Power consumption is forecast by the International Technology Roadmap of Semiconductors (ITRS) to pose long-term technical challenges for the semiconductor industry. The purpose of this paper is threefold: (1) to provide an overview of strategies for powering MEMS via non-regenerative and regenerative power supplies; (2) to review the fundamentals of piezoelectric energy harvesting, along with recent advancements, and (3) to discuss future trends and applications for piezoelectric energy harvesting technology. The paper concludes with a discussion of research needs that are critical for the enhancement of piezoelectric energy harvesting devices.

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Powering MEMS portable devices—a review of non-regenerative and regenerative power supply systems with special emphasis on piezoelectric energy harvesting systems

Carbon (C) is a crucial material for many branches of modern technology. A growing number of demanding applications in electronics and telecommunications rely on the unique properties of C allotropes. The need for microwave absorbers and radar-absorbing materials is ever growing in military applications (reduction of radar signature of aircraft, ships, tanks, and targets) as well as in civilian applications (reduction of electromagnetic interference among components and circuits, reduction of the back-radiation of microstrip radiators). Whatever the application for which the absorber is intended, weight reduction and optimization of the operating bandwidth are two important issues. A composite absorber that uses carbonaceous particles in combination with a polymer matrix offers a large flexibility for design and properties control, as the composite can be tuned and optimized via changes in both the carbonaceous inclusions (C black, C nanotube, C fiber, graphene) and the embedding matrix (rubber, thermoplastic). This paper offers a perspective on the experimental efforts toward the development of microwave absorbers composed of carbonaceous inclusions in a polymer matrix. The absorption properties of such composites can be tailored through changes in geometry, composition, morphology, and volume fraction of the filler particles. Polymercomposites filled with carbonaceous particles provide a versatile system to probe physical properties at the nanoscale of fundamental interest and of relevance to a wide range of potential applications that span radar absorption, electromagnetic protection from natural phenomena (lightning), shielding for particle accelerators in nuclear physics, nuclear electromagnetic pulse protection, electromagnetic compatibility for electronic devices, high-intensity radiated field protection, anechoic chambers, and human exposure mitigation. Carbonaceous particles are also relevant to future applications that require environmentally benign and mechanically flexible materials.

A review and analysis of microwave absorption in polymer composites filled with carbonaceous particles

The extensive development of electronic systems and telecommunications has lead to major concerns regarding electromagnetic pollution. Motivated by environmental questions and by a wide variety of applications, the quest for materials with high efficiency to mitigate electromagnetic interferences (EMI) pollution has become a mainstream field of research. This paper reviews the state-of-the-art research in the design and characterization of polymer/carbon based composites as EMI shielding materials. After a brief introduction, in Section 1, the electromagnetic theory will be briefly discussed in Section 2 setting the foundations of the strategies to be employed to design efficient EMI shielding materials. These materials will be classified in the next section by the type of carbon fillers, involving carbon black, carbon fiber, carbon nanotubes and graphene. The importance of the dispersion method into the polymer matrix (melt-blending, solution processing, etc.) on the final material properties will be discussed. The combination of carbon fillers with other constituents such as metallic nanoparticles or conductive polymers will be the topic of Section 4. The final section will address advanced complex architectures that are currently studied to improve the performances of EMI materials and, in some cases, to impart additional properties such as thermal management and mechanical resistance. In all these studies, we will discuss the efficiency of the composites/devices to absorb and/or reflect the EMI radiation.

Polymer/carbon based composites as electromagnetic interference (EMI) shielding materials

Rational design of core-shell Co@C microspheres for high-performance microwave absorption

Electrocaloric materials for future solid-state refrigeration technologies

Temperature dependence of resistivity, dielectric constant and dielectric loss have been investigated for four different compositions of nickel-zinc ferrites, Nii_IZnIFe2O4 (x = 0.2, 0.35, 0.5 and 0.6), prepared by the citrate precursor technique. Activation energies calculated from the resistivity versus temperature curves for the compositions sintered at 1200 °C and 1300 °C range from 0.55 eV to 0.73 eV. Samples sintered at 1200 °C exhibit higher activation energies and low dielectric losses compared to those sintered at 1300 °C. Samples of the composition with x = 0.6 show low dielectric losses up to a measurement temperature of around 200 °C at higher frequencies as compared to samples of other compositions. The variations in activation energy with composition and sintering temperature have been explained on the basis of the site occupancy in ferrites and the atomic radii of the constituent metal ions.

Temperature dependence of electrical properties of nickel–zinc ferrites processed by the citrate precursor technique

Dielectric properties such as dielectric constant, ϵ′ , and dielectric loss factor, tan δ ∈ , are reported for different compositions of NiZn ferrites prepared by the citrate precursor method and sintered in the temperature range 1100–1400°C. It is observed that ϵ′ and tan δ ∈ for samples prepared in the present work are much lower than those normally obtained for NiZn ferrites prepared by the conventional ceramic method. The low values are attributed to better compositional stoichiometry, single-phase spinel structure and uniform microstructure of the samples. The low dielectric loss makes these samples especially attractive for use at high frequencies.

Dielectric properties of NiZn ferrites prepared by the citrate precursor method

The dielectric properties of MnxNi0.5−xZn0.5Fe2O4 ferrites with x varying from 0.05 to 0.4 synthesized by the citrate precursor method have been investigated as a function of frequency, temperature, composition, and sintering temperature. An increase in the dielectric constant is observed with the increase in Mn concentration except for x=0.3. Dispersion in the dielectric constant with frequency in the range of 100 Hz–1 MHz is observed. Resonance peaks were observed in tan δ∈ versus frequency curves for all samples. A shift in the resonance frequency towards higher frequency is observed with increase in temperature. The peak height also increases with increase in temperature. Possible mechanisms contributing to these processes have been discussed. From the temperature variation of the dielectric relaxation, activation energies for various samples have been calculated and compared with those obtained from dc resistivity.

Tara Chand Goel

Papers

Temperature dependence of electrical properties of nickel–zinc ferrites processed by the citrate precursor technique

Dielectric properties of NiZn ferrites prepared by the citrate precursor method

Dielectric properties of Mn-substituted Ni–Zn ferrites

Magnetic properties of nickel–zinc ferrites prepared by the citrate precursor method

High-resistivity nickel–zinc ferrites by the citrate precursor method