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Biomedical Acoustics Designing a Probe for In Ear Signal

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					Biomedical Acoustics: Designing a Probe for In
  Ear Signal Acquisition and Interpretation of
                Hearing Health

                                      Moises Perez
                                            EEN 502
                                   Literature Project
                        Thursday, December 2, 2004
        Project Background

•   1 year design effort:
                                                   Electrical
    –   University of Miami, Dept.
        Biomedical Engineering
    –   Intelligent Hearing Systems
        (www.ihsys.com)
                                                   Probe
                                                   Design



                                      Mechanical                Biomedical




                                                                             2
          Project Purpose

Design ONE probe capable of entering the human ear
canal and acquire the following signals:

   1. Transient Otoacoustic Emissions (TEOAEs)
      –   Inner hair cell function
   2. Tympanograms (TYMPs)
      –   Middle ear function

   3. Acoustic Reflexes (ARs)
      –   Middle ear discontinuity and neuronal damage




                                                         3
Why Design and All-in-One Probe?

• Benefits for the Audiologist:
   – Efficiency ()
   – Costs ()
   – Error and False Positive Rates ()

• Benefits to the Manufacture:
   – New concept in diagnostics
   – $$$

                                          4
  Probe Design Summary

                                        Multi-Function Probe


                               Probe                                    Pressure System


Sound Recording                    Sound Production                                       Noiseless


                  Flat to 32 kHz                         Flat click                         Fast


                                                      Up to 2 stimuli                       Safe


                                                       100+ dBSPL



                                                                                                      5
Sound Recording
1. Flat frequency response up to 32 kHz in free field
2. Equalized response in ear canal
    Microphone Selection
• FG-3329 (Knowles Inc.)
   –   World’s smallest microphone!
   –   Ultrasonic performance
   –   Naturally flat response
   –   High sensitivity
   –   0.9 – 1.6 VDC

                                      www.knowles.com




                                                        7
EQ Filter Network
       Contains 4 major stages:
          1. Summing stage with AC coupling
          2. Multiple, non-inverting gain stage
          3. Band rejection stage
          4. Quasi-Band Pass (Q-BP) stage




                                                  8
EQ Frequency Response




                        12
Sound Production
 1. Flat frequency response for the click stimulus
 2. Up to two stimuli w/ 100+ dBSPL output
        Receiver Selection
•   FC-3265
    – 110 dBSPL average output
    – Designed for ITE and ITC applications
    – Flat response to 2 kHz

                                              www.knowles.com




                                                                14
        Smoothing Filters
• Consists of:
   1. Twin-T notch filter
   2. Buffer amplifier stage




                          3,400 Hz
                         Notch Adjust
                                        15
Plastics Design
 1. Four part design
 2. CAD/Rapid Prototyping
Objectives of Plastics Design


   1. Smallest possible design

   2. Capable of housing all FOUR components

   3. Sufficient isolation to protect from crosstalk

   4. Easy assembly for the removal of the disposable tip

   5. Looks good!



                                                            17
             Probe Design
• CAD: Pro Engineer 2001/Wildfire
• Animation: 3ds max 6




                                    18
             Probe Prototype
 • Rapid Prototype: Stratasys® Prodigy Plus

Problem:
   ABS material from RP too porous,
   causing signal leaks

Solution:
    Encase the probe with glue for tight
   seal




                                              19
Results
 1. TEOAE
 2. TYMPs
 3. ARs
             TEOAE Testing
Important:
   1.   Audio “fingerprint”
   2.   1 ms time jump on the 10D




                                    21
             TYMP Testing
Important:
   1.   Peak ear volume (admittance) at 0 daPa in healthy ear
   2.   Three trials of pressure and vacuum were taken




                                                                22
                     AR Testing
Comparisons with the literature (Wiley and Fowler, 1997)




                                                           23
        Conclusion

• Design ONE probe capable of entering
  the human ear canal and acquire:

  – OAEs
                           
  – TYMPS                  
  – Acoustic Reflexes      
                        Successful



                                         24
 Future Work

Improve Performance
• Better prototyping materials
• Lower acoustic noise floors
• More microphones?

Portability
• Smaller design
• Smaller pump system
• Faster pump
• Handheld operation


                                 25

				
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posted:6/3/2012
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