## 2 Radiated Coupling and Active Noise Cancellation
Protection facilities are classified in stages or levels according to their location and purpose. The most directly affected outermost facilities, such as buildings or HEMP protection facilities, are classified as 1 st level barriers, and their physical size ranges from a few meters to several tens of meters. There are enclosures or small screen rooms enclosing equipment inside the protection facility. These facilities are classified into 2 nd and 3 rd level barriers. These additional barriers are as small as a few centimeters to tens of centimeters [16; 17; 18]. In this paper, the 2 nd \(\sim\) 3 rd level barrier was studied. The acoustics field has been studied for a long time to cancel external noise. This technique, called ANC, detects external noise sources through speakers and cancels them with a microphone. For this purpose, the Finite Impulse Response (FIR) filter is used, and the most commonly used algorithm is the FxLMS technique. Recently, a canceling technique using the Genetic Algorithm (GA), one of the optimization techniques, was studied [10]. A technique for attenuating internally generated electromagnetic interference using the principle of the ANC technique was introduced in the paper [8]. External interference signals, expressed as sinusoids, are measured by sensors inside the shielding facility. At this time, we measure the amplitude, frequency, and phase of the external signal. Based on this measured information, it internally generates a signal with the same amplitude and frequency, but it is 180 degrees out of phase with the active source. At this time, the internally observed signal follows this formula for the sinusoidal signal. \[S_{obv}(t)=\frac{(A_{I}\cos(2\pi ft+\phi)+A_{ac}\cos(2\pi f^{\prime}t+\phi^{ \prime}(t)))^{2}}{Z} \tag{5}\]  
where \(A_{I}\) is the amplitude of the IEMI, \(f\) is the frequency of the IEMI, and \(\phi\) is the phase of the IEMI \(A_{ac}\) is the amplitude of the generated signal, \(f^{\prime}\) is the frequency of the generated signal, \(\phi^{\prime}\) is the phase of the generated signal. At this time, for the internally measured signal to be zero, the amplitude and frequency must be the same, and the phase must be different by \(\pi\). To satisfy this condition,  
\[A_{I}=A_{ac},\;f=f^{\prime},\;\left|\phi^{\prime}-\phi\right|=\pi \tag{6}\]  
This formula must be satisfied. It is relatively easy at this time to make the amplitudes equal or to make the phase difference 180 degrees, but it is challenging to make the frequency accurate. In the acoustics field, the ANC technique is used to cancel the audible frequencies, which are in the range of about 20 Hz to 20 kHz. It is relatively easy to measure and regenerate this frequency. However, the frequency applied to electronic warfare is several GHz, and it is impossible to make the same frequency for these attacks. Figure 2 below shows that the internal field is amplified rather than canceled when there is a difference of only 20 Hz internally for an external attack with a frequency of 2 GHz. MPM is used to solve this amplification. First, assuming that the same frequency cannot be generated, create a small signal equal to 2.5% of IEMI on active power. Then, the synthesized signal is analyzed once again. If there is a frequency difference of about 20 Hz, as in the above example, the internal signal is not canceled. The IEMI and the internal active signal combine to produce a 20 Hz sine wave. At this time, this signal is analyzed by MPM. MPM is a technique that performs extrapolation based on given data and is applied to a sinusoidal signal very accurately. This method has been verified through many papers. Figure 3 shows the results of estimating randomly generated signals using MPM. The red line represented the original signal and generated a signal with a total of 250 points. At this time, the estimation was performed using only about 1/10 of the signals. The red area shown in the Figure 3 is the sampling area, and the area indicated by the blue line is the estimated area.