Abstract: A contactless detection device, comprising a detection surface; a plurality of actuators acoustically coupled to the detection surface; an ultrasonic acoustic wave detector; an electronic and/or IT computer, the device being configured to detect one or more element(s) by repeating the following steps: focusing ultrasonic acoustic waves emitted by the actuators into a focusing region, obtained from waves emitted by the actuators and to which a first time reversal method has been applied, and measuring a duration between emitting the waves and receiving an echo of these waves by the detector, wherein the computer is configured to calculate the control signals such that the detection waves are focused successively into focusing regions of different shape and/or sizes.