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MEMS Endovascular Pressure Sensors

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Title: MEMS Endovascular Pressure Sensors


1
MEMS Endovascular Pressure Sensors
  • Jonathan Brickey, Niels Black, Charles Wang

December 14, 2007
2
Anatomy of the Heart
http//www.nhlbi.nih.gov/health/dci/Diseases/pda/p
da_heartworks.html
3
Abdominal Aorta Aneurysm
Healthy Blood Pressure Diastole lt80 mmHg (11
kPa) Systole lt120 mmHg (16 kPa) Hypertension
Stage 2 Diastole gt100 mmHg (13 kPa) Systole
gt160 mmHg (21 kPa)
http//www.ultrasoundspecialists.com/screenings.ht
ml
4
Prevalence of AAA
  • 10th leading cause of death 65-74 years old
  • 5-7 men over 60 diagnosed with AAA
  • 1-3 men over 65 experience aortic rupture
  • 75-90 mortality rate from rupture
  • 111 malefemale ratio 60-64 years old

5
Methods of Treatment
http//www.nhlbi.nih.gov/health/dci/Diseases/arm/a
rm_treatments.html
http//www.vascularweb.org/_CONTRIBUTION_PAGES/Pat
ient_Information/NorthPoint/Abdominal_Aortic_Aneur
ysm.html
6
EndoSure by CardioMEMS
  • EndoSure Wireless AAA Pressure Measurement System
  • Permanently implanted
  • Radio frequency transmission
  • Radio frequency powered
  • Size of a paper clip
  • Biocompatible

http//www.physorg.com/news10533.html
http//www.cardiomems.com/content.asp?displaymedi
calmbexpandess
7
Design Record
  • Jay S. Yadav, M.D and Mark G. Allen
  • 1995 cofound CardioMEMS
  • 2005 EndoSure sensor invented
  • April, 2007 granted FDA approval

http//www.physorg.com/news10533.html
8
  • 1967 C. C. Collins Miniature Passive Pressure
    Transensor for Implanting in the Eye

9
  • 1992 Lars Rosengren

1995, William N.Carr, NJIT Hartley Oscillator
10
1999-2002 Mark Allen, GA Tech
Wireless micromachined ceramic pressure sensors
High temperature self packaged wireless ceramic
pressure sensor
11
2006 Mark Allen, GA Tech
  • Flexible Wireless Passive Pressure Sensors for
    Biomedical Applications

12
Flexible Substrates Types
  • Liquid Crystal Polymers (LCP)
  • Almost as ordered as fully crystalline solids
  • Chemically inert
  • Easy to fabricate
  • Polyamide Films
  • Kapton-E (DuPont)
  • thermal expansion coefficient same as Cu
  • 13-50 micron thickness

13
Flexible Substrates Advantages
  • For machining application
  • Very high dimensional stability
  • High etchability heavily isotropic
  • For biomedical applications
  • Flexibility allows less invasive implantation
  • High levels of chemical inertness

14
MEMS Screenprinting
  • Additive process
  • Mesh overlay polyester or steel
  • Places where material does not go are painted
    over
  • Mesh screen placed on substrate, liquid poured
    over

15
MEMS Screenprinting
  • Advantages/Disadvantages
  • Cheap!
  • Does not require pressurization or extremely
    expensive equipment, like lithography
  • Mesh can be reused
  • Not particularly precise
  • Features can be no smaller than mesh spacing (50
    µm)

16
Lithography
Lithography mask for Inductor-Capacitor setup
Cross-section of Cu application
(Fonseca 2006)
17
Capacitance vs. Pressure

18
Power and Signal Transmission
19
Final Output
20
Problems in Simplification
  • Actual capacitor shape not circular
  • tapered in the center to reduce deflection and
    avoid shorting out the capacitor (Fonseca 2006)
  • Circular model shorts out just before 13 kPa
  • Inductance
  • Very simplified
  • Most MEMS inductors use complicated programs

21
Future Improvements
  • Major limitations Size, Sensitivity,
    Transmission Distance
  • MEMS fabrication results in increased sensitivity
  • Size and Transmission Distance invariably linked

22
Other Possible Design Improvements
  • Finite element analysis of coil design inductance
  • Substrates with low dielectric constants
  • Hartley oscillators or other more complex CMOS
    for improving sensitivity or transmission distance

23
References
  • Wiemer, M., Frömel, J., Jia, C., Geßner, T.,
    Bonding and contacting of MEMS-structures on
    wafer level. The Electrochemical Society - 203rd
    meeting, Paris (France), 2003 April 27- May 2
  • Fonseca, M.A. English, J.M. von Arx, M. and
    Allen, M.G., "Wireless Micromachined Ceramic
    Pressure Sensor for High Temperature
    Applications," IEEE J. Microelectromechanical
    Systems, vol. 11, no.4, p. 337-43 (2002)
  • Fonseca, M.A., Kroh, J., White, J., and Allen,
    M.G., Flexible Wireless Passive Pressure Sensors
    for Biomedical Applications, Tech. Dig.
    Solid-State Sensor, Actuator, and Microsystems
    Workshop (Hilton Head 2006), June 2006

24
References (continued)
  • New Medical Device Combines Wireless and MEMS
    Technology, Physorg.com, February 03, 2006,
    December 08, 2007, lthttp//www.physorg.com/news105
    33.htmlgt
  • Rosengren, L., Backlund, Y., Sjostrom, T., Hok,
    E., and Svedbergh, B., A System for Wireless
    Intra-Ocular Pressure Measurements Using a
    Silicon Micromachined Sensor, (1992)
  • Collins, C.C., Miniature Passive Pressure
    Transensor for Implanting in the Eye, IEEE
    Transactions on Biomedical Engineering, vol.
    BME-14, no. 2, April, 1967
  • Allen, M.G., Implantable micromachined wireless
    pressure sensors approach and clinical
    demonstration, 2nd International Workshop on BSN
    2005 Wearable and Implantable Body Sensor
    Networks, 2005, p 40-1.
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