Contactless element detection device

A contactless detection device, comprising:

• a detection surface;
• a plurality of actuators acoustically coupled to the detection surface and configured to emit ultrasonic acoustic waves;
• an ultrasonic acoustic wave detector;
• and
• processing circuitry;
• wherein the device is configured to perform detection of one or more elements by implementing the following steps a plurality of times:
• focusing detection ultrasonic acoustic waves emitted by the plurality of actuators via the detection surface into a focusing region belonging to a plane located opposite and away from the detection surface, by applying on the plurality of actuators, control signals calculated by the processing circuitry from a measurement of an audio impulse response and/or a vibratory impulse response of the detection surface that was generated by an emission of ultrasonic calibration acoustic waves by each of the plurality of actuators, and application of a first time reversal method to the audio impulse response and/or to the vibratory impulse response of the detection surface, and
• measuring a duration between the emission of the detection ultrasonic acoustic waves and a reception of an echo of the detection ultrasonic acoustic waves by the ultrasonic acoustic wave detector,
• wherein the processing circuitry is further configured to calculate the control signals such that the detection ultrasonic acoustic waves are focused successively into focusing regions having different shapes and/or dimensions.