Showing papers on "Frequency band published in 2012"

Wide-band negative permeability of nonlinear metamaterials

Abstract: We propose a novel way to achieve an exceptionally wide frequency range where metamaterial possesses negative effective permeability. This can be achieved by employing a nonlinear response of metamaterials. We demonstrate that, with an appropriate design, a frequency band exceeding 100% is available for a range of signal amplitudes. Our proposal provides a significant improvement over the linear approach, opening a road towards broadband negative refraction and its applications.

A Frequency Selective Radome With Wideband Absorbing Properties

Abstract: A frequency selective radome is presented, acting as a pass band filter at a given frequency band, while behaving as an absorber above the transmission band. The pass band behavior is obtained by a metallic FSS realized through a compact interdigitated Jerusalem cross element characterized by a very large rejection band. The metallic FSS is used as the ground plane of a thin wideband absorber based on resistive high-impedance surfaces within the total reflection band. The outer absorber reduces the signature of the antenna system when the radome is illuminated by out of band signals. The resistive FSS which comprises the absorber is designed so to minimize losses within the transmitting band of the radome. The composite structure is thoroughly analyzed by an efficient equivalent circuit approach and by full-wave numerical simulations.

Active Suspension Control With Frequency Band Constraints and Actuator Input Delay

Abstract: This paper investigates the problem of vehicle active suspension control with frequency band constraints and actuator input delay. First, the mathematical model of suspension systems is established, and the problem of suspension control with finite-frequency constraints is formulated to match the characteristics of the human body. Then, the finite-frequency method is developed to deal with the problem of suspension control with actuator input delay, based on the generalized Kalman-Yakubovich-Popov lemma. Compared with the traditional entire-frequency approach for active suspension systems, the finite-frequency approach proposed in this paper achieves better disturbance attenuation performance for the chosen frequency range while the constraints required by real situation are guaranteed in the controller design. The effectiveness and merits of the proposed method are verified by a number of simulations with several types of road disturbances.

Spectrally wide-band terahertz wave modulator based on optically tuned graphene.

Abstract: New applications in the realms of terahertz (THz) technology require versatile adaptive optics and powerful modulation techniques. Semiconductors have proven to provide fast all-optical terahertz wave modulation over a wide frequency band. We show that the attenuation and modulation depth in optically driven silicon modulators can be significantly enhanced by deposition of graphene on silicon (GOS). We observed a wide-band tunability of the THz transmission in a frequency range from 0.2 to 2 THz and a maximum modulation depth of 99%. The maximum difference between the transmission through silicon and GOS is Δt = 0.18 at a low photodoping power of 40 mW. At higher modulation power, the enhancement decreased due to charge carrier saturation. We developed a semianalytical band structure model of the graphene–silicon interface to describe the observed attenuation and modulation depth in GOS.

An Ultra-Wideband 80 GHz FMCW Radar System Using a SiGe Bipolar Transceiver Chip Stabilized by a Fractional-N PLL Synthesizer

Abstract: A radar system with an ultra-wide FMCW ramp bandwidth of 25.6 GHz (≈32%) around a center frequency of 80 GHz is presented. The system is based on a monostatic fully integrated SiGe transceiver chip, which is stabilized using conventional fractional-N PLL chips at a reference frequency of 100 MHz. The achieved in-loop phase noise is ≈ -88 dBc/Hz (10 kHz offset frequency) for the center frequency and below ≈-80 dBc/Hz in the wide frequency band of 25.6 GHz for all offset frequencies >;1 kHz. The ultra-wide PLL-stabilization was achieved using a reverse frequency position mixer in the PLL (offset-PLL) resulting in a compensation of the variation of the oscillators tuning sensitivity with the variation of the N-divider in the PLL. The output power of the transceiver chip, as well as of the mm-wave module (containing a waveguide transition), is sufficiently flat versus the output frequency (variation <;3 dB). In radar measurements using the full bandwidth an ultra-high spatial resolution of 7.12 mm was achieved. The standard deviation between repeated measurements of the same target is 0.36 μm.

Systems and methods for a self-optimizing distributed antenna system

Abstract: Systems and methods for a self-optimizing distributed antenna system are provided. In certain embodiments, a distributed antenna system comprises a host unit configured to control the operation of the distributed antenna system; and a plurality of remote units coupled to the host unit. In at least one embodiment, a remote unit in the plurality of remote antenna units comprises a scanning receiver configured to receive signals in a plurality of frequency bands; at least one transceiver configured to transmit and receive signals in a frequency band in the plurality of frequency bands; and a remote unit controller configured to control an uplink gain level of the at least one transceiver and tune the scanning receiver to a frequency band in the plurality of frequency bands.

Method and apparatus for controlling wireless power transmission

Abstract: A wireless power transmission controlling apparatus and method are provided The apparatus includes a power amplifier that receives a source power, amplifies the received source power, and outputs a wireless power transmission signal from the amplified received source power, a band pass filter that filters the wireless power transmission signal, and passes a harmonic wave corresponding to a communication frequency band, and a communication unit that transmits a wireless power transmission control signal using the harmonic wave corresponding to the communication frequency band

High-Capacity Chipless RFID Tag Insensitive to the Polarization

Abstract: Designing a reader for chipless RFID is a hard task since both the polarization and operating frequency agility have to be implemented. The new tag design proposed in this paper is polarization independent, making the design of the reader easier since only linear polarization is needed to detect the tag. The proposed chipless tag is based on multiple circular ring patch resonators. The coding capacity of this tag reaches 19 bits within a compact surface of cm . Further, the frequency band is within 3.1 to 10.6 GHz to be compliant with FCC and ECC regulations for UWB. This new design is experimentally validated in the frequency domain using bi-static measurement set-up. Both amplitude and group delay responses of the tag are investigated and carried out.

Design of a Broadband All-Textile Slotted PIFA

Abstract: A new broadband textile based PIFA antenna structure designed for wireless body area network (WBAN) applications is presented. The new topology can be directly integrated into clothing. The study starts by considering three different materials: flexible copper foil, and ShieldIt Super and pure copper polyester taffeta conductive textiles. Bandwidth broadening is successfully achieved by implementing a novel and simple slot in the radiating patch. The measured reflection coefficient and radiation characteristics agree well with simulations. Moreover, radiation characteristics and bandwidth show satisfactory immunity against detuning when operating on-body, especially when placed on the back. To our knowledge, the proposed structure is the first fully fabric based slotted PIFA to be reported in open literature with high bandwidth (more than 46%) and reasonable gain (ca. 1.5 dB), to be used for multiple applications in the frequency band of 1.8 to 3.0 GHz.

Development of Superconducting Spectroscopic Array Receiver: A Multibeam 2SB SIS Receiver for Millimeter-Wave Radio Astronomy

Abstract: We have developed a 3×3 multibeam sideband separation superconducting receiver-Superconducting Spectroscopic Array Receiver (SSAR)-for the 85-115 GHz frequency band. The receiver employs 2SB superconductor-insulator-superconductor (SIS) mixers with a typical single sideband (SSB) noise temperature of 60 K and image rejection ratio above 10 dB over the frequency band. Digital techniques are extensively applied in this receiver system for excellent operational stability and efficiency. They include fast Fourier spectrometers, digital LO and digital bias supplies. In our knowledge this is the first 2SB multibeam millimeter wavelength receiver in the world. This receiver has been successfully put into observation and its considerable enhancement of mapping speed has been demonstrated.

Systems, methods, and devices for increasing radio frequency (RF) power in distributed antenna systems

Abstract: A system, and related methods and devices, is disclosed for increasing an output power of a frequency band in a distributed antenna system that includes at least one RXU module that is operatively coupled to at least one RAU module. A first group of the plurality of channels within a first frequency band may be allocated to the RAU module, and a second group of the plurality of the channels within the first frequency band may be allocated to the RXU module. The at least one RAU module may be configured to receive RF signals from the first group of the plurality of channels being used in the first frequency band, and the at least one RXU module may be configured to receive RF signals from the second group of the plurality of channels being used in the first frequency band. In this manner, the amount of composite power per channel is increased.

Using multiple frequency bands with beamforming assistance in a wireless network

Abstract: A communication device communicates with other communication devices in a wireless network using a first and a second frequency band. In accordance with some embodiments, inter-band beamforming assistance may be provided by the lower frequency band.

Wideband High Directive Aperture Coupled Microstrip Antenna Design by Using a FSS Superstrate Layer

Abstract: In this communication a high directive electromagnetic bandgap (EBG) antenna operating in wide frequency band for both return loss (RL) and directivity is examined. In this EBG antenna an aperture coupled microstrip antenna (ACMA) is used as a feeding source and a frequency selective surface (FSS) is used as a superstrate layer. Suitable use of the superstrate layer, microstrip patch and coupling aperture simultaneously, leads to produce separate resonance frequencies and therefore the wide frequency band for RL. Also, high directivity is achieved only by using the superstrate layer that has been made by the FSS layer with square loop elements. At first, a wideband ACMA is designed to operate in x-band. In this step appropriate design of coupling aperture is of a great importance. Secondly, after the design of optimum superstrate layer by the FSS structure, it is added to the ACMA in order to increase both bandwidth and directivity.

Adaptive frequency with power-level tracking system for efficient magnetic resonance wireless power transfer

Abstract: To supply the optimum amount of required power to a load device, an adaptive frequency and power-level tracking system is proposed for an efficient magnetic resonance wireless power transfer in the high frequency band. As a result, the proposed system is able to maintain a power transfer efficiency (PTE) of more than 75% with an optimum received power-level of 88%W for any transfer distance within 0.6%m by directly monitoring the PTE and received power-level via wireless communication.

Mobile terminal with antenna to tune a resonance frequency band and operating method thereof

Abstract: A mobile terminal including an antenna to change an operating frequency band includes a sub-resonance generator that generates a sub-resonance to shift the operating frequency band. The sub-resonance generator may be electrically or physically connected to a main antenna of the mobile terminal. The sub-resonance generator is connected to at least one impedance matcher and switch, and the opening and closing of the switch results in the generation of the sub-resonance. A sub-resonance generated in a higher frequency band than a first frequency band of the antenna device may result in the shift to a third frequency band with a main resonance at a lower frequency than the main resonance of the first frequency band and vice versa.

Dual-Band Antenna With Compact Radiator for 2.4/5.2/5.8 GHz WLAN Applications

Abstract: This paper presents a dual-band planar antenna with a compact radiator for 24/52/58-GHz wireless local area network (WLAN) applications The antenna consists of an L-shaped and -shaped radiating elements to generate two resonant modes for dual-band operation The -element fed directly by a 50-Ω microstrip line is designed to generate a frequency band at around 55 GHz to cover the two higher bands of the WLAN system (using the IEEE 80211a standard) The L-element is coupled-fed through the L-element and designed to generate a frequency band at 244 GHz to cover the lower band of the WLAN system (using the 80211 b/g standards) As a result, the L- and E-elements together are very compact with a total area of only 8 × 113 mm2 Parametric study on the key dimensions is investigated using computer simulation For verification of simulation results, the antenna is fabricated on a 40 × 30 × 08 mm3 substrate and measured The effects of the feeding cable used in the measurement system and the housing and liquid crystal display of wireless devices on the return loss, radiation pattern, gain and efficiency are also investigated by computer simulation and measurement

Underwater wireless sensor communications in the 2.4 GHz ISM frequency band.

Abstract: One of the main problems in underwater communications is the low data rate available due to the use of low frequencies. Moreover, there are many problems inherent to the medium such as reflections, refraction, energy dispersion, etc., that greatly degrade communication between devices. In some cases, wireless sensors must be placed quite close to each other in order to take more accurate measurements from the water while having high communication bandwidth. In these cases, while most researchers focus their efforts on increasing the data rate for low frequencies, we propose the use of the 2.4 GHz ISM frequency band in these special cases. In this paper, we show our wireless sensor node deployment and its performance obtained from a real scenario and measures taken for different frequencies, modulations and data transfer rates. The performed tests show the maximum distance between sensors, the number of lost packets and the average round trip time. Based on our measurements, we provide some experimental models of underwater communication in fresh water using EM waves in the 2.4 GHz ISM frequency band. Finally, we compare our communication system proposal with the existing systems. Although our proposal provides short communication distances, it provides high data transfer rates. It can be used for precision monitoring in applications such as contaminated ecosystems or for device communicate at high depth.

Design of Compact and Auto-Compensated Single-Layer Chipless RFID Tag

Abstract: This paper presents a new radio frequency identification (RFID) chipless tag that is highly compact and potentially low-cost. This tag has a lot of advantages, such as being fully printable on products since no ground plane is needed for fabrication. The actual issue of the chipless tag family having a single layer, that is, their detuning effect, is compensated for the first time by a correction technique based on the use of a sensing resonator. The design is based on multiple λ/4 coplanar strip-line resonators where resonant frequencies can be shifted by setting an additional short circuit at particular locations. An accurate model is proposed to easily link the footprint of the structure to the resonant frequency. Considering a frequency resolution of 50 MHz for the reading system and a tag dimension of 15 × 20 mm2, 9 b can be encoded in the frequency band 2.0-5.5 GHz. Several experimental results validate the proposed design as well as its implementation in a realistic application and environment.

Sensitivity enhancement of magnetoelectric sensors through frequency-conversion

Abstract: Thin film magnetoelectric (ME) sensors show sensitivity levels as low as 7.1 pT/ Hz over narrow bandwidths at bandwidths of some Hz around their mechanical resonance frequency. The high sensitivity is making the sensors – in principle – suitable for biomagnetic measurements like magnetoencephalography (MEG) and magnetocardiography (MCG). Biomagnetic measurements, however, usually require high sensitivity over a wide frequency band of 0.1–100 Hz. Unfortunately, at such low frequencies far from resonance the ME coefficient decreases dramatically and the noise level increases; this leads to a significant reduction in sensitivity. This work proposes and demonstrates a novel frequency-conversion-approach, which represents a remedy to the sensitivity decay. It allows wideband measurements at low frequencies by utilizing the nonlinear characteristics of the magnetostriction curve. The new technique offers the possibility to achieve resonance enhanced sensitivities at virtually arbitrary frequencies outside and therefore also far below resonance. Measurements show that sensitivity at 1 Hz can be enhanced by a factor of ∼1000 compared to the non-resonant case using the proposed modulation technique. The new technique also offers advantages for the increase of the sensor slew rate, the suppression of mechanical noise and for the operation of such sensors in arrays.

Periodic materials-based vibration attenuation in layered foundations: experimental validation

Abstract: Guided by the recent advances in solid-state research in periodic materials, a new type of layered periodic foundation consisting of concrete and rubber layers is experimentally investigated in this paper. The distinct feature of this new foundation is its frequency band gaps. When the frequency contents of a wave fall within the range of the frequency band gaps, the wave, and hence its energy, will be weakened or cannot propagate through the foundation, so the foundation itself can serve as a vibration isolator. Using the theory of elastodynamics and the Bloch–Floquet theorem, the mechanism of band gaps in periodic composites is presented, and a finite element model is built to show the isolation characteristic of a finite dimensional periodic foundation. Based on these analytical results, moreover, a scaled model frame and a periodic foundation were fabricated and shake table tests of the frame on the periodic foundation were performed. Ambient, strong and harmonic vibration attenuations are found when the exciting frequencies fall into the band gaps.

Balanced homodyne detection of optical quantum states at audio-band frequencies and below

Abstract: The advent of stable, highly squeezed states of light has generated great interest in the gravitational wave community as a means for improving the quantum-noise-limited performance of advanced interferometric detectors. To confidently measure these squeezed states, it is first necessary to measure the shot-noise across the frequency band of interest. Technical noise, such as non-stationary events, beam pointing, and parasitic interference, can corrupt shot-noise measurements at low Fourier frequencies, below tens of kilo-hertz. In this paper we present a qualitative investigation into all of the relevant noise sources and the methods by which they can be identified and mitigated in order to achieve quantum noise limited balanced homodyne detection. Using these techniques, flat shot-noise down to Fourier frequencies below 0.5 Hz is produced. This enables the direct observation of large magnitudes of squeezing across the entire audio-band, of particular interest for ground-based interferometric gravitational wave detectors. 11.6 dB of shot-noise suppression is directly observed, with more than 10 dB down to 10 Hz.

A Novel Design of Reconfigurable Slot Antenna With Switchable Band Notch and Multiresonance Functions for UWB Applications

Abstract: A novel printed reconfigurable square slot antenna with switchable band-notched and multiresonance performances is designed and manufactured. In the proposed structure, in order to generate single band-notched characteristics, a Π-shaped slot is etched on the radiating stub. Furthermore, to achieve a reconfigurable function, a p-i-n diode is utilized across the slot. When this p-i-n diode is biased forwardly, the Π -shaped slot transforms to a pair of C-shaped slots, and also by changing to this new structure, an additional resonance is excited. Additionally, by cutting two modified L-shaped slits with variable dimensions on the microstrip feed line, new additional resonance is excited, and hence wider impedance bandwidth can be produced, especially at the higher band. The designed antenna has a small size of 20 × 20 mm2 while showing the radiation performance in the frequency band of 3.04 to over 11.17 GHz with a switchable band-rejection performance in the frequency band of 5.03-5.94 GHz. Simulated and experimental results obtained for this antenna show that it exhibits good radiation behavior within the ultrawideband (UWB) frequency range and also it has a reconfigurable frequency band-notched function in the range of 5-6 GHz that can eliminate the interference between UWB frequency band and other existing wireless communication systems.

Configurable metamaterial absorber with pseudo wideband spectrum

Abstract: Metamaterials attain their behavior due to resonant interactions among their subwavelength components and thus show specific designer features only in a very narrow frequency band. There is no simple way to dynamically increase the operating bandwidth of a narrowband metamaterial, but it may be possible to change its central frequency, shifting the spectral response to a new frequency range. In this paper, we propose and experimentally demonstrate a metamaterial absorber that can shift its central operating frequency by using mechanical means. The shift is achieved by varying the gap between the metamaterial and an auxiliary dielectric slab parallel to its surface. We also show that it is possible to create multiple absorption peaks by adjusting the size and/or shape of the dielectric slab, and to shift them by moving the slab relative to the metamaterial. Specifically, using numerical simulations we design a microwave metamaterial absorber and experimentally demonstrate that its central frequency can be set anywhere in a 1.6 GHz frequency range. The proposed configuration is simple and easy to make, and may be readily extended to THz frequencies.

Comparative Performance Evaluation of Spectrum Sensing Techniques for Cognitive Radio Networks

Abstract: Cognitive radio is the key technology for future wireless communication. Spectrum sensing is one of the most important functions in cognitive radio (CR) applications. It involves the detection of primary user (PU) transmissions on a preassigned frequency band. PU licensed band can be sensed via appropriate spectrum sensing techniques. In this paper, we consider three basic spectrum sensing techniques of transmitter detection: Matched filter detection, Energy detection, and Cyclostationary feature detection. Using simulations, a comparative analysis of the three techniques has been carried out in terms of probability of false alarm Pf, probability of detection alarm Pd, and probability of miss detection Pm. Finally, Numerical result shows that at low signal to noise ratio (SNR), cyclostationary feature detection outperforms other two techniques, thus have some difficulties like implementation is complex, long observation time, etc. For simulation we used MATLAB software.

Characterization of 60 GHz shadowing by human bodies and simple phantoms

Abstract: The 60 GHz band is very prominsing for high data rate (>1 Gb/s) wireless systems operating at short ranges. However, due to the short wavelengths in this frequency band, the shadowing effects cuased by human bodies and furniture are severe and needs to be modeled properly. In this paper, we present an experimental, measurement-based characterization of the reflection and shadowing effects in the 60 GHz band caused by human bodies and various phantoms, in order to find simple phantoms suitable for use in human shadowing measurements. It is shown that a water-filled human phantom serves as a good choice for this purpose.

Bandwidth Enhancement of CPW-Fed Circle-Like Slot Antenna With Dual Band-Notched Characteristic

Abstract: A novel single-layer dual band-notched printed circle-like slot antenna for ultrawideband (UWB) applications is presented. The proposed antenna comprises a circle-like slot, a trident-shaped feed line, and two nested C-shaped stubs. By using a trident-shaped feed line, much wider impedance bandwidth is obtained. Due to inserting a pair of nested C-shaped stubs on the back surface of the substrate, two frequency band-notches of 5.1-6.2 (WLAN) and 3-3.8 GHz (WiMAX) are achieved. The nested stubs are connected to the tuning stub using two cylindrical via pins. The designed antenna has a total size of 26 × 30 mm2 and operates over the frequency band between 2.5 and 25 GHz. Throughout this letter, experimental results of the impedance bandwidth, gain, and radiation patterns are compared and discussed .

Wireless communication system

Abstract: PROBLEM TO BE SOLVED: To provide a wireless communication system capable of increasing a processing speed of a scheduling process in a base stationSOLUTION: In a wireless communication system in which a base station and a terminal communicate with each other by using a plurality of frequency bands, the terminal measures a wireless line quality for each frequency band to notify the base station of it The base station decides the frequency band to be used by the terminal, based on the notification from the terminal The base station performs grouping of the terminals based on the difference in the frequency band to be used to notify the terminal of to which terminal group the terminal belongs The terminal sets the use frequency band and the terminal group of the self terminal based on the notification from the base station, and measures the wireless line quality of the notified use frequency band The base station is notified of the measurement result The base station carries out scheduling for each use frequency band based on the wireless line quality related to the use frequency band of the terminal, and starts communication with the terminal

Cluster-Based Control Channel Allocation in Opportunistic Cognitive Radio Networks

Abstract: Cognitive radio networks (CRNs) involve extensive exchange of control messages, which are used to coordinate critical network functions such as distributed spectrum sensing, medium access, and routing, to name a few. Typically, control messages are broadcasted on a preassigned common control channel, which can be realized as a separate frequency band in multichannel systems, a given time slot in TDMA systems, or a frequency hopping sequence (or CDMA code) in spread spectrum systems. However, a static control channel allocation is contrary to the opportunistic access paradigm. In this paper, we address the problem of dynamically assigning the control channel in CRNs based on time- and space-varying spectrum opportunities. We propose a cluster-based architecture that allocates different channels for control at various clusters in the network. The clustering problem is formulated as a bipartite graph problem, for which we develop a class of algorithms that provide different tradeoffs between two conflicting factors: number of common channels in a cluster and the cluster size. Clusters are guaranteed to have a desirable number of common channels for control, which facilitates for graceful channel migration when primary radio (PR) activity is detected, without the need for frequent reclustering. We perform extensive simulations that verify the agility of our algorithms in adapting to spatial-temporal variations in spectrum availability.