In some cities, mobile phone Base Transceiver Stations (BTSs) are found almost at every 500 m interval, and in other cities where there is no restriction on the location of the towers, more than 30 cell towers can be seen within 1 km. Since more users are emerging every day, the proliferation of mobile Base Transceiver Station (BTS) or mast is of great concern. The radiation emitted from the numerous antennas mounted on the mast of the cell are also of great concerns to the populace, especially people who live close to them.
Therefore, it is compulsory to extract the value of Electric (E) -field (volts/meter) from the individual frequency components of the GSM bands such as 0.9 GHz, 1.8 GHz and 2.1 GHz to be compared with ICNIRP level. Therefore, the main interest for this project is to measure the mobile signal from the base stations, which are mostly close to the residential area covering the GSM bands of 0.9 GHz, 1.8 GHz, and 2.1 GHz.
Currently, the radiated emissions from the GSM tower are detected by the spectrum analyzer which mobile frequency band network systems. However, the spectrum analyzer does not have any provision to broadcast or transmit any information obtained in the field over the internet. In addition, the data measured by spectrum analyzer is offline and not a real time results. It is difficult to give a real picture of the electromagnetic (EM) radiation level in the intended environment. Electromagnetic radiation should not exceed the radiation limit proposed by ICNIRP.
Therefore, this maximum allowable E-field limit has to be followed for human safety. Electromagnetic radiation readings below the radiation limit indicate that the radiations in that specific area are within the safety levels. Therefore, an automatic system capable of measuring the electric (E) fields at the mobile phone frequencies (0.9 GHz, 1.8 GHz, and 2.1 GHz) is designed as shown in Figure 1. These E-field data will then be “pushed” into the internet for continuous monitoring (24 hours a day). The designed unit acted as receiver / EM mobile sensor, consist of an antenna and detector that can produce an accurate DC voltage and eventually convert it into electric (E) field with calculated antenna factor (AF).
Figure 1: Overall system layout
A radiation detector complete system as shown in Figure 2. It consists of receiver sensor (antenna), 3V circuit, WIFI shield, and microcontroller. The rectangular patch antenna is the receiver to receive a signal from the base transceiver station. The microcontroller received the input voltage from the detector and convert it to E-field value. In addition, WIFI shield is the medium hub to connect the Arduino to Favoriot Platform through Internet. The extracted E field information would be plotted for each frequency in the FavorIoT Platform. As a result, the user can access the data via any internet enabled devices. The complete system will be placed in the proposed packaging as shown in Figure 3.
Figure 2: Measurement setup
Figure 3: Proposed packaging for the complete system
The new system has been calibrated and compared with an existing system in the market. Figure 4 shows the comparison between the existing system (using spectrum analyzer and horn antenna) and our product. Based on the results, the E field strength values show a good agreement as the percentage of deviation is quite small which is an average of 2%. The uncertainty of the measurement is ±4.6478 dB. Therefore, E field values for 0.9 GHz, 1.8 GHz, and 2.1 GHz are valid for the measurement as the maximum deviation is 2.4 dB, which is still in the range of the uncertainty. Therefore, the fabricated rectangular patch antenna can be used to detect mobile electromagnetic radiation accurately.
Figure 4: Comparison measurement using a new system and existing system in the market
The E field strength was calculated and the real-time data measurement was stored and displayed in the Favoriot platform. Figure 5 shows the E field strength data for operating frequencies of 0.9 GHz, 1.8 GHz, and 2.1 GHz. 121.28 dBuV/m is the maximum radiation reading shown in Figure 5. The reading does not exceed the radiation limit proposed by ICNIRF level, which is 155 dBuV/m. The result and data can be accessed by the end user using through Favoriot Platform.
Figure 5: E field strength graph display in Favoriot
The Author is Puteri Alifah Ilyana Nor Rahim and Supervisor is Syarfa Zahirah Sapuan from UTHM, our FAVORIOT-University collaborator.