MEMS Endovascular Pressure Sensors

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MEMS Endovascular Pressure Sensors

• Jonathan Brickey, Niels Black, Charles Wang

December 14, 2007
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Anatomy of the Heart
http//www.nhlbi.nih.gov/health/dci/Diseases/pda/p
da_heartworks.html
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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
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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

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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
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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
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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
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• 1967 C. C. Collins Miniature Passive Pressure
  Transensor for Implanting in the Eye

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• 1992 Lars Rosengren

1995, William N.Carr, NJIT Hartley Oscillator
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1999-2002 Mark Allen, GA Tech
Wireless micromachined ceramic pressure sensors
High temperature self packaged wireless ceramic
pressure sensor
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2006 Mark Allen, GA Tech

• Flexible Wireless Passive Pressure Sensors for
  Biomedical Applications

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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

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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

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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

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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)

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

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Power and Signal Transmission
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Final Output
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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

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Future Improvements

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

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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

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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

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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.