Tunable Ratio Research Articles

A real-time tunable arbitrary power ratios graphene based power divider

A real-time tunable arbitrary power ratios graphene based power divider

Utilization of CO2 as a carbon source for production of CO and syngas using a ruthenium(II) electrocatalyst

A new mononuclear Ru(II) complex, [Ru(phen-dione)(CH3CN)4](PF6)2 (phen-dione = 1,10-phenanthroline-5,6-dione), (I), has been synthesized and structurally characterized revealing a distorted octahedral environment around the central ruthenium(II) cation. The electrocatalytic activity of the complex was investigated for the reduction CO2 to CO in an acetonitrile solution using cyclic voltammetry under different reaction conditions (concentration of electrocatalyst, temperature, and scan rate). An increase in the complex concentration, or the scan rate led to a higher CO2 reduction peak current. Moreover, the electrocatalytic activity of (I) decreased at lower temperatures, because the activation energy is inversely temperature-dependent. Further, (I) was used for the electrocatalytic reduction of CO2 to CO and simultaneous reduction of H2PO4– as a hydrogen source to produce syngas with a tunable mole ratio of H2:CO by changing and controlling the H2PO4– concentration whereby the mole ratio of H2:CO increases with increasing amount of added H2PO4–. Consequently, the produced syngas had a wide range with respect to the H2:CO mole ratio (0–2.4). The proposed mechanisms for the electrocatalytic reduction of CO2 to CO and H2 evolution from H2PO4– in the presence of (I) were confirmed using density functional theory (DFT) calculations.

High-precision, resistor less gas pressure sensor and instrumentation amplifier in CNT technology

In this paper, a new high-precision, pressure sensor for sensing gas molecules using a controllable voltage-mode instrumentation amplifier (VMIA) in carbon nanotube field-effect transistor (CNTFET) technology is designed. The sensing mechanism is based on the applied force by Oxygen atoms on the surface of the carbon nanotube (CNT), which is considered as a movable electrode of sensing capacitor. The sensing mechanism is simulated in ANSYS which justifies the variations of sensing capacitance, while the sensor’s output voltage is applied to an accurate instrumentation amplifier (IA) via a switched-capacitor sensor driver. Therefore, due to the controllability of the transconductance and gain parameters of a CNTFET, the IA circuit provides a constant and controllable differential gain of up to 52 dB in a flat −3dB bandwidth of up to 3.6 MHz, which provides a tunable common-mode rejection ratio (CMRR) of up to 121 dB in a 1.8 GHz flat, −3dB frequency bandwidth. Moreover, due to the use of the differential pair stage, the total harmonic distortion (THD) value is obtained less than 0.67%. Finally, the proposed IA circuit consumes only 45.1 µW with a 22.52 nV/√Hz equivalent input referred noise value at ±0.5 V supply.

Methods for Extended Tunability in Quadrature Oscillators Based on Enhanced Electronic Control of Time Constants

New methods for extending the tunability range in second-order voltage-controlled oscillators (VCOs) with quadrature outputs are presented and compared in this paper. Linear dependence is the most common type of relation between frequency of oscillations (FO) and control voltage (or current) in communication subsystems (VCOs). However, there are other nonlinear types of dependencies that are advantageous (quadratic and cubic) and should be further studied. Positions of controllable blocks within the structure of the oscillator (providing parameters influencing time constants of integrators) in two scenarios are studied together. The impact of controllable parameters of these additional elements on FO as well as on produced output signal levels is evaluated. The simulation and experimental results are shown to confirm expected behavior of solutions in the case of the quadratic type of control of FO. Nowadays, standard linear control offers a tunability ratio 10:1 (for the same ratio of parameters that control the FO) only. However, in this paper, the experimental tests yield a tunability ratio 80:1 (50 kHz–4 MHz) for dc control voltage within the range 0.175–1.75 V (10:1). The presented approach is very beneficial for low supply voltage systems requiring a wide range of tunability and also for utilizing active devices having limited range of adjustability of their controllable parameters while still requiring wide tunability.

Tunable atom-light beam splitter using electromagnetically induced transparency

With electromagnetically induced transmission (EIT), an optical field can be converted into collective atomic excitation and stored in the atomic medium through switching off the strong-coupling field adiabatically. By varying the power of the coupling pulse, we can control the ratio between the transmitted optical field and the stored atomic mode. We use a cloud of cold $^{85}\mathrm{Rb}$ atoms prepared in magneto-optical trap as the experimental platform. Based on a model of EIT dark-state polariton, we consider the real case where the atomic medium has a finite length. The theoretical calculation gives numerical results that agree well with the experimental data. The results show that the ratio can be changed approximately from 0 to 100%, when the maximum power of the coupling pulse (the pulse length is 100 ns) varies from 0 to 20 mW, in the cold atomic ensemble with an optical depth of 40. This process can be used to achieve an atom-light hybrid beam splitter with tunable splitting ratio and thus find potential application in interferometric measurement and quantum information processing.

In situ glow discharge plasma electrolytic synthesis of reduced TiO2 for enhanced visible light photocatalysis

Reduced titanium dioxide (TiO2−x) due to its extraordinary visible light absorption has been widely investigated in photodegradation and water splitting nowadays. However, conventional routes to synthesize reduced TiO2 usually demand multiple preparation steps, harsh controlled conditions or expensive facilities. Here we developed a single-step in situ approach to prepare the gray TiO2−x nanoparticles (sub-10 nm) effectively by the glow discharge plasma electrolysis (GDPE) under atmospheric pressure. The co-existence of self-doped oxygen vacancies and Ti3+ in the generated TiO2−x nanoparticles is demonstrated by electron paramagnetic resonance (EPR). The tunable ratio of bulk/surface defect can be realized by controlling the glow discharge power directly. It should be noticed that Ti3+ in the synthesized TiO2−x are quite stable in ambient air. The UV–vis spectra of gray TiO2−x show an enhanced visible light absorption, which leads to high visible-light photocatalytic activity. Moreover, the as-prepared TiO2−x after 6 months storage still shows excellent stability during photocatalytic reactions. Owing to its simplicity and effectivity, this preparation method with GDPE should provide a large-scale production for TiO2−x with high photoactivity.

On the Use of Tunable Power Splitter for Simultaneous Wireless Information and Power Transfer Receivers

The use of a tunable power splitter (PS) as a constituent component of a simultaneous wireless information and power transfer (SWIPT) system is discussed. Two varactor diodes are used to achieve a tunable output power ratio P2 : P3 varying from 1 : 1 to 1 : 10 under good matching conditions. The SWIPT system that operates at 2.4 GHz consists of a typical patch antenna, cascaded with the tunable PS, and a voltage doubler rectifier. The constituent components were implemented and tested as stand-alone devices and were subsequently combined in a measurement system using interconnectors. The effect of the tunable PS was explored with respect to the SNR measurements on the port that is intended for the information decoding receiver and the DC voltage measurements on the termination load of the rectifier that is connected directly on the energy harvesting port of the tunable PS. A spectrum analyzer is used for the SNR measurements while the input power is controlled using a signal generator. Both wireless power transmission and on-board measurements verify that the harvested energy can be maximized by using the minimum SNR at the information decoding branch at the expense of DC power consumption required for the biasing of the varactor diodes.

Immobilized Pd-Ag bimetallic nanoparticles on polymeric nanofibers as an effective catalyst: effective loading of Ag with bimetallic functionality through Pd nucleated nanofibers

Here, we present a precise process for synthesizing Pd-Ag bimetallic nanoparticles (NPs) onto polymeric nanofibers by decorating Pd-NPs through atomic layer deposition followed by a chemical reduction process for tagging Ag nanostructures with bimetallic functionality. The results show that Pd-NPs act as a nucleation platform for tagging Ag and form Pd-Ag bimetallic NPs with a monodisperse nature with significant catalytic enhancement to the reaction rate over the bimetallic nature of the Pd-Ag ratio. A Pd-NP decorated polymeric nanofibrous web acts as an excellent platform for the encapsulation or interaction of Ag, which prevents agglomeration and promotes the interaction of Ag ions only on the surface of the Pd-NPs. We observed an effective reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) by sodium borohydride (NaBH4) to access the catalytic activity of Pd-Ag bimetallic NPs on a free-standing flexible polymeric nanofibrous web as a support. The captive formation of the polymeric nanofibrous web with Pd-Ag bimetallic functionality exhibited superior and stable catalytic performance with reduction rates of 0.0719, 0.1520, and 0.0871 min−1 for different loadings of Ag on Pd decorated nanofibrous webs such as Pd/Ag(0.01), Pd/Ag(0.03), and Pd/Ag(0.05), respectively. The highly faceted Pd-Ag NPs with an immobilized nature improves the catalytic functionality by enhancing the binding energy of the 4-NP adsorbate to the surface of the NPs. With the aid of bimetallic functionality, the nanofibrous web was demonstrated as a hybrid heterogeneous photocatalyst with a 3.16-fold enhancement in the reaction rate as compared with the monometallic decorative nature of NaBH4 as a reducing agent. The effective role of the monodisperse nature of Pd ions with an ultralow content as low as 3 wt% and the tunable ratio of Ag on the nanofibrous web induced effective catalytic activity over multiple cycles.

3D Long-Range Triplet Migration in a Water-Stable Metal-Organic Framework for Upconversion-Based Ultralow-Power in Vivo Imaging.

Triplet-triplet annihilation upconversion (TTA-UC) has gained increasing attention because it allows for harvesting of low-energy photons in the solar spectrum with high efficiency in relevant applications including solar cells and bioimaging. However, the utilization of conventional TTA-UC systems for low-power bioapplications is significantly hampered by their general incompatibility and low efficiency in aqueous media. Herein we report a metal-organic framework (MOF) as a biocompatible nanoplatform for TTA-UC to realize low-power in vivo imaging. Our MOF consists of a porphyrinic sensitizer in an anthracene-based Zr-MOF as a TTA-UC platform. In particular, closely aligned chromophores in the MOF facilitate a long-range 3D triplet diffusion of 1.6 μm allowing efficient energy migration in water. The tunable ratio between sensitizer and annihilator by our synthetic method also allows an optimization of the system for maximized TTA-UC efficiency in water at a very low excitation power density. Consequently, the low-power imaging of lymph node in a live mouse was successfully demonstrated with an excellent signal-to-noise ratio (SNR > 30 at 5 mW cm-2).

Next generation smart window display using transparent organic display and light blocking screen.

Transparent organic light emitting diodes (TOLED) have widespread applications in the next-generation display devices particularly in the large size transparent window and interactive displays. Herein, we report high performance and stable attractive smart window displays using facile process. Advanced smart window display is realized by integrating the high performance light blocking screen and highly transparent white OLED panel. The full smart window display reveals a maximum transmittance as high as 64.2% at the wavelength of 600 nm and extremely good along with tunable ambient contrast ratio (171.94:1) compared to that of normal TOLED (4.54:1). Furthermore, the performance decisive light blocking screen has demonstrated an excellent optical and electrical characteristics such as i) high transmittance (85.56% at 562nm) at light-penetrating state, ii) superior absorbance (2.30 at 562nm) in light interrupting mode, iii) high optical contrast (85.50 at 562 nm), iv) high optical stability for more than 25,000 cycle of driving, v) fast switching time of 1.9 sec, and vi) low driving voltage of 1.7 V. The experimental results of smart window display are also validated using optical simulation. The proposed smart window display technology allows us to adjust the intensity of daylight entering the system quickly and conveniently.

Asymmetric diffraction by atomic gratings with optical PT symmetry in the Raman-Nath regime

We propose and analyze an efficient scheme for the lopsided Raman-Nath diffraction of one-dimensional ($1\mathrm{D}$) and two-dimensional ($2\mathrm{D}$) atomic gratings with periodic parity-time ($\mathcal{PT}$)-symmetric refractive index. The atomic grating is constructed by the cold-atomic vapor with two isotopes of rubidium, which is driven by weak probe field and space-dependent control field. Using experimentally achievable parameters, we identify the conditions under which $\mathcal{PT}$-symmetric refractive index allows us to observe the lopsided Raman-Nath diffraction phenomenon and improve the diffraction efficiencies beyond what is achievable in a conventional atomic grating. The nontrivial atomic grating is a superposition of an amplitude grating and a phase grating. It is found that the lopsided Raman-Nath diffraction at the exceptional point (EP) of $\mathcal{PT}$-symmetric grating originates from constructive and destructive interferences between the amplitude and phase gratings. Furthermore, we show that the $\mathcal{PT}$-phase transition from unbroken to broken $\mathcal{PT}$-symmetric regimes can modify the asymmetric distribution of the diffraction spectrum and that the diffraction efficiencies in the non-negative diffraction orders can be significantly enhanced when the atomic grating is pushed into a broken $\mathcal{PT}$-symmetric phase. In addition, we also analyze the influence of the grating thickness on the diffraction spectrum. Our scheme may provide the possibility to design a gain-beam splitter with tunable splitting ratio and other optical components in integrated optics.

Compact Design of Planar Quadrature Coupler With Improved Phase Responses and Wide Tunable Coupling Ratios

This paper presents a compact planar tunable quadrature coupler with improved phase responses. Wide coupling-tuning ratio is achieved by using two varactors loaded on the center of the transmission lines of the modified coupler. Closed-form equations are derived for design parameters. For verification, a 1-GHz tunable coupler is designed and measured. The measured results agree well with the simulated ones. The measured power-dividing ratio can be tuned in a range from 16.2 to −35 dB (from 42 to 3.2E-4) with better than 20-dB return loss and isolation, while the phase imbalance is smaller than 10°. The coupler size is $0.21\lambda \text{g}\,\,\times \,\,0.08\lambda \text{g}$ and reduced by 73.1% compared with the conventional branch-line coupler. The theoretical analysis shows that the phase imbalance and insertion loss are mostly caused by the loss from varactors. Then, a tunable coupler with improved phase and loss responses is proposed, where the additional phase difference and insertion loss resulting from the varactors are compensated for by introducing a negative resistance from the negative impedance converter. Measured results of a demonstrative 1-GHz coupler show a power-dividing ratio tuning range from 24.4 to −22.2 dB (from 275.4 to 6E-4) while maintaining 20-dB return loss and isolation. The phase imbalance is smaller than 1° and the insertion loss is improved by 1 dB and nearly close to theoretical values across the tuning range.

Periodic Porous Alloyed Au-Ag Nanosphere Arrays and Their Highly Sensitive SERS Performance with Good Reproducibility and High Density of Hotspots.

Periodic porous alloyed Au-Ag nanosphere (NS) arrays with different periodic lengths and tunable composition ratios were prepared on Si substrates on a large scale (∼cm2) using stepwise metal deposition-annealing and subsequent chemical corrosion from a monolayer of colloidal polystyrene (PS) microspheres as the initial template. The porous alloyed Au-Ag NSs possessed a high porosity and bicontinuous morphology composed of hierarchically interconnected ligaments, which were obtained from an optimized dealloying process in nitric acid. Interestingly, when the dealloying time was prolonged, the average size of the porous alloyed NSs slightly decreased, and the width of the ligaments gradually increased. The periodic length of the array could be facilely changed by controlling the initial particle size of the PS template. Moreover, the porous alloyed Au-Ag NS arrays were explored as a platform for the surface-enhanced Raman scattering (SERS) detection of 4-aminothiophenol (4-ATP) and exhibited excellent reproducibility and high sensitivity because of the periodic structure of the arrays and the abundance of inherent "hotspots". After optimization experiments, a low concentration of 10-10 M 4-ATP could be detected on these porous Au-Ag NS array substrates. Such highly reproducible SERS activity is meaningful for improving the practical application of portable Raman detection equipment.

Nanoalloy Materials for Chemical Catalysis.

Nanoalloys (NAs), which are distinctly different from bulk alloys or single metals, take on intrinsic features including tunable components and ratios, variable constructions, reconfigurable electronic structures, and optimizable performances, which endow NAs with fascinating prospects in the catalysis field. Here, the focus is on NA materials for chemical catalysis (except photocatalysis or electrocatalysis). In terms of composition, NA systems are divided into three groups, noble metal, base metal, and noble/base metal mixed NAs. Their design and fabrication for the optimization of catalytic performance are systematically summarized. Additionally, the correlations between the composition/structure and catalytic properties are also mentioned. Lastly, the challenges faced in current research are discussed, and further pathways toward their development are suggested.

Strengthening nanocomposite magnetism through microemulsion synthesis

The magnetic strength and versatility of heterostructures generated via a simple microemulsion cluster-formation technique is demonstrated. This approach allows optimization of individual component magnetic nanoparticles prior to heterostructuring, expediting the discovery and optimization of hybrid magnetic materials. The efficacy of this method is validated through a magnetic study of nanoparticle clusters combining antiferromagnetic CoO and superparamagnetic CoFe2O4 nanoparticles with tunable particle ratio and size. An enhancement of coercivity compared with pure CoFe2O4 nanoparticles indicates that close interparticle contacts are achieved. Upon annealing, an exchange bias field of 0.32 T was observed—over twice that achieved in any other colloidally-synthesized system. Additionally, the unique microstructure is defined during cluster formation and thus protects magnetic coercivity during the annealing process. Overall, this work demonstrates a general approach for quickly exploring magnetic parameter space, designing interparticle functionality, and working towards the construction of high-value bulk magnets with low materials and processing cost.

Gold Nanorods Conjugated Porous Silicon Nanoparticles Encapsulated in Calcium Alginate Nano Hydrogels Using Microemulsion Templates

Porous silicon nanoparticles (PSiNPs) and gold nanorods (AuNRs) can be used as biocompatible nanocarriers for delivery of therapeutics but undesired leakage makes them inefficient. By encapsulating the PSiNPs and AuNRs in a hydrogel shell, we create a biocompatible functional nanocarrier that enables sustained release of therapeutics. Here, we report the fabrication of AuNRs-conjugated PSi nanoparticles (AuNRsPSiNPs) through two-step chemical reaction for high-capacity loading of hydrophobic and hydrophilic therapeutics with photothermal property. Furthermore, using water-in-oil microemulsion templates, we encapsulate the AuNRsPSiNPs within a calcium alginate hydrogel nanoshell, creating a versatile biocompatible nanocarrier to codeliver therapeutics for biomedical applications. We find that the functionalized nanohydrogel effectively controls the release rate of the therapeutics while maintaining a high loading efficiency and tunable loading ratios. Notably, combinations of therapeutics coloaded in the functionalized nanohydrogels significantly enhance inhibition of multidrug resistance through synergism and promote faster cancer cell death when combined with photothermal therapy. Moreover, the AuNRs can mediate the conversion of near-infrared laser radiation into heat, increasing the release of therapeutics as well as thermally inducing cell damage to promote faster cancer cell death. Our AuNRsPSiNPs functionalized calcium alginate nanohydrogel holds great promise for photothermal combination therapy and other advanced biomedical applications.

Surface-Plasmon-Enhanced Photo-electrocatalytic Ethylene Glycol Oxidation Based on Highly Open AuAg Nanobowls

Plasmonic metal nanocatalysts can be employed to efficiently boost the conventional catalytic reaction through the energy of photons. This work demonstrates a facile ultrasonic-assisted galvanic replacement method to successfully fabricate the highly open AuAg nanobowls with tunable atomic ratio, which act as the catalytically active site and the light absorbers simultaneously. By virtue of the synergistic and electronic effect between Au and Ag, as well as unique bowl-like structure, the resulted AuAg nanobowls exhibit superior electrocatalytic performances toward ethylene glycol oxidation than that of the bare Au. More interestingly, such AuAg nanobowls also show the surface plasmon resonance (SPR)-induced enhancement of electrocatalytic performances when the modified electrodes are upon the visible light irradiation, 2.3 times higher than that in the traditional ambient electrocatalytic oxidation. This finding opens a new way for designing a myriad of plasmonic metal nanocatalysts with desirable nanost...

Mechanically tunable integrated beamsplitters on a flexible polymer platform

We report the development of a monolithic, mechanically tunable waveguide platform based on the flexible polymer polydimethyl siloxane. Such devices preserve single mode guiding across a wide range of linear geometric distortions. This enables the realization of directional couplers with tunable splitting ratios via elastic deformation of the host chip. We fabricated several devices of this type and verified their operation over a range of wavelengths, with access to the full range of input/output ratios. The low cost and relative ease of fabrication of these devices via a modified imprint lithographic technique make them an attractive platform for investigation of large scale optical random walks and related optical phenomena.

Silicon photonic integrated circuit for fast and precise dual-comb distance metrology.

We demonstrate an optical distance sensor integrated on a silicon photonic chip with a footprint of well below 1 mm2. The integrated system comprises a heterodyne receiver structure with tunable power splitting ratio and on-chip photodetectors. The functionality of the device is demonstrated in a synthetic-wavelength interferometry experiment using frequency combs as optical sources. We obtain accurate and fast distance measurements with an unambiguity range of 3.75 mm, a root-mean-square error of 3.4 µm and acquisition times of 14 µs.

Cu nanoparticles decorating rGO nanohybrids as electrocatalyst toward CO2 reduction

Cu-based composites with different compositions and construction can seriously influence its electrocatalytic performance toward CO2 reduction reaction (CO2RR). Herein, we report a microwave-assistant route to prepare Cu nanoparticles decorating reduced graphene oxide (CuNPs/rGO) nanohybrids, which are characterized by a variety of techniques, demonstrating that Cu nanoparticles coupling with CuxO nanoparticles were uniformly anchored on the surface of rGO, as well as the existence of grain boundaries. The CuNPs/rGO composites are studied as electrocatalyst for CO2RR and show a favorable electrocatalytic activity toward CO2RR with an onset potential of −0.9V, corresponding to about only 190mv overpotential for CO generation. Besides with a small amount of HCOOH (<5%), H2 and CO are the main CO2 reduction products with a tunable ratio of from 1.16:1 to 6.38:1 by changing the applied potentials. The gaseous products with various ratio of H2 to CO can be potentially used as syngas to produce more valuable products in industry. This work demonstrates a simple, facile and effective way to improve the electrocatalytic CO2RR performance of Cu-based composites.