Mushroom Structure Research Articles

Viscous multi-species lattice Boltzmann solver for simulating shock-wave structure

The Onsager Bhatnagar Gross Krook kinetic model proposed by Mahendra et al. [32, 33] has been extended to arrive at the viscous compressible flow equations for a multi-species diffusion problem. The multi-species model ensures (i) correct exchange coefficients, (ii) positivity, (iii) that it follows indifferentiability principle and (iv) that correct amount of entropy get added as per the Onsager’s maximum entropy production principle (MEPP). A Lattice Boltzmann method (LBM) has been developed using the derived methodology within the framework of finite volume method (FVM). This solver incorporates the physics of polyatomic gases with internal degrees of freedom with flexible Prandl number. This solver can simulate the problem with species having different specific heat ratio and molecular weights. Although the equations are derived for multi-species, only binary test cases have been considered in this paper. The solver has been validated against binary shock-wave structure problems using experimental and theoretical data. Two dimensional Richtmyer Meshkov instability test case has been compared with and without viscous effects. The diffusive (viscous and mass diffusion) effects are manifested in the reduction in amplitude and increment in width of the mushroom structure. In the framework of FVM, the proposed scheme of LBM is efficient with good resolution of solutions and is easily adaptable.

Microtrip‐line‐slot feed dual‐band dual‐mode element and array antenna based on mushroom structure

One patch antenna with dual-band dual-mode (DMDB) characteristic based on mushroom structure is designed and analysed in this study. The antenna operates at two modes: the bidirectional mode with endfire radiation patterns and the directional mode with broadside radiation patterns. The equivalent circuit, dispersion diagrams, field distributions, reflection coefficients and radiation patterns are given for confirming the working principle. Compared with the former DMDB antennas, array antenna could be designed to realise gain enhancement for both the two modes. Both element and 1 × 2 array antenna prototypes were fabricated for verification. The measured results show that the two modes resonant at about 9.8 and 11.95 GHz, respectively. Comparing with the element, gain enhancement of about 2.8 and 2.1 dB are realised by the array for the endfire and broadside modes, respectively. With pattern diversity and array realisation, this antenna type owns potential application value in wireless communication systems.

Numerical study of tectonic structure evolution in a multi-layer evaporite sequence

Field studies carried out in the Kłodawa Salt Structure (KSS), Poland, reveal that within a carnallite-halite-kieserite sequence, finger-like structures developed during an early, pre-diapiric stage of the KSS evolution. We used 99 numerical simulations to model finger development and investigate mechanical properties of carnallite, halite and kieserite during deformation. Models used inverse density stratification of a three-layer set with varying 1) layer viscosities, 2) thicknesses and 3) density difference ratios. Finger shapes in the models were categorized into single and multiwavelength structures. Among the single-wavelength shapes, bulb, mushroom, thumb and bloated (i.e. without a regular shape) structures were distinguished. We show two transitions between the single and multiwavelength structures, which correspond to the cases of either the lower or upper layer having viscosity more than an order of magnitude larger than the two other layers. Through comparison of finger shapes developed in the models and in the natural structures, we estimate viscosities of >1017 Pa s for halite, <1017 Pa s for carnallite and <1016 Pa s for kieserite. The estimated low viscosity of kieserite can be attributed to the small grain size of the rock, the presence of fluids during deformation or to different mineral composition of the layer than presently observed.

Sustaining the Radiation Properties of a 900-MHz-Band Planar LoRa Antenna Using a 2-by-2 Thin EBG Ground Plane

In this work, a 2-by-2 array of a low-profile EBG ground plane is used as a means of sustaining the radiation performance of a 900-MHz LoRa antenna that could be installed at various construction sites. The proposed semi-circles added mushroom (SAM) structure enables a thin EBG height of 0.02λg on an FR-4 substrate at 900 MHz frequencies. A planar electric meander antenna for the 900-MHz LoRa band is integrated with the proposed 2-by-2 SAM plane. From a simulation and demonstration, it is found that the impedance and radiation properties of the integrated prototype in free space are well maintained with a minimum degradation even when it is placed on a concrete medium.

Multi-Mode High-Gain Antenna Array Loaded With High Impedance Surface

A novel and simple broadband antenna array loaded with high impedance surface is proposed in this letter. The unit cell is composed of a main radiating patch and a pair of EBG arrays placed symmetrically at the two radiating edges of the main radiating patch. The main radiating patch is responsible for the original TM10 mode while the electromagnetic bandgap (EBG) arrays is for another resonant mode characterized as quasi-TM20 mode. Thus, wideband performance is obtained due to the combination of the two generated resonant modes. And on this basis, by adding symmetrical mushroom structures at the other two edges of the main radiating patch, the impedance bandwidth and sidelobe suppression are improved. The current distributions on the all metal patches are almost uniform, therefore high gains can be obtained during the whole operating bandwidth. The antenna array is formed by 4 × 4 unit cells and the prototype is fabricated to validate the design. The measured results show that the impedance bandwidth is broadened from 11.1 to 15.6 GHz with the peak-gain reaching as high as 18.8dBi. Besides, the proposed antenna is easy fabrication with low profile which provides great convenience in the actual beam and point-to-point communication applications.

Control of Solder Bump Growing Morphology in Lead Free Plating

Abstract Plating Solder bump is one of the key enabling technologies for flip chip assembly methodology. Flip chip assembly has advanced to support higher levels of interconnect and small feature sizes. Electroplating is a very promising technology for finer bump features when compared with solder printing and ball mounting. Hence, the plated-solder bump morphology is quite important for process quality control and design realization. This paper aims to study the plated solder behavior from as-plated mushroom structure to after reflowed bump stage photoresist sizing. In addition, this activity will consider the full bumping process integration relative to the electroplated solder bump design rules.

Miniaturized RFID Reader Antennas Based on CRLH Negative Order Resonance

This article presents a type of miniaturized high-efficiency patch antennas for UHF radio frequency identification (RFID) reader applications based on the composite right-/left-handed (CRLH) negative order resonance. Miniaturization is achieved by using the first negative order resonance (−1st mode). These proposed CRLH resonators are realized by etching gap on the patch surface, which acts as a series left-handed (LH) capacitor as well as an effective radiator, and using metallic screws on the corner as steadying posts while also providing an LH inductor. Different from the traditional mushroom structures, these screws are placed on the two sides or corner of the unit cells allowing unobstructed current and field flowing inside the cavity. This enhances the quality factor and radiation efficiency. In addition, only metallic sheets, screws, and one thin substrate are used in the design, therefore dielectric loss is basically eliminated. Overall, these proposed antennas achieve a miniaturized size, as well as a high gain and radiation efficiency. The radiation characteristics of these RFID antennas are similar to the conventional patch antennas due to the −1st-order operation. Four antennas, including linearly polarized, circularly polarized (CP), frequency-tunable, and polarization/frequency-reconfigurable antennas, are carefully designed, investigated, and experimentally verified. Remarkable agreement has been observed between simulation and measurement. These antennas well cover 902–928 MHz UHF band. RF range tests are carried out for application verification. They demonstrate a compact size, low-cost, low-loss, and high efficiency with easy implementation. The CP antennas exhibit a good bandwidth and an excellent axial ratio in the whole upper semisphere. They have been selected for mass production, which illustrates a good engineering application example of CRLH metamaterial antennas.

Mutual coupling reduction in metamaterial antenna for terahertz application

We investigate in this work an effective approach to reduce mutual coupling between two metamaterial antennas operating at the THz frequency band by incorporating a metasurface designed using an electric inductive capacitive resonator. The metasurface is designed to provide a band stop functionality in the operating bandwidth of the antenna. The proposed method shows that the improvement of mutual coupling is at least 10 dB compared with conventional antennas. Thus, this proposed approach can be utilized to mitigate mutual coupling between antennas in THz application. Moreover, to enhance the antenna performances in terms of return loss, directivity, gain, and radiation efficiency, the antenna is designed with a mushroom structure based on the zeroth-order resonant characteristic of a composite right/left-handed transmission line. The electromagnetic behavior of the antenna is studied and an analytical equivalent-circuit model is also proposed.

High resolution numerical simulation of a shock-accelerated refrigerant-22 bubble

Computational results are presented for an evolving Refrigerant-22 bubble after its interaction with a Mach 1.22 shock wave. Initially, the bubble is kept stationary in surrounding air, presenting a fast/slow interface to the approaching shock wave. We solve the Euler equations in two dimensions using the low dissipation AUSMD algorithm coupled with a ninth-order upwind scheme for the convective terms and a four-stage third-order Runge–Kutta time integration scheme. The high resolution solver reveals intricate details of vorticity generation during and after the interaction. In the early phase, the detected wave structure matches with available experimental and computational results. Going beyond what is available in literature, we show how the central jet that has drawn attention of researchers could be explained by observing the Richtmyer–Meshkov instability driven mushroom structure that appears behind a cylindrical blast wave set off near the ground. Initial growth of vorticity generated by the baroclinic torque, appearance of opposite signed vorticity during emergence of the transmitted wave, interaction of vortices of various sizes and their accumulation in regions of intense mixing are all captured well. Tracking the area within the bubble where mole fraction of Refrigerant-22 is between 0.05 to 0.8, we show that mixing of air and Refrigerant-22 is increases with a period of time. Fourier spectra of streamwise kinetic energy is indicative of redistribution of energy to lower Fourier modes during long time bubble growth. This redistribution of energy occurs through merger of vortices during their interaction.

Design of a Broadband Common-Mode Filter With Four Transmission Zeros

This paper presents a design methodology on the broadband common-mode filter (CMF) with four transmission zeros for solving electromagnetic interference in high-speed differential digital systems. An equivalent circuit model is established based on the mushroom structure to characterize the common-mode bandstop response, and the simplified transmission zeros condition is derived to predict the transmission zeros. Furthermore, the design criteria as well as design flow through the simplified transmission zeros condition can be employed to synthesize the four zeros CMF systematically. Finally, in order to verify the proposed design methodology, a broadband CMF with four transmission zeros is fabricated on a four-layer printed circuit board. The experimental results show that the proposed CMF can reduce the common-mode noise over 10 dB from 1.23 to 5.15 GHz with a fractional bandwidth of 123%. Compared with other literature on mushroom-like CMFs, the proposed CMF has the widest common-mode suppression bandwidth. The electrical size is only ${\text{0.0427}}\lambda _{g}^{2}$ , where λ $_{g}$ is the guided wavelength of the central frequency of its common-mode stopband. The insertion loss of differential mode is below 3 dB from dc to 8.5 GHz. In addition, the measured eye diagram of the proposed CMF indicates that it maintains good signal integrity for high-speed differential signals.

Passive Matched Mushroom Structure for a High Sensitivity Low Profile Antenna-Based Material Detection System

A passive multi-layered structure based on a mushroom high-impedance surface is proposed as a part of a high sensitivity low profile antenna-based material detection system. The system consists of an interrogating antenna placed outside the near field of a three-layered planar sensor. The sensor is a periodic structure containing $10\times 10$ unit cells with overall dimensions of $180\,\,\text {mm}\times 180\,\,\text {mm}\times 10.2\,\,\text {mm}$ . Achieving high sensitivity at a large monitoring distance (150 MHz per unit relative permittivity at 430 mm), this sensor provides sensing capability in hazardous or inaccessible environments while also maintaining independence of the sensor and the antenna for greater system flexibility. Material detection is based on wireless tracking of frequency shifts in the absorption peak of the sensor. These shifts arise from changes in the permittivity of a sensing layer sandwiched between a bottom resonant layer (a mushroom high-impedance surface) and a top inductive matching layer. Two independent mechanisms contribute to the resonant shifts for heightened sensitivity at a low profile. Two sets of experiments were performed to verify the operation of the sensor over a wide range of solid and liquid material permittivities. First, solid samples of Teflon, Plexiglass, and Rogers microwave laminates (TMM06 and TMM10) were detected with frequency shifts up to 1233 MHz. Second, liquid samples of isopropyl alcohol, ethanol, methanol, and de-ionized water were detected with corresponding frequency shifts up to 130 MHz. Measurements are performed using a single reader antenna to reduce the cost and complexity for in-field applications.

Dual‐band monopolar microstrip antenna using a quasi‐circularly arranged mushroom resonator on meshed ground structure

AbstractThis article presents a new dual‐band monopolar microstrip antenna with a meshed ground structure to improve the radiation performances. The quasi‐circularly arranged seven mushroom structures are utilized for dual‐band operation, which supports the resonances of the infinite wavelength and the TM modes. To improve the radiation performance, the meshed ground is employed and investigated by lowering the Q‐factor of the resonator. The proposed antenna demonstrates that dual‐band monopolar radiations at 3.298 and 5.709 GHz are in good agreement with the simulation results.

Numerical investigation into primary breakup of diesel spray with residual bubbles in the nozzle

The paper presents a three-dimensional numerical investigation of the high-pressure diesel injection with residual bubbles in the nozzle using the Multi-fluid-Quasi-VOF (volume of fluid) model based on the OpenFOAM framework. The validity of the model to simulate the near-field spray was verified. It was found that the predicted primary breakup process was in good agreement with experimental imaging. Furthermore, the evolution of the instability waves at the gas-liquid interface, the formation of ligaments and the effects of bubbles initially residual in the nozzle on the primary breakup were analyzed. The results demonstrate that drag force is one of the main reasons to trigger the instability waves and consequently enhance the primary breakup. The residual bubble initially inside the nozzle can also improve the primary breakup and the turbulent perturbation especially in the mushroom-structure region. The large residual bubble near the nozzle inlet can lead to the formation of liquid filaments at the neck of the spray plume. On the other hand, the large residual bubble near the nozzle outlet considerably promotes the fragmentation of the mushroom structure. Meanwhile, residual bubbles will impact the development of cavitation and consequently enhance instability waves.

Differential-To-Common-Mode Conversion Suppression Using Mushroom Structure on Bent Differential Transmission Lines

In this paper, we propose a method to suppress differential-to-common-mode conversion noise from right-angle bent differential lines by installing a mushroom structure on the narrow inner line. We assessed the mode conversion noise suppression characteristics of the proposed structure by analyzing dispersion diagrams. The proposed structure exhibits differential-to-common-mode conversion ( $S_{cd21}$ ) below −20 dB up to 6 GHz, while $S_{cd21}$ of conventional right-angle bent differential lines is only maintained below −20 dB for frequencies up to 1.04 GHz. In addition, we suggest that further enhancements of the mode conversion suppression bandwidth can be achieved by installing multiple distributed mushroom structures on right-angle bent differential lines. The use of multiple distributed mushrooms enabled us to achieve a wider frequency bandwidth by compensating more fully for the phase difference between the inner and outer lines. Therefore, the right-angle bent differential lines with multiple distributed mushrooms can suppress mode conversion noise under −20 dB up to 10 GHz. We assessed the performance of our proposed structure by conducting measurements in both the frequency and time domains. We obtained a good agreement between our experimental and numerical results. In addition, we measured eye diagrams to demonstrate that the proposed structures suppress differential-to-common-mode conversion noise without degrading the differential signaling quality.

Hypersonic boundary layer transition on a concave wall: stationary Görtler vortices

This study investigates the stability and transition of Görtler vortices in a hypersonic boundary layer using linear stability theory and direct numerical simulations. In the simulations, Görtler vortices are separately excited by wall blowing and suction with spanwise wavelengths of 3, 6 and 9 mm. In addition to primary streaks with the same wavelength as the blowing and suction, secondary streaks with half the wavelength also emerge in the 6 and 9 mm cases. The streaks develop into mushroom structures before breaking down. The breakdown processes of the three cases are dominated by a sinuous-mode instability, a varicose-mode instability and a combination of the two, respectively. Both fundamental and subharmonic instabilities are relevant in all cases. Multiple modes are identified in the secondary-instability stage, some of which originate from the primary instabilities (first and second Mack modes). We demonstrate that the first Mack mode can be destabilized to either a varicose-mode or sinuous-mode streak instability depending on its frequency and wavelength, whereas the second Mack mode undergoes a stabilizing stage before turning into a varicose mode in the 6 and 9 mm cases. An energy analysis reveals the stabilizing and destabilizing mechanisms of the primary instabilities under the influence of Görtler vortices, highlighting the role played by the spanwise production based on the spanwise gradient of the streamwise velocity in both varicose and sinuous modes. The effects introduced by the secondary streaks are examined by filtering the secondary streaks in two new simulations with nominally identical conditions to those of the 6 and 9 mm cases. Remarkably, the secondary streaks can destabilize the Görtler vortices, therefore advancing the transition. The stability theory results are in good agreement with those from direct numerical simulations.

The Distinction between Mushroom and Umbrella Structures in Slovene Architecture

A brief historical overview of the development of tree-inspired structures is given first. It starts with the world’s first three mushroom slab constructions built from 1906 to 1908 and continues with several tree-inspired roof structures of the first half of the twentieth century. The main part of the paper describes eight selected buildings in Ljubljana, Slovenia, all of them examples of mushroom or umbrella structures made of reinforced concrete. The oldest described building is an experimental structure from 1933, then come two pavilions built at Ljubljana’s Exhibition Centre, three different examples of gas stations, canopies for cars, and canopies at the Ljubljana’s main railway station. Except the oldest one, all were built in the 1960’s and early 1970’s. The buildings are compared quantitatively regarding their overall size, shape of the roof, and the number of the repetitive structures these buildings are made of. The type of each described structure is examined and compared to others. Laymen and even some experts often use the terms mushroom and umbrella structure imprecisely, the indifference and the lack of knowledge being the most probable reasons. Based on the presented analysis it is asserted that the distinction between mushroom and umbrella structures must be made regarding how the load force is transferred from the roof to the pillar. This distinction should also be made first when classifying recently built tree-inspired structures.

In Situ Observation Reveals Local Detachment Mechanisms and Suction Effects in Micropatterned Adhesives

AbstractFibrillar adhesion pads of insects and geckoes have inspired the design of high‐performance adhesives enabling a new generation of handling devices. Despite much progress over the last decade, the current understanding of these adhesives is limited to single contact pillars and the behavior of whole arrays is largely unexplored. In the study reported here, a novel approach is taken to gain insight into the detachment mechanisms of whole micropatterned arrays. Individual contacts are imaged by frustrated total internal reflection, allowing in situ observation of contact formation and separation during adhesion tests. The detachment of arrays is found to be governed by the distributed adhesion strength of individual pillars, but no collaborative effect mediated by elastic interactions can be detected. At the maximal force, about 30% of the mushroom structures are already detached. The adhesive forces decrease with reduced air pressure by 20% for the smooth and by 6% for the rough specimen. These contributions are attributed to a suction effect, whose strength depends critically on interfacial defects controlling the sealing quality of the contact. This dominates the detachment process and the resulting adhesion strength.

Separated rows structure of vortex streets behind triangular objects

We discuss two distinct spatial structures of vortex streets. The ‘conventional mushroom’ structure is commonly discussed in many experimental studies, and the exotic ‘separated rows’ structure is characterized by a thin layer of irrotational fluid between two rows of vortices. In a two-dimensional soap film channel, we generate the exotic vortex arrangement by using triangular objects. This setting allows us to vary the thickness of boundary layers and their separation distance independently. We find that the separated rows structure appears only when the boundary layer is thinner than 40 % of the separation distance. We also discuss two physical mechanisms of the breakdown of vortex structures. The conventional mushroom structure decays due to the mixing, and the separated rows structure decays because its arrangement is hydrodynamically unstable.

Continuous Fabrication of Wide-Tip Microstructures for Bio-Inspired Dry Adhesives via Tip Inking Process

In this paper, we report a new method for continuous fabrication of dry adhesives composed of microstructures with mushroom-shaped ends. Conventional mushroom microstructure fabrication is performed with a simple molding technique using a reversed phase master. In a typical fabrication process, thin- and wide-tip portions may be ripped during demolding, making it difficult to use in a continuous process. It is also difficult to apply the mushroom structure master to a continuous process system in roll form. Here, a continuous fabrication process was developed by applying the method of fabricating a wide tip using a tip inking method after forming a micropillar. Through the continuous process, the dry adhesive was successfully fabricated and the durability was measured with a reasonable pull-off strength (13 N/cm2). In addition to the reasonable adhesion, high durability is guaranteed, and fabricated dry adhesives are expected to be used in various fields.

Feeding Coils Design for TE-Polarized Bessel Antenna to Generate Rotationally Symmetric Magnetic Field Distribution

Three feeding structures are proposed to feed a TE-polarized Bessel antenna for a rotationally symmetric magnetic field distribution. We first propose a spiral coil and a dual half-loop coil to achieve rotationally symmetric magnetic field, resulting in homogeneous current distribution on the coils. Unfortunately, the magnetic field distribution is very sensitive to the coil size for both structures. An alternative solution using a half-loop coil with mushroom structure is then designed to achieve robustness. Both the simulation and the measurement demonstrate that the proposed feeding structures can generate a rotationally symmetric magnetic field distribution; the proposed spiral coil is simple and efficient, while the half-loop coil with mushroom structure is robust.