Design of HAC compatible mobile phone with LC band-stop filter embedded in PWB

People who have some level of hearing loss normally have to use hearing aids to improve their hearing ability. Digital mobile phones can cause interference to hearing aids because of the electromagnetic (EM) energy emitted by the phone's antenna, backlight, GSM burst noise and other components. As required by the FCC, a certain percentage of all sold mobile phone models must be hearing aid compatibility (HAC) compatible. Even though some HAC compliant phones are available on the market, it still requires huge effort in doing so. Therefore, it is quite urgent for mobile phone makers to design HAC compatible mobile phones, in which the strength of the near-field EM fields of the phones reduces to a certain level in the HAC region. According to the FCC requirement, the E-field strength limits for low and high GSM bands are 266.1V/m and 84.1V/m, respectively, whereas the H-field strength limits are 0.804A/m and 0.254A/m. To meet this HAC requirement, approaches for reducing the undesirable effects of the near field EM scattering around the HAC region need to be developed. In particular, a metallization termination technique was used to reduce the EM field scattering at the edge of the printed wring board. A high-impedance thin layer was employed to reduce the EM field scattering at the edge of the PWB. However, these two approaches might cause a reduction of the total radiated power (TRP). In this paper, an alternative way for designing HAC compatible mobile phones is proposed.