Calculating the SAR to Power up an Implantable Neural Interface for Wireless Communications with Human Motor Cortex

CALCULATING THE SAR TO POWER UP AN IMPLANTABLE NEURAL INTERFACE FOR WIRELESS COMMUNICATIONS WITH

HUMAN MOTOR CORTEXM. A. Gazziro

Dept. of Computer Science – ICMCUniversity of São Paulo, São Carlos, SP BRAZIL

[email protected]

Workshop on Mathematics in IndustryICMC, São Carlos, Brasil, 12 December 2012

OUTLINE

• Neural Biomedical Devices

• Science without Borders Project

• Why Silicon Carbide

• SAR Calculation

• Conclusions

Direct Brain-Computer

Control

Robotic Assistant

ALS/ Paralysis/ Amputation

Cybernetic Replacement

Sensory/ Motor

Artificial Retina

Cochlear

Neural Bridge

Parkinson’sAlzheimer’s

ALSRegeneration

L. R. Hochberg, Nature, vol. 442, no. 7099, 2006.

http://www.brainharmonycenter.com/brain-facts.html P. Fromherz, 2003.

http://www.alsn.mda.org/article/robotic-caregiving-assistance-becoming-reality

http://www.dekaresearch.com/deka_arm.shtml

http://www.artificialretina.energy.gov/http://www.gizmag.com/retinal-implant-treats-blindness/8841/picture/42306/

http://www.alsn.mda.org/article/robotic-caregiving-assistance-becoming-reality

NEURAL BIOMEDICAL DEVICES - BMI

EEG

ECoG

Intracortical

Scalp

Non-Invasive

BrainSurface

Invasive

Neural TissueInvasive

Slow/ Evoked/ EventField Potentials (FP)

• Low S/N ratio• Low Bandwidth• No Stimulation

Medium FP• S/N ratio• Bandwidth• Population Stimulation (Low Selectivity)

Local FP - Population/ AP• S/N ratio• Bandwidth• Stimulation Selectivity**

M. A. L. Nicolelis, Proc. NAS USA, vol. 100, no. 19, 2003.C. T. Nordhausen, Brain Res, vol. 637, no. 1-2, 1994.K. D. Wise, Proce. of the IEEE, vol. 96, no. 7, 2008.

http://www.rcsed.ac.uk/journal/vol47_5/47500001.html

NEURAL BIOMEDICAL DEVICES - BMI

Dilvan MoreiraTechnical CoordinatorStephen Saddow

SiC Technology

Mario GazziroNeuroengineer

Eduardo SimõesRobotics

Valtencir ZucolottoNanotoxicology

Carlos ReisAnalog IC Advisor

Filipe TabaraniAnalog and RF

IC Designer

Carlos CapovillaAnalog RF Advisor

Claudius FegerPackaging Advisor

Cleber MendonçaLaser

Microstructuring

Jackeline MalheirosClinical

Mice Trials

“IMPLANTABLE NEURAL INTERFACE” DESIGN TEAM

http://www.youtube.com/watch?feature=player_embedded&v=MYMdfcKUe2c&noredirect=1

http://www.youtube.com/watch?feature=player_embedded&v=MYMdfcKUe2c&noredirect=1

SCIENCE WITHOUT BORDERS PROGRAM OBJECTIVES

Particulars:

2D probes with multiple electrodes per probe, electronics on tab, signal recording- Si signal conditioning chip(s)- Low Power Consumption- Multiplex multiple inputs- Hard-wired output

Year 1 – in-vitro operation

Electronics on tab section


Particulars:

2D probes packaged, hermetic and biocompatible, wireless link capable

Year 2 – in-vivo operation

Hermetic Package – must be biocompatible!


Particulars:

2D probes with multiple electrodes per probe, electronics on tab, signal recording

2D probes packaged, hermetic and biocompatible

2D probes packaged with wireless link, full operation demonstrated!

Year 1 – in-vitro operationYear 2 – in-vivo operationYear 3 – Wireless link in-vivo

Low-power operation with wireless link demonstrated

WHY SILICON CARBIDE (SIC)

Indwelling Neural Implants Strategies for Contending with the In Vivo Environment


Indwelling Neural Implants Strategies for Contending with the In Vivo Environment

CVD @ 1350 ºC

SiC film on Si7-10 µm/hour

Start with a Si Wafer (2”)



Saddow et al.

SiC Shank (basis for electrode) - Magnify 50x

SiC

3C-SiC


• Preliminary study caused extreme damage to CNS

• tissue reaction to materials was unobservable

• New shanks test both material and tissue reaction

• ~ 20 µm thick, 250 µm base, 7 mm long

• 3C-SiC compared with Si (negative cont.) and polyimide (positive cont.)

• Investigate carbon replacement of metal electrodes (diamond)

15 µm thick 3C-SiC bends butdoes not break!

Si 3C-SiC


3C-SiCShard

Silicon 3C-SiC

CD45 – Indicator of Microglia/ Macrophage - GREEN

GFAP – Indicator of Astrocyte Activity – RED

MAP2 – Indicator of Microtubule (Dendrite/ Axon) -BLUE

CA3

CA3

CA3CA3


Saddow et al.

SAR CALCULATION

Human tissues are composed primarily of molecules, which tend to absorb RFenergy. The rate of absorption is a dosimetric measure known as the Specific AbsorptionRate (SAR).

A dosimetric measure that has been widely adopted is the timederivative of the incremental energy (dW) absorbed by, or dissipated in an incrementalmass (dm) contained in a volume element (dV) of a given density (p), which isexpanded in equation below (E is the magnetic field):

A SAR limit of 2 W/kg averaged over any contiguous 10g head tissue was recommendedby the Council of European Union for the general public. The SAR limit for safe exposure of RF radiation as allowed by FCC is the US 1.6 W/kg.

SAR CALCULATION

Arumugam, D.D.; Engels, D.W.; , "Impacts of RF radiation on the human body in a passive RFID environment," Antennas and Propagation Society International Symposium, 2008. AP-S 2008. IEEE , vol., no., pp.1-4, 5-11 July 2008

SAR (W/kg) versus radiated power (W) at distances of 10cm and 100cm

SAR CALCULATION


SAR (W/kg) versus radiated power (W) at distances of 10cm and 100cm

Since, the FCC limit for RFID reader systems are at 1W of radiated power, it is clear that 2 reader, antennas placed 10cm away from the human face would provide much higher SAR than that allowed by FCC in the US:

SAR CALCULATION


SAR for the human head with antenna gain with 7.4dB

SAR CALCULATION



Motor Cortex Region

SAR CALCULATION



Motor Cortex Region

~100 times attenuation

SAR CALCULATION – 10 MW



Motor Cortex Region

~100 times attenuation

1W /100 = 0.01W = 10mWMax. Chip Power Source


Amini, S.; Plett, C.; , "Design and analysis of very low voltage charge pumps for RFID tags," Microsystems and Nanoelectronics Research Conference, 2008. MNRC 2008. 1st , vol., no., pp.9-12, 15-15 Oct. 2008

Basic Front End System Architecture for RFID Tags


VonBraunLabs

Test chip – several designs on the same DIE


VonBraunLabs

On-chip Antenna(Charge Pump)Test chip – several designs on the same DIE


VonBraunLabs

On-chip Antenna(Charge Pump)Test chip – several designs on the same DIE

Conventional Circuit for Charge Pump


Multi-stage Charge Pump circuit Multi-stage Charge Pump efficiency

* Proposed by: Tzu-Chia Huang; Fu-Ming Hsu; Chao, P.C.-P.; , "An energy harvesting system with a novel rectifier charge pump," Sensors, 2011 IEEE , vol., no., pp.32-35, 28-31 Oct. 2011

*

SAR CALCULATION – 10 MW – 5 MW

* Proposed by: Tzu-Chia Huang; Fu-Ming Hsu; Chao, P.C.-P.; , "An energy harvesting system with a novel rectifier charge pump," Sensors, 2011 IEEE , vol., no., pp.32-35, 28-31 Oct. 2011

*

Up to 7 uA our efficiency is about 50%

Multi-stage Charge Pump circuit Multi-stage Charge Pump efficiency

SAR CALCULATION – 10 MW – 5 MW / 5 UW

Channel model used for simulation of neural radio linkMeasurement setup of link through pig skull

Mark, M. et All Wireless channel characterization for mm-size neural implants. 2010 Annual International Conference of the IEEE,2010 , Page(s): 1565 - 1568

Mark et al estimates the power consumption in 5 uW to drive each electrode!

SAR CALCULATION – 10 MW – 5 MW / 5 UW + 25 UW = 30 UW

*Sungkil Hwang. A low-power asynchronous ECG acquisition system in CMOS technology. Engineering in Medicine and Biology Society (EMBC), 2010 Annual International Conference of the IEEE. Aug. 31 2010-Sept. 4 2010. Page(s): 5262 - 5265

Non-Nyquist ADC comsumption: 25 uW per channel against 54 uW Nyquist ones

Architecture of the asynchronous ADC *

RESULTS

* Miguel Nicolelis: Beyond Boundaries: The New Neuroscience of Connecting Brains with Machines---and How It Will Change Our Lives, 368 pages St. Martin's Griffin; Reprint edition, 2012, ISBN-10: 1250002613

Total power source (max SAR & efficiency of multi-stage charge pump): 5 mWTotal consumption per electrode (drive and async ADC): 30uW

5 mW / 30 uW = 0.005/0.00003 =166.666 eletrodes

CONCLUSIONS

* Miguel Nicolelis: Beyond Boundaries: The New Neuroscience of Connecting Brains with Machines---and How It Will Change Our Lives, 368 pages St. Martin's Griffin; Reprint edition, 2012, ISBN-10: 1250002613

In this preliminary work we estimate that is theoretically possible to power up about 160 electrodes into the brain, in the region of the human motor cortex, maintaining levels of security in the absorption of electromagnetic radiation (SAR).

Despite the fact of 1000 electrodes are estimated for a brain-computer interface capable of performing most everyday tasks *, using 100-200 electrodes is enough to coordinate movements of a hand and possibly walk.

http

://w

ww

.dw

.de/

ibm

-faz

-par

ceria

-com

-labo

rat%

C3%

B3r

io-b

rasi

leiro

-par

a-de

senv

olve

r-ch

ip-c

ereb

ral/a

-164

3498

4 NEWS RELEASE

THE END… QUESTIONS ?

Education

Calculating the SAR to Power up an Implantable Neural Interface for Wireless Communications with Human Motor Cortex