{"id":263,"date":"2025-04-14T08:41:22","date_gmt":"2025-04-14T08:41:22","guid":{"rendered":"https:\/\/zeugmatographix.org\/ocra\/?p=263"},"modified":"2025-04-14T08:41:59","modified_gmt":"2025-04-14T08:41:59","slug":"a4im-osi%c2%b2-sar-power-monitor","status":"publish","type":"post","link":"https:\/\/zeugmatographix.org\/ocra\/2025\/04\/14\/a4im-osi%c2%b2-sar-power-monitor\/","title":{"rendered":"A4IM OSI\u00b2 SAR Power Monitor \u00b5C Interface PCB"},"content":{"rendered":"\n<p>Hello OCRA, Tabletop and OSI\u00b2 community,<\/p>\n\n\n\n<p>In this blog post I want to share our SAR Power Monitor \u00b5C Interface for the OSI\u00b2 2MHz Halbach MRI as part of the A4IM project. The PCB uses the ADL5511 RF-to-RMS IC to convert the applied RF power to a envelope RMS voltage. This voltage gets sampled with a stepping of 10\u00b5s by the micro controller STM32L476RGT compute module.<\/p>\n\n\n\n<figure class=\"wp-block-image aligncenter size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"772\" height=\"1024\" src=\"https:\/\/zeugmatographix.org\/ocra\/wp-content\/uploads\/2025\/04\/SAR_Power_Monitor_Rev004_Image_Front_Cut-1-772x1024.png\" alt=\"\" class=\"wp-image-265\" srcset=\"https:\/\/zeugmatographix.org\/ocra\/wp-content\/uploads\/2025\/04\/SAR_Power_Monitor_Rev004_Image_Front_Cut-1-772x1024.png 772w, https:\/\/zeugmatographix.org\/ocra\/wp-content\/uploads\/2025\/04\/SAR_Power_Monitor_Rev004_Image_Front_Cut-1-226x300.png 226w, https:\/\/zeugmatographix.org\/ocra\/wp-content\/uploads\/2025\/04\/SAR_Power_Monitor_Rev004_Image_Front_Cut-1-768x1018.png 768w, https:\/\/zeugmatographix.org\/ocra\/wp-content\/uploads\/2025\/04\/SAR_Power_Monitor_Rev004_Image_Front_Cut-1-1158x1536.png 1158w, https:\/\/zeugmatographix.org\/ocra\/wp-content\/uploads\/2025\/04\/SAR_Power_Monitor_Rev004_Image_Front_Cut-1.png 1340w\" sizes=\"auto, (max-width: 772px) 100vw, 772px\" \/><figcaption class=\"wp-element-caption\"><em>Image1: SAR Power Monitor \u00b5C Interface PCB.<\/em><\/figcaption><\/figure>\n\n\n\n<p>The SAR Power Monitor \u00b5C Interface has two RF inputs.<\/p>\n\n\n\n<p>In 1 (Forward power):<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Peak detection<\/li>\n\n\n\n<li>10s running average SAR limit (10ms check interval)<\/li>\n\n\n\n<li>6min running average SAR limit (10s check interval)<\/li>\n<\/ul>\n\n\n\n<p>In 2 (Reflected power)<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Peak detection (programmable percentage of forward power, default 20%)<\/li>\n<\/ul>\n\n\n\n<p>The SAR Power Monitor gets integrated in the RF chain of the OSI\u00b2 Halbach MRI with a dual directional coupler (f.e. Mini-Circuits ZFBDC20-61HP+) on the RFPA output. When a limit is exceeded the SAR Power Monitor will switch off the RFPA blanking signal and so the RFPA. The blanking signal is switched by a solid-state relais (Finder 34.81.7.005.9024), which can handle external 1.5V-33V blanking signals.<\/p>\n\n\n\n<figure class=\"wp-block-image aligncenter size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"576\" src=\"https:\/\/zeugmatographix.org\/ocra\/wp-content\/uploads\/2025\/04\/SAR_Power_Monitor_RFchain-1024x576.png\" alt=\"\" class=\"wp-image-266\" srcset=\"https:\/\/zeugmatographix.org\/ocra\/wp-content\/uploads\/2025\/04\/SAR_Power_Monitor_RFchain-1024x576.png 1024w, https:\/\/zeugmatographix.org\/ocra\/wp-content\/uploads\/2025\/04\/SAR_Power_Monitor_RFchain-300x169.png 300w, https:\/\/zeugmatographix.org\/ocra\/wp-content\/uploads\/2025\/04\/SAR_Power_Monitor_RFchain-768x432.png 768w, https:\/\/zeugmatographix.org\/ocra\/wp-content\/uploads\/2025\/04\/SAR_Power_Monitor_RFchain-1536x864.png 1536w, https:\/\/zeugmatographix.org\/ocra\/wp-content\/uploads\/2025\/04\/SAR_Power_Monitor_RFchain-2048x1152.png 2048w, https:\/\/zeugmatographix.org\/ocra\/wp-content\/uploads\/2025\/04\/SAR_Power_Monitor_RFchain-1920x1080.png 1920w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\"><em>Image2: SAR Power Monitor integration into the OSI\u00b2 Halbach RF-chain.<\/em><\/figcaption><\/figure>\n\n\n\n<p>The blanking is secured by a blanking logic circuit on the PCB, that contains a watch-dog IC to monitor the functionality of the \u00b5-Controller, and a TLC555 timer IC. The TLC555 is used as an RS-flip-flop and ensures that the blanking signal stays off when an SAR error occurs (Out signal of the \u00b5C) or the \u00b5C is not in sampling mode. Only a dedicated Reset signal can to reset the blanking output. As the solid state relais is a power switch an 50Ohm terminating resistor may be required at the blanking input of the RFPA.<\/p>\n\n\n\n<figure class=\"wp-block-image aligncenter size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"576\" src=\"https:\/\/zeugmatographix.org\/ocra\/wp-content\/uploads\/2025\/04\/SAR_Power_Monitor_RF-RMS-1024x576.png\" alt=\"\" class=\"wp-image-267\" srcset=\"https:\/\/zeugmatographix.org\/ocra\/wp-content\/uploads\/2025\/04\/SAR_Power_Monitor_RF-RMS-1024x576.png 1024w, https:\/\/zeugmatographix.org\/ocra\/wp-content\/uploads\/2025\/04\/SAR_Power_Monitor_RF-RMS-300x169.png 300w, https:\/\/zeugmatographix.org\/ocra\/wp-content\/uploads\/2025\/04\/SAR_Power_Monitor_RF-RMS-768x432.png 768w, https:\/\/zeugmatographix.org\/ocra\/wp-content\/uploads\/2025\/04\/SAR_Power_Monitor_RF-RMS-1536x864.png 1536w, https:\/\/zeugmatographix.org\/ocra\/wp-content\/uploads\/2025\/04\/SAR_Power_Monitor_RF-RMS-2048x1152.png 2048w, https:\/\/zeugmatographix.org\/ocra\/wp-content\/uploads\/2025\/04\/SAR_Power_Monitor_RF-RMS-1920x1080.png 1920w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\"><em>Image3: SAR Hardware Monitor RF-to-RMS IC schematic. The VRMS output capacitor and resistor needs to be matched to the LARMOR frequency. This configuration is optimized for 62MHz (1.5T), but still usable for the Halbach Larmor frequency of 2MHz (50mT). This is due to the SAR Power Monitor software calibration process.<\/em><\/figcaption><\/figure>\n\n\n\n<figure class=\"wp-block-image aligncenter size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"576\" src=\"https:\/\/zeugmatographix.org\/ocra\/wp-content\/uploads\/2025\/04\/SAR_Power_Monitor_Blanking-1024x576.png\" alt=\"\" class=\"wp-image-268\" srcset=\"https:\/\/zeugmatographix.org\/ocra\/wp-content\/uploads\/2025\/04\/SAR_Power_Monitor_Blanking-1024x576.png 1024w, https:\/\/zeugmatographix.org\/ocra\/wp-content\/uploads\/2025\/04\/SAR_Power_Monitor_Blanking-300x169.png 300w, https:\/\/zeugmatographix.org\/ocra\/wp-content\/uploads\/2025\/04\/SAR_Power_Monitor_Blanking-768x432.png 768w, https:\/\/zeugmatographix.org\/ocra\/wp-content\/uploads\/2025\/04\/SAR_Power_Monitor_Blanking-1536x864.png 1536w, https:\/\/zeugmatographix.org\/ocra\/wp-content\/uploads\/2025\/04\/SAR_Power_Monitor_Blanking-2048x1152.png 2048w, https:\/\/zeugmatographix.org\/ocra\/wp-content\/uploads\/2025\/04\/SAR_Power_Monitor_Blanking-1920x1080.png 1920w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\"><em>Image4: SAR Hardware Monitor blanking logic schematic.<\/em><\/figcaption><\/figure>\n\n\n\n<p>Like the A4IM OSI\u00b2 TR-Switch the SAR Power Monitor has a EMI housing. <\/p>\n\n\n\n<p>The matching SAR Power Monitor \u00b5C software will be shared in future.<\/p>\n\n\n\n<p>The PCB .gerber files, schematic, material list and fabrication plan are in the .zip file:<\/p>\n\n\n\n<p><a href=\"https:\/\/cloud.ovgu.de\/s\/wMwiq5zaRJ6yXYa\">https:\/\/cloud.ovgu.de\/s\/wMwiq5zaRJ6yXYa<\/a><\/p>\n\n\n\n<p>CAD files, vector graphics material lists are in the following .zip file:<\/p>\n\n\n\n<p><a href=\"https:\/\/cloud.ovgu.de\/s\/f34NM6btnqFXwXS\">https:\/\/cloud.ovgu.de\/s\/f34NM6btnqFXwXS<\/a><\/p>\n\n\n\n<p class=\"has-vivid-red-color has-text-color has-link-color wp-elements-0deaf0b0c591b669e9c9c8ffe0410a5a\">When downloading the files, you declare to cite us as creator of the A4IM OSI\u00b2 SAR Power Monitor when using in your projects or publications (Marcus Prier, Forschungscampus STIMULATE, Otto-von-Guericke University Magdeburg). You are not allowed to remove logos or references.<\/p>\n\n\n\n<p>If you have questions about the A4IM OSI\u00b2 SAR Power Monitor or interest in preassembled PCBs, Tabletop and OCRA components or even a whole OCRA Tabletop MRI System contact me via marcus.prier@ovgu.de.<\/p>\n\n\n\n<p>Best regards,<\/p>\n\n\n\n<p>Marcus<\/p>\n","protected":false},"excerpt":{"rendered":"<div class=\"entry-summary\">\nHello OCRA, Tabletop and OSI\u00b2 community, In this blog post I want to share our SAR Power Monitor \u00b5C Interface for the OSI\u00b2 2MHz Halbach MRI as part of the A4IM project. The PCB uses the ADL5511 RF-to-RMS IC to convert the applied RF power to a envelope RMS voltage. This voltage gets sampled with&hellip;\n<\/div>\n<div class=\"link-more\"><a href=\"https:\/\/zeugmatographix.org\/ocra\/2025\/04\/14\/a4im-osi%c2%b2-sar-power-monitor\/\" class=\"more-link\">Continue reading<span class=\"screen-reader-text\"> &ldquo;A4IM OSI\u00b2 SAR Power Monitor \u00b5C Interface PCB&rdquo;<\/span>&hellip;<\/a><\/div>\n","protected":false},"author":3,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1],"tags":[42,16,49,19,43,44,25,47,48,50,11],"class_list":["post-263","post","type-post","status-publish","format-standard","hentry","category-uncategorized","tag-a4im","tag-mri","tag-mri-monitor","tag-open-source","tag-osi","tag-osii","tag-ovgu","tag-sar-hardware-monitor","tag-sar-monitor","tag-sar-power-monitor","tag-stimulate","entry"],"acf":[],"_links":{"self":[{"href":"https:\/\/zeugmatographix.org\/ocra\/wp-json\/wp\/v2\/posts\/263","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/zeugmatographix.org\/ocra\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/zeugmatographix.org\/ocra\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/zeugmatographix.org\/ocra\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/zeugmatographix.org\/ocra\/wp-json\/wp\/v2\/comments?post=263"}],"version-history":[{"count":2,"href":"https:\/\/zeugmatographix.org\/ocra\/wp-json\/wp\/v2\/posts\/263\/revisions"}],"predecessor-version":[{"id":270,"href":"https:\/\/zeugmatographix.org\/ocra\/wp-json\/wp\/v2\/posts\/263\/revisions\/270"}],"wp:attachment":[{"href":"https:\/\/zeugmatographix.org\/ocra\/wp-json\/wp\/v2\/media?parent=263"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/zeugmatographix.org\/ocra\/wp-json\/wp\/v2\/categories?post=263"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/zeugmatographix.org\/ocra\/wp-json\/wp\/v2\/tags?post=263"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}