Michael A. Marcus

Ferroelectric polymers and their applications

The piezoelectric and pyroelectric polymer poly(vinylidene fluoride) (PVF2) was recently classified as a polymeric ferroelectric. The physical properties of PVF2 are reviewed to justify this definition. Applications are classified on the basis of transduction mechanism including electrical to mechanical, mechanical to electrical, thermal to mechanical, thermal to electrical, and optical to mechanical. Applications in each of these classifications are surveyed, and advantages and disadvantages of using polymeric ferroelectrics rather than more conventional materials are described.

Performance characteristics of piezoelectric polymer flexure mode devices

Abstract The design theory for a variety of piezoelectric polymer flexure mode devices is presented. Resonance and deflection behavior are discussed as well as output characteristics. Among the types of devices described are the unimorph, the bimorph, and the multimorph. The effects of electrodes and bonding layers are included in the analysis. Nonuniform polarization in the piezoelectric layers alters device performance. Useful flexure mode devices can be constructed from nonuniformly polarized piezoelectric polymers. Methods of preparing bimorphs in a single sheet are described, including temperature-gradient and field-reversal poling. Experimental results on a variety of flexure mode devices are compared with the theory. Applications of these flexure mode devices are also surveyed.

The deflection-bandwidth product of poly(vinylidene fluoride) benders and related structures

Abstract Resonance and deflection behavior are discussed for a variety of electrically driven flexure-type devices. The deflection-bandwidth product (DBWP) is defined, and it is shown that when energy transfer is nonessential, the DBWP is a useful figure of merit. For piezoelectric and magnetostrictive devices, the maximum DBWP is a function of materials parameters only and not device dimensions. Even though the piezoelectric constants of poly(vinylidene fluoride) (PVF2) are much lower than those of typical ceramics, the maximum DBWP is higher. Theoretical and experimental results show that piezoelectric bender “bimorph” performance can be improved by using a relatively thick, low-density, low-modulus bonding layer.

All-fiber optic coherence domain interferometric techniques

Traditional white-light scanning interferometers utilize bulk optic components mounted on a mechanical scanning mechanism. Many emerging applications for these interferometers require fiber optic probes. By design, such fiber compatible instruments are expensive and are limited to slow scan rates. A new “all-fiber” design approach is presented, which reduces the cost of the design and enables higher scan rates.

Depth dependence of piezoelectric activity in poly(vinylidene fluoride) transducers: Control and measurement

Double‐layer and multilayer poling experiments have been performed to determine the depth dependence of piezoelectric activity in poly (vinylidene fluoride) (PVF2) films. The depth dependence of activity is highly dependent on poling field and time. Removal of the poling field before cooling alters the activity distribution. When central conductive layers are present during poling, cathode activity is increased. When a thermal gradient occurs across the sample’s thickness during poling, the cool side is the more active. A bulk measurement of activity asymmetry in transducer films is described, and use of asymmetric films as flexure devices is discussed. Reversing the field during poling is useful in increasing asymmetric activity.

Controlling the piezoelectric activity distribution in poly(vinylidene fluoride) transducers

Abstract The depth dependence of piezoelectric activity of poly(vinylidene fluoride) (PVF2) films was determined under a variety of conditions. When films of PVF2 were poled in stacks without central conductive layers present, the resulting piezoelectric activity profile was strongly field dependent. Lower poling fields favored anode activity, whereas at higher poling fields cathode activity increased. When central conductive layers were present during poling, the cathode side was more active than the anode side if the samples were cooled with the poling field applied. When the field was removed before cooling, the center of the stack was most active. In samples poled in temperature gradients, the cool side, whether anode or cathode, was most active. A technique for determining the overall asymmetry in a single sheet is described, and use of asymmetric films as flexure devices is discussed.

Acoustic transducers for acoustic position sensing apparatus

To improve mass productivity of acoustic position sensing apparatus of the type wherein the position of an object is sensed with respect to a sensing port in an acoustic resonator, acoustic transducers for generating an acoustic signal in the resonator and for sensing the acoustic signal in the resonator comprise a sheet of poled piezoelectric material having electrodes on opposite sides thereof. The sheet is fixed over a transducer port in the acoustic resonator. Mass productivity is further improved by integrating a plurality of such acoustic transducers on a sheet of piezoelectric material by appropriately patterning the electrodes thereon.

Fiber optic interferometry for industrial process monitoring and control applications

Over the past few years we have been developing applications for a high-resolution (sub-micron accuracy) fiber optic coupled dual Michelson interferometer-based instrument. It is being utilized in a variety of applications including monitoring liquid layer thickness uniformity on coating hoppers, film base thickness uniformity measurement, digital camera focus assessment, optical cell path length assessment and imager and wafer surface profile mapping. The instrument includes both coherent and non-coherent light sources, custom application dependent optical probes and sample interfaces, a Michelson interferometer, custom electronics, a Pentium-based PC with data acquisition cards and LabWindows CVI or LabView based application specific software. This paper describes the development evolution of this instrument platform and applications highlighting robust instrument design, hardware, software, and user interfaces development. The talk concludes with a discussion of a new high-speed instrument configuration, which can be utilized for high speed surface profiling and as an on-line web thickness gauge.

Real-Time Distributed Fiber-Optic Temperature Sensing In The Process Environment

In this paper we describe application of fiber-optic distributed temperature sensing to the process monitoring and control environment. The measurement technique utilizes a modified optical time-domain reflectometer (OTDR) arrangement, where an excitation pulse is launched into the fiber, and a temperature-sensitive property of the backscatter is analyzed as a function of time. From this information we deduce the temperature profile along the length of the fiber. The fiber itself is used as the sensor, and the temperature sensitive property measured is the spontaneous anti-Stokes Raman scattering of the fiber core material. The optical fiber is installed throughout the environment to be monitored, and temperature profiles are logged as a function of time. The fiber used is standard communication-grade, graded-index multimode fiber, although certain applications require fibers with special coatings. Typically, a 2 km loop is measured in 12 seconds to a point resolution of + 1°C (2.5 sigma) with a sample separation of 5 m. The performance characteristics of the distributed temperature measurement system are described including optical design, fiber properties, splice, connector and coiling effects. Installation design principles are discussed together with the interplay between the physical installation and the performance of the instrument. This discussion includes the relationships between spatial resolution, temperature resolution and accuracy, coil length, measurement time, and the environment. Use of distributed temperature sensing in a simulated production environment is discussed, including process capability study measurements and on-line process monitoring and control. A brief application review is also given.

Multimodal imaging system for dental caries detection

Dental caries is a disease in which minerals of the tooth are dissolved by surrounding bacterial plaques. A caries process present for some time may result in a caries lesion. However, if it is detected early enough, the dentist and dental professionals can implement measures to reverse and control caries. Several optical, nonionized methods have been investigated and used to detect dental caries in early stages. However, there is not a method that can singly detect the caries process with both high sensitivity and high specificity. In this paper, we present a multimodal imaging system that combines visible reflectance, fluorescence, and Optical Coherence Tomography (OCT) imaging. This imaging system is designed to obtain one or more two-dimensional images of the tooth (reflectance and fluorescence images) and a three-dimensional OCT image providing depth and size information of the caries. The combination of two- and three-dimensional images of the tooth has the potential for highly sensitive and specific detection of dental caries.