Wireless Telephone-Hearing Aid Electromagnetic Compatibility Research at the University of Oklahoma

Abstract

A multiphase study examining electromagnetic compatibility (EMC) between wireless digital telephones and hearing aids has been under way at the University of Oklahoma EMC Center since May 1995. In a phase 1 clinical study involving 68 hearing aid wearers, interference varied significantly by telephone technology, hearing aid type, and hearing loss characteristics. More than 80 percent of the tests resulted in either no interference or a detection threshold distance less than 1 meter. Metallic shielding of the units yielded positive results. Various elements of phase 2 involved instrument-based tests of hearing aid interference using telephones in a sound-isolation chamber and radio frequency signals in a waveguide, along with clinical studies of speech-to-interference ratios, all leading to the development of standards of measurement and performance criteria for telephone emissions and hearing aid immunity. Results to date confirm that bystander interference is of less concern than user interference, which is the focus of continuing research.

Abbreviations: ASC = Accredited Standards Committee, AMPS = advanced mobile telephone system, ANSI = American National Standards Institute, BTE = behind the ear, CDMA = code division multiple access, CIC = completely in the canal, EMC = electromagnetic compatibility, GSM = Global System for Mobile Communications, IRIL = input referenced interference level, IRIS = input referenced interference spectrum, IS = international standard, ITC = in the canal, ITE = in the ear, J-STD = “J” standard, NAL = National Acoustic Laboratories, PCS = personal communication services, RF = radio frequency, TDMA = time division multiple access

Keywords

Bystander interference - electromagnetic compatibility - electromagnetic interference - hearing aid - input referenced interference spectrum - radio frequency waveguide - speech-to-interference ratio - user interference - wireless digital communications

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