Intracranial MEMS Based Pressure
Sensor for Siphon Regulatory Devices
A “Bottom of the Pyramid” solution for living
with hydrocephalus
Nick Dunn, Nick Fountoulakis, Ian Flaherty, Alex Winters
Today’s Presentation








Introducing the Bottom of the Pyramid market
Hydrocephalus in the developing world
Fabrication of pressure sensor
Wireless telemetery
Remote monitoring via mobile phone
Computer software program/mainframe
Packaging of overall device
Funding opportunities
Bottom of the Pyramid
 The Bottom of the Pyramid is the largest but poorest social
economic group
 More than 4 billion people living on $2 a day or less
 Majority of these people live in parts of Africa, China, and India
 They represent an un-served or underserved market
 “Active engagement at the Bottom of the Pyramid
markets requires a new and an innovative
approach to business. Retrofitting business models
from the developed markets will not work” C. K.
Prahalad The Fortune at the Bottom of the Pyramid
 45 blind worldwide, 9 million
blind in India
 Goal to eradicate needless
blindness in India
 Specialize in providing
quality eye care, perform
cataract surgery
 Manufacture intraocular lens
in early 90’s import lenses
from west $200 now they
make lens of international
standards $5 a piece
 Prosthetic foot in the United
States $8000
 Jaipur Foot was designed to
simulate normal foot movement
and provide a quality solution
for the masses
 Produced a $30 prosthetic foot
 Main center in Jaipur, India
treats 60 patients a day
 Multiple doctor visits are
needed to have custom fitted
prosthetic device in United
States
Hydrocephalus
 Excess cerebrospinal fluid (CSF)
accumulates in the ventricles of
the brain
 Hydrocephalus affects 3 in
every 1000 infants worldwide
 Treated with surgery by
inserting a ventricular shunt
system
 Shunt system is regulated by
fixed pressure valve
 Doctor visits are needed to
check up on the system
Our Bottom of the Pyramid Solution
 Produce catheter system for regulation of
hydrocephalus of international standards at an
affordable price
 Educate women in villages of signs and symptoms of
hydrocephalus so treatment can be sought time
appropriately
 Utilize expanding cell phone market to provide remote
monitoring
Proposed Hydrocephalus Monitoring
System
 A MEMS based pressure sensor will be surgically
implanted into the skull
 This will monitor over extended periods of time the
internal pressure due to build up of cerebrospinal fluid
 Pressure readings will be relayed via telephone to the
computers at a hospital
 Optical Charging of lithium battery using photodiode
array
A Capacitive MEMS-Based Pressure
Sensor
Micromachined Capacitive Pressure
Sensor
• Highly sensitive (0.37 MHz / torr sensitivity)
• Healthy pressure range is between -5 to 10 torr.
• Our device will be able to measure pressures in the range of -25 to
200 torr
•Basic idea is that changes in pressure cause membrane to deflect
and decreases the distance between the two plates, thereby
changing the capacitance.
•Changes in capacitance are then converted to a frequency encoded
signal that is processed by external electronics that can be housed in
the packaged integrated circuit (IC) die.
Simplified Process Flow For Sensor
Fabrication
a) Anisotropic etch with KOH
SiO2
c) Shallow Boron Diffusion and
deposition of Dielectric material
Dielectric
P+
Si
Si
b) Deep Boron Diffusion creates
the supporting rim for diaphragm
e) Electrostatic Bonding to glass wafer
patterned with metal electrode and metalsilicon lead transfer. Dissolution of wafer.
P+
Si
glass
metal
LC CMOS Oscillator
• Differential Cross-coupled topology
technology
•The oscillation frequency is very
sensitive to changes in capacitance of the
tank capacitor (sensor).
•The inductors L and C0 are selected to
keep the oscillation frequencies in the
ISM band of 2.4000-2.4835 GHz.
•Signals can be transmitted over longer
distances than RF waves and doesn’t
require the use of large inductors which
would make system MRI incompatible.
• A CMOS timer is employed as a bias
control to save precious battery power.
LC CMOS Oscillator (cont)
• Differential Cross-Coupled Topology
• Historical Colpitts Oscillator
Design of Integrated Circuits for Optical
Communications
Vs.
Specs
•ISM band of 2.4000 – 2.4835 GHz
• Tank capacitor variation of 1.3 to 3.5 pF (deflection of the membrane)
• L = 22.9 nH , C0= 0.17 pF
• For core transistors (M1, M2) w/l ratio of 15.5 and 2.3 mA of bias current.
• CMOS timer circuit is employed to switch bias on and off with a period of T =
ms, and a pulse width of T0 = 1 µs.
10
• Duty cycle T0/T = 0.0001 corresponds to an average current of 1.1 µA (very low).
• Total DC current and consumed power
is 11.5 mA and 34 mW
• 3V 30mA/h battery will allow lifetime of
~2 months.
Power
• As previously stated Total DC current and consumed power is 11.5 mA and 34 mW
• A 3V 30mA/h Lithium coin cell will be used to power the device.
• Device will be recharged with an optical setup.
Optical Charging
• The photodiode array is embedded in the scalp directly above where the
module sits in the bore hole in the skull.
• Laser diode (810 nm near infared) shown through lens to focus on
photodiode array
• Results show that for photodiode area of 2.1 cm , 17min of exposure with
power density of 22 mW/cm can send enough energy to recharge a standard
3V pacemaker battery.
• Technology still young, inefficient
10-20% transmittance through skin
2mm thick.
Packaging
Side View of Device
Antenna
CMOS/ASIC
Battery
Packaging Cont.
10 mm
A titanium casing will be
acquired from a machine
shop.
One potential is Titanium
Fabrication Corporation
from NJ.
Prices are quoted.
Welded
8.85 mm
Catheter System



Medtronic is a supplier of
catheters to India and the world
Supply Our Sensor with
Medtronic Catheters prior to their
Delivery to Hospitals
 Bypass need to fabricate
catheters or purchase them
Making current technology a little
bit better
 Reduce inpatient care
 Doctor’s will know when they
have to adjust valves
 Better quality of life for
patients and doctors
Biotelemetry for “Bottom of the
Pyramid” Applications
Nick Dunn, Nick Fountoulakis, Ian Flaherty, Alex Winters
Issues Covered




Review of Wireless Telemetry Concepts
Challenges inherent in Wireless System Design
Overview of our device’s Telemetry system
Role of Cellphones
 In our device, and in developing a “bottom of the
pyramid” device
Telemetry Review



Wireless telemetry is a unique solution to
the challenge of allowing for
communication between an external
device, and the MEMS device that is
implanted in the body.
Coupling allows for the readings
(measured capacitance readings and
external pressure) from the pressure
sensor to be sent to an external
device/database. This is not limited to
data transfer, however; operational
parameters, manual shunt controls, and
error mitigation as well!
Improves quality of life for the patient as
well; allows the patient to “stay attached”
to sophisticated monitoring and treatment
devices, without bulky machines or
repeated hospital visits.
Challenges in Telemetry


Medication Adherence has been shown
to be the most important factor
determining Medical Outcomes,
according to the World Health
Organization.
We seek to create simple and
customized wireless technology, tailored
specifically for our desired “Bottom of the
Pyramid” market, that will provide
excellent healthcare to these regions,
while being designed to accommodate
deficiencies inherent in resource-limited
settings.
Our Telemetry System



Wireless telemetry is a unique solution to
the challenge of allowing for
communication between an external
device, and the MEMS device that is
implanted in the body.
The patients (in India) will use their
cellular telephone to receive the signals
from the hospital, and to send data back
to the medical staff. This can be
performed by holding the cellphone, with
any additional amplification add-ons
attached, up to the device.
From here, the signals can be sent
directly over the phone, and the device
can operate in the same way as it did
with our CMOS and RF model.
http://baby.indstate.edu/isb/publications/1
5th_isob_proceedings/7/7.htm
Cellphone Use



One of the biggest additions to our
device to tailor it to our “Bottom of the
Pyrimid Market”, India, was to have the
communication device we use to relay
the information from patient to doctor be
a CELLPHONE.
Leading global telecommunications
companies begun developing customized
products and telecom solutions for India.
As a result, cellphone use in India
skyrockets, and developing products that
assume cellphone ownership of the
general populace becomes much more
viable.
However, the Healthcare issues that face
resource-limited settings are still present,
including:
http://www.indiamag.in/wpcontent/uploads/2010/11/Bharti-Airtel.jpg
•
•
•
Lack of sufficiently
trained medical
professionals for
Hospitals.
Overcrowding in
Hospitals/Clinics…
not enough of them!
Lack of Sanitation,
improper medication,
lack of adherence to
regimen, etc.
Cellular Telemetry




While originally being developed for improving landline voice
communication, Cellular RF applications in medicine are a unique
and convenient alternative to repeated hospital visits.
The patient would likely need a modem, but that’s it!
The device in the patient does not need to be active for data to be
sent, stored, and implemented when sent by the hospital.
Some advantages and disadvantages:
•
•
•
•
Advantages to Cellular
Telemetry
Low profile, non directional
antenna
Easy to set up and low
maintenance costs
Two-way communications
Event notification by pager,
Internet, other cell phone, etc.
http://www.stevenswater.
com/telemetry_com/cell_i
nfo.aspx
Disadvantages to Cellular Telemetry
• Requires cell phone coverage area
• Monthly service fee (may vary
depending on local area cell phone
service provider)
• Cell phone service provides may
change cell towers or
communication protocol, thereby
effecting communications to your
remote location
• Connection may be dropped during
peck cellular transmissions activities
System Overview
Telemetry
Sensor
Phone
Process Patient
ID: Height + Weight
Hospital Computer
Log Files
Log File:
• Date + Time
• Pressure Reading
• Patient ID
Computer Program
Analyze Pressure
Readings + Display
Determine If Valve
Needs Alteration
Or Other Patient Care
Call Patient For
Clinical Visit
Frequency Encoded Capacitance
 The deflection of the diaphragm is related to pressure.
 In capacitive pressure sensors, the capacitance is related to the
deflection of the diaphragm and therefore the pressure.
 The presssure sensor will send frequency encoded capacitance
readings (tank circuit),
 Fit data with these equations to determine and analyze the
pressure.
Funding
 Venture Capitalists
 NSF Grants




BioMEMS Research
Hydrocephalus Research
Biotechnology
Global Initiatives
 Non-Governmental
 Hydrocephalus
Association
Overview and Recap
Preliminary:
 Capacitive Pressure
Sensor in Glass Casing
 Valve Control in
Catheter
 RF Telemetry for
Communication
 Developed General
Ideas
Interim
 Biocompatibility +
Regulations Check
 Titanium Packaging
Scheme
 Conceptual Framework
of Microwave Telemetry
+ Capacitive Sensing
 Novel Valve Idea - Over
enthusiastic
 Targeting General
Population in America
 Developed Conceptual
Framework Overall
The Final Proposal
 Global Health Initiative through BOP design
 Only 2500 cases per year in the US
 ~10,000 cases per year in India alone
 Bigger Impact
 Solidified Process Flow and Understand How to Analyze and
Transmit Pressure Data
 Wireless telemetry through mobile phone technology for patient
mobility
 Quantified Dimensions, Viable Pressures, and Power
Consumption
 Identified Potential Sources of Funding to Pursue the Project
Thank you!
References
1) Kurtom, K. H. Siphon regulatory Devices: Their Role in The Treatment of
Hydrocephalus. Nerurosurgery Focus 22, 2007
2) Tadigadapa, S. Applications of High Performance MEMS Pressure
Sensors Based on Dissolved Wafer Process. Integrated Sensing
Systems (ISSYS) Inc. 387 Airport Industrial Drive, Ypsilanti, MI 48198
3) Kawoos, U. et al. A permanently implantable intracranial pressure
monitor Bioengineering Conference, 2005. Proceedings of the IEEE
2005.
4) U.S. Patent Number 6,532,834 B1. Capacitive Pressure Sensor Having
Encapsulated Resonating Components. March 18, 2003.
5) Goto, K et al. An Implantable Power Supply with an Optically
Rechargeable Lithium Battery. IEEE Transactions on biomedical
Engineering 48(7) 830-833. 2001
6) W. P. Eaton and J. H. Smith, “Micromachined pressure sensors: review
and recent developments,”Smarter Material Structures Volume 6 530539 (1997)