doc. Ing. Radoslav Bortel, Ph.D.

From the signal processing perspective, parametric speakers are transmitter arrays controlled by beamforming techniques. The application of suitable algorithms allows to generate signals of the individual emitters, so that the resulting beam is radiated into a desired area, or radiation into a selected area is avoided. Parametric speakers typically utilize sound from ultrasound generation, i.e. a passive demodulation phenomenon, where the emitters radiate a modulated ultrasound signal that is subsequently demodulated to the audible acoustic band due to the nonlinearities of the propagation medium. Thanks to the short wavelength of the ultrasound waves, it is possible to achieve good control over radiated beam with minimal overall dimension of the emitter array. Current challenges of parametric speakers primarily include nonlinear distortion of resulting acoustic signals, a problem with generation of acoustic signals at lower frequencies (<300Hz) and partial radiation into undesired sidelobes. The construction of the parametric speakers also has to deal with limited bandwidth of commercially available ultrasound transducers. The aim of the dissertation thesis is to practically realize a system of a parametric speaker, and investigate techniques for the improvement of its properties and functionality. The student should primarily consider the usage of beamforming techniques for electronic steering and directionality control, the improvement of modulation algorithms in order to reduce the overall nonlinear distortion and possibilities to employ alternative ultrasound transducers with wider usable bandwidth. The systems realized within the scope of this dissertation thesis can find practical applications for example in indoor information systems (usable in shops, museums, schools), in navigation systems for visually impaired, in cars or in public warning systems.