Hearing aids have an annoying problem: acoustic feedback that sounds like howling in the ears. Scientists at DTU are working on a solution. (Photo: Shutterstock)

How scientists are designing the hearing aid of the future

New technology will fix sudden howling that plagues current hearing aids.

Almost everyone who uses a hearing aid will have experienced that the device can suddenly emit loud, high-frequency noises.

This is acoustic feedback, which occurs when the hearing aid microphone amplifies the sound from the unit's own loudspeaker.

In recent years, manufacturers have managed to decrease the risk of this feedback. But the problem persists--especially when you need to turn the volume up.

Assistant Professor Junghwan Kook from the Department of Electrical Engineering at the Technical University of Denmark (DTU) is working on a solution that will allow the hearing impaired to turn up the volume on their devices, without worrying about the annoying feedback.

"It’s mainly about getting the acoustics and mechanics to play together in the right way," says Kook, whose work is supported by The Danish Council for Independent Research.

New technological platform will remove current restrictions

Kook is investigating bandgap materials as a possible new technological platform in mechanical acoustic systems such as hearing aids.

Bandgap materials are a type of composite material that is composed of at least two elements. Unlike other composite materials, bandgap materials are built up periodically, and can potentially suppress noise and vibrations in specific frequency ranges.

"Our goal is to develop tools that will give users more freedom and remove some of the limitations imposed in manufacturing hearing aids today,” he says.

“Eventually it will benefit users, as manufactures will be able to design and produce better hearing aids," says Kook.

"If it goes as we hope, the new tools will be ready in a year’s time. But we also need to look at the practical design and this may take more time," he says.

Optimization of mechanical properties

Kook is using so-called topology optimization to improve hearing aids.

Topology optimization is a way of calculating the optimal mechanical properties of a structure built from the least possible material.

Recent research has shown that these kinds of solutions can be used to control the propagation of noise and vibration in a variety of materials.

Kook’s aims to find the right combination of bandgap materials using topology optimization. His challenge is to adapt the process of periodic build-up of materials to smaller dimensions and to the audible sound wave frequencies that are used in hearing aids.

Industry will take over

Jakob Søndergaard Jensen is director of the Centre for Acoustic Mechanical Microsystems at DTU and a partner on the project.

"The ultimate objective of the project, as I see it, is to develop a design platform that allows companies, including our sponsors Widex, GN Resound and Oticon, to use and develop their products," says Jensen.

These are the companies who have asked DTU to embark on the research in this particular field, adds Kook.

Various attempts to improve hearing aids

Manufacturers of hearing aids have been focused on solving the acoustic feedback problem in recent years.

One solution produced a device with open fittings. Instead of an earplug, the user had a thin tube or hose connecting the instrument behind the ear with a little cap placed inside the ear.

But these open adaptations are not suitable for everyone. For example, some hearing aid users still require a closed plug in the ear.

There is also room for improvement in other hearing aid features, including devices with open fittings.


Read the Danish version of this article on Videnskab.dk

Translated by: Catherine Jex

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