Measured equation of invariance in the time domain (TD-MEI) has been used as an FDTD-ABC. The TD-MEI coefficients, are derived using a new technique named "self metron". Unlike the traditional MEI, in this technique there is no need to use metrons to find the MEI coefficients. The real field values of the same FDTD problem but with a PEC surface instead of a radiation boundary condition are sampled and used to find the MEI coefficients. The key is to locate the PEC mesh truncation, farther away than the MEI truncation boundary, such that during the sampling time interval, no wave reflects into the MEI truncation boundary. After the MEI coefficients are found, according to the "time invariance" property of the TD-MEI coefficients, the MEI boundary absorbs the wave for all times. The proposed technique is very fast and the results show that the accuracy is much higher than traditional absorbing boundary conditions and some other ABC's.
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