Is There Loss of Vibration Amplitude Across the Snap Coupling of the Bone-Anchored Hearing Aid?

Abstract

There is loss of vibration transmission across the snap coupling connecting the Bone-Anchored Hearing Aid transducer to the implanted abutment on the head. The only nonrigid part of the Bone-Anchored Hearing Aid system is the connection between the output of the transducer and the abutment. Vibration losses across the coupling have not been previously measured. If a loss is found, a change in design could improve the efficiency of the Bone-Anchored Hearing Aid. This would be very helpful in borderline cases in which the Bone-Anchored Hearing Aid does not have enough power to achieve adequate hearing threshold levels. A laser Doppler vibrometer was used to measure vibrations on the output stem and four points on the abutment of the Bone-Anchored Hearing Aid. The Bone-Anchored Hearing Aid was coupled to a dry skull through a plexiglas bite bar screwed to the skull. The impedance load was varied by fixing the skull. A control loose coupling was measured. Five Bone-Anchored Hearing Aid Compacts were measured. There was little loss across the Bone-Anchored Hearing Aid snap coupling. At frequencies above 500 Hz, there was no more than 5-dB loss at any frequency. Changing the impedance load by fixing the skull did not change the loss across the coupling. The snap coupling is an efficient means of transmitting vibrations to the skull. There is little loss of vibration attenuation across it. Increases in functional Bone-Anchored Hearing Aid amplification gain cannot be achieved by further optimizing this interface.