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Auditory response to pulsed radiofrequency energy
1Motorola Florida Research Laboratories, Ft Lauderdale, FL 33322, USA. joe.elder@motorola.com
Bioelectromagnetics
|November 25, 2003
Summary
Radiofrequency (RF) hearing is a phenomenon where RF energy creates audible sounds. This effect, explained by thermoelastic expansion, is a biological response without adverse health implications.
Area of Science:
- Bioacoustics
- Electromagnetic bioeffects
- Auditory science
Background:
- Radiofrequency (RF) hearing, the perception of sounds induced by RF energy, is a recognized phenomenon.
- RF-induced sounds are typically low-intensity, requiring quiet environments and resembling common noises like clicks or buzzes.
- The ability to perceive these sounds depends on high-frequency acoustic hearing above 5 kHz.
Purpose of the Study:
- To explain the mechanism behind RF hearing.
- To determine the relationship between RF energy and auditory perception.
- To assess the health implications of RF-induced auditory effects.
Main Methods:
- Review of human, animal, and modeling studies on RF hearing.
- Analysis of the physical characteristics of RF-induced sounds (frequency, intensity).
- Comparison of pressure generated by RF pulses to acoustic and ultrasound pressures.
Main Results:
- RF hearing occurs across frequencies from 2.4 to 10000 MHz.
- Sound perception is linked to single pulse energy, not average power density.
- The thermoelastic expansion theory, involving rapid thermal expansion causing sound transients, best explains RF hearing.
- A temperature rise of only 5 x 10^-6 degrees C in tissue is sufficient for threshold detection.
Conclusions:
- RF hearing is a biological effect resulting from thermoelastic expansion within or near the cochlea.
- Perception of RF-induced sounds at high exposure levels is considered a biological effect without associated health risks.
- The pressure generated by RF pulses is significantly lower than that from hazardous acoustic energy or clinical ultrasound.