Intracranial MEMS Based Pressure Sensor for Siphon Regulatory Devices

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

Si

SiO2

a) Anisotropic etch with KOH

Si

P+

b) Deep Boron Diffusion creates the supporting rim for diaphragm

Si

P+

glass

c) Shallow Boron Diffusion and deposition of Dielectric material

Dielectric

metal

e) Electrostatic Bonding to glass wafer patterned with metal electrode and metal-silicon lead transfer. Dissolution of wafer.

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)

Design of Integrated Circuits for Optical Communications

• Historical Colpitts Oscillator• Differential Cross-Coupled Topology

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 = 10 ms, and a pulse width of T0 = 1 µs.

• 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

BatteryCMOS/ASIC

Antenna

WeldedA titanium casing will be acquired from a machine shop.

One potential is Titanium Fabrication Corporation from NJ.

Prices are quoted.

Packaging Cont.

8.85 mm

10 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/15th_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/wp-content/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.

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 activitieshttp://

www.stevenswater.com/telemetry_com/cell_info.aspx

System Overview

Sensor Phone

Telemetry

Hospital Computer Computer ProgramLog Files

Log File:• Date + Time• Pressure Reading• Patient ID

Analyze PressureReadings + Display

Process PatientID: Height + Weight

Call Patient ForClinical Visit

Determine If Valve Needs AlterationOr Other Patient Care

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 6 530-539 (1997)