B Tech

M Sc

Ph.D M Phil

S Nisitha

S Sreeja

T Satyanarayana #2

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Excerpt from the Proceedings of the 2013 COMSOL Conference in Bangalore 
 
Modeling of MEMS Based Bolometer for Measuring Radiations 
from Nuclear Power Plant 
S. Nisitha*1, T. Satyanarayana#2, S. Sreeja1 
1B. Tech 
2M.Sc., M. Phil., Ph.D 
*NPMASS Centre, Department of EIE, Lakireddy Bali Reddy College of Engineering 
(Autonomous), 
Mylavaram-521 230, Andhra Pradesh, India. 
*E-mail: neethusettipalli@gmail.com, #E-mail: satyamphysics@gmail.com 
ABSTRACT: There has been growing demand for 
high performance micro sensors capable of detecting 
nuclear radiations being released from various 
industries. Nuclear reactors produce large quantities 
of ionizing radiation.  During  normal  operations 
of nuclear power plant, penetrating radiation (like 
gamma and X-rays) emitted from the radioactive 
materials in the reactor and in the systems and 
buildings of the plant may be able to expose someone 
outside the boundary of the plant where ionizing 
radiation is invisible and not directly detectable by 
human senses. Nuclear radiation accounts for about 
0.16% of total ionizing. Thus it is highly essential 
to work on design of bolometers with absorptive 
elements having different geometries providing 
optimum sensitivity. 
 
The present work is aimed at design of MEMS based 
bolometer for detecting the nuclear radiation to 
provide high security and also an attempt has been 
made to improve the performance of the bolometer 
by changing materials. Specifically, the present work 
concentrated on resistive bolometer detectors as their 
responsivity is much higher than that of thermopile 
detectors and fabrication process also much easier 
than pyroelectric detectors through advanced micro 
machining technology. Thermal detection mechanism 
of the selected bolometer is to measure the change 
in electrical resistance of a material as that caused 
by change in temperature of that material due to 
absorption of electromagnetic radiation or pressure 
distribution across the plate. 
 
The energy of the incident radiation heats 
the thermally sensitive micro metal plates (held 
together and placed on both sides of a copper link 
connected to the substrate) that make them to deflect. 
This deflection contacts the copper links and the 
changes the voltage across it. Now, by measuring 
the voltage, the frequency of  incident  radiation 
can be determined. The micro plate and micro 
thermal links are designed and simulated using the 
physical interfaces viz., Heat transfer and Structural 
Mechanics in COMSOL Multiphysics. 
 
Keywords: Coefficient of thermal expansion (CTE), 
MEMS, Nuclear radiations 
 
1. Introduction 
 
 
The word ‘bole’ means ray. Bolometer is a 
thermal infrared sensor  that  measures  the  power 
of incident radiation. It absorbs electromagnetic 
radiation and temperature is increased. This 
temperature  increase  results  in  the  deformation  of 
 
Excerpt from the Proceedings of the 2013 COMSOL Conference in Bangalore 
 
absorptive element [1]. Absorptive element is a thin 
layer of metal, connected to the thermal reservoir 
through a link. 
 
The principal risks associated with  nuclear 
power arise from ill-effects of radiation. Nuclear 
power technology produces materials  that  are 
active in emitting radiation called "radioactive". 
These materials can come into contact with people 
principally through small releases during routine 
plant operation, accidents in nuclear power plants, 
accidents in transporting radioactive materials, and 
escape of radioactive wastes from confinement 
systems [2]. This radiation consists of subatomic 
particles traveling at or near the velocity of light- 
186,000 miles per second. They can penetrate deep 
inside the human body where they can damage 
biological cells and thereby initiate cancer, radiation 
sickness and death.  Various  techniques  are  used 
to detect them [3] Compared to more conventional 
particle detectors bolometers are extremely efficient 
in resolution and sensitivity [4]. 
In this paper we mainly focused to develop a 
MEMS based bolometer for detecting the nuclear 
radiation to provide high security around nuclear 
power plants and also to improve the performance of 
the bolometer by updating geometry and by studying 
different metal pairs. 
 
 
1.1 Working principle of bolometer: 
 
Bolometer works on the principle of thermal 
expansion of metals. Thermal expansion is the 
tendency of matter to change in volume in response 
to a change in temperature. When a substance is 
heated, its particles begin moving more and thus 
usually maintain a greater average separation. The 
degree  of  expansion  divided  by  the  change  in 
temperature is called the material's coefficient of 
thermal expansion  and generally  varies  with 
temperature. The coefficient of thermal expansion 
describes how the size of an object changes with a 
change in temperature 
A bolometer consists of an absorptive element, 
such as a thin layer of metal, connected to a thermal 
reservoir through a thermal link. The result is that 
any radiation impinging on the absorptive element 
raises its temperature above that of  the  reservoir. 
The greater the absorbed power, the higher the 
temperature. The intrinsic thermal constant which 
sets the speed of the detector, is equal to the ratio 
of the heat capacity of the absorptive element to the 
thermal conductance between the absorptive element 
and the reservoir 
 
 
2. Design of Micro Bolometer 
 
2.1 Usage of COMSOL Software Tool 
 
The software package selected to model 
and simulate the micro Bolometer is COMSOL 
MultiPhysics Version 4.3 a. It is a powerful 
interactive environment for modeling of various 
devices because there was previous experience and 
expertise regarding its use as well as confidence with 
its multiple physical interfaces. This software is also 
capable of facilitates for structural analyses which is 
highly essential for making present design. 
For any device to be constructed by using 
COMSOL software it is required to follow four 
fundamental steps like (1) defining geometry (2) 
adding physical interfaces (3) adding material to the 
solid structure and finally (4) meshing, simulation of 
model with inputs provided. 
 
Micro Bolometer was designed and 
analyzed by following above steps using COMSOL. 
 
Excerpt from the Proceedings of the 2013 COMSOL Conference in Bangalore 
 
Parameters Values (µm)
Width of the substrate 100
Depth of the substrate 100
Height of the substrate 11
Width of the metal plate 45
Depth of the metal plate 20
Height of the metal plate 1
Width of the copper link 10
Depth of the copper link 20
Height of the copper link 13
Width of the central support 20
Depth of the central support 20
Height of the central support 20
Initially, geometry is defined for the proposed model, 
after forming the complete structure, suitable material 
from the available built in Materials Library is 
added to the proposed structure. Then depending up 
on the analysis to be carried out required physical 
parameters are selected (discussed below). Finally the 
model is simulated; results are verified/observed with 
different materials and inputs. 
 
2.2 Geometry 
 
The device consists of two micro plates on 
either side of the support. The two micro plates are 
made of materials of different coefficient of thermal 
expansion (CTE). One of the micro plates is made of 
material with high CTE and the other is made of 
material of low CTE. Another such plate is designed 
and placed on either side of silicon support. Copper 
links are provided on either side of the substrate for 
contacts. Table 1 gives the dimensions of the device. 
height 20µm is built at the centre of the base. Two 
links of width 10µm, depth 20µm and height 13µm 
is built on the edges of the base. Two metal plates of 
width 45µm, depth 25µm and height 1 µm are built 
on either sides of the central support. Finally the 
union of 8 blocks is formed, and the model appears as 
follows. 
 
 
 
 
Figure 2: designed model of bolometer 
 
 
2.3 Addition of Materials 
After the construction, materials are added 
to the model. Silicon is added to base and central 
support. Copper is added to the two links and 
aluminum, tungsten are added to the plates. 
Schematic diagram of the model is illustrated in the 
figure given below. 
Aluminium 
Tungsten 
Silicon 
Copper 
 
 
Table 1: Design parameters 
With the above mentioned parameters model 
is constructed in COMSOL. Initially base of width 
100µm,  height  11µm  and  depth  100µm  is  built. 
 
 
 
 
 
 
Figure 1: structural details of bolometer 
Silicon 
Central support of width 20µm, depth 20µm, and 
All these materials are added to carry out 
 
the  final  simulation.  Aluminium  has  high  thermal 
 
Excerpt from the Proceedings of the 2013 COMSOL Conference in Bangalore 
 
Property Value
Thermal conductivity 160[W/mK]
Heat capacity 900[J/kg×K]
Coefficient of thermal 
 
expansion 
23M[1/K]
Heat Density 2700[Kg/m3]
conductivity and tungsten has high heat capacity. 
Various thermal properties of aluminium and 
tungsten are presented in table 2 and table 3. 
 
 
 
 
 
 
 
 
 
 
 
Table 2: Thermal properties of aluminium 
 
 
Property Value
Thermal conductivity 173[W/mK]
Heat capacity 1340[J/kg×K]
Coefficient of thermal 
expansion 
4.5M[1/K]
Heat Density 17800[Kg/m3]
Table 3: Thermal properties of tungsten 
 
 
3. Physical interfaces 
 
This model is carried out based on joule 
heating and thermal expansion physical interfaces 
which automatically facilitates for coupling of 
thermal, electrical and structural analyses. The linear 
thermal expansion coefficient relates the change in a 
material's linear dimensions to a change in 
temperature. The high value of coefficient of thermal 
expansion allows us to make use of aluminium as 
absorptive micro metal on which radiation is 
impinging rather than other metal plates. 
4. Results and Discussions 
 
After the completion of design process, the 
proposed micro bolometer has been simulated to 
study the pressure distribution across the  device. 
The model is simulated by providing the inputs 
temperature 300k and stress 10 N/m2. The pressure 
distribution of the model after simulation is shown in 
the figure. 
 
 
 
Figure 3: Pressure Distribution 
 
From the figure, it is clear that with the applied 
stress, deformation of aluminium metal plate taking 
place and thus touches the copper link. The 
maximum stress applied is found to be 7.9435 x 10-7 
N/m2. This changes the resistance of the absorptive 
element. Simulation result also confirms the entire 
distribution of pressure across the absorptive micro 
aluminium metal plate. It should also be noted that 
with increase in pressure, the deformation of metal 
plate increases. Thus the deformation occurs in metal 
plate causes change in resistance due to change in 
temperature. By measuring the change in resistance 
of the metal one can determine the intensity of the 
incident radiation. Based on intensity of incident 
radiation, necessary precautionary things will be 
done. Thus, the study allows us to know the pressure 
distribution across the metal plate such that changes 
in resistance and intensity of incident radiation. 
These studies would be useful in making of 
bolometers that prevent the people from powerful 
radiations. The study can be extended to find the 
pressure distribution for various metallic materials in 
place of aluminium which has high thermal 
coefficient of expansion. Thus the beam which 
posses optimum sensitivity for small pressure may be 
used in developing real time bolometers. 
 
Excerpt from the Proceedings of the 2013 COMSOL Conference in Bangalore 
 
 
5. Conclusion 
 
Resistive micro bolometer has  been  designed 
by using COMSOL 4.3 a. Specifically the stress 
distribution across aluminium metal surface is 
studied by simulating the model under necessary 
conditions. The maximum stress is found to be 
7.9435 x 10-7. Metals having optimum sensitivity for 
small pressures can be used as absorptive element in 
bolometer. 
Acknowledgements 
 
We would like to express our heartfelt note of deep 
gratitude to NPMASS Centre, Department of EIE, 
Lakireddy Bali Reddy College of Engineering for 
providing us all the necessary software. 
References 
 
1F. rank Niklaus, Christian Vieider, Henrik 
Jakobsen MEMS-Based Uncooled Infrared 
Bolometer Arrays – A Review. 
2. Bernard L. Cohen, Sc.D. Professor at the 
University of Pittsburgh Risks of Nuclear Power. 
3. R. Reichle, T. Nishitani, E.R. Hodgson, L.C. 
Ingesson, E. Ishitsuka, S. Kasai, K.F. Mast, T. 
Shikama, J.C. Vallet, S. Yamamoto, Radiation 
hardness test of mica bolometers for ITER in 
JMTR, in: 28th EPS Conference on Contr. Fusion 
and Plasma PhysFunchal, 2001. 
4. K. Umapathi, S. Swetha, K. Ranjitha, K. Vinodh, 
K. Deebiga,  R.  Harisudarsan,  Multiphysics 
and Simulation of MEMS based Bolometer for 
Detecting the Radiations in Nuclear Power Plants, 
Comsol Conference 2012. 


Modeling of MEMS Based Bolometer for Measuring Radiations from Nuclear Power Plant

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Modeling of MEMS Based Bolometer for Measuring Radiations from Nuclear Power Plant

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