Switchable Layer Research Articles

A Low-Profile Energy Selective Surface With Ultra-Wide Absorption Band

A low-profile energy selective surface (ESS) with an ultra-wide absorption band is proposed in this article. It consists of a switchable layer and an absorptive layer. The switchable layer uses p-i-n diodes to adaptively adjust the operating mode. When the incident wave power is low, the ESS operates in transmission mode. It behaves as a bandpass frequency selective surface (FSS) having an ultra-wideband (UWB) absorption out of the passband. As high-power microwaves (HPMs) are incident, the ESS changes to shield mode. The HPM in the passband are reflected, while those out of band are absorbed. As a result, stealth and shielding are realized at the same time. By loading metal patches on both sides of the dielectric substrate, the number of transmission zero out of the passband is increased. As a result, the shielding and absorption bandwidth (AB) are widened. The wide absorption band can absorb detection signals before the diodes are triggered and provide a shield in advance. The experimental results show that the ESS has an insertion loss (IL) of 0.6 dB at 3.8 GHz and an absorption band range of 5.97–13.97 GHz in transmission mode. While in shield mode, a shielding effectiveness (SE) of 13 dB and an absorption band range of 5.74–12.82 GHz are obtained. This novel ESS simultaneously achieving high-power electromagnetic (EM) protection and stealth in a wide band has various prospects of applications in EM protection, EM compatibility, and EM interference along with stealth technology.

Smart window with grating optical filter: Comparison with smart windows fully coated with chromogenic layer

A comparative analysis is presented of a smart window with grating filter and a conventional smart window fully covered with switchable layer using the same chromogenic material in its colored and bleached states. The filter, formed by two thin-film gratings with alternating transmissive and chromogenic strips, has an angular-selective transmission of direct sunlight. Both gratings are sloped on the window plane at an angle to the horizontal, calculated taking into account the window azimuth to adapt to the solar trajectory relative to this window. The previously obtained calculation methods are modified and expanded, on the basis of which the temporal characteristics of light and solar transmittance, as well as direct and diffuse illuminance and irradiance indoors, of windows with two different southeast azimuths for June 15, September and December are calculated. The results show two main advantages of a grating smart window over a conventional one. Firstly, in active (colored) mode, due to angular selectivity of transmission it has self-adjusting light and solar transmittance throughout the day and year without using the daylight shading/redirecting devices, and in the bleached state, it has a higher transmittance. Secondly, by adjusting the transmission of direct sunlight, the filter transmits more than twice as much diffuse light in both colored and bleached states, thereby increasing indoor comfort in any season.

Low-Profile FSS-Based Polarization-Insensitive Rasorber With Switchable Transmission Band

In this letter, a new polarization-insensitive, low profile frequency-selective rasorber (FSR) is presented with a switchable transmission band. This FSR consists of a lossy layer, a bandpass layer, and a switchable layer where p-i-n diodes are mounted and parallel fed. The lossy layer is composed of compact fractal elements with lumped resistors, which miniaturizes the unit dimensions. The bandpass layer is composed of a grided square loop and the switchable layer is integrated by coaxial hybrid square loops with an embedded bias network, whose configuration reduces the impact of bias lines on high-frequency transmission and, consequently, achieves polarization insensitivity. A prototype was fabricated and measured, which verified that the 3 dB transmission window covers 8.9–9.8 GHz, and the −10 dB wideband absorption covers 2.3–8.2 GHz. Good agreement is obtained between the numerical simulation and measurement results.

A Wideband Multifunctional Absorber/Reflector With Polarization-Insensitive Performance

A wideband and polarization-insensitive absorber/reflector with multifunctional characteristics is proposed in this communication. The designed structure comprises a switchable layer, an air spacer, and a metal ground. The switchable layer contains active resonant elements, whose switching properties are realized by controlling p-i-n diodes. Bias networks for the p-i-n diodes are integrated into the structures and no dedicated bias lines are required. Thus, the negative effect of extra bias lines can be alleviated. In order to achieve switchable and polarization-insensitive properties simultaneously, a super-element configuration is developed by combining four similar unitary elements. One unique feature of the designed device lies in its real-time and multifunctional capability to switch among multiple working states. In addition, the switchable bandwidth of the proposed structure covers a much wider frequency band compared with previous switchable absorber/reflector designs. Distributions of electric field and surface current as well as an equivalent circuit model are presented to gain the necessary physical insight into the working mechanism of the switchable structure. Finally, a prototype of the proposed design is fabricated and measured for validation.

Switching properties of switchable mirrors using palladium-ruthenium catalytic layers

In preparing switchable mirrors, palladium (Pd) was used as a catalyst for hydrogenation and dehydrogenation, and to prevent oxidation of the switchable layer. To reduce the cost, Pd was alloyed with ruthenium (Ru) and used as a catalytic layer, since the price of Ru is approximately one-tenth that of Pd. Switchable mirrors of magnesium-yttrium (Mg-Y) alloy thin films coated with a Pd-Ru layer were prepared by direct-current magnetron sputtering method. Their optical switching properties between reflective and transparent states were studied using gasochromic method. The mirrors coated with Pd1-αRuα of up to α ≈ 0.6 showed nearly the same switching time from reflective to transparent state as those coated with pure Pd, while the mirrors coated with Pd1-αRuα of 0.2 ≤ α ≤ 0.4 showed shorter switching times from transparent to reflective state than those coated with pure Pd. Furthermore, the alloy-coated mirrors with shorter switching times had approximately 2–3 times higher switching durability than those coated with pure Pd. These shorter time and higher durability may be because Pd-Ru alloy prevents oxidation of the underlying layers more effectively than pure Pd. Thus, Pd-Ru alloy is one of the most promising catalysts for switchable mirrors.

Improved optical properties of switchable mirrors based on Pd/Mg-TiO2 films fabricated by magnetron sputtering

For the past two decades, the reported magnesium-based gasochromic switchable mirrors have been limited to magnesium alloys. Herein, inspired by the excellent catalytic property of TiO2 for the magnesium‑hydrogen reaction, the novel gasochromic switchable mirrors based on Pd/Mg-TiO2 films were fabricated by magnetron sputtering and their optical properties, microstructures and structure-function relationship were investigated in this study. The results show that the mirror based on Pd/0.9Mg-0.1TiO2 film exhibits larger optical dynamic range at visible wavelengths and excellent structural recovery even after 100cycles of hydrogenation and dehydrogenation compared with Pd/Mg film. The brookite TiO2, crystalline Mg and some amorphous phases coexist in the Mg-TiO2 layer of Pd/0.9Mg-0.1TiO2 film with no trace of Pd. Interestingly, the TiO2 nanocrystal clusters are distributed in stripe among Mg matrix. In contrast, the Pd/0.63Mg-0.37TiO2 film consists of crystalline Mg and MgTi2O5 phase, where MgTi2O5 phase is derived from the reaction of superfluous TiO2 with a part of Mg and deteriorates the optical properties of the mirror dramatically. In summary, this work offers a novel strategy for improving optical performance of Mg-based switchable mirrors by introducing metal oxides into switchable layer and uncovers a broad field to be explored.

Microscopic model of domain wall motion

Polarization switching is simulated using a model based on a sequence of single dipole flips. The single dipole flips are assumed to be thermally activated with transition rates depending on the local field. The time to switch a single dipole depends on the deterministic transition rate and on a probabilistic factor. In each step, the dipole with the shortest flip time is switched. We investigate one dimensional dipole chains as well as two and three dimensional systems based on the barium titanate structure that comprises single charges fluctuating in double well potentials and induced dipoles. The two and three dimensional simulations yield intrinsic dead layers close to the electrodes that can not be switched even in very strong fields. These non switchable layers are nuclei for the domain wall motion and thus nuclei for the switching process. The switching time of the system decreases faster than exponential for low fields with increasing field. This decrease slows down for higher fields. Furthermore, we found intrinsic dead layers around a defect.

Evaluation of quantum dots applied as switchable layer in a light-controlled electrochemical sensor

Gold electrodes with switchable conductance are created by coating the gold surface with different colloidal quantum dots. For the quantum dot immobilization, a dithiol compound was used. By polarizing the electrode and applying a light pointer, local photocurrents were generated. The performance of this setup was characterized for a variety of different nanoparticle materials regarding drift and signal-to-noise ratio. We varied the following parameters: quantum dot materials and immobilization protocol. The results indicate that the performance of the sensor strongly depends on how the quantum dots are bound to the gold electrode. The best results were obtained by inclusion of an additional polyelectrolyte film, which had been fabricated using layer-by-layer assembly.

Solar control with thermotropic layers

Innovative means to control the light and energy flux according to demand are desirable for transparent façades and façade elements. One possibility to achieve this is presented by switchable layers that change their optical properties, either actively or passively, according to different control parameters. In addition to inorganic coatings on glass, there are several organic thermotropic systems that can be integrated into façade glazing. Above a certain temperature, thermotropic layers change from a clear to a translucent, light-diffusing state, thus switching from a highly transmitting to a diffusely reflecting state. We shall describe the basic principles of these systems and present an overview of some of the existing prototype systems. Installation options will be discussed and the results of an application in a retrofitted building presented.