Scattering Matrix Measurement Research Articles

Converging rainbow trapping silencers for broadband sound dissipation in a low-speed ducted flow

Rainbow trapping filters (RTFs) have been so far investigated to achieve broadband unit sound absorption in closed-end duct terminations. However, opened RTFs have been scarcely explored to realize broadband low-frequency dissipation of sound waves while being traversed by a low speed flow. To bridge the gap, we propose a RTF composed of coiled cavities whose inner radius follows a flow-compliant converging profile, referred to as a converging coiled CCRTF silencer. An effective medium approach and the transfer matrix method (TMM) showed the ability of such devices to produce slow sound, impedance matching and minute sound reflection and transmission over a wide bandwidth, confirmed by finite element simulations and scattering matrix measurements without flow. A causal analysis revealed that a large density of wall resonators enhances the silencer performance while its bandwidth is driven by the coiling factor, convergent contraction ratio and cavities axial growth. Particle swarm optimization of these parameters led to a sub-wavelength CCRTF silencer with near-unit dissipation over 3.5 octaves from 200 Hz upwards. Extended TMM and aeroacoustic measurements showed resilience of the CCRTF performance under upstream or downstream propagation conditions for outlet Mach numbers below 0.16, thereby opening up applications like the design of silent convergent nozzles.

Analysis of the Influence of Polarization Measurement Errors on the Parameter and Characteristics Measurement of the Fully Polarized Entomological Radar

Measuring the orientation, mass and body length of migratory insects through entomological radar is crucial for early warnings of migratory pests. The fully polarized entomological radar is an efficient device for observing migratory insects by calculating insect parameters through the scattering matrix obtained from the target. However, the measured target scattering matrix will be affected by system polarization measurement errors, leading to errors in insect parameter calculation, while the related analysis is currently relatively limited. Therefore, the scattering matrix measurement process is modeled, followed by an analysis of the effects of different errors on orientation, mass and body length estimation. The influence of polarization measurement errors on insect scattering characteristics is also analyzed. The results present that for fixed polarization measurement errors, the measurement errors of insect orientation, mass and body length will vary with insect orientation in specific patterns, and the distribution of measured insect parameters will be drastically distorted compared to the true parameter distribution. In addition, polarization measurement errors could seriously disrupt the reciprocity and bilateral symmetry of the measured insect scattering matrix. These analyses and conclusions provide a good basis for eliminating the effects of polarization measurement errors and improving the accuracy of insect parameter measurement.

Optimal Control of Coherent Light Scattering for Binary Decision Problems.

Because of quantum noise fluctuations, the rate of error achievable in decision problems involving several possible configurations of a scattering system is subject to a fundamental limit known as the Helstrom bound. Here, we present a general framework to calculate and minimize this bound using coherent probe fields with tailored spatial distributions. As an example, we experimentally study a target located in between two disordered scattering media. We first show that the optimal field distribution can be directly identified using a general approach based on scattering matrix measurements. We then demonstrate that this optimal light field successfully probes the presence of the target with a number of photons that is reduced by more than 2 orders of magnitude as compared to unoptimized fields.

Uncertainty evaluation method of the scattering matrix measurements for the polarized scanning nephelometer

The polarized scanning nephelometer (PSN) is an instrument for measuring the multiangle scattering matrix of aerosol particles. Prior to being used, its measurement accuracy should be first verified. However, due to the complexity of the errors involved, it is very difficult to evaluate the measurement accuracy of the instrument reasonably, which limits the application of the PSN. In this work, taking di-ethyl-hexyl-sebacate droplets as an example, an uncertainty evaluation method of the scattering matrix measurements for the PSN is proposed. According to the measurement characteristics, the sources of uncertainty are divided into systematic effects and random effects. The corresponding evaluation method is then proposed for these two uncertainty categories, and the uncertainty introduced by systematic effects is investigated in depth via the Monte Carlo method. The evaluation results clearly show the variation trend of each uncertainty component as a function of the scattering angle in different matrix elements. The combined uncertainty is calculated and analyzed, and the result shows that the measurement uncertainty of the instrument is less than 0.0185, which verifies the accuracy of the instrument. This method can provide a reference for the accuracy evaluation of similar instruments.

On the application of scattering matrix measurements to detection and identification of major types of airborne aerosol particles: Volcanic ash, desert dust and pollen

Atmospheric aerosols play key roles in climate and have important impacts on human activities and health. Hence, much effort is directed towards developing methods of improved detection and discrimination of different types of aerosols. Among these, light scattering-based detection of aerosol offers several advantages including applications in both in situ and remote sensing devices. In this work, new scattering matrix measurements for two samples of airborne desert dust collected in Spain and China are reported. The average extrapolated scattering matrices of airborne desert dust and of volcanic ash at two wavelengths have been calculated and compared with the aim of finding criteria to distinguish these two types of aerosol. Additionally, the scattering matrix of cypress pollen has been measured and extrapolated to explore differences with mineral dust that can be exploited in atmospheric detection. Field measurements of the backscattering linear depolarization ratio δL(180°) are used to obtain information about non-sphericity and discrimination between fine and coarse aerosol. However, the average δL(180°) for the three types of aerosols considered in this work in the visible spectral range is δL(180°) = 0.40 ± 0.05. This shows that δL(180°) is not informative about the composition or morphology of irregular particles. By contrast, measurements of scattering matrix elements or depolarization ratios at different scattering angles may provide information about the structural differences of particles, and in particular may enable to differentiate airborne volcanic ash from desert dust, which are otherwise similar in terms of size and optical constants. Cypress pollen shows a characteristic degree of linear polarization curve that is very different from that of polydisperse irregular mineral dust. Light scattering field instruments and remote sensing methods could extract more information about the characteristics of aerosol particles if modifications were introduced to measure the phase curves of several scattering matrix elements or depolarization ratios.

Optimisation of a Polarisation Nephelometer

An analysis of the influence caused by polarization nephelometer parameters on the scattering matrix measurement accuracy in a non-isotropic medium is presented. The approximation errors in the actual scattering volume and radiation beam by an elementary scattering volume and an elementary radiation beam are considered. A formula for calculating the nephelometer base is proposed. It is shown that requirements to an irradiation source of a polarizing nephelometer, i.e. mono-chromaticity and high radiation intensity and directivity in a wide spectral range can be satisfied by a set of high brightness LEDs with a radiating (self-luminous) small size body. A 5-wavelength monochromatic irradiation source, with an emission flux of (0.15–0.6) W required for a polarization nephelometer, is described. The design of small-sized polarizing phase control units is shown. An electronic circuit of a radiator control unit based on an AVR-Atmega 8-bit microcontroller with feedback and drive control realized by means of an incremental angular motion sensor and a software PID controller is presented. Precise and smooth motion of the radiator is ensured by standard servo-driven numerical control mathematics and the use of precision gears. The system allows both autonomous adjustment of the radiator’s reference positions and adjustment by means of commands from a personal computer. Both the computer and microcontroller programs were developed with the use of free software, making it possible to transfer the programs to Windows‑7(10), Linux and embedded Linux operating systems. Communication between the radiator’s position control system and the personal computer is realised by means of a standard noise immune USB-RS485 interface.

Identification of Organic Matter Dispersions Based on Light Scattering Matrices Focusing on Soil Organic Matter Management.

The origin of organic matter, its spread, scattering, and functioning are influenced by the physical structure of liquid or dispersed media of organic matter. Refractive indices of fodder yeast grown on paraffin oil (paprin) and natural gas (gaprin) as well as Lycoperdon spore and organelles were measured by laser phase microscopy. The scattering matrices of aqueous suspensions of paprin, gaprin, and Lycoperdon spores were measured using a laser polarimeter with the scattering angle ranging from 20 to 150°. The experimentally measured scattering matrices have been approximated by the weighted sum of theoretically calculated scattering matrices using the T-matrix code developed by Mishchenko. Most of the particle radii in the filtered fraction of paprin and gaprin were within the range of about 0.05–0.12 μm. Particle radii of the Lycoperdon spore suspension were within the range of 0.4–2.4 μm, which corresponded to both whole spores and their separate organelles. A possibility of identifying a suspension by its scattering matrices was shown for a small difference in the real parts of the refractive index in the example of paprin and gaprin. The measurements of the light scattering matrix showed that for a small size parameter of about 1, the identification of paprin and gaprin can be based only on a difference in the particle shape. Refractive index difference is manifested for the size parameter values higher than 3. An example of a suspension consisting of micron-sized spores and their submicron organelles shows high sensitivity of the scattering matrix to the composition of the dispersed material. The presented data and models help to extrapolate the results of the light scattering matrix study to a vast spectrum of media of organic matter origin and functioning. This study focused on the Biogeosystem Technique (BGT*) transcendental methodology to manage soil as an arena of biodegradation and organic synthesis. A BGT*-based robotic system for intra-soil pulse continuous–discrete water and matter supply directly into the dispersed–aggregated physical structure of the soil media was developed. The system enables transformation of soil into a stable highly productive organic chemical bioreactor for better controlled nanoparticle biomolecular interactions and adsorption by biological and mineral media. The scattering matrix measurement unit is supposed to be used in the robotic system as a diagnostic tool for the dispersion composition of soil organic components.

Discrimination of Parallel and Perpendicular Insects Based on Relative Phase of Scattering Matrix Eigenvalues

Current vertical-beam entomological radars record the polarization direction corresponding to the maximal ventral-aspect radar cross section (RCS) as the insect’s orientation. For so-called “parallel” insects, this direction is indeed their orientation; but for “perpendicular” insects, it is at right angles to the orientation. Current entomological radars cannot discriminate the parallel and perpendicular cases. This article shows here that discrimination is possible using the relative phase of the scattering matrix (SM) eigenvalues. Multifrequency fully polarimetric ventral aspect SM measurements of 80 insect specimens of 12 species have been made in a microwave anechoic chamber. The relationship of the polarization direction corresponding to the maximal RCS and the radar frequency has been analyzed, and from these results a method of discriminating parallel and perpendicular insects, based on the relative phase of the SM eigenvalues, is proposed. The method is applicable to X- and Ku-band observations, with a high correct-identification rate, and can be used with both fully polarimetric entomological radars and coherent rotating-polarization units, but not with the noncoherent rotating-polarization configuration used in traditional vertical-looking radars (VLRs). Finally, the performance of the method is discussed, and it is found that it has better performance for middle and large insects at X-band and small and middle insects at Ku-band.

Measurement of the Scattering Matrix and Extinction Coefficient of the Chaff Corridor

This article investigates the strategies to measure the scattering matrix and the extinction coefficient of the chaff corridor. A complete error model is adopted to describe the power transmission properties of the indoor measurement system. Based on this model, a polaristic calibration method is employed to correct the measurement errors. After calibration, a scattering matrix measurement method for different types of chaff corridors is addressed. When dealing with the extinction coefficient measurements, Beer-Lambert's law is introduced to describe the power loss of the electromagnetic wave passing through the chaff corridor. According to this law, a method of the extinction coefficient measurement for the chaff corridor is proposed. Finally, simulations and measurements are conducted to verify the methods presented in this article and obtain the electromagnetic scattering properties of various types of chaff corridors. Experimental results show that the scattering matrix and extinction coefficient are not sensitive to the polarization of the incident wave for uniformly distributed chaff corridor. Besides, high attenuation occurs when electromagnetic wave passes through the chaff corridor.

Moving Target Scattering Matrix Measurement Using the Three Polarizations Scheme

For classical alternate measurement schemes, the motion of the target during polarization switching introduces additional phase errors in measuring the polarization scattering matrix (PSM). In this letter, we address the moving target PSM measurement problem by alternately transmitting three polarizations (3-Pol). We fully discuss the problem, including 3-Pol generation, the optimal polarization selection, and the corresponding PSM estimation, as a complete measurement approach. This measurement approach is robust to different PSMs, and its performance is not affected by the movement of the target. Compared with the classical schemes, this approach will benefit a 13-dB signal-to-noise ratio (SNR) increase for targets with small cross-polar components. Furthermore, when the SNR is greater than 15 dB, the mean of the polarized correlation coefficients is higher than 0.95. Conclusions presented in this letter are validated by the experimental results.

Influence of the frequency deviation on the simultaneous polarisation scattering matrix measurement

Based on a pair of linear frequency modulation waveforms with opposite slopes, the mathematical model of the influence of intermediate frequency deviation (IFD) and sampling frequency deviation (SFD) on simultaneous polarisation measurement is derived. An IFD and SFD joint estimation and calibration method is proposed in this article. Simulation and real data results show that the radar frequency stability can change the position and phase of the polarisation scattering matrix (PSM) measurement. The approach proposed in this article can regulate the peak deviation effectively, compensate the phase error and accurately acquire the four elements of PSM.

Effects of wideband waveforms on simultaneous scattering matrix measurement of manoeuvring targets

Both polarimetry and Doppler characteristics can be employed in remote sensing applications. Doppler information provides insight into the dynamic properties of radar targets, and polarimetry is associated with the intrinsic attributes of targets. Determining how to obtain accurate polarisation measurements from Doppler information has been a concern. For high-speed targets, the relativistic effect on radar wideband echoes may be notable. With the conventional matched filter, this scale effect may produce significant amplitude and phase errors between two columns of the polarisation scattering matrix (PSM), except for signal-to-noise ratio (SNR) loss. On the basis of the Taylor series expansion, the amplitude and phase expressions are derived in this study. Theoretical analysis shows that the amplitude and phase errors are related to the time–frequency allocation of the orthogonal waveforms and that the accuracy of the PSM is more susceptible to scale factors using frequency modulation waveforms than phase-coded waveforms. To suppress these amplitude and phase errors, a compensation method is proposed for orthogonal linear frequency modulation signals. Furthermore, the performances of the SNR loss and the velocity error effect are given. Finally, some numerical experimental results are provided to illustrate the effectiveness of the compensation.

Scattering Properties of a Suspension Containing Plate-like Particles and Their Aggregates

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Polarized light interaction with tissues.

This tutorial-review introduces the fundamentals of polarized light interaction with biological tissues and presents some of the recent key polarization optical methods that have made possible the quantitative studies essential for biomedical diagnostics. Tissue structures and the corresponding models showing linear and circular birefringence, dichroism, and chirality are analyzed. As the basis for a quantitative description of the interaction of polarized light with tissues, the theory of polarization transfer in a random medium is used. This theory employs the modified transfer equation for Stokes parameters to predict the polarization properties of single- and multiple-scattered optical fields. The near-order of scatterers in tissues is accounted for to provide an adequate description of tissue polarization properties. Biomedical diagnostic techniques based on polarized light detection, including polarization imaging and spectroscopy, amplitude and intensity light scattering matrix measurements, and polarization-sensitive optical coherence tomography are described. Examples of biomedical applications of these techniques for early diagnostics of cataracts, detection of precancer, and prediction of skin disease are presented. The substantial reduction of light scattering multiplicity at tissue optical clearing that leads to a lesser influence of scattering on the measured intrinsic polarization properties of the tissue and allows for more precise quantification of these properties is demonstrated.

Scattering matrix measurements and light-scattering calculations of calcite particles

We present measurements of the complete scattering matrix as a function of the scattering angle of a sample of calcite particles collected near Lecce, Italy. The measurements are done at a wavelength of 647 nm in the scattering angle range 3 ◦ −177 ◦ . FESEM and SEM images show that the sample consists largely of flake-like particles. Ten different flake-like geometries are randomly generated and their scattering properties are simulated with DDA for sizes from 0.1 µm to 1 µm. Some preliminary comparisons of the simulations and the measurements are shown.

Spatial polarization characteristics and scattering matrix measurement of orthogonal polarization binary array radar

Polarimetry is an important trend in the development of modern radar. The technique for measuring polarization scattering property of the target is the key for polarization radar realization, but it faces challenges in engineering. Here, a new theoretical model for target scattering characteristic measurement radar, named orthogonal polarization binary array radar (OPBAR), is proposed. The spatial polarization characteristics of the radar antennas are addressed. A new polarimetric algorithm that needs only one channel is designed. The polarization scattering matrix measurement can be implemented by processing received signal in a short time interval while antenna’s beam mechanically scans the target. Through compactness field microwave dark room experiment, measurments of dynamic broadband polarimetry on OPBAR have been conducted and the validity of research work has been demonstrated. The result is helpful to exploiting the capability of current radar systems and enhancing their information acquiring and processing capacity.

A New Target Scattering Matrix Measurement Algorithm Based on Polarization Characteristics of Sum-and-Difference Beam

该文建立了一种基于常规单脉冲体制的目标全极化散射矩阵测量算法。首先证明了该型雷达天线具有复杂的极化结构，并且对回波信号的极化特性有一定的敏感性。利用单脉冲雷达和差通道的极化特性在获取目标角度信息的同时利用一个脉冲重复周期即可完成目标极化散射矩阵的测量，降低了全极化单脉冲雷达研发的系统复杂度和设计成本，通过电磁计算和仿真分析验证了上述研究的正确性。这对于开发现有雷达装备的极化测量处理能力、提升其抗干扰和目标识别能力具有一定的启发和指导意义。

The signal selection and processing method for polarization measurement radar

Based on the ambiguity function, a novel signal processing method for the polarization measurement radar is developed. One advantage of this method is that the two orthogonal polarized signals do not have to be perpendicular to each other, which is required by traditional methods. The error due to the correlation of the two transmitting signals in the traditional method, can be reduced by this new approach. A concept called ambiguity function matrix (AFM) is introduced based on this method. AFM is a promising tool for the signal selection and design in the polarization scattering matrix measurement. The waveforms of the polarimetric radar are categorized and analyzed based on AFM in this paper. The signal processing flow of this method is explained. And the polarization scattering matrix measurement performance is testified by simulation. Furthermore, this signal processing method can be used in the inter-pulse interval measurement technique as well as in the instantaneous measurement technique.

Target Detection beneath Canopy Using PolSAR Images

Polarization information is applied to detect target underneath forest by synthetic aperture imaging. At flrst, hard-in-loop PolSAR system is constructed in an anechoic chamber, then the resolution and sampling interval of system are analyzed. In order to obtain accurate polarization data, polarization scattering matrix measurement and calibration method are used. The data of echoes are processed by an improved back-projection algorithm. After comparing the difierence of images, target beneath canopy is detected according to the best combination polarization information. In the experiment, a PNA transmits two signals by wide-band anten- nas, and another two antennas receive returned signals coming back to the PNA. The antennas maintain downward at an incident angle of 20 degrees with ground. The area of scene is 1m 2 , which consists of three flr trees and a scaled tank. The height of trees is about 1meter, and the scaled tank is located beneath trees. The frequency is working at L-band, and the frequency sampling interval is 12.5MHz. Scanner moves 3 meters along the center of scene, and the spa- tial sampling interval is 1.5cm. The resolutions of cross-range and ground-range are 0.17m and 0.15m respectively. The results show that HH polarization image has a good efiect for target detection beneath canopy at L-band.

Forest type discrimination using calibrated C-band polarimetric SAR data

To promote the unique polarimetric capability of RADARSAT-2, the Canada Centre for Remote Sensing (CCRS) has investigated the potential of fully polarimetric C-band synthetic aperture radar (SAR) for forest type discrimination. Six forest types in the Mer Bleu region of eastern Ontario were considered in this study: mixed forest, poplar, red pine, white pine, a mixed forest of red and white pines, and white spruce. Multi-date and multiple incidence angle acquisitions were acquired over the study site with the Convair-580 polarimetric SAR under leafy (summer) and no-leaves (winter) conditions. In addition to the conventional linear polarizations, HH, HV, and VV, various polarimetric discriminators, which were synthesized from the scattering matrix measurements, were investigated. It is shown that the radiometric intensity of the conventional C-band SAR polarizations HH, HV, and VV can only perform a limited discrimination of various tree species. The polarization information provided by fully polarimetric SARs clearly improves forest type discrimination under leafy and no-leaves conditions and permits the demonstration of the significance of SAR illumination angle on forest scattering mechanisms.