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Designing the Switch/Router
Published in James Aweya, Designing Switch/Routers, 2023
The CPU runs at a specified internal clock speed or frequency (usually measured in megahertz (MHz) or gigahertz (GHz)) which represents the number of cycles per second it can execute instructions. This determines the speed at which the CPU executes instructions of various types. The motherboard on which the CPU resides provides an external clock which the CPU uses to determine its own operational speeds. The external clock is different from the CPU clock speed (its internal frequency). The system uses a clock multiplier (CPU multiplier or CPU Clock Ratio) to set the ratio of the internal CPU clock speed to the externally supplied clock. The internal CPU speed is obtained by multiplying the externally supplied clock speed by the clock multiplier.
Radio Frequency Utilization
Published in Gilbert Held, Wireless Mesh Networks, 2005
The IEEE 802.11a standard defined a series of new modulation methods that enable data transmission rates up to 54 Mbps. The higher data rates are obtained by the use of Orthogonal Frequency Division Multiplexing (OFDM), a technique in which the frequency band is divided into subchannels that are individually modulated. The IEEE 802.11a standard defines operations in the 5-GHz frequency band. This means equipment supporting the standard is not backward-compatible with the basic 802.11 standard because that standard defines operations in the 2.4-GHz frequency band. In addition, because high frequencies attenuate more rapidly than low frequencies, this results in 802.11a wireless LAN stations having a shorter range than stations operating in the 2.4-GHz band. This in turn requires an organization to deploy more access points to obtain a similar geographical area of coverage than would be required via the use of access points operating in the 2.4-GHz band.
Response to High-Frequency Current Passing Through the Body
Published in Leslie A. Geddes, Handbook of Electrical Hazards and Accidents, 1995
High-frequency alternating current is passed through the body Intentionally for electrosurgery and diathermy. In the former case, localized heating is produced at the tip of a hand-held probe to cut and coagulate tissue. In the latter case (diathermy), high-frequency current produces bulk heating to dilate blood vessels and thereby increase the circulation. High frequency current is induced into the body during magnetic resonance imaging (MRI). Radio, television and radar all use high-frequency current which can be encountered accidentally and cause injury. Prior to discussing the various uses and accidents that can result from exposure to a high-frequency source, it is useful to summarize the frequency spectrum; Table 5.1 presents a compilation of designations and services. Not shown in Table 5.1 are special frequencies reserved for armed forces and government use; these are selected frequencies in the range of 510-535 kHz, 25.33-50 MHz, 138-420 MHz, 890-2,900 MHz and 3.1-38.6 GHz. Cellular telephones operate at about 800 MHz.
Effect of radiation emitted from mobile phone on bone marrow haematopoietic stem cell in mice
Published in Radiation Effects and Defects in Solids, 2023
Pei Yinhui, Gao Hui, Zhang Mingzhu, Wang Xiaoping, Sun Jian, Zhou Fangyuan, Zhu Yufang, Yang Yajing
Mobile phones are low-power radio devices which work on electromagnetic fields with the frequency range of 900–1800 MHz. The rapid increase of mobile phone subscribers has given rise to more and more concerns about the potential adverse effect on health due to the frequency radiation emitted from such communication devices. Earlier studies related to phone emission radiofrequency radiation have verified adverse effects on health. In the past several decades, multiple studies by epidemiology (1), animal model (2) and cell culture (3) have been conducted to explore the various health hazards caused by cell radiation. The conclusions varied in different researches, and many factors as survey sample, radiation intensity of the magnetic field, as well as exposure duration may have contributed to those various results. To the best of our knowledge, previous research work mainly pertained to immune system (4), optic nerve (5), liver (6), brain (7), reproductive system (8), mental health (9), gene mutation (10) and tumour (11).
Compact UWB CPW-fed Monopole Antenna with Variable Triple-band-notched Property
Published in IETE Journal of Research, 2021
Loghman Asadpor, MirHamed Rezvani
Ultra-wideband (UWB) technology has attracted a great interest as the Federal Communication Commission (FCC) allowed the use of the 3.1–10.6 GHz band for commercial applications [1]. The attractiveness of UWB is in its capability of offering high capacity and short-range wireless communication links using low-cost and low-energy transceivers. Planar monopole antennas present very attractive features, which make them suitable for UWB applications. One of these features is avoiding the interferences with other wireless communication standards. For instance, WLAN (Wireless Local Area Network) in which the operating frequency bands are 2400–2484 MHz (2.4 GHz), 5150–5350 MHz (5.2 GHz) and 5725–5825 MHz (5.8 GHz). Also, WiMAX (Worldwide Interoperability for Microwave Access) in which the operating frequency bands are 2500–2690 MHz (2.5 GHz), 3400–3690 MHz (3.5 GHz) and 5250–5825 MHz (5.8 GHz). In particular, planar monopoles are small and low-cost antennas with broadband omnidirectional radiation patterns, and they are not dispersive [2–4]. Interference from this narrow band can be eliminated with a band-rejection filter in the RF front-end of a UWB system. This technique is, however, undesired as it complicates the design of UWB systems. Instead, the frequency-notched feature is integrated into the antenna itself. This is accomplished by inserting a resonant slot in the antenna’s geometry so that it resonates at the desired frequency. Different configurations for band-notching have been introduced, such as inverted U-shaped [5], U-shaped [6], V-shaped [7] and small strip bars [8]. Other configurations are the Hilbert-curve slot (HCS) [9], which uses conductor-backed plane such as window shaped conductor in the back of a monopole antenna [10,11]. Authors in [12] proposed an antenna with a rectangular aperture on a printed circuit board ground plane and a T-shaped exciting stub. In [13–15] antennas with U-shaped slots have been presented. Also, improving band-notched techniques have been proposed in [16,17].