Transcript Biomedical Acoustics: Designing a Probe for In Ear Signal

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
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1 year design effort:
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Electrical
University of Miami, Dept.
Biomedical Engineering
Intelligent Hearing Systems
(www.ihsys.com)
Probe
Design
Mechanical
Biomedical
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Project Purpose
Design ONE probe capable of entering the human ear
canal and acquire the following signals:
1. Transient Otoacoustic Emissions (TEOAEs)
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Inner hair cell function
2. Tympanograms (TYMPs)
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Middle ear function
3. Acoustic Reflexes (ARs)
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Middle ear discontinuity and neuronal damage
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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
– $$$
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Probe Design Summary
Multi-Function Probe
Probe
Sound Recording
Pressure System
Sound Production
Flat to 32 kHz
Noiseless
Flat click
Fast
Up to 2 stimuli
Safe
100+ dBSPL
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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.)
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World’s smallest microphone!
Ultrasonic performance
Naturally flat response
High sensitivity
0.9 – 1.6 VDC
www.knowles.com
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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
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EQ Frequency Response
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Sound Production
1. Flat frequency response for the click stimulus
2. Up to two stimuli w/ 100+ dBSPL output
Receiver Selection
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FC-3265
– 110 dBSPL average output
– Designed for ITE and ITC applications
– Flat response to 2 kHz
www.knowles.com
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Smoothing Filters
• Consists of:
1. Twin-T notch filter
2. Buffer amplifier stage
Notch
3,400Adjust
Hz
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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!
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Probe Design
• CAD: Pro Engineer 2001/Wildfire
• Animation: 3ds max 6
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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
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Results
1. TEOAE
2. TYMPs
3. ARs
TEOAE Testing
Important:
1.
2.
Audio “fingerprint”
1 ms time jump on the 10D
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TYMP Testing
Important:
1.
Peak ear volume (admittance) at 0 daPa in healthy ear
2.
Three trials of pressure and vacuum were taken
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AR Testing
Comparisons with the literature (Wiley and Fowler, 1997)
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Conclusion
• Design ONE probe capable of entering
the human ear canal and acquire:
– OAEs
– TYMPS
– Acoustic Reflexes
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Successful
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Future Work
Improve Performance
• Better prototyping materials
• Lower acoustic noise floors
• More microphones?
Portability
• Smaller design
• Smaller pump system
• Faster pump
• Handheld operation
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