China
Africa
Explore chapters and articles related to this topic
L
Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
linear multistep method this is a class of techniques for solving ordinary differential equations which is widely used in circuit simulators. linear network a network in which the parameters of resistance, inductance and capacitance are constant with respect to voltage or current or the rate of change of voltage or current and in which the voltage or current of sources is either independent of or proportional to other voltages or currents, or their derivatives. linear phase system where the phase shift produced by the filter at frequency w is a linear function of w ( H (w) = dw). If a signal x(t) is passed through a unit magnitude, linear phase filter with slope d, the output signal will be x(t + d), the input signal time-shifted by d seconds. linear polarization a polarization state of a radiated electromagnetic field in which the tip of the electric field vector remains on a line and does not rotate as a function of time for a fixed position. linear prediction for a stochastic process, the prediction of its samples based upon determining a linear model capable of estimating the samples with minimal quadratic error. linear prediction based speech coding ear predictive coding. See lin-
Polarization Measurement
Published in John G. Webster, Halit Eren, Measurement, Instrumentation, and Sensors Handbook, 2017
Measurement of polarization of light is essential in polarimetry, since polarized light to be examined is not limited to that generated in a laboratory. The instrument to measure the four Stokes parameters is called a photopolarimeter or a Stokesmeter. To measure linear polarization, pass the light beam through a linear analyzer oriented at angle A = 0°, 90°, and ±45° and measure the corresponding intensities Ix, Iy, I+, and I−. To measure circular polarization, first pass the light beam through a quarter-wave retarder with C = 0° then through an analyzer oriented at A = ±45° and measure the intensities IR and IL. The pair of quarter-wave retarder and analyzer constitutes a circular analyzer. A detector measuring intensity corresponds to an operation given by a row vector I = (1, 0, 0, 0). The combined operation of a detector following an analyzer is IA = 0.5 (1, cos 2A, sin 2A, 0). The operations for the linear and circular analyzers on a Stokes vector S and the intensities obtained are given in Table 49.3. The Stokes parameters can be obtained from the difference and sum of the intensities for these pair operations and are given by
Complex Light Beams
Published in Lingyan Shi, Robert R. Alfano, Deep Imaging in Tissue and Biomedical Materials, 2017
In a plane-wave description of the light, the electric field of a propagating electromagnetic wave oscillates linearly in the plane that is transverse to the propagation. In linear polarization, the electric field oscillates in a single plane that contains the propagation direction. If we denote the state of linear polarization along the x-direction by e^x, and similarly, for the linear polarization along y-direction by e^y, then a general expression for the electric field is a linear superposition of these two components [42]: E→=E0(cosαe^x+sinαe−i2δe^y),(2.105)
High efficiency and broadband wide-angle linear polarization converter based on dumbbell-like resonant structure
Published in Waves in Random and Complex Media, 2023
Ze Wang, Jinping Tian, Rongcao Yang
Electromagnetic (EM) waves are transverse, of which the polarization is defined as the direction of the electric field oscillation in a plane transverse to the propagation [1]. Polarization is also an intrinsic property of EM waves, and polarized EM waves can be divided into three categories: linear polarization, circular polarization and elliptical polarization. The electric field component of linear polarization waves polarized either in the y-direction or in the x-direction. The circular polarization means that the two mutually perpendicular electric field components have the same amplitude but the phase difference is π/2. Elliptical polarization corresponds to the case where the two components of the electric field are not equal in amplitude, and there is a phase difference between them. Polarization is useful in many areas of scientific research and practical application, such as astronomy, chemistry, display, industry test, life science microscopy [2], electronic communication, and so on. For example, in the field of electronic countermeasures, we often need to use antennas with horizontally polarized EM waves to suppress interference from vertically polarized EM waves. In satellite communication, it is often necessary to use circularly polarized EM waves to complete the communication due to the fact that circular polarization can keep the signal constant regardless of the anomalies existed in the ionosphere. Considering that EM waves with different polarization states are so widely used, it is especially important to control the polarization state or to convert the polarization state of EM waves effectively. Traditional devices used for polarization conversion are often designed based on the birefringence effect [3,4], such as grating [5], dichroic crystal [6], and twisted nematic crystals [7,8] etc. Since the refractive index difference of the birefringent material is small, therefore, in order to obtain a larger phase difference, the material needs to have a certain thickness. Furthermore, devices with polarization conversion function made of this material often have the disadvantages of not easy to miniaturize and integrate and narrow frequency band. In order to overcome these disadvantages, devices of polarization controlling based on metamaterials were introduced.