Low Input Power Research Articles

Printed and Flexible Microheaters Based on Carbon Nanotubes.

This work demonstrates a cost-effective manufacturing method of flexible and fully printed microheaters, using carbon nanotubes (CNTs) as the heating element. Two different structures with different number of CNT layers have been characterized in detail. The benchmarking has been carried out in terms of maximum operating temperature, as well as nominal resistance and input power for different applied voltages. Their performances have been compared with previous reports for similar devices, fabricated with other technologies. The results have shown that the heaters presented can achieve high temperatures in a small area at lower voltages and lower input power. In particular, the fully printed heaters fabricated on a flexible substrate covering an area of 3.2 mm2 and operating at 9.5 V exhibit a maximum temperature point above 70 °C with a power consumption below 200 mW. Therefore, we have demonstrated that this technology paves the way for a cost-effective large-scale fabrication of flexible microheaters aimed to be integrated in flexible sensors.

Assessment of heat transfer and flow characteristics of a two‐phase closed thermosiphon

AbstractIn this study, comprehensive modeling and simulations were developed and carried out to perform the investigation of the thermal performance of the enclosed thermosiphon through pool boiling in the evaporator sector and the condensation of the liquid film in the condenser part. To simulate these phenomena, the volume of fluid model was utilized. The simulation modeling using the computational fluid dynamics (CFD) technique was validated with existing experimental results, and a good agreement was reached. The simulation results were presented and evaluated in terms of temperature profiles and contours, the volume of fraction contours, and velocity vector distribution. Moreover, the thermal performance (ie, the heat transfer coefficient and thermal resistance) through the thermosiphon operation was analyzed. From the simulation results, it is found that the thermosiphon performance can be improved by the tilt angle and fill ratio. The results indicated that the optimal performance (ie, a high heat transfer coefficient and a low thermal resistance) was attained at a power input of 250 W, tilt angle of 90°, and fill ratio of 0.5. The established CFD simulations effectively predicted the formation of two‐phase flow pattern and boiling and condensation zones with water at a low power input, termed as geyser boiling.

Dual‐band CPW rectenna for low input power energy harvesting applications

A dual-frequency band low input power rectenna is proposed in this study. The rectenna is comprised of a co-planar waveguide (CPW) rectifier integrated with a rectangular split ring antenna loaded by a spiral strip line. A single diode series connection topology is used to miniaturise the losses at low input power. A spiral coil in addition to two short circuit stubs are used as a matching network for maximum power transfer between the antenna and the rectifying circuit. The proposed rectenna operates at low input power with relatively high measured RF-DC conversion efficiency up to 74 % at input power of − 6.5 dBm at the first resonant frequency f 1 = 700 MHz and 70 % at − 4.5 dBm at the second operating frequency f 2 = 1.4 GHz with a resistive load of 1.9 k Ω . The measured rectenna sensitivity (the rectenna ability to receive low power with acceptable conversion efficiency) reaches up to − 20 dBm with a conversion efficiency of 47 and 36 % at f 1 and f 2 , respectively, and a DC output voltage of 0.18 V . The measured efficiency is over 50 % from − 18 to − 3.5 dBm and from − 15 to − 1.5 dBm at f 1 and f 2 , respectively.

Linear-response and simple hot-wire fiber-optic anemometer using high-order cladding mode.

We present a single walled carbon nanotubes (SWCNTs)-coated tilted fiber Bragg grating (TFBG) hot-wire anemometer (HWA) with simple configuration, linear response, and high sensitivity. TFBG is utilized to effectively couple a pumping laser at 1550 nm to the cladding mode that is absorbed by the SWCNTs film immobilized on the fiber surface with good light-heat conversion efficiency. As a result, the TFBG is converted to a "hot wire", and the wind speed can be deduced from the output power of the laser, which is a function of both the wind-induced temperature change and the spectral profile of the cladding mode. The most significant aspect of the HWA system is that we use the Gaussian shape of the high-order TFBG cladding mode to compensate for the inherent nonlinear relationship between the heat loss and the wind speed that is an undesirable characteristic of existing HWA systems. The validity of this novel operating principle was verified theoretically and experimentally. Via careful control of the parameters, a good linear response of the HWA system was achieved, especially for the low wind speed range where nonlinearity was more conspicuous. It was demonstrated that, with a low input power of only 29.3 mW of the pump laser, an R2 value of 0.9927 was obtained in this fiber-optic HWA system with high sensitivity 7.425 dBm / (m/s) and resolution 0.0027 m/s in a small wind speed range (0-2m/s) considering the intensity resolution of OSA and the noise of the pump laser. Furthermore, the system also exhibits a simple and low-cost design with only one laser source and one low-cost power measurement component.

Evaluation of measuring thermal conductivity of isotropic and anisotropic thermally insulating materials by transient plane source (Hot Disk) technique

The transient plane source (TPS) technique, also referred as the Hot Disk method, has been widely used due to its ability to measure the thermal properties of an extensive range of materials (solids, liquids, and powder). Recently, it has been recognized that typical Hot Disk sensors can influence TPS results of thermally insulating materials and lead to an overestimation of thermal conductivity. Although improvements have been proposed, they have not yet been implemented in the commercial TPS, leaving researchers with non-standardized modifications or options provided by a commercial Hot Disk apparatus. An empirical study of thermally insulating materials such as extruded polystyrene (XPS) and aerogel blanket is conducted in order to address the factors that affect the reliability of thermal conductivity k obtained using the commercial TPS apparatus. Sensor size, input power, duration of the measurements, applied pressure, and, in the case of anisotropic materials, heat capacity are investigated, and the results are compared with those using a Heat Flow Meter apparatus. The effect of sensor size on the k value is ascribed to heat loss through connecting leads and is more pronounced in smaller sensors and in materials with lower k values. In the case of XPS and aerogel, the effect becomes minimal for sensors with a radius r ≥ 6.4 mm. The low input power yields a high scattering of the results and should be avoided. Applied contact pressure and the tested region of the specimen play an important role in experiments with low-density fibrous materials due to the large percentage of heat being transferred by radiation and the heterogeneous nature of the samples, respectively. Additionally, the sensitivity of anisotropic measurements to the value of the material’s volumetric heat capacity (ρCp) is shown, emphasizing the need for the precise determination.

Silicon Optical Diode Based on Cascaded Opto-Mechanical Microring Resonators

We propose and experimentally demonstrate a silicon optical diode with high nonreciprocal transmission ratio (NTR) based on three cascaded opto-mechanical microring resonators (MRRs). As half waveguides of the opto-mechanical MRRs are free-hanging, the nonlinear effects (including the thermo-optic effect and opto-mechanical effect) are both enhanced. With low input powers, the transmission characteristics of the opto-mechanical MRRs could be flexibly manipulated by the strong nonlinear effects. More importantly, due to the optimized design of the cascaded MRRs, the NTRs are improved. In the experiment, a high NTR is successfully obtained with a low input power. The proposed optical diode provides a complementary metal-oxide semiconductor (CMOS) compatible solution for on-chip nonreciprocal transmission with dominant advantages of high NTRs, low-power consumption and compact size, which has many significant applications in on-chip optical computing and logic gates.

Applying a repetitive time‐reversal method to reduce input power of a wearable hyperthermia applicator for breast cancer treatment

AbstractIn this article, a hyperthermia healing system is presented for cancer treatment. To alleviate most of the microwave hyperthermia systems problems, such as high input power, complicated beamforming method, unwanted hot spots for superficial tumors, and bulky profile, a simple repetitive time‐reversal method is proposed to design a low power wearable hyperthermia applicator with low hotspots at 915 MHz. The objective of this algorithm is to obtin the desired focusing by the minimum possible number of antennas in an appropriate time and minimum required input power. In this paper, first, a symmetric 11‐element patch array is considered. Then, by applying a repetitive time‐reversal method, the number of elements decreases to 7 for deep and 4 for both superficial and intermediate tumors, respectively. The steady‐state temperature/specific absorption rate focusing and transient thermal analysis are investigated in CST MWS and COMSOL, respectively. The target temperature of 43°C is met after less than 10 minutes. The focusing diameter size varies between 1 and 2 cm depending on the number of elements and arrangements considered for different tumors. Compared to literature, this applicator needs very low input power, produces less unwanted hotspots, improves pationt comfort, reduces treatment cost which all leads to patient treatment persistency. Moreover, it does not need any complicated beamforming method.

Design and analysis of 73-106 GHz CMOS injection-locked frequency divider

ABSTRACT A 73 ~ 106 GHz divide-by-2 injection-locked frequency-divider (ILFD2) using 90 nm CMOS technology is presented. To achieve a wide locking range, an optimal transistor width ratio of the injection transistor (or mixer) and cross-coupled transistors (CCT) is adopted. To enhance the operation frequency, distributed LC network is used as the load of the CCT. To enhance the input sensitivity, an input power matching network is included in the injection transistor. In addition, for further locking ranging enlargement, the inductive peaking and forward-body-bias techniques are used in the injection transistor for raising its quadrature output current (or conversion gain). The ILFD2 consumes 4.92 mW, and achieves an excellent phase noise of – 106.2 dBc/Hz (at 1 MHz offset from the output frequency of 50 GHz). The ILFD2 achieves a wide locking-range of 33 GHz (73–106 GHz (36.9%)), covering the 77 GHz automotive radar frequency band and the 94 GHz imaging radar frequency band. The ILFD2 can be operated at a low input power of – 60 dBm, one of the best input sensitivities ever reported for a W-band CMOS ILFD2. The core area of the ILFD2 is only 0.014 mm2.

Analysis, Design and Implementation of a Fully Integrated Analog Front-End for Microwave RFIDs at 5.8 GHz to Be Used With Compact MIMO Readers

In this paper we present the system and circuit level analysis and feasibility study of applying microwave Radio Frequency Identification (RFID) systems with multipleinput multiple-output (MIMO) reader technology for tracking machining tools in multipath fading conditions of production environments. In the proposed system the MIMO reader interrogates single-antenna tags, and a high RFID frequency of 5.8 GHz is chosen to reduce the size of the reader's antenna array. According to the requirements dictated by the performed system analysis at 5.8 GHz, a low power fully integrated analog frontend (AFE) is designed and fabricated in a standard 65-nm CMOS technology for low power passive transponders. Performance of the Differential Drive Rectifier (DDR) topology as the core of the energy harvesting unit is investigated in detail. A multi-stage DDR power scavenging unit is dimensioned to provide a 1.2 V rectified voltage for 20-30 kQ load range, with a high power conversion efficiency (PCE) for high frequency and low input power level signals. The rectified voltage is then converted to a 1 V regulated voltage for the AFE and the baseband processor with 30 to 50 μW of estimated power consumption. Transistors with standard threshold voltage (VT) have been used for implementation. Measurements of the fabricated multi-stage configuration of the circuit show a maximum PCE of 68.8% at -12.46 dBm, and an input quality factor (Q-factor) of approximately 10. Amplitude-shift keying (ASK) demodulator and backscattering modulator with 80% modulation index, operating according to EPC-C1G2 protocol are applied for data transfer. The AFE consumes less than 1 μW in the reading mode. The AFE tag chip is 0.55 × 0.58 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Nanosheet-Derived Ultrafine CoRuOx@NC Nanoparticles with a Core@Shell Structure as Bifunctional Electrocatalysts for Electrochemical Water Splitting with High Current Density or Low Power Input

A series of ultrafine core@shell electrocatalysts (CoRuOx@NC) are prepared using oleylamine (OA)-passivated metal-oxide nanosheets (CoRuOy@OA) as single precursors. The optimal catalyst Co0.8Ru0.2Ox@NC composed of the N-doped carbon (NC) shell and the endohedral hybrid of metal/metal oxide exhibits excellent catalytic activities in alkaline media with a low overpotential of 36 mV for hydrogen evolution reaction, 278 mV for oxygen evolution reaction, and an ultralow potential of −19 mV for hydrazine oxidation reaction (HzOR) at 10 mA cm–2. When used as both cathode and anode catalysts for overall water splitting, Co0.8Ru0.2Ox@NC drives 10/500 mA cm–2 with a cell voltage as low as 1.55/1.86 V and maintains long-term stability at 500 mA cm–2. Moreover, for HzOR-assisted electrochemical water splitting (EWS), the Co0.8Ru0.2Ox@NC-based electrode couple requires ultralow cell voltages of merely 79/674 mV to deliver 10/100 mA cm–2 with excellent long-term durability at 100 mA cm–2. The success of the present electrocatalyst shall be attributed to the combined effect of minor RuOx incorporation and carbon encapsulation, which results in not only enhanced catalyst conductivity and charge transfer kinetics but also surface-enriched active sites and improved intrinsic catalytic activity. Thus, our work may pave a new opportunity for rational design and facile synthesis of bifunctional electrocatalysts for EWS operated with high current density or low power input.

Experimental thermal/economic/exergetic evaluation of hot/cold water production process by thermoelectricity

Although economic analysis of thermoelectric power generator has been carried out extensively by many researchers, economic reports on the reverse application of thermoelectric (heating/cooling) are completely immature. No experimental-data-based economic evaluation has been carried out before for cooling/heating aim of Peltier effect. Obviously, lack of economic analysis results in incorrect or imperfect decision-making on marketing area of any product. This paper focuses on cold and hot water production by thermoelectricity and provides a comprehensive thermal/economic/exergetic evaluation for said application using recently developed SPECO (Specific Exergy Costing) method. The effect of all thermal/flow and electrical parameters are investigated. The formulation/evaluation process of economic factors is explained step by step to make it ease understanding for the future readers. The results showed that, obtaining for example 1 kWh energy in the form of water cooling or heating is much more cheaper if the input power (DC voltage) of any individual thermoelectric is adjusted in lower value. However, it will take more time to obtain 1 kWh cooling/heating energy when the input power is low. Hence, it is recommended to produce the cold/hot water in no-peak water consumption times with lower input power and store it (instead of cold/hot water production with higher input power through shorter time).

A Wideband Rectenna Using High Gain Fractal Planar Monopole Antenna Array for RF Energy Scavenging

This paper introduces a wideband rectenna that can scavenge ambient wireless power to a range of frequency band from 0.91 GHz to 2.55 GHz efficiently. The proposed rectenna is based on a wideband 2 × 2 fractal monopole antenna array with omnidirectional radiation patterns and high gains of 5 to 8.3 dBi at the desired bands. An improved two-branch impedance matching technique is presented which is designed to enhance the rectifier circuit performance with a relatively low input power ranging from −25 dBm to 10 dBm. Also, a full-wave wideband rectifier that can suitably improve the RF-to-DC power conversion efficiency is designed for the rectenna. A peak efficiency of 76%, 71%, 61%, and 62% is obtained at 950, 1850, 2100, and 2450 MHz, respectively. Measurement results show that a conversion efficiency of 68% has been achieved over an optimal 4.7 kΩ resistor when the simultaneous four-band input power level is −10 dBm. Moreover, an output DC voltage of around 243 mV with voltage varying within 160–250 mV can be achieved by gathering the low ambient wireless power inside laboratory. This study proves that the proposed rectenna can be applied to a range of many low-power electronic applications.

Supercontinuum Generation in Media with Sign‐Alternated Dispersion

AbstractWhen an ultrafast optical pulse with high intensity propagates through transparent material a supercontinuum can be coherently generated by self‐phase modulation, which is essential to many photonic applications in fibers and integrated waveguides. However, the presence of dispersion causes stagnation of spectral broadening past a certain propagation length, requiring an increased input peak power for further broadening. Overcoming such spectral stagnation will be key to achieve practical integrated supercontinuum devices. Here, a concept is presented to drive supercontinuum generation with significantly lower input power by counteracting spectral stagnation via repeatedly alternating the sign of group velocity dispersion along the propagation. The effect is experimentally demonstrated in dispersion alternating fiber in excellent agreement with modeling, revealing almost an order of magnitude reduced peak power compared to uniform dispersion. Calculations also reveal a similar power reduction with integrated optical waveguides, simultaneously with a significant increase in flat bandwidth, which is important for on‐chip broadband photonics.

Multiple shots averaging in laser flash measurement.

The laser flash method is a well-known procedure to determine the thermal diffusivity of a wide range of materials. However, in some cases there is the need of limiting the input power, measuring materials with high thermal capacity, or investigating thick samples. These conditions lead to a reduction of the signal-to-noise ratio. Therefore, we propose a new laser flash control and data acquisition system, that is able to repeat multiple times the emission of the laser impulse and the measurement of the thermal response of the specimen. With the average of several measurements, it is possible to obtain a decrease of the noise when working with low power inputs.

Improved transmission length in the presences of ambient noise and scintillation effect using duobinary modulation in 40 Gbps free space optical channel

AbstractFree space optical (FSO) communication has gained significant popularity in recent years due to large bandwidth, license‐free spectrum, high data rates, less power consumption, and low mass requirements. However, system performance strongly depends on atmospheric conditions and ambient noise. In this letter, the duobinary modulation technique is applied and the system performance is investigated in the presence of ambient noise. The system is evaluated on the basis of Q‐factor, eye diagram, input power, transmission distance, and bit error rate. A significant improvement is observed in the presence of noise while using duobinary modulation. This study exploits extensive simulations to investigate the performance of the system. All simulations are performed for a single link of FSO communication network having a data rate of 40 Gbps in the Optisystem simulator and ambient noise is created using LEDs. After the exhaustive set of simulations, a significant improvement in transmission length is observed. It is also observed that at low input power, doubinary modulation provides better results when compared with on‐off keying (OOK) format. Scintillation effect has also be observed for doubinary modulation and compared with OOK modulation format. It is concluded that doubinary modulation provides better results in the presence of low and moderate scintillation.

Two-dimensional simulation of near-longitudinally pumped dye laser amplifiers.

Simulations of near-longitudinally pumped dye laser amplifiers are demonstrated in this paper. We developed a two-dimensional model that considers the amplified spontaneous emission (ASE). The influence of the angle between the input beam and pump beam on the extraction efficiency, ASE, and heating process of the amplifiers is investigated. It was found that for the main amplifiers with high pump and input powers, both the extraction efficiency and the ASE are insensitive to variations in the pump angle. However, for preamplifiers with a low input power, the increase in the angle causes a more significant loss in efficiency and a higher ASE generation. For the heating caused by light, the influence of the pump angle is insignificant. The results suggest that near-longitudinal pumping is appropriate for main amplifiers but not for preamplifiers.

Altered Grey Wolf Optimization and Taguchi Method with FEA for Six-Phase Copper Squirrel Cage Rotor Induction Motor Design

This paper presents an altered grey wolf optimization, the Taguchi method, and finite element analysis (FEA) with two-phase multi-objective optimization for the design of a six-phase copper squirrel cage rotor induction motor (SCSCRIM). The multi-objective optimization design with high-performance property aims to achieve lower starting current, lower losses, lower input power, higher efficiency, higher output torque, and higher power factor. The multi-objective optimization design with high-performance property using the altered grey wolf optimization, the Taguchi method, and FEA in the first-phase program is used for minimizing the starting current, stator iron loss, stator copper loss, and input power. The multi-objective optimization design with high-performance property using the altered grey wolf optimization, the Taguchi method, and FEA in the second-phase program is used for maximizing the efficiency, output torque, and power factor. Finally, the proposed skill with higher performances is evaluated and verified via a two-phase program design and some performance tests.

HMDSO-Based Thin Plasma Polymers as Corrosion Barrier Against NaOH Solution

HMDSO-based films with excellent corrosion barrier properties against strong alkaline solutions were deposited on chemically non-resistant SiOx barrier coatings, which were previously applied on polished gold-coated Si-Wafers and PET films for coating analysis. The plasma process parameters are seen to have a strong influence on the achievable corrosion barrier properties of the plasma polymers. Coatings, which were applied in a pulsed microwave plasma with low mean power input, exhibit a substantially higher resistance against NaOH aqueous solution in electrochemical tests than those applied in higher energy plasmas. An analysis of the coatings revealed that the great difference in chemical resistivity of the investigated coatings can be explained by their chemical composition as well as their nano-porosity and surface topography. XPS measurements indicate that a higher organic content in the films contributes to their chemical resistivity. FTIR measurements showed that an ordered Si-O-Si network with methyl groups, which promote steric shielding, lead to superior corrosion resistance. Furthermore, a correlation of protective performance and nano-porosity was found in cyclic voltammetry measurements. Coatings with good corrosion protection proved to be initially pore free and even after 30 min of exposure to NaOH, an open pore surface of only 2% can be measured. Finally, measurements of the oxygen transmission rate (OTR) of coated PET substrates showed that the barrier of a coating system comprising a non-resistant barrier layer and a protective top coat can withstand up to at least 90 min of exposure to hot NaOH solution without significant loss in barrier performance. After this, the barrier of the system is gradually reduced. To slow down this reduction process, a multilayer approach proved to be effective.

(Invited) Polyoxometalate Electron-Coupled-Proton Buffers for Electrochemical and Photo-Electrochemical Water Splitting and Beyond

The storage of renewably-generated energy as hydrogen via the electrolysis of water is a fundamental cornerstone of a sustainable hydrogen economy. Conventional electrolysers usually require stable power inputs in order to operate effectively and safely and so may be unsuited to harnessing renewable power, which is often intermittent and diffuse. Electrolysis mediated by Electron-Coupled-Proton Buffers (see, for example: Nature Chem. 2013, 5, 403-409; Science, 2014, 345, 1326-1330; J. Am. Chem. Soc. 2016, 138, 6707–6710; Joule, 2018, 2, 1390-1395) has the potential to overcome some of the challenges surrounding electrolysis using low and/or sporadic power inputs (especially those related to gas crossover) as the use of Electron-Coupled-Proton Buffers allows the oxygen and hydrogen evolution reactions to be completely decoupled from one another. In this talk, we shall investigate these claims for decoupled electrolysis (Electrochimica Acta, accepted for publication) and also explore the use of Electron-Coupled-Proton Buffers (ECPBs) as redox mediators in high energy-density redox flow batteries (Nature Chem. 2018, 10, 1042-1047) and for chemical hydrogenation reactions (Chem. Commun. 2018, 54, 1093-1096). Figure 1

Non-reciprocal transmission of microwave acoustic waves in nonlinear parity–time symmetric resonators

Acoustic waves have emerged as versatile on-chip information carriers with applications ranging from microwave filters to transducers. Nonreciprocal devices are desirable for the control and routing of high-frequency phonons. This is challenging, however, due to the linear response of most acoustic systems. Here, we leverage the strong piezoelectricity of lithium niobate to demonstrate fully tunable gain, loss, and nonlinearity for surface acoustic waves using electric circuitry. This allows the construction of a nonlinear acoustic parity-time-symmetric system and enables nonreciprocal transmission. We achieve a nonreciprocity of 10 decibels for a 200-MHz acoustic wave at a low input power of 3 $\mu$W and further demonstrate one-way circulation of acoustic waves by cascading nonreciprocal devices. Our work illustrates the potential of this piezoelectric platform for on-chip phononic processing and exploration of non-Hermitian physics.