Back Ratio Research Articles

A wideband and low profile dual polarized antenna loaded with artificial magnetic conductor

In this paper, a wideband low profile dual-polarization antenna is proposed based on the in-phase reflection characteristic of artificial magnetic conductor (AMC). The AMC cells are designed as two concentric square metallic rings connected by a ‘*’ shaped metallic strip. Its in-phase reflection bandwidth is 2.12 GHz–3.31 GHz, and input-match bandwidth is 1.56 GHz–2.43 GHz. The relative bandwidth is 43.83% and 43.61%, respectively. In addition, the AMC cells are loaded on the reflector of the proposed dual polarized dipole antenna. The measured results show that the −10 dB reflection coefficient (|S 11|) bandwidth of the antenna is 1.55 GHz to 2.4 GHz (43%), and the height is only 0.136λ 0. Furthermore, the gain and front-to- back ratio of the antenna are increased by about 0.8 and 4 dB respectively due to the action of AMC.

Design and optimization of power conversion system for a steady state CFETR power plant

A promising magnetic fusion steady state reactor is Chinese Fusion Engineering Testing Reactor (CFETR) and a different power conversion system is required than tokamak reactor. The control and utilization of high outlet temperature and thermal power generated by the fusion reactor efficiently are the main challenges in the field of thermo-fusion technology. An efficient and optimized power conversion system is an urge for the thermo-fusion energy system with a candidate working fluid under high temperature and pressure. Five cycle topologies based on the Brayton cycle have been designed such as multi stage expansion and recompression cycle with intercooling, recompression cycle with intercooling, partial expansion with multistage compression, partial expansion and partial recompression with cooling across range of turbine and compressor inlet temperatures. Brayton cycle with different system configurations have been simulated with He-gas and supercritical Carbon Dioxide (CO2) to conceive high outlet temperature of CFETR about 500 °C and thermal power of 200 MWth for better thermal performance by using REFPROP, EES and analytical model has been developed with MATLAB. The supercritical CO2 has better thermal performance about 36.18 % as compared to He-gas has 29.81 % under same thermal conditions. The Schematic-I with addition of preheat and recompression enhance the thermal performance about 2 % and has been proposed for CFETR. The effect of change in pressure of the system, effect of the working fluid, isentropic efficiency, heat rate and back to work ratio on the thermal performance and network output have been analyzed and optimized based on analytical model with the MATLAB. The system net power is increased from 69.20 MW to 79.71 MW, heat rejected by the system is decreased from 134.46 MW to 127.06 MW and thermal performance is increased about 34.62 %–39.85 % with pressure from 24 MPa to 28 MPa. Using multi stage expansion and recompression cycle with intercooling instead of other topologies can improve the thermal performance up to 6.1 % depends upon the operation conditions and working fluid. The heat rate of the system decreased while back work ratio increased with the pressure and it reveal that calculations are correct.

Coordination of the back flashover probability of HVAC and HVDC on a hybrid transmission tower

The demand for power transfer has increased throughout the green transition, especially as power generation is becoming increasingly decentralized. However, constructing new transmission lines and towers has met with public opposition. One option to increase transmission capacity while minimizing the erection of new towers is to use hybrid HVAC-HVDC multi-circuit towers. If not carefully designed, considerably more back flashovers could occur to the more vulnerable DC circuit. This paper investigates the effect of a change in insulator size on the ratio of back flashovers between AC and DC circuits on the same hybrid tower by using a PSCAD model with HVAC-HVDC hybrid towers. A back flashover ratio calculation method is developed and used in combination with an algorithm to provide a DC insulator length based on a predetermined back flashover ratio. The algorithm allows for faster design of the insulator sizes for a multi-circuit tower, coordinating the ratio of back flashover probabilities to either the HVAC or the HVDC circuit.

Effect of back opening ratio and layout design on the performance of laser ablated point contact cell

In this paper we investigate the effect of the opening ratio and the back layout design on the electrical performance of the solar cell. First, the point contact solar cells are optimized by adjusting the laser opening ratio and the virtual-to-real ratio on each grid line of back side. The experimental results show that the open-circuit voltage (Voc) of the solar cell increases as the opening ratio decreases. Analysis of the PL images also shows that the damage to the passivation layer causes the Voc to drop. By characterizing the resistance of the back line, we found that laser drilling can cause an increase in the resistance of the back line. This can also lead to the FF loss. Then, by reducing the contact area of the bus-bar at the backside, the carrier recombination of the solar cell is reduced and the Voc of the cell is increased, resulting in a 0.07% increase in cell efficiency. Finally, the simulation shows that the openings lead to an increase in the recombination current (J01) at the base of the cell, which affects the efficiency of the cell.

A Broadband Suspended Plate Antenna with Dual Polarization for 2G/3G/Wi-Fi/4G/LTE

Design of a broadband, dual-polarized suspended patch antenna covering 2G/3G/Wi-Fi/4G bands (1710-2690 MHz) is presented. The prototype consists of two suspended plates and a feedline layer. Excitation of ±45 slant dual polarization is realized by a novel crossed elliptic-H slot. The prototype exhibits 48.7% impedance bandwidth (|S11|, |S22| < −15 dB) in 1660-2730 MHz. Port isolation (|S21|) is obtained as > 28 dB. In desired operating band, stable and symmetric radiation patterns with half-power beamwidths of 55-75 and 65-74 in E and H planes are measured, respectively. Gain variation lies within 8.3±0.8 dBi. Proposed antenna is low profile, has high port isolation and high front to back ratio without needing any secondary reflector ground plane. With these qualifications and performance specifications, it outperforms many of the similar works in the literature. Design considerations, simulations and measurement results of proposed antenna are presented and discussed.

Dual-band absorption due to simultaneous excitation of TE and TM modes in ITO-ES metamaterial for IR stealth technology

We proposed a plasmonic based Indium Tin Oxide Embedded Silver (ITO-ES) infrared dual-band perfect absorber for the utilization in IR stealth technology. The proposed structure comprised of nano size Ag ring and desk embedded in ITO. The optical losses in optical regime of nanoscale plasmonic Ag were incorporated in terms of collision frequency using the modified Drude model. The optical response of the proposed structure was predicted by exciting it with a planwave using full wave vector frequency domain solver by employing Finite Element Method (FEM) in Computer Simulation Technology (CST) Microwave Studio. The simultaneous excitation of higher order transverse electromagnetic (TE and TM) modes in the proposed structure lead to high values of both absorption and Front to Back ratio (FTBR). The controlled and selective wavelength multiband absorption is crucial for IR stealth technology. The proposed metamaterial structures exhibit dual-bands IR absorption at wavelengths λ = 1.40 μm and 6.4 μm. First absorption peak suppresses the back scattering of the laser used by laser guided devices for detection, while the second peak suppresses the IR signature of the structure due thermal radiation which can be used by tracking devices to detect warm/hot objects.

Theoretical and experimental study on the selection of pure and mixed refrigerants for a power-cooling system driven by ultra-low-grade heat

This study theoretically and experimentally evaluates the performance of a system that combines an organic Rankine cycle (ORC) and a vapor compression cycle (VCC) driven by ultra-low-grade heat (ULGH). A systematic method is developed for the selection of pure refrigerants for the efficient performance of ORC over a temperature range between 50°C to 100°C. Binary and ternary mixtures are developed followed by sensitivity analyses and composition optimization to determine the optimal performance of these mixtures. Several experimental tests are conducted to ensure the operability of the system with the developed refrigerants. The results show that the use of ternary and binary mixtures enhances the performance of the system with lower GWP and ODP compared to pure refrigerants. Several mixtures are developed with energy efficiencies higher than 9% at a heat source temperature of 75°C. A mixture of R142b/R152a/R600 improves the energy efficiency of the system by 22.80%, reduces the back work ratio by 19.40% with an increase in the evaporation capacity by 13.25%. The methodology and results presented herein will be useful in the development, design, and optimization of power and cooling systems driven by ULGH with pure and mixed refrigerants.

Control strategies of pumps in organic Rankine cycle under variable condensing conditions

The working medium pump and cooling water pump are important components in organic Rankine cycle system. However, they have not received as much attention as the expander and working medium. Simultaneously, the dramatic changes in condensing environment deviate the organic Rankine cycle working point from the designed operating conditions. Hence, this paper focused on the performance improvements and control strategies of working medium pump and cooling water pump in small-scale organic Rankine cycle under variable condensing conditions. A model was established to predict the performances of an organic Rankine cycle system with R245fa, especially the pumps in the system, under variable condensing conditions. The results showed that the overall efficiency of multi-stage centrifugal pump was between 14% and 39% at an estimated speed of approximately 1600 RPM to 2328 RPM. In winter conditions, the back work ratio increased from 0.05 to 0.19 with increasing evaporation pressure and decreasing mass flow rate. In other words, it is unnecessary to pursue excessively high evaporation temperature at low rotational speed of multi-stage centrifugal pump. As for the cooling water pump, it is feasible to reduce the power consumption of the cooling system through changing the rotational speed of water pump. The water pump can be operated with high efficiency (between approximately 58.4% and 65.3%, corresponding to an estimated speed range of 1374 RPM to 1813 RPM) when the system run in optimum operating conditions. It is also found that the performance of organic Rankine cycle was strongly influenced by fluctuating ambient temperature, with the net efficiency and net power increase of 3.36 % and 5.11 kW in winter compared to summer.

Effect of Charcoal, Probiotic, and Chlorhexidine Mouthwashes on Mechanical Properties and Surface Characterization of Ceramic-Coated Nickel-Titanium Orthodontic Arch Wires: A Comparative In-Vitro Study.

To determine the impact on the mechanical properties and surface features of ceramic-coated nickel-titanium (CC-Ni-Ti) archwires when subjected to charcoal, probiotic, and chlorhexidine mouthwashes in in vitro conditions. Eighty samples of 25 mm were cut from the posterior end of preformed maxillary 0.016'' CC-Ni-Ti super elastic archwires (Koden Company, USA) anddistributed into four equal groups. Each group of wires was immersed in artificial saliva (Wet Mouth Mouthwash, ICPA Health Products Ltd., India) (control), charcoal mouthwash (Hello activated charcoal extra freshening mouthwash, Hello Products LLC, USA), probiotic mouthwash (Perfora, Probiotic Rinse, India), and 0.2% chlorhexidine gluconate mouthwash (Sensorange, Orange Biotech, Pvt., Ltd., India) (experimental groups) for 90 min at 37 °C. All samples were taken out of their respective solutions and washed with distilled water prior to testing. A three-point bending test was performed on 15 samples from each group using a universal testing device. During the loading and unloading of the archwires, the yield strength (YS), flexural modulus of elasticity (E), and spring back ratio (YS/E) were calculated. The remaining five wires from each group were observed under the scanning electron microscope (SEM) for surface topography evaluation. The mean differences of loading YS, E, and YS/E between chlorhexidine and charcoal are 302.91 MPa, 4.28 GPa, and 0.0004, whereas unloading values are 172.32 MPa, 4.16 GPa, and 0.0003, respectively, with a statistical significance of <0.001 in terms of YS and E. The mean differences of loading YS, E, and YS/E between charcoal and probiotic are 305.36 MPa, 4.54 GPa, and 0.0005, whereas unloading values are 173.77 MPa, 3.66 GPa, and 0.0003, respectively, with a statistical significance of <0.001 in terms of YS and E. The mean differences of loading YS, E, and YS/E between chlorhexidine and probiotic are 2.45 MPa, 0.26 GPa, and 0.00007, whereas unloading values are 1.44 MPa, 0.49 GPa, and 0.0000533, respectively, with no statistical significance of >0.001 in terms of YS, E, and YS/E. Surface topography alteration was clearly appreciated in the charcoal and probiotic mouthwash groups compared to charcoal mouthwash. Loading and unloading of 0.016" ceramic-coated nickel-titanium archwires showed an increase in mechanical properties except for the spring back ratio on exposure to chlorhexidine, probiotic, and charcoal mouthwashes. Chlorhexidine and probiotic mouthwashes had a higher yield strength and flexural modulus of elasticity in comparison with charcoal mouthwash and artificial saliva on 0.016" ceramic-coated nickel-titanium archwires. More corrosive changes were seen on 0.016" ceramic-coated nickel-titanium archwires when immersed in chlorhexidine, followed by probiotic and charcoal mouthwashes.

SANISAND-H: A sand bounding surface model for high pressures

This paper presents a new bounding surface constitutive model for sand, named SANISAND-H, capable of predicting the shear and volumetric behavior of the material under extra-high range of pressures, in addition to normal pressures. The model is an extension of the SANISAND08 model (Taiebat and Dafalias, 2008) with a closed cone-type yield surface that obeys rotational and isotropic hardening. The critical state line and the limiting isotropic compression curve of the SANISAND08 model are modified to accommodate a wide range of pressures. A new constitutive ingredient is the definition of a reference compression curve that serves as bounding surface for establishing the isotropic hardening rule of the yield surface. The kinematic hardening rule and stress-dilatancy relationship of the SANISAND08 model are significantly modified, to better capture the response of sands under high pressure. The value of the back stress ratio at the initiation of a new loading process is re-introduced, ensuring a smooth elastic-plastic transition necessary for accurate simulation of the response under loading reversals. The SANISAND-H model simulations are in very good agreement with test data for Toyoura and Cambria sands under various drained and undrained monotonic stress loading paths in a wide range of densities and pressures.

Parametric study of a dual-band quasi-Yagi antenna for LTE application

Due to small size and lightweight properties, the development of microstrip (MS) patch antennas for wireless communication has become one of the mobile application devices in demand in recent years. This has helped to reduce reliance on wired cables. In this paper, a study has been performed on MS antenna by developing a quasi-Yagi structure on a fire retardant-4 (FR-4) substrate with a MS to coplanar strip line (CPS) transition feeding technique. The antenna is designed by using computer simulation technology (CST) to achieve the desired resonant frequency and bandwidth. The proposed dual band quasi-Yagi antenna has impedance bandwidths of approximately 0.3 GHz and 0.22 GHz resonating at 1.80 GHz and 2.60 GHz, respectively, which makes it suitable for long-term evolution (LTE) applications. Eight-director elements in four pairs are constructed to achieve directivity with magnitudes of 6 dB and 8.3 dBi at both resonant frequencies, 1.80 GHz and 2.60 GHz, respectively. Different parametric studies have also been performed to characterize the antenna radiation characteristics. The return loss, voltage standing wave ratio (VSWR), front to back (F/B) ratio and far-field radiation are analyzed and discussed.

Testing of chlorine dosage in drinking water using microstrip patch sensor

A new method using microstrip patch sensor is designed, simulated, and measured to detect the dosage of added chlorine to the drinking water using the relation between permittivity and matching impedance. The simulation is done using computer simulation technology-microwave studio software. The proposed sensor is designed on a single FR-4 layer with a low profile, 0.499 GHz bandwidth, center frequency of 2.94 GHz, gain of 6.55 dBi, and a good front to back ratio of 17.84 dB. In this work, the antenna design is started from a conventional patch antenna equation. Then, an optimization process is performed to achieve good parameter values for obtaining the desired objective. The objective is to utilize the microwave frequency to measure the chlorine dosage in water. The measurement results proved that the matching impedance can be used to find out the dosage of chlorine in drinkable water. The proposed method overcomes the open-ended coaxial probe method in terms of experimental time and contactless testing and shows high matching with the latter actual data. Moreover, the proposed method overcomes the conventional methods in terms of continuity and large scale of testing, non-contacting with the samples of water, and no additive chemical materials, which make the water samples not drinkable.

Compact low profile 5.8 GHz MPA for on-body applications

A compact microstrip patch antenna (MPA) with a T shape monopole technique is designed, simulated, and measured. By using fire retardant material (FR-4) as a substrate with a low profile, the proposed antenna is designed and simulated to be used for on-body biomedical applications. A center frequency of 5.78 is achieved with a gain of 11.78 dB and a matching impedance of -47.47 dB. A 1.48 W/Kg (10 gm) as a specific absorption rate (SAR) is achieved and 29.69 dB front to back ratio with a bandwidth of 3.376 GHz. The antenna was examined in free space as well as on-body using CST-MW software. The proposed antenna is fabricated and examined. Finally, a comparison is done among simulated results, measured results, and the dual-band dual-mode antenna. The proposed antenna overcomes the latter work in terms of small size, high matching impedance, high front to back ratio, and operating bandwidth.

Experimental Analysis of Partial Evaporation Micro-ORC for low-temperature Heat Recovery

In this paper, we present an experimental assessment of the performance of a partial evaporating organic Rankine cycle (PE-ORC) power system. The system converts low temperature heat into electrical energy, with a power size around 1 kW, thus suitable for micro-generation in the residential sector. Although the test bench was designed for operating with superheated vapour at the expander inlet, it has demonstrated to be able to work with the expansion occurring entirely in two-phase condition. Since the direct measurement of the vapour quality is not possible using the sensors installed in the test rig, the state of the fluid in the two-phase condition is estimated by means of the thermal balance at the heat exchangers, so the thermodynamic cycle can be evaluated. Temperatures of the heat source in the range between 40 °C and 75 °C have been tested, and for each temperature value the vapour quality at the expander inlet has been varied by regulating the feed-pump rotating speed. Experimental data are provided regarding the performance of the overall cycle, of the heat exchangers, of the expander and of the feed-pump. It was observed that the effectiveness of the evaporator and the efficiency of the pump are improved with respect to the operation with superheated vapour at the expander inlet. However, the overall performance is lower, especially due to the high ratio of the pump consumption over the expander produced power, commonly called back work ratio (BWR). The latter, under some boundary conditions, has resulted higher than the unit, meaning that the system is not able to produce net electrical power. The aim of the paper is to identify the design characteristics required by a micro-ORC energy system in order to enhance its performance in the PE operating mode.

Sparing old-growth maximises conservation outcomes within selectively logged Amazonian rainforest

Timber extraction threatens a vast area of tropical ecosystems, making it vital to design productive harvesting operations that limit biodiversity declines. Contrasting management options span a continuum from less-intensive, land-sharing logging applied over a larger area to land-sparing operations that combine intensive harvesting with the preservation of old-growth forest. Combining company-reported extraction rates with dung beetle surveys along an Amazonian logging gradient, we explore how individual species' abundances, geometric mean population sizes, functional diversity, and trait characteristics vary across simulated logging concessions and production targets. We substantially extend previous studies by evaluating 8000 mixed-harvesting scenarios and by assessing the profitability of contrasting practices. Simply maximising old-growth protection delivers the highest species' abundances and population sizes for species negatively affected by logging. Maximising old-growth also supports communities with a functional trait dissimilarity (FDis, RaoQ) and functional structure of nesting guilds, biomass, pronotum volume, front leg area, and front:back leg ratio traits that closely resembles old-growth forest. Functional evenness (FEve), richness (FRic), and divergence (FDiv) did not vary across logging strategies. Some 3 % of mixed approaches outperform extreme sparing (which maximises old-growth retention through intensive logging) but still involve substantial sparing, enabled by intensified logging elsewhere. However more-extensive business-as-usual harvesting is up to 90 % more profitable than extreme sparing, suggesting active policy mechanisms, standards, or regulations would be needed to make spatially-concentrated logging operations (which benefit biodiversity) more commercially attractive. Old-growth sparing appears key to limiting biodiversity declines within tropical timber concessions, but would require payments to compensate for reduced profits.

Open-Circuit Fault Detection in a Single Conductor Transmission Line Using TM0 Mode Launcher

A novel surface wave (SW) launcher design for power line fault detection is presented in this paper. The launcher is capable of converting TE10 to TM0 mode and exciting SW signal at 5.5 GHz frequency with high efficiency, on a single conductor line. The average attenuation of 2 dB/m and front to back ratio of 19 dB are observed and verified by simulation and experiments. Effect of bend, nearby obstacles, and extra wire connection on SW propagation is also investigated by experiments, and corresponding S-parameter results are presented. The optimization of launcher design with dielectric window and conical back plate is also demonstrated. The proposed launcher is compact and lightweight and can be easily installed without damaging the conductor line. Close structure makes it capable of withstanding outdoor environmental conditions. Using this launcher, microwave signal can be efficiently transmitted and received over existing conductor lines such as live power lines, pipes, and HVAC ducts, and it can be used in applications such as power line communication, fault detection, and permittivity measurement.

Interaction of shock train with cavity shear layer in a scramjet isolator

The interaction between the self-excited shock train flow and the cavity shear layer in a scramjet isolator is investigated numerically using detached-eddy simulations. The effect of changing the position of the shock train by controlling the back pressure ratio and the effect of changing the cavity front wall angle are analyzed using unsteady statistics and modal analysis. The propagation mechanism of the pressure disturbance was investigated by spatiotemporal cross-correlation coefficient analysis. In the present numerical study, a constant isolator section with a cavity front wall (θ = 90° and 60°) was considered, followed by a diffuser section simulated at Mach number 2.2 with three different back pressure ratios (pb/p∞ = 0.7, 5.0, and 6.0). The change in back pressure provides three different conditions (i.e., no shock train, shock train ends before the leading edge of the cavity, and shock train present above the cavity). To understand the unsteady dynamics of the interaction of the shear layer with the shock train, the spatiotemporal trajectory of the wall pressure and the centerline pressure distribution, the spatiotemporal cross-correlation coefficient, and the modal analysis by dynamic mode decomposition are obtained. The results show that the low-frequency shock train oscillation dominates the self-sustained cavity oscillation. The spatiotemporal cross-correlation between the wall surface and the center of the cavity bottom wall indicates the propagation of local disturbances originating from the separated boundary layer caused by the shock and the recirculation zone in the corners of the cavity. Dynamic mode decomposition analysis shows the shear layer at the leading edge of the cavity and the downstream propagation of large eddies from the cavity. It also shows the pairing of coherent structures between the shock train and the recirculation zone of the cavity.

The evaluation of mandatory audit firm and auditor rotation: literature review

Purpose- The purpose of this study it to evaluate the impacts of mandatory audit firm and auditor rotation on audit quality and auditor independence by literature review. Methodology- This study empoys a literature review on the auditor rotations in the auditing firms. Findings- In the first stage of literature review, it is determined that there are positive sides of mandatory audit firm and auditor rotation reflected on audit quality and auditor independence. Among them such facts are observed; a client’s be audited by the same audit firm and auditor for a long time can increase intimacy and therefore, professional skepticism can be declined. Furthermore, mandatory rotation can prevent poor audit procedures. Besides, it is also emphasized that financial information users’ perception regarding auditors’ independence is positively effected and with a new point of view, rotation decreases the risk of misevaluation caused by repetitional tasks and risk of making mistakes. It is also observed that a positive competition in the audit sector would be created and therefore, there would be an era for the firms other that the big four. On the other hand, negative sides of rotation draw the attention in the literature review, as well. It is underlined that it could take long time period to determine the firm’s organization structure, its operations, exposed risks, due to new auditor’s inexperience and this could lead to cost increases. Furthermore, following the rotation, long-term-based audit information could disappear and efficiency and productivity of audit process could decline. Besides these, by the approach of the planned rotation date, it is observed that especially in the last year careless behaviours could be seen and therefore, mandatory audit quality could be affected negatively. Limited number of nonaudit firms on behalf of clients, new auditors high confidence in existing audit reports and therefore, their incapability of making tiny distinctions, are the other findings of the study. Conclusion- Literature review indicates that there are mixed findings regarding mandatory rotations’ impacts on independence and quality other than positive and negative results. Hence, it is seen that there is no consensus on mandatory rotation in terms of rotation period and its impact on independence and quality. Field researches especially by considering qualitative methods are important to explain the results obtained by quantitative researches. In-depth interviews with experienced international audit sector representatives are important to explain the rotation impact levels of international audit network (Big Four and other international firms) and national audit firms and their comparisons, ex-audit firm turning back ratios and its reasons. In this way, it could be supportive to decide whether existing legislation is capable of creating independence and quality in audit and by new amendments it could be possible to develop confidence in audit firms, audited clients and capital markets. Keywords: Mandatory auditor rotation, mandatory audit firm rotation, quality in independent audit, auditor independence JEL Codes: M42, M48

Thermodynamic optimization of a linear thermomagnetic motor

Thermomagnetic motors can be applied to recover low-grade thermal energy waste and convert it into mechanical energy, therefore, used as an energy harvester. The present work proposes a mathematical model to simulate the heat transfer and the thermodynamic cycle of a linear thermomagnetic motor coupled to a spring mechanism. The simulation results are the input information in a subroutine to optimize the motor design based on two objective functions: to minimize the total entropy generated and to minimize the back work ratio, defined as the ratio between the pumping power and the total produced power. The mathematical model solves coupled the energy equations for the fluid and solid phases, and the entropy generation model includes four contributions: interstitial heat transfer (finite temperature difference), axial conduction in the fluid and solid phases, and viscous dissipation. Gadolinium is used as soft magnetic material due to the availability of properties data. Four design and operating conditions constraints are taken into account: heat exchanger length, spring constant, mass flow rate, and warm stream temperature (heat source), and their optimized values are, respectively, 52 mm, 1560 N/m, 80 kg/h at any warm stream temperature ranging from 310–330 K. At these combinations, the optimum thermomagnetic motor is able to produce a net power of 5.00 ± 0.15 W with a minimum back-work ratio of about 12%. The proposed methodology can be used to optimize the design of novel thermomagnetic motors or to optimize geometric parameters and operating conditions of state-of-the-art concepts.

Microwave Imaging With Novel Time-Domain Clutter Removal Algorithm Using High Gain Antennas for Concealed Object Detections

This paper presents a novel time-domain clutter removal algorithm for microwave imaging of concealed objects using a new high gain ultra-wideband (UWB) antipodal antenna. Bistatic antenna setup is employed to image the objects like a gun prototype, knife and blade using UWB Gaussian modulated pulses. A synthetic aperture radar (SAR) beamforming algorithm with a new clutter removal method is adopted for microwave imaging of the objects inside and outside the anechoic chamber. The proposed algorithm successfully removes the unwanted clutter from the measured scanning data, with only single scanning of the target area. The proposed method along with windowing, envelope detection and finally image reconstruction results in effective reconstruction of the concealed target as compared to the existing methods in the literature. An UWB high gain antipodal antenna is designed for the proposed imaging setup with a peak gain of 26 dBi at 8.4 GHz, which is the highest among previously reported UWB antennas. The proposed antenna achieves a wide gain bandwidth over 6 – 14 GHz (80%) with a gain of > 18 dBi. Simulation and measured results validate the design principle of the antenna with characteristics like high front to back ratio, narrow half-power beam width, and low cross-polarization. In the opinion of the authors, the proposed clutter removal algorithm is the simplest and effective method for single-time scanning of the concealed targets, in a realistic scenario.