Defective multiwalled carbon nanotubes display higher real permittivity than graphitic (CNTs). That is the conclusion of study presented here in which Fe‐filled and boron‐doped CNTs X‐band compared with that made by arc discharge. However, imaginary parts are still very low all three cases. This finding indicates defective excellent dielectric materials can be used as supercapacitor components, i.e., high‐energy storage systems.

A two-element time-modulated array system which can be configured to provide active electronic null scanning is presented. The received signal from each element of the time switched and combined a phase-modulated output in depth modulation dependent on angle arrival signal. angular response at first harmonic switching frequency exhibits deep scanned plusmn90deg by controlling mark-space ratio waveform

An experimental single-layer active microwave absorber in described. The is a planar structure based upon the topology of Salisbury screen, but which conventional resistive layer replaced by an frequency selective surface (FSS) controlled pin diodes. resulting has superior reflectivity-bandwidth characteristics compared to passive absorbers corresponding thickness. Measured data are presented and show that reflectivity response can be over band from 9 13 GHz.

The author derives expressions for the sheet resistance of a Salisbury screen radar absorber which will yield maximum bandwidth specified level reflectivity performance, angle incidence and polarisation. Design curves are also given relate bandwidth, performance spacer dielectric constant.

A brief description of the theory passive and active absorbers is presented followed by details an experimental study a new design adaptive absorber. The absorber single-layer planar structure based upon topology Salisbury screen, but in which conventional resistive layer replaced frequency selective surface (FSS) controlled PIN diodes. resulting has superior reflectivity–bandwidth characteristics compared to corresponding thickness. Experimental results are those obtained from transmission...

The design of wideband, multilayer radar absorbing materials involves the solution an N-dimensional optimisation problem. Genetic algorithms appear to offer significant advantages over conventional techniques for this type problem owing their robustness and independence performance function derivatives. To illustrate use, paper considers two problems: first optimum multilayer, passive Jaumann absorbers with or without outer high-permittivity skin; secondly, examination potential such when...

Abstract In this work a combined analysis of the out-of-plane mechanical and electromagnetic properties auxetic re-entrant honeycombs is performed. Experimental numerical simulations are carried out to evaluate correlation between anisotropicity transverse (shear compressive modulus) permittivity tensor honeycombs. The results evaluated assess feasibility kind cellular solid for absorption window applications with high structural integrity performance.

The authors consider the criteria for optimum design of multilayer, wideband Jaumann radar absorbers use at oblique incidence. If performance only one incident polarisation is required and spacer permittivity small, incidence normal designs are simply related. more general case both polarisations simultaneously investigated using an optimisation technique based on a genetic algorithm examples presented.

Dielectric honeycombs are cellular materials often used in applications that require structural and electromagnetic characteristics, e.g., LO (low observable) radome components. A re-entrant (or auxetic) honeycomb is a material with properties superior to those of conventional honeycomb. By employing the finite-difference time-domain (FDTD) technique periodic boundary conditions, determined compared Re-entrant shown have substantially properties. Measured permittivity data substantiate...

In this correspondence, an analysis of phase-switched screens (PSS) based on time-switched array theory is presented. Unlike conventional transmission line analysis, the approach allows finite-sized PSS to be analyzed. New modulation schemes for selective antiphase switching are introduced and Modulation sequences in which 50% switched shown operate differently conventionally modulated produce zero backscattered energy at harmonic frequencies. Measurements from experimental operating...

The fabrication of large area conducting polymer composities having prescribed loadings and electrical properties has enabled them to be characterised over the frequency range 2–18 GHz using a free-space reflectivity arch an HP 8510B network analyser. Representative examples practical narrow- broadband microwave absorber designs such films are presented evaluated experimentally.

In this paper we have presented the results of initial research into new switching and sub-arraying schemes for time-modulated antenna arrays. Conventional arrays employ in which each element array has a common start time an switch-off varies according to prescribed amplitude taper. examined strategies dasiaswitch-onpsila can be arbitrary. This approach introduces extra design variable used modify sidelobe pattern at harmonic frequencies. particular shown that relatively simple generate...

This paper proposes a configuration for smart radar absorber which is capable of both self-tuning and absorb while scan operation. The discussion complemented by modelled measured performance data.

Conventional (passive) radar absorbing materials operate either by phase cancellation or incident electromagnetic energy and converting it into heat. The paper examines some general properties of a new class active 'absorber', called the phase-switched screen (PSS). PSS operates quite differently from passive absorbers in that exhibits an apparently low value reflectivity redistributing upon over bandwidth which is wide enough to ensure little reflected falls within passband receiver....

Conventional (passive) radar-absorbent materials operate either by phase cancellation or absorbing incident electromagnetic energy and converting it into heat. This paper examines a new type of active "absorber," called the phase-switched screen (PSS). The PSS operates quite differently from passive absorbers in that exhibits an apparently low value reflectivity redistributing upon over bandwidth is wide enough to ensure little reflected falls within pass-band receiver. discussion considers...

The use of symmetrical waveforms having variable mark-space ratios to switch the reflectivity single and multiple layer configurations is shown result in adaptive radar absorbers useful dynamically controllable characteristics frequency agility.

Smart windows that regulate the transmission of visible light are well known, but with continuing interest in modifying radar signature military hardware, there is a need also for smart microwave and surfaces. The paper reviews progress on fabrication characterization poly(aniline)-silver-polymer electrolyte composite materials. Discs films this material have been characterized over frequency range 0.5-18 GHz. materials demonstrate rapid reversible change their reflectivity when small dc...

Conventional microwave-absorbing materials rely on the absorption and conversion into heat, of electromagnetic energy incident upon them. In an alternative approach, phase-switched screen (PSS) applies phase modulation to reflected signal so that is redistributed sidebands with, ideally, none remaining at original carrier frequency f/sub c/. Hence, by adjusting shape waveform controls PSS reflection coefficient, these may be positioned outside pass-band a receiver tuned An investigation has...

Owing to the limitations of presently available calibration standards and techniques, free space microwave reflection coefficient measurements, commonly used for characterising RAM reflectivity material parameters, are prone significantly more errors than those made in coaxial lines or waveguide. In this paper, most procedure using an empty room a metal plate is described, arising critically examined. Alternative procedures both two three term error correction investigated theoretically...

The design and fabrication of an experimental planar phase modulating screen consisting PIN diode-switched dipoles is described. measured reflectivity performance the presented compared with theoretical predictions.

Although conventional (i.e., passive) radar absorbers are widely used for modifying the cross-section (RCS) of current military platforms, such may not have adequate performance to satisfy future requirements. Active absorbers, however, offer potential overcome so-called Rozanov limit and enable additional smart functionality as monitoring damage, adaptive control RCS or target appearance, identification-friend-or-foe, absorb-while-scan. This paper outlines concept basic properties a novel...

The frequency characteristics of a Salisbury screen radar absorber that incorporates layer exhibiting both resistive and capacitive properties are considered. If the capacitance is fixed, thickness hence weight may be reduced but at expense bandwidth. variable then tuned via an external control signal. practical limitations applications discussed in relation to recent advances conducting polymer materials.

A technique is described for improving the low frequency performance of geometric transition (GT) radar absorbers based on lossy foam pyramids. The makes use fact that at high frequencies, only region absorber utilized whereas whole thickness interacts with incident wave. Hence may be improved, without compromising by electrically loading base layer using one or more selective surfaces (FSS) whose elements are typically in form single nested loops. Other advantages this include minimal...