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Date: Fri, Mar 9, 2012 at 9:46 AM
Subject: [ee-doctorate] Oral Exam Announcement: Daniel Pivonka
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From: Student Services <studentservices@ee.stanford.edu>
Date: Fri, Mar 9, 2012 at 9:46 AM
Subject: [ee-doctorate] Oral Exam Announcement: Daniel Pivonka
To: ee-students@lists.stanford.edu
A mm-sized Wirelessly Powered and Remotely Controlled Locomotive Implant
Daniel Pivonka
Department of Electrical Engineering
Advisor: Prof. Teresa Meng
Thursday, March 15th, 2012
3 pm (refreshments at 2:45 pm)
Paul G. Allen Auditorium (CIS-X 101)
http://cis.stanford.edu/directions/
Abstract
Fully autonomous implantable systems with locomotion can revolutionize medical technology, serving applications ranging from diagnostics to minimally invasive surgery. In addition, they open up possibilities for a variety of emerging technologies, allowing for new applications that were previously impossible. The key challenges in achieving such a device are the limited power budget imposed by the miniaturization of the device, the high power consumption of fluid propulsion techniques, and the need for highly efficient data transfer and circuit design. In addition, the device must be bio-compatible and operate safely, with the primary risks arising from RF exposure levels and the propulsion mechanism.
Most implantable devices require a battery or an inductive link as a power supply, and with current technologies miniaturizing these powering methods to the mm and sub-mm regime is not possible. Additionally, existing propulsion techniques often rely on piezoelectric materials and have complicated designs, use significant power, and have increasingly low thrust efficiency as they are scaled. Alternatives use magnetic structures in complex magnetic fields, but these devices move slowly even when used in MRI. In this work, a wireless powering method allows for a mm-sized antenna to receive up to 500μW at depths up to a few cm in tissue. Also, new propulsion methods have been developed that employ electromagnetic forces experienced by moving currents in a magnetic field, and these allow for a simple design and efficient thrust generation. Two methods operate with this principle: the first uses magnetohydrodynamics (MHD), and the second oscillates a structure that generates thrust from asymmetries in the fluid drag characteristics. Both methods have been evaluated via incompressible Navier-Stokes fluid simulations, and the results show that mm-sized devices can reach ~cm/sec speeds with ~mA of current.
To demonstrate these principles, a prototype chip was fabricated in the TSMC 65nm process. The entire system was integrated on chip with the exception of a 2mm x 2mm receive antenna. The power carrier is modulated with a minimal depth AM pulse-width technique to reduce the impact on power delivery. The on-chip circuitry includes a matching network with adaptive loading, a rectifier and regulator for the power supply, a demodulator for clock and data recovery, and a digital controller to interface with the propulsion system. The chip functions with either propulsion method, and can deliver 1-3mA from a 0.2V driver depending on the received power. Propulsion dominates power usage, with the active circuitry consuming less than 10% of the total power budget. The 3mm x 4mm prototype achieves .53cm/sec speeds in fluid with a .06T field using approximately 250μW, and receives up to 25Mbps from a 2W 1.86GHz signal.
Daniel Pivonka
Department of Electrical Engineering
Advisor: Prof. Teresa Meng
Thursday, March 15th, 2012
3 pm (refreshments at 2:45 pm)
Paul G. Allen Auditorium (CIS-X 101)
http://cis.stanford.edu/directions/
Abstract
Fully autonomous implantable systems with locomotion can revolutionize medical technology, serving applications ranging from diagnostics to minimally invasive surgery. In addition, they open up possibilities for a variety of emerging technologies, allowing for new applications that were previously impossible. The key challenges in achieving such a device are the limited power budget imposed by the miniaturization of the device, the high power consumption of fluid propulsion techniques, and the need for highly efficient data transfer and circuit design. In addition, the device must be bio-compatible and operate safely, with the primary risks arising from RF exposure levels and the propulsion mechanism.
Most implantable devices require a battery or an inductive link as a power supply, and with current technologies miniaturizing these powering methods to the mm and sub-mm regime is not possible. Additionally, existing propulsion techniques often rely on piezoelectric materials and have complicated designs, use significant power, and have increasingly low thrust efficiency as they are scaled. Alternatives use magnetic structures in complex magnetic fields, but these devices move slowly even when used in MRI. In this work, a wireless powering method allows for a mm-sized antenna to receive up to 500μW at depths up to a few cm in tissue. Also, new propulsion methods have been developed that employ electromagnetic forces experienced by moving currents in a magnetic field, and these allow for a simple design and efficient thrust generation. Two methods operate with this principle: the first uses magnetohydrodynamics (MHD), and the second oscillates a structure that generates thrust from asymmetries in the fluid drag characteristics. Both methods have been evaluated via incompressible Navier-Stokes fluid simulations, and the results show that mm-sized devices can reach ~cm/sec speeds with ~mA of current.
To demonstrate these principles, a prototype chip was fabricated in the TSMC 65nm process. The entire system was integrated on chip with the exception of a 2mm x 2mm receive antenna. The power carrier is modulated with a minimal depth AM pulse-width technique to reduce the impact on power delivery. The on-chip circuitry includes a matching network with adaptive loading, a rectifier and regulator for the power supply, a demodulator for clock and data recovery, and a digital controller to interface with the propulsion system. The chip functions with either propulsion method, and can deliver 1-3mA from a 0.2V driver depending on the received power. Propulsion dominates power usage, with the active circuitry consuming less than 10% of the total power budget. The 3mm x 4mm prototype achieves .53cm/sec speeds in fluid with a .06T field using approximately 250μW, and receives up to 25Mbps from a 2W 1.86GHz signal.
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