97 research outputs found
Methods of magnetic field switching for biomedical and power applications
Surrounded by electromagnetic (EM) fields humans continuously interact and utilize EM fields for domestic devices, telecom systems, power systems and different medical applications including MRI (Magnetic Resonance Imaging) and TMS (Transcranial Magnetic Stimulation). During the last century, numerous new electronic devices and technologies have been developed leading to an exponential increase in exposure to Electromagnetic Fields. Although all of these applications are byproducts of Maxwell\u27 experimentation, there are considerable differences in the way they interact with us.
In the treatment of noninvasive treatment of the human brain, the majority of the research has been mainly focused on realizing systems that can produce gigantic current and magnetic fields. Transcranial Magnetic Stimulation (TMS) in this application has provided numerous opportunities and possibilities. It has shown more promise in the therapeutic role for treatment of neurological disorders. TMS researchers are working towards improving the technical developmental tools for modeling, and magnetic field generation study for deep body penetration. The development stage of these devices with associated risks in manufacturing, tight medical tolerances, cost and reliability pose important research challenges which are addressed in this research.
The objective of this research is to understand, develop and offer alternative methods for the implementation of several magnetic field generators that satisfy the requirement for magnetic field applications in medical, and other fields. This work presents a continual progression of the magnetic field generators from larger scale to small scale with variable energy consumption, high speed, and deployable systems. Additionally challenges and practical designs are presented
Fully-Implantable Self-Contained Dual-Channel Electrical Recording and Directivity-Enhanced Optical Stimulation System on a Chip
This thesis presents an integrated system-on-a-chip (SoC), designed, fabricated, and characterized for conducting simultaneous dual-channel optogenetic stimulation and electrophysiological recording. An inductive coil as well as power management circuits are also integrated on the chip, enabling wireless power reception, hence, allowing full implantation.
The optical stimulation channels host a novel LED driver circuit that can generate currents up to 10mA with a minimum required headroom voltage reported in the literature, resulting in a superior power efficiency compared to the state of the art. The output current in each channel can be programmed to have an arbitrary waveform with digitally-controlled magnitude and timing. The final design is fabricated as a 34 mm2 microchip using a CMOS 130nm technology and characterized both in terms of electrical and optical performance.
A pair of custom-designed inkjet-printed micro-lenses are also fabricated and placed on top of the LEDs. The lenses are optimized to enhance the light directivity of optical stimulation, resulting in significant improvements in terms of spatial resolution, power consumption (30.5x reduction), and safety aspects (temperature increase of <0.1c) of the device
Doctor of Philosophy
dissertationInterfacing with the peripheral nervous system via stimulating neurotechnologies has allowed for therapies which can restore sensorimotor and autonomic function previously lost to injury or disease. Magnetic stimulation (MS) is one such technology that m
Low power circuits and systems for wireless neural stimulation
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 155-161).Electrical stimulation of tissues is an increasingly valuable tool for treating a variety of disorders, with applications including cardiac pacemakers, cochlear implants, visual prostheses, deep brain stimulators, spinal cord stimulators, and muscle stimulators. Brain implants for paralysis treatments are increasingly providing sensory feedback via neural stimulation. Within the field of neuroscience, the perturbation of neuronal circuits wirelessly in untethered, freely-behaving animals is of particular importance. In implantable systems, power consumption is often the limiting factor in determining battery or power coil size, cost, and level of tissue heating, with stimulation circuitry typically dominating the power budget of the entire implant. Thus, there is strong motivation to improve the energy efficiency of implantable electrical stimulators. In this thesis, I present two examples of low-power tissue stimulators. The first type is a wireless, low-power neural stimulation system for use in freely behaving animals. The system consists of an external transmitter and a miniature, implantable wireless receiver-and-stimulator utilizing a custom integrated chip built in a standard 0.5 ptm CMOS process. Low power design permits 12 days of continuous experimentation from a 5 mAh battery, extended by an automatic sleep mode that reduces standby power consumption by 2.5x. To test this device, bipolar stimulating electrodes were implanted into the songbird motor nucleus HVC of zebra finches. Single-neuron recordings revealed that wireless stimulation of HVC led to a strong increase of spiking activity in its downstream target, the robust nucleus of the arcopallium (RA). When this device was used to deliver biphasic pulses of current randomly during singing, singing activity was prematurely terminated in all birds tested. The second stimulator I present is a novel, energy-efficient electrode stimulator with feedback current regulation. This stimulator uses inductive storage and recycling of energy based on a dynamic power supply to drive an electrode in an adiabatic fashion such that energy consumption is minimized. Since there are no explicit current sources or current limiters, wasteful energy dissipation across such elements is naturally avoided. The stimulator also utilizes a shunt current-sensor to monitor and regulate the current through the electrode via feedback, thus enabling flexible and safe stimulation. The dynamic power supply allows efficient transfer of energy both to and from the electrode, and is based on a DC-DC converter topology that is used in a bidirectional fashion. In an exemplary electrode implementation, I show how the stimulator combines the efficiency of voltage control and the safety and accuracy of current control in a single low-power integrated-circuit built in a standard 0.35 pm CMOS process. I also perform a theoretical analysis of the energy efficiency that is in accord with experimental measurements. In its current proof-of-concept implementation, this stimulator achieves a 2x-3x reduction in energy consumption as compared to a conventional current-source-based stimulator operating from a fixed power supply.by Scott Kenneth Arfin.Ph.D
Suurikokoiset päällekkäiset kelat, uusi lähestymistapa monikanavaisen transkraniaalisen magneettistimulaatiolaitteen rakentamiseen
Transcranial magnetic stimulation (TMS) allows for studying the functionality of the brain. Present TMS devices have one or two separate stimulation coils. More stimulation coils would allow new types of stimulation sequences, and thus they could be used to reveal more about brain functionality. However, due to the dimensions of the existing TMS coils, having multiple separate coils is a very limited approach. Rather, the coils should be combined into a single multichannel (mTMS) device.
The purpose of this Thesis is to make mTMS more feasible. In order to realize this purpose, a new coil design paradigm is introduced which employs large thin overlapping coils. This paradigm requires a new coil design method and a new coil-former design method, which are developed and tested in this Thesis. This Thesis solves two problems that appear with existing mTMS designs and is a significant step towards successful mTMS.Transkraniaalinen magneettistimulaatio (TMS) mahdollistaa aivotoiminnan tutkimisen. Nykyisissä TMS-laitteissa on yleensä yksi tai joissain tapauksissa kaksi erillistä stimulaatiokelaa. Suurempi kelamäärä mahdollistaisi uudentyyppisiä stimulaatiosekvenssejä, jotka mahdollistaisivat monipuolisemman aivotoiminnan tutkimisen. Koska TMS-kelat ovat verrattain suurikokoisia, ei tätä tavoitetta kuitenkaan pystytä saavuttamaan yhdistämällä monta erillistä TMS-kelaa. Sen sijaan tarvittaisiin yksi monikanavainen (mTMS) laite, jossa eri kanavien kelat on yhdistetty yhdeksi suuremmaksi kokonaisuudeksi.
Tämän diplomityön tarkoitus on edistää osaltaan mTMS-laitteen suunnittelua. Tätä varten esitellään uusi mTMS-rakenne, jossa mTMS-kela koostuu suurikokoisista ohuista päällekkäisistä keloista. Tässä diplomityössä kehitetään ja testataan yksittäisten kelojen suunnittelumenetelmä tämäntyyppistä mTMS-kelaa varten. Diplomityössä esiteltävä rakenne ratkaisee kaksi nykyisissä mTMS-kelarakennesuunnitelmissa esiintyvää ongelmaa
Double-containment coil with enhanced winding mounting for transcranial magnetic stimulation with reduced acoustic noise
Objective: This work aims to reduce the acoustic noise level of transcranial
magnetic stimulation (TMS) coils. TMS requires high currents (several thousand
amperes) to be pulsed through the coil, which generates a loud acoustic impulse
whose peak sound pressure level (SPL) can exceed 130 dB(Z). This sound poses a
risk to hearing and elicits unwanted neural activation of auditory brain
circuits. Methods: We propose a new double-containment coil with enhanced
winding mounting (DCC), which utilizes acoustic impedance mismatch to contain
and dissipate the impulsive sound within an air-tight outer casing. The coil
winding is potted in a rigid block, which is mounted to the outer casing by its
acoustic nodes that are subject to minimum vibration during the pulse. The rest
of the winding block is isolated from the casing by an air gap, and sound is
absorbed by foam within the casing. The casing thickness under the winding
center is minimized to maximize the coil electric field output. Results:
Compared to commercial figure-of-eight TMS coils, the DCC prototype has 10-33
dB(Z) lower SPL at matched stimulation strength, whilst providing 22% higher
maximum stimulation strength than equally focal commercial coils. Conclusion:
The DCC design greatly reduces the acoustic noise of TMS while increasing the
achievable stimulation strength. Significance: The acoustic noise reduction
from our coil design is comparable to that provided by typical hearing
protection devices. This coil design approach can enhance hearing safety and
reduce auditory co-activations in the brain and other detrimental effects of
TMS sound.Comment: 8 pages, 5 figure
Power Control Techniques in Wireless Power Transfer System
Department of Electrical EngineeringWireless power transfer (WPT) technology has attract the attentions of researchers and industrial for new method of power transfer mechanism. WPT technology enables contactless energy transfer between two resonators through a magnetic field. WPT is a promising method of powering electrical devices, especially in environments where wired charging is inconvenient of even dangerous. Recently, the interest of WPT has been arise with the increase of mobile devices such as cell phones, PDAs, laptops, tablets, and other handheld gadgets equipped with rechargeable batteries has been widely spreading. In recent years, WPT technology has already been applied to tooth brushes and mobile phones. In addition, many researchers are interested in applying WPT technology to electrical vehicle, cordless zone, and biomedical application and are conducting research to realize it. The area where wireless power transmission technology is most needed is biomedical. Biomedical devices to be implanted in the body are most severely limited by their small volume and battery capacity limitations. WPT technology is the most suitable technology to solve this problem. However, power loss occurs during wireless power transmission, it is necessary to overcome this problem because the harmful effects on the human body. In this dissertation, two new power control techniques are introduced to increase the efficiency of wireless power transmission in biomedical systems. The first proposed technique is a technique for transmitting power more efficiently at a place where the transmission distance is long, the size of the device is small, the position of the device is not fixed, and the efficiency is very low like a capsule endoscopy. The second proposed technique is a power control technique which can increase the power transfer efficiency for applications with close distances for implanted biomedical devices under the skin like a cardiac pacemaker.
Chapter II presents a new power control technique to improve efficiency in magnetic resonance (MR)- WPT system for biomedical capsule endoscopy. Recently, capsule endoscopy technology has been developed and emerged as an alternative to small bowel endoscopy, gastroscopy, and colonoscopy, all of which cause discomfort to patients because of their relatively large-diameter and flexible cables. However, commercialized capsule endoscopy still suffers from limited battery capacity. Chapter II presents a theory for power control technique in MR-WPT system, along with its experimental verification. An MR-WPT system with a 9-mm-diameter receiver is implemented, which is small enough to fit in the current capsule endoscope. The proposed system improves the efficiency despite variations in the distance, angle, and displacement. The proposed system is found to have a low specific absorption rate, which demonstrated that it is safe to use in the human body.
Chapter III proposes power control technique for inductive power transfer (IPT) battery charging system using in-band communication that aims to minimize number of power stages and increase power transfer efficiency with low-cost hardware. Constant current and constant voltage mode are needed to effectively charge Li-ion batteries to ensure long life-span and maximum capacity utilization. These two charging modes require different feedback loops and circuitry, which increase system complexity and reduces efficiency. One approach is to use additional converter stages that ensure effective battery charging, but this introduces additional conversion losses, which decreases efficiency. The IPT system using proposed step charging method tracks the proper frequency to maintain the desired constant current or voltage for battery charging without the need for additional regulation circuits, and with minimized feedback control signal. In-band communication is used to send feedback signal from secondary side to primary side of the IPT system, which enables effective feedback control without conventional wireless communication module. This power control technique is a technique to eliminate power loss in an unnecessary regulator. This technology is applicable to IPT using in-band communication and is suitable for implantable devices because it reduces receiver loss.ope
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