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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
Workshop on Mathematics in IndustryICMC, São Carlos, Brasil, 12 December 2012
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OUTLINE
• Neural Biomedical Devices
• Science without Borders Project
• Why Silicon Carbide
• SAR Calculation
• Conclusions
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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
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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
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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
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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
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SCIENCE WITHOUT BORDERS PROGRAM OBJECTIVES
Particulars:
2D probes packaged, hermetic and biocompatible, wireless link capable
Year 2 – in-vivo operation
Hermetic Package – must be biocompatible!
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SCIENCE WITHOUT BORDERS PROGRAM OBJECTIVES
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
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WHY SILICON CARBIDE (SIC)
Indwelling Neural Implants Strategies for Contending with the In Vivo Environment
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WHY SILICON CARBIDE (SIC)
Indwelling Neural Implants Strategies for Contending with the In Vivo Environment
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CVD @ 1350 ºC
SiC film on Si7-10 µm/hour
Start with a Si Wafer (2”)
WHY SILICON CARBIDE (SIC)
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WHY SILICON CARBIDE (SIC)
Saddow et al.
SiC Shank (basis for electrode) - Magnify 50x
SiC
3C-SiC
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WHY SILICON CARBIDE (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
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WHY SILICON CARBIDE (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
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WHY SILICON CARBIDE (SIC)
Saddow et al.
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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.
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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
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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
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:
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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 for the human head with antenna gain with 7.4dB
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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 for the human head with antenna gain with 7.4dB
Motor Cortex Region
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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 for the human head with antenna gain with 7.4dB
Motor Cortex Region
~100 times attenuation
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SAR CALCULATION – 10 MW
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 for the human head with antenna gain with 7.4dB
Motor Cortex Region
~100 times attenuation
1W /100 = 0.01W = 10mWMax. Chip Power Source
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SAR CALCULATION – 10 MW
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
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SAR CALCULATION – 10 MW
VonBraunLabs
Test chip – several designs on the same DIE
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SAR CALCULATION – 10 MW
VonBraunLabs
On-chip Antenna(Charge Pump)Test chip – several designs on the same DIE
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SAR CALCULATION – 10 MW
VonBraunLabs
On-chip Antenna(Charge Pump)Test chip – several designs on the same DIE
Conventional Circuit for Charge Pump
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SAR CALCULATION – 10 MW
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
*
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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
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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!
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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 *
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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
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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.
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THE END… QUESTIONS ?