Hearing aids can unintentionally pick up radio signals, a phenomenon known as Radio Frequency Interference (RFI). A hearing aid is a miniature, highly sensitive electronic amplifier. When a strong electromagnetic field is present, the internal circuitry of this amplification device can inadvertently act as a radio receiver. RFI occurs when the hearing aid’s components are exposed to radio waves strong enough to be detected and converted into an audible signal.
The Phenomenon of Unintended Radio Frequency Interference
When a hearing aid encounters RFI, the user typically hears a variety of unwanted sounds. This interference often manifests as a distinct buzzing, clicking, or pulsing noise. Users may also hear garbled speech, fragments of music, or static, depending on the source of the radio waves. This reception is a function of physics involving strong electromagnetic energy.
Common sources of this interference include powerful, nearby AM or FM radio transmitters. Digital wireless devices, especially older digital cell phones using the GSM protocol, are frequent culprits, producing a characteristic, rapid buzzing due to their pulsed signal. Other sources of strong electromagnetic fields can also trigger RFI. These include taxi or police two-way radios, certain industrial machinery, and switching power supplies from computers.
Why Hearing Aids Act as Unintentional Receivers
The unintentional reception of radio signals results from the hearing aid’s compact electronic design. Small wires and conductive paths inside the device, such as those leading to the battery, microphone, or telecoil, function as miniature antennas. These internal conductors capture the strong external radio frequency (RF) energy, channeling it into the amplifier circuitry. The telecoil, intended to pick up magnetic signals from loop systems, can also inadvertently capture other electromagnetic energy.
Once the high-frequency RF signal enters the circuit, a process called rectification occurs within the amplifier at the semiconductor junctions of transistors or diodes. Rectification is the unintended demodulation of the RF signal, converting the high-frequency radio wave’s amplitude modulation (AM) envelope into a lower-frequency electrical signal. This low-frequency signal falls within the human hearing range and is treated as an audio input, which is then amplified and delivered to the wearer as sound.
Practical Steps for Prevention and Mitigation
Users experiencing RFI can take simple steps to mitigate the problem. The most effective action is to increase the distance between the hearing aid and the source of the interference. Moving away from a large appliance, a wireless router, or a cell phone significantly weakens the electromagnetic field and stops the unwanted reception. If the source is a portable device, turning it off or switching it to airplane mode eliminates the interference.
For persistent issues, professional intervention provides a lasting solution. An audiologist can adjust the hearing aid’s programming to decrease its overall sensitivity or reduce gain at the frequencies where the interference is most pronounced. Modern digital hearing aids are engineered with better RF immunity than older analog models and often incorporate internal shielding or filtering. The audiologist may also arrange to have RF suppression filters, such as miniature ferrite beads, installed on the internal wiring to block the unwanted high-frequency energy.