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Engineering, Technology & Applied Science Research Vol. 13, No. 1, 2023, 9837-9842 9837 
 

www.etasr.com Pathala & Jayasree: Design of a Shielded Room against EMP Signal as per MIL-STD 461 

 

Design of a Shielded Room against EMP Signal 

as per MIL-STD 461 
 

Venkata Sai Charishma Pathala 

Department of EECE, Gandhi Institute of Technology and Management, Deemed to be University, India 

cpathala@gitam.in 

(corresponding author)  

 

Pappu V. Y. Jayasree 

Department of EECE, Gandhi Institute of Technology and Management, Deemed to be University, India 

jpappu@gitam.in 

 
 

Received: 30 September 2022 | Revised: 3 November 2022 | Accepted: 5 November 2022 

 

ABSTRACT 

Electromagnetic shielding is the best technique to protect equipment from the Electromagnetic Pulse 

(EMP) signal. This paper explains how effectively the equipment will be protected within a shielded room 

against EMP signals. The shielded room is designed with different points of entry used to provide electrical 

connections to the Equipment Under Test (EUT) in a honeycomb structure for ventilation to protect the 

equipment from the EMP signal. The shielded room with four points of entry and honeycomb structures is 

designed, analyzed theoretically, and simulated in the CST Studio. The points of entry (PoE) and the 

honeycomb structure are designed based on MIL-STD-461 E/F/G (by following this standard the 

maximum frequency of EMP signal is 100MHz). It is observed that by increasing the size of the PoE the 

shielding effectiveness value decreases by 20dB for perfect electrical conductor (PEC) material of 2mm 

thickness. It is concluded that the equipment will be more protected when it is placed nearer to the front 

wall or in the middle of the shielded room. The performance of the shielded room will not be affected with 

honeycomb structures which will provide 220dB Shielding Effectiveness (SE). 

Keywords-Electromagnetic Pulse (EMP); Point of Entry (PoE); honeycomb structure; MIL-STD-461 E/F/G; 

Shielding Effectiveness (SE); Perfect Electrical Conductor (PEC) 

I. INTRODUCTION  

In the present electromagnetic environment, the protection 
of equipment related to medical or military applications is of 
utmost priority. Equipment shielding is achieved by designing 
a shielded room. Usually, the shielded room will be designed 
by placing gaskets during the design of the door of the room, a 
honeycomb structure for ventilation, and apertures for the 
routing of cables. The main motto of this shielded room is to 
protect the electronic equipment from the interference of the 
dangerous signal strength of EMPs. The most effective method 
to safeguard the equipment from Electromagnetic Interference 
(EMI) is shielding and filtering [1-4]. The performance of a 
shield is defined by its SE value which is obtained from taking 
the difference between the received power with shield material 
and without it [5]. The shielding technique is used in many 
fields like aerospace engineering or medical and military 
equipment. In aerospace applications, different combinations of 
shielding materials are used to provide shielding to the aircraft 
[6]. Even the human brain can be protected from mobile 
radiation by placing shields coated with different types of 
shielding materials [7]. 

The simulated data for electromagnetic calculations can be 
acquired by various numerical methods [8], but the 
computations usually require long time. So, the analytic 
method has a better performance than the numerical methods. 
The analytical methods are classified in two types, i.e. based on 
aperture coupling between the aperture [9, 10] and based on the 
transmission line theory. The design of metallic shielded rooms 
is used to reduce the leakage signals from external 
electromagnetic fields. According to the IEEE Standard 299, 
the SE is used for the calculation of the effectiveness of 
metallic shielded enclosures [11]. The materials used in the 
design of shielded rooms are considered based on their 
conductivity and the frequency of operation. In this paper, the 
material used in the design was a perfect electrical conductor, 
in theoretical calculations the conductivity value of the 
materials is not considered while calculating the SE of the 
shielded room. The calculations of SE can be done with many 
methods. One of these is to add three parameters (Reflection 
loss (R), Absorption loss (A), Multiple reflections (M)) to 
obtain the SE value. 

SEdB = RdB +AdB + MdB    (1) 



Engineering, Technology & Applied Science Research Vol. 13, No. 1, 2023, 9837-9842 9838 
 

www.etasr.com Pathala & Jayasree: Design of a Shielded Room against EMP Signal as per MIL-STD 461 

 

Another method for the calculation of electrical SE (ESE) is 
achieved by considering the difference between the field signal 
in the presence and the absence of the shield as in (2). EA and 
EP are the electric field intensities without and with an 
enclosure, respectively. 

ESE = 20 log
��
��[dB]        (2) 

The SE value depends on the size and the number of Points 
of Entry (PoE). The PoE is defined by the frequency of the 
input signal. The maximum frequency of the EMP signal is 
100MHz, so that the PoE are designed with a cut of frequency 
greater than the frequency of the input signal. Leakage of 
signal occurs when the wavelength of the signal is shorter than 
the size of the PoE. 

II. DESIGN OF THE SHIELDED ROOM 

The shielded room was designed to protect equipment 
against EMP signals. The EMP signal has a high amplitude and 
short duration. The characteristics of an EMP signal is a double 
exponential voltage pulse with amplitude of 55kV, rise/fall 
time 2.3ns, pulse width 22.73ns as per MIL-STD 461 E/F/G 
[12] (Figure 1). The EMP signal is given as an input to the 
shielded room, the equipment in the shielded room is protected 
by providing all power connections to the equipment. The 
design of PoE for a shielded room must consider the frequency 
component of the EMP signal. The frequency of the EMP 
signal is calculated by taking the inverse of its period. The 
maximum frequency of the EMP signal is 100MHz, considered 
from the military standard MIL-STD 461 E/F/G and the PoE 
are designed such that they should not allow the entry of the 
EMP signal. 

 

 

Fig. 1.  EMP signal waveform. 

 

Fig. 2.  A shielded room with different POE. 

The shielded room with different PoE for routing the power 
cables and honeycomb structure to provide ventilation to the 
equipment is shown in Figure 2.  

The shielded room was designed with 4 PoE with different 
cutoff frequencies to protect. The PoE is considered as the 
waveguide. The maximum frequency of the EMP signal is 
100MHz so that the waveguides are designed with a cutoff 
frequency greater than that, so that the equipment is protected 
from the EMP signal. The frequency of the PoE is shown in 
Table I. Honeycomb structures were considered for 
vendilation. Two honeycomb structures with cutoff frequency 
of 40GHz were placed in parallel at the top of the room. The 
design dimensions of the shielded room with honeycomb 
structure are also given in Table I. 

TABLE I.  SHIELDED ROOM DIMENSIONS 

Parameters Length Width Height 

RF shielded room d = 2m a = 2m b = 2m 

Honeycomb panel r = 0.45m 

PoE l (m) w (m) Cutoff frequency (fc) 

P1 0.1 0.05 1.5GHz 

P2 0.075 0.0375 2 GHz 

P3 0.06 0.03 2.5 GHz 

P4 0.05 0.025 3 GHz 

 

III. MATHMATICAL ANALYSIS 

A. Single Point of Entry 

The effectiveness of the metallic shielded room can be 
determined mathematically by considering a single PoE by 
using the Transmission Line Model (TLM) method [13]. The 
equivalent circuit of the shielded room with PoE is represented 
here. 

 

 
Fig. 3.  Circuit model of the shielded room with PoE. 

From the equivalent circuit model, Thevenin’s theorem is 
applied to calculate the value of SE. The Q point represents the 
position of the equipment. The length of the PoE is L. The 
applied input voltage is denoted by V0, the input impedance of 
the equivalent circuit is Z0, a single PoE is considered in the 
circuit model, and its impedance is ZPoE. The SE value is 
calculated at distance X from the aperture. 

�� � ��	�
�	��	�
�      (3) 

��� � ��

�
� �
�tan �

���
� �   (4) 

 
� �  	�	�
�	��	�
�      (5) 

k

V 



Engineering, Technology & Applied Science Research Vol. 13, No. 1, 2023, 9837-9842 9839 
 

www.etasr.com Pathala & Jayasree: Design of a Shielded Room against EMP Signal as per MIL-STD 461 

 

The dominant mode of propagation in the rectangular 
waveguide is the TE10 mode and its characteristic impedance 
is: 


� � �����( )"        (6) 
where # � $��  and the propagation constant %� is: 

%� � %� ∗ �1 − (#)�)     (7) 
where %� � �*$� . 

Zg and Pg are imaginary frequencies below the cutoff 
frequency. Then V1, Z1, which are the short circuit terminals of 
the wave guide to Q are transformed by attributing an 
equivalent voltage V2, source impedance Z2, and load 
impedance Z3: 

�� � �+,-./�012�345+506.78/�012
    (8) 


� � 	+�39:;8/�012��345+506:;8/�012
    (9) 


< � �
� tan(= − >)    (10) 
The voltage at point Q is:  

�? � ��	<(	��	<)     (11) 
The SE is: 

SE = -20 log10|2VQ /V0|      (12) 

B. Multiple Points of Entry 

A shielded room with multiple PoE of different sizes was 
designed to protect the equipment from the EMP signal. The 
maximum frequency of the EMP signal should be considered 
while designing the PoE, so that no external signal is allowed 
inside the room. The multiple PoE of the side wall of the 
shielded room can be seen in Figure 4. 

 

 
Fig. 4.  Hardening of EMP signal with multiple PoE. 

A shielded room with length and breadth a and b, 
respectively, with an array of entries with dimensions of l, w is 
considered. The distance between the PoE is defined as dh and 
dv. @�  and Y0 are the free-space wavelength and the intrinsic 
admittance. Each PoE is considered as a rectangular hole 
denoted as d, where h, s are its length and width. 

d = 0.636(h + s)    (13) 

The SE calculation for multiple PoE when an EMP signal is 
applied to shielded room follows. The admittance of the 
equivalent circuit is given by [19]: 

A�
�B
A� � −C

<DE DF  $�
*DG + �

�II
*$�D" J∑ ∑ 4

∈M N"
DF" +

∈O P"
DE"

6 C��(>)QNR�QPR� S (14) 
The argument of the Bessel function is: 

> � T*D(P" /DE" �N" /DF" )/�)+/"V(P" /DE" � N" /DF")/�)+/"    (15) 
ZPoEs = 1/YPoEs represents the PoE array connecting the free 

space [14]. Figure 4 shows multiple PoE placed on the shielded 
room wall. The effective wall impedance ZPoEs

1
 is the inverse of 

ZPoEs. Using an impedance ratio concept, ZPoEs becomes: 

zah
1 
  = Zah�W∗X�∗Y �    (16) 

where the length l and width w of multiple PoE are:  

Z �  D[� + \(] − 1) ∗ =ℎ) +
D[
�      (17) 

w�  D_� + \(` − 1) ∗ =a) +
D_
�     (18) 

where m and n represent the number of apertures in length and 
width of the array, respectively. 

�� � /��∗	�[
+2

(	��	�[+ )      (19) 


� � (	�∗	�[
+ )

(	��	�[+)    (20) 

The SE is: 

SE = -20 log10|2VQ /V0|    (21) 

C. Honeycomb Structure 

The attenuation constant for the wave guide is given below 
[15]. The attenuation constant is used for the calculation of the 
SE value of the wave guide: 

b � c(d ∈)+"e f − 1    (22) 
where fc is the cutoff frequency of the waveguide. The 
attenuation constant of the waveguide in dB can be calculated 
by placing the cutoff frequency value in (22). The SE value for 
a single hexagon cell (honeycomb structure) is calculated by 
using (23): 

SEij  �  17.5 D� e1 − �
�n

oppqr�
�
          (23) 

In [16], an infinite array of parallel-plate waveguides is 
analyzed by the Wiener-Hopf method. The resulting equation is 
shown below. The first part gives the SE of the unit cell of a 
hexagon waveguide, while the second term is the SE of an 
infinite array of parallel-plate waveguides [24]. 

SEij  �  17.5 D� e1 − �
�n

oppqr�
� − 20 log�� �x0 * cos { (24) 

where k is the wave number, g is a transverse dimension of the 
waveguide, and φ is the angle of an incident wave.  



Engineering, Technology & Applied Science Research Vol. 13, No. 1, 2023, 9837-9842 9840 
 

www.etasr.com Pathala & Jayasree: Design of a Shielded Room against EMP Signal as per MIL-STD 461 

 

The SE equation for a hexagon structure has been modified 
by adding a third term to (24), so the performance of the 
hexagon structure at lower frequency is increased. The 
normalized frequency during the design of the honeycomb 
structure should be greater than 5 times the radius of the cell of 
the honeycomb structure. SE value does not depend on the 
number of hexagon cells in the honeycomb structure, but on the 
size and the length of a single cell. 

|}D~  = 17.5 D� e1 − �
�n

oppqr�
�
  

−20 log�� �x0 * cos { − 20 log��
��0 

   (25) 

IV. SIMULATIONS 

A. Shielded Room with a Single Point of Entry 

A shielded room with a size of 2m×2m×2m with a single 
PoE of size 0.075m×0.0375m is shown in Figure 5. The probe 
was placed at the center of the shielded room. The position of 
the probe varied inside the room to find the fields inside the 
room with an EMP signal transmitted continuously to the 
shielded room. The material used in the design of the shielded 
room is Perfect Electrical Conductor (PEC). The thickness of 
the shielded material is 2mm. 

SE value varies with the size of the PoE. A PoE of size 
10cm×5cm is considered and the SE value is 255dB. If the size 
of the aperture is decreased, the SE value is increased as shown 
in Table II. The size of the PoE depends on the frequency of 
the EMP signal. Figure 6 shows the SE value for 4 apertures. 

TABLE II.  SE VALUES FOR DIFFERENT POINTS OF ENTRY 

PoE a (m) b (m) SE (dB) 

P1 0.1 0.05 290 

P2 0.075 0.0375 310 

P3 0.06 0.03 320 

P4 0.05 0.025 330 

 

 

Fig. 5.  Shielded room with a single PoE. 

B. Shielded Room with Multiple Points of Entry 

The shielded room with different entries was designed in 
CST simulation tool as shown in Figure 6. The SE value for an 
individual PoE is shown in Figure 7. 

Let us consider shielded rooms with 4 PoE with different 
dimensions. The dimensions of an entry depend on its cutoff 
frequency. The cutoff frequency should be greater than the 

frequency of the EMP signal. In this condition the SE value 
meets the military standards MIL-STD-188-125-1 and 2. 
Figure 8 shows the total SE value of 4 different dimensions. 
The SE value decreases with the frequency of operation, which 
is below the resonant frequency. The resonant frequency of the 
shielded room was calculated by considering the room 
dimensions along with mode of propagation. The electric field 
probe is considered at the center of the shielded room, so that 
maximum SE value is obtained at that point. The SE value for 
4 different PoE is 250dB. 

 

 

Fig. 6.  Shielded room with 4 PoE with different sizes. 

 

Fig. 7.  SE value for different PoE sizes when an EMP signal is given as 
input. 

 
Fig. 8.  Effect of SE when an EMP is applied to multiple PoE. 



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C. Shielded Room with Honeycomb Structures 

The shielded room was designed with honeycomb 
structures used for ventilation, placed at the top of the room. 
The honeycomb structures were designed such that no external 
signal would enter the shielded room. Figure 9 shows the 
honeycomb structure. The honeycomb structures placed on the 
shielded room are shown in Figure 10. The SE value is 
calculated when the EMP signal is applied to the room.  

 

(a) 

 

(b) 

 

Fig. 9.  Cell dimension details of the honeycomb structure, (b) total 
honeycomb structure. 

 

Fig. 10.  Shielded room with 2 honeycomb structures. 

D. Shielded Room with Points of Entry and Honeycomb 
Structure 

The shielded room was designed with 4 PoE and 2 
honeycomb structures, as shown in Figure 11. The EMP signal 
is incident on the shielded room with a voltage of 55kv. The SE 
value is calculated by placing the field probe at the center of 
the room. The total shielded room SE value is given in Figure 
12. 

 

Fig. 11.  Shielded room with 4 PoE and 2 honeycomb structures. 

 

Fig. 12.  The electric field value for a totally shielded room with 4 PoE and 
2 honeycomb structures. 

Total SE is calculated by taking the difference between the 
electric field with and without shield. 

E. Effect of Varying Field Probe 

The EMP signal is incident directly to the shielded room, 
which has dimensions of 2m×2m×2m with a single PoE. The 
EMP signal is parallel to the shielded enclosure. In this case the 
polarization type is fixed, so the field probe inside the 
enclosure is varied so that the SE value varies with changes in 
the position of the probe. The field probe gives the position of 
the equipment so that maximum SE is noted. The shielded 
room with a single PoE is shown in Figure 4. The change in the 
value of SE with the position of the field probe is shown in 
Figure 8. Consider a point Q at a different distances x1, x2, x3 
from the front panel of the shielded room. The SE value 
increases when the position of the probe is near the wall of the 
shielded room as clearly observed in Figure 13. 

 

 
Fig. 13.  Varying position of the field probe in the shielded room when the 
EMP is applied. 



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By observing the graph of Figure 13, we note that the SE 
value increases when the position of the probe is to the shielded 
room front wall and at the center of the room, and decreases 
when the probe is near to the back wall of the shielded room. 

V. CONCLUSION 

Theoretical calculations and simulation analysis were 
conducted in this paper for a shielded room against EMP 
signals. The transmission line method was used in the 
theoretical calculations of the shielded room with 4 different 
PoE dimensions. The smallest PoE with 0.05m length and 
0.025m width has better SE value of 330dB than a PoE with 
greater size, with 0.1m length and 0.05m width, where the SE 
value decreases to 250dB. Simulation analysis is done with 
3DEM CST modeling tool to verify the combined effect of 
multiple PoE and honeycomb structures. The total SE value for 
a shielded room with 4 PoE and 2 honeycomb structures is 
140dB. 

The novelty of this paper is that it was conducted as per 
MIL-STD-188-125-1/2 to protect the equipment from external 
EMP signals. This design of shielded room is useful for RF 
engineers that need to estimate the interference levels in 
sensitive equipment due to EMP signals. 

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