A Brief Summary of
“Collision Absorption and Resonance
Absorption of Electromagnetic Waves by
Array Plasma”
Authored by : Xiang
He, Yachun Zhang, Jianping Chen,
Yudong Chen, Xiaojun Zeng, Tingting Gu, Wei Yang
Published in : 10th International Symposium on Antennas, Propagation & EM Theory
(ISAPE), pp.795-798, 2012
DOI: 10.1109/ISAPE.2012.6408891
By Shadi Dalirian
This article described the experiment on the absorption of 1-18GHz electromagnetic (EM) waves by
array plasma which was produced by many standard commercial fluorescent lamps placed directly
against each other in two rows.
Weak reflection and strong absorption were observed. Predictive peak electron density and collision
frequency were discussed and compared with measurement.
I. INTRODUCTION
This article shows that it has a strong absorption in a wide range of the EM wave frequency bands. Such an
explanation is accepted that there are multiple partial reflections and transmissions of EM waves in
inhomogeneous plasma, and more collision tends to increase the amount of absorbed power [1],[2]. Many
studies propose that besides the collision absorption, the resonance absorption
is also an important factor of enhanced absorption [3].
many standard commercial fluorescent lamps placed directly against each other in two rows are used to produce
an array plasma layer. Two polarizations of 1-18GHz frequency waves are under investigation: electric field of
the wave is either parallel (Ewave) or perpendicular (H-wave) to tube axis.
We first describe the details of the experiment. Then the interactions of normal incidence E-wave and H-wave
with two-dimensional inhomogeneous plasma are analysed. Finally, the predictive peak electron density and
collision frequency are discussed and compared with the experiment.
II. EXPERIMENT PROCEDURE
using an electro-optical converter, a program provides the system with a set of instructions to make a
Wiltron68347B synthesized signal generator generate a series of discrete signal over the desired frequency
range. The discrete frequency interval is 25 MHz and their powers are 0 dBm. After passing though the
fluorescent light tubes, received by receiver horn antennas, the EM waves are treated by a Hp8563E spectrum
analyzer with the resolving bandwidth (RBW) 1 MHz. Then, the powers of received signals are presented in
desired format by the other electro-optical converter and displayed by computer finally.(Fig.1)
Fig. 1 Experimental setup for measuring the attenuations of 1-18GHz EM
wave by fluorescent lamp plasma.
Using an oscilloscope shows that the plasma property is periodic at 34.72 kHz, that is the reason forneglecting
the plasma evolution with time. When turn on the fluorescent plasma, part of EM wave power has been
absorbed by plasma or been reflected back before being received.
III. PROPAGATION OF EM WAVE IN PLASMA WITH TWODIMENSIONAL
INHOMOGENEITY
This analysis is acceptable as a first approximation under the assumption that the array plasma properties vary in
xdirection and z-direction, and keep constant in y-direction.
IV.RESULTS AND DISCUSSION
The measured results of received power of E-waves and Hwaves are illustrated in Fig.2. It shows that strong
absorption of E-wave and H-wave both are present to the incident frequency ranging from 1 to 8GHz. But the
received power fluctuates significantly for 8-18GHz frequency E-wave rather than H-wave. So the influences by
special structure of array plasma are all neglected except for 8-18 GHz E-wave.
From Fig.3, it is reasonable to take the predictive parameters as plasma parameters approximately: the collision
frequency is about 1.3 GHz, and the peak plasma density is about 3.56×1011 /cm3, namely the peak plasma
frequency is about 3.2 GHz. The experiment in [8] reported that the electron number density of conventional
fluorescent lamp plasma ranges from 3.5×1010 /cm3 to 2.6×1011/cm3, and collision frequency is from 7×109
Hz to 4×1010 Hz. These data are consistent with our measurement roughly. The predictive plasma parameters
will help us to understand the behaviour of collision and resonance absorption by inhomogeneous plasma.
REFERENCES
[1] M. Laroussi, and J. Reece Roth, “Numerical Calculation of the Reflection Absorption and Transmission of
Microwaves by a Nonuniform Plasma Slab,” IEEE Trans. Plasma Sci.,. vol. 21, no. 4, pp.366-372, 1993.
[2] K. R. Stalder, R. J. Vidmar, and D. J. Eckstrom, “Observations of strong microwave absorption in collisional
plasmas with gradual density gradients,” J. Appl. Phys., vol. 72, no. 11, pp. 5089-5094 1992.
[3] M. Yan, K. R. Shao, X. W. Hu, Y. G. Guo, J. G. Zhu, and J. D. Lavers, “Z-Transform-Based FDTD
Analysis of Perfectly Conducting Cylinder Covered With Unmagnetized Plasma,” IEEE Trans. Magn., vol.43,
no.6, pp.2968-2970, 2007.