• Effect of cell-size on the energy absorption features of closed-cell aluminium foams

      Nammi, Sathish K.; Edwards, Gerard; Shirvani, Hassan; Anglia Ruskin University, University of Chester, Anglia Ruskin University, (Elsevier, 2016-07-02)
      The effect of cell-size on the compressive response and energy absorption features of closed-cell aluminium (Al) foam were investigated by finite element method. Micromechanical models were constructed with a repeating unit-cell (RUC) which was sectioned from tetrakaidecahedra structure. Using this RUC, three Al foam models with different cell-sizes (large, medium and small) and all of same density, were built. These three different cell-size pieces of foam occupy the same volume and their domains contained 8, 27 and 64 RUCs respectively. However, the smaller cell-size foam has larger surface area to volume ratio compared to other two. Mechanical behaviour was modelled under uniaxial loading. All three aggregates (3D arrays of RUCs) of different cell-sizes showed an elastic region at the initial stage, then followed by a plateau, and finally, a densification region. The smaller cell size foam exhibited a higher peak-stress and a greater densification strain comparing other two cell-sizes investigated. It was demonstrated that energy absorption capabilities of smaller cell-size foams was higher compared to the larger cell-sizes examined.
    • Electromagnetic wave absorption properties of ternary poly (vinylidene fluoride)/magnetite nanocomposites with carbon nanotubes and graphene

      Tsonos, Christos; Soin, Navneet; Tomara, Georgia N.; Yang, Bin; Psarras, Georgios C.; Kanapitsas, Athanasios; Siores, Elias; University of Chester (Royal Society of Chemistry, 2015-12-21)
      Ternary nanocomposite systems of poly(vinylidene fluoride)/magnetite/carbon nanotube (PVDF/Fe3O4/CNT) and poly(vinylidene fluoride)/magnetite/graphene (PVDF/Fe3O4/GN), were prepared using high shear twin screw compounding followed by compression moulding. The electromagnetic (EM) microwave absorption properties of the nanocomposites were investigated in the frequency range of 3–10 GHz. PVDF/Fe3O4/CNT samples with the thickness d = 0.7 mm present a minimum reflection loss (RL) of −28.8 dB at 5.6 GHz, while all the RL values in the measurement frequency range 3–10 GHz are lower than −10 dB. PVDF/Fe3O4/GN with a thickness of 0.9 mm, presents a minimum RL of −22.6 dB at 5.4 GHz, while all the RL values in the measurement frequency range 3–10 GHz are lower than −10 dB as well. The excellent microwave absorption properties of both nanocomposites, in terms of minimum RL value and broad absorption bandwidth, are mainly due to the enhanced magnetic losses. The results indicate that the ternary nanocomposites studied here, can be used as an attractive candidate for EM absorption materials in diverse fields of various technological applications, not only in the frequency range 3–10 GHz, but also at frequencies <3 GHz for PVDF/Fe3O4/CNT and >10 GHz for PVDF/Fe3O4/GN with a realistic thickness of close to 1 mm.
    • Experimental demonstration of a transparent graphene millimetre wave absorber with 28% fractional bandwidth at 140 GHz

      Wu, Bian; Tuncer, Hatice M.; Naeem, Majid; Yang, Bin; Cole, Matthew T.; Milne, William I.; Hao, Yang; Queen Mary University of London (Nature Publishing Group, 2014-02-19)
      The development of transparent radio-frequency electronics has been limited, until recently, by the lack of suitable materials. Naturally thin and transparent graphene may lead to disruptive innovations in such applications. Here, we realize optically transparent broadband absorbers operating in the millimetre wave regime achieved by stacking graphene bearing quartz substrates on a ground plate. Broadband absorption is a result of mutually coupled Fabry-Perot resonators represented by each graphene-quartz substrate. An analytical model has been developed to predict the absorption performance and the angular dependence of the absorber. Using a repeated transfer-and-etch process, multilayer graphene was processed to control its surface resistivity. Millimetre wave reflectometer measurements of the stacked graphene-quartz absorbers demonstrated excellent broadband absorption of 90% with a 28% fractional bandwidth from 125-165 GHz. Our data suggests that the absorbers’ operation can also be extended to microwave and low-terahertz bands with negligible loss in performance.
    • Flicker mitigation strategy for a doubly fed induction generator by torque control

      Zhang, Yunqian Q.; Hu, Weihao; Chen, Zhe; Cheng, Ming; Hu, Yanting (IET, 2014-03)
      Owing to the rotational sampling of turbulence, wind shear and tower shadow effects grid connected variable speed wind turbines could lead to the power fluctuations which may produce flicker during continuous operation. A model of an megawatt (MW)-level variable speed wind turbine with a doubly fed induction generator is presented to investigate the flicker mitigation. Taking advantage of the large inertia of the wind turbine rotor, a generator torque control (GTC) strategy is proposed, so that the power oscillation is stored as the kinetic energy of the wind turbine rotor, thus the flicker emission could be reduced. The GTC scheme is proposed and designed according to the generator rotational speed. The simulations are performed on the national renewable energy laboratory 1.5 MW upwind reference wind turbine model. Simulation results show that damping the generator active power by GTC is an effective means for flicker mitigation of variable speed wind turbines during continuous operation. keywords: {asynchronous generators;oscillations;power generation control;torque control;wind power plants;wind turbines;GTC strategy;continuous operation;doubly fed induction generator;flicker emission;flicker mitigation strategy;generator active power;generator torque control;kinetic energy;megawatt-level variable speed wind turbine;power oscillation;tower shadow effects grid connected variable speed wind turbines;turbulence;upwind reference wind turbine model;variable speed wind turbines;wind shear;wind turbine rotor
    • Hybrid Heat Pump for Micro Heat Network

      Counsell, M. J.; Khalid, Yousaf; Stewart, M.; University of Chester (World Academy of Science, Engineering and Technology (WASET), 2017-10-17)
      Achieving nearly zero carbon heating continues to be identified by UK government analysis as an important feature of any lowest cost pathway to reducing greenhouse gas emissions. Heat currently accounts for 48% of UK energy consumption and approximately one third of UK’s greenhouse gas emissions. Heat Networks are being promoted by UK investment policies as one means of supporting hybrid heat pump based solutions. To this effect the RISE (Renewable Integrated and Sustainable Electric) heating system project is investigating how an all-electric heating sourceshybrid configuration could play a key role in long-term decarbonisation of heat. For the purposes of this study, hybrid systems are defined as systems combining the technologies of an electric driven air source heat pump, electric powered thermal storage, a thermal vessel and micro-heat network as an integrated system. This hybrid strategy allows for the system to store up energy during periods of low electricity demand from the national grid, turning it into a dynamic supply of low cost heat which is utilized only when required. Currently a prototype of such a system is being tested in a modern house integrated with advanced controls and sensors. This paper presents the virtual performance analysis of the system and its design for a micro heat network with multiple dwelling units. The results show that the RISE system is controllable and can reduce carbon emissions whilst being competitive in running costs with a conventional gas boiler heating system.
    • Impedance coordinative control for cascaded converter in bidirectional application

      Tian, Yanjun; Deng, Fujin; Chen, Zhe; Sun, Xiaofeng; Hu, Yanting; University of Chester (IEEE, 2015-06)
      Two stage cascaded converters are widely used in bidirectional applications, but the negative impedance may cause system instability. Actually the impedance interaction is much different between forward power flow and reversed power flow, which will introduce more uncertainty to the system stability. This paper proposes a control method for the constant power controlled converter in cascaded system, and consequently it can change the negative impedance of constant power converter into resistive impedance, which will improve the cascaded system stability, as well as merge the impedance difference between forward and reversed power flow. This paper addresses the analysis with the topology of cascaded dual-active-bridge converter (DAB) with inverter, and the proposed control method can also be implemented in unidirectional applications and other general cascaded converter system. The effectiveness has been validated by both simulation and experimental results.
    • Impedance interaction modeling and analysis for bidirectional cascaded converters

      Tian, Yanjun; Deng, Fujin; Chen, Zhe; Sun, Xiaofeng; Hu, Yanting (2015-06)
      For the cascaded converter system, the output impedance of source converter interacts with the input impedance of load converter, and the interaction may cause the system instability. In bidirectional applications, when the power flow is reversed, the impedance interaction also varies, which brings more uncertainty to the system stability. An investigation is performed here for showing that the forward and reverse interactions are prominently different in terms of dynamics and stability even though the cascaded converter control remains unchanged. An important guideline has been drawn for the control of the cascaded converter. That is when voltage mode converter working as the load converter; the constant power mode converter as the source converter, the system is more stable. The concluded findings have been verified by simulation and experimental results.
    • Micromachined Thick Mesh Filters for Millimeter-Wave and Terahertz Applications

      Wang, Yi; Yang, Bin; Tian, Yingtao; Donnan, Robert S.; Lancaster, Michael J.; University of Bolton (IEEE, 2014-03-01)
      This paper presents several freestanding bandpass mesh filters fabricated using an SU-8 based micromachining technique. The important geometric feature of the filters, which SU8 is able to increase, is the thickness of the cross-shaped micromachined slots. This is 5 times its width. This thickness offers an extra degree of control over the resonance characteristics. The large thickness not only strengthens the structures, but also enhances the resonance quality factor (Q-factor). A 0.3 mm thick, single layer, mesh filter resonant at 300 GHz has been designed, fabricated and its performance verified. The measured Q-factor is 16.3 and the insertion loss is 0.98 dB. Two multi-layer filter structures have also been demonstrated. The first one is a stacked structure of two single mesh filters producing a double thickness, which achieved a further increased Q-factor of 27. This is over six times higher than a thin mesh filter. The second multi-layer filter is an electromagnetically coupled structure forming a two-pole filter. The coupling characteristics are discussed based on experimental and simulation results. These thick mesh filters can potentially be used for sensing and material characterization at millimeter-wave and terahertz frequencies.
    • Microwave and terahertz dielectric properties of MgTiO3–CaTiO3 ceramics

      Huang, J. B.; Yang, Bin; Yu, Chuying; Zhang, Guang; Xue, Hao; Xiong, Zhaoxian; Viola, Giuseppe; Donnan, Robert S.; Yan, Haixue; Reece, Mike J.; College of Materials; Queen Mary University of London (Elsevier, 2015-10-05)
      The THz dielectric properties of MgTiO3–CaTiO3 ceramics are reported. The ceramics were prepared via a solid-state reaction route and the sintering conditions were optimized to obtain ceramics with high permittivity and low loss in the terahertz frequency domain. The amount of impurities (MgTi2O5) and grain size increased with increasing sintering temperature. The dielectric properties improved with increasing density, and the best terahertz dielectric performance was obtained at 1260 °C, with a permittivity of 17.73 and loss of 3.07×10−3. Ceramics sintered above 1260 °C showed a sharp increase in loss, which is ascribed to an increase in the impurity content.
    • Perovskite Srx(Bi1-xNa0.97-xLi0.03)0.5TiO3 ceramics with polar nano regions for high power energy storage

      Wu, Jiyue; Mahajan, Amit; Riekehr, Lars; Zhang, Hangfeng; Yang, Bin; Meng, Nan; Zhang, Zhen; Yan, Haixue; Queen Mary University of London; Uppsala University; University of Chester (Elsevier, 2018-06-06)
      Dielectric capacitors are very attractive for high power energy storage. However, the low energy density of these capacitors, which is mainly limited by the dielectric materials, is still the bottleneck for their applications. In this work, lead-free single-phase perovskite Srx(Bi1-xNa0.97-xLi0.03)0.5TiO3 (x=0.30 and 0.38) bulk ceramics, prepared using solid-state reaction method, were carefully studied for the dielectric capacitor application. Polar nano regions (PNRs) were created in this material using co-substitution at A-site to enable relaxor behaviour with low remnant polarization (Pr) and high maximum polarization (Pmax). Moreover, Pmax was further increased due to reversible electric field induced phase transitions. Comprehensive structural and electrical studies were performed to confirm the PNRs and the reversible phase transitions. And finally a high energy density (1.70 J/cm3) with an excellent efficiency (87.2%) was achieved using the contribution of PNRs and field-induced transitions in this material, making it among the best performing lead-free dielectric ceramic bulk material for high energy storage.
    • The power of VNA-driven quasi-optics to sense group molecular action in condensed phase systems

      Donnan, Rob; Tian, Kun V.; Yang, Bin; Chass, Gregory. A.; University of Chester (2014-12-08)
      The versatility for quasi-optical circuits, driven by modern vector network analysers, is demonstrated for the purpose of low energy (meV) coherent spectroscopy. One such example is shown applied to the curing dynamics of a non-mercury-based dental cement. This highlights the special place the methodology holds as a `soft-probe' to reveal the time-resolved energetics of condensed phased systems as they self-organise to adopt their low energy state.
    • Power System with Variable Speed Wind Turbine and Diesel Generation Units

      Hu, Yanting; Chen, Zhe; Glyndwr; Aalborg University (EER, 2014-01-20)
      Thispaper presents a power system consisting of wind turbines, diesel generation units, and energy storage system. Both wind turbines and diesel engine adopt variable speed operation mode;and power electronic interface are used for the generation units which provide flexible and wide range of control on the power. The system configuration, characteristics, operation principles are presented. The controller and control strategies are discussed. The simulation studies have been performed and the results are presented.
    • Programmable logic controllers and Direct digital controls in Buildings

      Khalid, Yousaf; University of Chester (2018-09)
      The concept of programmable logic controller (PLC) originated over the last century that has revolutionised the industrial sector. In the last few decades PLC in the form of DDC has been commonly used in Building Energy Management Systems (BEMS). The contribution of this work is to analyse PLC/DDC role in the ongoing BEMS advancements in the building sector. Currently DDC are not understood by building design and simulation engineers who assess the controllability of the building in practice. This paper would enhance the understanding of integrating DDC in buildings and influence creation of better modelling and simulation tools for assessing their impact on energy performance in practice.
    • Q-V droop control using fuzzy logic and reciprocal characteristic

      Wang, Lu; Hu, Yanting; Chen, Zhe; Glyndwr University; Aalborg University (Engineering and Technology Publishing, 2014-01-01)
      Today, the conventional power system is facing some global environmental problems, which is leading to a new trend of power grid by using “green and clear” energy sources. As the platform of smart grid technology, the microgrid associated with distributed energy resources (DERs) may provide electric power at distributed voltage level, which not only is an autonomous system, but also can be connected to the main grid. To improve the stability and controllability of the power grid, this paper presents an improved Q-V droop control strategy using fuzzy logic controller and reciprocal characteristic. Matlab/Simulink is used for analysing the performance of system. The feasibility of the improved droop control strategy has been verified and discussed. The results demonstrate the improved Q-V droop control strategy could have good effects in grid-connected and islanded mode, and during operation mode transitions.
    • Quality-Control of UV offset Lithographicaly Printed Electronic-Ink by THz Technology

      Zeng, Yang; Donnan, Robert; Edwards, Marc; Yang, Bin; University of Chester (IEEE Conference Publications, 2017-10-16)
      In this paper, a novel quality-monitor method of inkjet-printed electronics based on terahertz (THz) sensing is presented. Specifically, two different approaches, namely THz reflection spectroscopy and THz near-field scanning, are proposed.
    • Research on the synchronization control strategy for microgrid-connected voltage source inverter

      Cao, Yuanzhi; Hu, Yanting; Hu, Rui; Chen, Jianfei (IEEE, 2015-06)
      Microgrid is intended and featured to be able to operate in both grid-connected and islanded mode to ensure high quality and reliable power supply. In order to achieve stable operation of the microgrid-connected voltage source inverter (MVSI) units under paralleled or grid-connected mode, a novel synchronization method based on droop control is proposed in this paper. The difference of phase and amplitude between different MVSI units is detected and is used to calculate the output frequency and amplitude of the MVSI. This method can smooth transfer the MVSI units from standalone mode to paralleled mode. The simulation and experimental results show that the proposed method is effective in achieving paralleled operation of the MVSI units.
    • Smart guaranteed time-slot allocation algorithm for industrial wireless sensor networks emergency message transmission

      Chen, Qinyin; Hu, Yanting; Chen, Zhe; Davies, John N.; Excell, Peter (IET, 2015-04)
      This paper presents investigation on application of wireless sensor networks (WSNs) in wind power generation systems and highlights an important issue associated with the deadline for the delivery of messages among nodes based on the IEEE 802.15.4E standard. Owing to the limits of standard and the power system application requirements, this research proposes a smart guaranteed time slot (S-GTS) allocation algorithm which is based on the urgent/important matrix. This proposed algorithm promotes the utilisation of contention free period in a superframe. Besides, over seven GTSs can be allocated in a superframe, there are only seven GTSs that can be used in the standard. In addition, this study proves the value of BO and SO upper bound is 6 for the WSN application in power systems. Moreover, the network delay of S-GTS performs better than the 16-time-slot mechanism and i-GAME mechanism.
    • Spreadsheet tools to estimate the thermal transmittance and thermal conductivities of gas spaces of an Insulated Glazing Unit

      Nammi, Sathish K.; Shirvani, Hassan; Shirvani, Ayoub; Edwards, Gerard; Dunn, Jeremy; Anglia Ruskin University, Anglia Ruskin University, Anglia Ruskin University, University of Chester, Glazing Vision (Anglia Ruskin Research Online, 2014-03)
      An Insulated Glazing unit (IGU) is constructed with two or more layers of glass panes sealed together by gas spaces in-between. IGUs are prevalent in windows, doors and rooflights, primarily due to their improved thermal resistance. Today, most IGUs are either two or three layered. Adding further layers of glass improves thermal insulation but with the penalty of increased cost and weight. Low emissivity (Low-e) film coatings, when deposited on the glass panes, reduce long-wavelength radiative heat losses. Furthermore, filling the gas spaces with the inert gases (e.g. Argon, Krypton, Xenon and SF6), further reduce conduction and natural convection across the gap. In summary, higher thermal insulation performance of an IGU can be achieved with gas fillings and Low-e coatings on glass. This report discusses spreadsheets that have been developed, capable of estimating the thermal transmittance values of IGU, as per BS EN 673. The spreadsheet tools also have the ability to estimate the thermal conductivity of the gas spaces between the panes of IGU.
    • SrFe12O19 based ceramics with ultra-low dielectric loss in the millimetre-wave band

      Yu, Chuying; Zeng, Yang; Yang, Bin; Wylde, Richard; Donnan, Robert; Wu, Jiyue; Xu, Jie; Gao, Feng; Abrahams, Isaac; Reece, Mike J.; Yan, Haixue; Queen Mary University of London; Hunan University; National University of Defence Technology; University of Chester; Thomas Keating Ltd; Northwestern Polytechnical University (AIP Publishing, 2018-04-02)
      Non-reciprocal devices such as isolators and circulators, based mainly on ferromagnetic materials, require extremely low dielectric loss in order for strict power-link budgets to be met for millimetre (mm)-wave and terahertz (THz) systems. The dielectric loss of commercial SrFe12O19 hexaferrite was significantly reduced to below 0.002 in the 75 - 170 GHz band by thermal annealing. While the overall concentration of Fe2+ and oxygen vacancy defects is relatively low in the solid, their concentration at the surface is significantly higher, allowing for a surface sensitive technique such as XPS to monitor the Fe3+/Fe2+ redox reaction. Oxidation of Fe2+ and a decrease in oxygen vacancies is found at the surface on annealing, which is reflected in the bulk sample by a small change in unit cell volume. The significant decrease in dielectric loss property can be attributed to the decreased concentration of charged defects such as Fe2+ and oxygen vacancies through annealing process, which demonstrated that thermal annealing could be effective in improving the dielectric performance of ferromagnetic materials for various applications.
    • Terahertz Characterisation of UV Offset Lithographically Printed Electronic-Ink

      Zeng, Yang; Edwards, Marc; Stevens, Robert; Bowen, John; Donnan, Robert S.; Yang, Bin; University of London; National University of Defense Technology; University of Chester; Nottingham Trent University; University of Reading (Elsevier, 2017-06-10)
      Inkjet-printed electronics are showing promising potential in practical applications, but methods for real-time, non-contact monitoring of printing quality are lacking. This work explores Terahertz (THz) sensing as an approach for such monitoring. It is demonstrated that alterations in the localised dielectric characteristics of inkjet-printed electronics can be qualitatively distinguished using quasi-optically-based, sub-THz reflection spectroscopy. Decreased reflection coefficients caused by the sintering process are observed and quantified. Using THz near-field scanning imaging, it is shown that sintering produces a more uniform spatial distribution of permittivity in the printed carbon patterns. Images generated using THz-TDS based imaging are presented, demonstrating the combination of high resolution imaging with quantification of complex permittivities. This work, for the first time, demonstrates the feasibility of quality control in printed electronic-ink with THz sensing, and is of practical significance to the development of in-situ and non-contact commercial-quality characterisation methods for inkjet-printed electronics.