Abstract
njection of acoustic power from a piezoelectric transducer into a pressurized gas was studied in two cases. 1) Direct injection into the gas i.e. the acoustic system is placed in contact with the gas. 2) Injection through a metallic wall (the gas tank). We defined several indicators by which the acoustic injection could be quantified: the maximum injection efficiency (IEmax), the mean injection efficiency in a defined frequency range (MIE), the relative bandwidth of the injection (RBW), and a combined performance (CP) for the system, which combines MIE and RBW. The CP indicator efficiency was tested in case 1), of direct injection, where the optimal stack was found to be several λ/4 layers. In cases 2), the injection through a high impedance wall was more complex to investigate and less efficient in bandwidth. Several optimal designs were found with A/4 or A/2 matching layers, depending on whether the indicator was considered. High injection efficiency and wide bandwidth are difficult to obtain simultaneously. One of the best matching lines is a single A/2 layer, with low impedance compared to the transducer or wall impedance.