Temporal statistics of irradiance fluctuations in an underwater turbulent medium.

Expressions for the temporal covariance function and temporal frequency spectrum for a plane wave propagation in an underwater turbulent medium are developed analytically. Temporal correlation in moving natural water is presented, which is shown to be dependent upon the moving velocity, the delay between two instants of time, propagation distance, average temperature, and average salinity concentration. Coherence time and zero crossing time also are calculated. The results show that the velocity of the moving natural water has a significant impact on the temporal correlation of irradiance fluctuations. Additionally, the propagation distance, average temperature, average salinity concentration, and temperature-salinity gradient ratio also impact the temporal correlation up to a certain level.

Review of breast screening: Toward clinical realization of microwave imaging.

Microwave imaging (MI) technology has come a long way to introduce a noninvasive, inexpensive, fast, convenient, and safe screening tool for clinical breast monitoring. However, there is a niche between the existing understanding of MI by engineers versus clinicians. Our manuscript targets that niche and highlights the state of the art in MI technology compared to the existing breast cancer detection modalities (mammography, ultrasound, molecular imaging, and magnetic resonance). The significance of our review article is in consolidation of up-to-date breast clinician views with the practical needs and engineering challenges of a novel breast screening modality. We summarize breast tissue abnormalities and highlight the benefits as well as potential drawbacks of the MI as a cancer detection methodology. Our goal is to present an article that MI researchers as well as practitioners in the field can use to assess the viability of the MI technology as a competing or complementary modality to the existing means of breast cancer screening.

A novel discrete particle swarm optimization algorithm for estimating dielectric constants of tissue.

Global optimization algorithms basically create a set of solutions, classify them, and then search for the best answer, iteratively. In this paper, a new discrete particle swarm optimization algorithm is proposed to estimate the permittivity arrangements of lossy multilayer structures, which represent body tissue models. Microwave imaging (AMI) is the modality in which the proposed algorithm is used for reconstructing the image. The main objective of this article is to depict the flexibility of PSO-based methods in handling complex problems expeditiously and successfully. Our new algorithm improves the estimation time by 85% as compared to our previous proposed one. Here, the impact of various parameters, namely, the AMI frequency, the immersion medium, the number of agents, the smoothing coefficient, and the maximum velocity, on the estimation performance are studied in terms of the maximum estimation error. It is demonstrated that by choosing the parameters correctly, one can achieve estimation results with a maximum error less that 10% in only 0.1 minute.

Permittivity estimation for breast cancer detection using particle swarm optimization algorithm.

In this paper, particle swarm optimization (PSO) algorithm is used to estimate the permittivities of the tissue layers at microwave frequency band. According to the literature, microwave radiometry (MWR) is potentially a promising cancer detection technique. In addition, breast cancer is an appropriate candidate of MWR due to the breast's exclusive physiology. Several algorithms have been evaluated for analyzing the measurement data and solving the inverse scattering problem in MWR, and different levels of accuracy have been reported. In this paper, the potential of PSO in solving this problem is demonstrated at 1-2.25 GHz. Two distinct algorithms are developed for the two considered scenarios. In the first scenario, we assume no a priori knowledge of the tissue under the test, whereas, in the second scenario, a priori knowledge is assumed. It is noteworthy that, there are only a few research articles studying PSO for permittivity estimation. However, since these studies underestimate the loss encountered by the test samples, the methods are not valid for body tissue case. Here, measurement-based loss coefficients, reported in the existing literature, are included in the calculations. It is shown that the algorithm converges relatively fast, and, distinguishes between different tissues with an acceptable accuracy.

On the scintillation index of a multiwavelength Gaussian beam in a turbulent free-space optical communications channel.

The scintillation statistics of a multiwavelength Gaussian optical beam are characterized when the beam is subjected to a turbulent optical channel. It is assumed that the level of turbulence in the atmosphere ensures a weak-turbulence scenario and that fluctuations in the signal intensity are due to variations in the refractive index of the medium, which in turn are caused by regional temperature variations due to atmospheric turbulence. Furthermore, it is assumed that the propagation path is nearly horizontal and that the heights of the transmitter and receiver justify a near-ground propagation assumption. The Rytov approximation is used to arrive at the desired results. Furthermore, it is assumed that the first- as well as second-order perturbation terms are present in modeling the impact of atmosphere-induced scintillation. Numerical results are presented to shed light on the performance of multiwavelength optical radiation in weak turbulence and to underscore the benefits of the proposed approach as compared with its single-wavelength counterpart in combating the effect of turbulence. Furthermore, it is shown that if the separation of wavelengths used is sufficiently large, wavelength separation affects the scintillation index in a measurable way.

Scintillation index of a multiwavelength beam in turbulent atmosphere.

We characterize the scintillation index of a multiwavelength plane-wave optical beam that is subjected to a turbulent optical channel. It is assumed that the level of turbulence in the atmosphere ensures a weak-turbulence scenario and that the turbulence is due to the fluctuations in the index of refraction of the medium. It is assumed that the propagation path is nearly horizontal and that the heights of the transmitter and receiver justify a near-ground propagation assumption.