In this thesis, photoconductive antenna THz generation and EO sampling detection with ZnTe time-domain spectroscopy system is demonstrated. Using this THz TDS system, chirp-controlled THz enhancement is characterized through two photon absorption induced extra-photocarrier and narrow band THz. In two photon absorption enhancement, an anomalous THz radiation enhancement is observed and attributed to two-photon absorption induced extra-photocarrier. Besides, increasing high frequency component is also performed as theoretical expectation. This provides a novel potential for broadband THz radiation. For narrow band THz radiation enhancement is studied using chirp controlled double pulses generated with Michelson Interferometer. Specific frequency enhancement is observed as corresponding temporal spacing pulses applied for excitation. Meanwhile, more enhancement with positive chirp is studied and discussed as well.

In this thesis, carrier dynamics and broadband THz enhancement of photoconduction based THz system are studied with double pulses pump-probe and THz system. The carrier dynamics behavior of the second pulse excitation almost remain unchanged for various temporal spacing of double pulses excitation (from 264fs to 276fs). This is attributed to faster carrier life time of material (around 270fs). Meanwhile, broadband THz enhancement is also investigated under various chirp and temporal spacing of two excitation pulses using shaping pulse THz-TDS system. Compared to typical narrowband THz enhancement, enhanced broadband THz signal both in temporal profile and power is observed at specific temporal spacing and chirp of two excitation pulses. Suitable mechanics is also discussed in this thesis.

No description available.

No description available.

Malgré les nombreux avantages que procure la RFID, son déploiement demeure freiné par plusieurs facteurs aussi bien économiques, que technologiques. Parmi ces freins, on peut citer le coût encore trop élevé des tags, le manque de fiabilité et de sécurité dans les informations contenues dans la puce RFID mais aussi les aspects «recyclage» des tags. Dans cette thèse nous nous focalisons sur le développement de tags RFID sans puce, qui représentent une nouvelle famille de tags bas coût. Avec cette technologie, l'information est extraite à partir de la réponse électromagnétique du tag qui dépend uniquement de sa géométrie. Différentes solutions ont été développées dans le but d'augmenter la quantité d'informations, de réduire la surface du tag ou encore d'améliorer la robustesse de détection. Des considérations pratiques tel que l'aspect réalisation sur substrat papier, le développement d'un système de détection bas coût, ou encore l'aspect mesure dans un environnement réel on été adressés afin d'établir une preuve de concept. Des travaux sur la réalisation de capteurs RFID sans puce et sur le moyen de rendre un tag sans puce reconfigurable sont présentés en guise de perspective. / Despite the many benefits of RFID, deployment is still hindered by several factors both economic and technological. Among these barriers include the cost of tags still too high, lack of reliability and security in the information contained in the RFID chip but also aspects "recycling" of tags. In this thesis we focus on the development of chipless RFID tag, which represent a new family of low cost tags. With this technology, information is extracted from the electromagnetic response of the tag which depends only on its geometry. Various solutions have been developed to increase the amount of information, reduce the surface of the tag or to improve the robustness of detection. Practical considerations such as realization using paper substrate, the development of a low cost detection system, or measurements in a real environment have been addressed in order to establish proof of concept. The last works concerning chipless RFID sensor or about the way to make a chipless tag fully reconfigurable are presented as a perspective.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第22244号 / 理博第4558号 / 新制||理||1655(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 阪部 周二, 准教授 橋田 昌樹, 教授 鶴 剛 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Abstract This thesis focuses on THz band channel modeling and characterization. This vast frequency band spans from 100 GHz to 10 THz. The approximately 10,000 GHz bandwidth together with advances in THz capable electronics have made this band highly potential for many future applications, e.g., imaging and nanodevice-to-nanodevice communications. The latter is the reference application of this thesis and it focuses on the communication among very small and simple devices. The main focus of the thesis is on the THz channel characterization. Therefore, the channel models presented herein are also suitable for communications at macroscopic scale. The THz band offers opportunities, but has many problems as well. One of these is molecular absorption, which causes frequency selective fading to signals. The fading is caused by the signals’ energy absorption in the resonance frequencies of the molecules in the communication medium. Based on the conservation of energy, the absorption is understood to cause a new type of noise in the THz links: transmission induced noise. This noise component is analyzed from multiple physical viewpoints. The THz signals have short enough wavelengths to theoretically allow scattering on aerosols in the atmosphere. Scattering causes frequency dependent loss of the signals, but also a signal spread in time over multiple scattering events. It is shown here that in some specific atmospheric conditions the scattering causes signal loss and time spread. In addition to the theoretical channel models, measurements on a variety of propagation phenomena are con- ducted and analyzed. These include penetration losses, rough surface reflections and scattering, and diffraction. Through the measurements, it can be shown that the THz band communications is feasible in non-line-of-sight (NLOS) conditions in spite of the above phenomena. In the last part of this thesis, stochastic geometry is applied to the THz band in order to estimate the mean interference power and outage probabilities in dense networks formed from nanodevices. Because of the large losses in the channel, large interference levels require large numbers of devices. Stochastic geometry offers perfect tools to estimate the mean interference, and also in the case of directional antennas, which are most likely implemented in all the THz band devices due to large power losses in the channel. / Tiivistelmä Tämä väitöskirja paneutuu THz-taajuisien kanavien mallintamiseen. Tämä valtavan laaja kaista ulottuu sadasta gigahertsistä aina kymmeneen terahertsiin asti. Noin 10000 GHz:n kaistanleveys, yhdistettynä THz-taajuudet mahdollistavien elektroniikan komponenttien kehitykseen, tekee tästä kaistasta erittäin houkuttelevan vaihtoehdon moniin tulevaisuuden sovelluksiin. Näitä ovat mm. kuvantaminen ja nanolaitteiden välinen tietoliikenne. Viimeisin on tämän väitöskirjan viitekehys ja keskittyy hyvin pienien ja yksinkertaisien laitteiden väliseen viestintään. Työn keskittyy pääosin THz-kanavamallinnukseen, joten esitettyjä tuloksia voidaan hyödyntää myös nanoskaalaa suuremmissa verkoissa. THz-taajuudet avaavat mahdollisuuksia, mutta tuovat myös ongelmia. Yksi näistä on molekulaariabsorptio, joka aiheuttaa taajuusselektiivistä häipymää signaaleihin. Tämä ilmiö johtuu sähkömagneetisen energian absorbotumisesta ilman molekyylien resonanssitaajuuksilla. Sen on myös arveltu johtavan uudenlaisen kohinan syntyyn, lähetysten indusoimaan kohinaan, perustuen energian säilymislakiin. Lähetysten indusoimaa kohinaa tutkitaan tässä työssä erilaisista fysikaalisista näkökulmista. THz-taajuisen säteilyn aallonpituus on riittävän lyhyt mahdollistamaan sironta ilmassa olevista aerosoleista. Sironta aerosoleista johtaa taajusriippuvaan signaalitehon häviöön, mutta myös signaalitehon leviämiseen ajassa monisironnan kautta. Työssä todennetaan, että sopivissa olosuhteissa sironta lisää häviöitä ja viivehajetta kanavassa. Teoreettisten kanavamallien lisäksi analysoidaan mittauksin alemmilta taajuusalueilta tuttuja etenemisilmiöitä, kuten signaalin läpäisyä, heijastuksia ja sirontaa pinnoilta, sekä diffraktioita. Mittausten kautta voidaan näyttää, että THz-taajuinen tiedonsiirtolinkki voidaan luoda myös ilman näköyhteyttä yllä mainittujen ilmiöiden kautta. Työn viimeisessä osassa sovelletaan stokastista geometriaa THz-taajuuksille keskimääräisen häiriötehon ja toimintakyvyttömyystodennäköisyyden selvittämiseksi tiheissä nanolaitteiden muodostamissa verkoissa. Isojen kanavahäviöiden takia suuri häiriötaso vaatii suuren määrän laitteita. Stokastinen geometria antaa täydelliset työkalut häiriötason estimointiin. Tätä voidaan myös hyödyntää suuntaavien antennien tapauksessa, joita tullaan suurella todennäköisyydellä käyttämään kaikissa THz-laitteissa johtuen suurista signaalihäviöistä kanavassa.

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Plasmons can be generated in the two dimensional electron gas (2DEG) of grating-gated high electron mobility transistors (HEMTs). The grating-gate serves dual purposes, namely to provide the required wavevector to compensate for the momentum mismatch between the free-space radiation and 2D-plasmons, and to tune the 2DEG sheet charge density. Since the plasmon frequency at a given wavevector depends on the sheet charge density, a gate bias can shift the plasmon resonance. In some cases, plasmon generation results in a resonant change in channel conductance which allows a properly designed grating-gated HEMT to be used as a voltage-tunable resonant detector or filter. Such devices may find applications as chip-scale tunable detectors in airborne multispectral detection and target tracking. Reported here are investigations of InGaAs/InP-based HEMT devices for potential tunable resonant sub-THz and THz detectors. The HEMTs were fabricated from a commercial double-quantum well HEMT wafer by depositing source, drain, and semi-transparent gate contacts using standard photolithography processes. Devices were fabricated with metalized transmission gratings with multiple periods and duty cycles. For sub-THz devices, grating period and duty cycle were chosen to be 9 ?m and 22%, respectively; while they were chosen to be 0.5 ?m and 80% for the THz device. The gratings were fabricated on top of the gate region with dimensions of 250 ?m x 195 ?m. The resonant photoresponse of the larger grating-period HEMT was investigated in the sub-THz frequency range of around 100 GHz. The free space radiation was generated by an ultra-stable Backward Wave Oscillator (BWO) and utilized in either frequency modulation (FM), or amplitude modulation (AM) experiments. The photoresponse was measured at 4K sample temperature as the voltage drop across a load resistor connected to the drain while constant source-drain voltages of different values, VSD, were applied. The dependence of such optoelectrical effect to polarization of the incident light, and applied VSD is studied. The results of AM and FM measurements are compared and found to be in agreement with the calculations of the 2D-plasmon absorption theory, however, a nonlinear behavior is observed in the amplitude and the line-shape of the photoresponse for AM experiments. For detection application, the minimum noise-equivalent-power (NEP) of the detector was determined to be 235 and 113 pW/Hz1/2 for FM and AM experiments, respectively. The maximum responsivity of the detector was also estimated to be ~ 200 V/W for the two experiments. The far-IR transmission spectra of the device with nanometer scale period was measured at 4 K sample temperature for different applied gate voltages to investigate the excitation of 2D-plasmon modes. Such plasmon resonances were observed, but their gate bias dependence agreed poorly with expectations.

No description available.