The purpose of this paper is to determine the effect of infrasound noise from wind turbines (up to 20 Hz) on the changes in the EEG signal patterns in humans. The experimental study was undertaken to investigate the effect of a 20 minutes long infrasound exposure on humans. The acoustic signal was recorded at a distance of 750 meters from the wind turbine and the frequency components above 20 Hz were then filtered out. Research work undertaken so far to investigate the impacts of wind turbine noise on humans would mostly rely on questionnaire tools and subjective assessment given by respondents. This study focuses on the effects of infrasound noise from wind turbines on variations of EEG signal patterns in an attempt to develop a more objective measure of the infrasound noise impacts. The experimental study was conducted in a pressure cabin where the EEG procedure was performed. Analysis of the EEG signals reveals the changes between the EEG patterns registered during the three successive stages of the study. The results indicate some changes in EEG signal patterns registered under exposure to wind turbine noise. Moreover, the specific frequency ranges of the EEG signals are found to be altered.
Wind power has now become one of the most widely exploited and dynamically developing sources of electricity throughout the world. Taking advantage of wind power as a renewable source of energy brings a number of economical, social, environmental, and ecological profits. However, due to the typical size of turbines and their airspace configuration, they can adversely impact the natural environment posing potential hazards such as noise emission, vibrations, non-ionizing radiation effects, emergency situations, the shadow flicker effect, and permanent shade conditions. Turbines may have also a negative effect on the local fauna (particularly birds) as well as the landscape.
In case of wind turbines, both low-frequency noise and audible noise is produced by various aerodynamic noise sources (turbulent layer tearing o from blade edges, boundary layer tearing o , onset of vortex air flows, induction of a boundary vortex, vortices of laminar layer, turbulence of the in owing air stream) as well as by mechanical noise sources (gearboxes, generators, devices altering the headstock direction, cooling system pumps, ancillary facilities, etc.) .
Despite the fact that modern wind turbines operated at daytime generate far less noise than their prototypes, they still appear to strongly affect people. Under certain weather conditions, this noise is transmitted over large distances and exceeds (by about 10 15 dB) the noise levels obtained from numerical models . In most cases, this effect can only be sensed in a subjective manner which means that the very presence of wind turbines may bring about acoustic or beyond-acoustic annoyance reactions in humans (distraction, irritation). These factors are accounted for in the sound level models and questionnaire tools that were a part of experiments conducted mainly in Holland and Sweden and connected with the level and spectral composition of sound generated by wind turbines emitted over the neighboring areas (residential areas). When addressing the issue, other aspects have to be considered as well: time of the day, atmospheric conditions (wind speed and direction), personal attitude towards wind power generation (ardent supporters and fierce opponents), the actual distance from a windmill farm or the age of people being interviewed [3 6].
The noise produces negative reactions of the nervous system, affecting such abilities as reading ability, attention, problem solving, and memory. Noise appears to have a negative impact on children at school, mainly because it is impossible to control. It can also lead to elevated levels of stress hormones and increased blood pressure at rest. This unfavorable reaction is stronger in children whose school performance is poor.
Most people do not cope well with the effect of noise exposure, and because of that they run a higher risk of suffering from its harmful effects than it was proved in previous studies [7 9].
In 2001, at the University of Wisconsin Madison the research workers distributed a questionnaire among the residents who had lived for two years in close proximity of a wind power installation comprising 22 turbines. The results of their investigations showed that 44% of people living within a distance of 243-402 meters from wind turbines estimated the noise level as an important issue in their households. Similar tendency was observed among 52% of residents living 804-1600 meters away from turbines, as well as in the 4% of those residing 1600-3200 meters from the wind farm. Under certain conditions, wind turbines could still be heard from the distance of 3.2 km .
These findings have been confirmed by Van den Berg, doctor of medicine at Groningen University in Holland, located at the Dutch-German border in the vicinity of a modern wind power plant consisting of 17 turbines with total power of 30 MW. Residents who lived 500 m and further from the turbines reacted strongly to noise pollution, while those living in an approximate distance of 1.9 km displayed clear signs of annoyance (anger) .
In 2005, a survey was carried out among 200 people living 1.2 km from a French wind mill farm in St. Crepin. 83% of residents took part in the survey, 27% found the noise level unbearable at night, 58% claimed that noises during nights seriously interfered with their night's rest, while 10% stated that noise in the course of the day was at least distracting, and that was just a six-turbine installation with the rated power of 9 MW .
According to the Dutch standards, the noise of wind mill turbines is to be measured based on the average level of exposure Lden (day-evening-night) which is defined in correlation with the wind speed value at the height of the tower .
According to Schreurs , as long as the infra frequency noise level is kept below 40 dB(A), the annoying effects should not be acute and the residents' health should not be strongly affected. For average exposure levels Lden exceeding 45dB(A), the noise is expected to be perceived as irritating and may cause sleep disorders thus affecting human health.
The subjective assessment of sound emitted by wind mill parks was conducted on the basis of surveys collected from residents living nearby wind farms [5, 11]. The issues addressed included verbal evaluation of noise generated by wind turbine elements, subjective perception of this type noise for different wind conditions as well as the impact of non- acoustic factors (economical benefits, wind mill view, living conditions) on the perceptibility and inconvenience resulting from the noise. The results of surveys carried out in Holland, in which respondents were asked to come up with the most accurate term describing sounds generated by wind power plants located at a distance of 2.5 km from their permanent residence, revealed that 80% of respondents described the noise as whistling. This group included both those who sensed certain level of discomfort and respondents who did not complain about the wind mill presence at all . Research e orts aimed at defining the exposure-reaction curve for wind power plants noise both inside and outside houses are summarized in .
The purpose of the experiment presented in this paper was to determine the effect of infrasound waves on variations in Delta, Theta, Alpha, SMR, Beta1, and Beta2 waves in humans exposed to infrasound noise in an attempt to give a more objective evaluation of the impacts of infrasound generated by wind turbines.
Papers [13-18] report a statistically significant change in patterns of EEG and ECG signals in humans. Dominant changes were observed in the alpha rhythm during the infrasound exposure.
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