A Dual/Single Wideband Switchable Metamaterial Absorber at Low Frequency

Based on PIN diode and resistive film, a dual/single wideband switchable metamaterial absorber at low frequency is presented in this paper. Its absorption is over 90% from 0.8GHz to 1.5GHz and from 4.2GHz to 5.2GHz while the PIN diode operates in forward biased condition. On the contrary, with the PIN diode acting in reverse biased condition, the above 90% absorption occurs from 1.1GHz to 3.2GHz. The surface current distributions at the absorption frequencies are monitored to explain the reason of wideband absorption. The simulation results show that the absorption property of the metamaterial absorber is polarization-sensitive. The metamaterial absorber possesses the advantages of simple structure, wideband, dual/single band, and switchable performance.

Thin-Film Absorbing Elements of Adapter-Attenuators for HIC

One of the urgent tasks in the design of hybrid integrated circuits (HIC) is the construction of adapter-attenuators – film absorbing elements providing a wide range of attenuations with specified values of input and output resistances. Known variants of adapter-attenuators based on a homogeneous and piecewise homogeneous resistive film provide (by introducing asymmetry in the dimensions of the input and output contacts, changing the location of a piecewise homogeneous resistive film, introducing dielectric or conductive regions) a resistance transformation coefficient of no more than 3 and 10–12, respectively. In this work, promising topologies of adapter-attenuators for HIC with a close to optimal profile of input and output contacts are proposed, which allow not only to obtain a wide range of transformation coefficients (more than 100), but also to reduce the maximum values of the potential gradient and power density by 10‒30 times. The rectangular topology calculations were made using the apparatus of the theory of functions of a complex variable. Modeling of the optimized topology of adapter-attenuators for HIC was carried out by the finite element method implemented in the Elcut software package. The calculated ratios and graphs showing the relationship of attenuation, the transformation coefficient, the gain in the value of the potential gradient and the power density, depending on the ratio of the size of the film element and the resistivity of the resistive films used, have been provided. The features of adapter-attenuators fitting have been considered. The results obtained are especially important for the pulse mode of operation of adapter-attenuators’ film element for HIC.

A thin and optically transparent infrared-radar compatible stealth structure with low emissivity and broadband absorption

In this paper, an optically transparent structure that combines broadband absorption and low infrared emissivity for dual-band stealth is proposed. The whole structure includes two functional layers. The periodic resistive film of the upper functional layer acts on infrared stealth. Its emissivity in the infrared band of 8-14μm is lower than 0.3. Another functional layer achieves greater than 90% wide absorption from 6 to 18.5 GHz. The whole optically transparent composite structure has a low profile of 0.141λ0, where λ0 is the wavelength of free space at the center frequency. It has an absorptivity that greater than 90% in the region of 5.7-16.5 GHz and has wide angular stability. Measured result is consistent with the simulation which verify the performance of the proposal. The infrared-radar compatible stealth structure proposed in this paper has potential application in the field of multi-spectrum compatible stealth.

Design and Experimental Evaluation of an Electrorheological Haptic Module with Embedded Sensing

We present a miniature haptic module based on electrorheological fluid, designed for conveying combined stiffness and vibrotactile sensations at a small scale. Haptic feedback is produced through electrorheological fluid’s controllable resistive force and varies with the actuator’s deformation. To demonstrate the proposed actuator’s feedback in realistic applications, a method for measuring the actuator’s deformation must be implemented for active control. To this end, in this study, we incorporate a sensor design based on a bend-sensitive resistive film to the ER haptic actuator. The combined actuator and sensor module was tested for its ability to simultaneously actuate and sense the actuator’s state under indentation. The results show that the bend sensor can accurately track the actuator’s displacement over its stroke. Thus, the proposed sensor may enable control of the output resistive force according to displacement, which may lead to more informed and engaging combined kinesthetic and tactile feedback.

A Wideband Termination Based on Laser-Scribed Lossy Microstrip Line Structures

Laser-direct writing has become an alternative method to fabricate microwave devices. We present a laser-scribed wideband open-end termination that relies on conductor loss of the microstrip line structure to obtain effective absorption. The proposed design consists of a resistive film overlapped on a strip conductor, providing an enlarged sheet-resistance range (20 Ω/□ ~ 1.2 kΩ/□) of the resistive film to reduce the fabrication difficulties. The resistive film is in tapered shape to enable small gradual changes in impedance, yielding minimized reflections (|S11|). The prototype is demonstrated utilizing the laser-direct writing technique, with a measured |S11| over −15 dB from 6 GHz to at least 30 GHz. The termination can also be used for attenuation over a −10 dB attenuation level (>8.5 GHz) with a low reflection level better than −15 dB (>2.0 GHz). This study can be employed for the applications where cheap wideband planar terminations are needed and promote fast, flexible, and low-cost prototyping or modification of the existing microwave circuits.

Fabrication of Metal Nanowire Based Stretchable Mesh Electrode for Wearable Heater Application

In recent years, human-convenient smart wearable devices have attracted considerable attention as emerging applications in smart healthcare systems, soft robotics, and human-machine interfaces. In particular, resistive film heaters with mechanical flexibility and excellent mechanical and electrothermal performance have recently been widely explored for wearable thermotherapy applications. Here, we present a simple and efficient way of fabricating highly flexible and stretchable resistive film heaters based on a patterned silver nanowire (AgNW)/polymer composite structure. The AgNW/polymer composite electrodes were successfully prepared using a photolithographically patterned polymer mold based selective transfer of a AgNW percolation network. The photolithographic mold patterning process allows the heater fabrication to be precise and reproducible. The mesh-patterned AgNW/polymer composite heater exhibited the excellent electrothermal performance of ~46.7 oC at 3 V. This low-voltage operation is highly desirable in practical wearable device applications. Moreover, the AgNW/polymer heater can be stretched up to 20% without significant degradation in electrothermal performance thanks to its open-cell architecture, suggesting that the device can stably transfer heat to the skin after being attached to various body parts with curvilinear surfaces. The experimental results suggest that the mesh-structured AgNW/polymer composite heaters are highly feasible for use as a wearable thermotherapy tool in many emerging applications.

Signal «crosstalk» effect in the structure of the polarization attenuator channels

An ideal model of a polarization attenuator implies the full absorption of the tangential component of the electric field both in the resistive layer of rotor plates and those of stator plates. In a real attenuator, however, due to the incomplete absorption in the resistive layer of plates the so called “crosstalk” occurs. In most cases the “crosstalk” results in diminished attenuation values of a polarization attenuator. Furthermore, with the high frequencies and especially when the attenuation is high, it significantly affects the attenuation error of a polarization attenuator. This paper analyzes the effect of a series of geometric and electric parameters of the structure of a polarization attenuator’s channels on the “crosstalk” value. As distinct from the well-known calculation methods based on the calculation of separate elements of a polarization attenuator, an algorithm of point-to-point calculation from input to output ports of the entire device is offered. From the general principles of classical electrodynamics, in order to calculate the attenuation of electromagnetic wave in the longitudinal direction of the channel of the attenuator’s conduction system, a formula derived from the method of perturbation theory has been applied. This was possible thanks to an assumption about the weak perturbation of a conducted electromagnetic wave. This condition proves true in the said system thanks to choosing certain correlations between longitudinal and transverse dimensions of the polarization attenuator’s structural channels when the length of a plate with a resistive film is several times greater than the expanding electromagnetic wave as well as to choosing certain upper range values of a film’s surface resistance. From the general correlation of the perturbation theory method a precise expression aimed at defining the attenuation value in a polarization attenuator which is regarded as a result of functioning of geometric and electric parameters with consideration of frequencydependence of attenuation, is obtained. For numerical calculations an algorithm of reprojecting the electric field onto two orthogonal components with respect to a plate from the resistive film followed by defining with the help of the superposition principle the resulting field has been used. This procedure has been fulfilled with respect to each single unit every time the structure in the cross section of the polarization attenuator’s channels appeared heterogeneous. The authors performed the numerical calculations of characteristics of a polarization attenuator with operating frequency range from 53.57 to 78.33 GHz. A diagonally structured graph reflecting the changes of “crosstalk” in function of surface resistance of the film Rп in the range from 300 Оhm/m2 to 700 Оhm/m2 is offered. It graphically explains the physical process of transition from linear region of attenuation to saturation region. Recommendations on choosing Rп are provided. The authors demonstrate how with the use of the widely known in the literature results and the data on calculations provided in this paper one can evaluate the effect, which the heterogeneity of the plate with a film, in the form of out-of-flatness “fractures”, in particular, may have on the “crosstalk”. The numerical evaluations of the effect a diameter of the polarization attenuator channel has on the “crosstalk” are provided in the paper with the help of a double graph illustrating the “crosstalk” value being “expanded” on the attenuation deviations scale. The numerical calculation of the effect of a distortion of the plate with films in input/output ports of the polarization attenuator has been carried out. The paper proves the possibility of linearizing the characteristics and reducing the attenuation errors both by separate regulation of distortion wall in input/output ports and their common interaction. The physical interpretation of the calculation results of the polarization attenuator is provided. It describes the general principles and can be applied to any other operating frequency range of the polarization attenuator.