High Signal Attenuation Research Articles

An Adaptive INS-Aided PLL Tracking Method for GNSS Receivers in Harsh Environments.

As the weak link in global navigation satellite system (GNSS) signal processing, the phase-locked loop (PLL) is easily influenced with frequent cycle slips and loss of lock as a result of higher vehicle dynamics and lower signal-to-noise ratios. With inertial navigation system (INS) aid, PLLs’ tracking performance can be improved. However, for harsh environments with high dynamics and signal attenuation, the traditional INS-aided PLL with fixed loop parameters has some limitations to improve the tracking adaptability. In this paper, an adaptive INS-aided PLL capable of adjusting its noise bandwidth and coherent integration time has been proposed. Through theoretical analysis, the relation between INS-aided PLL phase tracking error and carrier to noise density ratio (C/N0), vehicle dynamics, aiding information update time, noise bandwidth, and coherent integration time has been built. The relation formulae are used to choose the optimal integration time and bandwidth for a given application under the minimum tracking error criterion. Software and hardware simulation results verify the correctness of the theoretical analysis, and demonstrate that the adaptive tracking method can effectively improve the PLL tracking ability and integrated GNSS/INS navigation performance. For harsh environments, the tracking sensitivity is increased by 3 to 5 dB, velocity errors are decreased by 36% to 50% and position errors are decreased by 6% to 24% when compared with other INS-aided PLL methods.

PRACTICAL INVESTIGATION OF DIFFERENT POSSIBLE TEXTILE UNIT CELL FOR A C-BAND PORTABLE TEXTILE REFLECTARRAY USING CONDUCTIVE THREAD

Investigation of a unit cell in terms of reflected wave amplitude and phase, for designing linearly polarized single layer Textile-Reflectarray (TRA) at C-band, is presented. The relative dielectric constant of the material is extracted using resonance method, and a WLAN antenna is designed to verify the accuracy of extracted material parameter. An error of 5% is observed in the extracted dielectric constant, when performance of WLAN antenna is measured at WI-FI Band (2.4 GHz). The extracted dielectric constant is used in the unit cell designing for TRA at the C-band (5.8 GHz). The radiating element is made using laying technique with conductive thread. A square patch with a ring is selected after analyzing multiple geometries of the patch providing the required reflected phase range and low losses. By varying size of patch and ring of single layer unit cell in CST periodic environment, reflected phase range of 360 degrees is achieved, which is required for reflectarray (RA) designing. The solid copper ground plane at the bottom of unit cell is replaced with conductive shielded fabric with high level signal attenuation. Four different sizes of textile unit cells are fabricated using conductive thread, and the reflected phase and amplitude are measured using waveguide method. The simulated and measured results are compared when solid copper ground plane at the bottom of unit cell has been replaced with shielded fabric. The proposed method provides the first step towards designing flexible high gain textile reflectarrays.

Robustness and filtering properties of ubiquitous signaling network motifs

Abstract: Biological systems are intrinsically robust. The system, being an open one, is permanently exposed to perturbations due to external noise from the surrounding environment. In this context, the architecture and information processing capabilities of a signaling network play an important role in attenuating the noise. Multi-layered phosphorylation cascades are architectures prevalent in some of our major signaling pathways. In this work, we investigate the robustness of such signaling cascades with respect to external input variations. We employ local sensitivity and output-variance based sensitivity as measures of robustness for such cascades and observe that the efficiency of high frequency signal attenuation increases with the number of in the cascades. Filtering properties of cascades have been observed previously but not under a very rigorous theoretical framework and not in comparison with other models. This work provides an example of optimality versus robustness tradeoff in the design principles of biological systems.

Design of light‐emitting‐diode array for solving problems of irregular radiation pattern and signal attenuation for infrared electronic‐toll‐collection systems

Infrared light emitting diodes (LEDs) with a half-intensity angle Φ1/2 ≃ 10° are suitable for electronic-toll-collection (ETC) applications. However, the radiation patterns of commonly available low-cost commercial infrared LEDs are irregular to some extent, which result in difficulties to construct an infrared ETC system with a proper communication area. Most low-cost infrared LEDs with a half-intensity angle Φ1/2 ≃ 10° exhibit a common irregularity in their radiation pattern – a notch in the central radiant direction. The adverse influence bccause of such irregularities can be reduced by a proper design of an LED array in the emitter. High attenuation for the infrared signal of some windshields is also a serious problem for infrared ETC systems, which leads to severe shrinkage of the communication area if the emitter has not been properly designed. In this study, the authors present some successful designs with the aid of an optimisation algorithm to adjust the mounting angle of each constituent LED. In spite of the aforementioned irregularity, the proposed design still exhibits good performance in terms of the ability to withstand high signal attenuation and extended communication area in the vehicle-travelling direction.

On-wafer magnetically tunable millimeter wave notch filter using M-phase Ba hexagonal ferrite/Pt thin films on Si

A prototype of a fully integrated on-wafer, magnetically tunable band-stop filter operating at millimeter wave frequencies is demonstrated on a Si substrate. In contrast to earlier studies, the filter uses a very thin barium hexagonal ferrite film incorporated into the dielectric layer of a microstrip transmission line to filter the signal. The zero-field operational frequency is about 34 GHz, increasing linearly with the strength of a static, perpendicularly applied magnetic field at a rate of about 2.7 GHz/kOe. Experimentally, high signal attenuation (33–67 dB/cm) at the resonance frequency and insertion losses as low as 4.5 dB were simultaneously observed, while the 3 dB device bandwidths were generally below 1 GHz. Our calculations are in quantitative agreement with the experimental results. We also find an important result that the thickness and conductivity of the Pt ground plane plays a key role in insertion losses, indicating directions for further improvements.

The Feasibility of Exploiting IEEE 802.11n for Addressing MAC Layer Overheads in UASNs

Underwater acoustic sensor networks (UASNs) consist of remotely deployed sensor nodes under sea or other water environments. Due to the extreme limitations faced by radio signals under water, acoustic channels are utilized for communication in such networks. However, UASNs are challenged by the characteristics of underwater acoustic channels such as lower signal propagation speed and higher signal attenuation. On top of such a challenged physical medium, MAC schemes which are designed based on their terrestrial counter parts are required to add extra overheads to the communication channel wasting the limited network resources. MAC layer overheads such as bandwidth wastage for interframe spaces and contention for occupying physical medium put limitations to the maximum reachable throughput of UASNs. IEEE 802.11n has well defined various MAC and physical layer enhancements to overcome throughput barrier in wireless LANs which includes two frame aggregation schemes, namely, A-MPDU and A-MSDU. In this paper, we study the feasibility of applying those frame aggregations well defined in IEEE 802.11n for reducing MAC layer overheads in UASNs. Based on simulation studies, we evaluate that these frame aggregation schemes are applicable in UWSNs.

Tomography in standing trees: revisiting the determination of acoustic wave velocity

The quality of acoustic tomographic images in standing trees is mainly function of the accuracy of the acoustic velocity computation. Improving the acoustic velocity determination is, furthermore, of great interest because acoustic tools are widely used in nondestructive testing of wood. Four different signal processing algorithms were used (1) to study the effect of the signal dynamic on the velocity determination, (2) to determine the validity range of each computation method, and (3) to compare the behavior between a homogeneous material and wood. The experiments were performed using the conventional experimental protocol for the ultrasonic characterization of materials in a tank (normal incidence transmission at 500 kHz). A polyurethane resin (homogeneous material) and two wood species (Bagassa guianensis Aubl., Milicia excelsa (Welw.) C.C. Berg) were used for the experiments. Computed velocity increased as the noise level increased. The Hinkley method appeared to be the most exact when the noise level exceeded 10 dB. The Fisher method was that most suitable for very noisy signals. No difference was found between the resin and the wood samples. A combination of the Fisher and Hinkley methods in the same algorithm would yield the most accurate acoustic velocity determinations in the tomography of standing trees. Wood acoustic velocity determination is affected by the wavelength and the detection algorithm used. The Fisher algorithm is optimal with high signal attenuation; otherwise, the Hinkley algorithm should be used.

Communication techniques and challenges for wireless food quality monitoring.

Remote measurement of product core temperature is an important prerequisite to improve the cool chain of food products and reduce losses. This paper examines and shows possible solutions to technical challenges that still hinder practical applications of wireless sensor networks in the field of food transport supervision. The high signal attenuation by water-containing products limits the communication range to less than 0.5 m for the commonly used 2.4 GHz radio chips. By theoretical analysis of the dependency of signal attenuation on the operating frequency, we show that the signal attenuation can be largely reduced by the use of 433 MHz or 866 MHz devices, but forwarding of messages over multiple hops inside a sensor network is mostly unavoidable to guarantee full coverage of a packed container. Communication protocols have to provide compatibility with widely accepted standards for integration into the global Internet, which has been achieved by programming an implementation of the constrained application protocol for wireless sensor nodes and integrating into IPv6-based networks. The sensor's battery lifetime can be extended by optimizing communication protocols and by in-network pre-processing of the sensor data. The feasibility of remote freight supervision was demonstrated by our full-scale 'Intelligent Container' prototype.

A novel technique for acoustic emission monitoring in civil structures with global fiber optic sensors

The application of acoustic emission (AE)-based damage detection is gaining interest in the field of civil structural health monitoring. Damage progress can be detected and located in real time and the recorded AEs hold information on the fracture process which produced them. One of the drawbacks for on-site application in large-scale concrete and masonry structures is the relatively high attenuation of the ultrasonic signal, which limits the detection range of the AE sensors. Consequently, a large number of point sensors are required to cover a certain area. To tackle this issue, a global damage detection system, based on AE detection with a polarization-modulated, single mode fiber optic sensor (FOS), has been developed. The sensing principle, data acquisition and analysis in time and frequency domain are presented. During experimental investigations, this AE-FOS is applied for the first time as a global sensor for the detection of crack-induced AEs in a full-scale concrete beam. Damage progress is monitored during a cyclic four-point bending test and the AE activity, detected with the FOS, is related to the subsequent stages of damage progress in the concrete element. The results obtained with the AE-FOS are successfully linked to the mechanical behavior of the concrete beam and a qualitative correspondence is found with AE data obtained by a commercial system.

Effects of Segmented Shield Wires on Signal Attenuation of Power-Line Carrier Channels on Overhead Transmission Lines—Part II: Signal Attenuation Results Analysis

A previous paper has been written on the generalized modeling method of overhead transmission lines for use in power-line carrier (PLC) systems. Knowledge of the effects of shield wires on PLC signal attenuation for various coupling methods would be useful to relay engineers. In addition to the effect of the coupling method on PLC signal attenuation, other problems, such as resonance conditions resulting in high signal attenuation may also occur depending on the PLC signal frequency and the length of the shield wire segments. Therefore, the purpose of this paper is to provide awareness to relay engineers of problems that may arise when applying PLC systems on transmission lines with segmented shield wires.

Non‐destructive Testing for the Characterization of Moai Statues (Easter Island, Chile)

ABSTRACTSeismic tomography and ground‐penetrating radar (GPR) were combined to determine weakness zones and the degree of alteration in rock making up the Moai statues of Easter Island. The surveys were carried out on stratified argillaceous tuff that had been subjected to weathering for long periods. The argillaceous nature and unsaturated condition of the rock creates ambiguity in both the seismic and georadar data interpretation, but this ambiguity is removed by using a combined interpretation of the data. Interpretation of the combined data shows that the high seismic velocities of the inner zones of the statues must be related to water content and not to better rock quality, because of the high attenuation of the georadar signal in those zones. The weathered zone is characterized by a high signal‐to‐noise ratio of georadar data and low P‐wave seismic velocities. Comparing the seismic and GPR data sets, we found that the seismic velocity and the signal attenuation of the georadar section differ for two statues in accordance with the degree of alteration of the rock. We show that the combined interpretation of seismic and georadar data allows the removal of the ambiguities in the interpretation of the seismic velocity in the massive tuff, the definition of the thickness of the weathered layer and the linking of seismic velocity to the degree of Moai preservation, which is useful for a classification of Moai health. Copyright © 2013 John Wiley & Sons, Ltd.

Wifi bluetooth based combined positioning algorithm

Nowadays positioning have become very important for many services (Localization based services) and positioning have become more accurate, despite, there are some territories that basic positioning systems like GPS or even hybrid ones like GPS-WiFi or GPS-WiFi-gsm can’t cover, specially indoor enviroments. In this paper we propose a positioning method merging WLAN and Bluetooth technologies based on trilateration technique. Simulated sceneario demostrate accuracy gains, even when we use a high signal attenuation parameter. A simulated sceneario taken from a real home with the real WLAN and Bluetooth stations validates our WLAN-Bluetooth method. Firstly we calculate each equation from each available station, then we decide how to overdetermine the generated equation system in a reason of 4 to 1 (4 equations for one unknown) and finally solve the system using mathematical methods. This work is a step more to better position in indoor enviroments and localization based services.

MAPPING THE UNDISCOVERED RUINS OF POMPEII (NAPLES, ITALY) USING GROUND PENETRATING RADAR*

The ground penetrating radar (GPR) technique was tested in Pompeii, in an unexplored area where the Roman ruins are partially buried in the volcanic deposits. The method was also combined with time domain reflectometry (TDR) measurements to estimate the dielectric properties of the different volcanic units. In spite of the total thickness of the covering materials and the high signal attenuation measured in some layers, the radar was able to show a detailed image of the volcanic sediments and to locate the manmade structures hidden in the ash deposits. Moreover, the present study shows that the integrated use of GPR and TDR techniques could be successfully employed to evaluate the performance of the radar in specific terrains covering archaeological sites. Since it is unlikely that a large part of Pompeii will ever be excavated, GPR could be successfully used to produce detailed maps of the ruins still hidden in the subsurface, giving archaeologists the possibility of reconstructing the entire urban development of this unique ancient city.

A Problem of Infrared Electronic-Toll-Collection Systems: The Irregularity of LED Radiation Pattern and Emitter Design

According to our measurements, the radiation pattern of many low-cost commercial light-emitting diodes (LEDs) is not smooth. Some LEDs even have serious irregularities that affect the performance of infrared communication systems. For systems where a definite communication area is required, such as electronic-toll-collection (ETC) applications, this problem is particularly serious. In this paper, we first present our measured results for the radiation pattern of several typical low-cost commercial LEDs, showing that almost all of them are irregular to some extent. We then use the most acceptable model with a suitable half-intensity angle to construct the emitter of an ETC system. The design was calculated with the aid of an optimization algorithm to determine the mounting angle for each LED such that the system has an extended communication area in the longitudinal direction, i.e., in the vehicle traveling direction, and can withstand high signal attenuation. For a typical LED with half-intensity angle Φ1/2 = 13°, a very simple two-group structure for the emitter is obtained, and the analysis results are verified by experimental measurements.

The Characterization of Radio-over-Fiber EmployedGPON Architecture for Wireless Distribution Network

already congested to high frequency of operations. However, the operations in smaller (micro-/pico-) cells lead to the increasing of hardware development costs while working in high frequency majorly suffers from high signal attenuation. Lined up with the popularity of wireless networks, optical technology has also played an important role in the telecommunication world. Fiber optic is widely used in the backbone network due to its high BW (up to THz) and low attenuation (~0.2 dB/km) characteristics. Thus, fiber optic is promising to be the core of wireless networks. The integration of wireless and fiber is known as Radio-over-Fiber (RoF) which complements the flexibility of wireless signal and the advantageous properties of fiber optics. Technically, RoF is a hybrid system that integrates the wireless and optical in one system leading towards high capacity, high data rate, transparent and mobility solution [2]. RoF allows the cost reduction and easier controlling and upgrading by a centralized architecture that connects a number of Remote Base Station (RBSs) to the Central Station (CS).

Testing network protocols and signal attenuation in packed food transports

Two sensor network protocols for the monitoring of packed food products were tested in different sea containers. The packet rate and the signal strength of all sensor-to-sensor links were recorded in the flash memory of the sensor nodes. The performance of the two protocols was compared and protocol improvements were tested by simulation based on this data. The high signal attenuation by water-containing products was identified as the major problem. One of the two tested protocols was newly developed with a focus on low energy consumption. A simplified link estimator, which required only a minimum number of control messages, detects the correct routing in most cases.

Physics-based propagation characterisations of UWB signals for the urine detection in human bladder

In this paper, an IR-UWB radar for the detection of water accumulation in human bladder is presented. The goal is to monitor the level of urine in patients who suffer from urinary incontinence. This is achieved by detecting the reflected UWB signals from the boundaries of human tissues such as muscle and bladder. However, the detection ability of the UWB radar system is strongly impaired due to the high attenuation and frequency dispersion of the UWB signal in human tissues. Based on the dielectric properties of the various human tissues, the physics-based propagation characterisations of electromagnetic waves are investigated with respect to their reflection, attenuation and transmission. A model of human bladder with different tissue layers including frequency dependent dielectric properties is proposed. Furthermore, a system concept of UWB radar for the detection of water accumulation in human bladder is introduced. The UWB pulse attenuation and distortion in different human tissues are investigated and evaluated with respect to the system performance. The results show the potential of detection of urine in the human bladder, which may lead to development of new non-invasive sensors locating water accumulations in human body.

Problems and features of spatiotemporal signal processing in ultrasonic testing of products manufactured from complexly structured materials

The main principles of spatiotemporal processing of signals during ultrasonic testing of articles manufactured from complexly structured materials with high signal attenuation are considered. Features of ultrasonic low-frequency testing limiting the application of the simplest algorithms for spatiotemporal signal processing in both ultrasonic flaw detection and ultrasonic tomography of articles manufactured from complexly structured materials are analyzed.

Design of the Radiation Pattern of Infrared Short-Range Communication Systems for Electronic-Toll-Collection Applications

This paper proposes a very simple method for enhancing the performance of infrared electronic-toll-collection systems. Using two typical low-cost commercial LEDs with different half-intensity angles Phi1/2 = 22deg and 10deg, the radiation pattern of the emitting module of an infrared short-range communication system for electronic-toll-collection applications is designed. This enables us to construct a system that has an extended communication region and can withstand high signal attenuation. When the module is fabricated with a proper combination of the numbers of these two different LEDs, together with a suitable mounting angle of each LED, an effective radiation pattern is obtained. The mounting angle of each LED is found with the aid of an optimization algorithm. The performances of three different designs are compared in terms of signal strength, communication length, and 2-D communication region. The results show that a module consisting of ten LEDs divided into three groups, with each group having a proper mounting angle and containing an appropriate number of LEDs, can have much better performance than conventional single-group unidirectional designs. The influence of the defect of the radiation pattern, which may happen on many LEDs, on system performance is also discussed. The results of the analysis are confirmed by experimental measurements.

Pulse shaper for ultra-wideband applications

A new pulse shaper is proposed for ultra-wideband applications. The pulse shaper consists of a third-order bandstop filter and a third-derivative Gaussian pulse generator. The bandstop filter is realised by means of a cascade of three newly proposed meandered V-sickle slotted ground structures. Experimental results reveal that the new design fully complies with the FCC emission mask and demonstrates high signal attenuation capability at the desired rejection band. The proposed pulse shaper also features compact size.