www.c2s2.org

2007 Technology in Medicine UNIVERSITY of VIRGINIA

Portable, Unobtrusive Medical Sensors using Ultra-Low Power Electronics

Benton Calhoun (ECE) , Travis Blalock (ECE) , and Alf Weaver (CS) . School of Engineering and Applied Science

Circuit Design in a Power-Limited Era

Micro-sensor networks

Ambient Intelligence

Medical devicesPortable Electronics

High Performance Applications(Power Density)

Power

Perf

orm

ance

Applications are Limited by Power

1.89mm256kb SRAM Array

32k

b

Blo

ck

Sub-threshold SRAM

Sub-VT Filters Ultra-Dynamic Voltage Scaling

Sub-threshold Operation of Digital Circuits

Sub-threshold logic operates with VDD < VT

Both on and off current are sub-threshold “leakage”

Leads to MINIMUM ENERGY/OPERATION

Gate Leakage Energy

90nm simulationfor 32-bit CLA addershowing minimum energy per operation

Total Leakage Energy

Total EnergyActive Energy

Eleak = VDD ● I ● TD

Sensor

Front End: Detect & digitize sensor data

u-Processor Bluetooth

Wireless “Patch”

Phase 1: Integrate onto printed circuit boardPhase 2: Build custom Integrated Circuit (i.e. chip)

RF transceiver

Sensor(s)A/D(s)

Radio Interface

Sensor Interface

HW Processing

HW ProcessingProgrammable Control Unit

Memory

Sh

are d

Bu s

Integrated Circuit

Plague Tracking via Flea Telemetry Goal: Study propagation of plague in Utah

prairie dog population Collaboration with Jeff Wimsatt - Biology, Ben Calhoun and

Travis Blalock - ECE Chip communication and power through magnetic field

coupling to on-chip coil Flea chip communicates with collar transceiver - collar

communicates with base station Each chip has unique code and reports temperature to

indicate flea status

Low Energy Operation Essential

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Automation of Test Animal Monitoring via Non-Contacting Bio-Telemetry

Remotely powered, internal chip-based monitoring of animal status Temperature, hydration, location, activity level, and other physiologic

indicators Allows real-time monitoring of large populations of test animals with

dramatically improved disease status information Non-contact monitoring reduces stressful handling events and allows for

better control of pain management Collaboration with Jeff Wimsatt - Biology, Travis Blalock, Ben Calhoun

and Ron Williams – ECE

Low Energy Operation Essential

Actual photo of dummy chipglued to flea (yes, it jumped

around with the chip)

Low Energy Consumption Enables New Applications:

Ultra-Low Energy Circuits for Energy Constrained Applications

Example: Wireless 1-Lead EKG “Patch”

What can Ultra-Low Energy Circuits Do for YOU?

Wireless transmissionto PDA, laptop, etc.

Circuit Techniques Proven in Silicon

Example: A wireless patch to capture and transmit EKG waveforms

Phase 1 Initial Implementation working:

Advantages of Ultra-Low Energy Hardware

Smaller Form Factor e.g. 1-Lead wireless EKG on 1-2 chips (<1cm3)

Lower Cost Smaller size and fewer parts lower cost

Built-in flexibility allows for reuse in different applications

Unobtrusive Wireless connectivity is easy on the user

Wear it home; put on and off like a BandAid

Longer Lifetime Modern Holter monitors (EKG recorders) record for ~24 hours

1 month lifetimes now possible but only with clunky, costly systems

Our approach: Lifetimes of months or years are possible

With Energy Scavenging, lifetime is unlimited by energy concerns

Phase 2: Integrate onto a chip

Sub-threshold logic for low energy

Energy scalability to adapt to requirements

Programmability for hardware reuse

Uses for Wireless EKG:

Detect Atrial Fibrillation Goal: Detect and record paroxysmal AFib

events based on heartrate statistics Collaboration with Ben Calhoun and Travis Blalock – ECE,

Randall Moorman - Cardiovascular Medicine Use a later version of the EKG patch Monitor statistical distribution of R-R intervals and record AFib

events

Low Energy Operation Essential to enable required Lifetime of the patch

Energy Scavenging Technology Power Density (µW/cm2)

Vibration – electromagnetic [Khulah, MEMS04] 4.0

Vibration – piezoelectric [Roundy, CComm03] 500

Vibration – electrostatic [Meninger, TVLSI01] 3.8

Thermoelectric (5oC difference) [Bottner, JMES04] 60

Solar – direct sunlight [Panasonic98] 3700

Solar – indoor [Panasonic98] 3.2

Triage ManagementRural HealthcareIn-home monitoring of the elderly…

Data security Goal: Protect Mobile Data Ensure continuous link with user after

authentication Place data in safe state if link is lost

Low Heart Rate EventSafe Mode Entered

Connect to Patch Simulator Policy Control EngineInitial Authentication

Other Applications for Low Energy Sensing Platforms:

<Your Data Sensing Application Here!> What data would help you …

… to diagnose problems?

… to treat patients?

… to see the impact of medication?

Cutting edge low power sensors are …

… unobtrusive.

… smaller.

… cheaper.

… much longer lasting.