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MEMS ENDOVASCULAR PRESSURE SENSORSJonathan 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/pda_heartworks.html
Vena Cava
Right Atrium
Right Ventricle
Pulmonary Arteries
Lungs
Pulmonary Veins
Left Atrium
Left Ventricle
Aorta
Body
3
2 cm
6 cm
Abdominal Aorta Aneurysm
Healthy Blood Pressure
Diastole: <80 mmHg (11 kPa)
Systole: <120 mmHg (16 kPa)
Hypertension Stage 2
Diastole: >100 mmHg (13 kPa)
Systole: >160 mmHg (21 kPa)
http://www.ultrasoundspecialists.com/screenings.html
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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
11:1 male:female ratio – 60-64 years old
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Methods of TreatmentOpen Repair Endovascular Repair
http://www.vascularweb.org/_CONTRIBUTION_PAGES/Patient_Information/NorthPoint/Abdominal_Aortic_Aneurysm.html
http://www.nhlbi.nih.gov/health/dci/Diseases/arm/arm_treatments.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?display=medical+mb&expand=ess
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Design Record
Jay S. Yadav, M.D and Mark G. Allen1995 – 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, NJITHartley 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
0 0
0 000
0
0
0 ))(2
1(2])(2
[2r r
rdrd
rw
drdr
rwdC
][16
)1(3)( 222
002
2
rrpEh
rw
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Power and Signal Transmission
dt
dIL
dt
dILV M
2112
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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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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
Other Possible Design Improvements
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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, <http://www.physorg.com/news10533.html>
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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