{"id":290084,"date":"2023-06-23T13:17:27","date_gmt":"2023-06-23T13:17:27","guid":{"rendered":"\/forum\/forums\/topic\/unexpected-s-matrix-from-eme-propagation\/"},"modified":"2023-06-23T13:17:27","modified_gmt":"2023-06-23T13:17:27","slug":"unexpected-s-matrix-from-eme-propagation","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/unexpected-s-matrix-from-eme-propagation\/","title":{"rendered":"Unexpected S matrix from EME propagation"},"content":{"rendered":"<p>Hello,<br \/>I have encountered an unexpected result in simulating the transfer matrix of a repeated unit cell with EME.<\/p>\n<p>Background:<\/p>\n<p>I have a waveguide bragg reflector with absorbing layer and I need to calculate the absorption in each layer. To do so, I need to calculate the coefficient of the various modes in a certain position of each unit cell, but because EME does not allow to do so, I need to extract the S-matrix of the unit cell and &#8220;propagate it&#8221; in Python. In this way I can retrieve the intensity of the modes also at intermediate position.&nbsp;<br \/>To validate my code, I decided to propagate a simple structure with my Python code and with EME and to compare the result. The structure is a waveguide bragg reflector (no absorbing layer) consisting of two units cells. After setting up the geometry, I did the following<\/p>\n<ul>\n<li>I calculated the S matrix of the basic unit cell with EME.&nbsp;\n<ul>\n<li>To do so, I set the period of&nbsp; the unit cells to 1, I run EME propagate, and I extracted the &#8220;internal S matrix&#8221; and sent it to Python.<\/li>\n<li>I used 20 modes in the calculation<\/li>\n<\/ul>\n<\/li>\n<li>I used the S matrix of the unit cell to calculate the S matrix of a 2-cell-structure in Python.\n<ul>\n<li>The calculation of the total S matrix of two cascaded cells is an analytical solution and I verified it by comparing with litterature (here: https:\/\/ieeexplore.ieee.org\/document\/1125369). Thus, I am pretty sure of the correctness of the formulation.<\/li>\n<\/ul>\n<\/li>\n<li>I calculated the total S matrix also in EME\n<ul>\n<li>I used EME propagate after setting the number of periods to 2.&nbsp;<\/li>\n<li>I extracted the &#8220;internal S matrix&#8221;<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p>Eventually, I compared the S matrices of the 2-unit-cells structure calculated with EME and with Python and I noticed that the results were quite different.<\/p>\n<p>I have checked the correctness of the code that calculates the total S matrix and I am fairly sure of its correctness. Therefore, I had the doubt that probably I am not interpreting correctly the meaning of the &#8220;Internal S matrix&#8221; that EME propagate provides. Because the documentation about the this result and how it is obtained is limited, is there anyone that can give me an insight of what could be wrong in my reasoning?<\/p>\n","protected":false},"template":"","class_list":["post-290084","topic","type-topic","status-closed","hentry","topic-tag-EME-1"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_subscription":["200502","2592"],"_bbp_author_ip":["23.217.200.71"]," _bbp_last_reply_id":["0"]," _bbp_likes_count":["0"],"_btv_view_count":["1450"],"_bbp_topic_status":["unanswered"],"_bbp_status":["publish"],"_bbp_topic_id":["290084"],"_bbp_forum_id":["27833"],"_bbp_engagement":["2592","200502"],"_bbp_voice_count":["2"],"_bbp_reply_count":["7"],"_bbp_last_reply_id":["290973"],"_bbp_last_active_id":["290973"],"_bbp_last_active_time":["2023-06-29 17:04:54"]},"test":"filippo001e-ntu-edu-sg"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/290084","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics"}],"about":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/types\/topic"}],"version-history":[{"count":0,"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/290084\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=290084"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}