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Triboelectric generators (TEG), based on contact electrification and electro-static induction, has received a significant attention because of their numerous applications. To improve the electrified surface charge density in TEG, increasing the surface area of dielectric materials or forming internal hollow structures are typically employed to increase capacitance. However, the fabrication processes of such structures are complex and time-consuming. Here, we provide a facile and cost-effective synthesis method for the porous PDMS based TEG via a novel vapor encapsulation casting (VEC). The double dielectric layer composed of the porous and dense PDMS layers are formed in-site through VEC. The thickness and the thickness ratio of the double dielectric layer can be precisely controlled by adjusting the uncured PDMS thickness and vapor penetration depth. The double dielectric layer TEG (DTEG) exhibits the improved harvesting performance because the porous dielectric layer increases the capacitance and compressibility, while the dense layer passivates the fully open pores which reduce the charging surface area as completely opening through the dielectric layer without contacting the bottom electrode. We obtain the maximum output voltage of 345 V and short circuit current of 3 μA/cm2 from DTEG having 0.95 porous thickness ratio, resulting 330% enhancement in the power output as compared to the dense PDMS based TEG. We further investigate the performance of DTEG under various operating conditions. We also demonstrate the operation of Bluetooth distance/temperature sensors using capacitors charged by DTEG. Image 1 • TEG based on the double dielectric layer composed of the sponge-like porous and flat dense elastomer is demonstrated. • Facile and affordable synthesis method for the porous PDMS is provided via the novel vapor encapsulation casting. • Highly deformable porous PDMS effectively enhances its capacitance under a pressure. • Flat dense second layer of PDMS reduces the device impedance and improves the contact interface with an electrode. [ABSTRACT FROM AUTHOR]

Abstract Poly(3,4-ethylenedioxythiophene) (PEDOT) derivatives are synthesized by oxidative polymerization using sodium dodecyl sulfate (SDS) as an anionic surfactant dopant. The resulting polymeric materials featuring nanofiber-type one-dimensional (1D) structures are identified as poly(2‐butyl‐2,3‐dihydrothieno[3,4‐b][1,4]dioxine:dodecyl sulfate (PEDOT-C 4 :DS) and poly(2‐hexyl‐2,3‐dihydrothieno[3,4‐b][1,4]dioxine:dodecyl sulfate (PEDOT-C 6 :DS). The ratio of the DS anion doped into PEDOT-C 4 :DS and PEDOT-C 6 :DS is 0.16 and 0.23, respectively. The contact angle of water on the PEDOT-C 4 :DS and PEDOT-C 6 :DS films is 76.6° and 87.7°, respectively, showing hydrophobic properties similar to that with water on PVDF. It facilitated the fully uniform film formation due to excellent surface matching. Peeling force of PEDOT-C 4 :DS and PEDOT-C 6 :DS is stronger than the one of PEDOT:PSS‐CNT composite. GIWAX analysis showed that PEDOT-C 4 :DS formed the highly ordered edge-on structure and PEDOT-C 6 :DS formed the bimodal orientation consisting of edge-on structure mainly and face-on structure slightly. The electrical conductivity (σ PEDOT‐C4:DS =50.0 S cm−1) of PEDOT-C 4 :DS is 41.7 times higher than that of PEDOT:PSS (σ PEDOT:PSS =1.2 S cm−1). The output signals (maximum voltages/currents) of piezoelectric nanogenerators (PNGs, electrode/PVDF/electrode) using these materials as electrodes are PNG-1 (PEDOT:PSS‐CNT composite) 1.25 V/128.5 nA, PNG-2 (PEDOT-C 4 :DS) 1.54 V/166.0 nA, and PNG-3 (PEDOT-C 6 :DS) 1.49 V/159.0 nA. Of these, PNG-2 & PNG-3 show maximum piezoelectric output power of 63.0 nW and 59.9 nW at 9 MΩ compared to PNG-1 (41.0 nW at 10 MΩ). They are enhanced up to 53.7%. The excellent surface matching between a piezoelectric active material and an electrode material leads to high output power. Graphical abstract fx1 Highlights • Two types of PEDOT-C x :DS show hydrophobic and one-dimensional structures. • PEDOT-C x :DS have excellent uniform film on PVDF due to good surface energy matching. • PEDOT-C x :DS have conductive nanofibrillar network and electrical homogeneity. • PNGs with PEDOT-C x :DS show higher piezoelectric output power than reference. [ABSTRACT FROM AUTHOR]

Abstract Conventional artificial muscles induce bending by aligning large-sized ions within the electrolyte upon bias application. Such design, alike many other actuator types, suffer from volatile actuation where the actuated position gets lost upon switch-off. Here, we develop a non-volatile artificial muscle with ion insertion electrode materials. Upon bias application, the inserted ions pose stress on the electrodes that sustain even after power shut-off. The demonstrated actuator consists of lithium germanide (Li x Ge) thin films deposited on both sides of a flexible polyimide (PI) substrate. The device exhibits 35.2 mm displacement when operated at 2 V and generates the blocking force of 0.67 mN. The observed stress and volume expansion reach 248 MPa and 8.2% for the 284 nm Li 3 Ge thin films, respectively. The actuated position is maintained against gravity with 12.1% decay in the actuated distance after 10 min. The novel actuator type proves the potential use of lithium insertion materials as actuation materials and shows that non-volatile actuation can be realized with ion-insertion electrodes. Graphical abstract fx1 Highlights • We develop a novel class of actuators based on Li x Ge thin films. • Applying voltage results in Li composition change and bends the actuator. • The actuation is non-volatile and maintains its position even after switch-off. [ABSTRACT FROM AUTHOR]

Abstract For a type-1 piezoelectric energy harvester (PEH), in which stress develops in the supporting system of the piezoelectric materials, the electromechanical coupling factor (k ij) of the piezoelectric materials is important for the output power at the resonance frequency. Therefore, soft-piezoelectric materials are good candidates for these PEHs. For type-2 PEHs, in which stress develops in the piezoelectric material and supporting system, the figure of merit (FOM) of the output power at the resonance frequency is (k ij 2 × Q m)/ s 11 E , where Q m and s 11 E are the mechanical quality factor and the elastic compliance of piezoelectric materials, respectively. In particular, the effect of Q m is very large for these PEHs, indicating that hard-piezoelectric materials are good candidates for type-2 PEHs operating at the resonance frequency. For both type-1 and type-2 PEHs operating at off-resonance frequency, the k ij 2 × d ij × g ij is the FOM of the output power of the PEHs, where g ij is a piezoelectric voltage constant. Therefore, soft-piezoelectric materials are also good candidates for both type-1 and type-2 PEHs operating at the off-resonance frequency. Graphical abstract fx1 Highlights • Piezoelectric materials for the maximum output power depend on the type of PEH. • Soft-piezoelectric materials are good for type-1 PEH at the resonance frequency. • Hard-piezoelectric materials are good for type-2 PEH at the resonance frequency. • Soft-piezoelectric materials are good for PEH at the off-resonance frequency. [ABSTRACT FROM AUTHOR]

Abstract Sound energy harvesting is one of the promising technologies due to the abundant and clean sound sources. It can be the semi-permanent alternative power supplies for wireless sensor networks (WSNs), which is significant in the Internet of Things (IoT). However, sound waves have the low energy density, so there are many kinds of research in recent years to overcome this problem. This paper provides a comprehensive review of sound energy harvesting, focusing on presenting principles, examples and enhancement methods of sound energy harvesters. In this paper, various approaches are introduced which are classified as sound pressure amplification and transduction mechanism. For sound pressure amplification, two typical types of energy harvesters are presented that one is using a resonator, another one is using an acoustic metamaterial, and these are based on piezoelectric, electromagnetic, and triboelectric mechanisms to convert sound energy to electrical energy. Graphical abstract fx1 Highlights • This paper summarizes the basic principles of sound energy harvesters and its state-of-the-art researches. • It mainly classifed sound energy harvesters as pressure amplification method and transduction mechanism. • Comparison of the reported sound energy harvesters are provided according to device size, and generated power etc. [ABSTRACT FROM AUTHOR]

Flexible piezoelectric generators have attracted considerable attention in recent years on account of their potential applications in mechanical energy scavenging devices using portable, wearable, and implantable electronics. Key issues for realizing a flexible piezoelectric generator include insufficient output power generation and poor efficiency at low frequency. We therefore propose structural approaches to enhancing the output power of the flexible piezoelectric generator using polyvinylidene fluoride. Specifically, we propose the use of a substrate and curved structure, and optimization of the aspect ratio of the generator for maximizing output power density. Through these approaches, induced stress and output voltage of the generator are analyzed by finite element modeling and validated through experiments. Considering these results for generator optimization, we fabricate a multilayered flexible curved generator, which produces ~200 V of the peak output voltage and ~2.7 mA of the peak output current. The output power density of the generator reaches ~17 mW/cm 2 , which is sufficient to drive various commercial electronics as a power source. Furthermore, it is demonstrated that this power source can illuminate 952 LED bulbs. This conceptual technology can provide the groundwork to enhancing the output power of conventional piezoelectric generators, thereby enabling novel approaches to realizing self-powered systems. [ABSTRACT FROM AUTHOR]

[Display omitted] Acoustic energy harvesting (AEH) has emerged as a promising powering process for the sustainable self-powered operation of wireless sensors in wearable, biomedical, and industrial applications. However, despite the abundance of sound sources in the environment, intrinsically low acoustic energy density still poses a critical challenge; therefore, the development of various sound amplification structures, such as Helmholtz resonators (HRs), phononic crystals, and acoustic metamaterials is required. In this study, we combined two distinct sound amplification mechanisms, Helmholtz resonance and omnidirectional acoustic wave focusing, to generate a sufficiently high power output within an ambient sound environment at practically low frequencies (< 1 kHz). A two-degree-of-freedom model was developed to systematically design a HR integrated with a piezoelectric device (HR-PEH). Subsequently, the HR-PEH was incorporated with a circularly symmetric gradient index phononic crystal (GRIN PnC) structure that enabled omnidirectional sound focusing. Finally, we constructed a coupled acoustic system GRIN-HR-PEH. Analytical modeling and experimental characterization revealed the existence of two distinct dual operating frequencies for power maximization: mechanical and acoustic resonances, which offers design flexibility in coupled AEH systems. As a result, the coupled GRIN-HR-PEH system yielded an output power of up to 4.1 mW under an ambient incident sound pressure of 47 dB, satisfying the power requirements of practical applications. • A gradient-index phononic crystal and Helmholtz coupled structure is proposed as a synergistic sound amplification mechanism. • The hybrid system exhibits omnidirectional acoustic energy focusing and harvesting capabilities. • The proposed system yields a remarkable output power generation of 4.1 mW at a low frequency of 471 Hz. [ABSTRACT FROM AUTHOR]

With the widespread use of wearable electronics, the flexible piezoelectric energy harvesting devices have been extensively studied to efficiently convert the physical motion of the human body into electrical energy. The major obstacles for realizing a flexible piezoelectric generator include the insufficient output power generation and the poor efficiency at the low-frequency regime. Here, we demonstrate a curved piezoelectric generator favorable for wearable applications, generating a high output power. The curved structure plays a key role to improve the power generation, by effectively distributing the applied force across the piezoelectric layer, as well as to allow operation at the low frequency vibration range. Accordingly, this generator produces ~120 V of peak output voltage and ~700 µA of peak output current during a cycle. Furthermore, our generator can operate at low frequencies below 50 Hz, generating ~55 V of output voltage and 250 µA of output current at 35 Hz, and it even works at frequencies as low as 1 Hz. With this generator, we successfully lit up 476 commercial LED bulbs. In addition, we experimentally demonstrate the possibility that the generator can be used in shoes, watches, and clothes as a power source. Our results will provide a framework to enhance the output power of conventional piezoelectric generators, and open a new avenue for realization of self-powered systems, such as wearable electronic devices. [ABSTRACT FROM AUTHOR]

The design method for a small lowpass filter (LPF) having a multilayer structure, which can be embedded in RF modules, is presented. Low loss, three dimensional inductors and capacitors have been investigated and incorporated to design a chip-type LPF. The Chebyshev LPF has been designed with a cutoff frequency of 2 GHz, a ripple of 0.1 dB, and a high attenuation (<−30 dB). The low temperature cofired ceramic (LTCC) materials have a dielectric constant of 7.8, a loss tangent of 0.0015, and a metallization of silver. The characteristics of the embedded passives (of which the structures were rectangular helical inductors and parallel-plate capacitors) have been analyzed by 3D structure simulator and the equivalent circuit simulated. [Copyright &y& Elsevier]

The microwave dielectric properties of (1−x)(Al1/2Ta1/2)O2−x(Mg1/3Ta2/3)O2 (AMT) (0≤x≤1.0) ceramics and design of small coplanar waveguide fed antenna (CPWFA) have been investigated. As (Mg1/3Ta2/3)O2 concentration increased, dielectric constant (&epsiv;r) and quality factor (Q) significantly increased and the temperature coefficient of resonant frequency (τf) changed from negative to positive value. The τf of 0 ppm °C−1 was realized at x=0.65 and the Qf0 value and &epsiv;r for this composition were 112 470 GHz and 26.1, respectively. A newly developed 0.35(Al1/2Ta1/2)O2–0.65(Mg1/3Ta2/3)O2 dielectric materials were used for 1.5 GHz band CPWFA design and fabrication. The size of the CPWFA can be reduced by using AMT ceramics with high dielectric constant, insetting slits into patch, and fabricating CPW feed line in the ground plane. The slits play roles in not only lowering a center frequency but also fine-tuning for the proposed CPWFA together with open stub of CPW feed line. The CPWFA with slits has the lower center frequency than the conventional CPWFA, which suggests that an antenna size can reduce as large as 16.3%. Experimental results of the fabricated device were in good agreement with the simulation. [Copyright &y& Elsevier]