Lightweight conformal design of optically transparent and broadband microwave absorbing metamaterial

The demand for optically transparent microwave absorbers has attracted increasing interest among researchers in recent years. However, integrating broadband microwave absorption and high optical transparency remains a challenge. This report demonstrates a scheme for broadband microwave absorbers, featuring a 90% absorption bandwidth of 10 GHz covering a frequency range of 25.2-35.2 GHz and high compatibility with good optical transparency in a wide band from the visible to infrared. The absorber is based on a Jaumann structure composed of two graphene sheets sandwiched by dielectric and backed by an arrayed-metallic-rings sheet. Guided by derived formulas, this absorber exhibits complete absorption if the sheet resistance of graphene is close to 500 Ω sq-1. The bandwidth and center frequency of the absorption spectra can be readily tuned simply via changes in the thickness of the dielectric between the graphene films and arrayed-metallic-rings sheet. Moreover, the absorber is insensitive to the incident angle of radiation and can achieve broadband and near-unity absorption even at oblique incidence. The graphene-based absorber proposed herein provides a viable solution for effectively integrating broadband and near-unity microwave absorption with high optical transparency, thereby enabling widespread applications in optics, communications, and solar cells.

Broadband RF and Microwave Amplifiers provides extensive coverage of broadband radio frequency (RF) and microwave power amplifier design, including well-known historical and recent novel schematic configurations, theoretical approaches, circuit simulation results, and practical implementation strategies. The text begins by introducing two-port networks to illustrate the behavior of linear and nonlinear circuits, explaining the basic principles of power amplifier design, and discussing impedance matching and broadband power amplifier design using lumped and distributed parameters. The book then: Shows how dissipative or lossy gain-compensation-matching circuits can offer an important trade-off between power gain, reflection coefficient, and operating frequency bandwidth Describes the design of broadband RF and microwave amplifiers using real frequency techniques (RFTs), supplying numerous examples based on the MATLAB programming process Examines Class-E power amplifiers, Doherty amplifiers, low-noise amplifiers, microwave gallium arsenide field-effect transistor (GaAs FET)-distributed amplifiers, and complementary metal-oxide semiconductor (CMOS) amplifiers for ultra-wideband (UWB) applications Broadband RF and Microwave Amplifiers combines theoretical analysis with practical design to create a solid foundation for innovative ideas and circuit design techniques.

In this paper, we propose and demonstrate a broadband microwave absorber based on magnetic metamaterial structure elements. We deploy FeCo soft magnetic composite with droplet shape as the primary resonant element. By investigating the resonant modes and the coupling between periodic unit-cells and the incident microwave, it is found the intrinsic magnetic susceptibility of the magnetic elements could make the magnetic field confined in the magnetic element, and thus results in a broadband microwave absorption. Our work provides a new approach to realize broadband microwave absorbers based on hybrid absorption mechanisms, including dielectric resonator effect, one quarter wavelength resonance effect, and grating effect.

With the advent of the 5G era, there has been increasing concern regarding the potential harm of electromagnetic wave radiation on human life. Consequently, the development of a simple and cost-effective broadband and high-performance microwave absorber becomes crucial. In this study, porous tremella like nanomaterials embedded with Ni–Fe nanoparticles in N-doped carbon were prepared by a simple salt template method. Given that carbon materials inherently lack magnetic loss due to their own dielectric loss, in order to enhance microwave absorption capacity, FeNi bimetal is added to introduce magnetic loss to achieve electromagnetic synergy. By changing the pyrolysis temperature, adding NaCl and urea, the morphology of the material can be adjusted, the electromagnetic parameters can be changed, and the impedance matching can be adjusted to improve the microwave absorption performance. At a 7.5% filling ratio of the synthesized FeNi/N–PCN(800) composite, the minimum reflection loss (RLmin) is −46.4 dB, with a mere 2 mm matching thickness. The effective absorption bandwidth extends up to 5.04 GHz, demonstrating successful broadband microwave absorption. The radar cross section further proves that the material has good microwave absorption characteristics in practical applications. This work offers a reliable idea for subsequent studies on broadband and high-performance microwave absorbing materials.

Broadband ferromagnetic resonance system and methods for ultrathin magnetic films

With the aim to design broadband microwave absorbers with optically transparent, flexible and stable performances in 8–18 GHz, a sandwich structure is designed and fabricated by sandwiching the periodic arrayed ITO film into two transparent and flexible polyvinyl chloride layers. With the induced metamaterial structure to tailor the effective input impedance, the proposed sandwich absorber can realize more than 90% absorption in 8–18 GHz for both TE and TM polarization when the incident angle is less than 30°. Meanwhile, the optical transmittance of the designed absorber reaches more than 80% transmittance with the wavelength larger than 532 nm, and the average optical transmittance for the visible light (400–800 nm) is 80.2%. The proposed absorber shows broadband microwave absorption in both X and Ku band with simultaneously high transmittance in visible frequencies, indicating that the proposed sandwich metamaterial absorber has great potentials for developing optical transparent absorbing devices.

The microwave and millimeter wave broadband amplifier is one of the key circuit blocks for high-speed optical communication systems. It is also of extreme importance for wideband wireless communications operating within microwave frequency range. Previously reported results were mostly designed using compound semiconductor III–V (Majid-Ahy et al., 1990; Masuda et al., 2003; Shigematsu et al., 2001) or SiGe (Mullrich et al., 1998; Weiner et al., 2003) technologies to take advantage of the superior transistor characteristics. Lately, CMOS technology with continuously scaled feature sizes attracts much attention of circuit designers for wideband amplifier applications owing to the impressive cut-off and maximum oscillation frequencies (Chan et al., 2008). Considering the requirements of modern integrated circuit design such as low cost, low power consumption, and high integration level with other circuit blocks, CMOS technology is of great potential for microwave and millimeter wave broadband amplifier applications. This chapter provides the fundamental design concepts of broadband amplifier using the modern CMOS technology. Various design techniques are introduced for achieving high performance microwave broadband amplifiers. The main design considerations and current trends are also discussed. We will give a brief overview about the applications of broadband amplifiers and background information in section 1. Section 2 discusses the considerations of transistors and inductive components in standard CMOS process for broadband amplifier design. Section 3 reviews different design techniques for broadband amplifiers with an emphasis on the inductor peaking technique. The bandwidth enhancement ratio (BWER) of each approach is calculated. In section 4, recent advances on CMOS broadband amplifier design for microwave applications are reported. We propose a pi-type inductive peaking (PIP) technique to realize a 40 Gb/s transimpedance amplifier (TIA) in 0.18-m CMOS technology (Jin & Hsu, 2008). We also propose an asymmetrical transformer peaking (ATP) technique to achieve a miniaturized 70 GHz broadband amplifier in 0.13-m CMOS technology (Jin & Hsu, 2008). The core area is only ~ 0.05 mm2 and the Gain-Bandwidth Product (GBP) is up to 231 GHz which is among the highest compared with other reported works with similar or even more advanced technologies. Finally, section 5 provides the closing remarks of this chapter and also some recommendations of further study on CMOS broadband amplifiers for microwave and millimeter wave applications. 18

We propose and experimentally demonstrate a novel technique to achieve broadband and precise microwave time reversal using a single linearly chirped fiber Bragg grating (LCFBG). In the proposed approach, the time reversal is realized by the LCFBG that is operating in conjunction with a polarization beam splitter (PBS) to enable a triple use of the LCFBG with the microwave waveform entering the LCFBG from either the long or the short wavelength end. Since the LCFBG has a wide bandwidth and is used three times with exactly complementary and identical dispersion, broadband and precise microwave time reversal is ensured. A theoretical analysis is performed which is validated by simulations and an experiment. The time reversal of three different microwave waveforms with a bandwidth over 4 $~$ GHz and a time duration of approximately 10 ns is demonstrated.

We propose and experimentally demonstrate a novel technique to achieve broadband and precise microwave time reversal using a single linearly chirped fiber Bragg grating (LCFBG). In the proposed approach, the time reversal is realized by the LCFBG that is operating in conjunction with a polarization beam splitter (PBS) to enable a triple use of the LCFBG with the microwave waveform entering the LCFBG from either the long or the short wavelength end. Since the LCFBG has a wide bandwidth and is used three times with exactly complementary and identical dispersion, broadband and precise microwave time reversal is ensured. A theoretical analysis is performed which is validated by simulations and an experiment. The time reversal of three different microwave waveforms with a bandwidth over 4 $~$ GHz and a time duration of approximately 10 ns is demonstrated.

In search of novel light weight broadband microwave absorber for defense and civilian applications, industrial waste hollow microsphere (fly ash cenosphere or FAC) filler based polymer composite system was studied in the present work owing to its attractive microwave absorbing characteristics. PDMS is chosen as the matrix. FAC, being dielectric, is coated with Ni using standard electroless coating method to synthesize core-shell filler (magneto-dielectric). The dielectrics and microwave absorption study was carried out for the frequency range 8.2-18 GHz (X-band and Ku-Band). The minimum reflection loss (RL) was obtained to be -43 dB with an excellent bandwidth. Hence, an ultra-thin Ni coated FAC loaded PDMS can be considered as a smart candidate for broad band microwave absorption.

Hexaferrites have become important candidates for a variety of microwave and millimeter wave devices due to their large uniaxial magneto-crystalline anisotropy and high saturation magnetization. The goal of the present investigation is to synthesize Barium hexaferrite/Yttrium Iron Garnet (BaFe12O19/Y3Fe5O12): (BaM/YIG) Nano-Composites (NCs) to be used in broad band microwave frequency range applications, especially as microwave absorber. X-ray diffractometry, Vibrating Sample Magnetometer (VSM), and ferromagnetic resonance (FMR) techniques were used to characterize these NCs. Using a Cu coplanar wave guide and a Vector Network Analyzer, broadband (C to U) microwave absorption were investigated by placing the bulk sample in flip chip mode. Various mathematical models were employed to fit the experimental data to yield intrinsic and extrinsic damping parameters.

Microwave absorption efficiency of poly (vinyl-butyral)/Ultra-thin nickel coated fly ash cenosphere composite

Green carbonization of waste coffee grounds into porous C/Fe hybrids for broadband and high-efficiency microwave absorption

Broadband and thin microwave absorber of nickel–zinc ferrite/carbonyl iron composite

Despite recent progress in the synthesis and application of graphene-based aerogels, some challenges such as scalable and cost-effective production, and miniaturization still remain, which hinder the practical application of these materials. Here we report a large-scale electrospinning method to generate graphene-based aerogel microspheres (AMs), which show broadband, tunable and high-performance microwave absorption. Graphene/Fe3O4 AMs with a large number of openings with hierarchical connecting radial microchannels can be obtained via electrospinning-freeze drying followed by calcination. Importantly, for a given Fe3O4:graphene mass ratio, altering the shape of aerogel monoliths or powders into aerogel microspheres leads to unique electromagnetic wave properties. As expected, the reflection loss of graphene/Fe3O4 AMs-1:1 with only 5 wt.% absorber loading reaches −51.5 dB at 9.2 GHz with a thickness of 4.0 mm and a broad absorption bandwidth (RL < −10 dB) of 6.5 GHz. Furthermore, switching to coaxial electrospinning enables the fabrication of SiO2 coatings to construct graphene/Fe3O4@SiO2 core‒shell AMs. The coatings influence the electromagnetic wave absorption of graphene/Fe3O4 AMs significantly. In view of these advantages, we believe that this processing technique may be extended to fabricate a wide range of unique graphene-based architectures for functional design and applications.