Making a humidity sensor using carbon nanotubes

Number of pages: 114 File Format: word File Code: 32229
Year: 2011 University Degree: Master's degree Category: Biology - Environment
  • Part of the Content
  • Contents & Resources
  • Summary of Making a humidity sensor using carbon nanotubes

    Master's Thesis in Electrical-Electronic Engineering

    Abstract

    Making a humidity sensor using carbon nanotubes

    Today, humidity sensors are used in many fields, including environmental control processes. Life, home applications, automotive industry, medicine, agriculture and chemical industries have been obtained.

    Until now, various structures have been proposed for the humidity sensor, after reviewing these studies, in this research, a new structure of the humidity sensor is presented with the aim of commercialization.

    The tests performed on the sensor include the investigation of temperature behavior, time of rise and fall, temperature annealing, effect of size, repeatability, effect of interference and its detection limit, and the results of each of the tests have been reported. Each with lithium chloride, the flow and behavior of each have been reported.

    Then, using the software, two complete and defective carbon nanotube structure samples were simulated with and without the presence of water molecules, and using density functional theory and local density approximation, the behavior of the structure was investigated, and the simulation results are consistent with the experimental results.

    The results of the experiments show This is that the proposed sensor is a good candidate for use in the industry.

    - Introduction

     

     

    Water vapor is an integral part of the air around us, and it actually has a great impact on the conditions of measuring different physical quantities in a wide range. Hygrometry[1] is actually a branch of applied physics whose many techniques are a sign of the complexity of this problem, and none of the solutions provided for it meet all demands at all times and places. Today, humidity sensors have found many applications in industrial processes and environmental control. To manufacture components and circuits with very high precision in the semiconductor industry, the humidity level is monitored during the manufacturing process. There are also many home applications, such as intelligent control of the environmental features of buildings, cooking control for microwave ovens, intelligent control of washing machines, and in the automotive industry, humidity sensors are used in the windshield defogging system and engine assembly lines. In the medical field, humidity sensors are used in breathing equipment [2], sterilizers, growth chambers for premature babies, drug manufacturing processes and biological products. In agriculture, humidity sensors are used for ventilation of greenhouses, protection of plants (prevention of dew), measurement of soil moisture and in grain storage. In industries in general, humidity sensors are used to control humidity in the purification of chemical gases, dryers, ovens, drying of thin films, paper, textile products and food-related processes.[1]

    The necessary conditions that humidity sensors must have in order to be used in a wide range of applications include:

    Good sensitivity in a wide range from humidity and temperature

    short response time

    good repeatability and low hysteresis

    suitable durability and long life

    resistant to pollution

    negligible temperature dependence

    The price is low

    ..[2-4]

     

    1-1 Humidity measurement units:

    Humidity measurement actually shows the amount of water vapor in a gas, which can be a mixture of several gases, such as air, or a pure gas such as nitrogen or argon. [5]

    Based on the measurement method, three common units have been defined for humidity:

    1) Relative humidity (RH) [3] in % %

    Relative humidity shows the amount of water in the air compared to the amount of water that the air can hold at that temperature. Relative humidity is a function of temperature and is therefore considered a relative measurement. 2) Dew Point (D/F PT) [4] According to

    Dew point is the temperature (above 0) at which water vapor in a gas turns into liquid water. And the dew point is the temperature (below 0) at which water vapor turns into ice. D/F PT is a function of gas pressure but independent of temperature. Therefore, it is the unit of absolute measurement of humidity.

    3) Absolute humidity in terms of parts per million (ppm)[5]

    Absolute humidity in ppm shows the amount of water vapor in a fraction of the volume, which is expressed as ppmv, or if it is multiplied by the ratio of the molecular weight of water to the molecular weight of air, it becomes ppmw. This measurement unit is used in industries to measure low humidity.

    2-1 Relationship between different units:

    In order to make the scope of humidity defined by each measurement unit more tangible, first we will examine the difference between dew point and relative humidity with an example, and then discuss how to convert relative humidity to absolute humidity.

    The warmer the air, the more water vapor it can hold. Below is the amount of water vapor that air can hold at three different temperatures:

    30?C ~ 30 gm-3 (grams per cubic meter of air)

    20?C ~ 17 gm-3

    10?C ~ 9 gm-3

    These numbers are measured at atmospheric pressure at sea level and determined based on physical principles.

    Suppose the air temperature is 30 degrees at 3 pm and the measured humidity is equal to 9 gm-3. Now, if the temperature drops to 10 degrees, while no water vapor has been added or subtracted from it, the air is saturated. That is, it cannot hold more water vapor than gm-3 9. Decreasing the temperature even to a small amount causes condensation of water vapor and can form clouds, fog or dew. Considering that this air has a long distance from the ground, it is above the ground or on the surface of the ground.

    So if we measure the humidity at 3 pm, we can say that the dew point of the air at this time is equal to 10 degrees Celsius. If the air cools down to 10 degrees at this time, its moisture starts to condense and form dew.

    Regarding relative humidity, it can be said that if at 3:00 pm at 30 degrees, the air has 9 gm-3 of water vapor, by dividing gm-3 9 by gm-3 30 and multiplying it by 100, the amount of relative humidity is equal to 30%. In other words, the air actually contains 30% of the water vapor that it can hold at the current temperature.

    By cooling the air to 20 degrees, gm-3 9 is divided by gm-3 17 and the relative humidity is equal to 53%.

    On the other hand, to convert relative humidity to absolute humidity in terms of temperature, the following relationship can be used Kurd:

    (1-1)         

    where Y is the maximum absolute humidity in milligrams of water per liter (mgH2OL-1) and T is the temperature in terms.

    This relationship is true for the temperature range of 0 to 100 degrees Celsius. For example, at a temperature of 25 degrees, the maximum absolute humidity is equal to 22.94 mgH2OL-1, which is equivalent to 100% RH. So, at a temperature of 25, the value of 50% RH is equivalent to absolute humidity equal to 11.47 mgH2OL-1. In this way, absolute humidity can be calculated at different temperatures. Figure (1-1) shows the relationship between RH, PPMv and D/F PT.

  • Contents & References of Making a humidity sensor using carbon nanotubes

    List:

    1 Introduction.. 1

    Humidity measurement units. 2

    Communication between different units. 3

     

    Chapter 2 types of humidity sensors. 6

    2-1- Different mechanisms for identifying humidity. 6

    2-1-1- Temperature humidity meter. 7

         2-1-2- LiCl dew point sensor. 8

         2-1-3- Capacitive humidity sensors. 9

         2-1-4- Resistive humidity sensors. 11

         2-1-5- Hygrometric humidity sensors. 12

         2-1-6- Optical hygrometers. 13

         2-1-7- Weighing humidity sensors. 14

    2-2- Chemical properties of materials used in different types of humidity sensors. 16

         2-2-1- Sensitive ceramic materials. 16

              2-2-1-1- aluminum oxide. 19

              2-2-1-2- titanium oxide. 19

              2-2-1-3- silicon oxide. 20

    2-2-1-4- Spinal compounds. 21

         2-2-2- The use of carbon nanotubes in humidity sensors. 22

    Title

    Chapter 3 How to make sensors and measuring devices. 26

    3-1- An overview of carbon nanotubes. 26

         3-1-1- The structure of carbon nanotubes. 29

         3-1-2- Production methods of nanotubes. 31

             3-1-2-1- Chemical vapor deposition (CVD) method. 31

             3-1-2-2- Electric arc method. 32

              3-1-2-3- laser vaporization method. 32

         3-1-3- Properties of carbon nanotubes and their applications. 33

    3-2- The method of making the sensor studied in this thesis. 36

    3-3- Circuit diagram of measurement systems. 39

         3-3-1- Measuring device number one. 39

         3-3-2- Measuring device number two. 42

         3-3-3- measuring device number three. 43

         3-3-4- measuring device number four. 44

     

    Chapter 4 simulation and experiments. 46

    4-1- Checking the performance of the sensor from a theoretical point of view. 46

         4-1-1- An introduction to density functional theory (DFT). 50

         4-1-2- Solving the Schr?dinger equation. 51

         4-1-3- Hohenberg-Cohen theories. 52

    4-1-4- Cohen-Shem theory. 54

    4-1-5- local density approximation (LDA). 56

         4-1-6- The results of simulating sensor performance using DFT theory and LDA approximation 58

    4-2- The results of experiments. 62

     

     

     

     

     

    Title                                    . 62

         4-2-2- Checking the rise and fall time. 63

         4-2-3- checking the temperature behavior of the sensor. 67

              4-2-3-1- variable temperature and constant humidity. 67

              4-2-3-2- Temperature and humidity are both variables. 68

         4-2-4- Check sensor size change. 69

         4-2-5- Examining the effects of disturbances. 72

         4-2-6- Checking the re-baking temperature of the sensor. 73

         4-2-7- Checking the detection limit of the sensor. 74

         4-2-8- Reproducibility check. 74

         4-2-9- Comparison with a sample sensor made in other articles. 76

         4-2-10- Investigation of other carbon nanostructures for humidity sensor. 78

     

    Chapter 5 conclusions and suggestions. 86

    5-1- Conclusion.. 86

    5-2- Suggestions to continue the work. 87

     

    References. 89

     

    Source:

    H.P. Penman, Humidity, Chapman and Hall, London. 1955.

    Y. Ma, S. Ma, W. Fang, T. Wang, Air-flow sensor and humidity sensor application to neonatal infant respiration monitoring, Sens. Actuaries A 49 (1995) 47-50.

    V. Matko, D. Donlagic, Sensor for high-air-humidity measurement, Sens. Actuators A 61 (1997) 331-334.

    K.V. Heber, Humidity sensing at high temperatures, Sens. Actuators 12 (1987) 145-157.

    http://www.iceweb.com.au/Analyzer/humidity_sensors.html (2005).

    Zhi Chen and Chi Lu Humidity Sensors: A Review of Materials

    Zhi Chen and Chi Lu Humidity Sensors: A Review of Materials and Mechanisms SENSOR LETTERS Vol. 3, 274–295, 2005

    G.J.W. Visscher, Standard psychrometers: a matter of (p) references, Meas. Sci. Technol. 6 (1995) 1451-1461

    J.R. Simoes-Moreira, A thermodynamic formulation of the psychrometer constant, Meas. Sci. Technol. 10 (1999) 302-311

    F.C. Quinn, The most common problem of moisture/humidity measurement and control, in: Proceedings of the Conference on Humidity and Moisture, Washington DC, 1985, pp. 1-5.

    H. Endres, H.D. Jander, W. Gottler, Test system for gas sensors, Sens. Actuators B 23 (1995) 163-172.

    H. Mitter, Humidity Calibration-Simple and accurate, Proc. Sensor 99, Nurnberg, May 18-20, 1999, pp. 623-628

    D.A. Mathews, Review of the Lithium Chloride radiosonde hygrometer, in: Proceedings of the Conference on Humidity and Moisture, Vol. VI, Washington DC, 1963, pp. 219-227

    H. Mitter, Humidity Calibration-Simple and accurate, Proc. Sensor 99, Nurnberg, May 18-20, 1999, pp. 623-628

    J.G. Korvink, L. Chandran, T. Boltshauser, H. Baltes, Accurate 3D capacitance evaluation in integrated capacitive humidity sensors, Sens. Mater. 4(6)(1993) 323-335.

    R.S. Jachowicz, S.D. Senturia, A thin film capacitance humidity sensor, Sens. Actuators 2 (1981) 171-186.

    K. Bratzler, Adsorption von Gasen und Dampfen in laboratorium und Technik, Theodor Steinkopf, Dresden, 1944.

    K. Bratzler, Adsorption von Gasen und Dampfen in laboratorium und Technik, Theodor Steinkopf, Dresden, 1944.

    G. Gerlach, K. Sager, A piezoresistive humidity sensor, Sens. Actuators A 43 (1994) 181-184

    R. Buchhold, A. Nakladal, G. Gerlach, K.J. Eichhorn, G. Dlubek, Multiplying sensitivity and tailoring transfer function of bimorph humidity sensors by ion bombardment of the hygroscopic polymer layer, Proc. Transducers 99, Sendai, Japan, pp. 230-233.

    N.T.T. Ha, D.K. An, P.V. Phong, P.T.M. Hoa, L.H. Mai, Study and performance of humidity sensor based on the mechanical optoelectronic principle for the measurement and control of humidity in store hoses, Sens. Actuators B 66 (2000) 200-202.

    E. Radeva, V. Georgiev, L. Spassov, N. Koprinarov, St. Kanev, Humidity adsorptive properties of thin fullerene layers studied by means of quartz microbalance, Sens. Actuators B 42 (1997) 11-13

    H.T. Sun, Z.T. Cheng, X. Yao, W. Wlodarski, Humidity sensor using sol-gel-derived silica coating on quartz crystal, Sens. Actuators B 13/14 (1993) 107-110

    F. Pascal-Delannoy, B. Sorli, A. Boyer, Quartz crystal microbalance (QCM) used as humidity sensor, Sens. Actuators A 84 (2000) 285-291

    B. Morten, G. De Cicco, M. Prudenziati, A thick-film resonant sensor for humidity measurements, Sens. Actuators A 37/38 (1993) 337-342

    A. Gluck, W. Halder, G. Lindner, H. Muller, P. Weindler, PVDF-excited resonance sensors for gas flow and humidity measurements, Sens. Actuators B 18/19 (1994) 554-557.

    A.J. Slobodnik, Surface acoustic waves and SAW materials, Proc. IEEE 64 (5) (1976) 581-595.

    Ansbacher and A. C. Jason, Nature 24, 177 (1953).

    T. Moromoto, M. Nagao, and F. Tokuda, J. Phys. Chem. 73, 243 (1969).

    E. McCafferty and A. C. Zettlemoyer, Faraday Discussions 52, 239 (1971).

    V. K. Khanna and R. K. Nahar, J. Phys. D:Appl. Phys. 19, L141 (1986).

    L. Young, Anodic Oxide Films, Academic Press, New York (1961).

    E. C. Dickey, O. K. Varghese, K. G. Ong, D. Gong, M. Paulose, and C. A. Grimes, Sensors 2, 91 (2002).

    C. A. Grimes, D. Kouzoudis, E. Dickey, D. Qian, M. A. Anderson, R. Shahidain, M. Lindsey, and L. Green, J. Appl. Phys. 87, 5341 (2000).

    S.A. Krutovertsev, A. E. Tarasova, L. S. Krutovertseva, and A. V. Zorin, Sens. Actuators A 62, 582 (1997).

    K. Robbie and M.J. Brett, J. Vac. Sci. Technol. A 15, 1460 (1997).

    G. Gusmano, G. Montesperelli, and E. Traversa, Sens.

Making a humidity sensor using carbon nanotubes