Features of airborne ultrasonic fields
A method for specifying desired quantities of the energy flux of the combined waves of acoustic radiation pressure to apply producing a mid-air haptic pushing force, which has the effect of simultaneously reducing the harmonic distortion present is described. Further, a method for communicating only the summaries of acoustic field contributions at the required locations in the form of summed portions of the relatively small matrix whose row and column count depend only on the control point count is described. Further, phased arrays of ultrasonic speakers can produce a relatively large amount of acoustic energy which is usually directed in a specific direction or focused to a particular point depending on the application of the array. Further, to allow the system to be driven more strongly than usual, the complex-valued linear system that governs the drive signal to each control point is solved twice. Further, to achieve mid-air haptics with high precision the radiation pressure generated must be modelled accurately.
1. 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.
2. The transducer array as in claim 1 , wherein the adjustment applied to each transducer coefficient is a scaling in a form of a per-transducer gain.
3. The transducer array as in claim 1 , wherein the mean value is within statistical properties of the first set of potentially estimated transducer activation amplitudes.
4. The transducer array as in claim 1 , wherein statistical properties of the first set of potentially estimated transducer activation amplitudes are obtained by estimated evaluation of quantile function for percentiles of a distribution.