A Primer of MICROPHONE SENSOR ARRAY PROCESSING Fundamentals and Hardware Design- Part 6

4.1.1 Digital MEMS Microphone

The selection of Microphone plays a vital role in the efficient Array processing. Now-a-days MEMS Microphones are considered as best choice for the development of Microphone Sensor Array due to following features

• • • Mechanically Robust and Low Manufacturing tolerances 
    • Stable and Consistent Performance
    • Sensitivity Matching from unit to unit ( very important for Arrays)
    • Temperature, RF and EMI Resistant

The digital MEMS Microphone ICS-52000 from Invensense is selected because of its excellent features, i.e. on chip signal conditioning, an analog-to-digital converter, decimation and anti-aliasing filters, e.g. High-pass filter to remove unwanted dc and very low frequency components and most important industry standard 24-bit TDM interface. The TDM interface enables precise array processing.by facilitating an array of up to 16 synchronously-sampled Microphones channels to interface directly to digital processors (MCU/DSP), without inclusion of additional electronics components like, Audio codec. Further, technical characteristics of ICS-52000 are

• • • Sensitivity:                                            −26 dB FS
    • Sensitivity Tolerance:                             ±1 dB
    • Wide Frequency Response:                    50 Hz to 20 kHz
    • Acoustic Overload Point (AOP):             117 dB SPL

4.1.2 Microprocessor

The software block of Microphone Arrays is responsible to perform the tasks of data acquisition, digital filters, estimation of sound source localization and steered response algorithms; demand such very high performance embedded processor which can perform very fast, highly précised and complex mathematical computation. 

The Digital signal controller (DSC) STM32F746 i.e., a perfect combination of the real-time control abilities of a Microcontroller and the signal processing performance of a double- precision floating point digital signal processor, and a variant of Cortex-M7 is chosen for Acoustic Measurement System. This embedded processor has a lot of hardware resources for communication and interfacing. It works at 216 MHZ frequency and it delivers the maximum theoretical performance 1082 CoreMark /462 DMIPS. This processor will be replaceable its future coming and more high performance version that is STM32H743 with 2010 CoreMark /856 DMIPS at the frequency of 400 MHz

4.1.3 Communication Interfaces and Mass Storage

Different communication (USB, SPI and UASRT) will be available on the hardware board of Microphone Array system for data transfer in between Host-PC and Array board and also for board to board communication. Further, on board SD/MMC card will be available for data logging.

4.1.4 Expansion Connectors

The additional GPIO and other unused interface will be routed toward the connectors on both side of board. It provision will be useful to expand the system with other sensors for the purpose of multi-sensor information processing.

References:

The following books, website, research papers and OEM application notes are consulted to prepare this document,

• [1] Frank Fahy. David Thompson, Fundamentals of Sound and Vibration, Second Edition, CRC Press, 2016.
• [2] Bert Zinserling , ' Silicon-based MEMS Microphone For Automotive Applications, Knowles Electronics Germany. [Online].Available: http://www.onboard-technology.com/pdf_febbraio2007/020705.pdf.
• [3] Heinrich Kuttruff, Acoustics An introduction, CRC Press, 2006.
• [4] http://resource.isvr.soton.ac.uk/spcg/tutorial/tutorial/Tutorial_files/Web-basics-nature.htm\ 
• [5]   Clarence W. de Silva, Vibration and Shock Handbook, CRC Press, 2005.
• [6]   Stephen A. Dyer, Wiley Survey of Instrumentation and Measurement, Wiley-IEEE Press, 2004.
• [7] SelfDuncanSinclairBriceHoodSingminDavisWatkinson
• [8]   Mendel Cleaner, Acoustics And Audio Technology, 3rd edition, J. Ross Publishing, 2011.
• [11] www.electrovoice.com/downloadfile.php?i=972304
• [12] Dr. John Carey, Test and Measurement Microphones, in Sensor Technology HANDBOOK, Jon S. WILSON, Newnes, 2004.
• [13] http://www.bksv.com/Products/transducers/acoustic/microphones
• [14] ELECTRET CONDENSER MICROPHONE BASICS, Projects Unlimited Inc, 2008.
• [15] Jerad Lewis, Analog and Digital MEMS Microphone Design Considerations, Analog Devices, Inc
• [16] Cirrus Logic. Appl. Note WAN_0290, An Introduction to MEMS Microphone Specifications
• [17] http://www.akustica.com/technology.asp
• [18] Jalen麥克風技術發展與應用趨勢’, Taiwan, Mar, 2016.
• [19] http://www.peledivais.com/mycgi/Hot_topics_e.cgi
• [20] http://electronicdesign.com/analog/analog-survival-means-learning-be-adaptable-
• [21] ST Microelectronics. Appl. Note 4598, Pre-amplifying the analog output of a MEMS microphone
• [22] Invensense, Appl. Note 1165, Op Amps for MEMS Microphone Preamp Circuits
• [23] STM32L4-System-Digital Filter for SD Modulators (DFSDM)’, STMicroelectronics, 2016.
• [24] Jerad Lewis, Common inter-IC digital interfaces for audio data transfer, Analog Devices Inc, 2012.
• [25] Invensense, Appl. Note 1112, MICROPHONE SPECIFICATIONS EXPLAINED
• [26] ST Microelectronics. Appl. Note 4426, Tutorial for MEMS microphones
• [27] Bert Zinserling, Silicon-based MEMS Microphone For Automotive Applications, Knowles Electronics Germany.
• [28] https://blogs.mentor.com/embedded/blog/tag/a2b/
• [29] Ken Waurin, New Digital Bus Architecture Reduces Audio System Costs, Analog Devices, Inc.
• [30] http://www.sae.org/dlymagazineimages/13671_20603_ACT.jpg
• [31] Mingsian R. Bai, Jeong-Guon Ih, Jacob Benesty, Acoustic Array Systems: Theory, Implementation, and Application, Wiley-IEEE Press, 2014.
• [32] Iain McCowan. Microphone Arrays : A Tutorial, April 2001. Available: http://www.idiap.ch/~mccowan/arrays/tutorial.pdf
• [33] Rahil Mahdian,’ Microphone Arrays Localization Beamforming’, University of Saarland, 2016.
• [34] Saeed V. Vaseghi, Advanced Digital Signal Processing and NoiseReduction, John Wiley & Sons Ltd,2009.
• [35] Vasudev Kandade Rajan MohamedKrini, Signal processing techniques for seat belt microphone arrays, , Keil University, 2016.
• [36] Hamma Tadjine , Daniel Goehring , Acoustic/Lidar Sensor Fusion for Car Tracking in City Traffic Scenarios, Freie Universit  Berlin, Berlin.
• [37] http://people.ee.duke.edu/~jk/
• [38] http://www.me.hs-mittweida.de/webs/huebelt
• [39] Olivier Besson. Introduction to Array Processing,(ISAE-Supaero)