The current state of the art of optical fiber sensors is reviewed. The principles of operation are detailed and the various types of fiber sensors are outlined. Achievable performance and limitations are discussed and a description of technology used to fabricate the sensor is presented. The characteristics of acoustic, magnetic, gyro, laser diode, and other sensors are described. Trends in the development of this sensor technology and expected application areas are briefly outlined.

Optical fiber sensor technology

A brief review of applications of piezoelectric bimorphs is presented. The constituent equations which describe the behavior of piezoelectric bimorphs for various mechanical boundary conditions are derived. The internal energy density of infinitesimally small volume elements in thermodynamic equilibrium is calculated in the presence of a voltage on the electrodes, a clamped cantilever beam condition on one side of the beam and a set of three different classical boundary conditions on the other side of the beam. These are a mechanical moment M at the end of the beam, a force F perpendicular to the beam, applied at its tip, and a uniformly distributed body force p.

The total internal energy content is calculated by integrating over the entire volume of the beam. Two different beam configurations are considered: parallel polarizations of the two adjoining elements of the beam with an internal electrode; and antiparallel orientation without an internal electrode.

The canonical conjugate of the moment is calculated as the angular deflection at the tip of the beam α, while that of the force at the tip is the local vertical deflection δ. The canonical conjugate of the uniform load on the beam is found to be the volume displacement V of the beam. The canonical conjugate of the voltage across the electrodes is the charge on the electrodes. The equations are given in the direct form, with external parameters (M, V), (F, V), and (p, V) as independent variables and also in a linear combination with (M, F, p, V) as variables.

These constituent equations can be used to calculate the behavior of the bimorph under any condition that can be described as a linear combination of forces at the tip, moments at the tip and uniform loads on the entire beam. This allows us to use the bimorph as a black box, without having to consider its internal movement or charges.

The constituent equations of piezoelectric bimorphs

Periodic phase changes in the 10(-6) -rad region have been induced and detected in a single-mode all-fiber Mach- Zehnder interferometer by stretching the fiber with a piezoelectric cylinder driven at frequencies between 40 and 10(4) Hz.

Measurement of small phase shifts using a single-mode optical-fiber interferometer

The discovery of highly active piezoelectric polymer materials was first reported in 1969. Since then an enormous amount of research work has been conducted, mainly aimed at discovering the structure and properties of these fascinating materials with the further aim of improving their piezoelectric and pyroelectric behaviour. An equally vast amount of literature devoted to applications of these polymers has appeared and even a cursory glance at all this shows that they have been applied as the basis for a wide range of devices. The subject has now reached a degree of maturity and in the nondestructive testing field, there is perhaps a 'niche market' emerging for transducers based on polyvinylidene fluoride and its derivatives. In certain areas such as miniature under water hydrophones, piezoelectric polymers have become the material of choice. This being so, it is appropriate to review the subject.

https://iopscience.iop.org/article/10.1088/0957-0233/6/3/001/pdf

Industrial applications of piezoelectric polymer transducers

The authors discuss the basic principles and applications of optical-fiber sensor technology, outlining the various sensing mechanisms which can be utilized to influence the propagation of light in an optical fiber and the various sensor types-intensity, phase-modulated (interferometric), intrinsic, and extrinsic. Sensors for the measurement of temperature, pressure, liquid level, chemical parameters, acoustic effect, magnetic field, and rotation (gyroscope) are briefly described. >

/pdf/applications-of-fiber-optic-sensors-2oe6vgpuzy.pdf

Applications of fiber-optic sensors

A polyvinylidene fluoride (PVF 2 ) phase shifter is characterized in terms of amplitude response linearity, frequency response uniformity, and ultimate sensitivity to electric field. Phase-drift compensation with this PVF 2 device is demonstrated in a Mach-Zehnder fiber interferometer. The compensator can be operated at the \pi/2 -phase mode for maximum sensitivity in detection applications, or the π-phase mode for maximum frequency mixing efficiency.

/pdf/an-electric-field-sensor-utilizing-a-piezoelectric-17u83lxbya.pdf

Kee Koo

Papers

An electric field sensor utilizing a piezoelectric polyvinylidene fluoride (PVF 2 ) film in a single-mode fiber interferometer