Optical, Acoustic, Magnetic, and Mechanical Sensor Technologies

Krzysztof Iniewski

• Publisher: CRC Press
• Year: 2017
• Print ISBN: 9781439869758
• eBook ISBN: 9781351832847
• Topic: Computer Science
• Subtopic: Computer Graphics
• Index: Computer Science

Light on physics and math, with a heavy focus on practical applications, Optical, Acoustic, Magnetic, and Mechanical Sensor Technologies discusses the developments necessary to realize the growth of truly integrated sensors for use in physical, biological, optical, and chemical sensing, as well as future micro- and nanotechnologies.

Used to pick up sound, movement, and optical or magnetic signals, portable and lightweight sensors are perpetually in demand in consumer electronics, biomedical engineering, military applications, and a wide range of other sectors. However, despite extensive existing developments in computing and communications for integrated microsystems, we are only just now seeing real transformational changes in sensors, which are critical to conducting so many advanced, integrated tasks.

This book is designed in two sections—Optical and Acoustic Sensors and Magnetic and Mechanical Sensors—that address the latest developments in sensors.

The first part covers:

• Optical and acoustic sensors, particularly those based on polymer optical fibers
• Potential of integrated optical biosensors and silicon photonics
• Luminescent thermometry and solar cell analyses
• Description of research from United States Army Research Laboratory on sensing applications using photoacoustic spectroscopy
• Advances in the design of underwater acoustic modems

The second discusses:

• Magnetic and mechanical sensors, starting with coverage of magnetic field scanning
• Some contributors' personal accomplishments in combining MEMS and CMOS technologies for artificial microsystems used to sense airflow, temperature, and humidity
• MEMS-based micro hot-plate devices
• Vibration energy harvesting with piezoelectric MEMS
• Self-powered wireless sensing

As sensors inevitably become omnipresent elements in most aspects of everyday life, this book assesses their massive potential in the development of interfacing applications for various areas of product design and sciences—including electronics, photonics, mechanics, chemistry, and biology, to name just a few.

Part 1

Optical and Acoustic Sensors

1 Optical Fiber Sensors

Rogério Nogueira, Lúcia Bilro, Nélia Alberto, Hugo Lima, and João Lemos Pinto

CONTENTS

Introduction

Intensity-Based Sensors

Transmission and Reflection Schemes

Macrobending or Microbending Sensors

Spectrally Based Sensors

Evanescent Wave-Based Sensors

Partial or Total Removal of the Cladding

Tapers

Side Polishing with Core Exposure

Self-Reference Techniques

Phase-Based Sensors

Phase Detection

Mach–Zehnder

Michelson

Fabry–Perot

Sagnac

Polarization Control

Wavelength-Based Sensors

Multiparameter Sensors

FBG Inscription Methods

Interrogation of FBG Sensors

References

INTRODUCTION

The laser invention in the 1960s and the advances toward low-loss optical fiber in the 1970s stimulated further scientific advances, both in telecommunications and in optical fiber sensors. With the first sensing applications of optical fibers the interest of the scientific community quickly grew for this new technology, and the number of research groups in optical fiber sensing rapidly increased.

The research on optical fiber sensors produced and continues to give life to a variety of measurement techniques for different applications, competing with traditional sensing methods, mainly in niche areas, from the airspace to the medical industry. The success of this technology relies on the intrinsic flexibility, low weight, immunity to electromagnetic interference, passive operation, and high dynamic range, associated with remote monitoring and multiplexing capabilities, which allows optical fiber sensors to succeed in difficult measurement situations where conventional sensors fail.

The technology is now in a mature state, with different applications already using commercial optical fiber sensors as a standard. This includes not only massive deployment for real-time structural health monitoring in airspace, civil and oil industry but also more specific applications such as environment monitoring, biochemical analyses, or gas leak monitoring in hazardous environments.

Optical fiber sensors operate by modifying one or more properties of the light passing through the sensor, when the parameter to be measured changes. An interrogation scheme is then used to evaluate the changes in the optical signal by converting them to a signal that can be interpreted. In this way, depending on the light property that is modified, optical fiber sensors can be divided into three main categories: intensity-, phase-, and wavelength-based sensors.

INTENSITY-BASED SENSORS

Of the range of optical fiber sensors reported in the literature, intensity-based sensors represent one of the earliest and perhaps the simplest type of optical fiber sensors. In applications where the precise signal intensity measurement is not critical or required, it has been shown that intensity-based systems are a valid solution for biomedical, structural health, and environmental applications. Generally, the system is based on a light source, an optical fiber, and a photodetector (or optical spectrum analyzer—OSA). Miniature solid-state light sources and photodetectors are available commercially, allowing the construction of rugged and portable hardware acquisition systems.

Intensity-based sensors offer the advantages of ease of fabrication, low price–performance ratio, and the simplicity of signal processing. These make them highly attractive, particularly in applications where the cost of implementation frequently excludes the use of other significantly more expensive optical fiber systems. Although high resolution and refined measurement capability are achievable using grating sensors and interferometric fiber sensors, it is not always necessary and, as such, less costly intensity-based sensing methods may offer an option in industry.

A wide number of intensity-based sensors are being presented and developed using different schemes; they can be grouped into two major classes: intrinsic- and extrinsic-type sensors. In the extrinsic type, the optical fiber is used as a means of transporting light to an external sensing system. In the intrinsic scheme, the light does not have to leave the optical fiber to perform the sensing function. In this class of sensors, the fiber itself plays an active role in the sensing function and this may involve the modification of the optical fiber structure.

TRANSMISSION AND REFLECTION SCHEMES

An additional classification scheme usually used is related to the way the optical signal is collected. If the receiver and emitter are at opposite ends of the fiber or fibers, the sensor is of a transmission kind, otherwise it is of reflection.

A straightforward example of the first situation is the intensity modulation based on the dependence of the power transmitted from one fiber to another on their separation. This basic sensing principle was used for structural health monitoring purposes by Kuang et al. [1]. The authors presented a comprehensive study where the performance of this sensor was evaluated in quasistatic tensile tests. The optical fiber sensor was surface-attached to an aluminum alloy specimen and revealed a high degree of strain linearity. Free vibration tests based on a cantilever beam configuration were also conducted to assess the dynamic response of the sensor. An impulse-type loading test was also performed to evaluate the ability to detect the various modes of vibration.

With respect to reflection methods, there are some variations, but most of them use reflecting surfaces to couple the light in the fiber, as presented by Binu et al. [2] for their fiber optic glucose sensor based on the changes in the refractive index (RI) with glucose concentration. Other sensors are based on Fresnel reflection mechanisms [3,4] or special geometries of the fiber tip [5]. One interesting application is described by Baldini et al. [6] with their optical fiber sensor for dew detection inside organ pipes. The working principle is based on the change in the reflectivity observed on the surface of the fiber tip when a water layer is formed on its distal end. Intensity changes around 35% were measured.

MACROBENDING OR MICROBENDING SENSORS

Several mechanisms in an optical fiber weaken the propagated signal, such as absorption and diffusion by impurities, Rayleigh scattering, ultraviolet and infrared absorption, and microbending and macrobending. Despite many efforts to minimize the power losses in an optical fiber, its dependen...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Preface
• Editor
• Contributors
• PART 1 Optical and Acoustic Sensors
• PART 2 Magnetic and Mechanical Sensors
• Index