Radio Frequency

Recent research and development has been incredibly successful at advancing the capabilities for vacuum electronic device (VED) sources of powerful terahertz (THz) and near-THz coherent radiation, both CW or average and pulsed. Currently, the VED source portfolio covers over 12 orders of magnitude in power (mW-to-GW) and two orders of magnitude in frequency (from 0 1 to 10 THz). Further advances are still possible and anticipated. They will be enabled by improved understanding of fundamental beam-wave interactions, electromagnetic mode competition and mode control, along with research and development of new materials, fabrication methods, cathodes, electron beam alignment and focusing, magnet technologies, THz metrology and advanced, broadband output radiation coupling techniques.

REPORT DOCUMENTATION PAGE OMS No. 0704-0188 la REPORT SECURITY CLASSIFICATION lb RESTRICTIVE MARKINGS Recent developments in accelerator technology and the optical guiding property of the free electron laser (FEL) radiation indicate that the RF linacs may be a strong contender for driving high average power FEL amplifiers. We discuss two RF linac driven FEL configurations: the master oscillator power amplifier (MOPA) and the single stage power amplifier (SSPA). Our numerical results are obtained using the source dependent expansion (SDE) method in the computer code SHERA. The SDE method and the code SHERA are discussed and illustrations of the MOPA and SSPA configurations presented. 20 DISTRIBUTION/AVAILABILITY OF ABSTRACT 21. ABSTRACT SECURITY CLASSIFICATION [JUNCLASSIFIED/UNLIMITED 0 SAME AS RPT 0 DTIC USERS

A miniature ion trap mass analyzer is reported. The described analyzer is a 1/5-scale version of a previously reported toroidal radio frequency (rf) ion trap mass analyzer. The toroidal ion trap operates with maximum rf trapping voltages about 1 kV p-p or less; however despite the reduced dimensions, it retains roughly the same ion trapping capacity as conventional 3D quadrupole ion traps. The curved geometry provides for a compact mass analyzer. Unit-mass resolved mass spectra for n-butylbenzene, xenon, and naphthalene are reported and preliminary sensitivity data are shown for naphthalene. The expected linear mass scale with rf amplitude scan is obtained when scanned using a conventional mass-selective instability scan mode combined with resonance ejection. (J Am Soc Mass Spectrom 2006, 17, 916 -922)

This study is established to better understand the requirements of radio frequency (RF) laboratories based on the electrical engineers' and technicians' perspectives working in this field. In that context, the study is conducted with the electrical engineering (EE) and the technical colleges (TC) graduates. Here, EE covers the Bachelor of Science (BS) and the Master of Science (MS) level of education in electrical engineering while TC represents the vocational education and training as well as technical and associative educations prior to ...

The flux variability of Jovian decametric radio emission (DAM) is analyzed to search for its possible modulations by magnetohydrodynamic waves of ultra-low frequencies (ULF). The ULF modulating waves are found in DAM dynamic spectra as a moving pattern (moire) on the background of Jovian millisecond radio bursts (S-bursts). Their frequency drift (∼55 MHz/s) corresponds to the wave motion to Jupiter with Alfvén velocity (∼4 × 10 4 km s −1). There are whistler-like drifting details in the dynamic power spectra of ULF variations of S-burst emission flux at fixed radio frequency. Their frequency drift rates are consistent with whistlers that are dispersed mainly in the Io torus. Formally our analysis of DAM reveals the specific 2s-modulation of S-burst emission corresponding to the known magnetic pulsations near gyrofrequencies of heaviest ions (SO + 2 and SO +) in the Io torus.

RFID (Radio Frequency Identification) systems are one of the most pervasive computing technologies with technical potential and profitable opportunities in a diverse area of applications. Among their advantages is included their low cost and their broad applicability. However, they also present a number of inherent vulnerabilities. This paper develops a structural methodology for risks that RFID networks face by developing a classification of RFID attacks, presenting their important features, and discussing possible countermeasures. The goal of the paper is to categorize the existing weaknesses of RFID communication so that a better understanding of RFID attacks can be achieved and subsequently more efficient and effective algorithms, techniques and procedures to combat these attacks may be developed.

Growing convergence among mobile computing devices and embedded technology sparks the development and deployment of "context-aware" applications, where location is the most essential context. In this paper we present LANDMARC, a location sensing prototype system that uses Radio Frequency Identification (RFID) technology for locating objects inside buildings. The major advantage of LANDMARC is that it improves the overall accuracy of locating objects by utilizing the concept of reference tags. Based on experimental analysis, we demonstrate that active RFID is a viable and cost-effective candidate for indoor location sensing. Although RFID is not designed for indoor location sensing, we point out three major features that should be added to make RFID technologies competitive in this new and growing market.

The crystalline quality of molecular beam epitaxy (MBE)-grown layers of GaN on sapphire strongly depends on the initial stage of film nucleation and growth. Thus, pre-conditioning of the substrate is of vital importance. In this study we use X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED) to examine in situ the case for surface cleaning and nitridation of c-plane sapphire substrates upon annealing in UHV and exposure to radio frequency (rf) plasmas of hydrogen and nitrogen, respectively. We find that low temperature (200-300°C) heat treatment in a hydrogen plasma offers effective removal of adventitious surface contaminants, contrary to annealing in vacuum. Moreover, our XPS data provide unambiguous evidence for formation of surface nitride upon heat treatment in nitrogen plasma at 300-7OO"C, in agreement with conclusions inferred from reflection high energy electron diffraction (RHEED).

The measurement of the transverse phase-space map, or transport matrix, of a relativistic electron in a high-gradient, radio-frequency linear accelerator ͑rf linac͒ at the UCLA photoinjector is reported. This matrix, which indicates the effects of acceleration ͑adiabatic damping͒, first-order transient focusing, and ponderomotive second-order focusing, is measured as a function of both rf field amplitude and phase in the linac. The elements of the matrix, determined by observation of centroid motion at a set of downstream diagnostics due to deflections induced by a set of upstream steering magnets, compare well with previously developed analytical theory ͓J. Rosenzweig and L. Serafini, Phys. Rev. E 49, 1599 ͑1994͔͒. The determinant of the matrix is obtained, yielding a direct confirmation of trace space adiabatic damping. Implications of these results on beam optics at moderate energy in high-gradient linear accelerators such as rf photoinjectors are discussed.

In magnetic fusion devices, radio frequency ͑rf͒ waves in the electron cyclotron ͑EC͒ and lower hybrid ͑LH͒ range of frequencies are being commonly used to modify the plasma current profile. In ITER, EC waves are expected to stabilize the neoclassical tearing mode ͑NTM͒ by providing current in the island region ͓R. Aymar et al., Nucl. Fusion 41, 1301 ͑2001͔͒. The appearance of NTMs severely limits the plasma pressure and leads to the degradation of plasma confinement. LH waves could be used in ITER to modify the current profile closer to the edge of the plasma. These rf waves propagate from the excitation structures to the core of the plasma through an edge region, which is characterized by turbulence-in particular, density fluctuations. These fluctuations, in the form of blobs, can modify the propagation properties of the waves by refraction. In this paper, the effect on rf due to randomly distributed blobs in the edge region is studied. The waves are represented as geometric optics rays and the refractive scattering from a distribution of blobs is formulated as a Fokker-Planck equation. The scattering can have two diffusive effects-one in real space and the other in wave vector space. The scattering can modify the trajectory of rays into the plasma and it can affect the wave vector spectrum. The refraction of EC waves, for example, could make them miss the intended target region where the NTMs occur. The broadening of the wave vector spectrum could broaden the wave generated current profile. The Fokker-Planck formalism for diffusion in real space and wave vector space is used to study the effect of density blobs on EC and LH waves in an ITER type of plasma environment. For EC waves the refractive effects become important since the distance of propagation from the edge to the core in ITER is of the order of a meter. The diffusion in wave vector space is small. For LH waves the refractive effects are insignificant but the diffusion in wave vector space is important. The theoretical model is general enough to study the effect of density blobs on all propagating cold plasma waves.

Thin ®lms of lead lanthanum titanate Pb,LaTiO 3 have been grown by radio-frequency magnetron sputtering on (0001) Al 2 O 3 substrates. The structure, the microstructure and the optical properties of the ®lms have been investigated as a function of the postdeposition annealing. Films deposited at low temperatures crystallize to a perovskite phase after the annealing treatment from 500 C to 650 C. X-ray y À 2y diffraction studies have shown that ®lms are crystallized with a strong (111) orientation and the best crystalline structure is reported at 600 C. The optical properties were both demonstrated by spectrophotometry and prism coupling. PLT thin ®lms with a transparency of 80% in the wavelength range 300±2000 nm have exhibited a refractive index of 2.38 @ 632.8 nm representing 97% of the bulk corresponding material. Investigation of optical propagation has been accomplished in a 10 mm long planar optical waveguide using a butt-coupling con®guration.

The use of programmability in Systems-on-Chip (SoC) brings as the main advantage the possibility of reducing the time-to-market and the cost of design, specially when different systems and functions must cover different markets, going from low-power and low-frequency instrumentation to high frequency communication. This paper presents a technique that can be used to increase the analog programmability in a SoC, also allowing one to integrate more analog functions, while guaranteeing the use of the analog part in a larger range of applications. Practical results are presented showing that the proposed technique can be used from DC to RF applications.

This study compared the potential for interference to medical devices from radio frequency (RF) fields radiated by GSM 900/1800-MHz, general packet radio service (GPRS) 900/1800-MHz, and wideband code division multiple access (WCDMA) 1900-MHz handsets. The study used a balanced half-wave dipole antenna, which was energized with a signal at the standard power level for each technology, and then brought towards the medical device while noting the distance at which interference became apparent. Additional testing was performed with signals that comply with the requirements of the international immunity standard to RF fields, IEC 61000-4-3. The testing provides a sense of the overall interference impact that GPRS and WCDMA (frequency division duplex) may have, relative to current mobile technologies, and to the internationally recognized standard for radiated RF immunity. Ten medical devices were tested: two pulse oximeters, a blood pressure monitor, a patient monitor, a humidifier, three models of cardiac defibrillator, and two models of infusion pump. Our conclusion from this and a related study on consumer devices is that WCDMA handsets are unlikely to be a significant interference threat to medical electronics at typical separation distances.

To improve interference robustness of wireless communication, spread spectrum techniques are often used. We use the chirp spreading technique along with FSK and PSK binary modulation schemes to obtain interference robust radio communication. The performance of chirped-FSK and chirped-PSK modulation through a white gaussian noise channel is simulated assuming a synchronized clock between transmitter and the receiver. We analyzed and simulated the error probability (BER) of the overall system in the presence of partial band of interference in the channel. The simulated BER is close to the estimated BER and they prove the superior performance of chirp-based modulation in the presence of interference.

This paper describes a novel down-converter architecture for radio receivers and for polarimetric radar systems. The mixing unit configuration is based on two 90/spl deg/ single balanced mixers, associated in anti-phase, to obtain wide-bandwidth differential IF signals. For analog receivers, the terminals of each of the mixing units are connected to produce single RF and LO signals. This is as opposed to polarimetric systems, where one LO and two RF signals are present. The broadband nature of the differential IF signals suggests that the proposed topology eliminates the need of either passive baluns or active baluns needed to produce 0/spl deg/ and 180/spl deg/ phase-shifted signals.

A new digital-signal-processing method for performing modulation tests on Bluetooth transmitters is presented and validated. No preliminary demodulation of the radio frequency transmitted signal is needed to gain the instantaneous frequency trace, on which standard measurement procedures have to be applied. The aforementioned task is, in fact, fulfilled through the application of the short-time Fourier transform (STFT), a typical time-frequency representation, to the acquired samples of the aforementioned signal. Moreover, no specific information concerning the operating conditions of the transmitter under test, such as carrier frequency and hopping sequence, is needed, thus facilitating measurement automation. The optimal tuning of STFT parameters, which are capable of providing the best reconstruction of the instantaneous frequency trajectory as well as the most accurate measurement outcomes, is established as the result of an exhaustive experimental activity.

An investigation is carried out into the design, modelling, construction and testing of a new, unique, bat bow-tie self grounded antenna. The purpose is to use it for the application of a dual band WiFi modem operating between the frequency ranges of 2.4-2.5Ghz and 5-6GHz. The antenna was a success and theoretically had a VSWR less than 2:1 and increased signal strength by 3db which corresponded to double the power. The existing model was analyzed and the results of the measurements and testing led to an upgraded MIMO model.

Accurate and detailed noise calculations for operational amplifier circuits using MATLAB are proposed. The analysis of the basic op amp circuits (inverting, non-inverting and differential circuits) is performed taking into account the specifics of current and voltage amplifiers. The MATLAB function m-files are developed to predict the noise. The following characteristics are calculated: total output spot noise voltage; total equivalent

The ultrasonic pulse-echo backscattered amplitude integral (BAI)-mode imaging technique [IEEE Trans. UFFC, 45:30 (1998)] has demonstrated sensitive detection of subwavelength channel defects (38-m diameter reliably and 6-m diameter occasionally) in flexible 220-m-thick food package seals (17.3 MHz, Ϸ 86 m). However, the underlying subwavelength defect detection mechanism is poorly understood. In this contribution, a theoretical modeling study was undertaken to elucidate the mechanism. The subwavelength diameter channel was fused in-between two plastic package films by applying heat from one side of the films. The sample cross-section microstructure was characterized from both optical and acoustic images. The cross-section impedance profiles along sample thickness dimension were determined. Although identical in nominal impedance properties before sealing, the two binding films showed an asymmetric impedance profile after sealing. Transient finite-element heat conduction analysis and impedance profiles of multiple-sealed package samples showed that the single-sided heating process caused an asymmetric impedance profile. A generalized impedance model was proposed based on these observations. An efficient two-dimensional simulation tool using a finite-difference time-domain method and the perfectly matched layer numerically evaluated the defect detection behavior of the radio-frequency (rf) echo waveforms. The normalized correlation coefficients between the simulated and the measured rf echo waveforms were greater than 95% for this generalized model, which suggested the validity of the proposed impedance model.

We present the design, fabrication, and characterization of AlGaN-GaN double-channel HEMTs. Two carrier channels are formed in an AlGaN-GaN-AlGaN-GaN multilayer structure grown on a sapphire substrate. Polarization field in the lower AlGaN layer fosters formation of a second carrier channel at the lower AlGaN-GaN interface, without creating any parasitic conduction path in the AlGaN barrier layer. Unambiguous doublechannel behaviors are observed at both dc and RF. Bias dependent RF small-signal characterization and parameter extraction were performed. Gain compression at a high current level was attributed to electron velocity degradation induced by interface scattering. Dynamic IV measurement was carried out to analyze large-signal behaviors of the double-channel high-electron mobility transistors. It was found that current collapse mainly occurs in the channel closer to device surface, while the lower channel suffers minimal current collapse, suggesting that trapping/detrapping of surface states is mainly responsible for current collapse. This argument is supported by RF large-signal measurement results.

Today, many knowledge-based technology applications form a business ecosystem: a set of complex products and services made by multiple firms in which no firm is dominant. For this paper the emerging radio frequency ID (RFID) ecosystem was built based on firms' alliance announcements, and propositions around the behavior of large, multi-line technology firms in this network were analyzed. The RFID network is used to empirically show that absorptive capacity, and exploration vs. exploitation theories may explain some behavior of large firms. Specifically, a propensity to form alliances in general makes it more likely large firms will join the RFID ecosystem, and more exploratory firms join earlier. Greater availability of slack resources also leads to the formation of more alliances in the network. The ecosystem perspective and these results may influence alliance decisions of firms entering into high cost technological innovations.

Adaptive polar work-function predistortion (WFP) reduces the spectral regrowth of radio frequency power amplifiers such as those used in the telecommunications industry. This paper describes adaptive polar WFP equations and a system implementation. The system description includes an adaptive digital signal processing (DSP) algorithm based on measurement of outof-band performance. It includes a discussion of the strengths and weaknesses of the DSP algorithm used and presents some current results with wide-band modulation signals.

Zinc oxide (ZnO) was incorporated into metal-insulator-semiconductor (MIS) structures featuring high dielectric constant (high-κ) barium tantalate (BaTa 2 O 6 )or alumina (Al 2 O 3 )as the insulator, and the structures were electrically evaluated for potential applications in transparent thin film transistors. The ZnO films were deposited by radio-frequency magnetron sputtering at 100°C whereas the dielectric films were deposited by the same method at room temperature. The leakage currents of both the BaTa 2 O 6 and Al 2 O 3 structures were on the order of 10 −7 A/cm 2 . The trap density and trapped charge concentration at the BaTa 2 O 6 /ZnO interface were determined to be 6.18 × 10 11 eV −1 cm −2 and 5.82 × 10 11 cm −2 from conductance-voltage and capacitance-voltage measurements. At the Al 2 O 3 /ZnO interface the trap density and trapped charge were more than an order of magnitude smaller at 1.09 × 10 10 eV −1 cm −2 and 1.04 × 10 10 cm −2 respectively. The BaTa 2 O 6 structures had significantly larger frequency dispersions due to the larger number of interface traps. Chemical analysis using X-ray photoelectron spectroscopy with depth profiling indicates that acceptor type defects associated with a deficiency of oxygen are related to the observed electron trapping in the BaTa 2 O 6 MIS structure. Overall, the results indicate that Al 2 O 3 would be better suited for transparent thin film transistors deposited at low temperature or without substrate heating.

Graded TiAlN layers were deposited by plasma reactive sputtering assisted by electron cyclotron resonance (ECR). For reactive sputtering, dual cathode radio-frequency (RF ) magnetron targets, Ti and Al, were used. The deposition process was monitored by optical emission spectroscopy (OES ). The OES results indicate that microwave excitation added to RF plasma has contrasting effects on Ti and Al concentration in the gas phase, enhancing titanium and quenching aluminium species reaching the deposited substrate. Thus, by the regulation of the ECR power and the ratio of the nitrogen flow to the nitrogen plus argon flow, the formation of graded layers is allowed. This approach was found to be appropriate for controlling and tailoring the interface between a metallic substrate and a hard coating. The layers were deposited on (100) oriented silicon and M2 steel tools using various combinations of variables, such as power input, bias substrate voltage and gas feed composition. The layers were characterized with regard to structure and composition using X-ray diffractometers and Auger electron spectroscopy. Layers deposited on grounded silicon at a low ECR power (≤100 W ) were found to have a (111) oriented crystalline structure; the crystallographic orientation is affected by the bias voltage and substrate composition. Layers deposited at an ECR power >100 W had a random or amorphous structure. The relationship between the OES analyses of the plasma layer and the processing parameters, the structure and the composition of the layers formed are presented and discussed.

Image registration is used in many fields for mapping one image to another. In magnetic resonance imaging (MRI) ap-plications, one of the main uses is for correction of motion-induced artifacts so that subsequent image analysis would be more reliable. This paper gives an ...

The objective of this research paper is to develop such a system which can transmit the pressure of the tire on a module, which can not only display the air pressure of the tire but also maintain the pressure of tire by operating an air filling machine. Key elements of this research are pressure sensor, microcontroller, RF transceiver, solenoid valve and analog to digital converter (ADC). This system is basically divided in to two section one is hanging on the tire other is placed on the car dash board. Whole system continuously monitor and display the tire pressure whenever air pressure inside the tire is decrease from certain level define inside the controller it starts the air filling machine.

ABSTRACT In view to the new epochal scenarios that nanotechnology disclose, nanoelectronics has the potential to introduce a paradigm shift in electronic systems design similar to that of the transition from vacuum tubes to semiconductor devices. Since many nano-scale devices and materials exhibit their most interesting properties at radio-frequencies (RF), nanoelectronics provides an enormous and yet widely undiscovered opportunity for the microwave engineering community. The aim of RF nanoelectronics is to close the gap between the nanosciences and a new generation of multifunctional devices, circuits, and systems, for a broad range of applications and operating frequencies, up to the optical region. The paper presents an overview of some of the main research fields of RF nanoelectronics, by i) introducing theoretical foundations of the novel nano-scale materials (in particular, carbon nanotubes, graphene), ii) highlighting novel concepts and applications, iii) focusing on the investigation of the electromagnetics and quantum transport phenomena in nanodevices.

LiPON films were deposited using radio-frequency magnetron sputtering in a pure N 2 gas atmosphere. The influence of rf power, N 2 pressure, target-substrate distance and target density on thin film composition and ionic conductivity has been studied. Impedance measurements performed between 25 and 80-C have indicated that ionic conductivity increases with nitrogen incorporation into the glass structure. An increase in the deposition rate with the target density has also been observed.

Medical-grade poly(vinyl chloride) (PVC) was chemically modified to study how the incorporation of monovalent silver influences Pseudomonas aeruginosa adhesion and colonization. The modification investigated consisted of a radio frequency-oxygen (RF-O 2 ) glow discharge pre-functionalization, followed by a two-step wet-treatment in sodium hydroxide and silver nitrate solutions. X-ray photoelectron spectroscopy (XPS) analysis and contact angle measurements were used to investigate the chemical nature and surface wettability of the films following each step of the modification. XPS analysis proved that the RF-O 2 plasma pre-functionalization of native PVC reproducibly increased the amount of functional groups representative of PVC additives, including ether/alcohol, esters and carboxyl groups. More specifically, we demonstrated that the O2 % CQO groups representative of the phthalic ester and zinc carboxylate additives identified for native PVC increased by two-fold following the RF-O 2 plasma pre-functionalization step. Although RF-O 2 pre-functionalization did not have an effect on the silver content of the NaOH/AgNO 3 treated substrates, such a modification was necessary for biomaterial products that did not have reproducible surfaces amongst production lots. XPS analysis also demonstrated that saponification with sodium hydroxide (NaOH) of esters, like those of the phthalic ester additives of PVC is a simple, irreversible method of hydrolysis, which produced sodium carboxylate and sodium phthalate salts. Exposure of native PVC to NaOH resulted in an increased surface hydrophilicity (from ca 90 to ca 60 ) due to dechlorination. XPS analysis following further incubation in silver nitrate demonstrated that silver ions can be trapped when the sodium of sodium carboxylate is replaced by silver after performing a second treatment with a monovalent silver-containing solution. The creation of silver salt on native PVC resulted in an ultra-hydrophobic (>120 ) surface. The chemical modifications using NaOH and AgNO 3 wet treatments completely inhibited bacterial adhesion of four strains of P. aeruginosa to both native and oxygen-pre-functionalized PVC, and efficiently prevented colonization over longer periods (72 h). Our results suggest that surface modifications that incorporate silver ions would be extremely effective at reducing bacterial colonization to medical devices. r

This study evaluates the application of (i) skull-stripping methods (hybrid watershed algorithm (HWA), brain surface extractor (BSE) and brain-extraction tool (BET2)) and (ii) bias correction algorithms (nonparametric nonuniform intensity normalisation (N3), bias field corrector (BFC) and FMRIB's automated segmentation tool (FAST)) as pre-processing pipelines for the technique of voxel-based morphometry (VBM) using statistical parametric mapping v.5 (SPM5). The pipelines were evaluated using a BrainWeb phantom, and those that performed consistently were further assessed using artificial-lesion masks applied to 10 healthy controls compared to the original unlesioned scans, and finally, 20 Alzheimer's disease (AD) patients versus 23 controls. In each case, pipelines were compared to each other and to those from default SPM5 methodology. The BET2+N3 pipeline was found to produce the least miswarping to template induced by real abnormalities, and performed consistently better th...

Software-based global positioning system (GPS) receivers perform all the baseband signal processing and the high level functions on a general purpose processor. The heavy computational loads of the signal correlation in baseband processing make it difficult for software receivers to operate in real time. In order to improve the real-time performance, an enhanced bit-wise parallel algorithm has been developed in this study. The enhanced algorithm has been implemented and tested in a 12 channels real-time GPS software receiver. The system consists of a radio frequency front end, a data acquisition board and software that runs on a laptop with a Pentium-M 1.5 GHz processor running the Window Ò XP operating system. The data acquisition board packs the 2-bit intermediate frequency samples with a 2-bit in/8-bit out shift register and transfers the packed samples to laptop through a USB port. The software running on the laptop performs all the baseband and navigation processing in real time. The test results show that the enhanced algorithm significantly improves the real-time performance of the software receiver by reducing the computational operations for signal correlation by 50% compared with the existing bit-wise parallel algorithm. Furthermore, the enhanced algorithm also reduces the amount of required memory for storing data for signal correlation.

Indium tin oxide (ITO) thin films were deposited by radio frequency (RF) magnetron sputtering onto glass substrates. The transparent and conducting ITO thin films were obtained on externally unheated glass substrate, without any post-heat treatment, and by varying the deposition process parameters such as the working pressure and the RF Power. The effect of the variation of the above deposition parameters on the structural, surface morphology, electrical, and optical properties of the thin films have been studied. A minimum resistivity of 2.36 9 10-4 X cm and 80% transmittance with a figure of merit 37.2 9 10-3 X-1 is achieved for the thin films grown on externally unheated substrate with 75 W RF power and 0.5 mTorr working pressure.

In this work, we present an analytical study of aliasing image spurs problem in digital-RF modulators. The inherent finite image rejection ratio of this types modulators is conceptually discussed. A pulse amplitude modulation (PAM) model of the converter is used in the theoretical discussion. Behavioral level simulation of the digital-RF converter model is included. Finite image rejection is a limiting issue in this architecture, and Digital-IF mixing is used to alleviate the problem which is also reviewed and simulated.

In this article, a new treatment to reduce boron contamination of the interface between the p-and i-layer is presented. An ammonia flush, performed at 10 Pa for 1 min, after deposition of the p-layer considerably reduces the boron contamination at the p -i interface of amorphous silicon p -i -n solar cells prepared in a single-chamber reactor. This treatment avoids the need to move the substrate out of the reactor during the full deposition process of a solar cell, thereby reducing costs. The measurement of boron contamination depth profile in the i-layer was done by Secondary Ion Mass Spectroscopy and the effectiveness of the treatment was supported by quantum efficiency and I -V measurements of solar cells.

This paper extends the Sub-carrier Phase Combination technique previously presented by the authors to mitigate the effect of frequency selective Radio Frequency (RF) propagation delay distortions in Alternate Binary Offset Carrier (AltBOC) receivers. Two major propagation delay distortion sources are considered: the ionosphere and multipath. Initial analysis shows that the ionospheric delay errors can be reduced to being comparable to the receiver impairments (when the error due to multipath is low) and the maximum multipath error (under low ionospheric distortions) can be reduced to half a meter. Under extremely high ionospheric delay distortions, the multipath delay error envelope, with the proposed technique, will suffer no change in the magnitude of the error except that the spatial characteristics are different. The underlying idea of the proposed technique is that difference in the phase delays of the E5a and E5b signal tracking is simply the slope of the phase response over the entire band and hence represents the group delay at the E5 center frequency of 1191.795 MHz. The group delay which appears as the code phase error for the E5 signal tracking, can thus be compensated except for the occurrence of higher order errors.

This article presents the design of a novel quadband LNA operating in the GSM 0.9GHz/GSM l.8GHz and ZigBee 0.9GHz/WLAN 2.4GHz communication standards. This pseudo-concurrent architecture uses a two bit mode switch for selecting between the frequency bands. An RF switch is implemented before the Low Noise Amplifier (LNA) module to improve the insertion loss and isolation between the frequency bands. The pseudo-concurrent LNA is designed and simulated in CADENCE using 130nm UMC technology. The current design is especially suitable for use in multi-standard wireless receiver frontends as it saves die area and reduces power consumption by replacing parallel LNAs for each channel frequency. Simulation results indicate a Noise Figure below 4dB and S 21 above 14 dB in all frequency bands while drawing 10mA current from a 1.2V power supply.

Objective: To evaluate the performance of continuous and pulsed Doppler systems a test signal generator has been developed, simulating an ultrasound radio frequency signal, to be injected by induction into the front-end of an ultrasound Doppler system. Unlike for flow rigs the characteristics of the simulated signal are exactly known and under full control of the user, allowing for an objective interpretation of the test results. Methods: Under software control specific signal characteristics, e.g. ultrasound carrier frequency, clutter frequency, amplitude of clutter signal with respect to Doppler signal amplitude, Doppler signal-to-noise ratio, mean Doppler frequency, shape and width of the Doppler spectral distribution, and its time-dependent behavior can be set and varied. Results: A software package was developed to manipulate the relevant characteristics of the radio frequency signal and to drive a PC compatible plug-in card for signal generation. To illustrate the applicabilit...

Mobile phones work by transmitting and receiving radio frequency microwave radiation. The radio frequency (RF) emitted by mobile phones is stronger than FM radio signal which are known to cause cancer. Though research and evidence available on the risk of cancer by mobile phones does not provide a clear and direct support that mobile phones cause cancers. Evidence does not also support an association between exposure to radio frequency and microwave radiation from mobile phones and direct effects on health. It is however clear that lack of available evidence of cancer as regards the use of mobile phone should not be interpreted as proof of absence of cancer risk, so that excessive use of mobile phones should be taken very seriously and with caution to prevent cancer.

We demonstrate a 60 GHz broadband picocellular Radio-over-Fiber network architecture that enables seamless connectivity for highly mobile end-users. Its seamless communication capabilities arise by the supported handover scheme that relies on a novel Moving Extended Cell (MEC) concept. MEC exploits user-centric virtual groups of adjacent cells that transmit the same data content to the user and utilizes a switch mechanism for restructuring the virtual multi-cell area according to the user's mobility pattern, so that a virtual antenna group moves together with the mobile user. We present the theoretical formulation for MEC and show that it can provide zero packet loss and call dropping probability values in high-rate wireless services for a broad range of mobile speeds up to 40 m/sec, independently of the fiber link distances. We also demonstrate the physical layer network architecture and switch mechanism both for a RoF network with a single 60 GHz radio frequency (RF) over each wavelength, as well as for a RoF configuration supporting simultaneous multi-RF channel transmission over each optical wavelength. The performance of the multi-RF-over-network implementation is evaluated via simulations showing successful 100 Mb/s radio signal transmission over fiber links longer than 30 km. To this end, MEC can enable seamless connectivity and bandwidth guarantees in 60 GHz picocellular RoF networks being also capable of serving multiple users over the same wavelength in a RF frequency-division-multiplexed (FDM) approach.

In recent years, new challenges and emerging applications have inspired increasing research interests in the area of underwater networks. However, field experiments are expensive and not all the research work can be evaluated in real world scenarios in a timely fashion. This motivates our interest on developing an affordable, accessible and user friendly platform for conducting field experiments. Aqua-TUNE, the Testbed for Underwater NEtworks, is presented in this paper. It can be used to experimentally evaluate the algorithms and protocols developed for underwater networks in real world scenarios. Our experience with the testbed shows that it could be a valuable tool to encourage rapid progress in underwater networks.

The use of portable wireless technology has increased dramatically over the past few years. This increased use has caused a heightened concern for electromagnetic interference from wireless-enabled technologies, such as laptop computers and cellular phones to aircraft communication and navigation radios. Researchers at NASA Langley Research Center, United Airlines and Eagles Wings Incorporated, have tested and collected interference path loss data on a United Airlines out-of-service B737 aircraft near Victorville, CA. This paper summarizes the results found from the measured data sets as well as includes graphical representations of the interference path loss data on a B737 plane with different system antennas.