127 lines
3.4 KiB
Python
127 lines
3.4 KiB
Python
# -*- coding: utf-8 -*-
|
|
"""
|
|
Tutorials / radar cross section of a metal sphere
|
|
|
|
Tested with
|
|
- python 3.10
|
|
- openEMS v0.0.35+
|
|
|
|
(c) 2016-2023 Thorsten Liebig <thorsten.liebig@gmx.de>
|
|
"""
|
|
|
|
### Import Libraries
|
|
import os, tempfile
|
|
from pylab import *
|
|
|
|
from CSXCAD import ContinuousStructure
|
|
from openEMS import openEMS
|
|
from openEMS.physical_constants import *
|
|
from openEMS.ports import UI_data
|
|
|
|
### Setup the simulation
|
|
Sim_Path = os.path.join(tempfile.gettempdir(), 'RCS_Sphere')
|
|
post_proc_only = False
|
|
|
|
unit = 1e-3 # all length in mm
|
|
|
|
sphere_rad = 200
|
|
|
|
inc_angle = 0 #incident angle (to x-axis) in deg
|
|
|
|
# size of the simulation box
|
|
SimBox = 1200
|
|
PW_Box = 750
|
|
|
|
### Setup FDTD parameters & excitation function
|
|
FDTD = openEMS(EndCriteria=1e-5)
|
|
|
|
f_start = 50e6 # start frequency
|
|
f_stop = 1000e6 # stop frequency
|
|
f0 = 500e6
|
|
FDTD.SetGaussExcite( 0.5*(f_start+f_stop), 0.5*(f_stop-f_start) )
|
|
|
|
FDTD.SetBoundaryCond( ['PML_8', 'PML_8', 'PML_8', 'PML_8', 'PML_8', 'PML_8'] )
|
|
|
|
### Setup Geometry & Mesh
|
|
CSX = ContinuousStructure()
|
|
FDTD.SetCSX(CSX)
|
|
mesh = CSX.GetGrid()
|
|
mesh.SetDeltaUnit(unit)
|
|
|
|
#create mesh
|
|
mesh.SetLines('x', [-SimBox/2, 0, SimBox/2])
|
|
mesh.SmoothMeshLines('x', C0 / f_stop / unit / 20) # cell size: lambda/20
|
|
mesh.SetLines('y', mesh.GetLines('x'))
|
|
mesh.SetLines('z', mesh.GetLines('x'))
|
|
|
|
### Create a metal sphere and plane wave source
|
|
sphere_metal = CSX.AddMetal( 'sphere' ) # create a perfect electric conductor (PEC)
|
|
sphere_metal.AddSphere(priority=10, center=[0, 0, 0], radius=sphere_rad)
|
|
|
|
# plane wave excitation
|
|
k_dir = [cos(np.deg2rad(inc_angle)), sin(np.deg2rad(inc_angle)), 0] # plane wave direction
|
|
E_dir = [0, 0, 1] # plane wave polarization --> E_z
|
|
|
|
pw_exc = CSX.AddExcitation('plane_wave', exc_type=10, exc_val=E_dir)
|
|
pw_exc.SetPropagationDir(k_dir)
|
|
pw_exc.SetFrequency(f0)
|
|
|
|
start = np.array([-PW_Box/2, -PW_Box/2, -PW_Box/2])
|
|
stop = -start
|
|
pw_exc.AddBox(start, stop)
|
|
|
|
# nf2ff calc
|
|
nf2ff = FDTD.CreateNF2FFBox()
|
|
|
|
### Run the simulation
|
|
if 0: # debugging only
|
|
CSX_file = os.path.join(Sim_Path, 'RCS_Sphere.xml')
|
|
if not os.path.exists(Sim_Path):
|
|
os.mkdir(Sim_Path)
|
|
CSX.Write2XML(CSX_file)
|
|
from CSXCAD import AppCSXCAD_BIN
|
|
os.system(AppCSXCAD_BIN + ' "{}"'.format(CSX_file))
|
|
|
|
|
|
if not post_proc_only:
|
|
FDTD.Run(Sim_Path, cleanup=True)
|
|
|
|
### Postprocessing & plotting
|
|
# get Gaussian pulse strength at frequency f0
|
|
ef = UI_data('et', Sim_Path, freq=f0)
|
|
|
|
Pin = 0.5*norm(E_dir)**2/Z0 * abs(ef.ui_f_val[0])**2
|
|
#
|
|
nf2ff_res = nf2ff.CalcNF2FF(Sim_Path, f0, 90, arange(-180, 180.1, 2))
|
|
RCS = 4*pi/Pin[0]*nf2ff_res.P_rad[0]
|
|
|
|
fig = figure()
|
|
ax = fig.add_subplot(111, polar=True)
|
|
ax.plot( nf2ff_res.phi, RCS[0], 'k-', linewidth=2 )
|
|
ax.grid(True)
|
|
|
|
# calculate RCS over frequency
|
|
freq = linspace(f_start,f_stop,100)
|
|
ef = UI_data( 'et', Sim_Path, freq ) # time domain/freq domain voltage
|
|
Pin = 0.5*norm(E_dir)**2/Z0 * abs(np.array(ef.ui_f_val[0]))**2
|
|
|
|
nf2ff_res = nf2ff.CalcNF2FF(Sim_Path, freq, 90, 180+inc_angle, outfile='back_nf2ff.h5')
|
|
|
|
back_scat = np.array([4*pi/Pin[fn]*nf2ff_res.P_rad[fn][0][0] for fn in range(len(freq))])
|
|
|
|
figure()
|
|
plot(freq/1e6,back_scat, linewidth=2)
|
|
grid()
|
|
xlabel('frequency (MHz)')
|
|
ylabel('RCS ($m^2$)')
|
|
title('radar cross section')
|
|
|
|
figure()
|
|
semilogy(sphere_rad*unit/C0*freq,back_scat/(pi*sphere_rad*unit*sphere_rad*unit), linewidth=2)
|
|
ylim([10^-2, 10^1])
|
|
grid()
|
|
xlabel('sphere radius / wavelength')
|
|
ylabel('RCS / ($\pi a^2$)')
|
|
title('normalized radar cross section')
|
|
|
|
show() |