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مقدمه‌ای بر حسگر‌های گازی

انسان همواره در پی کشف حقایق و قوانین حاکم بر طبیعت زندگی خود بوده است. و از گذشته تا کنون با استفاده از روش‌های ساده و پیچیده، راه‌های مختلفی را به منظور شناسایی عوامل محیطی به کار گرفته است. امروزه نیاز به حسگر‌های دقیق در کاربرد‌های محیط زیستی، کشاورزی، صنعتی، تشخیص‌های پزشکی و ... احساس می شود. در واقع، حسگر‌ها، تبدیل کننده‌های انرژی به یک نوع انرژی معین هستند که منجر به تولید یک سیگنال خروجی قابل فهم و قابل پردازش ایجاد می شود. حسگر‌های گاز، دسته‌ی مهمی از حسگر‌ها هستند که قادرند نوع و غلظت یک گاز معین را در محیط شناسایی کنند.

 

در طراحی این حسگر‌ها، گازی که غلظت آن مدّ نظر است را گاز هدف (target)می‌نامند. این گاز با تغییر در خواص فیزیکی و یا شیمیایی افزاره شناسایی می‌گردد. و برمبنای میزان تغیرات ایجاد شده توسط گاز هدف، نسبت به زمان عدم حضور آن غلظت محاسبه می‌شود. تاکنون روش‌های مختلفی در حسگری گاز‌ها به کار گرفته شده است. تغییر رسانایی نیمه‌هادی‌های جاذب گاز، تغییرات اپتیکی و تغییرات دمایی از این دسته اند. جدول1 خلاصه‌ای از روش‌های موجود را نشان می دهد.

در چند دهه‌ی اخیر، نیمه‌هادی به دلیل جذب مناسب، حساسیت بالا، قابلیت کوچک‌سازی و قیمیت پایین مورد توجه قرار گرفته‌اند. با استفاده از موادی چون اکسید روی، اکسید مس و اکسید قلع، حسگر‌هایی با حساسیت یک قسمت در میلیارد (1 ppb)  حاصل شده است. به کار بردن نانوساختار‌ها همانند نانو‌لوله‌های کربنی، نانو‌ذرات و نانو‌سیم‌های فلزی همگی روش‌هایی برای افزایش حساسیت حسگر‌های نیمه‌هادی محسوب می شود.

امروزه با وجود پیشرفت‌های گسترده و حتی ارائه نمونه‌های تجاری، طراحی و ساخت حسگر‌ها با چالش‌هایی چون طول عمر، تکرار پذیری، قدرت تشخیص کم و قابلیت مجتمع سازی مواجه است. به کارگیری فن‌آوری میکرو و نانو روش مؤثری در بهبود عملکرد حسگر‌ها است. انتظار می رود با استفاده از این تکنیک‌ها روز به روز شاهد پیشرفت این افزاره‌ها بود.

جدول 1- انواع حسگر‌های گازی مورد استفاده و خواص قابل تغییر

نوع حسگر تغییرات خواص
نیمه‌هادی رسانایی الکتریکی
اثر میدانی(خازن‌ها، دیود‌ها، ترانزیستور‌ها) تابع کار(قطبش الکتریکی)
پیزوالکتریک جرم
اپتیکی پارامتر‌های اپتیکی(بازتاب، عبور، جذب، ضریب شکست، طول نوری)
کاتالیزوری گرما یا دما
الکتروشیمیایی نیروی محرکه‌ی الکتریکی یا جریان الکتریکی در سلول‌های شیمیایی حالت جامد
خواندن 764105 دفعه آخرین ویرایش در شنبه, 10 بهمن 1394 ساعت 14:32

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