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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

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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.