Electromagnetic compatibility

: from PCB issues to human safety issues of electromagnectic fields radiation

Abstract

Electromagnetic Compatibility (EMC) can be dealt with in many ways - from a relatively microscopic level, such as in Printed Circuit Boards (PCB), to the level of stand-alone equipments and large systems, as well in relation to concerns regarding human safety with respect to the exposure to Radio Frequency Interference (RFI). All levels are becoming important due to both, the widespread utilization of the Electro-Magnetic (EM) frequency spectrum nowadays and the increases in the operating frequency of electronic products that has taken place over the last decade. In this thesis, several aspects of the EMC problems are looked into, including the signal integrity problem in high-speed digital PCBs, interference problems due to environmental noise at the equipment level, and the impact on human safety, particularly to the human head caused by mobile phone radiation. Certain EMC regulations and requirements are mandatory for electronic products intended for markets in either the European Union or the USA. In order to achieve EMC compliance, EMC techniques at the circuit level are important. Signal integrity problems in PCBs, such as cross-talk, ground bounce and ringing in traces, have become more common with the increase of the clock speeds in digital circuits. In Chapter 2, Ground Bounce (GB) effects in PCBs are investigated using the Generalized Transmission Line Equation (GTLE). GB effects in both power/ground and trace/ground configurations are characterized, the effects of the rise time of the digital signal, the dielectric properties of the PCB, and the source resistance to the frequency and magnitude of the GB waveform are analysed. In Chapter 3, the interference problem of the environmental noise in electronic equipments is discussed; a case study of the suitability of installing Information Technology Equipment (ITE) at a site in a typical, densely populated commercial region in Hong Kong is investigated. The RFI measured at the site is referenced to European and American standards. In recent years, an awareness has been developing that RFI may cause adverse effects on human health. Many RF equipment, such as for TV and radio broadcasting, satellite communication, and cellular communication, are being installed throughout Hong Kong both in public areas and in residential areas, which are in close proximity to each other. In Chapter 4, several case studies, ranging from power frequency to cellular communications frequencies, are presented. Firstly, an assessment of the magnetic field radiated at power frequency by a 3-phase transformer substation is described. Secondly, study of the safety zone for a high power transmitter at middle wave frequency for a radio station is presented. Finally, EM radiation levels in an urban area of Hong Kong within the communications and broadcasting frequency band of 30MHz to 2GHz are measured and analysed. Safety levels for the exposure of humans to mobile phone radiation are investigated in Chapters 5, 6 and 7. In Chapter 5, the characteristics of Specific Absorption Rate (SAR) due to different parameters, such as transmission frequencies and positions, and different antenna types and profiles of mobile phones, are presented. In Chapter 6, a study of the effectiveness of various commercially available SAR reduction products and shielding materials that can be externally attached to handsets is presented and summarised; the effects on SAR and on the far-field antenna pattern due to different attachment positions of shielding materials on mobile phones are also discussed. A simple dual-band internal antenna for both GSM900, PCS 1800 has been fabricated for the investigation of SAR, and is presented in Chapter 7. The effects on antenna performance such as return loss, far-field pattern and near-field pattern, due to the presence of human head are also analysed using both numerical and experimental methods. As a conclusion, the results and findings regarding various aspects of EMC are summarised in Chapter 8.

Date of Award	15 Jul 2004
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Sai Wing Peter LEUNG (Supervisor)