Electromagnetic Energy Transduction Using Metamaterials and Antennas

The advent of rectenna systems almost half a century ago has enabled numerous applications in a number of areas, with the main goal of recycling the ambient microwave energy. In previously presented rectennas, microstrip antennas were the main energy source used to capture and convert microwaves to AC power. However, the conversion efficiency of antennas have never been examined in terms of their capability of absorbing microwave energy, and hence any enhancements to the overall efficiency of rectenna systems were mainly attributed to the rectification circuitry instead of the antenna. In the first part of this dissertation, a novel electromagnetic energy collector is presented, consisting of an array of Split Ring Resonators (SRRs), used for the first time as the main electromagnetic source of energy in a rectenna system. The SRR array is compared to an array of patch antennas to determine the radiation to AC efficiency when both arrays are placed on the same footprint. Numerical simulations and experimental tests show that the SRRs achieve higher efficiency and wider bandwidth than microstrip antennas. The idea of electromagnetic energy harvesting using metamaterials is further explored by designing a metamaterial slab based on the full absorption concept. The metasurface material parameters are tuned to achieve a surface that is matched to the free space impedance at a certain band of frequencies to minimize any reflections and ensure full absorption within the metasurface. The absorbed energy is then channeled to a resistive load placed within each element of the metasurface. Different from previous metasurface absorber designs, here the power absorbed is mostly dissipated across the load resistance instead of the substrate material. A case study is considered where the metamaterial slab is designed to operate at 3 GHz. The simulation and experimental results show radiation to AC efficiencies of 97% and 93%, respectively. A novel method is proposed in the second part of the thesis that significantly increases the conversion efficiency of electromagnetic energy harvesting systems. The method is based on utilizing the available vertical volume above a 2-D flat panel by vertically stacking panels while maintaining the same 2-D footprint. The concept is applied to SRRs and folded dipole antennas. In both cases, four vertically stacked arrays are compared to a single array panel, both occupying the same flat 2-D footprint in terms of power efficiency. The numerical and experimental results for both the SRRs and the antennas show that the stacking concept can increase the conversion efficiency by up to five times when compared to a single 2-D flat panel. The third part presents the design of a near unity electromagnetic energy harvester that uses a Tightly Coupled Antenna array. Compared to the unit cell of metamaterial surfaces, the dimension of a TCA unit cell is about five times larger, thus providing simplified channeling networks and cost-effective solutions. The TCA surface contains an array of Vivaldi shape unit cells with a diode at each cell to convert the harvested electromagnetic energy to dc power. The dc power from each unit cell is channeled to one single load via series inductors. A sample 4 X 4 TCA array, when simulated, fabricated and tested shows solid agreement between the simulated and measured results. The thesis then discusses the idea and design of a dually polarized metasurface for electromagnetic energy harvesting. A 4 X 4 super cell with alternating vias between adjacent cells is designed to allow for capturing the energy from various incident angles at an operating frequency of 2.4 GHz. The collected energy is then channeled to a feeding network that collects the AC power and feeds it to rectification circuitry. The simulation results yield a radiation to AC, and AC to DC conversion efficiencies of around 90% and 80%, respectively. As a proof of concept, an array consisting of nine super cells is fabricated and measured. The experimental results show that the proposed energy harvester is capable of capturing up to 70% of the energy from a plane wave with various incident angles and then converting it to usable DC power. As future work, the last part introduces the concept of metasurface energy harvesting in the infrared regime. The metasurface unit cells consist of an H-shaped resonator with the load placed across the gap of the resonator. Different from infrared meta-material absorber designs, the resonator is capable of not only full absorption but also maximum energy channeling across the load resistance. The numerical simulation demonstrates that 96% of the absorbed energy is dissipated across the load resistance. In addition, a cross-polarized H-resonator design is presented that is capable of harvesting infrared energy using dual polarization within three frequency bands

Antennas and Metamaterials for Electromagnetic Energy Harvesting

The emergence of microwave energy harvesting systems, commonly referred to as rectenna or Wireless Power Transfer (WPT) systems, has enabled numerous applications in many areas since their primary goal is to recycle the ambient microwave energy. In such systems, microstrip antennas are used as the main source for collecting the electromagnetic energy. In this work, a novel collector based on metamaterial particles, in what is known as a Split Ring Resonator (SRR), to harvest electromagnetic energy is presented. Such collectors are much smaller in size and more efficient than existing collectors (antennas). A feasibility study of SRRs to harvest electromagnetic energy is conducted using a full wave simulator (HFSS). To prove the concept, a 5.8 GHz SRR is designed and fabricated and then tested using a power source, an Infiniium oscilloscope and a commercially available patch antenna array. When excited by a plane wave with an H-field normal to the structure, a voltage build up of 611 mV is measured across a surface mount resistive load inserted in the gap of a single loop SRR. In addition, a new efficiency concept is introduced, taking into account the microwave-to-AC conversion efficiency which is missing from earlier work. Finally, a 9X9 SRR array is compared with a 2X2 patch antenna array, both placed in a fixed footprint. The simulation results show that the array of SRRs can harvest electromagnetic energy more efficiently and over a wider bandwidth range

Near-field Sensors with Machine Learning for Breast Tumor Detection

In this work, we propose the use of an electrically small novel antenna as a probe combined with a classification algorithm for nearfield microwave breast tumor detection. The resonant probe ishighly sensitive to the changes in the electromagnetic properties of the breast tissues such that the presence of the tumor is estimatedby determining the changes in the magnitude and phase responseof the reflection coefficient of the sensor. The Principle Component placed at the middle of the probe as shown in Fig. 1. The mainAnalysis (PCA) feature extraction method is applied to emphasize the difference in the probe responses for both the healthy and thetumourous cases . We show that when a numerical realistic breast with and without tumor cells is placed in the near field of the probe, the probe is capable of distinguishing between healthy and tumorous tissue. In addition, the probe is able to identify tumors with various sizes placed in single locations

Corporate governance and firm performance in the Saudi banking industry

The current research aims to explore the impact of corporate governance on the Saudi banking performance for the period of 2014–2017. Though many researchers tested the relationship of corporate governance and firm performance, globally as well as in Saudi Arabia, however, during the literature review, it was found that many excluded the banking industry. This study tries to fill the gap by looking exclusively at the Saudi banking industry. Firm performance is measured through return on assets, return on equity, and Tobin’s Q as the dependent variables. The corporate governance practices are measured through the board characteristics (size, meeting, number of committees, independence, foreign board membership), and an audit committee (size, meeting, independence) as the independent variables. Firm size and firm age are the controls. Panel data analysis was implemented, using both descriptive and multivariate analysis through multiple regression to investigate the governance practices and firm performance. The empirical findings demonstrate that board size, audit committee meeting and bank size have a positive impact on ROE, whereas board independence has a negative impact on ROE. Similarly, board size and bank size have a positive relationship with ROA and board meeting has a negative relationship with ROA. Further, board (size and independence) and bank size have a positive relationship with Tobin’s Q, whereas number of board committees and bank age have a negative relationship with Tobin’s Q. Finally, audit committee (size and independence) and foreign board membership have no impact on the bank performance

Simpson-type inequalities by means of tempered fractional integrals

The latest iterations of Simpson-type inequalities (STIs) are the topic of this paper. These inequalities were generated via convex functions and tempered fractional integral operators (TFIOs). To get these sorts of inequalities, we employ the well-known Hölder inequality and the inequality of exponent mean. The subsequent STIS are a generalization of several works on this topic that use the fractional integrals of Riemann-Liouville (FIsRL). Moreover, distinctive outcomes can be achieved through unique selections of the parameters

Diseño y simulación de una rectenna para cosechar energía electromagnética a 2.4 GHz

Trabajo de InvestigaciónSe realizó el diseño y la simulación de una antena rectificadora con tecnología microcinta a 2.4 GHz junto con un filtro pasa-banda chebyshev de octavo orden y un rectificador de onda completa tipo puente de diodos con el fin de obtener la conversión de ondas electromagneticas a una señal DC.INTRODUCCIÓN 1. GENERALIDADES 2. RECTENNAS Y HERRMANIENTAS DE SIMULACIÓN 3. DISEÑO DE UNA ANTENA RECTIFICADORA A 2.4 GHz 4. DISEÑO Y SIMULACIÓN DE LA ANTENA RECTIFICADORA 5. CONCLUSIONES 6. RECOMENDACIONES Y TRABAJOS FUTUROS 7. ESTRATEGIAS DE COMUNICACIÓNPregradoIngeniero Electrónic

The Fourth-Linear aff(1)-Invariant Differential Operators and the First Cohomology of the Lie Algebra of Vector Fields on RP1

In this paper, we denote the Lie algebra of smooth vector fields on RP1 by V(RP1). This paper focuses on two parts. In the beginning, we determine the cohomology space of aff(1) with coefficients in Dτ,λ,μ;ν. Afterward, we classify aff(1)-invariant fourth-linear differential operators from V(RP1) to Dτ,λ,μ;ν vanishing on aff(1). This result enables us to compute the aff(1)-relative cohomology of V(RP1) with coefficients in Dτ,λ,μ;ν

Dipole Array Sensor for Microwave Breast Cancer Detection

In this paper, a novel design of a near-field dipole antenna sensor array for breast tumor detection is presented. The proposed sensor consists of four electrically small dipole antennas fed by a single port. Due to the proven fact that breast tumors have higher dielectric properties than the surrounding normal tissues, the proposed sensor is utilized for detecting breast tumors by evaluating the variations of the sensor’s response of two cases, normal and abnormal, of the breast tissues. A simulation study is performed using both normal and abnormal numerical breast phantoms with different sizes of tumors inserted at different locations. Simulation results show the proposed sensor detected the inserted tumors at various locations inside the normal breast phantom due to an increased area of sensitivity of the sensor by using multiple sensors array. An experimental study is conducted on breast chicken meat that mimics a healthy breast and two cases of tumors including tumors made of oil and gelatin mixture and conductive spheres with different sizes inserted at different locations inside the chicken meat. Experimental results show that the proposed sensor has higher sensitivity for detecting different sizes of breast tumors placed at multiple locations