Measurement of Water Reflection Coefficient in Microwave Range

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International Journal of Advance in Medical Science (AMS) Volume 2, 2014

Measurement of Water Reflection Coefficient in Microwave Range A. G. Shein*1, A. S. Penskoy2, A. P. Pustovalov3 Electronics and Computer Science Department Volgograd State Technical University, Volgograd, Russia Lenin ave. 28, Volgograd 40005, Russia alexandershein39@gmail.com; 2apenskoy@gmail.com; 3pustovalov-a-p@yandex.ru

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Received 28 Dec, 2013; Accepted 1 Mar, 2014; Published 10 May, 2014 © 2014 Science and Engineering Publishing Company

Abstract This paper is about measurement of water absorption and reflection coeffcicients. The dependence of electromagnetic waves reflection coefficient was received in water from the frequency and angle of radiation incidence. The results are compared with theoretical calculations, counting the Debye’s model for the dilute solutions of dipoles in liquids and solids.

Keywords Coefficient of Absorption; Coefficient of Reflection; Water; Permittivity; Brewster’s Angle

Introduction Nowadays, we pay attention to studding the microwave energy influence on different media due to development of technologies with using high frequency sources.

Water is one of the main elements of the world. A lot of biological organisms consist of more than 50% of water. So, we must take into consideration the electromagnetic waves reflection and absorption effects in water to study the microwave energy influence.

Theoretical Part There are a lot of surveys about measurement permittivity and the mechanisms of electromagnetic waves absorption and reflection in water (Calla O.P.N., 2005; Lyashchenko A.K., 2003; Yakovleva G. V., 2010; Kobelev A.V., 2011; Lileev A. S., 2011; Ellsion W.J., 2007; Zasetsky A. Y., 2011). The results show that for normal incident electromagnetic wave on the surface of air-nonreflective dielectric-water, the reflection coefficient isn’t less than 50% and slowly changes with

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frequency (Penskoy A. S., 2013). As a result it makes possible to study microwave influence and absorption in water medium due to reduction of the reflection coeffcicient with decreasing of incident angle of the electromagnetic wave. (Shein A. G., 2011).

The reflection coefficient is given as ratio of average (time average) reflection from the surface to incident energy flow in the plane wave incident on the interface of two dielectrics with different permittivity ε 1 and ε 2 , and angle of incidence ϕ , and in the perpendicular polarization, when the polarization plane, which contains vector E direction, is paralleled to incident plane it is: R=

( ε (ε

) φ)

ε 2 cos φ − ε1 ε 2 − ε1 sin 2 φ ε 2 cos φ +

1

2 2 − ε1 sin

2

(1)

This equation is valid for both transparent medium and absorbing reflecting one.

If the incident wave propagates in air then ε1 = 1 and (1) is defined as: R=

ε cos φ − ε cos φ +

(ε − sin φ ) (ε − sin φ )

2

2

(2)

2

It is said that the Brewster's angle (Landau L. D., 2003) (also known as the polarization angle) is an angle of incidence at which wave with a particular polarization is perfectly transmitted through a transparent dielectric surface, with no reflection. And it is defined as:

φB = arctg ε or cos 2 φ =

1

ε +1

International Journal of Advance in Medical Science (AMS) Volume 2, 2014

In case when reflected medium has dielectric loss and its dielectric permittivity is characterized as complex value where ε= (ω ) ε ′(ω ) + iε ′′(ω ) , one can calculate

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Cuvettes with 0°, 15°, 30°, 45°, 60°, 75°, and 82° sloped angles were placed in plane where E-field vector was parallel to the incidence plane wave.

the angle of minimum reflection from the surface and it can be expressed as:

ε ′′  ε ′ + 1  ε ′  ε ′ − 1  2(ε + 1)

1+ 1+ cos 2 φ =

(3)

To calculate the reflection coefficient for equation (2), this equation should contain the complex value of dielectric permittivity. And it is defined as: ε ′ cos φ − Re  R=  ε ′ cos φ + Re 

( (

) ε − sin φ )  

2

( + ε ′′ cos φ + Im ( 

ε − sin 2 φ  + ε ′′ cos φ − Im 2



2

) ε − sin φ )  

ε − sin 2 φ 

2

2

,

2

(4) where Re

(

ε − sin 2 φ=

)

(ε ′ − sin φ )

Im

(

ε − sin 2 φ=

)

(ε ′ − sin φ )

2

2

(

)

(

)

2

+ ( ε ′′ ) + ε ′ − sin 2 φ (5)

2

+ ( ε ′′ ) − ε ′ − sin 2 φ (6)

2

2

We used Debye equations (Debye P., 1931) to define real and imaginary part of dielectric permittivity. They are:

ε −ε ε ′(ω ) − ε ∞ =s 2 ∞2 , 1+ ω τ ε s − ε ∞ ) ωτ ( ε ′′(ω ) = .

1 + ω 2τ 2 Calculations with ε 0 = 78.4 , ε ∞ = 5.5 and relaxation time with τ = 9.04 ⋅ 10 −12 s show that the Brewster's angle is equal to 82.26 deg if we take electromagnetic incident waves with 10 GHz on the water surface.

1 – Back-wave oscillator; 2, 3– waveguide directional coupler; 4- measured cell; 5 – termination; 6 – detectors FIG. 1 SET UP FOR EXPERIMENT

Measurements that are shown in Fig. 2 (green dotted line with triangle markers), confirmed the reduction of reflection coefficient from water by changing the angle of incidence and it has a good compliance of the experimental data with theoretical calculations (blue solid line). Relative error does not exceed 5%. With decreasing of incidence angle the transmitting conditions of waveguide with cuvette is getting better, SWR is also decreasing from values 9 – 10, which are valid for perpendicular cell borders when the normal plane wave is incident.

It should be mentioned that the angle of incidence of the electromagnetic wave is measured from the normal to the surface, and therefore the cuvette with a small angle is equal to Brewster’s angle for water.

These cuvettes had long length, which didn’t allow to define the absorption coefficient with high accuracy.

Laboratory Measurements and Discussion of Results Laboratory measurements of water reflection coefficient were made by using panoramic SWR and attenuation meter R2-61. (Fig. 1) Cuvettes with one sloping wall (schematic picture is in the right corner of Fig. 2) made of radio-transparent material and without water have SWR values less than 1.1 in all measurement frequency ranges.

This cuvette with test sample was placed directly in the waveguide with TE10 mode (with one part of Evector, which is perpendicular to the metal surface).

FIG. 2 VARIATION OF REFLECTION COEFFICIENT WITH ANGLE OF INCIDENCE AT FREQUENCY 10 GHZ

Therefore, if the angle of incidence is equal 8 deg

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International Journal of Advance in Medical Science (AMS) Volume 2, 2014

waveguide with water medium will become nonreflecting system that leads to possibility to measure the absorption coefficient or dielectric permittivity for water.

Laboratory measurements (red dotted line with circle markers) of reflection coefficient for cuvettes with two sloping walls (schematic picture is in the left corner of Fig. 2) go against theoretical calculations. But, there is also a minimum of SWR and reflection coefficient for the angle with 8 deg as in the case with one sloped wall. The differences for other angles of incidence are caused by double reflection from second wall of the cuvettes, but it can be avoided if one takes a cuvette with a thicker water layer.

Laboratory measurements of water absorption coefficient were made by using the same panoramic SWR and attenuation meter R2-61 (Fig. 1), by connecting second waveguide directional coupler after measured element to define the level of passing power.

As cuvettes with one sloped wall has thicker water layer, they are not worth to be used to define the absorption coefficient due to absorption of normal incident wave is equal about 3 dB to 1 mm of water (Shein A. G., 2011). Thus, cuvettes with two slopped walls were used with the angles, which were mentioned above. The water thickness in cuvette is 1 mm. These cuvettes were also filled by water and gave good results in measuring absorption coefficient in water.

Conclusion As the imaginary part of the dielectric permettivity has a maximum value when the ωτ = 1 , laboratory measurements on reflection coefficient decreasing can be used to find experimental data of relaxation time, which are usually hard to define due to large values of reflection on the surface of air-water.

This work is also able to broad our mind about microwave influence on water mediums.

REFERENCES

Calla O.P.N., Bohra D. and Vyas R. “Measurement of dielectric constant of saline water and estimation of emissivity and scattering coefficient at different physical temperatures

at

microwave

frequencies.”

URSI

(International Union of Radio Science) Proceedings, Records & Resolutions, October, 2005 . http://www.ursi. org/Proceedings/ProcGA05/C_page1. Htm Debye P. Polar molecules. Moscow: GNTU, 1931.

Ellison W. J. “Permittivity of Pure Water, at Standard Atmospheric Pressure, over the Frequency Range 0-25 THz and the Temperature Range 0 – 100 oC.” J. Phys.

Chem. Ref. Data 36, no. 1 (2007) Kobelev A. V., Lyashchenko A. K. and Lileev A. S. “Microwave dielectric properties of aqueous potassium iodide solutions as a function of temperature” Russian journal of Inorganic Chemistry 56, no. 4 (2011): 697-704.

Landau L. D., Lifschitz E. M. Electrodynamics of Continuous Media. Course of Theoretical Physics. Moscow: Fizmatlit, 2003.

Lileev A. S., Loginova D. V. and Lyashchenko A. K. “Microwave dielectric properties of potassium hydroxide aqueous

solutions”

Russian

journal

of

Inorganic

Chemistry 56, no. 6 (2011): 961-967.

Lyashchenko A. K., Lileev A. S., Loginova D. V. and Ivanova FIG. 3 VARIATION OF ABSORPTION COEFFICIENT WITH FREQUENCY

Because of the large value of absorption coefficient the accuracy of measurements do not exceed 20%, although the order of magnitude and range prove the proper usage of: 2 ⋅π ε ′  ⋅ = α λ 2 

for calculation α.

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(

 ε ′′ = 1 + tgγ 2 − 1  , tg γ , ε′  

)

1 2

N. A. “Dielectric constant and relaxation in cesium formate and cesium propionate aqueous solutions.”

Coordination Chemistry, no. 10 (2003): 1541-1546.

Penskoy A. S., Maltsev N. I. and Pustovalov A. P. “Measurement

of

water

reflection

coefficient

in

microwave range.” Isvestia VSTU 7, no. 3 (2013): 91 – 95.

Shein A. G., Penskoy A. S. “Studying the dielectric properties of water in microwave range.” Biomedical Radioelectronics, no. 9 (2011): 62 – 66.

International Journal of Advance in Medical Science (AMS) Volume 2, 2014

Yakovleva G. V., Stekhin A. A., Savostikova O. N. and Alekseyeva A. V. “Changes in the electrochemical parameters and structural state of water exposed to microwave radiation.” Hygiene and sanitation, no. 4 (2010): 52-55.

Zasetsky A. Y. “Dielectric Relaxation in Liquid Water: Two Fractions or Two Dynamics?” PRL 107, 117601 (2011).

Alexander Shein received his Dr.Sci (1978) degree (in physical electronics) at the Kharkhov State University, Kharkhov, Ukrain. He is currently a Pofessor at the Volgograd State Technical University, Volgograd, Russia.

His research interests include electronics and radiophysics.

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biophysics,

physical

Arseniy Penskoy received his Master’s degree (in physics of modern radio-electronic technologies) at the Volgograd State Technical University, Volgograd, Russia in 2012. He is currently a research student at the Volgograd State Technical University. His research interests include radiophysics, biophysics and electronics.

Alexey Pustovalov received his Bachelor’s degree in Physics at the Volgograd State Technical University, Volgograd, Russia in 2013. He is currently a first year student of master course at the Volgograd State Technical University. His research intersts include radiophysics, biophysics and electronics.

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