Numerical analysis of direct time-domain response of transient electromagnetic field in homogeneous half space

Near source time-domain electromagnetic field has the advantages of strong signal, great detection depth, and high accuracy, but according to the traditional transient electromagnetic field theory, the dipole approximation in near source zone will cause a bigger error. To carry out direct time-domain analytical research is one of methods to solve the problem. Under the assumption of point charge element, the paper gives direct time-domain analytic expression of transient electromagnetic field on the surface of uniform half space, and then derives direct time-domain analytic expression of transient electromagnetic field excited by square loop source. Then, on the half-space surface, made a comparison with the expression under the assumption of electric dipole source. Numerical results show that their calculation results have a little difference in the far source area but a big error in the near source area.