130 research outputs found
Beam scanning by liquid-crystal biasing in a modified SIW structure
A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium
Design and analysis of metamaterial based microstrip patch antennas for wireless applications.
Doctoral Degree. University of KwaZulu-Natal, Durban.Due to the tremendous growth of wireless communication applications, there is an enormous demand for more compact antennas with high speed, wider coverage, high gain, and multi-band properties. The microstrip patch antennas (MPAs) and multiple-input multiple-output (MIMO) antennas with high gain and multi-band properties are suitable to fulfil these requirements. MPAs have been found to possess unique qualities such as light weight, low profile, easy fabrication, and integration. However, the low gain, narrow bandwidth, and mutual coupling in the MIMO antennas limit the performance of MIMO systems. Several techniques have been studied and implemented over the years, but they are not without limitations. The utilization of artificial materials such as metamaterials has proven to be efficient in overcoming the limitations of MPAs.
Due to the advancement in modern technology, it is necessary to study and use recently developed metamaterial structures. Metamaterials (MeTMs) are artificially engineered materials with electromagnetic properties that are not found in nature. MeTMs are used due to their electric and magnetic properties. The goal of this thesis is to design and investigate a novel metamaterial structure which can be integrated into the microstrip patch antennas for improving their performance. The design, simulation, and measurement of the metamaterial is carried out on the Computer Simulation Technology (CST) studio suite, Advance Design Systems (ADS) software, MATLAB, and the Rohde and Schwarz network analyzer etc.
In this thesis, a novel I-shaped metamaterial (ISMeTM) structure is proposed, designed, and investigated. The proposed novel ISMeTM unit cell structure in this work has a characteristic shape that distinguishes it from earlier multi-band MeTMs in the literature. The structure's unit cell is designed to have an overall compact size of 10 mm Ă 10 mm. The structure generates transmission coefficients at 6.31 GHz, 7.79 GHz, 9.98 GHz, 10.82 GHz, 11.86 GHz, 13.36 GHz, and 15. 5 GHz. These frequency bands are ideal for multi-band satellite communication systems, C, X, and Ku-bands, and radar applications etc.
The performance of the MPA is improved in this work, by integrating a novel square split ring resonator (SSRR) metamaterial. The performance of the proposed antenna is investigated and analyzed. The SSRR is designed to have a dimension of 25 x 21.4 x 1.6 mm2 which is the same dimension as the radiating patch of the MPA. The SSRR is etched over the antenna, and it operates at single operating frequency of 5.8 GHz with improved gain from 4.04 to 5.3 dBi.
Further, the MPA with improved parameters for multiband wireless systems is designed, analyzed, fabricated, and measured. The proposed design utilizes the ISMeTM array as superstrate with the area of 70 x 70 mm2. The superstrate is etched over a rectangular MPA exhibiting multi-band properties. This antenna resonates at 6.31, 9.65, 11.45 GHz with increased bandwidth at 240 MHz, 850 MHz, and 1010 MHz. The overall gain of the antenna increases by 74.18%. The antenna is fabricated and measured. The simulated results and the measured results are found to be in good agreement.
The mutual coupling and low gain problems in MIMO patch antennas is also addressed in this thesis. A 3 x 5-unit cell array of the ISMeTM is used as a superstrate over a two port MIMO patch antenna. The two port MIMO antenna with the superstrate provides triple-band operation and operates over three resonance frequencies at 6.31, 9.09, and 11.41 GHz. A mutual coupling reduction of 26 dB, 33 dB, and 22 dB for the first band, second band and third band, respectively is attained.
In this thesis, a novel I-shaped metamaterial structure is introduced, which produces multiband operation. The presented metamaterial is suitable for various multiband wireless communication applications. The integration of a square split ring resonator metamaterial enhances the performance of the antenna. Using the I-shaped metamaterial a high gain multiband microstrip antenna is designed. The I-shaped metamaterial array is utilized to improve the performance of the MIMO antenna. Various antenna parameters confirm that the presented MIMO antenna is suitable for multiband wireless communications
Displacement sensing using bi-modal resonance in over-coupled inductors
This paper presents the theory and key experimental findings for an investigation into the generation of bimodal resonance (frequency splitting) phenomena in mutually over-coupled inductive sensors, and its exploitation to evaluate relative separation and angular displacement between coils. This innovative measurement technique explores the bimodal resonant phenomena observed between two coil designs - solenoid and planar coil geometries. The proposed sensors are evaluated against first-order analytical functions and finite element models, before experimentally validating the predicted phenomenon for the different sensor configurations. The simulated and experimental results show excellent agreement and first-order best-fit functions are employed to predict displacement variables experimentally. Co-planar separation and angular displacement are shown to be experimentally predictable to within and using this approach. This study validates the first-order physics-based models employed, and demonstrates the first proof-of-principle for using resonant phenomena in inductive array sensors for evaluating relative displacement between array elements
Displacement sensing using bi-modal resonance in over-coupled inductors
This paper presents the theory and key experimental findings for an
investigation into the generation of bimodal resonance (frequency splitting)
phenomena in mutually over-coupled inductive sensors, and its exploitation to
evaluate relative separation and angular displacement between coils. This
innovative measurement technique explores the bimodal resonant phenomena
observed between two coil designs - solenoid and planar coil geometries. The
proposed sensors are evaluated against first-order analytical functions and
finite element models, before experimentally validating the predicted
phenomenon for the different sensor configurations. The simulated and
experimental results show excellent agreement and first-order best-fit
functions are employed to predict displacement variables experimentally.
Co-planar separation and angular displacement are shown to be experimentally
predictable to within and using this approach. This study
validates the first-order physics-based models employed, and demonstrates the
first proof-of-principle for using resonant phenomena in inductive array
sensors for evaluating relative displacement between array elements
Analysis and Design of Silicon based Integrated Circuits for Radio Frequency Identification and Ranging Systems at 24GHz and 60GHz Frequency Bands
This scientific research work presents the analysis and design of radio frequency (RF) integrated circuits (ICs) designed for two cooperative RF identification (RFID) proof of concept systems. The first system concept is based on localizable and sensor-enabled superregenerative transponders (SRTs) interrogated using a 24GHz linear frequency modulated continuous wave (LFMCW) secondary radar. The second system concept focuses on low power components for a 60GHz continuous wave (CW) integrated single antenna frontend for interrogating close range passive backscatter transponders (PBTs).
In the 24GHz localizable SRT based system, a LFMCW interrogating radar sends a RF chirp signal to interrogate SRTs based on custom superregenerative amplifier (SRA) ICs. The SRTs receive the chirp and transmit it back with phase coherent amplification. The distance to the SRTs are then estimated using the round trip time of flight method. Joint data transfer from the SRT to the interrogator is enabled by a novel SRA quench frequency shift keying (SQ-FSK) based low data rate simplex communication. The SRTs are also designed to be roll invariant using bandwidth enhanced microstrip patch antennas. Theoretical analysis is done to derive expressions as a function of system parameters including the minimum SRA gain required for attaining a defined range and equations for the maximum number of symbols that can be transmitted in data transfer mode. Analysis of the dependency of quench pulse characteristics during data transfer shows that the duty cycle has to be varied while keeping the on-time constant to reduce ranging errors. Also the worsening of ranging precision at longer distances is predicted based on the non-idealities resulting from LFMCWchirp quantization due to SRT characteristics and is corroborated by system level measurements. In order to prove the system concept and study the semiconductor technology dependent factors, variants of 24GHz SRA ICs are designed in a 130nm silicon germanium (SiGe) bipolar complementary metal oxide technology (BiCMOS) and a partially depleted silicon on insulator (SOI) technology. Among the SRA ICs designed, the SiGe-BiCMOS ICs feature a novel quench pulse shaping concept to simultaneously improve the output power and minimum detectable input power. A direct antenna drive SRA IC based on a novel stacked transistor cross-coupled oscillator topology employing this concept exhibit one of the best reported combinations of minimum detected input power level of â100 dBm and output power level of 5.6 dBm, post wirebonding. The SiGe stacked transistor with base feedback capacitance topology employed in this design is analyzed to derive parameters including the SRA loop gain for design optimization. Other theoretical contributions include the analysis of the novel integrated quench pulse shaping circuit and formulas derived for output voltage swing taking bondwire losses into account. Another SiGe design variant is the buffered antenna drive SRA IC having a measured minimum detected input power level better than â80 dBm, and an output power level greater than 3.2 dBm after wirebonding. The two inputs and outputs of this IC also enables the design of roll invariant SRTs. Laboratory based ranging experiments done to test the concepts and theoretical considerations show a maximum measured distance of 77m while transferring data at the rate of 0.5 symbols per second using SQ-FSK. For distances less than 10m, the characterized accuracy is better than 11 cm and the precision is better than 2.4 cm. The combination of the maximum range, precision and accuracy are one of the best reported among similar works in literature to the authorâs knowledge.
In the 60GHz close range CW interrogator based system, the RF frontend transmits a continuous wave signal through the transmit path of a quasi circulator (QC) interfaced to an antenna to interrogate a PBT. The backscatter is received using the same antenna interfaced to the QC. The received signal is then amplified and downconverted for further processing. To prove this concept, two optimized QC ICs and a downconversion mixer IC are designed in a 22nm fully depleted SOI technology. The first QC is the transmission lines based QC which consumes a power of 5.4mW, operates at a frequency range from 56GHz to 64GHz and occupies an area of 0.49mm2. The transmit path loss is 5.7 dB, receive path gain is 2 dB and the tunable transmit path to receive path isolation is between 20 dB and 32 dB. The second QC is based on lumped elements, and operates in a relatively narrow bandwidth from 59.6GHz to 61.5GHz, has a gain of 8.5 dB and provides a tunable isolation better than 20 dB between the transmit and receive paths. This QC design also occupies a small area of 0.34mmÂČ while consuming 13.2mW power. The downconversion is realized using a novel folded switching stage down conversion mixer (FSSDM) topology optimized to achieve one of the best reported combination of maximum voltage conversion gain of 21.5 dB, a factor of 2.5 higher than reported state-of-the-art results, and low power consumption of 5.25mW. The design also employs a unique back-gate tunable intermediate frequency output stage using which a gain tuning range of 5.5 dB is attained. Theoretical analysis of the FSSDM topology is performed and equations for the RF input stage transconductance, bandwidth, voltage conversion gain and gain tuning are derived. A feasibility study for the components of the 60GHz integrated single antenna interrogator frontend is also performed using PBTs to prove the system design concept.:1 Introduction 1
1.1 Motivation and Related Work . . . . . . . . . . . . . . . . . . . . . 1
1.2 Scope and Functional Specifications . . . . . . . . . . . . . . . . . 4
1.3 Objectives and Structure . . . . . . . . . . . . . . . . . . . . . . . . 5
2 Features and Fundamentals of RFIDs and Superregenerative Amplifiers 9
2.1 RFID Transponder Technology . . . . . . . . . . . . . . . . . . . . 9
2.1.1 Chipless RFID Transponders . . . . . . . . . . . . . . . . . 10
2.1.2 Semiconductor based RFID Transponders . . . . . . . . . . 11
2.1.2.1 Passive Transponders . . . . . . . . . . . . . . . . 11
2.1.2.2 Active Transponders . . . . . . . . . . . . . . . . . 13
2.2 RFID Interrogator Architectures . . . . . . . . . . . . . . . . . . . 18
2.2.1 Interferometer based Interrogator . . . . . . . . . . . . . . . 19
2.2.2 Ultra-wideband Interrogator . . . . . . . . . . . . . . . . . . 20
2.2.3 Continuous Wave Interrogators . . . . . . . . . . . . . . . . 21
2.3 Coupling Dependent Range and Operating Frequencies . . . . . . . 25
2.4 RFID Ranging Techniques . . . . . . . . . . . . . . . . . . . . . . . 28
2.4.0.1 Received Signal Strength based Ranging . . . . . 28
2.4.0.2 Phase based Ranging . . . . . . . . . . . . . . . . 30
2.4.0.3 Time based Ranging . . . . . . . . . . . . . . . . . 30
2.5 Architecture Selection for Proof of Concept Systems . . . . . . . . 32
2.6 Superregenerative Amplifier (SRA) . . . . . . . . . . . . . . . . . . 35
2.6.1 Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . 35
2.6.2 Modes of Operation . . . . . . . . . . . . . . . . . . . . . . 42
2.6.3 Frequency Domain Characteristics . . . . . . . . . . . . . . 45
2.7 Semiconductor Technologies for RFIC Design . . . . . . . . . . . . 48
2.7.1 Silicon Germanium BiCMOS . . . . . . . . . . . . . . . . . 48
2.7.2 Silicon-on-Insulator . . . . . . . . . . . . . . . . . . . . . . . 48
3 24GHz Superregenerative Transponder based Identification and Rang-
ing System 51
3.1 System Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
3.1.1 SRT Identification and Ranging . . . . . . . . . . . . . . . . 51
3.1.2 Power Link Analysis . . . . . . . . . . . . . . . . . . . . . . 55
3.1.3 Non-idealities . . . . . . . . . . . . . . . . . . . . . . . . . . 59
3.1.4 SRA Quench Frequency Shift Keying for data transfer . . . 61
3.1.5 Knowledge Gained . . . . . . . . . . . . . . . . . . . . . . . 63
3.2 RFIC Designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
3.2.1 Low Power Direct Antenna Drive CMOS SRA IC . . . . . . 66
3.2.1.1 Circuit analysis and design . . . . . . . . . . . . . 66
3.2.1.2 Characterization . . . . . . . . . . . . . . . . . . . 69
3.2.2 Direct Antenna Drive SiGe SRA ICs . . . . . . . . . . . . . 71
3.2.2.1 Stacked Transistor Cross-coupled Quenchable Oscillator
. . . . . . . . . . . . . . . . . . . . . . . . 72
3.2.2.1.1 Resonator . . . . . . . . . . . . . . . . . . 72
3.2.2.1.2 Output Network . . . . . . . . . . . . . . 75
3.2.2.1.3 Stacked Transistor Cross-coupled Pair and
Loop Gain . . . . . . . . . . . . . . . . . 77
3.2.2.2 Quench Waveform Design . . . . . . . . . . . . . . 85
3.2.2.3 Characterization . . . . . . . . . . . . . . . . . . . 89
3.2.3 Antenna Diversity SiGe SRA IC with Integrated Quench
Pulse Shaping . . . . . . . . . . . . . . . . . . . . . . . . . . 91
3.2.3.1 Circuit Analysis and Design . . . . . . . . . . . . 91
3.2.3.1.1 Crosscoupled Pair and Sampling Current 94
3.2.3.1.2 Common Base Input Stage . . . . . . . . 95
3.2.3.1.3 Cascode Output Stage . . . . . . . . . . . 96
3.2.3.1.4 Quench Pulse Shaping Circuit . . . . . . 96
3.2.3.1.5 Power Gain . . . . . . . . . . . . . . . . . 99
3.2.3.2 Characterization . . . . . . . . . . . . . . . . . . . 102
3.2.4 Knowledge Gained . . . . . . . . . . . . . . . . . . . . . . . 103
3.3 Proof of Principle System Implementation . . . . . . . . . . . . . . 106
3.3.1 Superregenerative Transponders . . . . . . . . . . . . . . . 106
3.3.1.1 Bandwidth Enhanced Microstrip Patch Antennas 108
3.3.2 FMCW Radar Interrogator . . . . . . . . . . . . . . . . . . 114
3.3.3 Chirp Z-transform Based Data Analysis . . . . . . . . . . . 116
4 60GHz Single Antenna RFID Interrogator based Identification System 121
4.1 System Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
4.2 RFIC Designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
4.2.1 Quasi-circulator ICs . . . . . . . . . . . . . . . . . . . . . . 125
4.2.1.1 Transmission Lines based Quasi-Circulator IC . . 126
4.2.1.2 Lumped Elements WPD based Quasi-Circulator . 130
4.2.1.3 Characterization . . . . . . . . . . . . . . . . . . . 134
4.2.1.4 Knowledge Gained . . . . . . . . . . . . . . . . . . 135
4.2.2 Folded Switching Stage Downconversion Mixer IC . . . . . 138
4.2.2.1 FSSDM Circuit Design . . . . . . . . . . . . . . . 138
4.2.2.2 Cascode Transconductance Stage . . . . . . . . . . 138
4.2.2.3 Folded Switching Stage with LC DC Feed . . . . . 142
4.2.2.4 LO Balun . . . . . . . . . . . . . . . . . . . . . . . 145
4.2.2.5 Backgate Tunable IF Stage and Offset Correction 146
4.2.2.6 Voltage Conversion Gain . . . . . . . . . . . . . . 147
4.2.2.7 Characterization . . . . . . . . . . . . . . . . . . . 150
4.2.2.8 Knowledge Gained . . . . . . . . . . . . . . . . . . 151
4.3 Proof of Principle System Implementation . . . . . . . . . . . . . . 154
5 Experimental Tests 157
5.1 24GHz System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
5.1.1 Ranging Experiments . . . . . . . . . . . . . . . . . . . . . 157
5.1.2 Roll Invariance Experiments . . . . . . . . . . . . . . . . . . 158
5.1.3 Joint Ranging and Data Transfer Experiments . . . . . . . 158
5.2 60GHz System Detection Experiments . . . . . . . . . . . . . . . . 165
6 Summary and Future Work 167
Appendices 171
A Derivation of Parameters for CB Amplifier with Base Feedback Capac-
itance 173
B Definitions 177
C 24GHz Experiment Setups 179
D 60 GHz Experiment Setups 183
References 185
List of Original Publications 203
List of Abbreviations 207
List of Symbols 213
List of Figures 215
List of Tables 223
Curriculum Vitae 22
Antenna System Design for 5G and Beyond â A Modal Approach
Antennas are one of the key components that empower a new generation of wireless technologies, such as 5G and new radar systems. It has been shown that antenna design strategies based on modal theories represent a powerful systematic approach to design practical antenna systems with high performance. In this thesis, several innovative multi-antenna systems are proposed for wireless applications in different frequency bands: from sub-6 GHz to millimeter-wave (mm-wave) bands. The thesis consists of an overview (Part I) and six scientific papers published in peer-reviewed international journals (Part II). Part I provides the overall framework of the thesis work: It presents the background and motivation for the problems at hand, the fundamental modal theories utilized to address these problems, as well as subject-specific research challenges. Brief conclusions and future outlook are also provided. The included papers of Part II can be divided into two tracks with different 5G and beyond wireless applications, both aiming for higher data rates.In the first track, Papers [I] to [IV] investigate different aspects of antenna system design for smart-phone application. Since Long Term Evolution (LTE) (so-called 3.5G) was deployed in 2009, mobile communication systems have utilized multiple-input multiple-output antenna technology (MIMO) technology to increase the spectral efficiency of the transmission channel and provide higher data rates in existing and new sub-6 GHz bands. However, MIMO requires multi-antennas at both the base stations and the user equipment (mainly smartphones) and it is very challenging to implement sub-6 GHz multi-antennas within the limited space of smartphones. This points to the need for innovative design strategies. The theory of characteristic modes (TCM) is one type of modal theory in the antenna community, which has been shown to be a versatile tool to analyze the inherent resonance properties of an arbitrarily shaped radiating structure. Characteristic modes (CMs) have the useful property of their fields being orthogonal over both the source region and the sphere at infinity. This property makes TCM uniquely suited for electrically compact MIMO antenna design.In the second track, Papers [V]-[VI] investigate new integrated antenna arrays and subarrays for the two wireless applications, which are both implemented in a higher part of the mm-wave frequency range (i.e. E-band). Furthermore, a newly developed high resolution multi-layer âAny-Layerâ PCB technology is investigated to realize antenna-in-package solutions for these mmwave antenna system designs. High gain and high efficiency antennas are essential for high-speed wireless point-to-point communication systems. To meet these requirements, Paper [V] proposes directive multilayer substrate integrated waveguide (SIW) cavity-backed slot antenna array and subarray. As a background, the microwave community has already shown the benefits of modal theory in the design and analysis of closed structures like waveguides and cavities. Higher-order cavity modes are used in the antenna array design process to facilitate lower loss, simpler feeding network, and lower sensitivity to fabrication errors, which are favorable for E-band communication systems. However, waveguide/cavity modes are confined to fields within the guided media and can only help to design special types of antennas that contain those structures. As an example of the versatility of TCM, Paper [VI] shows that apart from smartphone antenna designs proposed in Papers [I]-[IV], TCM can alsobe used to find the desirable modes of the linear antenna arrays. Furthermore, apart from E-band communications, the proposed series-fed patch array topology in Paper [VI] is a good candidate for application in 79 GHz MIMO automotive radar due to its low cost, compact size, ability to suppress surface waves, as well as relatively wide impedance and flat-gain bandwidths
1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface
A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance
High Efficiency Low Power Rectifiers and ZVS DC to DC Converters for RF Energy Harvesting
In recent years, advancements in modern technologies have grown the demand for low-power wireless devices. Considering that enhancing the lifetime of the required battery to maintain the operation of these devices is still impractical, harvesting energy from ambient sources has become a promising solution to power portable low power electronic devices. Harvesting ambient energy from the electromagnetic wave (EM), which is referred to as radio frequency energy harvesting (RFEH), is one of the most popular power extracting methods. Scavenging energy can be used to fully supply the power required for wearable electronics devices, RFID, medical implantable devices, wireless sensors, internet of things (IoT) etc. RF energy is readily available in urban environments due to the abundant existence of HF and UHF technologies. Therefore, there is a great interest in studying systems working in UHF bands, including 300MHz to 3GHz frequencies.
Radio frequency energy harvesting is a method which converts the received signals into electricity. This technique offers various environmentally friendly alternative energy sources. Specifically, RFEH has interesting attributes that make it very practical for low-power electronics and wireless sensor networks (WSNs). Ambient RF energy can be provided by commercial RF broadcasting stations such as Wi-Fi, GSM, radar or TV. In this study, particular attention is given to design efficient low power circuits suitable to be applied for RFEH as a green technology, which is very suitable for overcoming problems such as powering wireless sensors located in inaccessible places or harsh environments, the possibility to power directly electronic devices, recharge batteries and etc. In RFEH, it is very important to enhance the efficiency of the circuits and systems to maximize the amount of harvested energy.
This thesis is mainly concerned with the design, simulation, and implementation of AC to DC circuits including phase shifter, rectifier, and DC to DC converter which is specifically designed for RFEH. It can be applied in various applications such as telecommunications, wireless sensors, medical devices, wireless charging, Internet of Things (IoT) and etc. In the designed system in this thesis, the signal must be passed through a phase shifter, rectifier, and voltage multiplier to reach the required level of output voltage. In another word, this system rectifies the sinusoidal AC waveform to DC and multiplies it to get higher voltages.
In this thesis, we propose 1 and 7-stage rectifiers, phase shifters and isolated/non-isolated DC to DC converters will be investigated individually in a general manner and integrated together to have the desired range of outputs for considered applications. This research methodology has three major phases: Phase 1: Theoretical analyses, Phase 2: Simulation investigations and Phase 3: Practical verification.
This thesis presents a review on the history of different circuits used to design a low power system for EH. Certain achievements in recent decades make power harvesting a reality, capable of providing alternative sources of energy for a wider range of applications. This review provides a summary of RFEH technologies to use as a guide for the design of RFEH units. Additionally, comprehensive analysis and discussions of various designs of rectifiers, isolated and non-isolated DC to DC converters and phase shifters in addition to their trade-offs for RF energy harvesting purposes are included.
In this thesis, novel designs of Dickson rectifiers with high voltage gain and efficiency operating with an input frequency of 915MHz is presented. The proposed circuits introduce a new method of deriving output characteristics of rectification circuit in terms of voltage. The design consists of different stages of the Dickson voltage multiplier. The rectifiers benefit from two input AC sources with 180° phase shift. This Dickson circuit is further discussed in two levels; the first one is a 1-stage rectifier operating with Schottky diodes or diode-connected MOSFETs, and the second is a 7-stage rectifier discussed with both Schottky diodes and diode-connected MOSFETs producing higher output voltages.
Furthermore, the prototype of 1-stage rectifier is presented where the input voltage is between -10dBm and 2dBm and the output voltage gained is from 318mV to 1700mV, respectively. Also, the prototype of 7-stage rectifier is presented where the input voltage is -10dBm, -8dBm and -6dBm and the output voltage is gained 1220mV, 1330mV and 1550mV, respectively.
Additionally, a new non-isolated high voltage gain, high efficiency zero voltage switching (ZVS) resonant DC to DC converter working under ZVS condition is introduced, which can work in high frequencies with high power conversion rate as well as low losses. The proposed converter can provide 5V output from 350mV input voltage with efficiency of 72.8%. Furthermore, we proposed an isolated DC to DC converter which provides the output voltage of 6V with efficiency of 68%. Due to have an isolation transformer, this converter prevents electric shocks which makes it suitable for applications requiring more safety. All the theoretical analyses are verified by MATLAB and circuits are simulated in PSIM.
In addition, two combinations of high voltage gain circuits are introduced for low power applications such as RFEH. The first combination consists of a phase shifter, 1-stage rectifier and resonant ZVS DC to DC converter which has an output voltage of 6V with an efficiency of 71%. The second consists of a phase shifter, 1-stage rectifier and isolated resonant ZVS DC to DC converter with output voltage and efficiency of 5V and 65%, respectively.
In conclusion, this thesis is presented in 6 chapters discussing the designed high voltage gain high efficiency low power circuits to convert AC input with frequency of 915MHz to DC output. The circuits can be applied in different low power applications such as energy harvesting systems specifically RFEH
Liquid cooled micro-scale gradient system for magnetic resonance
Schaltbare magnetische Feldgradientspulen sind ein geeignetes Werkzeug fĂŒr die Modulation der KernspinprĂ€zession in der gepulsten Kernspinresonanzspektroskopie und Bildgebung. Die Magnetresonanztomographie von mikroskopischen Proben benötigt starke, schnell schaltbare Magnetfeldgradienten, um diffusionsbedingte Artefakte zu unterdrĂŒcken, SuszeptibilitĂ€tseffekte abzuschwĂ€chen und um die Messzeit zu verkĂŒrzen. Verschiedene Techniken können eingesetzt werden, um eine hohe GradientenintensitĂ€t zu erreichen, wie zum Beispiel die Erhöhung der StromstĂ€rke oder die Steigerung der Windungsdichte der Feldspule. Ein weiterer, geeigneter technischer Ansatz besteht darin, die Gradientenspulen nĂ€her an der Probe zu platzieren. Als Konsequenz wird aber die durch die Joule-ErwĂ€rmung verursachte WĂ€rmeentwicklung zu einem zentralen Problem.
In dieser Arbeit wird ein neuartiges Design, ein Mikroherstellungsprozess und eine Kernspin-Evaluierung eines Feldgradientenchips prĂ€sentiert. Die Gradientenspulen wurden besonders hoch miniaturisiert und durch den Einsatz von verbesserten und neuartigen Strukturierungsverfahren entwickelt. Zuerst wird ein Fertigungsverfahren zur Herstellung einer kompakten Hochfrequenzspule vorgestellt. Durch den Einsatz einer maskenlosen RĂŒckseitenlithographie konnte die ProzesskomplexitĂ€t reduziert werden. Dieses Verfahren wurde durch Tintenstrahldruck mit Nanopartikeln realisiert, wobei die gedruckten Strukturen selbst als lithographische Maske fĂŒr die Herstellung einer galvanischen Form dienen. Somit werden die SeitenwĂ€nde der galvanischen Form durch die gedruckte Seed-Schicht optimal selbst ausgerichtet. Dies ermöglichte eine anisotrope Galvanisierung, um eine höhere elektrische LeitfĂ€higkeit der gedruckten Leiterbahnen zu erzielen.
Aus den Erkenntnissen der ausgearbeiteten Herstellungsprozesse wurde ein optimiertes Spulendesign fĂŒr ein-axiale sowie drei-axiale linearen Gradientenchips entwickelt. Die einachsige lineare -Gradientenspule wurde mit der Stream-Function-Methode berechnet, wobei die Optimierung darauf abgestimmt wurde, eine minimale Verlustleistung zu erzielen. Die Gradientenspulen wurden auf zwei Doppellagen implementiert, die mittels Cu-Galvanik in Kombination mit fotodefinierbaren Trockenfilm-Laminaten aufgebracht wurden. Bei dem hier vorgestellten Herstellungsverfahren diente die erste Metallisierungschicht gleichzeitig dazu, Widerstands-Temperaturdetektoren zu integrieren. Um niederohmige Spulen zu realisieren wurde der Galvanisierungsprozess soweit angepasst, um eine hohe Schichtdicke zu erzielen. Die Chipstruktur beinhaltet ein aktives KĂŒhlsystem, um dem Aufheizen der Spulen entgegenzuwirken.
Thermographische Aufnahmen in Kombination mit den eingebetteten Temperatursensoren ermöglichen es, die Erhitzung der Spule zu analysieren, um die Strombelastbarkeit zu ermitteln. Die Gradientenspule wurde mit einer Hochfrequenz-Mikrospule in einer Flip-Chip-Konfiguration zusammengebaut, und mit diesem Aufbau wurde ein eindimensionales Kernspinexperiment durchgefĂŒhrt. Es wurde eine Gradienteneffizienz von 3.15 bei einer ProfillĂ€nge von 1.2 erreicht
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