Ideas how to use the big piezoelements for the gauge with the small aperture

1. a wave guide with refracting focusing surfaces

1.1. Fresnel lens

2. use of effect of diffraction

2.1. ultrasonic holography

3. Hammer method: to neglect geometrical accuracy and to deduce an energy stream through a small window somehow

4. a wave guide with focusing mirrors

4.1. a paraboloid

4.2. heart mirrors

5. diaphragm use

6. the classical acoustic concentrator

7. phased array