The cylindrical transducer provides stable 360° horizontal coverage and wide bandwidth, matching well with shielded receivers.
Basis for the material choice
Air ultrasound has long been dominated by piezo ceramics, whose acoustic impedance is badly mismatched to air — resulting in narrow bandwidth and long ringing. PVDF's impedance is closer to air, giving wide bandwidth and low Q at the cost of lower output pressure, which suits receiving and short-range transmission.
