INTRODUCTION
Dissertation Objective
We know that major problems can be eliminated through the use of an EM wave absorber. But the EM wave absorber using three absorbing materials has not been investigated and developed in the W band of millimeter wave.
Outline of Remaining Chapters
The original purpose of the development of the EM wave absorber was mainly its application to the anechoic chamber. As a result, the absorptivity of the sample containing Permalloy:CPE = 70:30 wt% has a maximum value in the frequency range of 65–110 GHz.
NAVIGATION RADAR FUNDAMENTAL
History of Radar Development
The decisive event that made the practical development of microwave radar possible was the invention of the cavity magnetron by Randall and Boot in Britain. In the transmitter area, the development of the high power reaching wave tube (TWT), millimeter wave power tubes, solid state microwave sources and stable computer controlled oscillators were important.
Radar System Fundamentals
A navigation radar requires at least three non-planar beams to measure the vector velocity, that is, the speed and direction, of the aircraft. This Doppler shift can be fed into a sermechanism that will align the antenna axes with the aircraft's ground track.
Millimeter Wave Radar
This shows several peaks that arise from absorption of the radio signal by water vapor (H2O) and oxygen (O2). One of the largest and most important uses of millimeter waves is to transmit large amounts of data.
Contributions of EM Wave Absorber
It is known that the absorbance of sample containing Carbon tends to increase from 10 wt% to 20 wt% and to decrease from 30 wt% to 50 wt%, the absorbance of sample containing TiO2 has a tendency to increase from 40 wt% to 70 wt% and decrease from 70 wt% to 80 wt%, and the absorbency of sample containing Permalloy has a. 1] Dong Il Kim, Chang Mook Choi, “A Study on the Electromagnetic Wave Absorbers,” The 6th Asia-Pacific Engineering Research Forum on Microwaves and Electromagnetic Theory, Shanghai, China, pp.
THEORY OF EM WAVE ABSORBER
History of EM Wave Absorber
Halpen at the MIT Radiation Laboratory in the United States, an application type absorber was developed. The reduction in the radar cross section (RCS) of a target has been achieved by a number of methods such as the adaptation of geometric shapes to reduce the reflection at certain sensitive angles and the application of the RAM on the target surface [34].
Electromagnetic Theory
3.8) represents a wave traveling in the negative z direction; hence the notation E+ and E− for these wave amplitudes. The positive traveling wave then has a propagation factor of the form . z j z. z e e .. which has the form in the time domain.
Loss mechanism
The absorption capacity of the absorber is measured quantitatively by the reflection coefficient in decibels. This value of -20 dB corresponds to an electric field reflection coefficient value of 0.1 and an electricity reflection coefficient value of 0.01, as shown in Table 3.1.
Classification of EM Wave Absorber
The matching characteristic depends on the frequency dispersion characteristic of the complex relative dielectric constant of the absorber. It can absorb the EM wave because it depends on the frequency dispersion characteristics of the complex relative permeability. The planar type absorber has the shape of a flat surface in the plane of incidence of the EM wave, as shown in Fig.
This wave absorber has the shape of a sawtooth in the plane of incidence of the EM wave, as shown in Fig.
Application of EM Wave Absorber
The sample containing TiO2 : CPE = 70 : 30 wt% has a maximum value in the imaginary part of the permittivity. The sample containing Permalloy : CPE = 70 : 30 wt% has a maximum value in the imaginary part of permittivity and permeability. The fabricated EM wave absorber containing Carbon:CPE = 30:70 wt% has a thickness of 0.7 mm and an absorption power higher than 24 dB at 94 GHz, as shown in Fig.
The fabricated EM wave absorber containing Permalloy:CPE = 70:30 wt% has a thickness of 1.15 mm and an absorption power higher than 18 dB at 94 GHz, as shown in Fig.
DESIGN OF EM WAVE ABSORBER
Introduction
For the EM wave absorber made of a conductor supported single layer as shown in Fig. From the measured values of z, the frequency characteristics of material properties are calculated in terms of the following expression: .. where λ is the wavelength, d is the thickness of the sample, μris the complex relative permittivity, and εr is the complex relative permittivity. If the EM wave absorber is designed in a rectangular waveguide as shown in Fig. 4.2, TE10 mode is the only propagation mode in waveguide region [38], and the normalized input impedance is expressed as [22].
4.5) has been solved, the relationship between the material properties (complex relative permittivity and permeability) and the sample thickness can be simulated.
Single-layer Absorber
In the case of normal incidence of the TE wave, we can get the reflection coefficient by setting θi =0.
Multi-layer absorber
The optimized result of sample containing carbon:CPE=30:70 wt% has a thickness of 0.7 mm and absorption capacity higher than 22 dB at 94 GHz as shown in fig. The optimized result of sample containing TiO2:CPE=70:30 wt% has a thickness of 1.45 mm and absorption capacity higher than 25 dB at 94 GHz as shown in fig. The optimized result of sample containing Permalloy:CPE=70:30 wt% has a thickness of 1.4 mm and higher absorption capacity than 22 dB in the frequency range 76-77 GHz as shown in fig.
The optimized result of sample containing Permalloy:CPE=70:30 wt.% has a thickness of 1.15 mm and absorption capacity higher than 20 dB at 94 GHz as in Fig.
MATERIAL PROPERTIES
Introduction
The observed change in the frequency and resonance width is related to the real and imaginary parts of the permittivity. The transmission line methods are also classified as one-port method and two-port method. One-port method is a reflection measurement taken on two short-circuited samples of lengths.
The waveguide sample holder has the advantage that the rectangular shape makes the sample easy to shape.
Measurement Techniques of Material Properties
gate method is a reflection measurement performed on two short-circuited longitudinal samples. Within the sample region, the characteristic impedance normalized to ZO and the propagation constant are obtained as follows: where εr and μr are the complex relative permittivity and permeability of the sample, respectively. 5.3) or (5.4), respectively, the normalized characteristic impedance and propagation constant allow us to solve the complex relative permittivity and permeability.
Assuming that no source and load match, then Eq. 5.16) describes the electromagnetic connections in each area of Fig. 5.2 Two-port method using air line with filled material.
Manufacturing Process of Absorber
Measured Material Properties
The complex relative permittivity of samples containing different composition ratios of carbon and CPE is calculated in the frequency range of 65–110 GHz using measured S-parameters. Figures present plots of the real and imaginary parts of the permittivity as a function of frequency for samples. The complex relative permittivity of samples with different composition ratios of TiO2 and CPE is calculated in the frequency range of 65-110 GHz using measured S-parameters.
The complex relative permittivity and permittivity of samples containing different compositional ratios of permalloy and CPE is calculated in the frequency range 65–110 GHz using the measured S-parameters.
SEM Photographs
Optimized sample result containing carbon:CPE=20:80 wt. %, has a thickness of 2 mm and an absorption capacity higher than 20 dB in the frequency range of 76-77 GHz, as shown in the figure. Optimized result of sample containing TiO2: CPE=70:30 wt. % has a thickness of 1.85 mm and an absorption capacity higher than 20 dB in the frequency range of 76-77 GHz as shown in the figure. The EM wave absorber has a thickness of 0.7 mm and an absorption capability higher than 24 dB at 94 GHz for missile guidance radar.
An EM wave absorber has a thickness of 1.4 mm and an absorption capability greater than 18 dB in the frequency range of 76-77 GHz for collision avoidance radar.
ABSORPTION ABILITY
Introduction
However, since the construction of most finished absorber products is unsuitable for insertion into small coaxial lines or waveguides, free-space methods are used as a non-destructive evaluation. Transmission line methods and free space methods are described in section 6.2 and 6.3 respectively. Sections 6.4 and 6.5 show the simulated absorptive capacity and the measured absorptive capacity of the produced absorbers, respectively.
In this research, a rectangular waveguide as a transmission line method is used to evaluate the fabricated absorbers.
Measurement Techniques of Absorption Ability
Good contact is generally ensured if the specimens fit snugly in the holder without deformation, which is sometimes difficult to achieve when the test material is soft or rubbery. Although these are labeled free-space methods, the label refers only to the fact that the test panel is not mounted in a waveguide or transmission line. Since arc antennas are placed at best a few meters from the test specimen, the phase fronts incident on it are spherical.
The test panel used in the RCS method of absorber evaluations should probably be at least 5λ along a side at the lowest frequency used in the measurements, but no greater than 25λ at the highest frequency.
Simulated Absorption Ability
Absorption capabilities of the EM wave absorbers are simulated using the measured complex relative permittivity by changing the thickness without changing the composition. It is shown that the absorbency tends to increase with increased composition ratio of Permalloy. Note also that the maximum absorbency for sample containing Permalloy 40% by weight is approx. 4.5 dB at 92 GHz, the maximum absorption power for sample containing Permalloy 50% by weight is approx. 10 dB at 76 GHz, the maximum absorption capacity of the sample containing Permalloy 60% by weight.
The absorption capacity of the EM wave absorbers is simulated using the measured complex relative permittivity and permeability by changing the thickness without changing the composition.
Measured Absorption Ability
The EM wave absorber has a thickness of 2 mm and an absorption capacity higher than 20 dB in the frequency range of 76-77 GHz for collision avoidance radar. The EM wave absorber has a thickness of 1.85mm and an absorption capacity greater than 20dB in the frequency range of 76-77GHz for collision avoidance radar. The EM wave absorber has a thickness of 1.45 mm and an absorption capability higher than 17 dB at 94 GHz for missile guidance radar.
The EM wave absorber has a thickness of 1.15 mm and an absorption capability higher than 18 dB at 94 GHz for missile guidance radar. 8] Dong Il Kim, Chang-Mook Choi, Rui Li, and Dae Hee Lee, “Study on electromagnetic wave absorber for W-band radars using permalloy,” IEICE Trans. 10] Dong Il Lim, Chang-Mook Choi, Rui Li, and Dae Hee Lee, "Study on electromagnetic wave absorber for W-band radars using permalloy," IEICE Trans.
CONCLUSIONS
