## 3 Experimental Methodology  
The analysis of ultrasonic communication was performed using a diverse range of tests including temperature variation, stress tensor test, stress tensor test with temperature variation, and the UT misalignment test in a multiple barrier configuration. In addition, these temperature tests were also performed with the transducer in different positions and with fluid in the middle. These four types of tests led to the development of two models of specimens, called SP.1 and SP.2. Both were developed in AISI 316 stainless-steel and have a chemical composition of 16% chromium, 10% nickel, and an additional addition of 2% molybdenum. This combination, which is among the most common and usual, is classified in the austenitic family [52]. The dimensions of SP.1 are presented in Figure 3a. This specimen model is used in the temperature and temperature tests with variations in the positioning of the plates with fluid in the middle. Figure 3b shows the dimensions of SP.2 used in the strain tests. The cross-section of SP.2 is 40 mm \(\times\) 6 mm, which results in a cross-sectional area of A = 240 mm\({}^{2}\). The Young's modulus for this stainless-steel is 200 GPa, so by applying this to Equation (5), it is possible to deduce that the maximum force in the specimen not to occur plastic deformation is 69.9 kN. This results in a yield strength of 291 MPa and a strain of 1456 \(\upmu\)m/m. Furthermore, the SP.2 specimen was designed for the size of the ultrasonic transducer. However, due to limits in the geometry of the Instron machine used in the tests, this did not follow the standard norm for traction tests ASTM E8/E8M-9 [53]. The test was carried out in two different configurations of data transmission. In the first one, Conf.1, the ultrasonic transducers are fixed and aligned on opposite sides of the specimen. The energy is transferred horizontally through the propagation medium, which is the body of the specimen, as shown in Figure 1a. In the other configuration (Conf.2), two ultrasonic transducers are fixed on different plates, submerged parallel in a fluid that forms a fluid barrier between them. The propagation media are the two stainless-steel plates and the fluid layer in the middle, as illustrated in Figure 1b. In Conf.1, a climatic chamber was coupled to the setup test. The climatic chamber is from [PERSON] (model VCL4010), depicted by number 2 in Figure 4a. This equipment allows temperature control from \(-40\) to 180 \({}^{\circ}\)C, with a variable rate of 3 \({}^{\circ}\)C/min and stability of \(\pm 0.5\) \({}^{\circ}\)C. Test programming is carried out and controlled by the climatic chamber itself. In Conf.2, the setup was immersed in a thermal bath (Lauda, model Alpha RA 24), which heated the fluid in a controlled manner varying from \(-25\) \({}^{\circ}\)C to 80 \({}^{\circ}\)C and stability \(\pm 0.05\) \({}^{\circ}\)C and was used to maintain the same temperature--30 \({}^{\circ}\)C. A mobile support was made that allowed the plates to maintain a vertical position even when immersed in the thermal bath. Figure 2: Schematic of the wave propagation. (**a**) Wave propagation parallel to the applied stress, i.e., stress \(x\)-axis (\(\sigma_{x}\)) and \(v_{l_{x}}\); (**b**) Wave propagation perpendicular to the applied stress, i.e., stress \(x\)-axis (\(\sigma_{x}\)) and \(v_{l_{y}}\). The VNA model E5061B from Keysight, is a versatile tool that can adapt to various measurement needs. It sends and reads the UT waves and can measure impedance in a frequency range from 5 Hz to 3 GHz. According to the specifications of the manufacturer, it has a wide dynamic range, around 125 dB, a measurement speed of 3 ms, a trace noise of 0.0005 dBrms, and temperature stability of 0.005 dB/\({}^{\circ}\)C. The UTs are excited by consecutive sinusoidal pulses sweeping in frequency through a previously determined Hz window. The VNA sends this frequency range for the UT according to the piezoelectric ceramic (PZT) resonant frequency, which in this case is 1 MHz.