Active Frequency Selective Surface with Simultaneous Absorption/Transmission Mode Switching and Frequency Tuning Characteristic

A dual-function switchable and frequency tunable active frequency selective surface (AFSS) is proposed in this article. The proposed AFSS consists of a dielectric substrate and metal patches on the top and bottom surfaces of the substrate, while varactor diodes and PIN diodes are soldered on the top and bottom layers, respectively. A simple bias network is designed to facilitate the function adjustment of the AFSS. By controlling the OFF and ON states of the PIN diode, the AFSS can switch between filtering and wave absorbing functions. Furthermore, by adjusting the bias voltage of the top varactor diode, the AFSS can achieve continuous frequency tunability. Simulation and experimental results confirm the dual-function switchable and frequency tunable performance of the proposed AFSS.

This paper proposes a novel dual-band reconfigurable electromagnetic (EM) structure capable of dynamically switching among transmission, absorption, and reflection modes. The design integrates two varactor diodes and two PIN diodes on the top layer, along with four PIN diodes on the bottom layer, allowing independent biasing and real-time control. The transmission mode is achieved over <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1.10-2.75 \text{GHz}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$4.55-4.75 \text{GHz}$</tex> when all diodes are turned OFF. In the absorption mode, occurring over <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{2. 1 5}-\mathbf{3. 2 2 ~ G H z}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{4. 8 0}-\mathbf{5. 1 2}$</tex> GHz, the top-layer diodes remain OFF while the bottom-layer diodes are activated. The reflection mode covers a broad frequency band and is realized when all diodes are <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$O N$</tex> and the varactor capacitance is tuned to 3.2 pF. Detailed biasing network design and current distribution analysis ensure efficient switching and minimal insertion loss. Full-wave simulation results validate the structure's performance, demonstrating frequency agility, absorption above 90 %, lowloss transmission, and near-total reflectivity. The proposed design is compact, low-profile, and polarization-insensitive, making it suitable for applications such as adaptive radomes, reconfigurable radar systems, stealth platforms, and smart communication surfaces. The multifunctional capability establishes this structure as a promising candidate for nextgeneration EM systems requiring adaptive and tunable responses.

A reconfigurable active frequency selective surface (AFSS) with ultra-wideband (UWB) characteristics is presented in this article. The proposed AFSS is a periodic array structure which consists of three metal layers and two dielectric layers. PIN diodes are arranged on the top and bottom metal layers which can rebuild the function of AFSS. The transmission bandwidth of the OFF-state AFSS is 8-12.5 GHz with a fractional bandwidth of 44%, and the transmission coefficient of the ON-state AFSS is lower than -10 dB from 2 to 18 GHz. Additionally, the AFSS has dual polarization characteristics, and it is angular stable and polarization-insensitive for two polarizations. The simulation results show the proposed AFSS is a valuable candidate for radome applications.

In this paper, an octahedron electronically beam-scanning antenna using a novel slot active frequency selective surface (AFSS) is presented. The antenna consists of eight panels of octagonal slot AFSS array and an omnidirectional feed antenna located in the center. The beam-scanning of the antenna is obtained by switching the states of the PIN diodes to reconfigure the AFSS as EM transparent or reflective to the incident electromagnetic waves. By controlling the DC bias voltages to PIN diodes which are grouped by columns, the directive beam of the antenna can be switched to cover the entire azimuth plane. A prototype is fabricated and measured. Simulation and measurement results of the antenna are presented to verify the design concept. It is shown that the designed octahedron electronically beam-scanning antenna can cover a full 360°horizontal angular range. The presented design shows obvious advantages in terms of low power consumption, low cost and easy fabrication.

In this paper, a beam switching antenna with a novel active frequency selective surface (AFSS) is proposed at 5.2 GHz. The antenna is composed of an omnidirectional patch antenna and AFSS. The AFSS is made up of 6 columns, each with 2 unit cells, which are placed vertically around a patch antenna to form a hexagonal wall. To steer beam of the antenna, high frequency pin diodes are precisely inserted into the AFSS to reconfigure electromagnetic (EM) response of surfaces. The reflection and transmission characteristics of the proposed AFSS unit cell are investigated. The simulation results show that the transmission and reflection bands of AFSS unit cell can be changed by setting diodes on and off. This new AFSS can be used to implement a sweeping radiation pattern at all azimuth angles. The antenna can sweep the entire azimuth plane in six steps and effectively operate over a bandwidth of more than 500 MHz.

A reconfigurable antenna with frequency agility and pattern-switching ability is presented in this paper. The proposed design comprises a planar and compact frequency reconfigurable monopole antenna and an active frequency selective surface (AFSS) with reconfigurable transmission and reflection properties in dual bands. The AFSS screen is divided into four sections and each section is composed of four FSS elements with only one PIN diode in each unit cell. The monopole antenna, which is situated at the center of the box-shaped AFSS to illuminate , can reconfigure its resonating frequency between 2.5 and 3.6 GHz with the help of only one PIN diode. With the help of this transformation ability of AFSS behavior electronically, the pattern can be steered across the entire X–Z plane in eight steps at two different operating frequencies independently. This antenna can be very useful in various wireless applications such as drones, small base stations, etc.

Conventional active frequency selective surfaces (AFSS) are designed with a DC biasing circuit to apply DC biasing voltage across active components. An innovative method to design AFSS is proposed in this paper to use an induced voltage across both ends of the surface loading components as the biasing signal to control FSS's transmission properties. The result from simulation proved that, a pass band exists on the AFSS at 3.5GHz when it is exposed to an electric field at a smaller intensity; at the electric field intensity (EFI) over 70 V/m, the insertion loss of the electromagnetic wave (EMW) increases at 3.5 GHz; in the case that the incident microwave's field intensity reaches 5000 V/m, the insertion loss is over 20 dB. This interesting phenomenon make the new AFSS has the ability of HPM protection, which mean that a pass band exists when EFI is weak enough, along with increasing incident field intensity, the pass-band finally turns into a stop-band because of the break though of the diodes.

In this article, a transmission and reflection states switchable Luneburg lens (LL) reflector based on active frequency selective surface (AFSS), namely LL-AFSS reflector, is proposed. The reflector is composed of a miniaturized AFSS reflector, which can change the working state, and a LL composed of six layers and five media from inside to outside. By changing the bias voltage of the PIN diode loaded on the AFSS reflector, the transmission and reflection working states of the LL reflector can be freely switched in the frequency range of 3.5–5 GHz. When the PIN diodes are in ON state, the incident electromagnetic wave will not be reflected through the LL reflector. When the PIN diodes are in OFF state, the radar cross section (RCS) generated by the LL reflector to the incident electromagnetic wave reaches about 15 dB within the angle range of −30 ≤ φ ≤ 30°. The electromagnetic numerical simulation and experimental sample verification of LL-AFSS reflector are carried out. The results show that the proposed design method is feasible and the RCS changes of transmission and reflection characteristics of LL reflector are obvious.

This paper presents a working state switchable Luneburg lens (LL) reflector, based on active frequency selective surface (AFSS). By changing the bias voltage of PIN diodes loaded on AFSS, the working state of LL and radar cross section (RCS) can be switched in the frequency range of 6 GHz-8 GHz. When the PIN diode is in ON state, the AFSS working in a reflective state, and the LL reflector’s RCS can be improved to at least 15dB, the effect is the same as the metal plate. When the PIN diode is in OFF state, the AFSS working in a transmission state, and the RCS of the LL reflector can decreased by about 2-3dB in all OFF state, 5-22dB in OFF-ON strate.

A novel symmetric anchor-shaped active frequency selective surface (AFSS) with a wide tuning frequency range is proposed. Varactor diodes are used as the active tuning components at the center of each AFSS unit. The equivalent circuit model of the AFSS unit is extracted. SPICE-based circuit simulation and full-wave simulation are compared to predict the resonant frequency. A wide tunable frequency range from 1.76 to 2.45 GHz with a relative bandwidth of 33% is achieved. A prototype of AFSS is fabricated and tested. The measurement result is consistent with the simulation. The design has low power consumption and is potentially used for selectively shielding or reusing of GSM, TD-SCDMA, or Wi-Fi spectrums.

The problem addressed here is the challenge of determining the best production strategy for multilayer reservoirs which varies from field to field as well as from well to well. Commingled production strategy is one of the most commonly used for several multilayer wells. However, there are some limitations to this method. Mostly, when very complex multilayer wells which contain different types of fluid in each productive layer are identified, the selection process of production approach is basically trial and error and later found to be a poor choice. One attempted solution to choosing the optimal production strategy is using numerical reservoir simulation. In this study, we used reservoir simulation to compare the performance of four different production strategies for different combinations of types of fluid present in a two-layer system. Strategy 1 in which the fluid is produced from two layers simultaneously is the best production approach when oil is present in the top and bottom layers. Strategy 2 in which the fluid is produced from one layer at a time starting with the bottom layer is the best production approach when reservoir fluid at the top layer is gas while fluids present in the bottom layer can vary from oil, gas&amp;oil, gas&amp;water and oil&amp;water. Strategy 3 produces fluid from one layer at a time, starting with the bottom layer. When the production rate decreases to half of the original rate, the two zones are produced in a commingled fashion. Similar to strategy 1, strategy 3 is also the best production approach when oil is present in the top and bottom layers. Strategy 4 is similar to strategy 3 but starting with the top layer. This strategy is the best production approach when oil is present in the top layer and gas&amp;water in the bottom layer. This approach can delay water production and sustain reservoir pressure.

A novel antenna with both frequency and pattern reconfigurability is presented. The reconfigurability is achieved by integrating an active frequency selective surface (AFSS) with feed antenna. The smart FSS comprises a printed slot array loaded by varactors. A novel dc biasing arrangement is proposed to feed the slots vertically so that the unwanted effects caused by bias lines are minimized. A monopole antenna is designed to illuminate the AFSS. The resulting structure can operate in a frequency tuning range of 30%. By reconfiguring the different sections of active FSS cylinder into a transparent or reflector mode, the omnidirectional pattern of the source antenna can be converted to a directive beam. As an illustration, half of the AFSS cylinder is successively biased, enabling the beam switching to cover the entire horizontal plane over a range of frequencies. An antenna prototype was fabricated and measured. Experimental results demonstrate the capability of providing useful gain levels and good impedance matching from 1.7 to 2.3 GHz. The antenna offers a low-cost, low-power solution for wireless systems that require frequency and beam reconfigurable antennas. The proposed design consumes about 1000 times less dc power than the equivalent narrowband beam-switching antenna design using p-i-n diode-loaded AFSS.

Wavelength discrimination (WLD) detector optimization for time-of-flight positron emission tomography with depth of interaction information

This paper reports the results from numerical modeling of spudcan deep penetration through three-layer clays. Two typical seabed strength profiles commonly encountered in the field, and identified as critical for potential punch-through failure, were considered: (1) uniform stiff-soft-stiff clay and (2) nonuniform clay with an interbedded stiff clay layer. Three-dimensional large deformation finite-element (LDFE) analyses were carried out with and without simulating strain softening and strain rate dependency of the shear strength. The results were compared with previously published LDFE results and centrifuge test data. A detailed parametric study was undertaken, varying the relevant range of layer thicknesses (relative to the spudcan diameter), strength ratios, normalized strength, and strength nonhomogeneity. Punch-through and rapid leg penetration (for stiff-over-soft) and squeezing (for the reverse) were demonstrated by the penetration resistance profiles and associated soil failure mechanisms. The results emphasized that the resistance profile from a spudcan continuous penetration in a three-layer sediment (e.g., stiff-soft-stiff) may be significantly different from the combined profiles resulting from two separate analyses on first-second layers and second-third layers, even if an appropriate depth factor is accounted for. For uniform stiff-soft-stiff clays, the presence of the bottom stiff clay layer within a short distance of one diameter affected spudcan bearing response in the top layer and suppressed the potential for punch-through failure (apart from rapid leg run for t1/D=0.75 and su1s/su2=3). A trapped soil plug beneath the advancing spudcan, following penetration of the top stiff layer, caused the bottom stiff layer to be sensed earlier and led to enhancement of the limiting squeezing depth. For nonuniform clay with an interbedded stiff layer, spudcan bearing response was dominated by squeezing (with limiting squeezing depth of approximately 0.18D) in the top soft layer and potential punch-through and rapid leg run (for t2/D≥0.5 and su2/su3s=2.5) in the middle and bottom layers. In contrast to ISO recommendations, the soft soils in between the advancing spudcan base and the stronger layer did not squeeze out completely. Instead, some of the trapped material was forced into the underlying stronger layer. Punch-through distance was found to reduce significantly with increasing positive strength gradient of the bottom layer.

Thermo-physiological comfort of the fabric is achieved through the ability to manage heat and transmit sensible and insensible perspiration through the fabric. Ergonomic comfort aspects of sports clothing can be improved by enhancing the moisture management properties of knitted fabrics. Double-face knitted structures were developed by selecting the right type of material for the top and bottom layer. In this paper, the moisture management properties of four double-face knitted fabrics with hydrophobic fibre in the top layer (Polypropylene and micro-fibre polyester) and hydrophilic fibre in the bottom layer (Bamboo) were studied to find out the suitability for sportswear. The subjective perception was carried out using thermal state parameters and was correlated with Overall Moisture Management Capacity (OMMC). Double-face fabric knitted with micro-fibre polyester in the top layer and bamboo in the bottom layer has excellent moisture management properties which seem suitable for next-to-skin application. However, micro-fibre polyester (20%)/polypropylene (20%) yarns in the top layer on account of polypropylene due to its dry feel shows good OMMC followed by micro-fibre polyester in the top layer. Univariate analysis of variance with a confidence level of 95% showed that all the moisture management indices are statistically significant.