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GNSS Signals and Range Determination
Published in Basudeb Bhatta, Global Navigation Satellite Systems, 2021
A series of waves transmitted at constant frequency and amplitude is called a continuous wave. When a continuous wave is modified in some manner, this is called modulation. When this occurs, the continuous wave serves as a carrier wave for information.
Nucleate boiling heat transfer performance of different laser processed copper surfaces
Published in International Journal of Green Energy, 2020
Vishal V. Nirgude, Santosh K. Sahu
The laser systems produce a laser beam consisting of photons. It generates heat at the incident point on the metal surface due to photon electron interaction. This heat melts and evaporates metal present at incident point. However, the emission of laser beam is different for a continuous wave and nanosecond pulsed laser system. A continuous electromagnetic wave is emitted in case of CW laser (Figure 1c). While, pulsed laser emits an electromagnetic wave consisting of a pulse train. Also, the sites of the heat-affected zone (HAZ) are found to vary depending on the type of laser. In the case of continuous wave (CW) lasers, the material is primarily removed by melting and this creates a bigger HAZ. In such a case, the material ejection is mainly dominated by thermal processes. In nanosecond lasers, it involves three primary stages which lead to the formation of a plasma. In first stage, laser photons couple both with electrons and phonons of the target material. The photon–electron coupling results in an immediate rise of the electron temperature, leading to vaporization of the target. In comparison to CW lasers, the HAZ developed by nanosecond pulsed lasers is smaller (Stauss et al. 2016). As smaller HAZ is developed in case of nanosecond pulsed laser, it affects the very thin top surface layer.
Historical Developments and Recent Advances in High-power Magnetron: A Review
Published in IETE Technical Review, 2022
Patibandla Anilkumar, Dobbidi Pamu, Tapeshwar Tiwari
Magnetron operates in continuous wave or pulsed modes. Continuous-wave magnetrons are constant in amplitude and frequency like a sine wave, mainly used for industrial purposes. Depending on the recent applications, designing the magnetron with high power pulses with shorter wavelengths is needed. A pulse wave is a non-sinusoidal waveform that includes square waves of the duty cycle of 50% and asymmetrical waves of duty cycles other than 50%. The pulse durations are from 0.1–10 μsec, delivering 1–3 MW power. The output power ranges from few Watts to Giga Watts, wavelengths from centimetre level to sub-millimetre, and frequencies from hertz to terahertz. High-power S-band pulse magnetrons are used in accelerators useful in medical science for cancer treatment and non-destructive testing in defence and space technology. These magnetrons are available commercially in the market with an operating frequency range of 1-35 GHz and output power of 100 W – 35 MW [45]. SAMEER developed the S-band medical linac system, which requires an RF source. The magnetron is a helpful device to generate RF fields to energize the resonator cavity. So, simulation and in-depth understanding of this S-band magnetron were analyzed and simulated within effective software CST Particle Studio. In 2018, SK Vyas and T Tiwari designed a 12 hole and slot type S-band pulsed magnetron to generate a 3.25 MW peak power at an operating frequency of 2.998±0.005 GHz for linac applications and attained the operational efficiency of the magnetron 56%. Table 1 shows the pulsed magnetron maximum output power and efficiencies for different microwave bands from the previous studies and analysis [46].
Integrated instrumentation for combined laser-induced breakdown and Raman spectroscopy
Published in Instrumentation Science & Technology, 2019
Guangmeng Guo, Ke Liu, Jie Wang, Shuai Wang, Qingyu Lin, Yu Ding, Di Tian, Yixiang Duan
Matroodi et al.[50] made a comparison of two setups with different laser systems. A continuous-wave laser was used for Raman spectroscopy and a pulsed laser for LIBS in the first setup, and in the second setup a single pulsed laser excited both Raman and LIBS signals simultaneously. The authors demonstrated that the intensity of the central and marginal areas of the laser spot responds to LIBS and Raman, respectively. The design of a single laser in one hybrid instrument is undoubtedly a great technological progress but increases the complexity of the structural components and the instability of the measurements which should be avoided.