# Communication System Based on Magnetic Coils for Underwater Vehicles
## 5 Results  
To evaluate the system's performance, data transmission tests were performed following the description of the previous section. Two square coils were built according to the specifications in Table 2.  
During the test, the emitted signal consumed 75 mA with a voltage of 2.5 V at a frequency of 600 kHz. The magnetic field generated has a maximum magnitude of 1.2 uT, so a transmission range of up to 45 cm is observed. The induced voltage at 20 cm is 260 mV.  
The test message is a text string with 100 characters. This message was sent consecutively 100 times for each position sampled at a transmission speed of 9600 bps. In Table 3, the number of times the test message was transmitted incorrectly is displayed. Each box corresponds to different locations of the receiver coil, using the center of the transmitter coil as a reference.  
When the underwater vehicle is positioned in the center of the transmitter coil, the data reception does not contain errors; these appear when the submarine is about to leave the coverage area and there is no communication when both coils (transmitter and receiver) stop sharing parallel planes.  
With the data obtained in Table 3, the data transmission area was plotted and shown in Figure 12a. It can be observed that for the information transfer to be carried out successfully, it is sufficient for a part of the receiver coil to enter the indicated space.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Coil** & **Transmitter** & **Receiver** \\ \hline Length \(a\) & 0.12 m & 0.12 m \\ Length \(b\) & 0.10 m & 0.10 m \\ Height & 0.03 m & 0.03 m \\ Number of loops & 20 & 40 \\ Conductor diameter & 1.024 mm & 0.4049 mm \\ \hline \hline \end{tabular}
\end{table}
Table 2: Characteristics of the coils.  
Figure 11: Experimental test system.  
Table 4 shows the number of messages transmitted incorrectly. When the submarine is placed within the coverage area but with 45\({}^{\circ}\) of rotation, the data are received satisfactorily without affecting the transmission of information.  
In Figure 12b, the data transmission area for the second test is plotted, as can be seen the transmission is not affected by changes in orientation around the axis of the coils.  
Additional tests were carried out while varying the temperature of the water; modifying the level of salinity concentration; adding impurities such as clay, cardboard, plastic, and glass; and without these variables modifying the behavior of the system.  
The temperature tests were carried out in a range from 10 \({}^{\circ}\)C to 35 \({}^{\circ}\)C. The measurements were taken in real time using a MS5837-30 BA sensor, which has a precision of \(\pm 1\) \({}^{\circ}\)C. By measuring the amount of salt in a given amount of water, we can examine the concentration of salt in it. Concentration is the amount (by weight) of salt in the water, which can be expressed in parts per million (ppm). For the salinity tests, transmission tests were made  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c c c c} \hline \hline
**Y/X** & \(-\)**24** & \(-\)**22** & \(-\)**20** & \(-\)**18** & \(  
by mixing salt directly into the water in a range from 1000 ppm to 35,000 ppm. For the tests with different concentrations of clay, this element was mixed directly, from 0 g to 1 kg.  
When carrying out data transmission tests, it was observed that it is necessary to place the receiver magnetic coil at least 15 cm away from the closest propeller to avoid interference due to the magnetic field that it generates when it is in operation.  
Figure 13 shows a test run according to the specifications of the previous section. Due to the fact that the field lines travel through air or water and the magnetic permeability values of these elements differ, the information does not suffer distortion due to the change of medium. For this reason, this communication system can send and receive information underwater with the same efficiency as it does in the air.