Figure 9

Output signal dependence on acoustic excitation frequency, or shortly the FRF of the system. The blue solid line is FRF at \(0^{\circ }\hbox {C}\), and the black dashed line is FRF at \(+\,20^{\circ }\hbox {C}\). 0 dB response is observed at 10 kHz and \(0^{\circ }\hbox {C}\).