Weinong Sun

Single-Layer Microstrip High-Directivity Coupled-Line Coupler With Tight Coupling

A novel symmetrical coupled-line circuit structure without patterned ground plane is proposed to design tight-coupling high-directivity couplers, which would be found in numerous applications in a microstrip RF front end because of its simple structure and inherent excellent compatibility. Based on a traditional even- and odd-mode technique, closed-form mathematical equations for both circuit electrical parameters and scattering parameters are obtained. Due to the use of two coupled-line sections placed in the vertical direction, the directivity of this novel coupler without any other compensation techniques can be enhanced while maintaining tight-coupling performance of almost 3 dB. For demonstrative purposes, three typical full-wave simulation examples with realized physical dimensions in microstrip technology are presented, indicating high directivity and tight coupling coefficient. Finally, a practical microstrip coupled-line coupler is designed and fabricated to operate at approximately 2 GHz. The measured results show good return loss, quadrature phase characteristics, high directivity, and strong coupling performances.

A NOVEL COMPACT DUAL-FREQUENCY COUPLED- LINE TRANSFORMER WITH SIMPLE ANALYTICAL DESIGN EQUATIONS FOR FREQUENCY-DEPENDENT COMPLEX LOAD IMPEDANCE

In order to perfectly match arbitrary frequency-dependent complex load impedances at two uncorrelated frequencies, a novel coupled-line impedance transformer without transmission-line stubs is proposed in this paper. This transformer mainly features small size, wide bandwidth, simple analytical design method, and easy planar implementation. The transformer simply consists of a coupled- line section and an additional transmission-line section. Due to the usage of a coupled-line section, the theoretical synthesis of the proposed transformer becomes very simple when compared with previous transformers and the total size of the planar circuit without deterioration of operating bandwidth becomes small. Furthermore, several numerical examples are presented to demonstrate the ∞exible dual-frequency matching performance. Finally, the proflle of matching frequency-dependent complex load impedance at two arbitrary frequencies has been examined by simulation and measurement of two microstrip generalized T-junction power dividers. Good agreement between the calculated results and measured ones justifles this proposed transformer and the design theory.

Equivalent current model for assessing human exposure to inhomogeneous LF magnetic fields

A novel equivalent current model is proposed for evaluation of the induced electric field inside the human body due to exposure to a low-frequency magnetic field. The reconstruction of the equivalent current source adopts radial basis functions, which requires measurement of only one single magnetic field component. The magnetic vector potentials inside the human body obtained from the equivalent current is then incorporated into numerical calculations of the induced electric field inside human body. The accuracy of the proposed model has been demonstrated by comparing the electric field inside a homogeneous human model to that of the full-wave simulation.

THE EFFECT OF GAZE ANGLE ON THE EVALUATIONS OF SAR AND TEMPERATURE RISE IN HUMAN EYE UNDER PLANE-WAVE EXPOSURES FROM 0.9 TO 10 GHZ.

This article investigates the effect of gaze angle on the specific absorption rate (SAR) and temperature rise in human eye under electromagnetic exposures from 0.9 to 10 GHz. Eye models in different gaze angles are developed based on biometric data. The spatial-average SARs in eyes are investigated using the finite-difference time-domain method, and the corresponding maximum temperature rises in lens are calculated by the finite-difference method. It is found that the changes in the gaze angle produce a maximum variation of 35, 12 and 20 % in the eye-averaged SAR, peak 10 g average SAR and temperature rise, respectively. Results also reveal that the eye-averaged SAR is more sensitive to the changes in the gaze angle than peak 10 g average SAR, especially at higher frequencies.

Detailed modeling of palpebral fissure and its influence on SAR and temperature rise in human eye under GHz exposures

This article investigates variations in specific absorption rate and temperature rise in human eye caused by changes in palpebral fissure, the extent of opening between eyelids, under GHz plane-wave electromagnetic (EM) exposures. Detailed human head models with different palpebral fissure features were developed with a refined spatial resolution of 0.25 mm. These head models were then incorporated into both EM and bio-heat simulations, but using finite-difference time-domain method and finite-difference method, respectively. Maximum temperature rise in lens was found to be 0.8°C under EM exposure at 100 W/m(2). Results reveal that changes in palpebral fissure would produce a 0.23°C variation in maximum temperature rise in lens.

Impact of magnetic field generated by wireless power transfer system of electric vehicle on retinal pigment epithelium cell in vitro

This pilot study investigated the potential risk of damage to DNA of Retinal Pigment Epithelium (RPE) cells due to the exposure of acute magnetic field (MF) of wireless power transfer (WPT) of electric vehicles (EV) at 100 kHz. In our controlled experiment, two lines of RPE cells were cultured at the same level in the incubator with 37°C and 5% CO2, while a new exposure system generating homogeneous magnetic field was designed and fabricated used for imitation of exposure of WPT systems at selected frequencies and field intensity. A group of Retinal Pigment Epithelium (RPE) cells were exposed continuously for 24h in the derived magnetic field of 3A/m, and compared with the sham-exposed control group after the same time. The impact of derived magnetic field on the induced DNA damage was investigated by comet assay and DNA fragment concentration test in two cell lines. This study has indicated that the 24h magnetic field exposure of WPT would barely cause any impact on DNA damage in RPE cell.

Impact of magnetic-field generated by wireless power transfer of electric vehicles on brain waves and neuro-psychological changes

This pilot study investigates the neuro-psychological impacts of wireless power transfer (WPT) of electric vehicles, by correlating the electromagnetic radiation (EMR) with brain wave activities. In our experiments, fourteen subjects participated, under a one-blind controlled 10 MHz EMR of WPT environment. Electroencephalographs (EEGs) were recorded for each 5-minute time session before, during, and after exposure to the EMR. The psychological responses of the participants were inquired by questionnaires with psychometric scales before and after the experiments to correlate the EMR exposure with their psychological status. This study has indicated that the short term EMR of WPT would barely cause any impact on the brain wave activities, and did not lead to specific emotional changes of the participants in the short term exposure to EMR.

Prediction of magnetic field radiation using equivalent current distribution

Near field measurement has commonly been used as an efficient and effective method for EMC diagnosis purpose for prediction of electromagnetic field radiation in an electronic circuit design; the near field values are obtained on scattered points on the measurement plane. In the paper, we investigated a novel method in predicting the magnetic field radiation using measurement of only a single magnetic field component, by reconstruction of an equivalent current source of the interpolated measurement data. Numerical tests have demonstrated the effectiveness of the proposed method.

Impacts of radio frequency interference on human brain waves and neuro-psychological changes

This study investigates the neuro-psychological impacts of radio frequency interference (RFI) by correlating the brain waves under RFI exposure. In our experiments, twelve participants were tested under controlled RF exposure at 1.8 GHz in an anechoic chamber under one-blind condition. The electroencephalograph (EEG) were recorded for each 5-minute time trial before, during and after RF exposure with an intensity of 10% of the ICNIRP Guideline exposure limits. The psychological responses of the participants are inquired with psychometric scales before and after the experiment to analyze the correlationship between RFI and the emotional reaction of humans. Statistical tests indicate that theta and alpha waves were able to be characterized, and the significant differences were observed in both alpha waves and theta waves between the data before and after exposure from the consequence of paired t-tests. This initial study indicated that short term exposure to RFI may cause impacts on brain waves, but may not lead to any direct emotional changes by the participants.

A Compact Microstrip Wideband Arbitrary Branch-Line Coupler with Coupled-Line Impedance-Transforming Structures

Abstrct A novel coupled-line impedance-transforming structure with two parallel short-circuit stubs is proposed to design a wideband branch-line coupler with arbitrary power division in this article. In order to design this modified wideband branch-line coupler, analytical synthesis equations are obtained. As typical examples, four wideband branch-line couplers with different power dividing ratios are presented. The widest 20-dB return loss and isolation fractional bandwidth in these four numerical examples is almost 38%. Finally, two microstrip branch-line couplers operating at 1 GHz are fabricated and measured. One of these couplers has equal power division and a measured 13.9-dB return loss and isolation fractional bandwidth of 32.8%. The other one has 3-dB unequal power division and a measured 12.7-dB return loss and isolation fractional bandwidth of 37.6%. Obviously, this proposed branch-line coupler has several advantages, including a wide band, a compact size, an unequal power division, easy implementation (simple structure), and an analytical design method.