Novel directional microphone design for speech enhancement in complex environments

In the UK, more than 50% of people over 60 suffer from hearing loss, but only 20% of them actually use hearing aids. Part of this poor take-up is due to issues with current hearing aids, including poor sound quality and poor performance in noisy and complex environments. But one feature of hearing aids that does help people is a "directional microphone", made-up from a combination of digital signal processing and two (at least) separate actual microphones. These can reject noises from the back or the side of the user. They help the user but come with severe problems. They add extra cost, weight, and power requirements. They have to be a certain distance apart, severely constricting the design of the hearing aid as a whole. And, with just two microphones accuracy is quite limited: they can tell whether a sound source is in front or behind, but struggle to detect sounds from below or above, such as echoes in a large room.

Despite remarkable advances in sound analysis in hearing aids, the actual microphone itself has remained essentially unchanged for decades. Here, we aim to solve the problems of current directional technology by instead using a new type of miniature directional microphone, inspired by how some insects tackle the problem of locating sounds. This new device retains its directionality while keeping the miniature dimensions similar to an insect ear. The research project will take the new insect-inspired microphone design and evaluate it as a component for hearing aids. From this initial evaluation, there will be an iterative process of new, improved, designs being simulated, fabricated, lab tested, and then evaluated. The end result will be microphones that can significantly solve the problems faced in hearing aid design.

The primary objective is to create a hearing aid system that can reduce or control unwanted noises, focusing the hearing aid on only the sound arriving from in front of the user. This includes reducing noises not only from behind, but above, below and distant, so for example reducing the problems caused by echoes from floors and ceilings. The research will also look at problems caused by the distance from which a sound emanates, for example how to separate a sound from a loud source far away, like a train or plane, from a quiet sound from nearby, like a human voice. Finally, the new microphones will require new mounting methods in hearing aid devices. The project will investigate using 3D printing techniques to achieve this. This allows the research to consider how to optimise the hearing aid housing so that it works best acoustically in conjunction with the new microphone, and how it might be possible to extend that to produce hearing aids that are personalised for both the user's ear and their user's sense of hearing.

This research will develop new hearing aid systems with significantly increased performance compared to traditional devices, using a novel, bio-inspired miniature wideband directional microphone. The use of this microphone design will not only increase performance, but also drastically reduce the signal processing and physical dimensions required in traditional approaches to this problem area. The usefulness of these new hearing aid system designs will be demonstrated by evaluation at the laboratories of the MRC Institute for Hearing Research (Glasgow) through listening trials. This research therefore has multiple impacts as it aims to investigate and develop the acoustic capabilities of the miniature microphone as a component of an overall hearing aid system in order to improve the noise-control capability of hearing aids. This research will thus directly benefit the international academic community, industry, and end-users in the general public.

The project goal is ultimately to produce new technological solutions which will improve the quality of life associated with improved hearing aid performance and usability. This will require commitment from both end-users and supply chain companies in the future development of the technology. The proposed approach will find application across a wide range of hearing aid types and user profiles. By so improving the performance, delivery and usability of hearing aid systems the project will have an obvious impact on UK society and, importantly, will lead to an increase in the adoption of hearing aids by patients from their current low levels of uptake.

Further beneficiaries would be in academia. Given the multidisciplinary characteristics of the proposed research involving aspects of both engineering and hearing research, this research would benefit people working in these areas. Engineers would take advantage of the ideas and improvements at the core of the new miniature microphone devices since using the directivity of the microphones as proposed in this research represents a novel, and useful approach to numerous problems. The ultimate aim of implementing this system within hearing aids will produce a transformational change in the academic understanding of hearing aid systems.

All staff involved will gain new knowledge and improve skills in techniques such as the three dimensional dynamic measurement of the vibrations of the microphone structures, the acoustic simulations of their responses, and the experiments to evaluate their capabilities for new hearing aid systems. Expertise in the electroacoustic signal evaluation techniques for the hearing aid systems, and the behavioural testing of hearing-aid technologies will also be developed and enhanced. Finally, the implementation of the hearing aid systems through 3D printing will provide for the first time customization techniques using miniature directional microphones integrated into custom-built hearing aid structures.

The project's researcher will have the opportunity to strengthen their skills in MEMS design and simulation, performing experiments, and setting up complex scenarios when evaluating the new hearing aid systems in the lab. These skills are useful for both industrial engineering positions, as well as academia. The collection of all these skills will have a great impact on their employability at the end of the project and help to cement strong future links between academia and industry in key sectors. The researcher would have the opportunity of publishing in high quality journals and of attending both engineering and hearing conferences. The researcher will be encouraged to develop Fellowship applications during this work to further their ambition of progressing into an academic career. Overall, the researcher will have the opportunity to develop a unique skill set, combining an engineering outlook with hearing research. The investigator team will provide mentoring support to help achieve this aim.