Illustration: Gert K. Nielsen

On the edge of the possible

Monday 15 Jul 19


Hans Nørgaard Hansen
Head of Department, Professor, PhD, Dr. techn., R.
DTU Construct
+45 45 25 48 16

About CAMM

CAMM, Centre for Acoustic-Mechanical Micro Systems, provides the framework for the world’s leading research within the field of microscale acoustics and design.

The centre was founded in 2014 and is run by the three Danish manufacturers of hearing aids and headphones, Oticon, Widex, and GN Hearing, in collaboration with DTU Electrical Engineering and DTU Mechanical Engineering.

Among other things, this collaboration means that employees from the three companies function as guest lecturers at DTU, just as students and researchers from DTU work on solving some of the specific challenges the companies are facing.

The centre contributes to a fruitful collaboration between university and industry, including, among other things, shared exam and PhD projects. 

The Danish hearing aid manufacturers are among the world leaders in their field.

Maintaining that position means that the manufacturers must constantly develop their products which in turn need to be increasingly smaller while accommodating more and more features. In a DTU centre, companies and researchers collaborate on pushing the technology to its absolute limit.

We’ve all been at events where a microphone comes too close to a speaker which then emits a high-pitched howling noise. Now try to imagine how close to each other the microphone and speaker are in a hearing aid.

It requires knowledge to place both parts in a way that does not create that noise. Especially considering that the sound level in speakers for the hard-of-hearing needs to be as high as 140 dB—a sound level that would make others deaf.

For that reason, it is difficult to completely avoid the unpleasant howling that will be a nuisance to users and their surroundings.

This acoustic feedback is a challenge that all manufacturers of hearing aids want to get rid of. They face the same challenges in the development and production of headphones.

The relationship beween acoustics and mechanics

However, the current knowledge of this special field—the relationship between microscale acoustics and mechanics—is relatively small. Very different rules apply to microscale acoustics than to large-scale acoustics. Large-scale acoustics enables the use of sound-absorbing materials on walls and ceilings in order to adapt the acoustics to the room’s purpose and, for example, to suppress the noise of children’s voices in kindergartens and classrooms.

“All manufacturers of hearing aids and headphones have experienced major challenges when trying to understand how the electromechanical components behave on a microscale. It is not possible to transfer knowledge about acoustics in living spaces to the micro conditions found in a small hearing aid no bigger than three or four centimetres long and half a centimetre wide. This requires knowledge of both the acoustic and mechanical domains, because the acoustic loss behaves very differently in such a small space than it does in a large room,” says Morten Kroman, Chief Technology Officer at Widex.

The unique conditions in a hearing aid have direct influence on the kind of materials and shapes that would be most ideal to use. Researchers and companies are therefore working on gaining knowledge about these conditions.

“At the same time, there is an increased tendency towards adding an even wider variety of components in our headphones and hearing aids. For instance, it is still a relatively new thing that an antenna can enable two hearing aids to communicate wirelessly between the user’s ears or, for example, with a mobile phone. And there are requests for more features, such as incorporating sensors into the hearing aid. Such sensors could issue a warning if the wearer has special needs that require intervention. It’s very sophisticated to have so much technology assembled in such a small space, and it’s clearly on the edge of what is possible,” says Karsten Bo Rasmussen, Innovation and Project Manager at Oticon.

Denmark has unique knowledge

The need to get a greater fundamental insight into the relationship between acoustics and mechanical engineering is the reason why three of the world’s leading companies, Oticon, Widex and GN Hearing, together with DTU has created the research centre CAMM, Centre for Acoustic-Mechanical Micro Systems.

The centre will be an internationally leading institution, which everyone will naturally turn to if they have any questions about microscale acoustics and mechanics.

“It is important for us to get a deeper insight into the phenomena that occur at a microscale level when we are working on improving the current hearing aids and headphones. For example, when we challenge the limits of sound quality. With this partnership, researchers at DTU are working on developing new scientific methods that we as companies can then adopt and use in our product development. The centre also ensures that new, young engineers are trained who have knowledge of the issues challenging Danish companies within this field,” says Andreas Schousboe, Product Development Manager of GN Hearing..

Companies as well as researchers are convinced that the CAMM centre’s work will result in changes in the design of both headphones and hearing aids. Changes that we as users will experience in the form of better sound quality and more features, but which will not be visible to the naked eye, as they will consist of minimalistic changes within the devices or tiny adjustments to the shape of the hearing aid or headphone.

Current research

Below are examples of four projects that improve the acoustics or mechanics of hearing aids.

Antenna cast in plastic

The researchers will examine whether the antenna can be removed from the hearing aid’s interior and instead be moulded into the plastic shell encasing the hearing aid’s many electronic elements.


You normally need ventilation in the hearing aid, so that the ear is not fully closed. This prevents occlusion, which sounds like having your head under water or your fingers in your ears. However, it would be desirable to be able to close the vent when the user is streaming music or talking on the phone, as this results in a better reproduction of the deepest sounds—the bass. DTU researchers have developed a prototype of a small electromagnetic actuator, i.e. a magnetic function that can open and close the vent.


New types of materials are being tested for use in the manufacturing of hearing aids, such as nanomaterials. These materials can be electrically conductive, which prevents electrical appliances in the vicinity from interfering with the microphone, speaker, etc. inside the hearing aid, or they can be dirt and water repellent, making the hearing aid easier to keep clean and resistant to wetness due to fog or rain.

Changing batteries

Most hearing aids are equipped with very small batteries that are just a few millimetres in diameter, which may be difficult to handle, especially for senior users. In collaboration with DTU’s students, a number of ideas for improvement of battery change have been developed, such as a small tool to facilitate the replacement, which has subsequently been tested among hearing aid users who were very enthusiastic.