Biomedical Acoustics: Designing a Probe for In Ear Signal

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

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!

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)

Conclusion

• Design