Generation of holographic ultrasound patterns

Ultrasound technology is already commonly used in biomedical echography, gesture recognition in car consoles and several commercially available platforms for haptic feedback. The piezoelectric micromachined ultrasound transducer (PMUT) technology developed at imec aims to take the next steps towards further miniaturization, increased pressure levels and display-compatibility, targeting wearables, smart houses and VR gaming as potential markets.

Fig. 1: (left) Polymer PMUT arrays developed at imec. (right) Measured plane wave acoustic pressure field.

Using accurate control of the amplitude and phase of the driving signals for the individual elements forming a PMUT array, the ultrasound pressure can be steered or focused in in time and 3D space. The first goal of this thesis is to enhance and implement the algorithms to produce pressure holograms in mid-air, from 1D (line) focusing over 2D (point) focusing, towards multipoint holographic patterns. These concepts are illustrated in Fig. 2.

    

Fig. 2: (left) Measured 1D focused ultrasound. (middle) Measured 2D focused ultrasound. (right) Simulated acoustic V-shape hologram.

The driving parameters extracted from the algorithms and simulations will subsequently be applied to the microfabricated arrays using dedicated hardware. The existing boundaries and limitations will have to be considered and dealt with. The generated pressure fields will be mapped, analysed, and used in further iterations of the development. As an ultimate goal, haptic feedback should be envisioned, allowing the user to feel the patterns in mid-air due to high intensity, modulated or moving pressure points.