Cavity Gap Research Articles

Sub-20 nm GaAs junctionless FinFET for biosensing application

This work proposes a dielectric modulated GaAs junctionless FinFET as a biological sensor in the sub-20 regime. In the proposed biosensor, HfO2 (ᴋ = 25) is used as a base oxide which is found to have improved the switching ratio (three times) of the device. For immobilizing the biomolecules, a Nano-cavity (18 nm) is embedded between gate and source/drain. For the detection of biomolecules, electrical characteristics such as switching ratio, energy band profile and change in surface potential have been studied and thereafter, sensitivity has been evaluated which has been improved by 80%. Change in current is recorded for different materials due to change in gate capacitance owing to different biomolecules: Protein (ᴋ = 8), streptavidin (ᴋ = 2.1), biotin (ᴋ = 2.63). Higher sensitivity is observed for protein biomolecules (1.07) as compared to streptavidin (1.015) and biotin (1.045). The sensitivity is compared to with the absence of biomolecules (assumed as the vacuum) as well. Furthermore, modulation of the cavity gap length was also investigated, revealing that its increase (from 8 to 18 nm) significantly enhanced the sensitivity of the proposed biosensor. All the results pave way for biomolecule detection with the existing CMOS technology.

Improvement of Steam Turbine Stage Efficiency by Controlling Rotor Shroud Leakage Flows—Part I: Design Concept and Typical Performance of a Swirl Breaker

In high and intermediate pressure (HIP) steam turbines with shrouded blades, it is well known that shroud leakage losses contribute significantly to overall losses. Shroud leakage flow with a large tangential velocity creates a significant aerodynamic loss due to mixing with the mainstream flow. In order to reduce this mixing loss, two distinct ideas for rotor shroud exit cavity geometries were investigated using computational fluid dynamics (CFD) analyses and experimental tests. One idea was an axial fin placed from the shroud downstream casing to reduce the axial cavity gap, and the other was a swirl breaker placed in the rotor shroud exit cavity to reduce the tangential velocity of the leakage flow. In addition to the conventional cavity geometry, three types of shroud exit cavity geometries were designed, manufactured, and tested using a 1.5-stage air model turbine with medium aspect ratio blading. Test results showed that the axial fin and the swirl breaker raised turbine stage efficiency by 0.2% and 0.7%, respectively. The proposed swirl breaker was judged to be an effective way to achieve highly efficient steam turbines because it not only reduces the mixing losses but also improves the incidence angle distribution onto the downstream blade row. This study is presented in two papers. The basic design concept and typical performance of the proposed swirl breaker are presented in this part I, and the effect of axial distance between a swirl breaker and rotor shroud on efficiency improvement is discussed in part II [8].

On the transient behaviour of a laminar rotor–stator cavity

The unsteady laminar flow between two large rotating disks when one of them is impulsively started is described using the von Kármán similarity analysis to reduce the solution of the Navier–Stokes equations to a set of ordinary differential equations. It is found that the transient phenomenon consists of three distinct phases. Firstly, the development of the Ekman boundary layer, where a quasi-steady Stewartson-type of flow is created. Secondly, angular momentum is initially diffused in the axial direction until the inward radial convection of angular momentum becomes dominating. Thirdly, a Batchelor flow is created once the Bödewadt boundary layer is developed and the entrainment of disk and stator boundary layers are balanced. The dependences of the characteristic dimensionless times on the Reynolds number based on the cavity gap for the second and third stages have been identified numerically and analytically. It is found that the diffusive part of the transient is bypassed if the flow, initially at rest, is perturbed with a small circumferential velocity. The flow and heat transfer transient during a ramp of finite duration has been computed numerically. The integral angular momentum and energy balances of the cavity have been performed in order to understand the energy and momentum budget of the cavity. It is concluded that the spin-up and the spin-down process of a rotor–stator cavity using a quasi-stationary approximation of the fluid, where the time derivatives are neglected, is questionable for realistic gas turbine applications. Finally, the self-similar solution is compared against two-dimensional axisymmetric, steady and unsteady, laminar simulations to assess the limitations and validity of the self-similar analysis. It has been identified that in a closed squared cavity the outer shroud modifies the physics of the transient, but the general conclusions drawn from the one-dimensional model are still valid.

Measurement of milli-Newton axial force and temperature using a hybrid microsilica sphere Fabry-Perot sensor.

An optical fiber sensor based on the Hybrid Fabry-Perot for simultaneous measurement of milli-Newton axial force and temperature is proposed. This structure is composed of a single-mode optical fiber (SMF) integrated to a silica capillary tube (SCT) with polydimethylsiloxane (PDMS). A microsilica sphere cavity (MSSC) is fabricated at the tip of a capillary tube. Consequently, an air gap followed by a microsilica sphere forms two cascade cavities. To explain the transferring load from the SMF to the SCT through PDMS, a shearing mechanism is employed. The experimental results show that axial force and temperature sensitivities of the air gap cavity in the range of 0-3.43mN and 30-65°C are 170pm/mN and 24pm/°C, respectively, while the MSSC did not show any force sensitivity due to its rigidity. However, its temperature sensitivity is 34pm/°C. The different sensitivities enable us to implement simultaneous sensing of force and temperature.

Ultralow-power dielectric-modulated nanogap-embedded sub-20-nm TGRC-MOSFET for biosensing applications

This work examines a transparent gate recessed channel (TGRC) metal–oxide–semiconductor field-effect transistor (MOSFET) for biosensing, including a nanogap cavity for detection of biomolecules and a transparent gate to enhance the overall current efficiency of the RC-MOSFET. For the detection of neutral biomolecules, electrical characteristics such as ION/IOFF, shift in threshold voltage and change in surface potential have been studied and thereafter, sensitivity of has been evaluated. The biosensor showed enhanced sensitivity for biomolecules with increase in their dielectric value, due to greater on-current owing to the change in capacitances. The capacitances were therefore also evaluated. In addition, immobilization of biomolecules degrades the noise immunity of MOSFET and thereby their overall biosensing performance, while the noise immunity of the TGRC device was very high even in the presence of biomolecules. Furthermore, modulation of the cavity gap length was also investigated, revealing that its increase (from 8 to 20 nm) significantly enhanced the sensitivity of the proposed biosensor. Overall, the results of this analysis reveal that such TGRC-MOSFET biosensors can exhibit high sensitivity (1.45) at very low drain bias (0.2 V), enabling their use for biosensor applications to diagnose various diseases which require lower noise, high speed, low power, and high density.

Improving the performance of solar chimney by addressing the designing factors

Solar chimney is a reliable system totally based on solar energy to enhance natural ventilation in buildings, but challenge still exists to optimize its performance with the lowest cost. In this study, three designing factors, including configuration, installation conditions, and material usages, were reviewed to provide a technical guide for engineering applications. Regarding the configuration, the performance of solar chimney can be enhanced with a high cavity, an appropriate cavity gap (usually 0.2-0.3 m), equivalent inlet and outlet area, and height/gap ratio of 10-15. Regarding installation conditions, an optimum inclination angle of 45° was usually suggested, and large openings can enhance the performance while the increasing rate keeps decreasing. The principles of material usage are to maximum the heat absorption and reduce the heat losses, considering properties such as thermal conductivity, absorptivity, emissivity, transmissvity, and reflectivity.

A mmWave Wideband Slot Array Antenna Based on Ridge Gap Waveguide With 30% Bandwidth

A wideband $8 \times 8$ element slot antenna array based on ridge gap waveguide feeding network has been proposed for mmWave applications. The antenna subarray consists of four radiating slots which are excited by a groove gap cavity layer. Compared with previously published works, the proposed planar antenna array has quite wide impedance bandwidth. The antenna covers a wideband of 50–67.8 GHz with 30% impedance bandwidth (VSWR < 2). Also, the antenna has only 2.5 dB gain variation over the entire bandwidth which implies also good radiation characteristics for the proposed antenna. The maximum measured gain value is about 27.5 dBi with a total efficiency of 80% for the proposed antenna within the band of interest. With this performance, the proposed antenna array is a promising candidate for mmWave communication systems.

Mitigation of radial exciting force of rotary lobe pump by gradually varied gap

ABSTRACTThis paper presents a new structure of a rotary lobe pump cavity with gradually varied gap to mitigate the magnitude and fluctuation of the radial exciting force on the rotor. The geometry of the rotary lobe pump cavity is specially designed, so that the gap between the rotor and cavity is gradually changed during the rotors’ engaging. The flow in this geometry is numerically studied, and its effect on the pressure pulsation and radial exciting force is analysed, based on the dynamic mesh and local mesh reconstruction. Also, the mechanism of the mitigation of radial exciting force is briefly discussed. The value of the gap is an addition of gradually varied gap r (0∼rmax) and the base gap (original constant gap: 0.2 mm). As for the results, it is found that as the varied gap rmax value increases, the intensity of the reverse rotating vortex at the outlet decreases, and the secondary flow pulsation of the outlet section is effectively weakened. When rmax =0.1 mm, the radial exciting force in the y-direction on the rotor is reduced by 12% comparing with the equal gap, and the radial exciting force pulsation coefficient is 0.31. Meanwhile, the radial exciting force in the x-direction is reduced by 19% accordingly. The gradually varied gap cavity can effectively reduce the peak value of the pressure pulsation at outlet, weakening the influence of the rapid change of the outlet pressure on the radial exciting force. It is found that an optimal rmax of 0.1∼0.15 mm has a remarkable effect on the mitigation of pressure pulsation and radial exciting force.

Design of crusher liner based on time - varying uncertainty theory

This article puts forward the time-dependent design method considering the load fluctuation factors for the liner based on the time-varying uncertainty theory. In this method, the time-varying uncertainty design model of liner is constructed by introducing the parameters that affect the wear rate, the volatility and the drift rate. Based on the design example, the timevarying design outline of the moving cone liner is obtained. Based on the theory of minimum wear, the gap curve of wear resistant cavity is designed, and the optimized cavity is obtainedby the combination of the thickness of the cone and the cavity gap. Taking the PYGB1821 multi cylinder hydraulic cone crusher as an example, it is proved that the service life of the new liner is improved by more than 14.3%.

Central-wavelength-tunable multi-wavelength fiber laser based on micro-air gap cavity and tapered fiber structure

A multi-wavelength erbium-doped fiber laser based on a micro-air gap cavity filter and the tapered fiber structure is proposed and demonstrated. The micro-air gap cavity filter is constructed by aligning two polished single mode fiber facets carefully through a capillary. Then a tapered fiber structure is applied to compose a cascaded filter with the micro-air gap cavity filter. According to the experiment, the transmission spectrum of the tapered fiber structure acts as the outer envelope of the cascaded structure, which is used as a tunable filter. Moreover, the periodically localized peaks of the tapered fiber structure are modulated by sinusoidal spectral response of the micro-air gap cavity filter. And the micro-air gap cavity filter acts as a comb filter, which determines the channel space of the cascaded filter structure. By using the above superimposed filter, four wavelengths with a wavelength spacing of about 1.20 nm are generated under the pump power of 270 mW. The side-mode suppression ratio of all lasing wavelengths is about 35 dB. The tapered fiber structure is fixed on a furnace, when the temperature varies from 30 °C to 120 °C, the first wavelength can be tuned within the range of 5.31 nm.

Experimental analysis of the hydrodynamics, flow pattern and wet agglomeration in rotor-stator vortex separators

The effect of the stator geometry, cavity gap and fluid volume on the turbulent aggregation, hydrodynamics and flow pattern in rotor-stator vortex reactors have been investigated using a digital 2D Particle Image Velocimetry (PIV) and visual observation. The results of the study showed a more uniform distribution of the quantified flow parameters—velocity profile and vorticity map in the continuous reactor when compared to the batch reactor. In addition, a high velocity recirculating jet which creates a diverging flow as the jet hits the reactor wall was observed in the batch reactor creating two distinct vortex structures (core and marginal vortex). Frictional losses across the cavity account for much of the difference between the theoretically computed and measured values of the hydrodynamic parameters. The stream pattern obtained from the PIV analysis unexpectedly shows a fairly good correlation with the flow pattern created from the digital video recordings of the pellet motion during the wet agglomeration experiments.

ALMA unveils rings and gaps in the protoplanetary system HD 169142: signatures of two giant protoplanets

The protoplanetary system HD 169142 is one of the few cases where a potential candidate protoplanet has been recently detected via direct imaging. To study the interaction between the protoplanet and the disk itself observations of the gas and dust surface density structure are needed. This paper reports new ALMA observations of the dust continuum at 1.3\,mm, $^{12}$CO, $^{13}$CO and C$^{18}$O $J=2-1$ emission from the system HD 169142 at angular resolution of $\sim 0".18 - 0".28$ ($\sim 20\,$au$ - 33\,$au). The dust continuum emission reveals a double-ring structure with an inner ring between $0".17-0".28$ ($\sim 20 - 35\,$au) and an outer ring between $0".48-0".64$ ($\sim 56 - 83\,$au). The size and position of the inner ring is in good agreement with previous polarimetric observations in the near-infrared and is consistent with dust trapping by a massive planet. No dust emission is detected inside the inner dust cavity ($R \lesssim 20\,$au) or within the dust gap ($\sim 35 - 56\,$au). In contrast, the channel maps of the $J=2-1$ line of the three CO isotopologues reveal the presence of gas inside the dust cavity and dust gap. The gaseous disk is also much larger than the compact dust emission extending to $\sim 1'.5$ ($\sim 180\,$au) in radius. This difference and the sharp drop of the continuum emission at large radii point to radial drift of large dust grains ($>$ \micron-size). Using the thermo-chemical disk code \textsc{dali}, the continuum and the CO isotopologues emission are modelled to quantitatively measure the gas and dust surface densities. The resulting gas surface density is reduced by a factor of $\sim 30-40$ inward of the dust gap. The gas and dust distribution hint at the presence of multiple planets shaping the disk structure via dynamical clearing (dust cavity and gap) and dust trapping (double ring dust distribution).

Design and Fabrication of a High-Gain 60-GHz Cavity-Backed Slot Antenna Array Fed by Inverted Microstrip Gap Waveguide

This communication deals with the design of a $16\times 16$ slot array antenna fed by inverted microstrip gap waveguide (IMGW). The whole structure designed in this communication consists of radiating slots, a groove gap cavity layer, a distribution feeding network, and a transition from standard WR-15 waveguide to the IMGW. First, a $2\times 2$ cavity-backed slot subarray is designed with periodic boundary condition to achieve good performances of radiation pattern and directivity. Then, a complete IMGW feeding network with a transition from WR-15 rectangular waveguide to the IMGW has been realized to excite the radiating slots. The complete antenna array is designed at 60-GHz frequency band and fabricated using Electrical Discharging Machining Technology. The measurements show that the antenna has a 16.95% bandwidth covering 54–64-GHz frequency range. The measured gain of the antenna is more than 28 dBi with the efficiency higher than 40% covering 54–64-GHz frequency range.

Radiation Bandwidth Improvement of Electromagnetic Band Gap Cavity Antenna

Abstract In this paper, an electromagnetic band gap cavity antenna with improved radiation and impedance bandwidths is presented. The proposed antenna is constructed by placing a triple-layer heterogeneous printed-unprinted partially reflective surface (PRS) above a primary aperture-coupled patch antenna. The PRS unit-cell provides a positive gradient reflection phase behavior over the desired frequency range. A prototype antenna is fabricated and measured that highlighted its ability to achieve 3-dB gain bandwidth of about 35.9 %, from 7.93 GHz to 11.4 GHz, with a peak gain of 14.25 dBi at 8.5 GHz. In addition, the impedance bandwidth is 40.32 %, from 7.9 GHz to 11.89 GHz. Thus, the designed antenna outperforms many other competitors for improving the radiation bandwidth of planar antennas with the same presented concept.

Effect of Bolts on Flow and Heat Transfer in a Rotor–Stator Disk Cavity

Previous studies have indicated some differences between steady computational fluid dynamics (CFD) predictions of flow in a rotor–stator disk cavity with rotating bolts compared to measurements. Recently, time-dependent CFD simulations have revealed the unsteadiness present in the flow and have given improved agreement with measurements. In this paper, unsteady Reynolds averaged Navier–Stokes (URANS) 360 deg model CFD calculations of a rotor–stator cavity with rotor bolts were performed in order to better understand the flow and heat transfer within a disk cavity previously studied experimentally by other workers. It is shown that the rotating bolts generate unsteadiness due to wake shedding which creates time-dependent flow patterns within the cavity. At low throughflow conditions, the unsteady flow significantly increases the average disk temperature. A systematic parametric study is presented giving insight into the influence of number of bolts, mass flow rate, cavity gap ratio, and the bolts-to-shroud gap ratio on the time-dependent flow within the cavity.

Anatomical Characteristics of Stem and Leaf in &amp;lt;i&amp;gt;Euphorbia hirta&amp;lt;/i&amp;gt; L.

The stem and leaf anatomical studies of Euphorbia hirta L. were conducted for finding identical traits. The fresh hand sections were stained with safranin and examined under light microscope. Cross section of the stem has a circular shape where epidermis was uniseriate and isodiametric. Cortex was distinctly formed with about 5-6 rows composed of chlorenchyma and found laticifers. Tracheary elements were resembled by vessels and trachieds. In most cases, some pith cells were filled laticifers at young stage and it has a distinct gap or central cavity at maturation stage. In leaf, the epidermis was uniseriate, regular, thin walled, usually similar in diameters and covered with thin cuticle layer. Multicellular uniseriate or gland-like trichomes occur in rugose hairs at epidermis. Mesophyll was differentiated into palisade and spongy layers, was composed of parenchyma cells. The palisade layer assembled with 2 rows of cells. The spongy layer thickness was different around the midrib region, compared with other parts, has 2-6 rows of cells. Laticifers were present at the middle part of the mesophyll. Xylem elements in midrib initiated perfectly and composed of many straight rows of mainly vessels where the phloem elements were abundant and occupied a good part of the vascular bundle as a semicircle shape. The stem and leaf anatomy of this species studied here showed laticifers in cortex zone and pith cells, and middle part of the mesophyll, respectively, was a taxonomic trait for this species.

An Improved Ku-band MILO With Tapered Choke Cavity and Enlarged First Interaction Cavity

In order to further enhance the power capacity, and speed up the microwave start-up and saturation, an improved Ku-band magnetically insulated transmission line oscillator (MILO) with tapered choke cavity and enlarged first interaction cavity is proposed and investigated in this paper. The simplified plate model of MILO is analyzed to investigate the movement of individual electron. According to the theoretical analysis, the Ku-band MILO is optimized designed. In order to make the electrons emitted from the launch point of the cathode closer to the slow wave structure (SWS), especially the surface of the first interaction cavity, help to speed up the microwave start-up and saturation, the launch point of the cathode is optimized and designed 1.5 cm in front of the second choke vane. A tapered choke cavity is used to replace traditional uniform choke cavity, which helps further speed up the microwave start-up and saturation. An enlarged first interaction cavity with increased cavity gap is introduced to enhance the power capacity. Typical particle simulation results show that the improved Ku-band MILO can generate a microwave with a power of 1.65 GW and a frequency of 12.3 GHz under the diode voltage of 474 kV and the beam current of 42 kA. Compared with the traditional Ku-band MILO, the microwave start-up and saturation of the improved one are 2.5 and 5.5 ns faster, respectively. The power capacity of the improved Ku-band MILO is enhanced greatly due to that the RF electric field is decreased much from 1.3 to 1 MV/cm. At last, the experimental investigation of the improved Ku-band MILO is conducted. The device achieves a microwave output with a power of 1.2 GW, a frequency of 12.36 GHz, and a pulsewidth of 35 ns in the experiment. Both the power and the pulsewidth are enhanced significantly.

Improved Sound Absorption Performance of Nonwoven Fabric using Fabric Facing and Air Back Cavity

This paper presents the improvement methods to increase sound absorption performance of polyethylene based nonwoven fabric (PNF). The methods are placing a woven fabric in front of the sample as well as providing air cavity behind the sample. The samples were experimentally tested in an impedance tube based on ISO 10354-2:2001 whereby two microphones are used and the transfer matrix methods are employed. From the results, it can be seen that placing front woven fabric effectively increases sound absorption performance. Moreover, introducing air cavity gap behind the sample is also found to be more significant to increase sound absorption.

Oil palm empty fruit bunch fibres as sustainable acoustic absorber

This paper discusses the utilisation of fibres from the oil palm empty fruit bunch (OPEFB) to be an alternative natural acoustic material. The study was carried out by fabricating samples from raw OPEFB fibres with different densities and thicknesses to observe their effects on the sound absorption performance. It has been demonstrated that the sound absorption performance can be improved by increasing the thickness of the sample and also by having optimum densities of fibres. In particular for lower frequencies, this can be achieved by introducing air cavity gap behind the fibre samples. Measurement of the normal incidence absorption coefficient in an impedance tube based on ISO 10534-2 found that the OPEFB fibres can have absorption coefficient of 0.9 on average above 1kHz. The sound absorption performance of OPEFB fibres is also shown to be comparable to that of the commercial synthetic rock wools.

Completely Tuned Coupled Cavity Filters in Defected Bed of Nails Cavity

The design of perfectly tuned bandpass filters on defected bed of nails cavity and ridge gap waveguide (RGW) is investigated. The proposed technology eliminates the need for intact electrical contact between the metal parts of the filter. A space mapping method and coupling matrix are used to tune and optimize the proposed structures, which are computationally expensive and have beneficial characteristics for high-frequency applications. RGW is used as the input/output for the filters. A new coaxial transition to RGW and input/output coupling method is designed and used. A fifth-order Chebyshev bandpass filter is designed, fabricated, and measured. The performance of the designed filter is compared to a rectangular waveguide filter. Classic bandpass filters with transmission zeros at finite frequencies using this technology are designed for the first time. Sample models for triplet and quadruplet sections are proposed and optimized.