Mems Gas Sensor
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کاربردهای سسورهای گازی
پارامتر های مهم در بهینه سازی روش ساخت سنسور های گازی
انواع سنسورهای گازی
catalytic gas sensor
thermal conductivity gas sensor
electrochemical gas sensor
acoustic gas sensor
فهرست
Applications of Gas Sensor:
Process control industries
Environmental monitoring
Boiler control
Fire detection
Detection of harmful gases in mines
Home safety
Gas sensors
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پارامتر های مهم در بهینه سازی روش ساخت سنسور های گازی:
Sensitivity
Selectivity
detection limit
response time
recovery time
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Sensitivity
The sensitivity (S) of a sensor is determined as Δf/Δc, where Δc is the change in analyte concentration.
S is expressed in terms of Hz/ppm or Hz/vol %.
Selectivity
the characteristics that determine whether a sensor can respond selectively to an analyte or a group of analytes.
detection limit
the lowest concentration of the analyte that can be detected by the sensor under given conditions.
response time
the time it takes for the sensor to respond to a step concentration change.
recovery time
the time it takes for the signal to return to its initial value after a step concentration value.
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The different types of gas sensors technologies
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در اسلاید بعدی اولین ساختار سنسورهای گازی دیده می شود که به صورت سیم پیچ از جنس پلاتین بوده است
اما این سنسور برای کار در دمای بالا و تشخیص هیدروکربن ها مناسب نبوده زیرا پلاتین در دمای
1000-900 درجه سانتی گراد نرم و ذوب می شود بنابراین لایه اکسید بر روی آن کشیده شد برای استحکام بیشتر.
سنسور گازی براساس قوانین catalytic
نامناسب برای تشخیص هیدرو کربن ها
نرم شدن در دمای 1000 درجه سانتی گراد
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pellistor type : Modern catalytic gas sensors called as “pellistors” was suggested by Baker
Thermoelectric gas sensor: thermoelectric type of H2 sensor has been also proposed to reduce the sensor operation temperature
slow response poor ratio of sensing surface to mass
Problems:
توان مصرفی بالا:300-700
مقاومت داخلی خیلی کم
هزینه بالا
قابلیت ساخت یا تولید مجدد پایین
The catalytic gas sensor is divided into two namely:
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در اسلاید بعد روش ساخت یک سنسور گازی catalytic با روش mems نشان داده شده است که این سنسور به شکل پل وتسون طراحی شده است برای کاهش تلفات
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R(T) = R(To)[1 + ˛(T − To)]
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The power consumption was very low (55.68 mW) to operate the catalytic combustion sensor at 115◦C
small size of microheater
the superior thermal insulation provided by the suspended configuration
high response
selectivity
rapid response/recovery and
the present gas sensor can be used in realizing portable sensing devices such as gas analyzers and gas leak detectors.
conclusion
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Thermal conductivity measurements for gas analysis have been used for many decades. It is usually used for the detection of gases with high thermal conductivities greater than air.
دسته بندی دیگر سنسور های گازی به صورت زیر می باشد
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Problem of chemical sensor:
Long-term stability is limited
contamination of the interface during chemical interaction
their chemical interaction is strongly dependent on environment temperature.
thermal conductivity sensors are generally not as selective or sensitive as chemical gas sensors they are faster and more
reliable since they will not be temperature depended or contaminated when they sense the gases.
thermal conductivity sensors indicates that even very low concentration of hydrogen leakage in air is able to be detected due to the notable increase in gas thermal conductivity. Therefore, thermal conductivity gas sensors are especially suitable for the hydrogen leakage detection before hydrogen concentrations reach the lower explosive limit (LEL) of 4% in air in safety applications.
slow response time
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Thermopile, Thermocouples and Seebeck Effect
A thermopile is an electronic device that converts thermal energy into electrical energy.
A thermocouple is a junction between two different metals that produces a voltage related to a temperature difference.
The Seebeck effect is the conversion of temperature differences directly into electricity
Vout = α 𝑇 . T [V]
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the changes in the thermal conductivity of measurand gas can be detected by measuring the changes in the temperature of the “hot element”.
Basic Principle of Thermal Conductivity Gas Sensors
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Surface-micromachining Process
To achieve a high sensitivity for micro-scaled thermal conductivity gas sensors, it is important to reduce the heat loss through the suspended membrane to negligible values.
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گاز از درون مویرگ وارد محفظه می شود و با الکترود حسگر واکنش می دهد و یون مثبت ایجاد شده توسط محلول الکترولیت به سمت الکترود کانتر می رود.الکترود مرجع برای به تعادل رساندن و جبران سازی واکنش ها در محیط می باشد.با محاسبه این جریان برقرار شده غلظت و نوع گاز مشخص می گردد طبق فرمول زیر:
i: جریان به دست آمده
F: ضریب فارادی
در اسلاید بعد سنسور گازی الکترو شیمیایی توضیح داده شده است
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Surface acoustic wave sensors are a class of microelectromechanical systems (MEMS) which rely on the modulation of surface acoustic waves to sense a physical phenomenon. The sensor transduces an input electrical signal into a mechanical wave which, unlike an electrical signal, can be easily influenced by physical phenomena. The device then transduces this wave back into an electrical signal. Changes in amplitude, phase, frequency, or time-delay between the input and output electrical signals can be used to measure the presence of the desired phenomenon.
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High sensitivity
Low power consumption
Wireless
قرارگرفتن برروی قسمت های متحرک و چرخان
مراحل ساخت ساده
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But why mems for sensors?
Sensors made using MEMS are better than
their conventional counterparts because they are :
Smaller in size
Have lower power consumption
More sensitive to input variations
Cheaper due to mass production
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GAS SENSORS,Prepared by:Jiturvi ChokshiENPM-808B
Micromachined catalytic combustible hydrogen gas sensor,Eui-Bok Leea, In-Sung Hwangb, Jung-Ho Chac, Ho-Jun Leec, Won-Bae Leec, James Jungho Pakd,Jong-Heun Leeb, Byeong-Kwon Jua,
Gas Sensors: A Review,Zainab Yunusa, Mohd. Nizar Hamidon, 3 Ahsanul Kaiser, Zaiki Awang, 30 April 2014
A Catalytic Sensor using MEMS process for Methane Detection in Mines,
MEMS-based electrochemical gas sensors and wafer-level methods, Doctoral Thesis Stockholm, Sweden 2015
Surface-Micromachined Thermal Conductivity Gas Sensors For Hydrogen Detection,Author: Shuoxi Chen,Daily Supervisor: Ir. Huaiwen Wu,Supervisor: Dr. Ir. Reinoud Wolffenbuttel,October 2010
Microelectromechanical Systems (MEMs) ,Chemical Sensors ,Dr. Lynn Fuller,Webpage:http://www.people.rit.edu/lffeee
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