External Interference Sources Research Articles

Interference resisting design for guided wave tomography

RAPID (reconstruction algorithm for the probabilistic inspection of damage) is a new promising tomography approach for the detection and monitoring of critical areas in a structure. With the sensors permanently installed on or embedded in structures, changes in effective thickness and material properties caused by structural damage can be detected and mapped to the tomogram. However, in this method, the tomographic feature SDC (signal difference coefficient) captures the overall change of the received ultrasonic signals, which makes it sensitive to environmental factors (e.g. rain, changes in temperature and humidity). As a result, the approach is restricted in the laboratory environment. In this paper, the influence of measurement data length on the SDC and the tomogram are investigated, and a new strategy is established on how to choose the measurement data to obtain good reconstruction by matching the coverage zone of each transmitter–receiver pair with the corresponding affected zone. The proposed method is then applied to identify defects of the specimen in the presence of external sources of interference, such as water droplets and structural variations outside the critical area. The results demonstrate its capability of improved robustness in the presence of external sources of interference.

WLAN channel selection without communication

We propose a new class of channel allocation algorithms that are simple, robust and require no communication between interfering WLANs. We show they are provably correct and yet remarkably efficient under a wide range of network conditions and topologies. The algorithms are suited to implementation on standard equipment, requiring no special hardware support and making only light demands on computational resources. We demonstrate this by implementing algorithms on an experimental testbed using commodity hardware. We present detailed measurements of performance in a real office environment. This environment includes complex spatially-varying noise, channel-dependent interference between WLANs, time-varying channel quality and external interference sources. Despite these challenges the algorithm performs well.

Repeatable Experiments with Mobile Nodes in a Relocatable WSN Testbed

Many sensor network application scenarios include mobile nodes, such as a moving sink. Evaluation of such applications in a testbed is challenging as the testbed has to support mobile nodes. Here, we present Sensei-UU, a sensor network testbed that supports mobile sensor nodes. The testbed is inexpensive, relocatable and possible to reproduce by other researchers. Its primary design objectives are to support experiments with repeatable mobility and relocating the testbed deployment to different locations. Mobile sensor nodes are carried by robots that use floor markings for navigation and localization. The testbed can be used to evaluate applications in which sensor nodes move in the order of meters rather than millimeters, e.g. when a human carries a mobile phone that collects data while passing stationary sensor nodes. To investigate the repeatability of robot movements, we measure the achieved precision and the timing of the robots, and find that our robot localization is accurate to ±1Â cm. Furthermore, we investigate variations in radio signal strengths between mobile and stationary nodes. We study the impact of imprecise movements, external sources of interference and environmental influences. We conclude that Sensei-UU supports experiments in which these variations are acceptably low to capture small-scale fading phenomena in IEEE 802.15.4.

Emission and Susceptibility Modeling of Finite-Size Power-Ground Planes Using a Hybrid Integral Equation Method

A novel method based on hybrid integral equation for electromagnetic emission and susceptibility modeling of power-ground planes with a finite size is proposed in this paper. First, the entire computational domain is divided into the internal subdomain including the substrate sandwiched between the power and ground planes and the external subdomain surrounding the power-ground planes. The internal subdomain is modeled by using the integral equation with dyadic Green's functions of the rectangular cavity, while the free-space Green's function is used to model the outside subdomain. These two kinds of integral equations are coupled through the equivalent electric and magnetic currents that are placed on the interfaces. The key advantage of this proposed method is its ability to model both emission and susceptibility problems. This method can accurately simulate the impedance of the power-ground planes and the radiated field. In particular, it is able to predict the induced electric currents inside the power-ground planes that result from external interference sources. Therefore, this technique is able to provide a complete solution for the electromagnetic compatibility analysis of the system-level package.

The Effect of Interference Source Proximity on Cuff Imbalance

The presence of cuff imbalance degrades the signal-to-interference (ENG/EMG) ratio in tripolar nerve cuff electrode recordings. Known causes of cuff imbalance include inhomogeneous tissue growth after cuff implantation and cuff manufacturing tolerances. In this paper, we report on an additional contribution to cuff imbalance that stems from variations in orientation and distance of the tripolar cuff relative to the external interference source. The latter is represented here by a dipole. Interference amplitude is also shown to depend on orientation and distance variations, here both factors included in the term "proximity." The study was conducted using field simulations and saline-bath experiments.

Electromagnetic modeling of finite length wires buried in a lossy half-space

The horizontal buried wire of a finite length is analyzed by using the scattering theory. The current distribution along the wire due to an external electromagnetic interference (EMI) source is governed by the half-space Pocklington integral equation. The effect of the lower half-space is taken into account via the transmission coefficient (TC) appearing within the integral equation kernel. The principal advantage of the TC approach vs rigorous Sommerfeld integral approach is the formulation simplicity and reduced computational cost. The variational boundary element procedure is used for solving the Pocklington integral equation and the current induced along the buried wire due to the transmitted plane wave or current source excitation is obtained.

Signal processing in adaptive arrays using power basis

The development of the theory of adaptive arrays (AAs) is proposed based on the representation of the inverse covariance matrix (CM) of a noise in the AA channels as a finite power series expansion using the direct CM and by representation of a weight vector of the AA as a finite series expansion of the power vectors. The dimension of the power CM basis is equal to the power of the minimum polynomial of the CM. In the case when the number of external interference sources is less than the number of AA channels, such polynomials have the same fundamental role as the characteristic polynomial of the CM in an opposite case. Proofs for the existence of the above mentioned polynomials of the CM are given. A new method for the calculation of the polynomial coefficients is presented, and the physical properties of the power vector basis are studied. It is shown that the power vectors are correlated and that there are two stages of AA signal processing.

EMC testing Rover cars

The immunity of modern vehicles to external sources of radiofrequency interference is important because of the amount and criticality of the electronic systems within. Assuring this immunity traditionally requires a representative vehicle to be operated in a strong electromagnetic field in a screened room while any malfunctions are observed. The research work described in this paper has produced a method of testing an individual electronic system and statistically relating the results to those that would be obtained from a complete vehicle. The method is now in use in the civil aircraft community and by Rover Cars.< >

Evaluation of distortion in f.m. trunk radio systems by a Monte Carlo method

There exists a considerable body of published work concerned with the theoretical evaluation of distortion arising from various sources in trunk radio systems. The analytical difficulties, however, are often formidable, and simplifying approximations have usually to be made. As a consequence, the theory has developed in a piecemeal fashion, different approaches having to be followed depending on the origin of the distortion. By contrast, the measurement method prescribed by international agreement is of universal application, though it is liable to suffer from the uncertainties inevitable when measurements are carried out in complex and often somewhat ill-defined situations.It is the purpose of the present paper to describe a method of computer simulation of the standard measurement technique, and to give some representative numerical results. The method is in principle capable of good accuracy, and greatly extends the range of distortion problems amenable to theoretical treatment. It is applicable to the evaluation of distortion arising from external interference sources, such as added thermal noise, as well as distortion due to echoes, filtering etc. The present approach is found to give good agreement with existing theory where this may be expected to apply.