Cavity Gap Research Articles

M13 bacteriophage-based high-sensitivity Fabry-Pérot etalon for detecting humidity and volatile organic compounds

Various sensor applications have been developed for protection against hazardous environments, and research on functional materials to enhance performance has also been pursued. The M13 bacteriophage (M13) has found utility in sensor applications like disease diagnosis and detection of harmful substances due to its potential for controlling interaction with target substances through adjustments in electrochemical and mechanical properties via genetic engineering technology. However, while optimizing reactivity or binding affinity between M13 and target materials is crucial for sensor performance enhancement, precise dynamic measurement methods for this were lacking. This study demonstrates the application of an M13-based dynamic actuator in a Fabry–Pérot etalon (M13-FPE) as a spacer for precise measurement of humidity and reactivity to volatile organic compounds (VOCs). The transmission spectrum is optimized by adjusting the reflectance and cavity gap size (dM13) of the two mirrors comprising the M13-FPE, and changes are measured in a rainbow-color-dotted (RCD) pattern using a customized spectrometer. Utilizing the peak wavelengths of the RCD pattern, the change in dM13 is dynamically and precisely measured, revealing approximately 3% and 0.3% swelling for ethanol and isopropyl alcohol, respectively. M13 demonstrates binding affinities of 827 ppb and 158 ppb for ethanol and isopropyl alcohol, respectively, with its low reactivity measured precisely, exhibiting an error of 0.03 nm using the peak wavelength change rate.

Multipactor analysis of 431 MHz L-shaped inductive output tube cavity

Gridless inductive output tubes (IOTs) offer compact size and high-power amplification at sub-GHz frequencies. Minimizing cavity dimensions in the interest of compactness leads to smaller gaps, which may cause multipactor discharge under high-power operating conditions. The uncontrolled electron growth resulting from multipactor breakdown can lead to undesired effects including surface damage and system failure. This paper performs a parallel-plate multipactor analysis for a high-Q, L-shaped, aluminum, 431 MHz cavity designed for a gridless IOT to be operated in the MW-power regime. The cavity gap is 27 mm, and diameter is 339 mm. Multipactor susceptibility regions are calculated for non-zero emission energy, half-cycle, and non-half-cycle multipactor using a semi-analytic approach and a standard aluminum secondary electron yield (SEY) curve. The analytical results are validated with particle-in-cell simulation in CST Studio. Simulation results show a voltage range of 6.4–19 kV, compared to the analytically calculated values of 8.2 and 18.3 kV for the lower and upper bounds, respectively. Fluorocarbon coating as a means to reduce secondary electron emission is simulated, which shows 46% reduction in peak particle population with an 11.2 nm PTFE coating, with further reduction as coating thickness increases. The results show that the L-shaped cavity is a suitable choice for this IOT design as it does not exhibit single-surface multipactor and will not develop two-surface multipactor at full-power operation.

Mode management in Bottom‐Up, Parity‐Time‐Symmetric Micro‐Cavity Lasers

AbstractThe intrinsic non‐Hermiticity of photonic devices with tunable optical gain and loss makes them excellent platforms to explore and implement applications based on parity‐time symmetry, and a notable example is mode management in micro‐cavity lasers. Thus far, parity‐time‐symmetric lasers are fabricated via conventional top‐down etching processes, which are known to cause cavity sidewall roughness that is potentially detrimental to laser performance. Bottom‐up fabrication of parity‐time‐symmetric lasers, however, has seen limited success due to strict requirements on the uniformity of cavity morphology. Here, parity‐time‐symmetric lasing is demonstrated in coupled InP micro‐ring cavities grown directly by selective area epitaxy. With a facet engineering technique, ring laser cavities with a highly deterministic morphology are realized, enabling parity‐time‐symmetric laser designs. Furthermore, benefiting from the versatility and controllability of this bottom‐up process, lasing mode selectivity can be enhanced through coupling gap tuning and cavity shape engineering, leading to single‐mode lasing with a peak side mode suppression ratio exceeding 17 dB and a threefold single‐mode brightness enhancement compared to a single, uncoupled laser cavity. This work unlocks a lasing mode management strategy that is previously unavailable to bottom‐up laser cavities, which is a major step toward the realization of on‐chip, low‐loss, and single‐mode micro‐cavity lasers.

Dynamic Ultrastrong Coupling in a 2 nm Gap Plasmonic Cavity at the Sub-Picosecond Scale.

Localized surface plasmon resonances (LSPRs) can enhance the electromagnetic fields on metallic nanostructures upon light illumination, providing an approach for manipulating light-matter interactions at the sub-wavelength scale. However, currently, there is no thorough investigation of the physical mechanism in the dynamic formation of the strongly coupled LSPRs on sub-5 nm plasmonic cavities at the sub-picosecond scale. In this work, through femtosecond broadband transient absorption spectroscopy, we reveal the dynamic ultrastrong coupling processes in a nanoparticle-in-trench (NPiT) structure containing 2 nm gap cavities, and demonstrate a coherent motional coupling between vibrating AuNPs and the nanogaps. We achieve a maximum Rabi splitting energy of ∼660 meV in the sub-picosecond hot-electron relaxation time scale under the resonant excitation of the nanogap cavity's LSPR, reaching the ultrastrong coupling regime. This leads to a change of global vibration modes for the 2 nm gap cavity, potentially related to the dynamical Casimir effect with nanogap resonators.

A theoretical and numerical analysis of solar chimney in multi-storey atrium building

Current research efforts on solar chimney are much on those configurations with single space or single vent, hampering its applications in complex buildings. To expand its implementation, the viability of solar chimney in multi-storey atrium buildings was explored numerically and theoretically. It was known that its natural ventilation performance can fulfil the WHO requirements (i.e., 6 air change per hour, ACH) even under low solar radiation of 200 W/m2 if it is appropriately designed, such as cavity gap (d), cavity height (Hc), solar radiation (Q), and window width (W). Its natural ventilation rate was found to be positively linear to the exponential form of the analyzed factors in this study, including cavity gap (d0.63∼0.69), cavity height (Hc0.59∼0.60), solar radiation (Q0.42∼0.43), and window width (W0.14∼0.20). The impacts of cavity gap and solar radiation are relatively weaker for big space such as atrium than those scenarios with single-space ventilation in the literature. The volume of the connected space was found to affect its natural ventilation performance, where the obtained ventilation rate of 4-storey is averagely 5.1 % lower than those of 3-storey buildings. A theoretical model was developed and experimentally validated, for the first time, to predict the natural ventilation rate of solar chimney when it is applied to the atrium with multiple air inlets. It was also noticed that the same theoretical model can be applied to the atrium buildings with odd and even storeys, but the area coefficients are different. The research outcomes of this study confirm the viability of solar chimney in complex buildings and offer a theoretical foundation for its implementation.

A compact linearly polarized RLSA antenna integrated with circular ring resonator (CRR) for 5G mm-wave applications

This article introduces a compact linearly polarized (LP) radial line slot array antenna (RSLA) that incorporates a metamaterial of circular ring resonator (CRR) reflector for improving the bandwidth. Hence, this enables the antenna to operate at n257 (26.5–29.5), n258(24.25–27.5), and n261(27.5–28.35) frequency bands which are standardized by Federal Communications Commission (FCC) with a minor reduction of the directivity. Due to the short wavelength of the millimeter wave bands, the technique of the RLSA design has been advantageous for achieving high gain. The prototype of the RLSA antenna and the metamaterial CRR reflector are designed and fabricated at 28 GHz resonance frequency utilizing Rogers 5880 substrate and fed using an SSMA coaxial connector with an air gap cavity equivalent to half guide wavelength (λg/2) between substrate and ground plane. The method of integrating the CRR reflector with the LP-RLSA antenna delivered a passband transmission operating at (22–29.5) GHz. The proposed antenna has a similar agreement between simulated and measured for directivity and bandwidth. it achieved a peak directivity of 20 dB with a squinted main lobe at 12° and a fractional bandwidth of 29.13%. The fabricated RLSA antenna dimensions are 130 mm × 130 mm × 10.65 mm which is compact compared to conventional RLSA antennas.

A signal-on photoelectrochemical sensor based on the target-triggered double-ion exchange reaction for Hg2+ under visible light

A photoelectrochemical (PEC) sensor driven by visible light has been developed to detect Hg2+ with a signal output "turn-on" mode on basic of the double ZIF-Cds@Zns@HgS type-II heterojunction formed by a target-triggered double-ion exchange reaction. The type-II heterojunction photocatalysts ZIF-CdS@ZnS were prepared through growing ZnS nanoparticles onto ZIF-CdS hollow nanocages which were innovatively synthesized using ZIF-67 as a template by MOF-engaged directional deposition strategy. An obvious photocurrent amplification effect induced by mercury ions is evident in ZIF-CdS@ZnS modified ITO electrodes, compared to ZIF-CdS or pure ZnS modified electrodes. The ZIF-CdS@ZnS heterojunction would successfully utilize visible light to promote the photoelectric response process due to the synergistic effect of the narrow band gap component and cavity structure. More importantly, the photocurrent can be greatly amplified by the target-triggered double-ion exchange reaction, which results in the generation of double type-II heterostructures HgS@ZnS@CdS, where an electrical field resulting from the unification of the fermi level facilitates the separation of photogenerated charges and increases the output photocurrent. Besides, the target-triggered double ion exchange strategy can provide guidance for the design of signal-on PEC sensors to detect other heavy metal ions sensitively.

FAIR SIS100 accelerating RF system - Modeling and analysis of the coupled LLRF control loops

The SIS100 heavy ion synchrotron as core part of the Facility for Antiproton and Ion Research (FAIR) will be equipped with 14 accelerating RF stations in the first stage of realization. Each RF station consists of a tunable ferrite-loaded cavity powered by a tetrode amplifier. Further key components are a solid-state pre-amplifier, a power supply unit, and dedicated Low-Level Radio Frequency (LLRF) feedforward and feedback systems to control amplitude and phase of the cavity gap voltage as well as the resonance frequency. Each cavity has to provide up to 20 kV peak gap voltage in the frequency range from 1.1 to 3.2 MHz. While all components of the system have been successfully tested in the factory acceptance tests and transferred to the FAIR storage, the First-of-Series (FoS) RF station is still persistently operated at GSI to gain experience. For further insight into the LLRF part, especially the stability of the control loops, the inter-coupling of the three local control loops was analyzed with methods from control theory based on simplified but realistic models, which have been developed based on extensive measurements and analysis of the systems’ behavior. In this contribution, the modeling as well as the analysis of the coupling between the LLRF control loops are discussed and the results are presented in comparison with measurements on the FoS system.

Tuner Loop Based on FPGA for Petra Cavity at TPS Booster Ring

The low-level radio frequency system of the Taiwan Photon Source, TPS, booster ring was replaced by the digital low-level RF system, DLLRF, in 2018. After that, the phase drift compensation loop for energy-saving operation and the tuner loop were also implemented in the DLLRF system sequentially. We used Altera-DE3 to build the core of DLLRF and handle the high-speed ADC/DAC procedure for RF signal sampling. As we con-sider the response time of the tuner, we choose an-other low-cost board, Altera-DE0-Nano, to develop the tuner loop for 5-Cell-Petra-Cavity. It has an eight-channel 12-bits-ADC, 150 ksps, ADC128S022, to detect the positions of two tuners and two transmitted powers sampled from two cells of the 5-Cell-Petra-Cavity for a power balance function. The phase information of for-ward power and cavity gap voltage will come from the Altera-DE3 to tell the tuner loop in the Altera-DE0-Nano whether the cavity is on resonance or not. The tuner loop controls the cavity to work not only at the resonance frequency but also with a balanced electric field distribution. This study presents the tuner loop’s architecture, including the locking resonance frequency and field balance functions. The performance of the field balance function is observed by the archive data of the two tuners positions and two transmit power signals.

Experimental Measurements of Flow-Averaged Toroidal Vortices in Buoyancy-Dominated Rotating Cavities

Abstract The flow structures and heat transfer within rotating cavities of aero-engine axial compressors influence the thermal expansion of the rotor disks, and consequently the blade-tip clearances. To investigate the flow field at the bore and lower cavity region, experimental measurements have been acquired in an engine-representative test facility. Axial, tangential, and radial velocities were measured using a miniature five-hole probe at a range of axial and radial positions. Time-averaged results from 28 tests carried out at nondimensional parameters comparable to engine conditions: 1.3 × 104 ≤ Rez ≤ 8.2 × 104, 3.0 × 105 ≤ Reθ ≤ 3.2 × 106, 0.11 ≤ Ro ≤ 3.24, 0.14 ≤ βΔT ≤ 0.36 are presented in this paper. The axial and tangential velocity measurements conform to previous work, while the radial velocity component provides quantitative evidence of an asymmetric toroidal vortex in the cavity gap, biased toward the downstream disk. The vortex is characterized by the local vorticity and grows in strength and size as Rossby number increases above Ro = 0.34 to 1.63. The effect of βΔT on the vortex formation is negligible compared to the influence of the tangential Reynolds number as the local circulation is suppressed by the Coriolis forces at high rotational speeds. Both the tangential and radial velocity results suggest that as Ro is increased, the proportion of air that is radially ingested and expelled from a cavity decreases.

RF behavior of a second harmonic photonic band gap cavity gyrotron oscillator

RF behavior of a second harmonic photonic band gap cavity gyrotron oscillator

Design, fabrication, and characterization of a drift tube linac type double gap re-buncher cavity.

The Low Energy High Intensity Proton Accelerator (LEHIPA) at Bhabha Atomic Research Centre, India, has recently been commissioned to the target energy of 20MeV by beam acceleration through a 352MHz radio frequency quadrupole (RFQ) and drift tube linac (DTL). The medium energy beam transport (MEBT) line of LEHIPA matches the 3MeV beam from RFQ to the DTL using four electromagnetic quadrupoles and a re-buncher cavity. In the beam transport lines of high frequency linacs, TM010 mode single gap buncher cavities are conventionally used, while a double gap re-buncher cavity was chosen for the short length LEHIPA MEBT based on beam dynamics simulations. The 352MHz double gap re-buncher cavity has been designed in a DTL type geometry with a cell length of βλ. This double gap cavity is found to be more power efficient with a higher shunt impedance and transit time factor than the conventional single gap buncher cavity. Electromagnetic design simulations, fabrication details, low power and high-power RF test results, and beam test results of the re-buncher cavity are presented in this paper.

Experimental investigation of the effect of absorption material on the non-linear properties of perforated plates

Combinations of perforated plate and porous material are used in numerous applications for noise reduction at high sound pressure level, such as in aircraft engines and automotive mufflers. Therefore, it is important to have a better understanding of the acoustic property of these systems. A semi-empirical model is a common way to calculate and understand the sound absorption of these systems. Previous studies show that the interface between a perforated plate and porous material have direct effect on the non-linear property of the perforated plate and sound absorption. Therefore, in this study two conditions of perforated plate and porous material combinations was considered. First, when the perforated plate has direct contact to the porous material and second, when there is air gap between them. Results of this research shows that the variation of non-linear acoustic resistance in case either with or without a cavity gap of air is relatively small.

Enhancing forming accuracy in aluminum alloy variable-diameter tubes through dual-coil controllable electromagnetic forming

High-accuracy forming of aluminum alloy variable-diameter tubes imposes strict requirements on force field design. Although electromagnetic forming has shown unique advantages in enhancing the formability of aluminum alloy materials, its shortcomings lie in the single and difficult-to-adjust force field, which limits its application in variable-diameter tubes. To address this challenge, a novel dual-coil electromagnetic forming approach with good controllability of force field is proposed. Numerical simulations and experiments are both conducted to showcase the superiority of this approach in forming variable-diameter aluminum alloy tubes. The results demonstrate that the forming accuracy of AA6061-O variable-diameter tubes has significantly improved compared to a traditional single-coil system, in which the maximum die-fitting gap is reduced from approximately 2 mm to less than 0.22 mm. Furthermore, it is identified the force field produced by the single-coil system causes a local cavity gap between the tube and the die, which adversely affects the forming accuracy. In contrast, the improved force field produced by the dual-coil system facilitates bottom-to-top deformation of the tube, thereby avoiding undesirable cavity gaps and achieving high forming accuracy. Importantly, the dual-coil forming system offers significant controllability of the Lorentz force field by adjusting the coil discharge, making it suitable for variable-diameter tubes of different sizes without changing the coil structure. This work represents a substantial advancement in controllable tube forming, offering a new approach to force field design and holding promise for extensive applications in the forming of variable-diameter tubes.

Effects of Building Materials on Building Thermal Load in Malaysian Institutional Library

Green building, net-zero energy building, low energy building, and sustainable building are the common terms being used in the building industry nowadays, with the primary aim to produce buildings with low energy and low carbon dioxide (CO2) emissions. Different types of building materials can have significant implications for energy efficiency, especially in the warming climate. The energy crisis, future global warming, and climate change can be mitigated by choosing the right building materials, which will also lower the building's energy consumption and carbon dioxide emissions. This paper presents the effects of different building materials on the cooling capacity and cooling energy consumption of a building for four (4) different climate change weather data, namely, the present time scenario, the 2020s, 2050s, and 2080s time scenario using TRNSYS simulation software. The main library of a university in Petaling Jaya, Malaysia, was chosen as the case study. Three (3) types of building materials were studied, namely, Type 1 (brick walls with single-glazed windows), Type 2 (foam insulation cavity walls with double-glazed windows), and Type 3 (air gap cavity walls with double-glazed windows). The simulation results showed that the Type 2 building materials could reduce the yearly cooling energy consumption by 14.5%, compared with the current building materials (brick walls with single-glazed windows). The Type 3 building materials (air gap cavity walls with double-glazed windows) with the lower installation were wound to reduce the yearly cooling energy consumption by 9% compared with the Type 1 building materials. For architects, designers, politicians, and library administrators, the research's conclusions have immediate practical implications that will help them make decisions and implement energy-saving plans. In the end, this research helps libraries in Malaysia remain sustainable and resilient in the face of global warming and the energy crisis.

Advances in Physics of Semiconductors

It is my pleasure to write this preface to the Special Section in the May 2023 issue of pss(b), dedicated to the collection of selected works presented during the 35th International Conference on Physics of Semiconductors (ICPS) held in Sydney, Australia in 2022. It was one of the first meetings post the pandemic and it was wonderful to see the community gathering physically together. The ICPS series traditionally encompasses a variety of topics spanning device physics, quantum technologies, spin physics, wide bandgap materials, light–matter interactions, and other branches of materials science, physics and engineering. The collection to follow offers a glimpse into what has been presented, and showcases the excellent science undertaken around the globe. A growing interest in the scientific community is currently evolving around van der Waals crystals, and other two-dimensional systems. It is therefore no surprise, several works focus on these topics – discussing various excitonic, photonic, magnetic, and terahertz properties. Various spin phenomena effects are also discussed in traditional semiconductors such as GaAs/GaN and SiGe. Works on plasmonic gap cavities and electroluminescence as well as theoretical calculations of electronic structures are also included. The ICPS series has been continuously going now for over 70 years, one of the longest running conference series in the world. As we are preparing for the next meeting in Ottawa, Canada, the collection of papers should inspire our junior colleagues, that not only semiconductor physics is here to stay, but in fact, it is a multi-disciplinary and burgeoning field of research.

Numerical study of the performance for a curved double-skin façade in summer

Recently, curved double-skin façades (CDSFs) have been increasingly used in buildings due to the advantages of aesthetics and structure. However, existing studies mainly focus on planar double-skin facades (PDSFs) and barely address the thermal and ventilation performance of CDSFs. In this study, the influences of geometric parameters, glass material and solar radiation on the thermal and ventilation performance of the CDSF are studied with a CFD model validated by a reduced-scale experiment. The results show that the optimal cavity gap ranges from 0.75 m to 1 m, and the optimal ellipse aspect ratio is 0.5. Moreover, glass material shows a significant influence on the ventilation performance of the CDSF – an enhancement of 8.20%–21.31% more cavity velocity is found by replacing the clear glass with a low-e glass. Further analysis shows that the ventilation performance is more sensitive to the optical properties of glass material, and a higher absorptivity is more conducive to natural ventilation. Solar radiation – solar radiation intensities and solar incident angles - show predominant impacts on the cavity velocities of CDSFs with non-linear relationships. Because of the surface's non-uniformity distribution of solar radiation, solar radiation shows more impact on the cavity velocities of CDSFs than PDSFs. The influence of solar incident angles is found to be more sensitive, especially in the regions of big solar incident angles - the variation rates of cavity velocities for the CDSF under high solar incident angles (>45°) are much larger than that under low solar incident angles (<45°).

Improvement of Output Power and Bandwidth for Terahertz Extended Interaction Klystron With Multiple Resonance Cavities

In this article, an extended interaction klystron (EIK) in a terahertz band with high power, high efficiency, and wide bandwidth based on a mode overlap scheme and multiple resonance cavities is proposed. The high-frequency characteristics and electric field distribution of modes in 17-gap cavity are analyzed. And <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> mode and 15/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$16\pi $ </tex-math></inline-formula> mode are selected as the two adjacent working modes to realize mode overlap to expand the bandwidth. The number of cavity gaps and the length ratio of long and short slots are carefully optimized to achieve the appropriate frequency interval between modes. Then the sensitivity analysis of key parameters requires that the processing tolerance of the circuit should not exceed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5~\mu \text{m}$ </tex-math></inline-formula> . The stability of the circuit is analyzed by using the normalized electronic conductance to ensure that the circuit will not produce oscillation. Finally, with the conditions of 0.3-A current, 18.5-kV voltage, and 0.02-W input power for the designed G-band six-cavity EIK, the PIC simulation results shows that the mode overlap can be achieved in different cavities, and the circuit can obtain a power of 740 W, a gain of 45.68 dB, a 3-dB bandwidth of 1.92 GHz, and an efficiency of 13.3%. The power, bandwidth, and efficiency have obvious improvement compared with other reported EIKs in the same frequency band. In addition, the consistency of the simulation results trend between AJDISK and CST also proves that the circuit we designed is reliable and feasible for the terahertz band EIKs with high performance in the future.

A kinematic excess in the annular gap and gas-depleted cavity in the disc around HD 169142

ABSTRACT We present ALMA band 6 images of the 12CO, 13CO, and C18O J = 2-1 line emissions for the circumstellar disc around HD 169142, at ∼8 au spatial resolution. We resolve a central gas-depleted cavity, along with two independent near-symmetric ring-like structures in line emission: a well-defined inner gas ring [∼25 au] and a second relatively fainter and diffuse outer gas ring [∼65 au]. We identify a localized super-Keplerian feature or vertical flow with a magnitude of ∼75 ms−1 in the 12CO map. This feature has the shape of an arc that spans azimuthally across a position angle range of −60° to 45° and radially in between the B1[26au] and B2[59au] dust rings. Through reconstruction of the gas surface density profile, we find that the magnitude of the background perturbations by the pressure support and self-gravity terms are not significant enough to account for the kinematic excess. If of planetary origin, the relative depletion in the gas-density profile would suggest a 1 MJ planet. In contrast, the central cavity displays relatively smooth kinematics, suggesting either a low-mass companion and/or a binary orbit with a minimal vertical velocity component.

Ventilation performance of solar chimney integrated into a multi-storey building

Previous studies have mainly focused on solar chimneys in single-chamber/zone or single-story buildings. Its theoretical development in multi-chamber or multi-story buildings is lagging, which hampers its practical applications in multi-storey buildings. This study investigated ventilation capacity characterized by volume flow rates numerically and theoretically for a multi-storey building with a solar chimney. Three mathematical methods based on simplified models were introduced to predict the ventilation rates for each floor. By comparing the three methods, Method 1, based on the bifurcation hypothesis, was found suitable for two-storey or single-storey cases; and Method 3, based on empirical flow equations, is practical for those cases greater than two-storey. To optimize the ventilation rate, a wider cavity gap and a higher stack height for a multi-storey solar chimney were the most effective ways compared to the single-zone/floor cases. A larger window area and air inlet size promoted the ventilation capacity, where the growth rate of volume flow was small and critical values exist. It was observed that the solar chimney dimensions show a more significant effect on the volume flow rates than the solar radiation intensity. The main contribution of this study is that it establishes the links between the single-zone and the multi-storey theoretical models and proposed practical mathematical methods to obtain acceptable prediction accuracy of ventilation rates for a solar chimney in a multi-storey building.