1,078 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
Autonomous Sensing Nodes for IoT Applications
The present doctoral thesis fits into the energy harvesting framework, presenting the development of low-power nodes compliant with the energy autonomy requirement, and sharing common technologies and architectures, but based on different energy sources and sensing mechanisms. The adopted approach is aimed at evaluating multiple aspects of the system in its entirety (i.e., the energy harvesting mechanism, the choice of the harvester, the study of the sensing process, the selection of the electronic devices for processing, acquisition and measurement, the electronic design, the microcontroller unit (MCU) programming techniques), accounting for very challenging constraints as the low amounts of harvested power (i.e., [μW, mW] range), the careful management of the available energy, the coexistence of sensing and radio transmitting features with ultra-low power requirements. Commercial sensors are mainly used to meet the cost-effectiveness and the large-scale reproducibility requirements, however also customized sensors for a specific application (soil moisture measurement), together with appropriate characterization and reading circuits, are also presented.
Two different strategies have been pursued which led to the development of two types of sensor nodes, which are referred to as 'sensor tags' and 'self-sufficient sensor nodes'. The first term refers to completely passive sensor nodes without an on-board battery as storage element and which operate only in the presence of the energy source, provisioning energy from it. In this thesis, an RFID (Radio Frequency Identification) sensor tag for soil moisture monitoring powered by the impinging electromagnetic field is presented. The second term identifies sensor nodes equipped with a battery rechargeable through energy scavenging and working as a secondary reserve in case of absence of the primary energy source. In this thesis, quasi-real-time multi-purpose monitoring LoRaWAN nodes harvesting energy from thermoelectricity, diffused solar light, indoor white light, and artificial colored light are presented
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 −100 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 −80 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 author’s 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 0.34mm² 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
The quantification of Pinus patula recovery and productivity of manually orientated biomass collection in post mechanised full tree and semi mechanised tree length harvesting operations
The use of biomass as an alternate source of energy has grown in popularity. Different types of biomass are obtained from a variety of sources including natural forests, forestry plantations and agriculture residues. However, forestry residues have been identified as the most promising source, due to the wide variety of plant products including leaves, twigs, branches, merchantable stem, stumps and roots. The main sources of plantation forest biomass are residues from thinning, clearfell and conventional products such as pulpwood and sawn timber operations. These residues can accumulate between 4.3 to 9.4 billion tonnes annually around the world. The biomass availability in plantation forests has led to the development of different harvesting systems to help collect the products from infield to sawmill. Biomass harvesting has mainly been achieved through mechanised systems because of their high yields. However, the use of manual systems has been neglected due to technical limitations and financial viability. Thus, in South Africa, there is no scientific research looking at manual systems of collecting biomass from plantations. Because of this, different forestry stakeholders, including small growers and contractors using manual systems for biomass harvesting have limited knowledge regarding what to expect in terms of recoverable amounts, productivity and cost. This research examines the productivity of the manual biomass collection and the quantification of recovered and unrecovered residues after mechanised full tree (FT) and semi mechanised tree length (TL) harvesting operations in Pinus patula compartments. A total number of 8 plots with +/-200 standing trees were marked in each system. The diameter and height of all marked trees were measured to determine tree volume. Moreover, the quantification of recoverable woody biomass was determined, where after, a residues assessment method using plots and line transects was used to determine the amount of unrecovered residues.Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 202
The Europa Clipper Gravity and Radio Science Investigation
The primary objective of the Europa Clipper mission is to assess the habitability of Europa, an overarching goal that rests on improving our understanding of Europa’s interior structure, composition, and geologic activity. Here we describe the Gravity and Radio Science (G/RS) investigation. The primary measurement, the gravitational tidal Love number k2 , will be an independent diagnostic of the presence of a global subsurface ocean, but G/RS will make a number of other key measurements related to Europa’s deep interior, silicate mantle-ocean interface, ice shell, ionosphere, and plasma environment. Although radio science is common to many missions, Europa Clipper’s orbit and spacecraft configuration during flybys present special challenges for the design of this experiment. The information obtained through G/RS will be complementary to the measurements by the other instruments onboard Europa Clipper, and their combined analysis will refine the geophysical understanding of Europa necessary to best assess its potential habitability
Intersatellite clock synchronization and absolute ranging for gravitational wave detection in space
The Laser Interferometer Space Antenna (LISA) is a European Space Agency (ESA) large-scale space mission, aiming to detect gravitational waves (GWs) in the observation band of 0.1mHz to 1Hz. The constellation is formed by three spacecrafts (SCs), exchanging laser beams with each other. The detector adopts heterodyne interferometry with MHz frequency offsets. GW signals are then encoded in optical beatnote phases, and the phase information has to be extracted by a core device called phasemeter (PM). Unequal and time- varying orbital motions introduce an overwhelming laser noise coupling that impedes the LISA performance levels of 10 ucycle/sqrt(Hz). Thereby, the post-processing technique called time-delay interferometry (TDI) time-shifts phase signals to synthesize virtual equal-arm interferometers. TDI requires absolute-ranging information, as its input, to the accuracy of 1 m rms, which will be provided by monitors like pseudo-random noise ranging (PRNR) and time-delay interferometry ranging (TDIR). An additional challenge is independent clocks on each SC that time-stamp PM data. This, alongside TDI, requires the synchronization of the onboard clocks in post-processing.
This thesis reports on the experimental demonstrations of such key components for LISA. This is done by extending the scope of the hexagonal optical testbed at the Albert Einstein Institute (AEI): the "Hexagon". The first part of the thesis focuses on clock synchronization, utilizing the TDIR-like algorithm. With representative technologies both in devices and data analysis, this shows a new benchmark performance of LISA clock synchronization, achieving a 1 ucycle/sqrt(Hz) mark above 60 mHz and a TDIR accuracy of 1.84 m in range. This part also includes the first-ever verification of three noise couplings stemming from TDI and clock synchronization in an optical experiment.
The second part of the thesis evolves the Hexagon further with PRNR. It commences with a review of the latest development using a transmission/reception loopback on a single hardware platform. This is followed by the research on the impact of the pseudo-random noise (PRN) modulation on phase tracking. This reveals that the codes, used at best knowledge so far, hinder the carrier phase extraction from achieving the 1 ucycle/sqrt(Hz) mark with realistic data encoded for intersatellite data communication. Some adaptations of PRN codes are proposed, and it is shown that these offer enough suppression of the noise coupling into phase tracking. After phase tracking is confirmed to be compatible with PRN modulations, PRNR itself is inves- tigated. The key novelty of this thesis in terms of PRNR is the study of its absolute-ranging feature, while previous research on this technology focused on stochastic noise properties. This requires the resolution of PRNR ambiguity and the correction of ranging biases. There suggests that the PRNR estimate, alongside some calibrations, can constantly function as absolute ranging with sub-meter accuracy
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
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