Electromagnetic Reflection Characteristics Research Articles

The effect of metal objects on the SAR and temperature increase in the human head exposed to dipole antenna (numerical analysis)

Wearable metal objects with high electromagnetic reflection characteristics can cause interference with the incident waves during exposure to the electromagnetic (EM) radiation. Therefore, it is of interest to investigate the effect of metal objects capable of increasing the absorption of EM energy and temperature within the tissues when get exposed to EM radiation. A numerical analysis of increase in specific absorption rate (SAR) and temperature distribution in a human head model when metal objects are placed between the head and radiating source is performed. A realistic three-dimensional heterogeneous human head model, metal objects of different shapes and sizes, and spectacles with different lenses are used. A half-wavelength dipole antenna operating at 1800 MHz served as an EM radiation source. Results show that the presence of metal objects in proximity to the head alters SAR and temperature increase within the tissues. In most cases, metal objects redistribute the EM field incident upon them to a smaller region increasing power absorption, thereby increasing SAR and temperature in that region. The power absorption in head layers is found to be sensitive to metal object's size and shape, and distance of the antenna from the objects.

A Reflection Measurement System With High Accuracy Using Binary Coded Signals

The measurement of the electromagnetic reflection characteristics of a device under test (DUT) is of interest in a large variety of applications. For this task, the established low-cost approach of using pulse-shaped excitation signals is more and more replaced by employing continuous binary coded excitation signals. The reason behind this is that reflection measurement systems with continuous signals offer a larger signal-to-noise ratio (SNR), which allows for a larger dynamic range compared to pulsed systems for the same measurement time. However, a correlator is needed to access the impulse response function (IRF) of the DUT. In this contribution, a reflection measurement system is presented using a hybrid correlation approach. In the latter, the correlation is performed using a combination of a hardware and a software correlator. The hardware of the developed measurement system has been optimized to achieve a high dynamic range and a high measurement accuracy. A demonstrator system has been realized using the so-called almost perfect auto-correlation sequences (APASs) with a chip clock of 5Gchips/s. With the optimized hardware, a dynamic range of 82 dB has been achieved. The measurement accuracy has been validated by means of distance measurements versus a high accuracy laser reference system achieving a maximum error of 25 ${\mu }\text{m}$ . Furthermore, the measured reflection coefficient of a low-pass filter has been compared with the results obtained with a vector network analyzer (VNA).

A Novel Passive Jamming Method Against ISAR Based on Resonance Absorption Effect of Metamaterials

Based on resonance absorption effect of metamaterials, a novel passive jamming method against Inverse Synthetic Aperture Radar (ISAR) is proposed in this paper. By adopting a cross-shaped metamaterial, the resonance frequency is designed within the ISAR bandwidth. Using the finite integration technique to calculate the electromagnetic reflection characteristics, the scattering point model and distorted radar echo of the target coated with the designed metamaterial are obtained. Then, the ISAR imaging analysis model of the target coated with the cross-shaped metamaterial is established. Finally, jamming effects of the cross-shaped metamaterial on the ISAR imaging are studied and verified. The range profile result indicates that besides the energy attenuation, the single radar target becomes two false radar targets, both of which are not located at the real target position. The ISAR imaging result shows that the target becomes blurred and many low-brightness points are produced. The passive jamming method could have a negative impact on the ISAR image target recognition applied to aircrafts, ships, and missiles.

Residual stress and electromagnetic characteristics in loop type frequency selective surface embedded hybrid structures

Residual stresses occur in frequency-selective surface (FSS)-embedded composite structures after co-curing due to differences between the coefficients of thermal expansion between composite skins and FSSs. Furthermore, the electromagnetic characteristics may be affected by the deformation of the FSS pattern by residual stresses. Therefore, we studied the changes in electromagnetic characteristics due to the deformation of FSS, using residual stresses to deform loop-type FSS-embedded hybrid composites. We considered the effects of loop-type FSS patterns of equal dimension as well as the stacking sequences of composite laminates on the electromagnetic characteristics of FSSs: Square loop, triangular loop and circular loop. The stacking sequences of composite laminates considered in this study were [0]8, [0/90]4, [±45]4 and [0/±45/90]2. The FSS was located between composite laminates in the middle plane. To determine the residual stresses and deformations in the FSS embedded laminate structures, the thermal loading condition in the finite element analysis was induced by cooling the hybrid structures from 125°C to 20°C based on the cure cycle of the composite. Also, the electromagnetic reflection characteristics of the hybrid structures were predicted using deformed models by residual stresses, considering the effects of stacking sequence of composite laminates. The results showed that the maximum residual stresses and deformations were produced in the [0]8 composites with all three loop-types of FSS pattern. However, the maximum resonance frequency shifts occurred in the square and triangle loop-types with stacking sequence of [0]8, while the maximum resonance frequency shift occurred in the circular loop-type with stacking sequence of [0/±45/90]2.

The Design and Application of Aircraft Flight Stimulation and Visualization Based on HLA

Aircraft training simulator has integrated combat training ability not only needs to simulate the aircraft flight and radar, inertial navigation and avionics equipment, but also to generate realistic battlefield environment and visual effects, and to simulate the interaction between the system and the complex interaction. In the realization of the simulator, using HLA/RTI as its architecture and the supporting platform, make the device emulator is to achieve interoperability, can improve the system's flexibility and scalability. [ The target and the electromagnetic reflection characteristics of ground data and radar detection model based on the dynamic radar image generation. The blackboard model is based on the virtual machine technology, which is easy to modify and evolution of CGF system. [Combat aircraft is the main weapon platform in modern war, and aircrew training level is an important factor which affects the combat effectiveness of an aircraft. Research on the domestic and abroad aircrew training methods and training methods with simulate system, develops advanced technology, which can achieve close to actual combat to training effect and save a lot of training funds.

The Physics of Microwave Calorimeters

The electromagnetic reflection characteristics of a system of nonideal isotropic dielectrics in nearly ideal wave guides are formally developed. The general analytical results are applied to several cases of practical importance. Consideration is given to the manner of deriving optimum characteristics of flow calorimeters normally used for microwave measurements of power. Other applications include the determination of the complex dielectric constant of high loss quid dielectrics. Considerations relating to bandwidth of microwave calorimeters are included.