set of focal point basis functions;
• wherein the second set of transducer activations are used to drive the transducer array.