Energy-efficient Applications Research Articles

Magnetic straintronics: Manipulating the magnetization of magnetostrictive nanomagnets with strain for energy-efficient applications

The desire to perform information processing, computation, communication, signal generation, and related tasks, while dissipating as little energy as possible, has inspired many ideas and paradigms. One of the most powerful among them is the notion of using magnetostrictive nanomagnets as the primitive units of the hardware platforms and manipulating their magnetizations (which are the state variables encoding information) with electrically generated static or time-varying mechanical strain to elicit myriad functionalities. This approach has two advantages. First, information can be retained in the devices after powering off since the nanomagnets are nonvolatile unlike charge-based devices, such as transistors. Second, the energy expended to perform a given task is exceptionally low since it takes very little energy to alter magnetization states with strain. This field is now known as “straintronics,” in analogy with electronics, spintronics, valleytronics, etc., although it pertains specifically to “magnetic” straintronics and excludes phenomena involving non-magnetic systems. We review the recent advances and trends in straintronics, including digital information processing (logic), information storage (memory), domain wall devices operated with strain, control of skyrmions with strain, non-Boolean computing and machine learning with straintronics, signal generation (microwave sources) and communication (ultra-miniaturized acoustic and electromagnetic antennas) implemented with strained nanomagnets, hybrid straintronics–magnonics, and interaction between phonons and magnons in straintronic systems. We identify key challenges and opportunities, and lay out pathways to advance this field to the point where it might become a mainstream technology for energy-efficient systems.

Negative capacitance FETs for energy efficient and hardware secure logic designs

Negative capacitance field effect transistors (NCFETs) have attracted good attention for energy efficient circuit designs. However, there are no clear design insights with NCFET based circuit designs for energy efficient and hardware secure applications. However, the lack of clear design insights make energy efficient and hardware secure NCFET circuit design more challenging. This paper presents important design insights and scope of NCFETs for energy efficient and hardware secure logic design at scaled supply voltages. Initially, NCFET device characteristics have been analyzed by varying the ferroelectric layer thickness (tfe) to identify optimum device performance window. At 40 nm technology node, NCFET device demonstrates enhanced characteristics for logic design with tfe in the range of 3 nm–5 nm due to steep subthreshold swing characteristics. NCFET with tfe of 5 nm exhibits 1.22 × higher ON current, 66 × lower leakage current and a SS of 50mV/dec compared to baseline MOSFET (tfe = 0 nm). Further, NCFET based static complementary inverter design exhibits better performance and higher energy efficiency compared to baseline MOSFET. NCFET inverter with tfe of 3 nm achieves optimum performance in terms of voltage transfer characteristics, differential gain, and noise margins. In addition, NCFET with tfe of 3 nm shows minimum energy consumption with the different supply voltages in the range of 0.6–0.8 V. Moreover, NCFET based buffer, logic gates and half-adder designs with tfe of 3 nm achieve approximately 3 × lower energy consumption compared to baseline designs. Apart from this, the NCFET designs exhibit 2 × higher ON current variations, 12 × higher inverter delay variations, and 3.1 × higher ring oscillator frequency variations compared to baseline designs against 5% process parameter variations at a supply voltage of 0.5 V. With the higher variations resulted from ferroelectric layer, NCFET demonstrate the potential and suitability towards the design of hardware security primitives like physically unclonable function (PUF) and true random number generator (TRNG).

A mixture of carbon dioxide and dimethyl ether as a refrigerant for ground air conditioning system

BACKGROUND: The selection of refrigerants for modern air conditioning systems (ACS) in ground facilities is a multidisciplinary task. Particularly, meeting the required energy efficiency of the refrigeration cycle as well as ensuring ecological safety of production, operation, and utilization of the refrigeration system. Herein, the working pressure levels of the refrigeration cycle considerably affect the availability, cost, and safety of the refrigeration equipment. The fire safety of the working substance is also important.
 AIM: To investigate the feasibility of a mixture of dimethyl ether and carbon dioxide as refrigerant for energy efficient and safe application of ACS in ground facilities.
 METHODS: Comparative analysis of a simple one-stage vapor–compression cycle using traditional working substances (R22 and R410A) and the proposed working substance, which is in the form of a mixture of dimethyl ether and carbon dioxide, using packages, such as Mathcad, HYSYS, CoolPack, and REFPROP, was performed.
 Results: An ecofriendly mixture of dimethyl ether and carbon dioxide with low global warming potential and zero ozone depletion potential was proposed as refrigerant. Increasing the percentage of dimethyl ether in the blend reduces the temperature glide in the gas cooler, a property of CO2, and pressures at which the blend operates. The mixture has limited operational properties due to the flammability of dimethyl ether, but its environmental performance makes the material of some practical interest.
 CONCLUSION: Fire safety of the proposed working substance was calculated. The concentration of dimethyl ether in the mixture at which it becomes flammable and unsafe for ACS was determined to be 8.3%.
 With an increase in the dimethyl ether content in the mixture with CO2 from 4% to 8%, the refrigeration coefficient of the cycle increases from 2.53 to 2.88, but it is 1.57 times less than that of R410A.
 The difference in operating pressures between the used non-ecological refrigerants and proposed mixture was determined. Results indicate that the mixture of dimethyl ether and carbon dioxide is currently inapplicable to mass production compressors, which use R410A as refrigerant. The condensation pressure of the most effective and nonflammable mixture of dimethyl ether and CO2 (with dimethyl ether concentration of 8%) is 101 bar against 30 bar for R410A.
 Therefore, we intend to evaluate test mixtures of dimethyl ether with other substances in the future.

High-performance voltage controlled multilevel MRAM cell

In the recent past, spin-transfer torque (STT) and spin-orbit torque (SOT) based magnetic random access memories (MRAMs) have been studied for future energy efficient and non-volatile memory applications. Multilevel cell (MLC) design has emerged as one of the promising solutions to enhance the storage density of these MRAMs. However, the conventional MLC design adds a larger magnetic tunnel junction (MTJ) stack that makes it difficult to maintain low switching current and high speed. Moreover, it becomes very difficult to reduce the driver transistor size. This paper describes the application of voltage controlled magnetic anisotropy effect to design energy efficient and fast MLC MRAM cell. So far, this approach has been reported only in single-bit MTJ devices. In the proposed MLC the voltage control is able to reduce both SOT and STT switching currents. The results show that the voltage control in MLC enhances energy efficiency and switching speed by more than 80 times and 3 times, respectively, in comparison to conventional SOT based MLCs. The reduction in switching currents also achieves smaller transistor size and enhances area efficiency by 3.5% as compared to conventional SOT-MLC. The effect of different channel materials on SOT switching current has also been explored. Furthermore, the system level evaluation shows that voltage controlled MLC outperforms STT-MRAM and SOT-MRAM for designing cache memory.

A case study on experimental and statistical analysis of energy consumption of domestic refrigerator

This paper presents the energy consumption analysis of the refrigerator and the effect of the condenser on it. According to the Bureau of Energy Efficiency (BEE), India, the energy efficiency of electric appliances is the key parameter for testing their performance before domestic use. For energy consumption analyses, the experimentation was conducted on the domestic refrigerator (165 L) top-mounted evaporator by retrofitting the refrigerator with an Elliptical Helical Coil Condenser (EHCC) and existing refrigerator with a Straight Tube Condenser (STC). Box-Behnken Design (BBD) is very significant in determining the significant factor and reducing the number of experiments. BBD has been performed to analyze the significance of factors ambient temperature, fresh food compartment temperature and the heat load in energy consumption, and the Coefficient of Performance (COP) of a refrigerator. The heat load and the ambient temperature are both very significant in determining the refrigerator's energy consumption. The most important thing is to increase the liquid content in the charge before it is supplied to the evaporator to extract more amount of heat to increase the cooling effect. The ANOVA (Analysis of Variance) results show that the ambient temperature and the heat load were more significant in increasing energy consumption and decreasing the COP and vice versa. The results of ANOVA and the experiment are very close; the R2 value 0.995 precisely matches the R2 adj. value 0.994. The statistical analysis using the Box-Behnken design produces a good fitting of the modeled and experimental data set. The present study aims to examine the effects of said factors and the condenser on the domestic refrigerator's energy consumption and COP. The study exhibits some enhancement in the COP to 2.59 contrary to 2.45 and energy consumption reduced to 1191 Wh from 1755 Wh during the trial of 24 h.

User Deep Energy Efficiency Evaluation via Load Perception and Clustering

With the constantly upgrading of the living level of urban residents, the types and quantities of domestic appliances continue to increase, and the electricity consumption behaviour is becoming more and more complex. Based on the fine-grained user energy consumption data obtained by load intelligent perception, this paper proposes a user energy efficiency evaluation method through fuzzy comprehension evaluation. First, the energy consumption characteristics at appliance level which can effectively represent energy consumption behaviour of users are designed and filtered, and then the energy efficiency evaluation strategy of appliances based on fuzzy comprehensive evaluation is established. The strategy adopts two-level fuzzy comprehensive evaluation. The first appliance-level fuzzy evaluation realizes the energy efficiency evaluation of the appliances. The second level is the comprehensive evaluation of user energy efficiency based on the appliance energy efficiency assessment, and the target users are divided into different energy efficiency levels. The measured data-based analysis results prove the effectiveness of the proposed method, and the results can guide users to optimize their electricity consumption behaviour scientifically and realize energy saving and carbon reduction.

Building institutional capacity for addressing climate and sustainable development goals: achieving energy efficiency in India

ABSTRACT Capacity-building is acknowledged as an essential requirement for addressing environmental and developmental challenges in developing countries. In particular, the capacity to manage technological change is an important prerequisite for climate change mitigation, adaptation and green growth. Despite the importance of such capacity, there are surprisingly few empirical accounts unpacking its different dimensions and exploring how it might be built in developing countries in the context of climate and sustainable development challenges. In this paper, we contribute to this sparse literature through an in-depth qualitative case study on energy efficiency in India. Specifically, we take a systemic and evolutionary perspective to investigate how the Bureau of Energy Efficiency developed and implemented its programs to promote energy efficiency in household appliances, light-emitting-diode lamps and energy-intensive industries – and how in doing so, both drew upon existing capacity within and outside the country, and also built new capacity, to achieve significant energy savings. Key policy insights Since the capacity to manage technological change is distributed among a range of actors, policymakers require the ability to understand capacity needs from multiple actors’ perspectives. Policymakers need to respond to evolving capacity needs over the course of a program – from strategic program design, trust-building and resource mobilization in early stages, to administration in later stages. ‘System operators/integrators’ can play a crucial role during the early stages of a program by helping develop capacity and sustaining it by creating a demand for such capacity, as well as bringing together actors, enabling coordination, and building coalitions among them. Preliminary analysis suggests that the Bureau of Energy Efficiency programs investigated in this paper resulted in significant energy savings and CO2 emission reductions.

Parallelized POD-based suboptimal economic model predictive control of a state-constrained Boussinesq approximation

Motivated by an energy efficient building application, we want to optimize a quadratic cost functional subject to the Boussinesq approximation of the Navier-Stokes equations and to bilateral state and control constraints. Since the computation of such an optimal solution is numerically costly, we design an efficient strategy to compute a sub-optimal (but applicationally acceptable) solution with significantly reduced computational effort. We employ an economic Model Predictive Control (MPC) strategy to obtain a feedback control. The MPC sub-problems are based on a linear-quadratic optimal control problem subjected to mixed control and state constraints and a convection-diffusion equation, reduced with proper orthogonal decomposition. To solve each sub-problem, we apply a primal-dual active set strategy. The method can be fully parallelized, which enables the solution of large problems with real-world parameters.

Climatic zoning for energy efficiency applications in buildings based on multivariate statistics: The case of the Brazilian semiarid region

This study aimed to propose climatic zones in the Brazilian semiarid region using multivariate statistical techniques and to characterize these zones for energy efficiency applications in buildings. Principal component analysis (PCA) was used to select the variables with the greatest practical relevance. From this selection, hierarchical cluster analysis (HCA) was used to spatially define climatically homogeneous zones. For each defined zone, the most feasible constructive thermal conditioning strategies were defined, and the thermal indexes of heat and degree-hours of cooling and heating were calculated. As result, PCA reduced the dimensionality of the initial database from 104 to 48 variables, among which the climatic and bioclimatic variables related to temperature stood out. From the HCA, three climatic zones were defined for the Brazilian semiarid region. For all zones, there was a high demand for constructive conditioning strategies, which have to be adopted in more than half of the total annual hours. The proposed zoning is adapted to the climatic aspects of the Brazilian semiarid and has significant potential for applications in construction planning in this region. Moreover, the methodology presented can be applied for establishing climatic zones in other regions, which can contribute to increasing the energy efficiency of buildings.

Introduction to Heterostructured Materials: A Fast Emerging Field

Strong and tough materials are desired for lightweight, energy efficient applications such as electric cars and aerospace applications. Recently, heterostructures are found to produce unprecedented strength and ductility that are considered impossible based on the materials science in our textbooks. Such superior mechanical properties are enabled by a new scientific principle: hetero-deformation-induced (HDI) strengthening and work hardening. Heterostructured (HS) materials consist of heterogeneous zones with dramatic difference (> 100 pct) in flow stresses. The inter-zone interaction produces back stress in the soft zones and forward stress in the hard zones, which collectively produces the HDI stress. HS materials possess a significant synergistic effect where the integrated property exceeds the prediction by the rule of mixtures. Importantly, HS materials can be produced by current industrial facilities at large scale and low cost. The new materials sciences and promising applications are driving the fast development of the HS materials as an emerging field. There are many fundamental issues that need to be probed so as to effectively design HS materials for superior properties. To solve these issues, it requires collaborative efforts by the communities of experimental materials science and computational material science and mechanics.

Numerical investigation on novel water distribution for natural draft wet cooling tower

Natural draft wet cooling tower is widely used in cold end system of thermal power plants, however, the water droplets in the central area cannot be sufficiently cooled due to small air flow rate. In this paper, a novel water distribution mode is proposed for the wet cooling tower, in which the water distribution area is divided into four subdomains equally in the radius direction, with the diameters of sprayed water droplets from the inside to the outside of 4 mm, 3 mm, 1 mm and 0.5 mm, respectively. The three-dimensional numerical model of natural draft wet cooling tower is developed and validated by the published data, and the cooling performance with the novel water distribution mode is then obtained. The results show that the air velocity in the central area is significantly increased thus the velocity gets more uniformly distributed with the novel water distribution mode. Besides, the thermal performance in the external area is also improved thanks to the larger contact area between the cooling air and water droplets. By comparing the proposed water distribution with the conventional one, it can be found that the outlet water temperature decreases by up to 0.69 °C, and the tower with the proposed water distribution can achieve better heat and mass transfer performances with a lower air mass flow rate, which can be recommended in engineering applications for an ideal energy efficiency of cold end system.

Factors Affecting Renters’ Electricity Use: More Than Split Incentives

This paper uses data from the 2015 Residential Energy Consumption Survey to explore the extent to which renters’ electricity use in the United States exceeds that of otherwise similar non-renters. Renting households are found to use approximately 9% more electricity than non-renters when controlling for location, socioeconomic, and many appliance-quantity controls. There are multiple factors that explain this extra electricity use, including inferior energy efficiency of appliances, behavioral factors, differences in bill payment responsibilities, and additional reliance by renters on electric space and water heaters. The paper finds that none of these factors are dominant. The phenomenon of renters’ (conditionally) higher electricity use is thus best understood as one that emerges from multiple sources.

Friction stir processing of ZE41 Mg alloy: Optimizing the process parameters

Friction stir processing is a novel processing route used to develop fine grained structures. Processing by FSP is influenced by tool rotational speed, tool travel speed, workpiece temperature, tool tilt angle, etc. Processing at optimum parameters is important to avoid defects and to develop grain refined materials by FSP. In the current research work, ZE41 magnesium alloy was processed by FSP to develop fine grained structure. FSP was done at different tool rotational and travel speeds. Decreased grain size and increased hardness was observed for all FSPed samples. However, variations were clearly observed within the measured grain size, hardness and nugget zone width of the FSPed samples. From Taguchi optimization studies using gray relation analysis; optimum set of parameters which yield smaller grain size and higher hardness were identified. From the results, 1400 rpm and 25 mm/min were observed as optimum. The design model presented in the current study helps to select optimized parameters in producing fine grained ZE41 for upcoming energy efficient applications.

An Improved P-Type Doped Barrier Surface AlGaN/GaN High Electron Mobility Transistor with High Power-Added Efficiency.

An improved P-type doped barrier surface AlGaN/GaN high electron mobility transistor with high power-added efficiency (PDBS-HEMT) is proposed in this paper. Through the modelling and simulation of ISE-TCAD and ADS software, the influence of the P-type doped region on the performance parameters is studied, and the power-added efficiency (PAE) obtained and effectively improved is further verified. The drain saturation current and the threshold voltage of PDBS-HEMT has no major change compared with the traditional structure; the peak transconductance decreases slightly, but the breakdown voltage is significantly enhanced. Furthermore, the gate-source capacitance and gate-drain capacitance are reduced by 14.6% and 14.3%, respectively. By simulating the RF output characteristics of the device, the maximum oscillation frequency of the proposed structure is increased from 57 GHz to 63 GHz, and the saturated output power density is 10.9 W/mm, 9.3 W/mm and 6.4 W/mm at the frequency of 600 MHz, 1200 MHz and 2400 MHz, respectively. The highest PAE of 88.4% was obtained at 1200 MHz. The results show that the PDBS structure has an excellent power and efficiency output capability. Through the design of the P-type doped region, the DC and RF parameters and efficiency of the device are balanced, demonstrating the great potential of PDBS structure in high energy efficiency applications.

MLEE: Method Level Energy Estimation — A machine learning approach

Battery life is one of the main concerns for today’s mobile users. Due to an imbalance in demand and supply of energy in mobile devices, the burden to make battery last longer upon each charge has shifted towards application developers, who, in turn attempt to create energy efficient applications. However, mobile developers lack the tools to detect energy consumption hot-spots in their code. We aim to provide developers with a technique that helps them to precisely locate energy hot-spots at the method-level. In this paper we present MLEE, a novel approach for estimating energy consumption of methods. MLEE uses machine learning models to predict the energy consumption at method-level using software metrics as features. We use the Snapdragon power profiler to measure the energy consumption of applications using the shortest time interval to develop a method-level energy dataset for training machine learning prediction models. We demonstrate that several structural metrics of methods are highly co-related with energy consumption. Thereafter we use these features to predict the energy consumption of methods using linear regression, random forest and decision tree with an average mean-absolute-error of 2.6e−2 J.

Strong, robust cellulose composite film for efficient light management in energy efficient building

Energy-saving materials in buildings enable meaningful reduction of indoor energy consumption and are critical to develop a carbon-neutrality society. Accordingly, lighting in modern buildings should be properly managed toward energy-efficient buildings. Here, we developed a broadband light-management cellulose composite film, composed of 75 wt% cellulose bonded by phenol formaldehyde resin, which shows a high transparency (~86%) and haze (~90%) for effective light propagating and scattering, and more importantly, a superior anti-ultraviolet capability (~83% absorptance and ~17% reflectance), thus enabling a soft, uniform, large areal, and safe illumination of the sunlight in buildings toward a comfortable, healthy yet energy-saving environment. In addition, our cellulose composite film features a strong mechanical strength (140 MPa tensile strength) and superior robustness (e.g., high hydro-stability with a high wet strength of 135 MPa, thermal stability and fire-resistance ability, as well as excellent impact absroption capacity), proving its durability for long-term indoor or outdoor applications. The cellulose composite film is synthesized by a simple and scalable calendaring-like process which can be fully compatible with current paper-making industry. These integrated merits of our cellulose composite film make a promising candidate for energy efficient building applications toward a sustainable society.

Implementation of 32-BIT Pipelined ADC Using 90nm Analog CMOS Technology

After seeing the technological evolution, we have understood about the A/D converter that it is the meeting point of the analog to digital domains. As technology is being continuously scaled down, the transistor sizes have decreased drastically resulting in reduced area and power consumption in the digital domain. The successive approximation ADC is best suitable for low power applications with moderate speed and simple design. Here, the implementation of 32-bit pipelined analog-to-digital converter with the help of successive approximation register based Sub-ADC. The SAR ADC architectures are popular for achieving high energy efficiency and low power applications. But they suffer from resolution and speed limitation. To overcome the speed limitations of SAR ADC, we proposed the implementation of 90nm using CMOS technology of a low power, high speed pipelined analog-to-digital converter (ADC). The capacitive digital-to-analog converter (DAC), two stage CMOS comparator with output inverter of proposed ADC are lower than those of a conventional ADC. To achieve low power and to minimize the size of the input sampling capacitance in order to ease durability.

Paas EUD Tool for Developing Expert Context-Aware Mobile Applications

Context-awareness enables systems to be tailored to the needs of users and their real circumstances at certain times. A noteworthy trend in software development is that an increasing number of software systems are being developed by individuals with expert knowledge in other sectors. Because most of the current context-aware development toolkits are intended for software developers, these types of systems cannot be easily developed by non-technical consumers. The development of tools for designing context-aware frameworks by consumers who are not programming experts but are specialists in the area of implementation would result in faster adoption of such services by businesses. This paper provides a cloud-based framework for people without programming experience to create context-aware mobile applications. The platform can provide a lightweight distribution of packaged applications that allows experts to send specified information to mobile users based on their context data without overlapping between the rules of the application. An energy-efficient mobile application was developed to acquire contextual information from the user device and to create quality data accordingly. The framework adopts Platform as a Service (PaaS) and containerization to facilitate development of context-aware mobile applications by experts in various domains rather than developing a tool for each domain in isolation, while considering multitenancy.

Preparation and properties of capric acid: Stearic acid/hydrophobic expanded perlite-aerogel composite phase change materials

Phase change materials (PCMs) have been applied widely in various energy savings, storage, and efficiency applications, including building and construction, building systems, aerospace, and biological engineering. In order to solve the shortcomings of poor thermal stability and easy leakage of PCMs, a strong adsorbent expanded perlite-aerogel (AEP) composite matrix was prepared and its key thermal properties and effects on PCMs examined. Particularly, when it adsorbed capric-stearic acid, a binary PCM, it reached the level of 200 %. The rate of mass loss after heating could still be less than 1.0 %, indicating that the AEP composite matrix designed here had strong material and thermal stabilities. Various mass ratios of composite components were also tested and compared, and the optimal setting for the best adsorption rate was subsequently determined in this work. Because of these excellent characteristics, this newly designed AEP composite matrix can be used as an appropriate carrier for PCMs for energy savings and efficiency purposes in the building and construction field.

Determination of the spin Hall angle by the inverse spin Hall effect, device level ferromagnetic resonance, and spin torque ferromagnetic resonance: A comparison of methods

The spin torque ferromagnetic resonance (STFMR) is one of the popular methods for measurement of the spin Hall angle, θSH. However, in order to accurately determine θSH from STFMR measurements, the acquired data must be carefully analyzed. The resonance linewidth should be determined to an accuracy of a fraction of an Oe, while the dynamical interaction leading to the measured response consists of the conventional field-induced ferromagnetic resonance (FMR), the spin-torque induced FMR, and the inverse spin Hall effect (ISHE). Additionally, the signal often deteriorates when DC is passed through the device. In this work, we compare the STFMR method with two other FMR-based methods that are used to extract θSH. The first is a device-level FMR, and the second is based on the ISHE. We identify artifacts that are caused by the noise floor of the instrumentation that make the measurement of θSH illusive even when the signal to noise ratio seems to be reasonable. Additionally, we estimate a 10% error in θSH that results from neglecting the magnetic anisotropies as in conventional measurements. Overall, we find the STFMR to be the most robust of the three methods despite the complexity of the interaction taking place therein. The conclusions of our work lead to a more accurate determination of θSH and will assist in the search of novel materials for energy efficient spin-based applications.