Polypyrrole (PPy) has unique features such as easy synthesis, environmental stability, and high electrical conductivity (approximately 105 S/cm and even >380 S/cm) for bulk and thin‐film materials. Thus, PPy is applied in numerous well‐established applications, such as in sensors, supercapacitors, and resonators. These applications take advantage of the unique properties achieved through the structure and properties of PPy. This article comprehensively elaborates the methods used to synthesize conductive PPy, along with the important factors affecting its conductivity. Emphasis is given to versatile and basic approaches that enable control of the microstructural features that eventually determine PPy conductivity. Despite the intensive research in this area, no previous study has presented all possible relevant information about PPy fabrication and the important factors influencing its electrical conductivity.

AbstractResearchers have shown that techniques such as microwave-assisted extraction, ultrasound-assisted extraction, pressurized liquid extraction, and supercritical fluid extraction developed for extraction of valuable components from plants and seed materials have been successfully used to effectively reduce the major shortcomings of the traditional method such as Soxhlet extraction. These include shorter extraction time, increase in yield of extracted components, decrease in solvent consumption, and improvement of the quality of extracts. This review presents a detailed description of the principles and mechanisms of the various extraction techniques for better understanding and summarizes the potential of these techniques in the extraction of oil from plants and seed materials. Discussions on some of the parameters affecting the extraction efficiency are also highlighted, with special emphasis on supercritical fluid extraction. A comparison of the performance of traditional Soxhlet extraction with that of other extraction techniques is also presented.

Millimeter waves (mm‐waves) within frequency bands of 10 to 86 GHz will be used for both microwave and access link fifth‐generation (5G) systems. Thus, it is very important to investigate these bands to ensure reliability when 5G is applied in tropical regions like Malaysia in the coming few years. One of the major obstacles facing the propagation of mm‐waves in tropical regions is the rain attenuation. Rainfall results in the absorption, scattering, and diffraction of radio waves. This contributes to increased transmission losses and a reduction in the received signal levels. The effect is more severe in tropical regions that are characterized by intense heavy rainfall and large raindrop sizes. This paper provides a general overview on rain attenuation of mm‐wave bands. It highlights the nature of rain in tropical regions and its effects on the propagation of mm‐waves. It also reports the latest measurement studies focused on rain attenuation in mm‐wave frequency bands and the prediction methods used to estimate rain attenuation in mm‐waves. It contributes to the understanding of channel behavior and the characterization of mm‐wave bands during rainfall in tropical regions, especially in Malaysia. This study further strives to determine research gaps in this field as well as the future work and various propagation measurement systems that can be used to conduct real measurements and to develop prediction models for rain attenuation in mm‐waves for 5G systems. Furthermore, this paper analyzes the rain rate and rain attenuation on the basis of real measurement data conducted in Universiti Teknologi Malaysia at Skudai Campus, Malaysia. The analyzed results indicated that the rain attenuation at 38 GHz is critical and it can result in 18.4 dB/km as specific rain attenuation at 0.01% percentage of the time.

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