1
MEMS ENDOVASCULAR
PRESSURE SENSORS
December 14, 2007
Jonathan Brickey, Niels Black, Charles Wang
Anatomy of the Heart
2
Vena Cava
Right Atrium
Right Ventricle
Pulmonary Arteries
Lungs
Pulmonary Veins
Left Atrium
Left Ventricle
Aorta
http://www.nhlbi.nih.gov/health/dci/Diseases/pda/pda_heartworks.html
Body
Abdominal Aorta Aneurysm
3
2 cm
Healthy Blood Pressure
Diastole: <80 mmHg (11 kPa)
Systole: <120 mmHg (16 kPa)
6 cm
Hypertension Stage 2
Diastole: >100 mmHg (13 kPa)
Systole: >160 mmHg (21 kPa)
http://www.ultrasoundspecialists.com/screenings.html
Prevalence of AAA
4

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
Methods of Treatment
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Open Repair
Endovascular Repair
http://www.nhlbi.nih.gov/health/dci/Diseases/arm/arm_treatments.html
http://www.vascularweb.org/_CONTRIBUTION_PAGES/Patient_Information/NorthPoint/Abdominal_Aortic_Aneurysm.html
EndoSure by CardioMEMS
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





EndoSure Wireless AAA Pressure
Measurement System
Permanently implanted
Radio frequency transmission
Radio frequency powered
Size of a paper clip
Biocompatible
http://www.cardiomems.com/content.asp?display=medical+mb&expand=ess
http://www.physorg.com/news10533.html
Design Record
7
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
1999-2002 Mark Allen, GA Tech
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Wireless
micromachined
ceramic pressure
sensors
High temperature
self packaged
wireless ceramic
pressure sensor
2006 – Mark Allen, GA Tech
11
Flexible Wireless Passive Pressure Sensors for Biomedical
Applications
Flexible Substrates: Types
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
Liquid Crystal Polymers (LCP)
 Almost
as ordered as fully crystalline solids
 Chemically inert
 Easy to fabricate

Polyamide Films
 Kapton-E
 thermal
(DuPont)
expansion coefficient same as Cu
 13-50 micron thickness
Flexible Substrates: Advantages
13

For machining application:
 Very
high dimensional stability
 High etchability – heavily isotropic

For biomedical applications:
 Flexibility
allows less invasive implantation
 High levels of chemical inertness
MEMS Screenprinting
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
Additive process:
 Mesh
overlay – polyester or steel
 Places where material does not go are “painted” over
 Mesh screen placed on substrate, liquid poured over
MEMS Screenprinting
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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)
Lithography
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Lithography mask for Inductor-Capacitor
setup
Cross-section of Cu application
(Fonseca 2006)
Capacitance vs. Pressure
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r0
C  2  [
0
0
d 0  2w(r )
]rdr  2 
r0
0
0
2 w(r )
(1 
)rdr
d0
d0
3(1   2 )
2
2 2
w(r ) 
p
[
r

r
]
0 0
2
16 Eh
Power and Signal Transmission
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V2  L1
dI1
dI
 LM 2
dt
dt
Final Output
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Problems in Simplification
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
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
Future Improvements
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


Major limitations: Size, Sensitivity, Transmission
Distance
MEMS fabrication results in increased sensitivity
Size and Transmission Distance invariably linked
Other Possible Design Improvements
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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
References
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

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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. 33743 (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
References (continued)
24
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“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.