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
• – 1 year design effort: University of Miami, Dept. Biomedical Engineering – Intelligent Hearing Systems ( www.ihsys.com
) Electrical 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 Sound Recording Flat to 32 kHz Probe Sound Production Flat click Pressure System Noiseless 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 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!
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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)
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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