K. H. Chan

Electromagnetic Interference Immunity Testing of Medical Equipment to Second- and Third-Generation Mobile Phones

There has been concern regarding the effect of electromagnetic interference (EMI) on medical equipment from portable wireless communication devices in hospitals in Hong Kong. The latest third-generation (3G) mobile communication system was fully implemented in 2004. As a result, an investigation to examine the EMI issues surrounding medical equipment, due to interference from communication devices, including GSM900, PCS1800, and 3G digital mobile phones, has been carried out. A statistical analysis has shown that the cumulative distribution function of base station signals within the hospitals environment follows the Weibull distribution for all three mobile phone systems in Hong Kong and that the percentage of failed medical equipment increases with a correlation of an increase in the radiated power level of the mobile phone. This is a direct result of a weakening in base station signals. The EMI effect from 3G mobile phones is also found to be four to eight times lower than that of the GSM900 and PCS1800, in locations inside the hospitals with weak base station signal strength, such as a basement or in operation theaters.

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.

An investigation of the SAR reduction methods in mobile phone applications

Due to the rapid growth in the use of wireless communication systems, there has been a recent increase in public concern regarding the exposure of humans to radio frequency (RF) electromagnetic radiation. This is particularly evident in the case of mobile telephone handsets. This paper aims to provide an investigation of the effectiveness of various commercially available Specific Absorption Rate (SAR) reduction products and shielding materials that can be externally attached to the handsets in Hong Kong. Also, the SAR values of different mobile phones are measured. Results are compared to the USA and European standards and then characterized for SAR reduction applications.

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.

Effect of internal patch antenna ground plane on SAR

This paper investigates the effect of different ground plane configurations of a typical internal planar inverted-F patch antenna (PIFA) on specific absorption rate (SAR). The effect of the size and the addition of vertical sidewall of the ground plane are investigated; it is found that by varying the ground plane locations and configurations, SAR value can be reduced by 15%

Effects of Phase Difference in Dipole Phased-Array Antenna Above EBG Substrates on SAR

In this letter, we investigate the specific absorption rate (SAR) of a dipole phased-array antenna above an electromagnetic band-gap (EBG) substrate. A two-element array antenna above an EBG substrate is considered for fourth-generation mobile applications at the 3.5-GHz band. The computational results indicate that the use of an EBG substrate in a phased-array antenna can provide an SAR reduction of over 70%. The SAR reduction also depends on the phase difference of the phased-array antenna.

Development of electromagnetic compatibility courses at the City University of Hong Kong

EMC compliance is a mandatory requirement for electronic and electrical devices export to European countries and the USA. Hong Kong is an export-oriented city with 23% of the total export in electronic and electrical products; knowledge in EMC design and standards are highly desirable to engineers in Hong Kong. To cater for these particular needs of the local industry, EMC was introduced as an undergraduate course in 1994, prior to the effective date of implementation of EMC Directive 89/336/EEC in 1996. After 15-years of development and modification, the EMC course has now become one of the most popular postgraduate courses in Hong Kong. The course includes lectures, EMC standard interpretation, case studies, together with an emphasis on the hands-on experience of EMC tests and facilities in the EMC test laboratory. In this paper, a summary of the development of the EMC course at the City University of Hong Kong in the last decade are presented, and some possible future EMC needs are discussed at the end.

Experimental study of ESD effect on metallic enclosure

Electrostatic Discharge (ESD) can cause serious problems in digital electronic devices. Indirect coupling through apertures on the metallic enclosure to the internal circuitries can also affect the performance of the devices. In this paper, we investigate experimentally the effect of the coupling field through apertures on the metallic enclosure.

Specific absorption rate evaluation for people using wireless communication device in vehicle

In this paper, a specific absorption rate (SAR) evaluation on human exposure from wireless communication devices inside a vehicle is investigated. A finite-difference time-domain method (FDTD) is used for simulating the electromagnetic field distribution inside the vehicle. Results have shown that the maximum SAR induced for a mobile phone user in the vehicle is only increased by 5% when compared to free space. Results have also indicated that other passengers in the vehicle are also inducing various levels of the SAR values in their bodies. The induced SAR values can be as high as about 40% of the maximum SAR value induced in the mobile phone user.

Antenna performance of mobile phone and corresponding human exposure inside fully and partially enclosed metallic elevator

The effects of using mobile phone inside both fully and partially enclosed metallic elevators on the antenna performance and the human exposure have been studied by using FDTD numerical method. It has been found that the antenna performance is degraded in all the enclosed metallic elevators studied due to the low radiation efficiency. Results have also shown that, for the human exposure, the electric field strength and the peak SAR of mobile phone user in the fully enclosed metallic elevator is the largest due to the resonance effect.