## 3 Relevant Research in Wind Farm Design and Optimization
### Electromagnetic Interference (EMI)
It is suggested that, in the back-scatter region, reflection is caused only by the metallic parts of the blades, thus the blade dimensions are used to calculate the radar cross section and typically results in a smaller \(Fz\), in contrast with the forward-scattering \(Fz\) in which the whole WT is considered to contribute to the electromagnetic signal modulation. A common accepted relation for \(\sigma_{S}\) [dBm\({}^{2}\)] was proposed by [PERSON] [314], as shown in Equation (48):  
\[10\log_{10}(\sigma_{S})=20\log_{10}\left(A_{B}\frac{f(\theta)}{\lambda}\right) +11-C \tag{48}\]  
where \(A_{B}\) [m\({}^{2}\)] is the superficial area of one blade, \(f(\theta)\) is a function describing the amplitude of the scattered signal in the direction \(\theta\), and \(C\) is a calibration constant with an approximated value of 15 dB. Other complex approaches have been proposed [36, 311], however, significant further work is required to develop more precise techniques to calculate the radar cross section area and the overall EMI effects of WTs and wind farms. In particular, techniques to determine the effects of irregular terrain and the effects of the blade shape and structural materials have yet to be developed and validated. value of the sound pressure, and \(P_{0}=2\ \times 10^{-5}\) Pa, a reference pressure value, respectively. The total sound pressure (\(L_{\mathrm{P,T}}\)) of \(n_{s}\) sound pressure levels can be quantified using Equation (52):  
\[L_{\mathrm{P,T}}=10\log_{10}\sum\
olimits_{s=1}^{s=n_{s}}10^{L_{\mathrm{P}(s)} /10} \tag{52}\]  
Equation (52) implies that by adding two sound pressure levels of the same magnitude an increase of 3 dB can be obtained over the base level. An equivalent sound pressure level \(L_{\mathrm{eq,T}}\) is the value of a continuous steady sound that, within the specified time interval (\(T\)), has the same mean square sound pressure level as the sound under consideration, which varies with time [124,125]:  
\[L_{\mathrm{eq,T}}=10\log_{10}\left(\frac{1}{T}\int_{0}^{T}\frac{P^{2}}{P_{0}^{ 2}}\,\mathrm{d}t\right) \tag{53}\]  
A similar calculation can be performed using A-weighted values to give \(L_{\mathrm{Aeq,T}}\):  
\[L_{\mathrm{Aeq,T}}=10\log_{10}\left(\frac{1}{T}\int_{0}^{T}\frac{P_{A}^{2}}{P_ {0}^{2}}\,\mathrm{d}t\right) \tag{54}\]  
where \(L_{\mathrm{Aeq,T}}\) is the equivalent continuous A-weighted sound pressure level determined over time \(T\) and \(P_{\mathrm{A}}\) is the instantaneous A-weighted sound pressure. The sound intensity (\(I=W/A\)) is the sound power transmitted through and unit area, \(A\). The sound intensity far from the source, assuming a uniform noise flux, can be approximated as \(I=P^{2}/Z_{0}\), where \(P\) is the RMS value of the sound pressure level, and \(Z_{0}\) is the characteristic acoustic impedance. The sound pressure level may be expressed in terms of sound intensity as shown in Equation (55):  
\[L_{\mathrm{P}}=10\log_{10}\left(\frac{I}{I_{\mathrm{ref}}}\right) \tag{55}\]  
where \(I_{\mathrm{ref}}\) is a reference intensity (e.g., \(10^{-12}\) W/m\({}^{2}\)). In addition, the sound may spread in an isotropic or anisotropic way. In the former case, a spherical or a hemispherical spreading can be assumed. For a spherical spreading, the intensity will decrease with distance from the source of sound as \(I=W/4\pi r_{s}^{2}\), where \(r_{s}\) is the radial distance from the source. Hence, under conditions of ideal spherical spreading, the sound pressure level can be approximated as shown in Equation (56):  
\[I_{S}=P_{\mathrm{T}}-A_{\mathrm{TW}}+10\log_{10}\left(\frac{4\pi\sigma_{S}}{ \lambda^{2}}\right)-A_{\mathrm{WR}}+G_{\mathrm{WR}} \tag{44}\]0  
Equation (56) implies that for each doubling of distance the sound pressure level is reduced by 6 dB. In addition, it implies that the terrain surface and all the nearby objects will act as perfect noise absorbers, otherwise sound reflections may occur and the sound pressure level may not decay with the same rate.