Iranian Journal of

Backgrounds and Objectives: There is a considerable notice in the use of noise barriers in recent years. Noise barriers as a control noise solution can increase the insertion loss to protect receivers. This paper presents the results of an investigation about the acoustic efficiency of primitive root sequence diffuser (PRD) on environmental single T-shape barrier.
Materials and Methods: A 2D boundary element method (BEM) is used to predict the insertion loss of the tested barriers. The results of rigid and with quadratic residue diffuser (QRD) coverage are also predicted for comparison.
Results: It is found that decreasing the design frequency of PRD shifts the frequency effects towards lower frequencies, and therefore the overall A-weighted insertion loss is improved. It is also found that using wire mesh with reasonably efficient resistivity on the top surface of PRD improves the efficiency of the reactive barriers however utilizing wire meshes with flow resistivity higher than specific acoustic impedance of air on the PRD top of a diffuser barrier significantly reduces the performance of the barrier within the frequency bandwidth of the diffuser. The performance of PRD covered T-shape barrier at 200 Hz was found to be higher than that of its equivalent QRD barriers in both the far field and areas close to the ground. The amount of improvement compared made by PRD barrier compared with its equivalent rigid barrier at far field is about 2 to 3 dB, while this improvement relative to barrier model .QR4. can reach up to 4- 6 dB.
Conclusion: Employing PRD on the top surface of T-shape barrier is found to improve the performance of barriers compared with using rigid and QRD coverage at the examined receiver locations.

Background and Objectives: Sound of motorcycles plays an important role in noise pollution in big cities. This is due to the lack of national law or standards to control the noise of domestic and also imported motorcycles. This study tries to introduce a practical limit value in different stage of motorcycle life cycle by assessing their noise pollution.
Materials and Methods: First the motorcycles noise standards at different countries were studied and they were compared with the results from noise level of 622 motorcycles in 3 different groups. The sample volume in each group corresponds to the amount of their annual production rate. Then using statistical tests, a limit was determined in which 90% of the domestic motorcycles can be covered. The limit is proposed as the standard for domestic motorcycle noise.
Results: The limit for motorcycles of groups 1, 2 and 3were 84, 86 and 87 dB (A) ,respectively in the TA stage. For the COP stage (Conformity of Production), the limit increases according to certain formula. In the end, a flowchart was proposed as a standard method for measuring the sound of motorcycles in the TA and COP stages was proposed.
Conclusion: Noise level of the domestic motorcycles is at least 9 dB (A) higher than the noise limit value of European motorcycle. If European limit value is considered for producing the national motorcycle, 90% of them will get out of production cycle and this would not be practical.

Background and objectives: In recent decades, progress of telecommunication industry resulted in public availability to cost-effective cellular mobile hence, boom of base stations of cellular mobile in response to vast public demands. Base stations of cellular mobile are specific source of microwave production in a certain frequency in environment. Antennas are installed on high towers to create proper coverage. General public exposure because of possible health effects resulting from radiofrequency fields has become challenging problem. The purpose of this study was to investigate microwave radiation status in actual exposure in inside buildings vicinity of macro cellular base stations in Zanjan. Materials and methods: considering location of base station antenna in city, power density of microwave around 64 base stations in indoor sites such as health care places and residential areas at different distances and different heights was measured. Measurements were performed based on IEEE Std C95.1 standard method using a portable SPECTRAN, HF– 4060 Rev. 3. Analyzing of data was conducted using SPSS Ver. 18 software and statistical tests like Kolmogorov-Smirnov, univariant variance, and multi variant linear regression. Results: It was found that the maximum level of power density was measured at a distance of 20 m from base station about 0.03787mW/m². With increasing distance from base station, the density of wave power decreased. Minimum measured at a distance of 300 m from tower was 0.00108mW/m². The positive variation of power density with height increase was shown. Conclusions: The maximum level of power density among total of 252 measurements, in indoor sites was7.320mW/m². This is about 0.166 % of the Permissible Exposure Limits of the standards for public exposure. We did not consider factors such as building location and interior furniture. Therefore, we suggest such factors be included in the future studies.

Background and Objectives: Due to the increasing use of mobile phone in recent years, the number of BTS antennas has also increased. .Proliferation of BTS antennas in cities and villages, and perpetuation of encountering with waves from one side and  increasing the anxiety of many people in encountering with their waves from the other side convinced more investigations in this field. Therefore, the purpose of this study was to investigate  the propagation of microwave around the BTS antennas of Maragheh and to compare power density measurements  with allowable environmental standards.

Material and Methods: In this research, the frequency of BTS antennas was determined through field monitoring. Then, measurements were performed using a calibrated Spectran 4060 and the standard method IEEE Std C95.1 was adopted in close and far fields from each antenna. Then, the obtained data were analyzed  after entering to SPSS environment. In this study, the Kolmogrov-Smirnov test, Kruskal-Wallis, and Mann-Whitney tests were used.

Results: This research found  that in both  Irancel and Hamrah Aval operators, the power density increased with distance in close fields and decreased in far fields. Moreover, at the distance of 20 meter, the maximum value of power density was measured. Significant difference between these distances was observed (P-value ≤0.05).

Conclusion: Out of 1804 cases in far and close fields, the highest power density measured at 900 MHz band was 4.51 mW/m²,  which is in accordance with 0.1% permissible exposure.