3D printed cross-shaped terahertz metamaterials with single-band, multi-band and broadband absorption

2021 ◽  
Vol 122 ◽  
pp. 111739
Author(s):  
Shengnan Li ◽  
Zhonglei Shen ◽  
Wei Yin ◽  
Liuyang Zhang ◽  
Xuefeng Chen
Keyword(s):  
Single Band ◽  
Broadband Absorption ◽  
3D Printed ◽  
Terahertz Metamaterials ◽  
Multi Band

scholarly journals Evaluation of Base Station Efficiency Using Test Drives on Single-Band and Multi-Band Antennas

2016 ◽  
Vol 3 (2) ◽  
pp. 20-25
Author(s):  
Adith Ismail Shaleh
Keyword(s):  
Urban Areas ◽  
Measurement Data ◽  
Base Station ◽  
Single Band ◽  
Network Throughput ◽  
Base Stations ◽  
Network Efficiency ◽  
Coverage Area ◽  
3G Network ◽  
Multi Band

Telecommunications support equipment and systems play a vital role in the network. Multi-band sectoral antennas are starting to replace single-band sectoral antennas at several base stations. The use of a single-band antenna that requires many antennas at the base station is not practical. The following research is conducting tests to evaluate the coverage area, rx signal level and network throughput produced by a multi-band sectoral antenna. Comparison of coverage area calculation using the walfisch-ikegami method. Testing the coverage area with the rx signal level utilizes a drive test so that the optimization of the success of the multi-band antenna is paired to obtain data to support decision making and determine the efficiency of the device in urban areas. From the test results of these 3 factors, the network efficiency generated by multi-band sectoral antennas and single-band sectoral antennas on the antenna coverage area shows that the results of single-band antennas are further than multi-band antennas. Meanwhile, on the signal side that is measured in the drive test process, the 2G network produced by the multi band antenna is better, for the 3G network the single band antenna is better. The 3G network throughput measurement data shows that the uplink access speed results are not good, because the good throughput value is only 42.54%. Measurements on the downlink side are also in poor condition, because the good throughput value is 38.57%.

POLARIZATION-INDEPENDENT METAMATERIAL ABSORBER FOR SINGLE BAND AND MULTI-BAND FREQUENCY

2015 ◽  
Vol 77 (10) ◽  
Author(s):  
Osman Ayop ◽  
Mohamad Kamal A. Rahim ◽  
Noor Asniza Murad
Keyword(s):  
Ring Structure ◽  
Circular Ring ◽  
Unit Cell ◽  
Single Band ◽  
Frequency Separation ◽  
Dual Band ◽  
Band Frequency ◽  
Ring Shape ◽  
Polarization Independent ◽  
Multi Band

This paper presents the design and simulation of polarization-independent type of metamaterial absorbers (MMAbs) at X-band frequency. The advantage of polarization-independent MMAbs is it can absorbs incident electromagnetic (EM) wave in all polarization states. It can be achieved by applying circular ring shape in a unit cell of MMAbs because the shape is very symmetry. The simulation is done in a unit cell for each proposed MMAbs structures. The FR4 substrate is used for MMAbs structure designs. The designed MMAbs structures can be divided into two parts which is circular ring and modified circular ring. The characteristics of both structure are studied through simulation process using CST software. Parametric study is conducted to observe the effect of each parameters in unit cell on the absorbing magnitude and frequency. It is observed that circular ring structures can achieve high EM wave  absorbance for single band and multi band frequency. Since frequency separation distant limitation occurred, the modified circular ring structure is proposed by adding copper lines on the original circular ring structure. Thus, dual band frequency with close separation distant between two resonant frequencies is obtained as close as 1 GHz compared to the original dual band circular ring which is 2 GHz.

Acoustic Metamaterial With Air-Backed Diaphragm for Broadband Absorption: A Preliminary Study

2020 ◽  
Author(s):  
Qian Dong ◽  
Xiaolei Song ◽  
Subhrodeep Ray ◽  
Haijun Liu
Keyword(s):  
Impedance Match ◽  
Center Frequency ◽  
Acoustic Metamaterials ◽  
Perforated Plates ◽  
Broadband Absorption ◽  
Unit Cells ◽  
Equivalent Mass ◽  
3D Printed ◽  
Mass Spring ◽  
Sub Wavelength

Abstract Membrane-based acoustic metamaterials have been reported to achieve 100% absorption, the acoustic analogue of photonic black-hole. However, the bandwidth is usually very narrow around some local resonance frequency, which limits its practical use. To address this limitation and achieve a broadband absorption, this paper first establishes a theoretical framework for unit cells of air-backed diaphragms, modeled as an equivalent mass-spring-dashpot system. Based on the impedance match principle, three different approaches are numerically investigated by tuning the cavity length, the static pressure in the cavity, and the effective damping of perforated plates. A prototype with polyimide diaphragm and 3D printed substrate is then fabricated and characterized using an acoustic impedance tube. Preliminary experiments show the feasibility to achieve an absorption bandwidth of ∼200 Hz at center frequency of 1.45 kHz. This work pays the way for developing a sub-wavelength light weight broadband acoustic absorber for a variety of applications in noise control.

scholarly journals Object-Based Time-Constrained Dynamic Time Warping Classification of Crops Using Sentinel-2

2019 ◽  
Vol 11 (10) ◽  
pp. 1257 ◽  
Author(s):  
Ovidiu Csillik ◽  
Mariana Belgiu ◽  
Gregory P. Asner ◽  
Maggi Kelly
Keyword(s):  
Dynamic Time Warping ◽  
Vegetation Indices ◽  
Single Band ◽  
Time Constraints ◽  
Time Warping ◽  
Object Based ◽  
Crop Mapping ◽  
Dynamic Time ◽  
Sentinel 2 ◽  
Multi Band

The increasing volume of remote sensing data with improved spatial and temporal resolutions generates unique opportunities for monitoring and mapping of crops. We compared multiple single-band and multi-band object-based time-constrained Dynamic Time Warping (DTW) classifications for crop mapping based on Sentinel-2 time series of vegetation indices. We tested it on two complex and intensively managed agricultural areas in California and Texas. DTW is a time-flexible method for comparing two temporal patterns by considering their temporal distortions in their alignment. For crop mapping, using time constraints in computing DTW is recommended in order to consider the seasonality of crops. We tested different time constraints in DTW (15, 30, 45, and 60 days) and compared the results with those obtained by using Euclidean distance or a DTW without time constraint. Best classification results were for time delays of both 30 and 45 days in California: 79.5% for single-band DTWs and 85.6% for multi-band DTWs. In Texas, 45 days was best for single-band DTW (89.1%), while 30 days yielded best results for multi-band DTW (87.6%). Using temporal information from five vegetation indices instead of one increased the overall accuracy in California with 6.1%. We discuss the implications of DTW dissimilarity values in understanding the classification errors. Considering the possible sources of errors and their propagation throughout our analysis, we had combined errors of 22.2% and 16.8% for California and 24.6% and 25.4% for Texas study areas. The proposed workflow is the first implementation of DTW in an object-based image analysis (OBIA) environment and represents a promising step towards generating fast, accurate, and ready-to-use agricultural data products.

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