Hearing Microwaves: The Microwave Auditory Phenomenon

In common usage, the handset of a wireless telephone is held against the ear. Computational and experimental studies have demonstrated that about 50% of the radiated RF/microwave energy is deposited in tissues on the same side of the head, nearest to the telephone. The deposited energy measured in specific absorption rates (SAR) of RF/microwave energy is nonuniformly distributed inside the head. Depending on the specific model used, the SAR inside the inner ear is about 20-40% of that permissible by existing rules and regulations. The permissible SAR from exposure to cellular mobile telephone radiation in Europe, Japan, and by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) is 2 W/kg in any 10 g of tissue in the head. The maximum SAR allowed by rules of the U.S. Federal Communication Commission (FCC) and IEEE standard is 1.6 W/kg in 1 g of tissue. The possible health risk associated with mobile telecommunication devices, used close to the human head and, in particular, effects on the inner ear and hearing of users have been recommended for further investigation by several groups. Recently, a number of projects have been initiated in France, Germany, and Italy to investigate the structures and functions of the middle and inner ear following exposure to wireless communication radiation. Examination of the organic correlation of damage to hearing and any functional otoacoustic effects on the cochlear epithelium in the inner ear of rats exposed to wireless communication radiation is still in the preliminary stage [1]. Thus, the potential effect on the auditory system, as may be revealed through objective evaluation of organic correlates, must await the conclusion of ongoing experiments. However, the phenomenon of microwave-induced auditory sensation in humans and animals is a well-established effect [2]. The microwave auditory phenomenon, or microwave hearing effect, pertains to the hearing of short pulses of modulated microwave radiation at high peak power by humans and laboratory animals. Anecdotal and journalistic reports of the hearing of microwave pulses persisted throughout the 1940s and 1950s. The first scientific report of the phenomenon appeared in 1961 [3]. The effect has been observed for RF exposures across a wide range of frequencies (450-3,000 MHz). It can arise, for example, at an incident energy density threshold of 400 mJ/m for a single 10-μs-wide pulse of 2,450 MHz microwave energy, incident on the head of a human subject, and it has been shown to occur at an SAR threshold of 1.6 kW/kg for a single 10-μs-wide pulse of 2,450 MHz microwave energy, impinging on the head. A single microwave pulse can be perceived as an acoustic click or knocking sound, and a train of microwave pulses to the head can be sensed as