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Revised EPBD directive has set ambitious targets for renovation. It is stated that Member States shall establish a long-term strategy facilitating the cost-effective transformation of existing buildings into nearly-zero energy buildings. The long-term strategy should set out a roadmap with a view to the long-term 2050 goal of reducing greenhouse gas emissions in the European Union. This creates the need for cost-efficient renovation solutions which can be implemented in large scale. The impact assessment shows that roughly a doubled renovation rate of 3 % would be needed to accomplish the energy efficiency ambitions in a cost-effective manner. The objective of this study is to specify renovation concepts with adequate heating and ventilation, based on Estonian and German apartment buildings and corresponding local solutions. Energy performance and sizing analyses were conducted for selected multifamily apartment buildings typical for 1960-70es with three different renovation concepts. Energy calculations wereconducted with national energy calculation methods and national energy requirements for major renovation. In the renovation, the building envelope insulation, air tightness, and heating and ventilation systems were improved so that the renovated building complies with national nearly zero-energy requirement for major renovation.
Voltage manipulation of skyrmions is a promising path toward low-energy spintronic devices. Here, voltage effects on skyrmions in a GdOx/Gd/Co/Pt heterostructure are observed experimentally. The results show that the skyrmion density can be both enhanced and depleted by the application of an electric field, along with the ability, at certain magnetic fields to completely switch the skyrmion state on and off. Further, a zero magnetic field skyrmion state can be stabilized at a negative bias voltage using a defined voltage and magnetic field sequence. The voltage effects measured here occur on a few-second timescale, suggesting an origin in voltage-controlled magnetic anisotropy rather than ionic effects. By investigating the skyrmion nucleation rate as a function of temperature, we extract the energy barrier to skyrmion nucleation in our sample. Further, micromagnetic simulations are used to explore the effect of changing the anisotropy and Dzyaloshinskii-Moriya interaction on skyrmion density. Our work demonstrates the control of skyrmions by voltages, showing functionalities desirable for commercial devices.
Tämän diplomityön tarkoituksena oli tutkia sähkömagneettisen säteilyn sirontaa kappaleista, jotka toteuttavat lähteettömän reunaehdon. Lähteettömän reunaehdon mukaan kappaleen pinnalle indusoituneet ekvivalentit sähköiset ja magneettiset pintavirtatiheydet ovat lähteettömiä. Lähteetön reunaehto tunnetaan myös nimellä DB-reunaehto, koska ekvivalenttien pintavirtatiheyksien lähteettömyydestä seuraa se, että pinnan normaalinsuuntaiset sähkö- ja magneettivuontiheyskomponentit (D,B) häviävät pinnalla. DB-reuna voidaan toteuttaa anisotrooppisen väliaineen avulla, missä pinnan normaalinsuuntaiset väliaineparametrit permittiivisyys ja permeabiilisuus lähestyvät nollaa. Sirontatehtävä ratkaistiin numeerisesti pintaintegraaliyhtälömenetelmällä, joka tunnetaan myös nimellä BEM (Boundary element method). Integraaliyhtälömenetelm ässä Maxwellin yhtälöiden reuna-arvo-ongelma formuloidaan integraaliyhtäl öiksi, missä tuntemattomia ovat ekvivalentit pintavirtatiheydet. Integraaliyhtälöt diskretoidaan ja muutetaan lineaariseksi yhtälöryhmäksi momenttimenetelmällä. Lineaarinen yhtälöryhmä voidaan ratkaista Gaussin eliminaatiolla ja ratkaisusta voidaan laskea sironneet kentät. Sirontapoikkipinta laskettiin erilaisille DB- ja ideaalijohtaville eli PEC-kappaleille. Mielenkiintoisin tulos oli, että symmetrisillä DB-kappaleilla ei ole takaisinsirontaa. DB-kuutiolle ja pallolle laskettiin sirontatehokkuus taajuuden funktiona ja tuloksia verrattiin PEC-kuution ja pallon sirontatehokkuuksiin. Tuloksista huomattiin, että PEC-kappale verrattuna DB-kappaleeseen on voimakkaampi sirottaja matalilla taajuuksilla. Työssä näytettiin myös, että dynamiikan pintaintegraaliyhtälömenetelmällä on mahdollista laskea staattinen polarisoituvuus DB-kappaleille ilman perinteisiä matalan taajuuden ongelmia.
We present radiofrequency thermometry based on a tunnel junction between a superconductor and proximitized normal metal. It allows operation in a wide range of biasing conditions. We demonstrate that the standard finite-bias quasiparticle tunneling thermometer suffers from large dissipation and loss of sensitivity at low temperatures, whereas thermometry based on a zero-bias anomaly avoids both of these problems. For these reasons, the latter method is suitable down to lower temperatures, here to about 25 mK. Both thermometers are shown to measure the same local temperature of the electrons in the normal metal in the range of their applicability.
This thesis demonstrates the use of pole zero identification method to stabilize a 2.32 - 2.37 GHz class AB power amplifier. In addition, the thesis presents a procedure to obtain values of stabilization components. Power amplifiers are used to drive transmitting antennas with high power in applications such as RADAR’s, cellular base stations and RF-driven lighting. They operate at large signal level to achieve these high output power levels. This increases the risk of potential oscillations in power amplifiers, which are undetectable using conventional linear stability factors. The oscillations degrade amplifier’s performance and may cause interference and transistor burnout. Non-applicability of linear stability factors for large-signal operation has led to development of new stability analysis methods such as Ohtomo, NDF and AG. Ability to detect oscillation due to large-signal has been the priority of these methods. A drawback is that, they are either complex to use or not fully complete in stabilizing a power amplifier. A recent method based on pole zero identification is shown to be rigorous and simple to use. However, this method requires a special additional software STability ANalysis(STAN) to identify poles and zeros of power amplifiers. This work utilized a simulation template in ADS 2011 to design the 2.32-2.37 GHz class AB power amplifier. The template requires measured load pull data of the transistor used in the amplifier design. The realized design has met maximum performance in first trial with little optimization. This design approach is useful to circumvent modeling problems in power transistors. However, the stability analysis is highly dependent on the transistor model accuracy. The designed and constructed class AB power amplifier in this work is unconditionally stable for small-signal operation and potentially unstable for large-signal operation. The amplifier is able to deliver an output power of 140 Watts with 15.2 dB gain and 42.08% efficiency at 2.345 GHz. Load pull measurements (peak power, peak gain and peak efficiency) of the amplifier and transistor used to design the amplifier are compared for design evaluation.
Abstract Multiantenna systems can increase the spatial reuse of the wireless spectrum by nulling the interfering directions. However, the efficiency of the spatial interference suppression is highly sensitive to errors in the progressive phase applied to the antenna elements. We examine the impact of one particular source of error resulting from the quantization of the analog beamforming weights. In particular, we focus on vector-modulator based RF beamforming system. To improve the quantization error, we propose a sliding reference approach for using a floating phase reference minimizing the quantization error of the RF beamformer. Monte-Carlo simulations are performed to analyze the performance of the zeroforcing with quantized coefficients. With small arrays, the simulation results showed almost 10 dB of improvement in the average null depth compared to the conventional round-off method.
Impulsive sound can be perceived more annoying than a steady-state sound having the same A-weighted equivalent sound pressure level, LAeq. The difference in perceived noise annoyance can be compensated by adding a penalty or an adjustment k to LAeq (rating level). Many legislations apply a constant penalty value, such as 5 dB or more, but the validity of this procedure has been questioned. Nordtest method NT ACOU 112 identifies an impulse from the time profile of sound pressure level by using two measures describing the onset of an impulse: level difference (DL) and onset rate (Ron). The purpose of this study was to determine how the annoyance penalty depends on DL (5-40 dB) and Ron (5-800 dB/s) and to compare obtained results to the penalty prediction model of Nordtest method. A psychoacoustic laboratory experiment of 32 participants was conducted. Synthetic and periodic impulsive sounds were studied with two alternative spectra. The sounds were presented at 55 dB LAeq. Steady-state sounds at levels 49-70 dB were used to derive the penalty of impulsive sounds. The observed penalty values ranged between 0 and +8 dB. The penalty values depended somewhat on spectrum. The penalty deviated from zero when DL > 10 dB or Ron > 15 dB/s and increased with increasing DL and Ron. The penalty predicted by Nordtest method usually overestimated the observed penalty when Ron ≥ 200 dB/s. The results are against constant penalty values and they can be used to develop future penalty schemes.
In this article, the adoption and performance of a constant envelope (CE) type spatial precoder is addressed in large-scale multiuser MIMO based cellular network. We first formulate an efficient computing solution to obtain the antenna samples of such CE precoder. We then evaluate the achievable CE precoder based multiuser downlink (DL) system performance and compare it with the corresponding performance of more ordinary zero-forcing (ZF) spatial precoder. We specifically also analyze how realistic highly nonlinear power amplifiers (PAs) affect the achievable DL performance, as the individual PA units in largearray or massive MIMO systems are expected to be small, cheap and operating close to saturation for increased energy-efficiency purposes. It is shown that the largely reduced peak-to-average power ratio (PAPR) of the PA input signals in the CE precoder based system allows for pushing the PA units harsher towards saturation, while allowing to reach higher signal-to-interference-plus-noise ratio (SINRs) at the intended receivers compared to the classical ZF precoder based system. The obtained results indicate that the CE precoder can outperform the ZF precoder by up to 5-6 dBs, in terms of the achievable SINRs, when the PA units are pushed towards their saturating region. Such large gains are a substantial benefit when seeking to improve the spectral and energy-efficiencies of the mobile cellular networks.
Abstract The paper presents a novel dual polarized dual fed Vivaldi antenna structure for 1.7–2.7 GHz cellular bands. The radiating element is designed for a base station antenna array with high antenna performance criteria. One radiating element contains two parallel dual fed Vivaldi antennas for one polarization with 65 mm separation. Both Vivaldi antennas for one polarization are excited symmetrically. This means that the amplitudes for both antennas are equal, and the phase difference is zero. The orthogonal polarization is implemented in the same way. The dual polarized dual fed Vivaldi is positioned 15 mm ahead from the reflector to improve directivity. The antenna is designed for 14 dB impedance bandwidth (1.7–2.7 GHz) with better than 25 dB isolation between the antenna ports. The measured total efficiency is better than 0.625 dB (87%) and the antenna presents a flat, approximately 8.5 dB, gain in the direction of boresight over the operating bandwidth whose characteristics promote it among the best antennas in the field. Additionally, the measured cross polarization discrimination (XPD) is between 15 and 30 dB and the 3 dB beamwidth varies between 68° and 75° depending on the studied frequency.
Power density and conversion efficiency are two critical parameters of inductive power transfer (IPT) systems. These parameters are related to the number of components in the power conversion circuit as well as its modulation method. The combination of Midpoint Matrix Converter and pulse-density modulation (PDM) has a potential to improve these parameters, due to a low number of semiconductor switches utilization as well as constant efficiency at the maximum output and partial load operations. In this context, this paper analyzes the performance of a three-phase to single-phase Midpoint Matrix Converter using a Free-wheeling Switch (MMCFS) and the PDM in a high coupling factor series-none IPT application. This converter utilizes on–off control to manage power transfer, which automatically tracks the load resonant frequency. Dynamic and steady-state mathematical equations were derived to represent the converter and the IPT system characteristics. These equations show a relationship between the link efficiency, the link gain, the damping ratio and the coupling factor. A kick-start method and a multistep switching strategy were developed to start and operate the converter, respectively. Additionally, a 150 W MMCFS-based IPT prototype was built to verify the improvement, which demonstrated an efficiency of around 80% at the maximum output and partial load operations.
A set of boundary conditions requiring vanishing of the normal components of the D and B vectors at theboundary surface is introduced and labeled as that of DB boundary. Basic properties of the DB boundary arestudied in this paper. Reflection of an arbitrary plane wave, incident with a complex propagation vector, isanalyzed for the planar DB boundary. It is shown that waves polarized transverse electric TE and transversemagnetic TM with respect to the normal of the boundary are reflected as from respective perfect electricconductor and perfect magnetic conductor planes. The basic problem of current source above the planar DBboundary is solved by applying TE and TM decomposition for the source. Realization of the DB boundary interms of an interface of uniaxially anisotropic metamaterial half-space with zero axial medium parameters isconsidered. It is also shown that such a medium with small axial parameters acts as a spatial filter for wavesincident at the interface which could be used for narrowing the beam of a directive antenna. Application of DBboundary as an isotropic soft surface with low interaction between antenna apertures also appears possible.
The magnitude and sign of the gravitational coupling 1/G depend on the relations between different contributions from scalar, fermionic and vector fields. In principle, this may give the zero and negative values of 1/G in some hypothetical Universes with the proper relations between the fermionic and bosonic species. We consider different conjectures related to gravity, such as the wave function collapse caused by gravity, entropic gravity and maximum force. We find that some of them do not work in the Universes with zero or negative 1/G, and thus cannot be considered as universal. Thus, the extension of the gravitational coupling to 1/G ≤ 0 provides the test on the universality of the proposed theories of gravity.
This paper describes a voltage controlled oscillator(VCO) -based ADC for biomedical applications which employs a relaxation oscillator for voltage-to-frequency conversion. The proposed circuit uses a redundant pair of capacitors to mitigate the conversion error resulting from the time required for resetting the capacitor. A switch matrix with feedback helps sustain oscillations. Further, the VCO frequency approaches zero as the input voltage approaches zero unlike a converter with ring oscillator, thereby reducing power consumption. Post-layout simulation of the proposed ADC designed with a 28 nm FDSOI CMOS technology shows an ENOB of 8 and power consumption of 12 uW from a 0.7 V supply.
In this paper we extend earlier results on Hosoya entropy (H-entropy) of graphs, and establish connections between H-entropy and automorphisms of graphs. In particular, we determine the H-entropy of graphs whose automorphism group has exactly two orbits, and characterize some classes of graphs with zero H-entropy.
Työssä tutustuttiin D-luokan vahvistimen ja PWM-ohjatun H-sillan toimintaan ja mahdollisuuksiin. Työssä suunniteltiin, rakennettiin ja mitattiin D-luokan vahvistin. Vahvistin suunniteltiin tyhjältä pöydältä käyttäen erilliskomponentteja. Suunnittelu aloitettiin hahmottamalla koko kytkennän lohkokaavio, jonka avulla määritettiin tarvittavat signaalit ja tasot. Jokainen lohko suunniteltiin erillisenä osana, joiden toimintaa voitaisiin optimoida muista lohkoista riippumatta. Kytkennästä jätettiin kolmioaaltogeneraattori pois ja tilalla käytettiin funktiogeneraattoria, koska kytkennässä haluttiin tutkia kytkentätaajuuden merkitystä. Työtä varten teetettiin piirilevyt suuren reikämäärän, komponenttien pienten juotostäplien ja juotteenestopinnoitteen vuoksi. Piirilevyt kasattiin käsin ja juottaminen tehtiin paistinpannulla. Korjauksiin käytettiin juotinta. Vahvistimen käyttöönotossa jokaisen lohkon toiminta mitattiin erikseen. Lohkojen oikean toiminnan varmistamisen jälkeen ne liitettiin toisiinsa. Laite toimi riittävän hyvin, jotta vahvistimen audiosuorituskyky pystyttiin mittaamaan. Mittauksissa käytettiin kuormana 8 ohmin kaiutinta ja taajuusvaste oli hieman mutkainen, mutta kaikki taajuudet toistuivat 20 kHz asti halutuissa määrin. Muissa mittauksissa pienillä tehoilla lähdön kohina heikensi mittauksia selvästi, mutta suuremmilla tehoilla kohina jäi suhteessa pienemmäksi ja tulokset paranivat tehon kasvaessa. Harmoniseksi säröksi saatiin parhaimmillaan 0,5 %, signaali-kohinasuhteeksi 52 dB ja SINAD:ksi 45 dB. Hyötysuhde noin 90 % teholla oli 83 %.
In this paper, we parameterize an excess loss-based multipath component (MPC) cross-polarization ratio (XPR) model in indoor and outdoor environments for above-5-GHz frequency bands. The results are based on 35 measurement campaigns in several frequency bands ranging from 5 to 80 GHz. A conventional XPR model of an MPC assuming a constant mean value fits our measurements very poorly and moreover overestimates the depolarization effect. Our measurements revealed a clear trend that the MPC XPR is inversely proportional to the excess loss in reference to the free-space path loss. The model is physically sound as a higher loss is attributed to more lossy interactions or to a greater number of interactions with objects, leading to a greater chance of depolarization. The measurements furthermore showed that the MPC XPR is not strongly frequency or environment dependent. In our MPC XPR model, an MPC with zero-dB excess loss has a mean XPR of 27 dB. The mean XPR decreases half-a-dB as the excess loss increases by every dB and the standard deviation around the mean is 7 dB. The model is applicable to existing channel models to reproduce realistic MPC XPRs for the above 5-GHz radio links.
Velvet noise is a sparse ternary pseudo-random signal containing only a small portion of non-zero values. In this work, the derivation of the spectral properties of velvet noise is presented. In particular, it is shown that the original velvet noise is white, i.e. has a constant power spectrum. For velvet noise variants with altered probability of polarity, the spectral characteristics are analytically derived. Crushed additive velvet noise is shown to have potential in the design of coloured sparse noise sequences, which are useful in acoustic signal processing.
Viime vuosien aikana on esitelty monia teknisiä edistyksiä kommunikaatiosysteemeihin viidennen sukupolven kommunikaatioverkon mukana. Merkittävimpiä trendejä integroitujen lähetinvastaanottimien kannalta ovat korkeampien taajuuksien käyttöönotto, 24.24-43.5 GHz äskettäin julkaistun 5G NR standardin mukaan FR2:lle, radiopohjaisten havaintosysteemien sisällyttäminen, ja CMOS teknologian käyttö. Tutkimusryhmämme on vastannut näihin haasteisiin suunnittelemalla ja implementoimalla 5G NR FR2:lla toimivan integroidun lähetinvastaanottimen edistyneellä 22-nm CMOS teknologialla. Vastaanotin tarjoaa kaksoistila heterodynevastaanottoa vastaanotin- ja tutkatilalla sisääntulotaajuuskaistalla 24-40 GHz ja ulostulovälitaajuuksilla 7-8 GHz. Kaksi lähetintä toteuttaa kaksielementtisen keilanmuodostuksen homodynelähetyksellä ja D-luokan vahvistuksella taajuuksilla 16-33 GHz. Paikallisoskillaattorisignaalin jakoketju tarjoaa laajakaistaista vaihesäätöä ja pulssin generoimista. Tässä työssä keskitytään vastaanottimen ensimmäisten lohkojen, muuntajan ja matalakohinaisen vahvistimen, suunnitteluun. Muuntaja tarvitaan yksipuolisen tulosignaalin muuntamiseksi differentiaaliseksi, ja suunnittelun kannalta tärkeintä oli minimoida häviöt. Tässä tapauksessa vahvin kytkeytyminen ja seurauksena matalimmat häviöt saavutettiin päällekkäin asetetuilla ensiö- ja toisiopuolella. Vahvistimen täytyy toteuttaa samanaikaisesti laajakaistainen sisääntulosovitus, vahvistusvaste, ja matala kohinakerroin, kuten myös riittävä lineaarisuus. Säädettävä biasointi toteutettiin digitaalisella virransäädöllä, jotta vahvistin voidaan sammuttaa tutkatilassa. Matala kohinakerroin saavutettiin yhteisporttivahvistimen siirtokonduktanssin kasvattamisella kapasitiivisesti ristiinkytketyllä rakenteella. Muuntajan ja vahvistimen simulaatiotulosten mukaan kohinakerroin on 6.4-9.1 dB taajuuskaistalla 24-40 GHz. Sisääntulosovituksen taajuuskaistaa ja -leveyttä dominoivat reaktiiviset elementit vahvistimen sisääntulossa, ja vahvistimen kapasitiivisesti ristiinkytketyn rakenteen avulla saavutettiin matalampi S11 kuin -7 dB. Laajakaistainen vahvistusvaste 7.1-15.4 dB:n vahvistuksella toteutettiin kaistanleveyttä kasvattavalla kuormalla, jossa kela ja vastus on kytkettynä sarjaan. Lisäksi vahvistimen tehonkulutus on 4.5 mW, ja lineaarisuus on tyydyttävä 1.0 dBm IIP3:lla ja -8 dBm 1-dB kompressiopisteellä. Digitaalisesti säädettävä biasointi mahdollistaa mukautettavan suorituskyvyn, eli vaihtokauppa on mahdollista S11, vahvistuksen, ja kohinakertoimen välillä.
For any (real) algebraic variety X in a Euclidean space V endowed with a nondegenerate quadratic form q, we introduce a polynomial EDpolyX,u(t2) which, for any u∈V, has among its roots the distance from u to X. The degree of EDpolyX,u is the Euclidean Distance degree of X. We prove a duality property when X is a projective variety, namely EDpolyX,u(t2)=EDpolyX∨,u(q(u)−t2) where X∨ is the dual variety of X. When X is transversal to the isotropic quadric Q, we prove that the ED polynomial of X is monic and the zero locus of its lower term is X∪(X∨∩Q)∨.
Abstract In this paper, we propose an accurate two-phase millimeter-Wave (mmWave) beamspace channel tracking mechanism. Particularly in the first phase, we train an extreme reservoir machine (ERM) for tracking the historical features of the mmWave beamspace channel and predicting them in upcoming time steps. Towards a more accurate prediction, we further fine-tune the ERM by means of Xavier initializer technique, whereby the input weights in ERM are initially derived from a zero mean and finite variance Gaussian distribution, leading to 49% degradation in prediction variance of the conventional ERM. The proposed method numerically improves the achievable spectral efficiency (SE) of the existing counterparts, by 13%, when signal-to-noise-ratio (SNR) is 15dB. We further investigate an ensemble learning technique in the second phase by sequentially incorporating multiple ERMs to form an ensembled model, namely adaptive boosting (AdaBoost), which further reduces the prediction variance in conventional ERM by 56%, and concludes in 21% enhancement of achievable SE upon the existing schemes at SNR = 15dB.
Advanced coding algorithms yield high quality signals with good coding efficiency within their target bit-rate ranges, but their performance suffer outside the target range. At lower bitrates, the degradation in performance is because the decoded signals are sparse, which gives a perceptually muffled and distorted characteristic to the signal. Standard codecs reduce such distortions by applying noise filling and post-filtering methods. In this paper, we propose a post-processing method based on modeling the inherent time-frequency correlation in the log-magnitude spectrum. The goal is to improve the perceptual SNR of the decoded signals and, to reduce the distortions caused by signal sparsity. Objective measures show an average improvement of 1.5 dB for input perceptual SNR in range 4 to 18 dB. The improvement is especially prominent in components which had been quantized to zero.
We describe a decisional attack against a version of the PLWE problem in which the samples are taken from a certain proper subring of large dimension of the cyclotomic ring Fq [x]/(Φpk (x)) with k > 1 in the case where q ≡ 1 (mod p) but Φpk (x) is not totally split over Fq. Our attack uses the fact that the roots of Φpk (x) over suitable extensions of Fq have zero-trace and has overwhelming success probability as a function of the number of input samples. An implementation in Maple and some examples of our attack are also provided.
The ETSI's Zero touch network and Service Management (ZSM) framework is a prominent initiative to tame the envisioned complexity in operating and managing 5G and beyond networks. To this end, the ZSM framework promotes the shift toward full Automation of Network and Service Management and Operation (ANSMO) by leveraging the flexibility of SDN/NFV technologies along with Artificial Intelligence, combined with the portability and reusability of model-driven, open interfaces. Besides its benefits, each leveraged enabler will bring its own security threats, which should be carefully tackled to make the ANSMO vision a reality. This paper introduces the ZSM's potential attack surface and recommends possible mitigation measures along with some research directions to safeguard ZSM system security.
Motivated by recent progress in electron quantum optics, we revisit the question of single-electron entanglement, specifically whether the state of a single electron in a superposition of two separate spatial modes should be considered entangled. We first discuss a gedanken experiment with single-electron sources and detectors, and demonstrate deterministic (i. e. without post-selection) Bell inequality violation. This implies that the single-electron state is indeed entangled and, furthermore, nonlocal. We then present an experimental scheme where single-electron entanglement can be observed via measurements of the average currents and zero-frequency current cross-correlators in an electronic Hanbury Brown-Twiss interferometer driven by Lorentzian voltage pulses. We show that single-electron entanglement is detectable under realistic operating conditions. Our work settles the question of single-electron entanglement and opens promising perspectives for future experiments.
Abstract In this article, a compact printed monopole dual-band antenna using artificial magnetic conductor (AMC)-plane with improved gain and broader bandwidth, applicable for off-body internet of things (IoT) devices is presented. The monopole antenna consists of two C-shaped resonators connected through a U-shaped monopole, parasitic elements, discrete ground circular rings and a co-planar waveguide (CPW) feedline. Each artificial magnetic conductor (AMC) unit cell consists of a slotted circular and a square stubs, designed with two zero-crossing phases for improving the radiation characteristics and to achieve the high gain. The overall size of the proposed AMC-backed antenna is 44.4 mm ×44.4 mm ×1.6 mm with electrical dimensions of 0.75λg ×0.75λg × 0.027λg. This AMC-backed antenna featured measured bandwidths of 9.6% and 12.4% with improved measured gain values of 4.88 dB and 4.73 dB at 2.45 GHz and 5.8 GHz, respectively. The specific absorption rate (SAR) values are analysed and found to be 1.58 W/kg at 2.45 GHz and 0.9 W/kg at 5.8 GHz. Therefore, the proposed AMC-backed antenna is useful for off-body IoT devices operating at 2.45 and 5.8 GHz industrial, scientific, and medical (ISM) band applications.
The dynamics of a two-dimensional superconductor under a constant electric field E is studied by using the gauge-gravity correspondence. The pair breaking current induced by E first increases to a peak value and then decreases to a constant value at late times, where the superconducting gap goes to zero, corresponding to a normal conducting phase. The peak value of the current is found to increase linearly with respect to the electric field. Moreover, the nonlinear conductivity, defined as an average of the conductivity in the superconducting phase, scales as similar to E-2/3 when the system is close to the critical temperature T-c, which agrees with predictions from solving the time-dependent Ginzburg-Landau equation. Away from T-c, the E-2/3 scaling of the conductivity still holds when E is large.
Abstract. High-speed and wideband ADCs have become increasingly important in response to the growing demand for high-speed wireless communication services. Continuous time sigma delta modulators (CTƩ∆M), well-known for their oversampling and noise shaping properties, offer a promising solution for low-power and high-speed design in wireless applications. The objective of this thesis is to design and implement a wideband CTƩ∆M for a global navigation satellite system(GNSS) receiver. The targeted modulator architecture is a 3rdorder single-bit CTƩ∆M, specifically designed to operate within a 15 MHz signal bandwidth. With an oversampling ratio of 25, the ADC’s sampling frequency is set at 768 MHz. The design goal is to achieve a theoretical signal to noise ratio (SNR) of 55 dB. This thesis focuses on the design and implementation of the CTƩ∆M, building upon the principles of a discrete time Ʃ∆ modulator, and leveraging system-level simulation and formulations. A detailed explanation of the coefficient calculation procedure specific to CTƩ∆ modulators is provided, along with a "top-down" design approach that ensures the specified requirements are met. MATLAB scripts for coefficient calculation are also included. To overcome the challenges associated with the implementation of CTƩ∆ modulators, particularly excess loop delay and clock jitter sensitivity, this thesis explores two key strategies: the introduction of a delay compensation path and the utilization of a finite impulse response (FIR) feedback DAC. By incorporating a delay compensation path, the stability of the modulator can be ensured and its noise transfer function (NTF) can be restored. Additionally, the integration of an FIR feedback DAC addresses the issue of clock jitter sensitivity, enhancing the overall performance and robustness of the CTƩ∆M. The CTƩ∆Ms employ the cascade of integrators with feed forward (CIFF) and cascade of integrators with feedforward and feedback (CIFF-B) topologies, with a particular emphasis on the CIFF-B configuration using 22nm CMOS technology node and a supply voltage of 0.8 V. Various simulations are performed to validate the modulator’s performance. The simulation results demonstrate an achievable SNR of 55 dB with a power consumption of 1.36 mW. Furthermore, the adoption of NTF zero optimization techniques enhances the SNR to 62 dB.Laajakaistaisen jatkuva-aikaisen sigma delta-AD-muuntimen suunnittelu ja toteutus. Tiivistelmä. Nopeat ja laajakaistaiset AD-muuntimet ovat tulleet entistä tärkeämmiksi nopeiden langattomien kommunikaatiopalvelujen kysynnän kasvaessa. Jatkuva-aikaiset sigma delta -modulaattorit (CTƩ∆M), joissa käytetään ylinäytteistystä ja kohinanmuokkausta, tarjoavat lupaavan ratkaisun matalan tehonkulutuksen ja nopeiden langattomien sovellusten suunnitteluun. Tämän työn tarkoituksena on suunnitella ja toteuttaa laajakaistainen jatkuva -aikainen sigma delta -modulaattori satelliittipaikannusjärjestelmien (GNSS) vastaanottimeen. Arkkitehtuuriltaan modulaattori on kolmannen asteen 1-bittinen CTƩ∆M, jolla on 15MHz:n signaalikaistanleveys. Ylinäytteistyssuhde on 25 ja AD muuntimen näytteistystaajuus 768 MHz. Tavoitteena on saavuttaa teoreettinen 55 dB signaalikohinasuhde (SNR). Tämä työ keskittyy jatkuva-aikaisen sigma delta -modulaattorin suunnitteluun ja toteutukseen, perustuen diskreettiaikaisen Ʃ∆-modulaattorin periaatteisiin ja systeemitason simulointiin ja mallitukseen. Jatkuva-aikaisen sigma delta -modulaattorin kertoimien laskentamenetelmä esitetään yksityiskohtaisesti, ja vaatimusten täyttyminen varmistetaan “top-down” -suunnitteluperiaatteella. Liitteenä on kertoimien laskemiseen käytetty MATLAB-koodi. Jatkuva-aikaisten sigma delta -modulaattoreiden erityishaasteiden, liian pitkän silmukkaviiveen ja kellojitterin herkkyyden, voittamiseksi tutkitaan kahta strategiaa, viiveen kompensointipolkua ja FIR takaisinkytkentä -DA muunninta. Viivekompensointipolkua käyttämällä modulaattorin stabiilisuus ja kohinansuodatusfunktio saadaan varmistettua ja korjattua. Lisäksi FIR takaisinkytkentä -DA-muuntimen käyttö pienentää kellojitteriherkkyyttä, parantaen jatkuva aikaisen sigma delta -modulaattorin kokonaissuorituskykyä ja luotettavuutta. Toteutetuissa jatkuva-aikaisissa sigma delta -modulaattoreissa on kytketty peräkkäin integraattoreita myötäkytkentärakenteella (CIFF) ja toisessa sekä myötä- että takaisinkytkentärakenteella (CIFF-B). Päähuomio on CIFF-B rakenteessa, joka toteutetaan 22nm CMOS prosessissa käyttäen 0.8 voltin käyttöjännitettä. Suorityskyky varmistetaan erilaisilla simuloinneilla, joiden perusteella 55 dB SNR saavutetaan 1.36 mW tehonkulutuksella. Lisäksi kohinanmuokkausfunktion optimoinnilla SNR saadaan nostettua 62 desibeliin.
Abstract A novel flexible single-layered and single-sided linear to-circular polarizer is proposed in this work. The proposed polarizer is designed for a deployable format for application in a 3U Cube Satellites. It features a near-zero 3 dBAR, with a size of 0.22 λ0×0.27λ0×0.03λ0 and a 3dB AR fractional bandwidth of 34.39 %, starting from 1.95 GHz to 2.76 GHz. It performs with a conversion efficiency bandwidth covering 90% of 43.47 %, starting from 1.8 GHz to 2.8 GHz. This indicates the polarizer’s wideband CP performance, with a pure CP centered at 2.41 GHz.
This paper explains an initial current injection method of a direct three-phase to single-phase AC/AC converter for an inductive charger. The converter has a lesser number of switches than a matrix converter and uses a resonant circuit to utilize zero-current switching. The method applies a DC resonant charging to charge a primary resonant capacitor, by taking advantage of the converter topology. The charged voltage is used to boost the initial current since in practice an affordable current transducer has only a limited measurement range, due to its accuracy and noise characteristics. The method is applied to kick-start the inductive charger without adding an amplification circuit to the current transducer output. Simulation results are presented to verify theoretical calculations.
Metasurfaces can be employed for designing waveguides that confine the electromagnetic energy while they are open structures. In this communication, we introduce a new type of such waveguides, formed by two penetrable metasurfaces having complementary isotropic surface impedances. We theoretically study the guided modes supported by the proposed structure and discuss the corresponding dispersion properties. We show the results for different scenarios in which the surface impedances possess nonresonant or resonant characteristics, and the distance between the two metasurfaces changes from large values to the extreme limit of zero. We also derive and describe the general condition for existence of two modes with orthogonal polarizations having the same phase velocity. In the particular case in which the metasurfaces are complementary and the distance between them is not small, we indicate that such phenomenon occurs within a broad frequency range. This property can be promising for applications in leaky-wave antennas and field focusing.