اثر پارامترهای شکل‌شناسی بر خواص الکترومغناطیسی اسفنج میکروسلولی پلی‌یورتان گرمانرم در محدوده بسامد نوار X

نوع مقاله : پژوهشی

نویسندگان

1 تهران،دانشگاه تربیت مدرس، دانشکده مهندسی شیمی،گروه مهندسی پلیمر، صندوق پستی 111-14115

2 تهران،دانشگاه تربیت مدرس،دانشکده مهندسی برق،گروه مهندسی مخابرات، صندوق پستی 111-14115

چکیده

در این پژوهش، خواص الکترومغناطیسی اسفنج‌­های میکروسلولی پلی­‌یورتان گرمانرم به­‌عنوان مواد جاذب رادار به روش تجربی در محدوده بسامد نوار (X (4/12-2/8GHz تحلیل شد. در چارچوب پژوهش حاضر، هدف این است که به ارتباط میان شکل‌شناسی اسفنج شامل اندازه و کسر حجمی سلول­‌های هوا و خواص الکترومغناطیسی آن شامل درصد جذب، عبور و بازتاب پی­برد. نانوکامپوزیت­‌ها با درصدهای مختلف دوده با روش انعقاد تهیه و نانوکامپوزیت %15 وزنی، با استفاده از روش اسفنج­‌سازی ناپیوسته و گاز CO2 ابربحرانی، در کسر حجمی و اندازه سلول­‌های مختلف به اسفنج میکروسلولی تبدیل شدند. شکل‌شناسی سلولی اسفنج‌­ها، با استفاده از تصاویر میکروسکوپ الکترونی و خواص الکترومغناطیسی با دستگاه Vector Network Analyzer ارزیابی شد. اثر پارامترهای شکل‌شناسی اسفنج شامل کسر حجمی و نیز اندازه سلول­‌های هوا روی خواص جذب بررسی شد که در طراحی اسفنج­‌های جاذب رادار نقش بسزایی دارند. در نهایت، ارتباط میان ساختار اسفنج و خواص الکترومغناطیسی آن بنا شد. اسفنج‌‌­سازی سبب کاهش آستانه شبکه‌ای‌شدن نانوکامپوزیت به علت کاهش متوسط فاصله میان نانوذرات می­‌شود. اسفنج­‌سازی با کاهش ثابت دی­‌الکتریک مقدار بازتاب را به مقدار قابل توجهی کاهش داده و افزایش کسر حجمی سلول­‌های هوا به علت تعدد پراش داخل ماده سبب افزایش درصد جذب به ازای واحد جرم اسفنج می­‌شود. حساسیت موج الکترومغناطیسی در برابر تغییرات اندازه سلول نسبت به تغییرات کسرحجمی اسفنج­‌های میکروسلولی به مراتب کمتر است. خواص الکترومغناطیسی اسفنج­‌های میکروسلولی از نظریه­‌های محیط مؤثر قدری انحراف دارد. کسر حجمی سلول­‌های هوا تابع اندازه سلول نیز هستند و سلول­‌های ریزتر خواص جذب بهتری نشان می‌دهند.

کلیدواژه‌ها

عنوان مقاله [English]

Morphological Parameters in Relation to the Electromagnetic Properties of Microcellular Thermoplastic Polyurethane Foam in X-Band Frequency Ranges

نویسندگان [English]

  • Mohammad Hassan Moeini 1
  • Mohammad Hossein Navid Famili 1
  • Kayvan Forooraghi 2
  • Mazyar Soltani Alkouh 1
  • Mozafar Mokhtari Motameni Shirvan 1
1 Polymer Engineering Group, Faculty of Chemical Engineering, Tarbiat Modares University, P.O. Box: 14115-111, Tehran, Iran
2 Communication Engineering Group, Faculty of Electrical Engineering, Tarbiat Modares University, P.O. Box: 14115-111, Tehran, Iran
چکیده [English]

Microcellular thermoplastic polyurethane foams are examined as absorbing materials in the X-band (8.2-12.4 GHz) frequency range by means of experiment. In this work, we aim to establish relationships between foam morphology including cell size and air volume fraction and electromagnetic properties including absorption, transmission and reflection quality. Nanocomposites based on thermoplastic polyurethane containing carbon black were prepared by coagulation method. In this procedure 15 wt% carbon black-containing nanocomposite was converted to microcellular foams using batch foaming process and supercritical carbon dioxide as physical foaming agent. The morphology of the foams was evaluated by scanning electron microscopy. S-parameters of the samples were measured by a vector network analyzer (VNA) and the effect of morphological parameters such as cell size and air volume fraction on the absorbing properties was investigated. We also established structure/properties relationships which were essential for further optimizations of the materials used in the construction of radar absorbing composites. Foaming reduced the percolation threshold of the nanocomposites due to the reduction in the average distance between nanoparticles. Foaming and dielectric constant reduction dropped the reflection percentage significantly. The increase in air volume fraction in the foam increased absorption per its weight, because of multiple scattering in composite media. The sensitivity of electromagnetic wave toward the variation of cell size is strongly weaker than that toward the variation of air volume fraction. Electromagnetic properties of the microcellular foams deviated a little from effective medium theories (EMTs). Air volume fraction of the cells was a function of cell size and smaller cells showed higher absorption.

کلیدواژه‌ها [English]

  • microcellular foam
  • radar absorbing materials
  • thermoplastic polyurethane
  • foam morphology
  • electromagnetic properties

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مجله علوم و تکنولوژی پلیمر
دوره 30، شماره 1 - شماره پیاپی 147
فروردین و اردیبهشت 1396
صفحه 19-30

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