Gain Drop Research Articles

Impact of temperature on the linewidth enhancement factor of chirped InAs/InP broadband quantum-dash lasers around 1610 nm

We report on the effect of temperature on the differential gain, differential refractive index, and linewidth enhancement factor (α-factor) of ∼1610-nm chirped barrier thickness multistack InAs quantum-dash (Qdash)-in-a-well laser diodes with an extended active region inhomogeneity. By employing Hakki–Paoli method, the performance is found to be comparable at a lower temperature region (16°C to 25°C), exhibiting higher differential gain and lower α-factor values of ∼0.7 ± 0.1 cm − 1 mA − 1 and ∼2.6 ± 1.0, respectively, at gain maximum. At higher temperatures of 25°C to 35°C, the performance degrades mainly due to drop of the differential gain at a rate of ∼0.03 cm − 1 mA − 1 ° C − 1 and α-factor values reaching ∼4.7 ± 2.0 at 40°C. The room temperature (20°C) measured values are in good agreement with the literature, and we qualitatively explain the temperature influence on these results from the highly inhomogeneous Qdash system viewpoint. This study will assist in further optimization of these nanostructure-based high active region gain laser devices that are promising candidates in L-band optical communications, capable of providing low-frequency chirp and high-performance operation.

Phased Transmitarray Antennas for 1-D Beam Scanning

A transmitarray antenna (TAA) fed by a phased array antenna (PAA) for one-dimensional (1-D) beam scanning is proposed at 10 GHz in this letter. The TAA is composed of two types of elements, i.e., the hexagonal subwavelength low-pass elements as well as the pure dielectric ones. The PAA feed is a 1-D printed dipole array loaded with the short-circuited dummy ones. The proposed PAA-fed TAA, with a feeding-distance-to-TAA-diameter ratio ( H / D ) of mere 0.375, achieves a peak simulated gain of 25.6 dBi at 0° scanning (corresponding to peak aperture efficiency of 57.5%) and a 3.13 dB gain drop for ±30° beam scanning, along with a ∼2 dB beam crossover. The measured results agree reasonably well with the simulated ones, validating the proposed design.

Visual Input Is the Main Trigger and Parametric Determinant for Catch-Up Saccades During Video Head Impulse Test in Bilateral Vestibular Loss.

Patients with vestibular deficit use slow eye movements or catch-up saccades (CUS) to compensate for impaired vestibulo-ocular reflex (VOR). The purpose of CUS is to bring the eyes back to the visual target. Covert CUS occur during high-velocity head rotation and overt CUS are generated after head rotation has stopped. Dynamic visual acuity is improved with an increased rate and gain of CUS. Nevertheless, the trigger and the parametric determinants of CUS are still under debate. To clarify the underlying mechanism, especially the visual contribution, we analyzed the number, amplitude and latencies of the CUS in relation with the extent of VOR deficiency. The head and eye movements were recorded in 17 patients with bilateral vestibular loss (BVL) and in 33 subjects with normal VOR gain using the Video Head Impulse Test (vHIT) in two conditions: with visible target and in darkness with an imaginary target. Our study shows that in darkness without visible target the number of CUS is significantly reduced and the relationship between the amplitude of CUS and gaze position error is lost. Results showed that there is a correlation between the number of CUS and the drop in VOR gain. CUS occurring during the head movement and when the head remained still were not always sufficiently accurate. Up to four consecutive CUS could be required to bring eyes back to the visible target. A positive correlation was found between the amplitude of overt saccades with visible target and the gaze position error, namely the remaining eye movement to reach the target. These results suggest that the visual inputs are the main trigger and parametric determinant of the CUS or at least the presence of a visual target is necessary in most cases for a CUS to occur.

Ultrafast X-Ray Detector and its Gain Uniformity

An ultrafast x-ray detector consisted of an electron pulse time-dilation device, a combined electromagnetic lens system, a microchannel plate (MCP) gated imager, and an electrical pulse generator is reported. The time-dilation device is used to magnify the temporal width of the electron beam created from the photo-cathode (PC), and then the combined electromagnetic lens system images the dilated electron beam onto the MCP. Finally, the MCP imager samples the dilated electron signal and outputs corresponding visible light. A measured temporal resolution of 80 ps for the detector is achieved while the electron pulse is not dilated. The resolution is improved to 12 ps while an excitation pulse with 3.1 V/ps rising edge gradient is used to drive the PC to dilate the electron pulse. Moreover, the gain uniformity of the detector is also tested, which shows the gain is decreased gradually with the excitation pulse propagating on the PC and the drop in gain is about $1.7\times $ .

Study of the space charge effect in straw tube detectors for the PANDA experiment

The straw tube detectors in the PANDA experiment will work in high particle fluxes reaching up to 25 kHz/cm2. We performed measurement of the gas gain drop in the PANDA straws due to the space charge effect expected at the high particle fluxes. The applied experimental method and obtained results are presented and are compared with calculations of the gas gain drop based on known mobility of positive ions.

A Cylindrical Lens Antenna With Extremely Flat Beams

This paper presents an extremely flat-beam cylindrical lens antenna with a 180 mm ($36~\lambda$ ) diameter lens at 60 GHz. The parameters of lens antennas in the horizontal plane i.e. dielectric constants, radii, and focal length are optimized to widen beams in the vertical plane while obtaining pencil beams in the horizontal plane. The optimization procedure consists of a theoretical method and differential evolution (DE) algorithm. This beam-widening idea is analyzed and proved to be feasible owing to cylindrical apertures, which is quite different from the results of antennas with planar apertures. Then, the permittivity distribution which results in an extremely flat beam is investigated and shows a novel S-shape rather than following either the law of modified Luneberg lens or the Luneberg's Law. Finally, the proposed lens antenna is fabricated and measured. At the design frequency of 60 GHz, the measured 3-dB E- and H-plane beamwidths separately are 100.4° and 2.3°. As compared to the gain peak, the measured and simulated gain drop at ±60° in the E-plane are less than 4 dB and 5 dB, respectively. Measured results show good agreements with the simulated results, thus validating the extremely flat beam of the proposed lens antenna and the effectiveness of the optimization procedure.

Cryogenic Characterization of RF Low-Noise Amplifiers Utilizing Inverse-Mode SiGe HBTs for Extreme Environment Applications

The cryogenic performance of radiation-hardened radio-frequency (RF) low-noise amplifiers (LNAs) is presented. The LNA, which was originally proposed for the mitigation of single-event transients (SETs) in a radiation environment, uses inverse-mode silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) in its core cascode stages. In this prototype, the upper common-base SiGe HBT is configured in inverse mode for balanced RF performance and reduced SET sensitivity. In order to better exploit the inverse-mode LNAs in a variety of extreme-environment applications, the RF performance of the LNA was characterized using liquid nitrogen to evaluate cryogenic operation down to 78 K. While the SiGe LNA exhibits acceptable RF performance for all temperature conditions, there is a noticeable gain drop observed at 78 K compared to the conventional forward-mode design. This is attributed to the limited high-frequency performance of an inverse-mode SiGe HBT. As a guideline, compensation techniques, including layout modifications and profile optimization, are discussed for the mitigation of the observed gain degradation.

Three-strip microchannel plate gated x-ray framing camera

A microchannel plate (MCP) gated x-ray framing camera with three-strip is reported. The diameter of the MCP is 56 mm and the width of each microstrip line cathode deposited on the MCP is 8 mm. While the microstrip line cathode is driven by a gating electrical pulse with width of 200 ps and amplitude of −1.9 kV overlapped with a −200 V DC bias, the measured temporal resolution is about 68 ps. Furthermore, the gain uniformity of the microstrip line cathode is measured showing that there is a 3.6× drop in gain along the pulse propagation direction, whereas the variations in the gain transverse to the pulse propagation direction are within 10%.

A Wideband and Low-Profile Discrete Dielectric Lens Using 3-D Printing Technology

In this paper, a novel wideband and low-profile discrete dielectric lens (DDL) antenna is presented. The proposed unit cells of DDL with the square-pyramid structure can realize wideband antireflection at an air-dielectric interface. By increasing the phase compensation range, the DDL antenna with very large gain bandwidth but large DDL thickness would be achieved. Furthermore, based on the large gain bandwidth technology, a novel multifolded lens structure is proposed to realize the low-profile design, in which a broadband polarization rotation reflection surface is proposed, while a polarized grid is used appropriately. Finally, the proposed multifolded DDL antenna can achieve a very large gain bandwidth, while the thicknesses of the DDL unit cell and the total antenna can be greatly reduced. For demonstration, the proposed multifolded DDL antenna is fabricated and measured. The fabrication was implemented by using a simple and low-cost 3-D printing technology. The results show that the proposed lens antenna can realize a 1 dB gain drop bandwidth of 43%, thickness of less than 1/3 focal-length-to-diameter ratio, and maximum aperture efficiency of 32%. Good agreement can be observed between the measurement and simulation.

Octave Bandwidth Transmitarrays With a Flat Gain

A wideband linearly polarized transmitarray antenna operating in 7–16 GHz is presented in this paper. First, a wideband element with three metallic layers is proposed, which is composed of a split circular ring connected by a narrow strip in the middle layer, and two polarizers in the upper and bottom layers. This element features a low transmission loss and approximately linear phase curves in a wide frequency band over one octave. Then, an optimization method is introduced to design the transmitarray that follows the bandwidth definition of 1 dB gain drop. The first key point of this method is determining the transmitarray element distribution with the weighted reference phases. The second is realizing wideband performances by controlling the calculated directivities and radiation patterns of the modified wideband transmitarray model at all operating frequencies. In the experiment, a $25\times 25$ -element horn-fed transmitarray with a $240 \times 240$ mm2 aperture area is designed and fabricated. The simulated results show that its bandwidths of 0.5, 1.5, and 3 dB gain drop are 41%, 56%, and 71%, respectively. Moreover, a peak aperture efficiency of 40.7% is achieved. Measured results agree reasonably well with the simulated ones. These results validate the proposed wideband element and the optimization method.

Impact of swirl and bluff-body on the transfer function of premixed flames

The frequency response of three lean methane/air flames submitted to flowrate perturbations is analyzed for flames featuring the same equivalence ratio and thermal power, but a different stabilization mechanism. The first flame is stabilized by a central bluff body without swirl, the second one by the same bluff body with the addition of swirl and the last one only by swirl without central insert. In the two last cases, the swirl level is roughly the same. These three flames feature different shapes and heat release distributions, but their Flame Transfer Function (FTF) feature about the same phase lag at low frequencies. The gain of the FTF also shows the same behavior for the flame stabilized by the central insert without swirl and the one fully aerodynamically stabilized by swirl. Shedding of vortical structures from the injector nozzle that grow and rollup the flame tip controls the FTF of these flames. The flame stabilized by the swirler-plus-bluff-body system features a peculiar response with a large drop of the FTF gain around a frequency at which large swirl number oscillations are observed. Velocity measurements in cold flow conditions reveal a strong reduction of the size of the vortical structures shed from the injector lip at this forcing condition. The flame stabilized aerodynamically only by swirl and the one stabilized by the bluff body without swirl do not exhibit any FTF gain drop at low frequencies. In the former case, large swirl number oscillations are still identified, but large vortical structures shed from the nozzle also persist at the same forcing frequency in the cold flow response. These different flame responses are found to be intimately related to the dynamics of the internal recirculation region, which response strongly differs depending upon the injector used to stabilize the flame.

Ku-Band Transmitarrays With Improved Feed Mechanism

Combining the advantages of lens antenna and array techniques, transmitarrays have been widespreadly concerned in recent years. In the first part of this paper, a wideband four-layer transmitarray operating at 13 GHz fed by a horn with a focus-to-diameter ratio (F/D) of unity is proposed. The employed elements composed of dual-resonance double hexagonal rings are closely arranged in the honeycomb lattice. The simulated results show that the transmitarray can achieve a 53.34% peak aperture efficiency and a 19.23% bandwidth for 1 dB gain drop, respectively. The factors with strong influences on the measured results are analyzed. In the second part, an improved feed mechanism, which is aimed at reducing the transmitarray profile, is discussed in detail. The conjugate field matching technology is utilized to realize an ideal compensation. The small-scale antenna array, which has a nearly identical aperture size to the feed horn applied in the first design, can effectively excite the transmitarray with a profile reduction of 64.5%. These prototypes confirm the feasibility of designing a wideband transmitarray and a low-profile array-fed transmitarray.

4H-SiC monolithic Darlington transistors with slight current gain drop at high collector current density

Profit from high current gain features, 4H-SiC power Darlington transistor has the capacity for handling high current transmission. In this paper, monolithic Darlington transistors were fabricated using a simultaneous formation process for both n-type (emitter) and p-type (base) ohmic contact. The isolated device shows current gain of 1061 and 823 with collector current density ( J C) increasing from 200 to 800 A/cm2, exhibiting a slight current gain drop at high J C. By extracting the interface state density ( D it) between SiO2 and p-type 4H-SiC, it is found that this advantage owes to the improvement of the shallow bulk minority carrier lifetime in base region. Furthermore, ISE-TCAD (technology computer aided design) simulation was carried out to study the relationship between base minority lifetime and the current gain, from which the total base minority lifetime is estimated to be 48 ns. The open base breakdown voltage ( BV CEO) is 850 V at a leakage current of 2 μA due to the electric filed crowding at the isolation bottom between drive bipolar junction transistor (BJT) and output BJT. To solve this, non-isolated devices were also fabricated with improved BV CEO of 2370 V, indicating the superior potential of 4H-SiC monolithic Darlington transistors for high power application, while the current gain is deceased to 420, which needs further improvement.

Leaf‐shaped CPW‐fed UWB antenna with triple notch bands for ground penetrating radar applications

AbstractA compact (38.31 mm × 34.52 mm × 0.8 mm) leaf shaped CPW fed ultra‐wideband antenna is proposed. The antenna gives wide impedance bandwidth from 2.58 GHz to 11.62 GHz with sharp triple notch bands (3.28 GHz–3.82 GHz, 5.12 GHz–5.4 GHz, and 5.7 GHz–6 GHz) to eliminate interference from co‐existing IEEE 802.16 WiMAX (3.3 GHz–3.8 GHz), IEEE 802.11y (3.65 GHz–3.69 GHz), IEEE 802.11a WLAN (5.15 GHz–5.35 GHz and 5.725 GHz–5.825 GHz), and IEEE 802.11p DSRC (5.85 GHz–5.925 GHz) bands. The antenna provides minimal gain variation (2–5 dBi), flat group delay response and non‐varying transfer function with high average efficiency of 88% in the pass band. Significant drop in gain and efficiency, nonlinearity in transfer function, and high variation in group delay are observed at notch bands. Antenna VSWR, and efficiency are measured in close proximity of sand, wood, and glass. Satisfactory results ensure its ability to work as Ground penetrating radar antenna.

The Steady-State DC Gain Loss Model, Efficiency Model, and the Design Guidelines for High-Power, High-Gain, Low-Input Voltage DC–DC Converter

The phase modulated full bridge resonant transition converter (PMRTC) is commonly used for high-gain, high-power applications, as PMRTC converters retain the qualitative nature of hard switched pulse-width modulation counterparts with additional damping ( $R_d$ ), where $R_d$ is load, transformer turns ratio and frequency dependent. The PMRTC converter enables operation at a higher switching frequency due to the soft-switching nature, thereby achieving better power density. For battery fed high-power, high-gain applications, PMRTC exhibits a significant drop in the dc gain due to $R_d$ and other nonidealities, limiting the maximum frequency of operation. Thus, computing this drop and analyzing the effects of switching frequency becomes necessary in achieving the required steady-state dc gain. From the analysis, it is observed that, for a choice of switching frequency above $f_{s\;{\rm critical}}$ , the required steady-state dc gain is not achieved for any turns ratio. Hence, to increase the switching frequency of operation of a PMRTC converter, a two-transformer configuration is adapted and with this configuration, the dc gain loss model, power loss, and efficiency model and small-signal model are established. The design guidelines on the choice of switching frequency and transformer turns ratio based on the proposed models is described. The proposed models with the presented design guidelines are validated in simulations and hardware prototype for a 1 kW PMRTC converter.

Enhanced antioxidant activity of fish gelatin–chitosan edible films incorporated with procyanidin

ABSTRACTGelatin and chitosan are edible polymers, which may be used in combination with antioxidant extracts as films to extend shelf life of foods. In this work, fish gelatin–chitosan edible films with procyanidin (PC) are successfully prepared. The effects of PC on the antioxidant, microstructure, physical properties, and antimicrobial activity of the films and solutions are studied. The results suggest that the addition of PC makes the gelatin–chitosan film possess the highest 2,2‐azinobios‐(3‐ethylbenzothiazoline‐6‐sulfonic acid) radical scavenging activity up to 95.63% at 1.00 mg/mL. As to mechanical properties, drop in tensile strength (27.17 ± 2.35%) and gain in elongation at break (33.42 ± 2.48%) are found for film with 1.00 mg/mL of PC. Owing to the simultaneous antioxidant and antimicrobial activities displayed for these films based on blends of gelatin and chitosan and additivated with PC could provide an alternative as active packaging material for food applications such as fish, meat, and cheese. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45781.

SiC-Based Z-Source Resonant Converter With Constant Frequency and Load Regulation for EV Wireless Charger

Traditional load regulation methods for a resonant converter mainly rely on frequency modulation. It is always a tradeoff between the design of the resonant network and the range of load. Especially for wireless power transfer (WPT) systems, the resonant network usually has a high quality factor. Small variation on frequency leads to huge drop in gain and efficiency. Due to this problem, many WPT systems are unregulated and they need one or two more front-end stages to regulate the dc bus voltage and perform power factor correction (PFC). In order to lower the cost and complexity of two- or three-stages structure, a single-stage solution with a silicon carbide (SiC) based Z-source resonant converter (ZSRC) was recently proposed. The Z-source network provides high reliability as being immune to shoot-through problems. Additionally, a ZSRC can boost the dc bus voltage while the traditional voltage-source inverter can only produce a lower voltage. However, the load regulation of this new topology has not been addressed. Two effective load regulation methods with constant frequency are presented for this SiC-based ZSRC specifically. Operation principle of the two load regulation methods are described in this paper. Experimental results based on a 200-W scale-down prototype with a full-bridge series resonant dc–dc converter are presented to illustrate the mechanism of these two methods.

Modified planar Luneburg lens millimetre‐wave antenna for wide‐angle beam scan having feed locations on a straight line

This study presents the design and characterisation of a modified planar Luneburg lens antenna operating at 30 GHz. A parallel plate lens structure with varying separation between the metal plates realises the required variation of phase velocity of the guided TE mode in the device. The focal points for different beam radiation directions are all placed on a straight line, thus simplifying the mechanical setup for steered beam and multi-beam systems. A planar slotline radiator excites the TE mode in the parallel plate structure. An optimisation process leads to best compromise between large directivity, large maximum scan angle and small side-lobes. As a result, measurements show that by moving the feed radiator on a straight line over ±40 mm, the beam maximum can be steered over more than ±35° with a gain drop of <3 dB. While scanning the beam from broadside direction towards ±35° scan angle, the worst-case side-lobe level deteriorates from 15 dB to about 10.5 dB. The proposed antenna shows peak directivity of 15.2 dBi and a large simulated power efficiency of 95%.

Gain stability in fluorine polymer modified PbS Quantum dot fiber amplifier

The fluorescence intensity drop rate of PbS quantum dot with fluorine-containing polymer is 9.76% and the gain drop rate of quantum dot fiber amplifier (QDFA) with fluorine-containing polymer is 57.66% separately with temperature, which is more stable than no fluorine polymer QDFA.

Lens Antenna for Wide Angle Beam Scanning at 79 GHz for Automotive Short Range Radar Applications

This communication presents the design and experimental verification of a substrate integrated waveguide fed lens antenna for 79 GHz automotive radar applications. The proposed integrated lens antenna consists of a six layer cylindrical Luneburg lens illuminated by 17 source elements of substrate integrated waveguide fed by a planar log periodic dipole antenna array. The Luneburg lens is developed by using a unique foam material AirexR82 ( $\varepsilon _{r} = 1.12$ ), which is drilled and pressed to achieve the different dielectric constant needed to follow the index law inside the lens. The return loss and the radiation characteristics of the proposed integrated lens antenna are investigated and validated by measurements. A good agreement between the measured and simulated results is observed. The measured results confirm the beam scanning capability of the proposed integrated lens antenna for a wide scan angle of ±85° in azimuth plane having a maximum antenna gain of 15 dBi at 82.5 GHz and gain drop of less than 2.75 dB for the edge feeds. The estimated radiation efficiency of the antenna is found to be 67% at 82.5 GHz.