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Biodiesel Production Techniques – The State of the Art
Published in Anand Ramanathan, Babu Dharmalingam, Vinoth Thangarasu, Advances in Clean Energy, 2020
Anand Ramanathan, Babu Dharmalingam, Vinoth Thangarasu
In the electromagnetic spectrum, 0.3 to 300 GHz frequency ranges correspond to microwaves, which are located between infrared and radio wave frequencies. Microwaves generate heat through polarization of polar molecules such as alcohol and water. The polar molecules oscillate to rearrange their position against intermolecular force through a continually changing electric field. The molecules’ absorbed energy is released as heat by the collision of polar molecules. Nevertheless, the oscillation is expeditious at high frequency, resulting in no heat generation. This is due to the stronger intermolecular force between molecules that stops the motion. Hence, household and laboratory microwave ovens are operated at 2.45 GHz. Microwave-assisted (MA) techniques are extensively used in many applications, including chemical synthesis and catalyst preparation. The primary benefits of MA techniques are higher yield in shorter reaction time, rapid heat generation, and eco-friendliness compared to conventional techniques. Moreover, in the MA technique heat is generated from inside out, which results in higher local temperatures and reduces the activation energy required for the transesterification reaction (Motasemi and Ani 2012).
Introduction to Cognitive Radio
Published in Mohamed Ibnkahla, Cooperative Cognitive Radio Networks, 2018
Spectrum scarcity is one of the biggest challenges that are being faced by modern communication systems. The efficient use of available licensed spectrum bands is becoming a predominant issue due to the ever-increasing demand of the radio spectrum as well as the inefficient utilization incurred by the rigid and static spectrum allocation set by the telecommunications regulating authorities. Cognitive radio (CR) has emerged as one of the most promising paradigms to address spectrum scarcity and underutilization problems. The basic idea of CR is that unlicensed users (or secondary users [SUs]) are allowed to use the spectrum when licensed users (or primary users [PUs]) are not present or when the interference caused by SUs is below a given threshold. Thus, by introducing cognition in the network, the spectrum utilization can be enhanced.
RF/Microwave Spectrum Analysis
Published in John G. Webster, Halit Eren, Measurement, Instrumentation, and Sensors Handbook, 2017
Roberto Ambrosini, Stelio Montebugnoli, Claudio Bortolotti, Mauro Roma
Spectrum analysis is normally done in order to verify the harmonic content of oscillators, transmitters, frequency multipliers, etc., or the spurious components of amplifiers and mixer [1]. Other specialized applications are possible, such as the monitoring of radio-frequency interference (RFI), electromagnetic interference (EMI), and electromagnetic compatibility (EMC). These applications, as a rule, require an antenna connection and a low-noise, external amplifier. Which are then the specifications to look for in a good spectrum analyzer? First, we would suggest evaluating what are the critical parameters that are most relevant for your application. Then identify what is the instrument performance that has to drive the selection of the industrial product that best matches your needs.
A Novel Hardware Efficient High Resolution Spectrum Hole Detection Technique for Cognitive Radio
Published in International Journal of Electronics, 2023
Sushmitha Sajeevu, Sakthivel Vellaisamy
In a country, spectrum is allocated by government agencies for defence, satellite operators, aviation, railways, service providers (Bhattarai et al., 2016). Conventionally, different regions of the radio spectrum with specific bandwidth are allocated to different services. With such an allocation only the licenced user can utilise the spectrum assigned to that particular service irrespective of whether the licenced user is active or not. Even though this particular allocation reduces the interference among different services, efficient utilisation of spectrum cannot be achieved through this conventional allocation. Studies conducted worldwide such as Singapore, US, China, New Zealand and Germany have disclosed that a huge amount of the alloted spectrum is inefficiently utilised (El Rharras et al., 2020). It can be inferred that the under utilisation of the spectrum contributes to this spectrum crunch even more than the physical shortage of the spectrum.
SCAN-CogRSG: Secure Channel Allocation by Dynamic Cluster Switching for Cognitive Radio Enabled Smart Grid Communications
Published in IETE Journal of Research, 2022
Smart grid (SG) represents the modernized grid system that is specified to monitor, protect, and optimize the operation of conventional electrical grids [1,2]. The major element of SG is bi-directional power and communication flow. The underlying communication network consists of home area networks (HANs), neighborhood area networks (NANs), and wide area network (WAN), which form multiple communication layers[3]. HAN is the local SG network that gathers information from the individual segment, i.e. home. Multiple HANs are connected with a NAN gateway, which is responsible to aggregate the data from HANs and transmit it to WAN. The following requirements are needed to be addressed to establish efficient SG communications: bandwidth, latency, data rate, throughput, and reliability [5]. It is clear that SG communications require a huge spectrum for data transmission. On the other hand, the cognitive radio network (CRN) is witnessed as an evolving and promising technology for wireless communications to resolve increasing spectrum insufficiency [6–8]. Spectrum scarcity is the increasing and challenging issue in wireless communications. To tackle this spectrum scarcity problem, CRN uses an unused licensed spectrum, which is often known as spectrum holes. Thus, research interest has been developed in the integration of CRN for SG communications [9]. CRN concept can be adopted in HANs, NANs, and WAN for spectrum efficiency. In the CRN-based SG scenario, the HAN and NAN gateways act as secondary users (SUs), while the TV spectrum is the primary user (PU). It is more beneficial in rural areas where the possibility of TV whitespace is large.
A novel simple BiCMOS Current Controlled Current Conveyor for RF applications
Published in International Journal of Electronics Letters, 2020
Mohamed A. Yakout, Tareq A. Alawadi
In this paper, a simple yet viable design of a BiCMOS CCCII is introduced. The proposed circuit has high input resistance, high bandwidth for both voltage and current mode and high output resistance which is advantageous. Radio Frequency (RF) spectrum spreads in the range between 3 KHz and 300 GHz. Most analogue and modern digital wireless communication systems exploit RF for communications. Therefore having amplifiers, oscillators, multipliers and filters capable of utilising RF is paramount. In this paper, we introduced an RF oscillator based on the novel BiCMOS current conveyor. The proposed oscillator circuit is very simple and is comprised of three passive elements; two capacitors and one resistor.