하이드로젤 기반의 터치 센싱과 무선 전력 전송 이온-전자 혼성 장치에 관한 연구

학위논문(박사)--서울대학교 대학원 :공과대학 재료공학부,2020. 2. 오규환.As the rise of ubiquitous computing and the Internet of Thing facilitate the frequent interaction between human and machines, the importance of human machine interfaces (HMI) has been emphasized. Despite recent advances in HMI, current devices based on metals or semiconductors are still limited in use due to mechanical mismatches with humans having soft skins and tissues. In this respect, hydrogels are promising alternative for conventional conductive materials. The hydrogels are polymer networks swollen with the water. The polymer networks enable the hydrogel to maintain their shape like a solid and to withstand deformation. The water in the hydrogel dissolves the ions, making the hydrogel ionic conductive. Thus, hydrogels with ions can be served as stretchable ionic conductors to transmit electrical signals and power even in the stretched state. However, there are also issues that arise because of the use of ions as charge carriers. Herein, I demonstrate how to solve the issues when using hydrogels and how to take advantage of their characteristics. Two ionic devices were developed and explored; a hydrogel touchpad that can stretch more than 1000% and a gel receiver that can receive electrical power wirelessly. In first part, highly stretchable and transparent touch panel consisting of hydrogels was explored. Because human-computer interactions are increasingly important, touch panels may require stretchability and biocompatibility in order to allow integration with the human body. However, most touch panels have been developed based on stiff and brittle electrodes. We demonstrate an ionic touch panel based on a polyacrylamide hydrogel containing lithium chloride salts. The panel is soft and stretchable, so it can sustain a large deformation. The panel can freely transmit light information because the hydrogel is transparent, with 98% transmittance for visible light. A surface-capacitive touch system was adopted to sense a touched position. The panel can be operated under more than 1000% areal strain without sacrificing its functionalities. Epidermal touch panel use on skin was demonstrated by writing words, playing a piano, and playing games. In second part, we have explored a wireless power transfer system using an ionic conductor as a power receiving parts. A number of implantable biomedical devices that require electric power have been developed and wireless power transfer (WPT) systems are emerging as a way to provide power to these devices without requiring a hardwired connection. Most of WPT have been based on conventional conductive materials, such as metals, which tend to be less biocompatible and stiff. Herein, we describe a development of an ionic wireless power transfer (IWPT) system on the basis of ionic conductor. A power receiver of the IWPT consisting of polyacrylamide hydrogel with NaCl salts was delivered power through the ionic current induced by capacitive coupling. The hydrogel receiver, easy to fabricate, flexible, transparent, and biocompatible, received power at a distance of 5 cm from the transmitter, and even when inserted inside the mouse. Charge accumulation caused by the prevention of discharge on electrical double layers (CAPDE) induced electrochemical reactions in the IWPT. The mechanism of CAPDE was studied and the amount of products was controlled by tuning the circuit parameter.유비쿼터스 컴퓨팅과 사물인터넷의 등장으로 사람과 기계간의 상호작용이 빈번해짐에 따라 휴먼-머신 인터페이스의 중요성이 점점 강조되어왔다. 휴먼-머신 인터페이스 기술의 발전에도 불구하고 금속과 반도체를 기반으로 한 현재의 디바이스들은 부드러운 피부와 조직을 가지고 있는 사람과의 기계적 물성의 불일치로 인해 사용이 제약되고 있다. 이런 측면에서 하이드로젤은 기존의 전도성 물질들의 대안으로서 등장했다. 하이드로젤은 다량의 수분을 머금고 있는 고분자 네트워크이다. 고분자 네트워크는 하이드로젤이 형체를 유지하고 또 변형을 견딜 수 있게 해주며 하이드로젤 내부의 수분은 이온을 녹여 하이드로젤이 이온 전도성을 가질 수 있게 해준다. 따라서 하이드로젤은 늘어난 상태에서도 전기 신호와 전력을 전달할 수 있는 신축성이 있는 전도체로 사용될 수 있다. 하지만 이온을 전하전달체로 사용한다는 것은 새로운 문제들을 야기할 수 있다. 이 논문에서 하이드로젤을 어떻게 이온 전도체로 이용하는지 또 그로 인한 문제들을 어떻게 다뤄야 하는지 말하고자 한다. 두 가지의 이온성 장치를 제작하였고 그에 대한 논의를 할 것이다. 첫 번째 장에서는 하이드로젤로 이루어진 투명하고 늘어날 수 있는 터치패널에 대해 논의할 것이다. 인간과 컴퓨터의 상호작용이 중요해짐에 따라 인간과의 통합이 가능하도록 생체적합성을 가지면서도 늘어날 수 있는 터치패널에 대한 수요가 증가하였다. 우리는 LiCl 염을 포함한 폴리아크릴아마이드 (polyacrylamide) 하이드로젤로 터치패널을 만들었다. 하이드로젤 터치패드는 부드럽고 신축성이 있어서 높은 변형을 견딜 수 있었다. 또한 하이드로젤은 높은 투명성을 가진 재료이기 때문에 가시광선 영역에서 98 %의 투명도를 보였다. 하이드로젤 터치패드는 표면 정전용량 식 터치 감지 시스템을 기반으로 제작되었으며 1000%가 넘는 변형이 주어진 상황에서도 정상적으로 작동하였다. 하이드로젤 터치패드는 피부에 부착된 형태로도 사용이 가능하였으며 피부에 부착된 상태로 글을 쓰거나 피아노를 치거나 게임을 하는 등의 동작을 수행할 수 있었다. 두 번째 장에서는 이온 전도체를 이용해서 무선으로 전력을 전달 할 수 있는 시스템에 대해 논의할 것이다. 이식형 의료장비에 전력을 제공할 수 있는 방법들 중에서 무선 전력 전송 방식은 지속적으로 충분한 양의 전력을 공급할 수 있다는 면에서 주목받고 있다. 대부분의 무선 전력 전송 시스템은 효율을 높이기 위해 전도성이 높은 금속을 사용하지만 금속은 딱딱하고 생체적합성이 부족한 재료이다. 이 논문에서 우리는 이온성 무선 전력 전송 장치를 제작하였다. 이온성 무선 전력 전송 장치는 부드럽고 투명하고 생체적합성이 뛰어난 하이드로젤 수신부를 통해 전력을 전달받는다. 이온성 무선 전력 전송 시스템은 5 cm 떨어진 거리에서도 전력을 전달 할 수 있었고 심지어 쥐의 피하에 이식된 전력 수신장치에도 피부를 통과하여 전력을 전달 할 수 있었다. 또한 이온성 장치에서 문제로 여겨지는 전기화학반응을 의도적으로 발생시키는 회로를 구성하여 원하는 전기화학반응을 유도해 낼 수 있었다. 이온성 무선 전력 전송 시스템 내에서의 전기화학반응의 발생 기작을 확인하였고 회로 설계를 통해 전기화학반응으로 인한 생성물의 양을 조절할 수 있었다.Chapter 1. Introduction 1 1.1. Study Background 1 1.1.1 Ionic conduction 1 1.1.2 Stretchable ionics. 2 1.1.2.1 Issues on the stretchable ionic devices 2 1.1.2.2 Applications of stretchable ionic devices 4 1.2. Purpose of Research 12 Reference 13 Chapter 2. Highly stretchable, transparent ionic touch panel 16 2.1. Introduction 16 2.2. Experimental section 18 2.2.1 Materials 18 2.2.2 An ionic touch strip. 19 2.2.3 Transparent ionic touch panel. 20 2.2.4 Epidermal touch panel. 20 2.3. Results and Discussion 21 2.3.1 A working principle of an ionic touch strip. 21 2.3.2 Sensing mechanism for a 1-dimensional touch strip 27 2.3.3 Latency of the ionic touch panel 29 2.3.4 Parasitic capacitance and baseline current. 32 2.3.5 Accumulated currents induced by touches during the stretching of a gel strip. 34 2.3.6 Strain rate effects of a gel strip during a uniaxial stretching. 35 2.3.7 Resolution of the ionic touch panel. 38 2.3.8 Position-sensing in a 2D ionic touch panel. 40 2.3.9 A stretchable touch panel. 49 2.3.10 Operation of an ionic touch panel under an anisotropic deformation. 55 2.3.11 An epidermal touch panel that is soft and transparent. 57 2.3.12 The insulation of the epidermal touch panel. 58 2.4. Conclusion 63 Reference 64 Chapter 3. Ionic wireless power transfer 67 3.1. Introduction 67 3.2. Experimental section and backgrounds 70 3.2.1 Materials and synthesis 70 3.2.2 Experimental setup for IWPT 71 3.2.3 Power transfer in series resistorinductorcapacitor (RLC) circuits. 71 3.2.4 The structure of the coupling capacitor. 75 3.3. Results and Discussion 77 3.3.1 Basic princibles and operations of an Ionic wireless power transfer (IWPT) 77 3.3.2 Characteristics of IWPT 83 3.3.3 Implantation of an IWPT system. 89 3.3.4 CAPDE for NADPH regeneration 98 3.3.5 Analysis of the voltages generated in the CEDL 112 3.4. Conclusion 114 Reference 115 Chapter 4. Conclusion 119 Abstract in Korean 121 Biography 124Docto

Implantable Wireless Sensor Networks: Application to Measuring Temperature for In Vivo Detection of Infections

It is has been proven that infection in the body cause a local temperature increase due to localized inflammation. Therefore, a method to provide early diagnostic or long-term tracking of this infection will provide great benefits to patients with diabetic foot ulcers or sickle cell disease, and those receiving hemodialysis where they suffer from a weakened immune system. The goal of this project is to develop an implantable wireless temperature sensor based on a wireless sensor network system for monitoring infections in situ. The analog signals from the thermistors are digitized and wirelessly transmitted to a computer with an ez430-rf2500 wireless sensor network (Texas Instruments). The sensor device is designed to monitor temperature at a fixation plate of a rodent under an infection model. Two prototypes of the system, T1 and T2, were designed and fabricated during this work. The sensors displayed good sensitivity, stability and reliability during the testing. The system was optimized for better timing accuracy to allow power management. Such a sensor could be used for long term monitoring of infections associated with orthopedic implants

Low power CMOS IC, biosensor and wireless power transfer techniques for wireless sensor network application

The emerging field of wireless sensor network (WSN) is receiving great attention due to the interest in healthcare. Traditional battery-powered devices suffer from large size, weight and secondary replacement surgery after the battery life-time which is often not desired, especially for an implantable application. Thus an energy harvesting method needs to be investigated. In addition to energy harvesting, the sensor network needs to be low power to extend the wireless power transfer distance and meet the regulation on RF power exposed to human tissue (specific absorption ratio). Also, miniature sensor integration is another challenge since most of the commercial sensors have rigid form or have a bulky size. The objective of this thesis is to provide solutions to the aforementioned challenges

소형동물의 뇌신경 자극을 위한 완전 이식형 신경자극기

학위논문(박사)--서울대학교 대학원 :공과대학 전기·정보공학부,2020. 2. 김성준.In this study, a fully implantable neural stimulator that is designed to stimulate the brain in the small animal is described. Electrical stimulation of the small animal is applicable to pre-clinical study, and behavior study for neuroscience research, etc. Especially, behavior study of the freely moving animal is useful to observe the modulation of sensory and motor functions by the stimulation. It involves conditioning animal's movement response through directional neural stimulation on the region of interest. The main technique that enables such applications is the development of an implantable neural stimulator. Implantable neural stimulator is used to modulate the behavior of the animal, while it ensures the free movement of the animals. Therefore, stable operation in vivo and device size are important issues in the design of implantable neural stimulators. Conventional neural stimulators for brain stimulation of small animal are comprised of electrodes implanted in the brain and a pulse generation circuit mounted on the back of the animal. The electrical stimulation generated from the circuit is conveyed to the target region by the electrodes wire-connected with the circuit. The devices are powered by a large battery, and controlled by a microcontroller unit. While it represents a simple approach, it is subject to various potential risks including short operation time, infection at the wound, mechanical failure of the device, and animals being hindered to move naturally, etc. A neural stimulator that is miniaturized, fully implantable, low-powered, and capable of wireless communication is required. In this dissertation, a fully implantable stimulator with remote controllability, compact size, and minimal power consumption is suggested for freely moving animal application. The stimulator consists of modular units of surface-type and depth-type arrays for accessing target brain area, package for accommodating the stimulating electronics all of which are assembled after independent fabrication and implantation using customized flat cables and connectors. The electronics in the package contains ZigBee telemetry for low-power wireless communication, inductive link for recharging lithium battery, and an ASIC that generates biphasic pulse for neural stimulation. A dual-mode power-saving scheme with a duty cycling was applied to minimize the power consumption. All modules were packaged using liquid crystal polymer (LCP) to avoid any chemical reaction after implantation. To evaluate the fabricated stimulator, wireless operation test was conducted. Signal-to-Noise Ratio (SNR) of the ZigBee telemetry were measured, and its communication range and data streaming capacity were tested. The amount of power delivered during the charging session depending on the coil distance was measured. After the evaluation of the device functionality, the stimulator was implanted into rats to train the animals to turn to the left (or right) following a directional cue applied to the barrel cortex. Functionality of the device was also demonstrated in a three-dimensional maze structure, by guiding the rats to navigate better in the maze. Finally, several aspects of the fabricated device were discussed further.본 연구에서는 소형 동물의 두뇌를 자극하기 위한 완전 이식형 신경자극기가 개발되었다. 소형 동물의 전기자극은 전임상 연구, 신경과학 연구를 위한 행동연구 등에 활용된다. 특히, 자유롭게 움직이는 동물을 대상으로 한 행동 연구는 자극에 의한 감각 및 운동 기능의 조절을 관찰하는 데 유용하게 활용된다. 행동 연구는 두뇌의 특정 관심 영역을 직접적으로 자극하여 동물의 행동반응을 조건화하는 방식으로 수행된다. 이러한 적용을 가능케 하는 핵심기술은 이식형 신경자극기의 개발이다. 이식형 신경자극기는 동물의 움직임을 방해하지 않으면서도 그 행동을 조절하기 위해 사용된다. 따라서 동물 내에서의 안정적인 동작과 장치의 크기가 이식형 신경자극기를 설계함에 있어 중요한 문제이다. 기존의 신경자극기는 두뇌에 이식되는 전극 부분과, 동물의 등 부분에 위치한 회로부분으로 구성된다. 회로에서 생산된 전기자극은 회로와 전선으로 연결된 전극을 통해 목표 지점으로 전달된다. 장치는 배터리에 의해 구동되며, 내장된 마이크로 컨트롤러에 의해 제어된다. 이는 쉽고 간단한 접근방식이지만, 짧은 동작시간, 이식부위의 감염이나 장치의 기계적 결함, 그리고 동물의 자연스러운 움직임 방해 등 여러 문제점을 야기할 수 있다. 이러한 문제의 개선을 위해 무선통신이 가능하고, 저전력, 소형화된 완전 이식형 신경자극기의 설계가 필요하다. 본 연구에서는 자유롭게 움직이는 동물에 적용하기 위하여 원격 제어가 가능하며, 크기가 작고, 소모전력이 최소화된 완전이식형 자극기를 제시한다. 설계된 신경자극기는 목표로 하는 두뇌 영역에 접근할 수 있는 표면형 전극과 탐침형 전극, 그리고 자극 펄스 생성 회로를 포함하는 패키지 등의 모듈들로 구성되며, 각각의 모듈은 독립적으로 제작되어 동물에 이식된 뒤 케이블과 커넥터로 연결된다. 패키지 내부의 회로는 저전력 무선통신을 위한 지그비 트랜시버, 리튬 배터리의 재충전을 위한 인덕티브 링크, 그리고 신경자극을 위한 이상성 자극파형을 생성하는 ASIC으로 구성된다. 전력 절감을 위해 두 개의 모드를 통해 사용률을 조절하는 방식이 장치에 적용된다. 모든 모듈들은 이식 후의 생물학적, 화학적 안정성을 위해 액정 폴리머로 패키징되었다. 제작된 신경자극기를 평가하기 위해 무선 동작 테스트가 수행되었다. 지그비 통신의 신호 대 잡음비가 측정되었으며, 해당 통신의 동작거리 및 데이터 스트리밍 성능이 검사되었고, 장치의 충전이 수행될 때 코일간의 거리에 따라 전송되는 전력의 크기가 측정되었다. 장치의 평가 이후, 신경자극기는 쥐에 이식되었으며, 해당 동물은 이식된 장치를 이용해 방향 신호에 따라 좌우로 이동하도록 훈련되었다. 또한, 3차원 미로 구조에서 쥐의 이동방향을 유도하는 실험을 통하여 장치의 기능성을 추가적으로 검증하였다. 마지막으로, 제작된 장치의 특징이 여러 측면에서 심층적으로 논의되었다.Chapter 1 : Introduction 1 1.1. Neural Interface 2 1.1.1. Concept 2 1.1.2. Major Approaches 3 1.2. Neural Stimulator for Animal Brain Stimulation 5 1.2.1. Concept 5 1.2.2. Neural Stimulator for Freely Moving Small Animal 7 1.3. Suggested Approaches 8 1.3.1. Wireless Communication 8 1.3.2. Power Management 9 1.3.2.1. Wireless Power Transmission 10 1.3.2.2. Energy Harvesting 11 1.3.3. Full implantation 14 1.3.3.1. Polymer Packaging 14 1.3.3.2. Modular Configuration 16 1.4. Objectives of This Dissertation 16 Chapter 2 : Methods 18 2.1. Overview 19 2.1.1. Circuit Description 20 2.1.1.1. Pulse Generator ASIC 21 2.1.1.2. ZigBee Transceiver 23 2.1.1.3. Inductive Link 24 2.1.1.4. Energy Harvester 25 2.1.1.5. Surrounding Circuitries 26 2.1.2. Software Description 27 2.2. Antenna Design 29 2.2.1. RF Antenna 30 2.2.1.1. Design of Monopole Antenna 31 2.2.1.2. FEM Simulation 31 2.2.2. Inductive Link 36 2.2.2.1. Design of Coil Antenna 36 2.2.2.2. FEM Simulation 38 2.3. Device Fabrication 41 2.3.1. Circuit Assembly 41 2.3.2. Packaging 42 2.3.3. Electrode, Feedthrough, Cable, and Connector 43 2.4. Evaluations 45 2.4.1. Wireless Operation Test 46 2.4.1.1. Signal-to-Noise Ratio (SNR) Measurement 46 2.4.1.2. Communication Range Test 47 2.4.1.3. Device Operation Monitoring Test 48 2.4.2. Wireless Power Transmission 49 2.4.3. Electrochemical Measurements In Vitro 50 2.4.4. Animal Testing In Vivo 52 Chapter 3 : Results 57 3.1. Fabricated System 58 3.2. Wireless Operation Test 59 3.2.1. Signal-to-Noise Ratio Measurement 59 3.2.2. Communication Range Test 61 3.2.3. Device Operation Monitoring Test 62 3.3. Wireless Power Transmission 64 3.4. Electrochemical Measurements In Vitro 65 3.5. Animal Testing In Vivo 67 Chapter 4 : Discussion 73 4.1. Comparison with Conventional Devices 74 4.2. Safety of Device Operation 76 4.2.1. Safe Electrical Stimulation 76 4.2.2. Safe Wireless Power Transmission 80 4.3. Potential Applications 84 4.4. Opportunities for Further Improvements 86 4.4.1. Weight and Size 86 4.4.2. Long-Term Reliability 93 Chapter 5 : Conclusion 96 Reference 98 Appendix - Liquid Crystal Polymer (LCP) -Based Spinal Cord Stimulator 107 국문 초록 138 감사의 글 140Docto

Towards on line monitoring the evolution of the myocardium infarction scar with an implantable electrical impedance spectrum monitoring system.

The human heart tissue has a limited capacity for regeneration. Tissue and cellular therapies based on the use of stem cells may be useful alternatives to limit the size of myocardial infarction. In this paper, the preliminary results from an experimental campaign for on-line monitoring of myocardium scar infarction are presented. This study has been carried out under a research project that has as main objective the development and application of a bioactive patch implant for regeneration of myocardial infarction. Electrical Impedance Spectroscopy (EIS) has been chosen as a tissue state monitoring technique. What is presented in this communication is the first results of an implantable EIS measurement system which has been implanted in a subset of the animals corresponding to the control group, along one month. In all the animals, the myocardial infarction was induced by the ligation of the first circumflex marginal artery. In the animal group presented,the bioactive patch scaffold and the electrodes were implanted without the stem cells load. The scaffold is a piece of decellularized human pericardium, lyophilized and rehydrated with hydrogel RAD16-I. Nanogold particles were also placed near the electrodes to improve the electrode area conductivity. The results presented correspond to the subset of animals (n = 5), which had implanted the bioimpedance system monitoring the electrical impedance spectrum in vivo during 1 month. Two electrodes were connected to the bioactive patch implant. A total of 14 logarithmically spaced frequencies were measured every 5 minutes, from 100 Hz to 200 kHz. Results show a convergence of low-frequency and high frequency impedance magnitudes along the measurement period, which is coherent with the scar formation.Postprint (published version

Wireless Power Transfer in Wearable Smart Contact Lenses [Open access]

In 2016, a smart contact lens was developed by Google company which aimed to directly implanting micro-smart lenses into the human eye to test blood sugar percentage by tears. However, small sizes implantable devices such as contact lens requires power transfer unit for continuously power supply. Thus, this project aims to design a power transfer unit with Inductively Coupled Power Transfer (ICPT) technology for smart contact lens which works under 2.45GHz to power an LED at load. The coil size is designed as 10mm inner diameter, 12mm outer diameter and 0.2mm wire width. Additionally, polydimethylsiloxane (PDMS) is used as the contact lens substrate. During the simulation, different eye models were built since the coil needs to be warped on top of lens and the eyeball, and under different conditions the S11 parameter is adjusted to around -10dB. The antenna is fabricated by technician in school, due to the technology restriction, the antenna was fabricated with unequal line width, which causes a resonate frequency shift to 900MHz with -8dB S11 value. To power an LED at load side, full-wave and half-wave rectifiers are built separately with different component values and send to fabrication. The antenna performance was tested under three conditions, in air, on human hand, and on water surface to imitate the liquid condition in human eye, but since the dielectric constant varies in each case, and for fabrication there is an extra circuit unit which effecting the copper coil numbers, the tested resonant frequency is not as desired values

Wireless Power Transfer in Wearable Smart Contact Lenses [Open access]

In 2016, a smart contact lens was developed by Google company which aimed to directly implanting micro-smart lenses into the human eye to test blood sugar percentage by tears. However, small sizes implantable devices such as contact lens requires power transfer unit for continuously power supply. Thus, this project aims to design a power transfer unit with Inductively Coupled Power Transfer (ICPT) technology for smart contact lens which works under 2.45GHz to power an LED at load. The coil size is designed as 10mm inner diameter, 12mm outer diameter and 0.2mm wire width. Additionally, polydimethylsiloxane (PDMS) is used as the contact lens substrate. During the simulation, different eye models were built since the coil needs to be warped on top of lens and the eyeball, and under different conditions the S11 parameter is adjusted to around -10dB. The antenna is fabricated by technician in school, due to the technology restriction, the antenna was fabricated with unequal line width, which causes a resonate frequency shift to 900MHz with -8dB S11 value. To power an LED at load side, full-wave and half-wave rectifiers are built separately with different component values and send to fabrication. The antenna performance was tested under three conditions, in air, on human hand, and on water surface to imitate the liquid condition in human eye, but since the dielectric constant varies in each case, and for fabrication there is an extra circuit unit which effecting the copper coil numbers, the tested resonant frequency is not as desired values

Implantable Piezoresistive Microcantilever-based Wireless Cocaine Biosensors

Cocaine is a well-known, illegal, recreational drug that is addictive due to its effects on the mesolimbic reward pathway in the human body. Accurate and real-time measurement of the concentration of cocaine in the body as a function of time and physiological factors is a key requirement for the understanding of the use of this drug. Current methods for such measurements involve taking samples from the human body (such as blood, urine, and hair) and performing analytical chemistry tests on these samples. This techniques are relatively expensive, time consuming, and labor intensive. To address this issue, a new implantable sensor for the automated detection and measurement of the relative cocaine concentration is presented here. The device is more economical and provides for higher sampling frequencies than the current methods. The active sensor elements consist of piezoresistive microcantilever arrays, which are coated with an oligonucleotide-based aptamer, i.e. a short sequence of RNA with high affinity for specific target molecules, as the cocaine receptor. A Wheatstone bridge is used to convert the biosensor signal into an electronic signal. This signal is transmitted wireless at an operating frequency of 403.55 MHz, which complies with the US Medical Implant Communication System (MICS) FCC 47CFR Part 95. The limit of detection for the in vitro experiment is found to be 1 ng/ml. The device has successfully measured the relative concentration of cocaine upon implantation in the subcutaneous interstitial fluid of male Wistar rats