humidity sensing

1. Review of Different
Approach in Humidity
Sensing
Presented by Tathagata Bhattacharjya

2. What is humidity
Humidity measurement determines the amount of water vapor present in a gas
that can be a mixture such as air, or a pure gas, such as nitrogen or argon.
 Based on measurement techniques, the most commonly used units for humidity
measurement are Relative Humidity (RH).
 Relative Humidity (RH) is the ratio of the amount of water vapor present in a
given volume of a gas to the water vapor required for saturation in same
volume at a given temperature. RH is a function of temperature . The RH
measurement is expressed as a percentage.

3. Preliminary review of humidity sensing in
few different research
 There are many approaches and procedure to measure humidity in different
mechanism. Here we can see few approaches how the sensing mechanism works.
 1.Humidity sensing in textile electronics for human physiological monitoring.
 2.Humidity sensing in traditional printing technology.
 3.Humidity sensing in daily writing carbon ink.
 4.Paper electronics based humidity sensing.
 5.Humidity sensing on a CDS nanoparticle coated paper sensor.
 6.Optical humidity sensing

4. 1.Basic idea of humidity sensing in textile
electronics for human physiological
monitoring.
 Yarn based flexible and wearable sensor is fabricated here for humidity sensing.
 This device mainly measures the water molecules which are a lot in the breathing air .This sensing
process is categorized capacitive type. The main work is to measure the change in capacitance with
relative humidity.
 The yarn based sensor with a biaxial type yarn wrapping structure is twice wound on a copper wire.
Functional yarn act as a dielectric layer in this sensor.
 The larger surface specific area of the fiber is easier for sensing which effect the relative humidity
around the mouth and nose while exhale and inhale during human respiration.
 Durability of this sensor performance is maintained by coating process.

5. Analysing some facts
By SEM analysis Clean cool fiber is preferred for this yarn based sensor
The sensitivity of this yarn sensor s=∆C/∆ RH,∆C is the capacitance
change with time mainly it is called the sensor response. Here we can
see the different fibers capacitive response .

6. 2.Humidity sensing in
traditional printing technology.
 This sensor that employ inter digited capacitors (IDC) printed with silver nano
particle based ink on a flexible poly ethylene terephthalate.
 Here also measure the capacitive response of the sensor towards relative
humidity 30% RH to 80% RH
 This works is based on fully traditional printing technology . mainly Gravure
printing
 The development of this sensor is cost effective and accurate .it is essential
for application in the environmental agriculture.
 PMMA polymer has been proven the highest response among known polymers
due to the formation of hydrogen bonds between the OH group.

7. 3.Humidity sensing in daily writing
carbon ink.
 In this paper the results show that the daily writing carbon ink is mainly composed of carbon
nanoparticles, and has good hydrophilicity and very stable dispersion.
 The humidity sensor was fabricated using daily writing carbon ink and its humidity sensing
performances were investigated at room temperature (20 ◦C).
 The testing results show that the resistance of the humidity sensor increases with the increase of
relative humidity (RH), showing a positive humidity sensitive characteristic.
 Compared with most of the reported humidity sensors, the carbon ink humidity sensor has better
humidity sensing performances on wide detection range (2 􀀀 95 % RH), low detection limit (2% RH)
and high detection resolution (1% RH)

8. 4.Paper electronics based humidity
sensing.
 Humidity sensors based on glycidyl trimethyl ammonium chloride (EPTAC)
modified cellulose paper via a facile solution method were fabricated,
among which the paper is used for the purpose of the humidity sensing
material and the sensor substrate.
 Here this paper-based humidity sensor is provided with well flexibility.
 It exhibits multifunctional applications in respiratory monitoring, non-
contact switch and skin humidity monitoring.
 Here this research concludes paper is not only the humidity sensing
material, but also a substrate of the sensor, which provides a unique porous
framework, allow physical or chemical modifications and could be prepared
on a large scale.

9. 5.Humidity sensing on a CDS nanoparticle
coated paper sensor.
 The key idea of choosing cadmium sulphide nanoparticles have exquisite
optical and electrical properties .It is also capable of adsorbing humidity from
the gas and vapours .
 Here the main work is to study the variation in electrical conductivity of a
film of cds nanoparticle with the variation in the flow rate of humid gas.
 The computational study show that the increase in the concentration of
adsorbed molecules with the enhancement of the flow rate of humid gas can
lead to a variation of electrical conductance of cds nanoparticle film.
 Porosity plays major roles in this process.
 CdsNps is prepared by Chemical precipitation technique.
 This research shows us cdsNps and nanostructures are easy to fabricate
humidity sensing.

10. We can here see basics of the fabrication step
shows the three-dimensional (3-D)
schematic diagram of the humidity
chamber used in the experiments.
The broken line in the schematic
shows the cut-plane, which is the
equivalent two-dimensional (2-D)
geometry considered for simulation,
as shown in the image

11. Basics of optical humidity sensing
 Consider an unpolarized beam of light of intensity Ii travelling through a
medium of refractive index μg incident at an angle θi on the interface of the
dielectric medium of refractive index μa. If θt is the corresponding angle of
refraction, the intensity Ir of the light reflected back from the interface to the
medium of the RI μg . By Snells law -
 The glass surface is interfaced with metal oxide film, the glass film interface
behaves like a humidity sensor. Humidity detection would depend significantly
on the thickness of the deposited film as the extent of adsorption of water
molecules depend on it.
µ g sin i =µa sin t