Advanced Magnetostrictive Materials for Sonar Applications

Piezoelectric or magnetostrictive materials can be utilised as active materials for electroacoustic underwater transducers. Piezoceramic materials gained edge over the conventional magnetostrictive materials during 1940s due to their unique electro-acoustic properties. At present, inspite of passive sonars there is a need of low-frequency high-power active sonars for the Navy. This led toresearch for new activematerials with competing characteristics to that of the existing piezo transducers. The discovery of a giant magnetostrictive material, commercially known as Terfenol-D, led to a breakthrough in the development of a new generation of sonar transducers. Now, the materials (including composites) as well as sensors are commercially available. A new generation of transducers have emerged in ocean-related areas like acoustic tomography, longrange underwater communication, geophysical exploration, oil well exploration, etc.Indian Institute of Technology Madras, Chennai, has also developed the basic material technology a few years back. At present, in India, National Institute of Ocean Technology, Chennai, is developing underwater transducers utilising giant magnetostrictive materials as well as piezoelectric materials for marine applications like sub-bottom profiling (seafloor mapping) and long-range underwater communications. A prototype of a portable, low-frequency medium power transmitter operating over a wide-frequency range has been developed. The main advantage of this transducer is its simplicity in design. In this paper, (he recent developments in material processes, importance of device-oriented material characterisation, and transducer design aspects have been emphasised. Some results on the underwater performance of a wide-band transducer have also been presented. These materials also have ultrasonic applications, capable of revolutionising the processing industry

Advanced Magnetostrictive Materials for Sonar Applications

Piezoelectric or magnetostrictive materials can be utilised as active materials for electroacoustic underwater transducers. Piezoceramic materials gained edge over the conventional magnetostrictive materials during 1940s due to their unique electro-acoustic properties. At present, inspite of passive sonars there is a need of low-frequency high-power active sonars for the Navy. This led toresearch for new activematerials with competing characteristics to that of the existing piezo transducers. The discovery of a giant magnetostrictive material, commercially known as Terfenol-D, led to a breakthrough in the development of a new generation of sonar transducers. Now, the materials (including composites) as well as sensors are commercially available. A new generation of transducers have emerged in ocean-related areas like acoustic tomography, longrange underwater communication, geophysical exploration, oil well exploration, etc.Indian Institute of Technology Madras, Chennai, has also developed the basic material technology a few years back. At present, in India, National Institute of Ocean Technology, Chennai, is developing underwater transducers utilising giant magnetostrictive materials as well as piezoelectric materials for marine applications like sub-bottom profiling (seafloor mapping) and long-range underwater communications. A prototype of a portable, low-frequency medium power transmitter operating over a wide-frequency range has been developed. The main advantage of this transducer is its simplicity in design. In this paper, (he recent developments in material processes, importance of device-oriented material characterisation, and transducer design aspects have been emphasised. Some results on the underwater performance of a wide-band transducer have also been presented. These materials also have ultrasonic applications, capable of revolutionising the processing industry

Fast response Antiwindup PI speed controller of Brushless DC motor drive: Modeling, simulation and implementation on DSP

Most of the Brushless DC (BLDC) motors drive adopts proportional, integral and derivative (PID) controller and pulse width modulation (PWM) scheme for speed control. Hence, BLDC motor drive has strong saturation characteristics. The saturation results in a typical windup phenomenon. The paper presents an Antiwindup drive for BLDC motor. An Antiwindup controller (AWC) has been used in the paper. AWC has been modeled in MATLAB/Simulink and comparison has been done between conventional PI controller and AWC at different starting loads. Dynamic characteristics of the BLDC motor drive have been examined and results are presented and discussed in detail in this paper. Details of DSP based experimental validation of the simulated results are also presented here

A study on the effect of pulsed power ultrasound waves on marine biofouling

2169-2174<span style="font-size:9.0pt;line-height: 115%;font-family:" times="" new="" roman";mso-fareast-font-family:calibri;mso-bidi-font-family:="" "times="" roman";background:white;mso-ansi-language:en-us;mso-fareast-language:="" en-us;mso-bidi-language:ar-sa"="" lang="EN-US">Ultrasonic technique is one of the promising non-invasive technologies to control biofilm formation on the marine substratum.  A prototype ultrasonic system was designed and developed to control biofouling in the marine environment. The Ultrasonic technique was utilized to control the biofilm formation on copper test coupons suspended in a continuous seawater flow through system. The colonization of microorganisms promotes settlement of higher order organisms; therefore, deactivation of microorganisms is likely to affect the fouling density. <span style="font-size:9.0pt;line-height: 115%;font-family:" times="" new="" roman";mso-fareast-font-family:"times="" roman";="" mso-bidi-font-family:"times="" roman";mso-ansi-language:en-us;mso-fareast-language:="" en-us;mso-bidi-language:ar-sa"="" lang="EN-US">Ultrasonic sound waves at 25 kHz with an electric drive power of 500 watts were used to control aquatic biofouling and growth in an open seawater circulation experimental setup. The ultrasonic waves create microscopic cavitations which damages the outer cell structure of microorganisms destroying them and preventing them from growing around the ultrasound exposure areas.<span style="font-size:9.0pt; line-height:115%;font-family:" times="" new="" roman";mso-fareast-font-family:calibri;="" mso-bidi-font-family:"times="" roman";background:white;mso-ansi-language:en-us;="" mso-fareast-language:en-us;mso-bidi-language:ar-sa"="" lang="EN-US"> The experiments were conducted continuously over a period of 21 days and were repeated several times to ensure reliability. A reduction in the microorganism activation was observed on the ultrasound exposed area besides preventing damages to the structure of the test coupon. Based on the encouraging results, a low cost prototype ultrasonic digital system controlled by pre-programmed microchips was custom built and the same is being planned for further studies in the frequency range 20 – 40 kHz. </span

Techniques adopted in the post processing of active sonar data from Royapuram site-off Chennai

164-171<span style="font-size:9.0pt;font-family: " times="" new="" roman","serif";mso-fareast-font-family:"times="" roman";mso-ansi-language:="" en-gb;mso-fareast-language:en-us;mso-bidi-language:hi"="" lang="EN-GB">A buried object detection SONAR has been developed by the marine sensors and systems group of National Institute of Ocean Technology and the analysis of the data from a specific site is reported in the paper.  Handling the unpredictable noise is a major concern in sonar signal processing, especially in buried object detection sonar systems. To improve the signal to noise ratio and also to preserve the boundaries of targets, special post processing techniques are to be applied. Signal averaging is found to be a useful technique in this regard and this paper compares and analyzes various averaging techniques including moving averaging, exponential averaging, and median filter. The exponential averaging with median filter is found to be one of the best suitable methods for noise reduction in detecting buried objects in shallow waters, since it significantly improves the signal to noise ratio by preserving the boundaries of targets. It is observed that the original sonar image with 6% noise level is improved to 0.03 to 0.04 noise variance using the combination of exponential moving average and median filter and the same trend is observed up to 35% noise level when corrupted by Gaussian noise. Performance evaluation of the techniques has been carried out and is quantitatively verified with the data collected during the sea trials.</span