###### Abstract
Other authors explored the subject and reported experimental results for transmission through single metallic walls with thicknesses spanning from 1.6 to 304.8 mm, using a diversity of types and sizes of ultrasonic transducers at different ranges of excitation frequencies (e.g., [7; 8; 9; 10; 11]), and reaching close to 60% efficiency, transferring over a 100 W of power [12] with data rates of the order of hundreds of Mbps [13]. [PERSON] et al. [14] explored using a single transmitter UT with one of its electrodes divided into multiple patches. They aimed to demonstrate using a multiple-input single-output (MISO) strategy to localize the input ultrasonic waves onto the receiver, increasing power efficiency and improving the robustness of the system. Using a UT receiver smaller than the electrode-etched transmitter, they demonstrated that the system's response improved whether both transducers were aligned or not. [PERSON] et al. [15] also employed a piezoelectric stack as the transmitter UT, with all layers in an aligned polarization and a single-layer receiver. They demonstrated that this configuration improved the normalized transmitted power and the power density of the system. [PERSON] et al. [16] present a completed system for data transmission through a metal barrier. The paper describes its behavior through experiments and analytical and numerical modeling. The numerical simulations obtained results close to the experiments, and it was also possible to deliver 17.5 W of DC power to a resistive load through a 3 mm aluminum barrier with an efficiency of 68%. Later, [PERSON] et al. [17] worked on the problem of data and power transfer through detached metal layers. The work focused on the issue of the coupling fluid that influences handling, so [PERSON] et al. proposed soft elastomers for dry coupling, which facilitate the detachable transducers. As a result, using the soft elastomer allowed the delivery of 3 W DC of power with an efficiency of 50% through a 3 mm thick aluminum plate with gaps of 0.5 mm. [PERSON] et al. [18] extended the analysis from a single wall to a three-layer configuration consisting of two plane metallic walls, respectively, 15.97 and 10.92 mm thick, surrounding an intermediate 88.3 mm fluid layer. Two identical, 25.4 mm diameter, 1 MHz piezoceramic discs were concentrically coupled to the opposite sides of each metallic wall surrounding the fluid layer. The discs were bonded to the walls by using an epoxy-based adhesive layer. Their experiments yielded a data transmission rate of 4 Mbps with power transfer efficiency better than 30%. Furthering the investigation on multi-layer acoustic channels, [PERSON] et al. [10] designed and performed experiments on a curved, three-layer system formed by two concentric metallic pipes with a fluid-filled annulus. Their goal was to investigate the wireless transmission of power and data from the production tubing of an oil well through an annulus filled with a water-based fluid and across the casing pipe wall to access sensors placed behind the casing string. To isolate the piezoceramic UT from the annular fluid, they were coupled, using an epoxy resin, to the inside face of a metallic cover that played the role of a first wall. A MEMS-based temperature and pressure sensor was successfully powered and interrogated through all the layers, with a power insertion loss of 10.72 dB and a data transmission rate of 1.2 kbps using an amplitude modulated scheme with Manchester coding. [PERSON] et al. [11] demonstrated utilizing a pair of co-axially aligned piezoelectric transducers to communicate power and data through two steel plates separated by a fluid layer. The authors employed a frequency shift key (FSK) scheme with automatic gain and carrier control, significantly reducing energy consumption and improving the data transfer error rate. With an overall consumption of 1.2 W, they could transfer 66 mW of power through two flat steel plates (5 mm) separated by a fluid layer (100 mm) at 19.2 kbps. To enhance communication, [PERSON] et al.