Underwater Acoustic Sensors Based on Fiber Bragg Gratings

We report on recent results obtained with a fiber optic hydrophone based on the intensity modulation of the laser light in a FBG (Fiber Bragg Grating) under the influence of the sound pressure. In order to control the behavior of the hydrophone in terms of sensitivity and bandwidth, FBGs have been coated with proper materials, characterized by different elastic modulus and shapes. In particular, new experiments have been carried out using a cylindrical geometry with two different coating, showing that the sensitivity is not influenced by the shape but by the transversal dimension and the material characteristics of the coating

Design and Instrumentation of a Measurement and Calibration System for an Acoustic Telemetry System

The Juvenile Salmon Acoustic Telemetry System (JSATS) is an active sensing technology developed by the U.S. Army Corps of Engineers, Portland District, for detecting and tracking small fish. It is used primarily for evaluating behavior and survival of juvenile salmonids migrating through the Federal Columbia River Power System to the Pacific Ocean. It provides critical data for salmon protection and development of more “fish-friendly” hydroelectric facilities. The objective of this study was to design and build a Measurement and Calibration System (MCS) for evaluating the JSATS components, because the JSATS requires comprehensive acceptance and performance testing in a controlled environment before it is deployed in the field. The MCS consists of a reference transducer, a water test tank lined with anechoic material, a motion control unit, a reference receiver, a signal conditioner and amplifier unit, a data acquisition board, MATLAB control and analysis interface, and a computer. The fully integrated MCS has been evaluated successfully at various simulated distances and using different encoded signals at frequencies within the bandwidth of the JSATS transmitter. The MCS provides accurate acoustic mapping capability in a controlled environment and automates the process that allows real-time measurements and evaluation of the piezoelectric transducers, sensors, or the acoustic fields. The MCS has been in use since 2009 for acceptance and performance testing of, and further improvements to, the JSATS

Integrated optical pressure sensors in silicon-on-insulator

An optical pressure sensor can be useful in many applications where electronics fall short (e.g., explosive environments). We have fabricated and characterized compact, integrated optical pressure sensors on a silicon-on-insulator platform using ring resonators and Mach-Zehnder interferometers. The silicon substrate is locally etched using KOH to produce very thin membranes of 3.28 mu m. Measurements have shown that spectral features in our devices can shift up to 370 pm going from 0 to 80 kPa

Reliable Fiber Sensor System with Star-Ring-Bus Architecture

This work presents a novel star-ring-bus sensor system and demonstrates its effectiveness. The main trunk of the proposed sensor system is a star topology and the sensing branches comprise a series of bus subnets. Any weakness in the reliability of the sensor system is overcome by adding remote nodes and switches to the ring and bus subnets. To construct the proposed star-ring-bus sensor system, a fiber ring laser scheme is used to improve the signal-to-noise ratio of the sensor system. The proposed system increases the reliability and capacity of fiber sensor systems

A Cabled Acoustic Telemetry System for Detecting and Tracking Juvenile Salmon: Part 1. Engineering Design and Instrumentation

In 2001 the U.S. Army Corps of Engineers, Portland District (OR, USA), started developing the Juvenile Salmon Acoustic Telemetry System, a nonproprietary sensing technology, to meet the needs for monitoring the survival of juvenile salmonids through eight large hydroelectric facilities within the Federal Columbia River Power System (FCRPS). Initial development focused on coded acoustic microtransmitters and autonomous receivers that could be deployed in open reaches of the river for detection of the juvenile salmonids implanted with microtransmitters as they passed the autonomous receiver arrays. In 2006, the Pacific Northwest National Laboratory began the development of an acoustic receiver system for deployment at hydropower facilities (cabled receiver) for detecting fish tagged with microtransmitters as well as tracking them in two or three dimensions for determining route of passage and behavior as the fish passed at the facility. The additional information on route of passage, combined with survival estimates, is used by the dam operators and managers to make structural and operational changes at the hydropower facilities to improve survival of fish as they pass the facilities through the FCRPS

Design and characterisation of long period grating (LPG) - based optical fibre sensors for acoustic wave detection

Fibre optic sensors have demonstrated a broad range of commercial potential due to their intrinsic characteristics such as low loss, very small size, light weight and immunity to electromagnetic interference. Representing one type of optical fibre sensors, long period gratings (LPGs) have shown a high sensitivity to a number of parameters, including temperature, strain, refractive index and bending, therefore they have been explored widely for a range of potential sensing applications. This thesis is focused on the design, implementation and evaluation of LPGs for acoustic wave detection. In doing so, the LPG-based sensor has been evaluated and optimized under low frequency conditions (up to 3 kHz) both in air and underwater, with varying acoustic pressure values. This complements the research widely reported for the detection of ultrasounds. The LPG-based sensor, fixed between two pillars with one pillar being movable, is found to be sensitive over a specific frequency range with a minimum detectable sound pressure to be 63dB (ref 1μPa) in water and 66.8dB (ref 20μPa) in air. The sensor has demonstrated a linear response to the variation of the amplitude of the acoustic pressure applied. The sensor performance, by varying the acoustic frequencies, acoustic pressure amplitude and the bending curvature, fits well with the theoretical model derived from the bending effect of the LPG. Both the in-air and underwater tests of the LPG-based sensor have confirmed the potential of using optical fibre sensors for acoustic signal detection and for working in harsh working conditions, where conventional acoustic sensors have shown some limitations