algebraic3d
solid k1 = orthobrick (-0.1, -0.1, -0.8; 0.9, 0.1, 0.8);
solid k2 = orthobrick (0.1, -0.2, -0.6; 0.7, 0.2, 0.6);
solid k3 = orthobrick (0.6, -0.2, -0.02; 1, 0.2, 0.02);
solid kernel = k1 and not k2 and not k3;

solid box = orthobrick (-2, -2, -2; 3, 2, 2) -bc=1;

solid pl1 = plane (1.03, 0, 0; 1, 0, 0) -bc=5;
solid pl2 = plane (1, 0, 0; -1, 0, 0) -bc=6;

solid shield = orthobrick (0, -1.5, -1.5; 2, 1.5, 1.5)
	and pl1 and pl2 -bc=3;

solid coil = cylinder (0, 0, -1; 0, 0, 1; 0.4)
	and not cylinder  (0, 0, -1; 0, 0, 1; 0.2)
	and plane (0, 0, 0.4; 0, 0, 1)
	and plane (0, 0, -0.4; 0, 0, -1) -bc=3;


solid air =  box and not coil and not shield -bc=3;

tlo shield -col=[1, 0, 0];
tlo coil -col=[0, 1, 0];
tlo air  -col=[0, 0, 1] -transparent;

identify closesurfaces pl1 pl2;