## 5 Conclusions  
The UT used in the test, a piezoelectric ceramic Type 4 in a disk format, 25 mm in diameter and 1 mm in thickness, plays a pivotal role in the experiments. Its natural frequency selected this model to resonate at 1 MHz, the excitation frequency used in the experiments. Far from the natural frequency, it would not allow the signal to propagate perfectly, preventing energy and data transmission. For this reason, the setup is programmed for this resonance window, optimizing the system communication. In the four test models developed, S21 is the analyzed parameter. It is a ratio between the signal emitted by the transmitter and that received by the receiver, and this value is optimized when it is close to zero. Test Model 1 uses the Conf.1 configuration and the SP.1 specimen; in this case, there is only one physical barrier, which is made of steel. This test characterizes the ultrasound signal variation by temperature variation between 40 \({}^{\circ}\)C and 140 \({}^{\circ}\)C. For the temperature range from 40 to 100 \({}^{\circ}\)C, S21 increased by approximately +0.71 dB. After 100 \({}^{\circ}\)C, from 101 to 140 \({}^{\circ}\)C, S21 decreased by \(-1\) dB. Figure 13: Test Model 4 result: values that maximize the parameter S21 (dB) by the temperature variation compensating for the deformation factor, where each point corresponds to a different temperature. **(a)** Test 4-1: Variation in parameter S21 from ambient temperature to the temperature that maximizes signal S21 (100 \({}^{\circ}\)C) is 0.5 dB, and the rapid decay of the parameter after 100 \({}^{\circ}\)C to 140 \({}^{\circ}\)C, where the \(\Delta\)dB is 1.2 dB. **(b)** Variation in parameter S21 from ambient temperature to the temperature that maximizes signal S21 (100 \({}^{\circ}\)C) is 0.6 dB, and the rapid decay of the parameter after 100 \({}^{\circ}\)C to 140 \({}^{\circ}\)C, where the \(\Delta\)dB is 1.3 dB. **(c)** Test 4-3: Variation in parameter S21 from ambient temperature to the temperature that maximizes signal S21 (100 \({}^{\circ}\)C) is 0.9 dB, and the rapid decay of the parameter after 100 \({}^{\circ}\)C to 140 \({}^{\circ}\)C, where the \(\Delta\)dB is 1.2 dB. **(d)** Test 4-4: Variation in parameter S21 from ambient temperature to the temperature that maximizes signal S21 (100 \({}^{\circ}\)C) is 0.8 dB, and the rapid decay of the parameter after 100 \({}^{\circ}\)C to 140 \({}^{\circ}\)C, where the \(\Delta\)dB is 1.3 dB. The second test, which uses the Conf.2 configuration and the SP.2 specimen, has three physical barriers between the ultrasonic transducers: two steel and an acoustic fluid barrier. This test is to understand both the transmission of the signal under the condition of multiple layers and the consequence of the communication of the transducers due to their misalignment. Therefore, it selects which UTs were used. Five were fixed to the left plate, three to the left plate, three were fixed to the right plate, and a 100 mm layer of water separated the two plates. This UT organization allowed them to be coupled to have a horizontal alignment of 100%, 40%, 12.5%, and 0%, with 100% completely aligned and 0% completely misaligned. For 100%, the transmission was aligned with a physical barrier, and the signal strength of the S21 was measured at \(-\)13 dB; this level is considered unacceptable. However, regarding communication and data transmission, these results are considered favorable for multi-layer data transmission. For the tensile test near the yield strength, our Test Model 3 uses specimen SP.2 and configuration Conf.1. In this case, the test is conducted without the influence of temperature. The specimen is carefully and gradually stressed up to almost 86% of its yield strength, resulting in a strain of 1250 \(\upmu\)m/m. This strain causes a variation in S21 of approximately +0.7 dB. Even with the high deformation, the communication between the UTs remained uninterrupted.