Hearing aid ‘implantable in outpatient surgery’

Researchers in Germany have developed a low-cost, implantable hearing aid that can be inserted into a recipient in outpatient surgery.

The new solution is said to be composed of three parts: a case with a microphone and battery; wireless, optical signal and energy transmission between the outer and middle ear; and an electro-acoustic transducer – the centrepiece and loudspeaker of the implant.

Researchers from the Fraunhofer Institute for Manufacturing Engineering and Automation IPA in Stuttgart are developing the electro-acoustic transducer, which will eventually be round in shape and measure approximately 1.2mm.

IPA’s partners in the project, which is sponsored by the Federal Ministry of Education and Research, are the University Department of Otolaryngology, Head and Neck Surgery Tübingen, the Natural and Medical Sciences Institute (NMI) at the University of Tübingen, and the hearing aid specialist Auric Hörsysteme.

‘Our goal is to take the better sound quality of implantable hearing aids and combine it with a much simplified operation,’ said Dominik Kaltenbacher, engineer at IPA. ‘To implant our system, all surgeons have to do is make a small incision at the side of the eardrum and then fold it forward. This can be done in outpatient surgery.’

The electro-acoustic transducer, which takes the form of a piezoelectric micro-actuator, is then placed directly at the connection between the middle and inner ear known as the ‘round window’.

From there it transmits acoustic signals to the inner ear in the form of amplified mechanical vibrations, thereby enhancing the hearing capacity of patients.

‘The electro-acoustic transducer works on the same principle as bending actuators,’ said Kaltenbacher in a statement. ‘The bending elements, which are arranged in the shape of a pie, consist of a laminated composite made from piezo-ceramics and silicon. If voltage is applied, the elements bend upwards and generate a mechanical vibration. This spreads to the membrane of the round window and the inner ear, stimulating the auditory nerve.’

Although the round window implant is no larger than a pinhead, it can output volumes of up to 120 decibels.

‘This high performance is necessary for very good speech comprehension, particularly for high-pitched sounds, which people who are severely hard of hearing find especially difficult to pick up,’ said Kaltenbacher.

Experts are currently testing a first working prototype in the laboratory and results to date are said to have been positive.

‘The individual components of the hearing aid have all been developed. The next step is to optimize and assemble them,’ said Kaltenbacher.

The optimised individual components should be ready by June of this year, with testing of the overall system planned for 2014.