A multichannel adaptive integrated MEMS/CMOS microphone
Lead Research Organisation:
University of Stirling
Department Name: Computing Science and Mathematics
Abstract
There are many different types of microphones: their primary function is transduction: converting pressure waves (within some range of frequencies) into a single electrical signal, usually as precisely as possible. After this, the signal may be used for recording or for interpretation (which is our interest here). A major problem in interpretation is that the signal may have a large amount of energy in some parts of the auditory spectrum, but much less in others, and that this distribution may alter rapidly. Often, it is the energy in these lower energy areas that is critical for interpretation. Current practice is to filter the single electrical signal from the microphone (whether using FFTs, or bandpass filters), then examine the signal so produced. We propose a different approach in which the pressure wave is directly transduced into multiple electrical signals, corresponding to different parts of the audible spectrum. By making the transducers active (i.e. providing them with a rapidly adjusting gain control), we will be able to increase the sensitivity of the filters in those areas where additional sensitivity can be useful in the interpretation task, and reduce the sensitivity in those areas where the signal is very strong. The auditory interpretation tasks undertaken by animals (solving the what and where tasks when there are - as is normally the case - multiple sound sources in a reverberant environment) is the same task that an autonomous robot's auditory system needs to undertake. Animal hearing systems include multiple transducers, and provide numerous outputs for different parts of the spectrum, whilst adjusting their sensitivity and selectivity dynamically. Current microphones provide a single electrical output, which is then either processed into a number of bandpass streams (maintaining precise timing), or into a sequence of FFT-based vectors, such as cepstral coefficients (losing timing precision). The proposed active MEMS microphone performs the spectral breakdown at transduction, providing an inherently parallel output whilst maintaining precise timing. Further, it is adaptive. This adaptive capability, non-existent in current microphones is important in hearing aids. Precise timing information is important for source direction identification using inter-aural time and level differences. Where there are multiple active sources, accurate foreground source interpretation requires some degree of sound streaming, requiring the ability to examine features of the sound, often in spectral areas which with relatively low energy.The active MEMS bandpassing microphone will consist of a membrane which will vibrate due to the external pressure wave. The membrane is physically linked to different resonant elements (bars) in the MEMS structure - these elements will have a range of resonant frequencies. Further, these bars will act as gates for MOS transistors, resulting in their vibration modulating the current passing through these transistors. The modulated current will be coded as a set of sequences of spikes, and these spikes processed to provide a signal to adjust the sensitivity of each of the resonators by using an electrostatic effect to change the response of the transistors to the vibration of the bars. The modulation will be used to adjust the gain so that quiet areas of the spectrum are selectively amplified and loud areas of the spectrum selectively attenuated. In this way, it will be possible to build an integrated MEMS/CMOS microphone which can attenuate loud areas of the spectrum concurrently with amplifying quiet areas of the spectrum. The spike coded output will be made available in a way compatible with the address-event representation (AER), making it compatible with existing and proposed neuromorphic chips form other laboratories.
Publications
Latif R
(2010)
Microelectromechanical systems for biomimetical applications
in Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena
Latif R
(2011)
Low frequency tantalum electromechanical systems for biomimetical applications
in Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena
Leslie Smith (Co-Author)
(2011)
Using spiking onset neurons and a recurrent neural network for musical sound classification
Mastropaolo E
(2012)
Bimaterial electromechanical systems for a biomimetical acoustic sensor
in Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena
Newton M
(2012)
A neurally inspired musical instrument classification system based upon the sound onset
in The Journal of the Acoustical Society of America
Rojo-Hernandez, A
(2016)
A compact digital gamma-tone filter processor
in Microprocessors and microsystems
Smith LS
(2015)
Toward a neuromorphic microphone.
in Frontiers in neuroscience
Wang S
(2015)
A Bio-Realistic Analog CMOS Cochlea Filter With High Tunability and Ultra-Steep Roll-Off.
in IEEE transactions on biomedical circuits and systems
Description | (i) Building MEMS devices on top of silicon structures is possible: however, the structures are difficult to fabricate. The papers referenced show what was fabricated, but do not concentrate on the difficulty of using these structures in conjunction with devices embedded in the silicon itself. (ii) Creating structures that are large enough to respond to auditory frequencies, yet small enough to be micro fabricated is difficult. The materials to be sedate not always compatible with MEMS device creation. (This has led to another project, see below). (iii) It is possible to do quite a lot of the processing that we proposed to do in MEMS directly in the Silicon, but clearly this takes power, which passive MEMS does not. |
Exploitation Route | The work is continuing, using a graphene based membrane. This project (EP/M026914/1) included purchasing a laser based measuring system (Laser Doppler Vibrometer) as well as using graphene for the membrane, on top of a redesigned resonant gate FET. I am not officially part of this project, so cannot comment much further on it - presumably Dr Michael Newton will write about their findings on ResearchFish. Otherwise, my suggestions would be that future work starts by building a RGFET, and optimises the sensitivity of such a device first, before attempting to turn it into a microphone. |
Sectors | Aerospace Defence and Marine Digital/Communication/Information Technologies (including Software) Electronics Healthcare |
Description | Findings have been used too contribute towards the purchase of a Silicon Cochlea from INILabs, Zurich (https://inilabs.com/products/dynamic-audio-sensor/) using funds from Incite Ltd (cost: Swiss Francs 7,000). This Silicon Cochlea is now being used to further investigate spike based processing of sound. |
First Year Of Impact | 2018 |
Sector | Digital/Communication/Information Technologies (including Software) |
Description | Acoustical Society of America 2014 |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Participants in your research and patient groups |
Results and Impact | One talk given, one poster presented. Good questions and discussions from both Interest from abroad - collaboration with groups in Barcelona and Mexico looks likely. |
Year(s) Of Engagement Activity | 2014 |
Description | Acoustical Society of America meeting Spring 2011 |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Participants in your research and patient groups |
Results and Impact | Good questions, discussions, international interest in research area. Real interest from a number of US groups, particularly those involved in music analysis |
Year(s) Of Engagement Activity | 2011 |
Description | DemoFest2014 |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Regional |
Primary Audience | Professional Practitioners |
Results and Impact | Activity involved presenting research to a mixture of interested parties, including SMEs, industry partners, as well as academics. There has been some interest as a result , but it is still early days.. Considerable interest in possible application of t=some of the techniques demonstrated, most notably our new sound segmentation technique. |
Year(s) Of Engagement Activity | 2014 |
URL | http://www.sicsa.ac.uk/knowledge-exchange/industry-collaboration/demofest/ |
Description | ICANN 2014 conference |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Participants in your research and patient groups |
Results and Impact | Good questions and discussion afterwards Possible collaboration with a group in Hamburg. |
Year(s) Of Engagement Activity | 2014 |
Description | IJCNN workshop |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Participants in your research and patient groups |
Results and Impact | Good questions, discussions Good discussions and questions, also applicants for a PhD applied to Stirling internationally. |
Year(s) Of Engagement Activity | 2011 |
Description | Public lecture 2014 |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Public/other audiences |
Results and Impact | Public lecture (in public lecture series organised by the University of Stirling) entitled "Hear here: from the ear to the brain". |
Year(s) Of Engagement Activity | 2014 |
URL | http://www.maths.stir.ac.uk/lectures/lectures%202014.html |