Synhetic aperture radars have progressed radar imaging applications to the point where physically controlled beams are becoming a rarity instead of the norm. Acoustic methods are now following the same path using new materials working as wave guides. Crystal matrices with acoustic refraction properties are being used to focus and direct acoustic fields at specific frequencies. This opens up new application possibilities for a wide range of uses such as targeted medical imaging and non destructive testing of structures like bridges, aircraft fuselage etc.
Through design of the phase gradient profiles of crystalline surfaces acoustic convex and concave lenses can focus the incoming plane waves and collimate the converging waves, respectively. On the basis of the high converging and diverging capability of these lenses, two kinds of lens combination scheme, including the convex–concave type and convex–convex type are able to tune the incoming beam aperture as needed. The aperture of the acoustic beam can be shrunk or expanded through adjusting these phase gradients that are constructed by the stacking ultrathin labyrinthine structures, which are obtained by the geometry optimization procedure and exhibit high transmission coefficient and a full range of phase shift.
Acoustic Fire Fighting
A combination of pulsed infrasound and interferometry patterns have been tested for extinguishing fires and has the potential to evolve into a new and highly capable fire fighting technology. Wild fires are becoming a growing problem and current fire fighting efforts are not able to keep up so being able to use acoustic methods both from the ground and air could be very useful. Especially for putting out electrical and chemical fires where water can do more damage.
Acoustic Insect Screens
Ultrasonic pulses above 35kHz can be effective to repel insects from areas. There are many such products available but they all share one major problem and that is their design which disperses (spreads out) the US field quickly. Different frequencies affect different insects and a combined set of sweeping frequency bands can only be effective if the effective power is powerful enough. In order for this to work the beam needs to be focused. Acoustic lists can be designed to form a sheet field like an invisible curtain covering a window, door opening or even outside covered area. Since the sheet field is focused it will be more effective against insects while the opening can be used by people and when tuned properly even pets like dogs.