The present paper aims at sensing the temperature. A sensor metamaterial consisting of two concentric metallic rings and a thin metallic wire deposited on the surface of BaTiO3 substrate is reported. The use of BaTiO3 makes the resonant frequency of the structure shift as the temperature varies and makes the sensor applicable in many fields of applications. Numerical simulations and theoretical results are presented and compared to each other; there was a good agreement between them. This sensor is smaller, easier to fabricate, and very sensitive to the changes in temperatures.
In this decade, metamaterials (MTM) or left handed materials (LHM) have attracted much attention among researchers in the microwave communities because of their unusual properties, such as negative permittivity [
Metamaterials are better in sensing than the conventional resonators (e.g., spiral coils), because they are easy and rapid in detection [
The aim of this paper is to design a high sensitive and smaller electrical sensor of temperature based on metamaterial operating in GHz regime. The proposed structure consists of a combination of two concentric circular metallic rings opened in the opposite sides commonly called SRR and a thin metallic wire placed on a dielectric substrate. Because the resonant frequency of the MTM structure is very sensitive to the changes of the capacitive effects (since its fundamental resonance behavior can be modeled by an
In this work, we have designed the equivalent circuit model of the proposed structure and we have derived the relations of its coefficients of reflexion and transmission using the ABCD Matrix approach; then we have compared them to those resulting from the simulation. The results were very close. In this study the metamaterial sensor is smaller, is easier to fabricate, possesses higher sensitivity, and is useful in a wide range of applications. The mechanism behind this is the use of a varying dielectric characteristics substrate.
The MTM structure is composed of a combination of PEC (perfect electric conductor) circular SRR and thin wire placed on a dielectric substrate of 0.1 mm of thickness
Variation of the dielectric constant of BaTiO3 versus the temperature [
SRR
The simulation of the MTM structure has been executed using the High Frequency Structure Simulator (HFSS) software. A perfect magnetic conductor (PMC) boundary condition was set along
In Figure
Variation of the coefficient of transmission S21 versus frequency at 40°C.
The effective permittivity of the LHM structure is different from the relative permittivity of the BaTiO3 substrate
The variation of the real (red) and imaginary part (blue) of the permittivity (
We notice that the resonant frequency of the simulated structure is 2.3 GHz with return loss of −20 dB. The relative permittivity at this frequency is −12.19, whereas the relative permeability is −12.65.
The resonant frequency of the MTM structure is inversely related to the total capacitance
When
When a time harmonic external magnetic field is applied along
Because the LHM structure has a size much smaller than the operating wavelength, we can describe its electromagnetic characteristics by lumped circuit components capacitors and inductors. The overall structure can be represented by an
Figure
The distribution of the current around the wire and the SRR.
Equivalent circuit model for the LHM structure.
In Figure
The variation of S21 versus frequency calculated using the ABCD Matrix approach from the equivalent circuit model.
The resonant frequency calculated is 2.4 GHz with return loss of −52 dB. We note that the calculated and the simulated results are very close.
Each time the temperature varies, it leads to a variation in the dielectric characteristics of the substrate BaTiO3 of the LHM structure which affects its capacitance which depends inversely on the frequency of resonance of the structure.
To obtain the effects of the temperature on the
Variation of frequency versus the temperature.
The minimum and maximum temperatures that can be detected by this sensor depend on the minimum and maximum temperatures that can be supported by the BaTiO3 substrate.
The BaTiO3 material is sintered at high temperatures, which allows an operation at wide range temperatures [
We have done this study in GHz regime, but the variations of the frequency are in the order of MHz; that is why in Table
The interval of temperature |
|
The sensibility [MHZ] |
---|---|---|
|
80 | 4 |
|
30 | 1.5 |
|
90 | 4.5 |
|
100 | 5 |
|
140 | 7 |
|
70 | 3.5 |
This paper presents a sensor of temperature using the metamaterial. We have studied the variations of the resonant frequency according to the permittivity of structure which depend on the temperature.
We have proposed an equivalent circuit model of our LHM structure and using the software MATLAB we have calculated the coefficients of reflection and transmission; the obtained curves are in accordance with those obtained by the HFSS.
Using the two methods HFSS and Matrix ABCD, we can notice that the variation in the temperature involves a variation of the frequency of resonance and it is illustrated in a curve.
Because the BaTiO3 has big dependence of the relative permittivity with the temperature, this sensor can be tailored in a wide range of applications.
Based on the promising results of this sensor, we believe that the use of the proposed sensor’s topology will efficiently be used in various sensing applications including pressure and humidity and also in biological and chemical sensing for any region of wavelengths.
The authors declare that there is no conflict of interests regarding the publication of this paper.