1. 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

2. 2 Project Background 1 year design effort: –University of Miami, Dept. Biomedical Engineering –Intelligent Hearing Systems (www.ihsys.com)www.ihsys.com Probe Design ElectricalBiomedicalMechanical

3. 3 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

4. 4 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 –$$$

5. 5 Probe Design Summary Multi-Function Probe Probe Sound Recording Flat to 32 kHz Sound Production Flat click Up to 2 stimuli 100+ dBSPL Pressure System Noiseless Fast Safe

6. Sound Recording 1.Flat frequency response up to 32 kHz in free field 2.Equalized response in ear canal

7. 7 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

8. 8 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

9. 9 EQ: Key Points 1 Multiple NI-Gain stage 1.G1 = 2.33 (  7 dBSPL) 2.G2 = 26.6 (  28 dBSPL) C2 activates at 387 Hz with R5

10. 10 EQ: Key Points 2 Band Rejection stage 1. LP+HP = BR 2. f 0 = 2.8 kHz 3. -25 dBSPL Note: meatal resonance Occurs b/w 2.7-3 kHz 584 Hz13,100 Hz

11. 11 EQ: Key Points 3 Quasi BP stage –Additional gain of 10 (i.e. 20 dBSPL) for all frequencies – Optional high frequency gain boost (i.e. 16-32 kHz) High Pass: Gain  Low Pass: Gain 

12. 12 EQ Frequency Response

13. Sound Production 1.Flat frequency response for the click stimulus 2.Up to two stimuli w/ 100+ dBSPL output

14. 14 Receiver Selection FC-3265 – 110 dBSPL average output – Designed for ITE and ITC applications – Flat response to 2 kHz www.knowles.com

15. 15 Smoothing Filters Consists of: 1. Twin-T notch filter 2. Buffer amplifier stage 3,400 HzNotch Adjust

16. Plastics Design 1.Four part design 2.CAD/Rapid Prototyping

17. 17 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!

18. 18 Probe Design CAD: Pro Engineer 2001/Wildfire Animation: 3ds max 6

19. 19 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

20. Results 1.TEOAE 2.TYMPs 3.ARs

21. 21 TEOAE Testing Important: 1.Audio “fingerprint” 2.1 ms time jump on the 10D

22. 22 TYMP Testing Important: 1.Peak ear volume (admittance) at 0 daPa in healthy ear 2.Three trials of pressure and vacuum were taken

23. 23 AR Testing Comparisons with the literature (Wiley and Fowler, 1997)

24. 24 Conclusion Design ONE probe capable of entering the human ear canal and acquire: –OAEs –TYMPS –Acoustic Reflexes Successful

25. 25 Future Work Improve Performance Better prototyping materials Lower acoustic noise floors More microphones? Portability Smaller design Smaller pump system Faster pump Handheld operation