Enhanced Detection Techniques based on Distance Estimation with Radar for Human Bio-signals

Yun, Younguk Kwangwoon University Graduate School 2020 국내박사

This dissertation aims to increase the detection performance of distance estimation exploiting radar-based technology. We provide the various signal processing schemes to improve distance and detection performance through various signal processing of time-series signals and data collected by radar. There are two types of radar that we exploited, impulse radio ultra-wideband (IR-UWB) and Doppler radar. It has verified that are distance detection scheme and vital sign detection scheme. The former one is studied by exploiting IR-UWB radar and the latter one is studied by exploiting IR-UWB and Doppler radar. we limit the scope of vital signs that are heartbeat and respiration rate. Recently, it has been developed that are various technologies such as hyper-connected society, the 4th industrial revolution, cyber-physical system (CPS), and on-demand and expanded beyond the IoT and IoE epoch. Accordingly, it is emerging as a core technology that are location estimation, localization, or indoor positioning technology. In relation to the 4th Industrial Revolution, the indoor positioning system (IPS) is needed to complete the technologies used in industrial sites such as smart factories of CPS, smart city, smart building, and smart environment. In the case of outdoor, the location tracking technology is mainly based on the GPS system, but indoor and factory cannot exploit GPS and requires more accurate location tracking technology in the indoor environments, so various IPS are studied by using various sensors. However, it is being actively conducted researches on bio-signal detection schemes with increasing interest in healthcare along with positioning technology utilized in service aspects such as on-demand and fin-tech. We study the distance tracking technique that estimates the location or position exploiting the radar. And we discuss and proposed schemes to improve the performance of signals measured using radar through signal processing algorithms and verify the proposed scheme through experiments. The IR-UWB radar uses the 6.0-8.5GHz frequency band and the Doppler radar uses the 24GHz frequency band. For the distance estimation experiment, the experiment was conducted on the 6th floor of Kwangwoon University's Hwado-building using IR-UWB to move back and forth to the wide corridor 12m and the narrow corridor 15m. the movement speed was 0.5m/s. Bio-signal was measured using IR-UWB and Doppler radar. First, in the distance estimating experiment, the radar was installed at the height of the chest position of the subject and measured at a distance of 50cm from the subject. The experiment is repeated 30times for 1 minute with a total of 5 subjects. Bio-signal detection experiments using Doppler radar were conducted in general offices and vehicles. It is divided into the case with and without the subject's movement when the bio-signal experiment measure. The absence of the subject's movement includes both measurements with a distance of 0.5 to 2m and a case where only the vehicle is turned on. The motion test is conducted that is driving situation on the straight section of a normal highway. Various signal processing schemes are used that are singular value decomposition, low-rank approximation, and cross-correlation for estimating distance using IR-UWB. In the case of distance estimating scheme, the performance is increased by about 12 times compared with the conventional scheme. The conventional scheme has a maximum of 10m, an average error of 2.257m, and the proposed scheme has a maximum distance of 15m and an average error of 0.22m. In the respiratory detection study exploiting IR-UWB, the estimated performance is approximately 94.02% using Gram Schmidt orthogonalization techniques. In the case of using Doppler radar, the data are examined on the frequency axis through fast Fourier transform. The respiratory detection accuracy at stop status was 93.75%, heart rate 96.64%, the respiration detection accuracy at driving was 68.75%, and heart rate 84.48%. Various signal processing techniques can be utilized to increase the accuracy of driving.

Effects of exercise timing on blood glucose in adults : a systematic review and meta-analysis

Kim, Jong Hoon Kwangwoon University Graduate School 2024 국내석사

Effects of Exercise Timing on Blood Glucose in Adults : A Systematic Review and Meta-Analysis Kwangwoon University, Graduate School Department of Convergence Sports Science Kim Jong Hoon Modern lifestyles have contributed to the worsening of cardiovascular and metabolic diseases in recent years, modern lifestyles, including lack of sleep, exposure to artificial light, and decreased physical activity, have contributed to the worsening of cardiovascular and metabolic diseases. Modern lifestyles are associated with poor glycemic control, which, in turn, is associated with negative outcomes such as diabetes. Furthermore, one of the commonalities of these lifestyles is the disruption of circadian rhythms, which affect body temperature, sleep, and various hormonal changes. Disrupted circadian rhythms can lead to metabolic diseases, and there is growing evidence that different time-based interventions are associated with distinct metabolic effects and health-related outcomes. Therefore, this review aimed to examine the effects of exercise timing on glycemia in adults using subgroup analyses based on the participants' health status and type of exercise training. We performed a systematic literature search of Medline/CINAHL and PubMed (core collection) between inception and December 15, 2022. Of the 118 potentially eligible studies, six were analyzed (one paper was split into two for comparative analysis according to the participants' health status). A random-effects model was used and a meta-analysis was performed on the standardized mean difference (SMD) calculated using a hedged g between the morning and afternoon exercise groups. Meta-effects are presented as forest plots with 95% confidence intervals (CIs). The meta-analysis showed that blood glucose decreased after both morning and afternoon exercise, but there was no significant difference in blood glucose reduction between morning and afternoon exercise (SMD, -0.13; 95% CI, -0.57 to -0.30; p = 0.55). Subgroup analyses showed that there was no significant difference when subjects were divided into groups with and without diabetes (SMD, -0.05; 95% CI, -0.36 to 0.27; p = 0.06), and there was no significant difference when subjects were divided into aerobic and combined exercise groups according to the type of exercise training (SMD, -0.13; 95% CI, -0.57 to -0.30; p = 0.55). In conclusion, this review found no significant difference between the effects of morning and afternoon exercise on glycemia in adults; however, the higher-intensity exercise groups had higher effect sizes than the other groups.

Development of ultrasensitive MERS-VLP biosensor composed of multi-functional DNA/Hybrid nanoparticle based on surface-enhanced raman spectroscopy

Kim, Gahyeon Kwangwoon University Graduate School 2020 국내석사

The Middle East Respiratory Syndrome (MERS) virus is one of the most harmful pathogens in humans because it can’t determine the exact route of infection and has a mortality rate of about 35 %. So far, there is no vaccine or specific treatment for MERS infection. To prevent spread of MERS virus, the rapid detection method is highly needed. Therefore, in this study, the surface-enhanced Raman spectroscopy (SERS)-based biosensor composed of aptamer-tagged DNA 3-way junction (DNA 3WJ) and graphene oxide encapsulated MoS2 hybrid nanoparticle (GO@MoS2) was fabricated to detect the MERS virus like particle (MERS-VLP). The MERS aptamer that specifically binds to the spike protein on the MERS-VLP was produced by the SELEX (Systematic evolution of ligands by exponential enrichment) technique, and then, connected to the multifunctional DNA 3WJ. Subsequently, GO@MoS2 was synthesized for SERS-based MERS-VLP biosensor construction. Due to the optical and absorption specificity, graphene and MoS2 were synthesized to produce GO@MoS2 which provides chemical enhancement (CM) in SERS, followed by DNA 3WJ. The proposed biosensor can detect MERS-VLP not only in PBS buffer solution (LOD:1pM) but also in diluted saliva (LOD:1pM). This study can be applied to future MERS virus detection technique in the near future.

Preparation of long lifetime g-C3N4 by using phosphorescence material

Hong, Keonyoung Kwangwoon University Graduate School 2020 국내석사

Existing photocatalysts have a problem in that decrease photocatalytic efficiency when illuminated light source are over the UV region or none. to offset disadvantage, g-C3N4, which have responsive with visible light are coupled with phosphorescence material which green light emission when light source is disappeared. As prepared sample was found to have a low recombination rate between excited electron and holes as well as higher performance than the standard g-C3N4 through photocurrent measurement. We demonstrate performance of sample via photodegradation experiments through methylene blue (MB), methyl orange (MO) and rhodamine B (RhB). As results show that phosphorescence material coupled g-C3N4 was better efficiency than g-C3N4, moreover the decomposition of dyes from phosphorescence even after the light source was disappeared.

(A) comparative study on the perception of human translation and machine translation post-editing among Vietnamese translators

Phan, Thi-Huong Kwangwoon University Graduate School 2021 국내석사

Several studies have shown that the process and product of translation varies as a function of translation method. The latest trends indicate that human translation (HT) is unable to deal with such big materials in a short time as machine translation (MT), on the contrary, MT on its own is also not good enough to guarantee the quality of translation products as HT. Previous studies have not only figured out the shortcomings of these two translation methods, but also recognized their strengths. As a result, machine translation post-editing (MTPE) in which has a combination of advantages in HT and MT method turned out. In this paper, we would expect to find out differences in the process and product of HT and MTPE. Ninety-four Vietnamese translators were collected and given a questionnaire as the research methodology. Most of translators perceived that it would be easier to search for ‘vocabulary’ and ‘terminology’ in the process of MTPE than HT since ‘vocabulary’ and ‘terminology’ were searched and presented in advance through data in the process of MTPE. This result indicates that there is a relation between the level of difficulty and the translation method. However, the translators also perceived that the product produced by MTPE was as satisfied as that of HT in terms of the ‘accuracy’, ‘fluency’, the usage of ‘terminology’ and ‘idiom’. This result indicates that there is no relation between the level of satisfaction with the product and the translation method. It was suggested that the translation result produced by MT are supervised again by humans in the process of MTPE for why the product of MTPE can obtain high-quality of HT. Những nghiên cứu gần đây cho thấy con người không thể xử lý một khối tài liệu lớn trong thời gian ngắn như các công cụ dịch thuật có thể làm được. Ngược lại, các công cụ đó không mang lại những bản dịch chất lượng như con người. Những nghiên cứu trước đây cũng chỉ ra những ưu điểm và nhược điểm của hai phương pháp dịch này. Chính vì vậy, sự kết hợp những ưu điểm của hai phương pháp này tạo nên hình thức dịch mới, dịch chỉnh sửa hậu kỳ. Trong bài nghiên cứu này, chúng tôi muốn chỉ ra sự khác nhau trong quy trình và chất lượng sản phẩm của biên dịch thủ công và dịch chỉnh sửa hậu kỳ. Chúng tôi đã thu thập thông tin dựa trên kết quả khảo sát của 94 dịch giả Việt Nam. Hầu hết các dịch giả nhận thấy việc tìm kiếm từ vựng và thuật ngữ trong dịch chỉnh sửa hậu kỳ dễ dàng hơn vì chúng được tìm kiếm và trình bày bởi những dữ liệu trong quá trình dịch chỉnh sửa hậu kỳ.Kết quả là độ khó và phương pháp dịch có mối quan hệ chặt chẽ với nhau. Tuy nhiên, các dịch giả cũng nhận định bản dịch của dịch chỉnh sửa hậu kỳ đáp ứng được độ chính xác, độ trôi chảy, và cách sử dụng thuật ngữ cũng như thành ngữ. Kết quả nghiên cứu cho thấy không có mối liên hệ nào giữa mức độ hài lòng với bản dịch và phương pháp dịch. Điều này cho thấy rằng kết quả bản dịch máy được chỉnh sửa bởi người dịch ở quy trình dịch chỉnh sửa hậu kỳ sẽ đạt chất lượng như bản dịch do người dịch trực tiếp thực hiện.

Scalable Cooperative Relay Scheme for Visible Light Communication Systems

Park, Inhwan Kwangwoon University Graduate School 2012 국내석사

3D vertical structured cation (filamentary) based ReRAM for high-density storage class memory and deep neural network

Kim, Myungjun Kwangwoon University Graduate School 2021 국내석사

To process numerous and complicated data effectively, neuromorphic computing system has been considered as a strong candidate which can overcome challenges from conventional Von-Neumann computing system. On the neuromorphic system, synapse device and the structure that includes synapse device are strongly dependent on their performance (high-density storage class memory and deep neural network) in processing numerous and complicated data. Thus, to achieve excellent performance in processing these data, advanced synapse device and structure containing them is essential. In this thesis, to realize high-density storage class memory (SCM) and deep neural network (DNN), scalable cation-based resistive random access memory (ReRAM) synapse device and 3D vertical structured containing them have been employed. Firstly, the author investigated cation-based (Ag-ion in this thesis) ReRAM by controlling Ag-ion doping concentration into the active layer to realize two-terminal synapse device. As Ag doping concentration increased from 0 w/v% to 20 w/v%, the device exhibited resistive memory switching due to thick and stable Ag filament. The Ag filament which bridges active layer between two electrodes can be formed or ruptured by applying an external electric field. By forming or rupturing the filament, set or reset operation which means storing and erasing information can be explain. Moreover, by controlling the current compliance, gradual conductance state of the device can be obtained and showed the feasibility in usage of synapse device. Secondly, the investigated two-terminal cation-based ReRAM (synapse device) is employed in a 3D vertical structure for high-density SCM and DNN. By consisting several layers of planar bottom electrodes (BE), isolation layer (IL) and vertical electrodes (VE), 3D vertical structure can be successfully realized. The resistive memory switching characteristics were obtained by applying external electric field (forming or rupturing Ag filament). Moreover, by modulating current compliance, gradual conductance state of the device can be achieved. As a result, high-density SCM and DNN can be realized for numerous and complicated data processing with 3D vertical ReRAM structure. However, the IL which plays an essential role in preventing interference from other cells occupies a large volume in 3D vertical ReRAM. As an approach to utilize 3D vertical ReRAM more energy efficiently, the author employed Li-ion based all-solid state battery as an IL. As a result, hybrid 3D vertical structure which can store information and energy in a single volume can be realized for high-density SCM and DNN 방대하고 복잡한 데 이터를 효율적으로 처리하기 위해위해, 뉴로모픽 컴퓨팅 시스템은 기존의 폰폰-노이만 컴퓨팅 시스템을 능가할 수 있는 기술로서 각 광 받고 있다있다. 뉴로모픽 시스템에서는시스템에서는, 시냅스 소자와 이들을 포함하는 구조는 방대하고 복잡한 데이터를 처리할 수 있는 성능에 (고집적 스토리지 클라스 메모리와 딥 뉴럴 네트워크네트워크) 강하게 의존적이다의존적이다. 따라서따라서, 이 러 한 데이터를 처리함에 있어서 훌륭한 성능을 확보하기 위해서는 발전된 시냅스 소자와 이를 응용한 발전된 구조가 필수적이다필수적이다. 본 학위논문에서학위논문에서, 고집적 스토리지 클라스 메모리와 딥 뉴럴 네트워크를 구현하기 위해서위해서, 축소가 가능한 양이 온 기반의 저항 변화 메모리 (ReRAM) 시냅스 소자와 이들을 적용한 3D 수 직 구조를 이용하였다이용하였다. 첫째 첫째, 저자는 2-단자의 시냅스 소자를 구현하기 위해 두 전극 사이에 존 재하는 활성 층에 Ag 이온의 도핑 농도를 조절하여 양이 온 기반의 (본 학 위논문에서는 Ag이온을 사용하였다사용하였다) ReRAM를 연구하였다연구하였다. Ag 이온의 도핑 농도가 0 w/v%에서 20 w/v%로 증가하게 되면되면, 소자 내에 두껍고 안정화된 Ag 필라멘트로 인해 저항 변화 메모리 스위칭 특성을 보였다보였다. 두 전극 사이 에 존재하는 활성 층에서 다리 역할을 하는 Ag 필라멘트는 외부 전기장에 의해 형성이 되고 붕괴된다붕괴된다. 필라멘트를 형성하거나 붕괴 시킴으로써 정보 를 저장하거나 지우는 동작을 설명 할 수 있는 셋 동작 혹은 리셋 동작을 설명할 수 있다있다. 추가적으로추가적으로, 전류 컴플라이언스를 조절하여 소자의 완만한 전도도를 확보할 수 있고있고, 이를 통해 시냅스 소자로서 사용 가능성을 보였 다다. 둘째 둘째, 연구된 2-단자 양이온 기반의 ReRAM (시냅스 소자소자)은 고집적 스토 리지 클라스 메모리와 딥 뉴럴 네트워크를 위해 3D 수직 구조에 적용을 하 였다였다. 3D 수직 구조는 여러 층의 평면 전극 (하부 전극전극), 절연 층 그리고 수 직 전극으로 구성을 하여 성공적으로 구현할 수 있다있다. 외부 전기장 을 인가 하여 (필라멘트를 형성 혹은 붕괴붕괴) 저항 변화 메모리 스위칭 특성을 확보하 였다였다. 더욱 나아가나아가, 전류 컴플라이언스를 조절하여 소자의 완만한 전도도 변 화 특성을 얻을 수 있었다있었다. 그 결과 3D 수직 구조의 ReRAM을 통해 방대하 고 복잡한 데이터를 처리하기 위한 고집적 스토리지 클라스 메모리와 딥 뉴 럴 네트워크를 구현 할 수 있었다있었다. 하지만하지만, 3D 수직 구조의 ReRAM 내에서 절연 층은 셀간 간섭을 방지하는 필수적인 요소이지만 부피를 많이 차지한 다다. 이러한 3D 수직 구조의 ReRAM을 더욱 에너지 효율적으로 사용할 수 있는 방안으로 저자는 리튬리튬-이온 기반의 전 고체 배터리를 절연 층으로 사 용하였다용하였다. 그 결과결과, 단일 부피 내에 정보와 에너지 모두 저장 가능한 혼합형 3D 수직 구조를 구현 할 수 있다있다.

Research of effective transmittance tuning spatial light modulator using ion intercalation

Song, Yubin Kwangwoon University Graduate School 2021 국내석사

As 2-dimension (2D) display technology develops, research on next-generation displays is also being actively conducted. For this, various researches such as quantum dot display, hologram, and free display are being conducted. Among them, the method of implementing a 3-dimension (3D) display beyond the 2D display is drawing attention for application fields such as AR, VR, medicine and education. There are many types of technologies for implementing a 3D display, but among them, the method using a hologram can be said to be efficient. To realize a hologram that is an effective method for implementing three-dimensional display, a novel spatial light modulator (SLM) which can generate the hologram by light interference and diffraction was developed based on transmittance changes. For high resolution hologram, pixel size of the SLM needs to be scaled down to visible light wavelength (380 780 nm). However, conventional liquid crystal or micro-mirror based SLM has a limitation in scaling down; few micrometers sized unit parts are required based on its operation mechanism. For the micro SLM, herein, an ion intercalation based SLM utilizing nano-scale ions as the unit parts was developed. Consequently, basic operations of the SLM (light interference and diffraction) are achieved based on the gradual transmittance changes, which clearly demonstrates the feasibility of ion intercalation based SLM 2차원 디스플레이 기술이 발전하면서 그에 따른 차세대 디스플레이에 대한 연구도 활발히 진행되고 있다있다. 이로는 퀀텀 닷 디스플레이디스플레이, 홀로그램홀로그램, 프리 디스플레이 등 다양한 연구가 진행되고 있고있고, 이 중에서도 2차원 디스플레이를 넘어 3차원 디스 플레이를 구현하는 방식이 AR, VR, 의학 및 교육용 등의 응용 분야를 위하여 주목받고 있다있다. 3차원 디스플레이를 구현하는 기술에도 많은 종류가 있지만 그 중에서도 홀로그램을 사용하는 방식이 효율적이라고 할 수 있다있다. 3차원 디스플레이를 구현하는 효과적인 방법인 홀로그램을 구현하기 위해 투과율 변화를 기반으로 빛의 간섭과 회절로 홀로그램을 생성할 수 있는 새로운 공간 광 변조기 (SLM)를 개발했다개발했다. 기존의 액정 또는 마이크로 미러 기반 SLM은 기본적으로 작동 유닛의 크기가 나노 대역 이상이기 때문에 성능을 개선하는 데에 있어서 한계가 존재한다존재한다. 고해상도 홀로그램의 경우 SLM의 픽셀 크기 가 작으면 작을수록 좋기 때문에때문에, 작동 메커니즘에 따라 수 마이크로 미터 이하의 단위 가 필요 하 다다. 본 연구에서는 마 이크로 SLM의 경우 나노 크기 가 유닛의 단위가 되는 리튬 이온을 기반 으로 한 이온 이동 SLM을 개발했다개발했다. 결과적으로 제안된 공간 광 변조기 의 기본 작동은 점진적인 투과율 변화를 기반으로 이루어지 며며, 이는 이온 삽입 기반 SLM의 실현 가능성을 명확하게 보여 준다준다. 이러한 이온 삽입 기반의 SLM은 다양한 어플리케이션에 적용 될 수 있으며있으며, 본 논문에서는 제안 된 소자의 추후 Optical Neural Network로써의 응용에 대해서 설명하려고 한다한다.

Development of RF MEMS tunable capacitors and switches for advanced reconfigurable RF systems

Cho, Hyunok Kwangwoon University Graduate School 2021 국내박사

최근 모바일 기기의 급속한 발전과 이동 통신 기술 세대의 변화에 따른 주파수 대역 추가로 인하여 RF 프론트-엔드 모듈의 크기와 복잡성이 증가하였다. 또한, 모바일 기기에 내장된 센서와 카메라의 수가 급속도로 증가함에 따라 성능을 유지함과 동시에 프론트-엔드 모듈의 크기를 줄이는 것이 매우 중요해졌다. 지난 10 년동안 다중대역 통신 표준의 개발로 인해 대역 선택을 위한 스위칭 및 튜닝 기술 또한 필요하다. 버랙터, 스위치드 커패시터 및 RF MEMS 가변 소자와 같은 스위칭 및 가변소자를 사용하여 주파수 대역을 선택할 수 있다면 다중 대역으로 동작이 필요한 재구성 가능한 프론트-엔드 모듈의 크기 감소에 상당한 영향을 미칠 수 있다. RF MEMS 가변 소자는 낮은 손실, 높은 Q factor, 높은 격리도, 저전력 소비, 사이즈 감소 등에서 반도체 스위치나 튜닝 소자에 비해 성능이 우월하기 때문에 RF MEMS 소자를 무선 통신 시스템에 사용하는 연구가 지속적으로 수행되어 왔으며, 주파수 대역 선택을 위한 스위칭 기술 혹은 주파수 튜닝 기술의 중요도가 높아짐에 따라 MEMS 가변 소자의 유용성도 점점 더 기대되고 있다. RF MEMS 가변 소자 및 스위칭 소자는 프론트-엔드의 주파수 튜닝, 송/수신 회로의 스위칭, 가변 필터 등에 사용되기 위하여 계속해서 개발되어 왔지만 대부분 RFIC 의 외부에서 와이어본딩을 통해 연결하기 때문에 크기 감소에 대한 효과가 현저히 떨어졌다. RF MEMS 스위칭 소자 기술의 경우도 마찬가지로, 스위치의 크기 감소가 절실하며, 동작전압을 낮추는 연구들이 필요하다. 본 연구에서는 차세대 재구성 가능한 RF 시스템을 위한 RF MEMS 가변 커패시터 및 스위치를 개발하고, 측정 및 평가하였다. 제안된 RF MEMS 가변 커패시터 상부 전극(멤브레인)과 하부 전극(신호선) 사이에 인가된 전압에 의해 구동되며, CMOS 공정과 호환 가능한 저온 MEMS 공정을 통해 제작되었다. 제작된 RF MEMS 가변 커패시터를 개별 소자로써 먼저 측정하여 커패시턴스 변화를 통한 주파수 선택 가능성을 타진하였다. 실제로 RFIC 의 주파수 선택에 응용하기 위하여 제작된 가변 커패시터와 CMOS 전력 증폭기와 외부 와이어본딩을 통해 연결하였고, RF MEMS 가변 커패시터의 동작 여부에 따라 전력 증폭기의 동작 주파수가 선택되는지 확인하였다. 최종적으로 CMOS 전력증폭기가 제작된 8 인치 웨이퍼 기판 위에 RF MEMS 를 post 공정하여 RF MEMS 가변 커패시터와 CMOS 전력증폭기가 완전히 집적된 재구성 가능한 전력 증폭기를 제작하였고, RF MEMS 가변 커패시터의 동작 여부에 따른 전력 증폭기의 동작 주파수 변화를 확인하였다. 본 연구에서 제안한 RF MEMS 스위치는 소형화 및 저전압 구동을 위하여 수치적 계산, 전기기계 시뮬레이션 및 전자기 시뮬레이션을 통하여 설계되었다. 설계를 바탕으로, CMOS 호환 가능한 저온공정으로 제작된 RF MEMS 스위치는 총 세가지 타입으로 제작되었다. 각각의 다른 접점 방식 및 구조를 통하여 차세대 RF FEM 사용 가능할 정도의 성능을 발현하는지 확인하였다. 본 연구에서 개발된 RF MEMS 가변 커패시터 및 스위치를 통하여 다중 대역 및 모드로 동작하는 모바일기기 프론트 엔드 모듈의 크기 및 복잡성을 현저하게 줄일 수 있을 것으로 기대되며, 더 나아가 모바일 기기가 더 많은 주파수 대역을 지원할 수 있도록 하는 핵심 기술로 사용될 수 있을 것으로 기대한다. Recently, the size and complexity of the RF (Radio Frequency) front-end modules have increased due to the development of advanced mobile communication devices and the addition of frequency bands caused by the change of mobile communication technology generations. In addition, as the number of sensors and cameras embedded in mobile communication devices rapidly increases, it becomes more important to reduce the size of the RF frontend modules while maintaining performance. Due to the development of multiband communication standards over the past decade, switching and tuning technologies for band selection are also being required. The ability to select a frequency band using the switching and tunable elements such as varactors, switched capacitors and RF MEMS (Micro-Electro-Mechanical Systems) tunable elements can have a significant impact on the miniaturization of reconfigurable RF front-end modules with a multi-band operation. Since the RF MEMS tunable devices have superior performance compared to semiconductor switches or tuning devices in terms of low loss, high Q factor, high isolation, low power consumption, and size reduction, much research on the use of RF MEMS devices in wireless communication systems has been continuously performed. As the importance of switching technology or frequency tuning technology for frequency band selection increases, the use of MEMS switching and tunable devices becomes more important. The RF MEMS tunable elements and switching elements have been continuously developed for the use of frequency tuning in the RF front-end modules, switching of transmitting/receiving circuits, tunable filters, RF matching networks, etc. However, since most of them are interconnected through wire bonding from the outside of the RFIC chip, so the effect of size reduction of devices and modules is insignificant. Similarly, in the case of RF MEMS switching device technology, research is needed to reduce the size of the switch and lower the operating voltage. In this thesis, RF MEMS switched (tunable) capacitors and switches for advanced reconfigurable RF systems were developed, measured, and evaluated. The proposed RF MEMS switched capacitors and switches have been fabricated by using a CMOS-compatible low-temperature process. First, RF MEMS switched capacitor was designed, fabricated, and evaluated. The RF MEMS switched capacitors were fabricated on the high-resistivity silicon (HRS) wafer to reduce the loss from the substrate. The fabricated RF MEMS switched capacitor is operated by a voltage applied between the top electrode (membrane) and the bottom electrode (signal line). By measuring the fabricated RF MEMS switched capacitor as an individual device, the possibility of frequency selection through capacitance change was investigated. Next, the RF MEMS switched capacitor was assembled with the CMOS PA for frequency selection through an external wire bonding technique and the operating frequency of assembled reconfigurable PA was selected by the operation of the RF MEMS switched capacitor. The RF MEMS switched capacitor was post-fabricated on an 8-inch wafer which the CMOS PA was already fabricated to make a fully integrated reconfigurable PA. The capacitor was fabricated by using a photoresist sacrificial layer and electroplating technique. The fully integrated reconfigurable PA was then measured and evaluated. Second, high-performance RF MEMS switches with the low-voltage operation have been designed through numerical calculation, electromechanical simulation, and electromagnetic (EM) simulation for miniaturization and lowvoltage operation. Three different switches were designed by varying the contact and spring beams for lowering the operation voltage and improving the performance. These RF MEMS switches were fabricated and characterized by using CMOS compatible low-temperature processes. It is expected that the size and complexity of the RF front-end modules operating in multiple-bands and -modes can be significantly reduced and simplified through the RF MEMS tunable capacitors and switches developed in this thesis. Furthermore, it is expected that it can be used as a key technology to enable mobile communication devices to support more frequency bands.

Beamforming-based cognitive radio for RF energy harvesting

Jung, Kuk Hyun Kwangwoon University Graduate School 2015 국내석사

본 연구에서 우리는 효율적 RF 에너지 하비스팅 기술 개발을 위해 주파수를 효율적으로 공유하여 사용할 수 있는 무선 인지 통신 시스템(CR: cognitive radio) 기술을 연구한다. 최근 음성 및 데이터 서비스 등과 같은 무선 서비스의 제공을 위해 많은 양의 네트워크 용량이 필요하게 되었다. 그래서 인지 무선 통신기술은 기존의 제한된 주파수 자원을 원활하게 사용이 가능하게끔 만들어 주는 기술이다. 우리는 높은 주파수 활용을 제공하는 cognitive radio 시스템을 ad-hoc 네트워크에 적용한다. 그러면 ad-hoc 기반 cognitive radio 시스템은 기존 CR 보다 다양하고 확장된 네트워크 서비스를 제공한다. 하지만 ad-hoc 네트워크를 기반으로 하는 인지무선시스템에서, 각 단말들의 움직임에 따른 도플러 효과, 건물 등으로 인한 쉐도잉 및 페이딩 현상에 의해 1차 사용자의 신호 검출 성능저하라는 단점이 있다. 이러한 점을 보완하고 ad-hoc 네트워크 기반 cognitive radio 시스템에서 신호들의 detection probability를 향상시키기 위하여 우리는 2차 사용자의 ad-hoc 단말들에게 높은 1차 사용자의 전송 파워를 전송해줄 수 있는 beamforming 기법을 이용하였다. 실험 결과는 신호검출 성능을 보여주며, 본 논문의 실험결과는 ah-hoc 네트워크기반 인지무선시스템에 적용 가능하다. We study a cognitive radio technology that makes it possible to share and use a frequency to efficiently harvest RF energy. Modern networks require extensive capacity to provision wireless services, such as voice and data. As a result, cognitive radio has been developed as a technology to facilitate limited conventional frequency resources. We have implemented a cognitive radio system that provides a high frequency utilization for an ad-hoc network. Then, the cognitive radio system based on an ad-hoc configuration therefore provides more diverse, expanded network services than an existing CR. However, signal detection for a primary user has a disadvantage in that the performance is negatively impacted as a result of fading, the shadow phenomenon and the Doppler Effect in a cognitive radio system based on an ad-hoc network. To address these issues and to improve the detection probability of a signal from a cognitive radio system based on ad-hoc network, we apply beamforming techniques that can produce a high transmission power for the primary user to the ad-hoc terminals of a secondary user. The results of the experiment report the performance for the signal detection, and these results are useful for implementing a cognitive radio system based on an ad-hoc network.