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Formation Control of Networked UAVs
Published in Fei Hu, Xin-Lin Huang, DongXiu Ou, UAV Swarm Networks, 2020
Because of the major resource constraints of multi-UAV systems such as battery power, communication bandwidth and computation processing capabilities, the lifetime of UAVs and onboard transceiver transmission distances are both limited. A longer distance will cause higher propagation loss and more serious signal degradation. The distance configuration in the UAV network must not exceed the receiver's sensitivity and needs to be restricted to the boundaries of minimum signal-to-noise-ratio (SNR) or received signal strength indicators (RSSIs), respectively. A disruption-free connectivity is indispensable to control UAVs' behaviors. On the other hand, high spatial coverage is required for gaining required information from disjunct network regions that cover a large area of interest. There is a trade-off between coverage and connectivity.
Piezoelectric Devices
Published in Kenji Uchino, Ferroelectric Devices, 2018
In actual SAW applications, the value of ks2 relates to the maximum bandwidth obtainable and the amount of signal loss between input and output, which determines the fractional bandwidth as a function of minimum insertion loss for a given material and filter. Propagation loss is one of the major factors that determines the insertion loss of a device and is caused by wave scattering at crystalline defects and surface irregularities. Materials which show high electromechanical coupling factors combined with small temperature coefficients of delay are generally preferred. The free surface velocity, vf, of the material is a function of cut angle and propagation direction. The TCD is an indication of the frequency shift expected for a transducer due to a temperature change and is also a function of cut angle and propagation direction. The substrate is chosen based on the device design specifications which include operating temperature, fractional bandwidth, and insertion loss.
Broadband Rectenna for Radio Frequency Energy Harvesting Application
Published in IETE Journal of Research, 2018
Sachin Agrawal, Manoj Singh Parihar, P. N. Kondekar
Figure 11(a) shows the plot of received power as a function of distance (d). It can be seen that increasing the operating frequency and the distance between transmitting and receiving antenna, the received power decreases, which is very obvious due to higher propagation loss at higher frequencies. Further, the rectenna RF-to-DC conversion efficiency as a function of the frequency for different power levels is shown in Figure 11(b). As seen, for the input power of −20 dBm, the rectenna system offers more than 20% efficiency for all frequency signals except 4.8 GHz. Rectenna yields maximum efficiency of 62.5% for an input power of 0 dBm and frequency 1.8 GHz.
A Brief Review on mm-Wave Antennas for 5G and Beyond Applications
Published in IETE Technical Review, 2023
Paikhomba Loktongbam, Debasish Pal, A. K. Bandyopadhyay, Chaitali Koley
Atmospheric attenuation is one of the main drawbacks of mm-wave applications. They may be classified into two broad categories [205]. The first is free space path loss, and the second is propagation loss. Propagation loss can be further classified as (a) reflection loss, (b) diffraction loss, (c) scattering loss, (d) atmospheric gaseous loss, [206,207] (e) precipitation attenuation due to rain [208–210].
Broadband wavelength conversion in hydrogenated amorphous silicon waveguide with silicon nitride layer
Published in Journal of Modern Optics, 2018
Jiang Wang, Yongfang Li, Zhaolu Wang, Jing Han, Nan Huang, Hongjun Liu
Recently, a variety of materials for wavelength conversion based on FWM have been proposed, such as crystalline silicon (6, 7), silicon nitride (8, 9), and a-Si:H (10, 11). Crystalline silicon has a high non-linear refractive index with low linear propagation loss. However, at telecommunication wavelengths, the silicon platform has the disadvantage of the presence of two-photon absorption (TPA) and the accompanying free carrier absorption (FCA). Silicon nitride significantly mitigates the TPA and the FCA, but it lacks potential integration with active devices; a-Si:H is a promising material for optical processing in integrated silicon photonics. It is widely used in many fields, such as optical parametric oscillators (12), phase-sensitive amplification (13), wavelength converters (10, 11), and in supercontinuum generation (14). These reports show that a-Si:H has many potential advantages: (a) the material properties of deposited a-Si:H can be tuned by controlling deposition parameters, while having low TPA and FCA effects in the communication band due to operation in the lower half of the band gap (15). (b) a-Si:H can be deposited at a relatively low temperature (about 300 °C), using plasma-enhanced chemical vapour deposition (PECVD), which can be deposited on different substrates while maintaining the effect with complementary metal oxidation semiconductor (CMOS) process (16). (c), a-Si:H with a high Kerr nonlinearity of n2 = 7.43 × 10−13 cm2 W−1 (10) and a high non-linear figure of merit, greater than five (ten times larger than for crystalline silicon) (17, 18). It is worth noting that the conversion efficiency is higher than for crystalline silicon under the same conditions (5). However, a-Si:H has relative high linear propagation loss, from 2 to 14 dBcm−1 (19, 20), that is detrimental to all-optical signal processing (21). To cope with this difficulty, Rong Sun et al. proposed a method to decrease linear propagation loss. This research determined that a-Si:HN waveguides have low optical transmission loss of about 2.7 dBcm−1 for TE mode in 1.55 μm range (22). However, as far as we know, there are few reports on the study of a-Si:HN waveguide in all-optical signal processing for waveguide design and fabrication.