No abstract

Recently, more and more attention is paid to protect sensitive data transmitting across network.Currently,there are methods which use RDH with cover image also as information to transfer. To ensure confidentiality of cover image, it is encrypted and data hiding is done in encrypted image. In real-time scenarios we need to use color images as cover image and large amount of data to hide in image. The standard encryption methods which encrypt every bit of cover image waste large amount of time for encryption and decryption process. Our proposed methods use chaotic encryption to secure cover image which selectively encrypt some of the bits in image using confusion and diffusion methods. Since our method use RDH using reserving room in advance approach original cover can be losslessly recovered after extraction of embedded data. All the existing methods embed data by reversibly vacating room in the encrypted images. But these methods may result in some errors on image restoration and data extraction. In proposed method image recovery and data extraction are free of any error and achieves real reversibility.

One of t h e high power limitations quite often encountered in modern sonar systems is caused by t h e 'mutual interaction effect' among t h e densely packed elements of projector arrays. This will cause severe complex effects at higher drive levels.This effect c a n be minimised by restructuring t h e array f o r m a t with suitable selection of appropriate inter-element spacing. The design considerations of uniform linear projector a r r a y formats t h a t minimise t h e mutual interaction effect a r e presented in this paper. The radiation pattern and array gain of t h e proposed array a r e found t o be improved, as far as c e r t a i n signal and noise models a r e concerned.

Closely packed multi-element transducer arrays are extensively used in underwater applications for achieving better directionality and longer transmission range. With the current tendency of extending their operation toward lower frequency and particularly near resonance, the acoustic interaction among the elements grows stronger and in turn will degrade the predicted transmitting characteristics. This troublesome effect is much alleviated in uniform planar arrays by restructuring it with the optimal interelement spacing at which the interaction force is minimum [P.M. Joseph and P. R. Saseendran Pillai, Acoust. Lett. 12 (11), 190—193 (1989)]. It has been seen from the results of computation that a further reduction in interaction can be achieved by incorporating the nonuniform array concept. A simple method for predicting the optimum configuration of element locations that reduce the interaction to a lower level, without altering the aperture dimension, is proposed in this paper. Here, the element locations are dispersed in accordance with Gaussian distributed random numbers by keeping the optimum spacing as the mean. Even though a large standard deviation value will greatly reduce interaction, a reasonable value is chosen, as large deviations produce deteriorated beams. This optimally formulated array does not exhibit any grating lobes nor does its radiation pattern differ much from the conventional λ/2 spaced and restructured arrays.

The transmitting and receiving characteristics of sonar transducer arrays depend on various factors like its geometry, number of elements, source strength, relative phases of the elements, etc. An array with narrow main beam and low sidelobes is desirable for a variety of applications. But, these are conflicting requirements. One of the requirements can be achieved only at the cost of the other. It is the designer’s choice to select the parameters depending on the nature of application. Due to mechanical and electrical limitations, the measured array parameters are found to differ from the theoretically formulated ones, especially at higher drive levels. An array design package has been developed and presented in this paper for predicting the optimum array, based on the requirements of the user, taking into account various high-power electrical and mechanical limitations. In order to make the package more user friendly, the array design software has been split into different modules, each carrying out a specific task like array shape selection, element shape selection, power level selection, mode selection, etc.