Effects of Chassis Currents on Hearing Aids Compatibility in the Handset

In this paper, we investigate the effects of the chassis wavemodes on the near-field electromagnetic intensities that contribute to hearing aid compatibility (HAC) tests at two different frequencies, 900 and 1880 MHz. For a comprehensive view, we also examine the far-field properties of the antenna total efficiency and bandwidth. Additionally, we examine the specific absorption rate in relation to the chassis wavemodes. The examined parameters are then related to the HAC. It was found that the chassis wavemodes have a significant effect on the antenna near-field performance, especially at the 900-MHz frequency range. We show that the optimum near-field antenna performance is achieved when the antenna resonant frequency is aligned with the chassis resonant frequency. With this, a decrease of about 50% can be achieved in the peak magnetic field intensity and a 30% decrease in the peak electric field intensity; hence, a better possibility in passing the HAC compliance tests. Moreover, controlling the chassis wavemodes has a similar effect to that of increasing the distance from the HAC scan plane-a rapid decrease in the field intensities can be achieved. Our analyses are done through simulations and these are validated against measurements.