1,721,290 research outputs found
Tunable Microwave Components based on Few Layer Graphene
Full text linkThis doctoral thesis is about the use of graphene for microwave tunable passive components. It opens a new paradigm in the use of innovative and cost-effective methods for producing tunable microwave components based on graphene. Specifically, it paves the way for future key components of microwave and wireless communication systems such as attenuators, phase shifters and antennas. A review of the state-of-the-art microwave passive components based on graphene in terahertz and microwaves is also provided.
The integration of a number of components on a transmitter receiver system requires functional materials of nanometric scale. The use of innovative nanomaterials for designing state of the art microwave components is not new. The signature property of monolayer graphene that can be exploited for tunable microwave components is its electronically tunable resistance. This property is valid for dimensions as large as mm/cm to as small as micro and nanometers keeping a constant aspect ratio. The big challenge in research on future communication systems is to cost effectively design, implement and measure such proposed components. To this aim, in this thesis few layer graphene is deployed in the design of tunable attenuators, phase shifter and antenna. The advantage of using FLG is its cost effectiveness, technological simplicity and eco friendliness unlike most nanomaterials.
A new design of tunable graphene attenuator was proposed based on shunt grounded vias connected to FLG flakes and a microstrip line. The grounded vias were symmetrically placed on each side of the microstrip line with two ports. The design, even though of not very high structural complexity resulted in superior functionality both in terms of dynamic range of insertion loss and the reflective insertion loss. The number of vias were then increased for improved functionality. With the increase in the number of vias, emerging structural parameters were optimized for higher insertion loss and improved mismatch. Simulations were performed for the optimization while fabrication of prototype and measurements were performed which were in good agreement to the simulated results. For the final case of eight vias connected to FLG, a total of more than 65 dB insertion loss was measured with reflective insertion loss as low as 2dB.
Phase Shifter being a vital component of a communication system was also made incorporating FLG flakes. The tunable FLG resistance was converted to tunable reactance by the help of a stub composed of tapered line connected to FLG and a shorted stub. The various lengths and widths of the line were optimized so as to provide maximum shift in reactance when the change in FLG resistance would occur by an applied DC bias voltage. Subsequently, the optimized stub with variable reactance was connected to a two-port 50 Ω transmission line, the transmission on which would cause a phase shift by an applied DC voltage across the FLG. The maximum phase shift obtained was 43 degree with an additional insertion loss of 3 dB. The concept can be applied to a number of such units connected in cascade since the insertion loss is not very high. A combination of the phase shifter and attenuator can be used in the design of a tunable modulator based on a combination of amplitude and phase variation.
The concept of the phase shifter was applied to a frequency reconfigurable patch antenna. FLG accompanied by a shorted stub optimized for maximum reactance change were deployed in a microstrip antenna. A total shift in the radiating frequency of 450 MHz was measured at an applied DC bias voltage of 5V with limited gain degradation.This doctoral thesis is about the use of graphene for microwave tunable passive components. It opens a new paradigm in the use of innovative and cost-effective methods for producing tunable microwave components based on graphene. Specifically, it paves the way for future key components of microwave and wireless communication systems such as attenuators, phase shifters and antennas. A review of the state-of-the-art microwave passive components based on graphene in terahertz and microwaves is also provided.
The integration of a number of components on a transmitter receiver system requires functional materials of nanometric scale. The use of innovative nanomaterials for designing state of the art microwave components is not new. The signature property of monolayer graphene that can be exploited for tunable microwave components is its electronically tunable resistance. This property is valid for dimensions as large as mm/cm to as small as micro and nanometers keeping a constant aspect ratio. The big challenge in research on future communication systems is to cost effectively design, implement and measure such proposed components. To this aim, in this thesis few layer graphene is deployed in the design of tunable attenuators, phase shifter and antenna. The advantage of using FLG is its cost effectiveness, technological simplicity and eco friendliness unlike most nanomaterials.
A new design of tunable graphene attenuator was proposed based on shunt grounded vias connected to FLG flakes and a microstrip line. The grounded vias were symmetrically placed on each side of the microstrip line with two ports. The design, even though of not very high structural complexity resulted in superior functionality both in terms of dynamic range of insertion loss and the reflective insertion loss. The number of vias were then increased for improved functionality. With the increase in the number of vias, emerging structural parameters were optimized for higher insertion loss and improved mismatch. Simulations were performed for the optimization while fabrication of prototype and measurements were performed which were in good agreement to the simulated results. For the final case of eight vias connected to FLG, a total of more than 65 dB insertion loss was measured with reflective insertion loss as low as 2dB.
Phase Shifter being a vital component of a communication system was also made incorporating FLG flakes. The tunable FLG resistance was converted to tunable reactance by the help of a stub composed of tapered line connected to FLG and a shorted stub. The various lengths and widths of the line were optimized so as to provide maximum shift in reactance when the change in FLG resistance would occur by an applied DC bias voltage. Subsequently, the optimized stub with variable reactance was connected to a two-port 50 Ω transmission line, the transmission on which would cause a phase shift by an applied DC voltage across the FLG. The maximum phase shift obtained was 43 degree with an additional insertion loss of 3 dB. The concept can be applied to a number of such units connected in cascade since the insertion loss is not very high. A combination of the phase shifter and attenuator can be used in the design of a tunable modulator based on a combination of amplitude and phase variation.
The concept of the phase shifter was applied to a frequency reconfigurable patch antenna. FLG accompanied by a shorted stub optimized for maximum reactance change were deployed in a microstrip antenna. A total shift in the radiating frequency of 450 MHz was measured at an applied DC bias voltage of 5V with limited gain degradation
A review on graphene and graphene composites for application in electromagnetic shielding
No full text<p>This document is an author version of review paper ragarding new shielding materials. <span>To design an EMI shielding product, a compromise must be achieved between the electromagnetic shielding efficiency, the thickness of shielding materials, durability, mechanical strength, reduced volume and weight, and elasticity. Due to its ability to block EMWs, flexibility, lightweight, and chemical resistivity, graphene has been identified as a promising candidate material for efficient EMI shielding. Herein, we reviewed the studies that investigated various graphene-based composites as potential EMI shielding materials, with a focus on the composites based on graphene and silver nanowires due to their high EMI shielding efficiency, low production price, and favorable mechanical properties. </span></p>
THE EFFECT OF CARBON NANOTUBES CONCENTRATION ON COMPLEX PERMITTIVITY OF NANOCOMPOSITES
No full textThere is growing interest in the use of nanocomposites based on carbon nanotubes (CNT) due to their excellent mechanical, thermal and electrical properties. The electromagnetic characteristics of nanocomposites with different types of multi-walled carbon nanotubes were investigated. CNTs with different geometries (length and diameter) were chosen in order to analyze the effect of the geometrical parameters on the electromagnetic properties. Nanocomposites with various percentages of CNT were made and the number of CNTs per cm3 in the composite was computed. The composites were characterized by Field Emission Scanning Electron Microscopy (FESEM) analysis in order to examine the dispersion of the filler. The complex permittivity of the NCs was measured with two different techniques and the variation of the permittivity with the number of CNT per cm3 was investigated
Voltage-Controlled and Input-Matched Tunable Microstrip Attenuators Based on Few-Layer Graphene
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Analisa Keausan Pahat Karbida Sebelum Dan Sesudah Di Karburasi Menggunakan Serbuk Arang Tempurung Kelapa
No full textSelama proses permesinan berlangsung terjadilah interaksi antara pahat dengan
benda kerja dimana benda kerja terpotong sedangkan pahat mengalami gesekan.
Gesekan yang dialami pahat oleh permukaan geram yang mengalir dan
permukaan benda kerja yang telah terpotong. Akibat gesekan ini pahat mengalami
keausan. Keausan pahat ini akan makin membesar sampai batas tertentu sehingga
pahat tidak dapat dipergunakan lagi atau pahat telah mengalami kerusakan. Maka
dari itu bagaimanakah cara agar pahat dapat bertahan lama atau tahan aus. Maka
kita bisa bereksperimen membuat pahat tersebut menjadi lebih keras dari
standartnya, dengan melakukan kabarburasi. Karburasi atau Carburizing adalah
proses perlakuan thermokimia, umumnya diterapkan pada jenis baja yang mudah
dikeraskan. Arang tempurung kelapa sebagai sumber karbon padat yang mudah
merekat pada baja dapat melapisi baja, dengan cara dirubah terlebih dahulu dalam
bentuk butiran. Bentuk butiran akan membantu proses perubahan karbon padat
menjadi gas melalui pemanasan. Dengan demikian agar baja tersebut dapat
dikeraskan permukaannya. Proses penambahan karbon (Carburizing) pada pahat,
bertujuan untuk menambah kandungan karbon agar bisa ditingkatkan
kekerasannya. Penelitian ini menggunakan pahat sisipan jenis karbida, jenis pahat
ini dibuat dengan campuran antara lain serbuk arang, tempurung kelapa.
Penelitian ini dilakukan agar kita mengetahui Keausan yang terjadi pada pahat
yang sebelum dan sesudah dikarburasi menggunakan serbuk arang tempurung
kelapa
Pengaruh Motivasi Pimpinan Terhadap Produktivitas Kerja Pegawai Di Kantor Kecamatan Medan Denai
Full text linkKemampuan manusia juga dapat ditingkatkan dengan memberikan
motivasi pimpinan yang tepat. Dapat dilihat dengan jelas bahwa organisasi hanya
akan berhasil mencapai tujuan dan berbagai sasarannya, apabila semua komponen
organisasi tersebut berupaya menampilkan kerja yang optimal agar dapat
tercapainya produktivitas dan salah satunya dengan motivasi pimpinan yang baik.
Namun, masalah yang timbul pada saat pegawai/staf dari organisasi yang
sebenarnya memiliki potensi yang baik untuk mengerjakan tugas dan wewenang
yang diberikan kepadanya tetapi tidak melaksanakan tugas tersebut dengan baik
dikarenakan banyak faktor yang mempengaruhinya. Dalam penelitian ini penulis
akan membahas pengaruh motivasi pimpinan terhadap produktivitas kerja
pegawai Di Kantor Kecamatan Medan Denai.
Metode yang digunakan dalam penelitian ini adalah metode deskriptif
dengan analisis kuantitatif. Adapun teknik pengumpulan data yang dilakukan
dalam penelitian ini adalah dengan quesioner yaitu pengumpulan data dengan cara
penyebaran angket. Adapun yang menjadi populasi dalam penelitian ini adalah
seluruh pegawai pada Kantor Kecamatan Medan Denai yang berjumlah 35 orang,
sedangkan sampelnya adalah sejumlah populasi yaitu 35 orang.
Dari hasil penelitian terbukti bahwa tingkat korelasi antara variabel bebas
(X) dengan variabel terikat (Y) berada pada tingkat sedang, yaitu berada antara
0,400 – 0,799. Hasil perhitungan tersebut menghasilkan rxy = 0,448. Dengan
melihat rtabel yakni sampel 35 orang dengan taraf signifikan 5 % maka nilai rtabel
tersebut 0,334. Hal ini nilai r hitung yang nilainya 0,448 lebih besar dari pada rtabel
yakni 0,334, maka dari itu hipotesis alternatif berpengaruh. Tingginya pengaruh
variabel bebas (X) terhadap variabel terikat (Y).
Sementara dari hasil uji t diperoleh signifikan antara variabel bebas (X)
dengan variabel terikat (Y) 2,879. Dari hasil determinasi diperoleh besarnya
persentase antara variabel bebas (X) dengan variabel terikat (Y) 20,07 %,
sedangkan hasil prediksi regresi linear antara variabel bebas (X) dengan variabel
terikat (Y) diperoleh 21,92.
Berdasarkan hasil penelitian yang penulis lakukan bahwa motivasi
pimpinan sudah baik dalam penerapannya dengan tujuan meningkatkan
produktivitas kerja pegawai Di Kantor Kecamatan Medan Denai. Hal ini dapat
dilihat dari pegawai yang selalu termotivasi untuk meningkatkan hasil kerjanya.
Adapun perumusan masalah yaitu “Bagaimana Pengaruh Motivasi Pimpinan
Terhadap Produktivitas Kerja Pegawai Pada Kantor Kecamatan Medan Dena
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