Large-area PVDF thin films have been prepared and characterized for quasi-static and high frequency dynamic strain sensing applications. These films are prepared using hot press method and the piezoelectric phase (beta-phase) has been achieved by thermo-mechanical treatment and poling under DC field. The fabricated films have been characterized for quasi-static strain sensing and the linear strain-voltage relationship obtained is promising. In order to evaluate the ultrasonic sensing properties, a PZT wafer has been used to launch Lamb waves in a metal beam on which the PVDF film sensor is bonded at a distance. The voltage signals obtained from the PVDF films have been compared with another PZT wafer sensor placed on the opposite surface of the beam as a reference signal. Due to higher stiffness and higher thickness of the PZT wafer sensors, certain resonance patterns significantly degrade the sensor sensitivity curves. Whereas, the present results show that the large-area PVDF sensors can be superior with the signal amplitude comparable to that of PZT sensors and with no resonance-induced effect, which is due to low mechanical impedance, smaller thickness and larger area of the PVDF film. Moreover, the developed PVDF sensors are able to capture both A(0) and S-0 modes of Lamb wave, whereas the PZT sensors captures only A(0) mode in the same scale of voltage output. This shows promises in using large-area PVDF films with various surface patterns on structures for distributed sensing and structural health monitoring under quasi-static, vibration and ultrasonic situations. (C) 2010 Elsevier B.V. All rights reserved.

Characterization of a large-area PVDF thin film for electro-mechanical and ultrasonic sensing applications

This paper gives a bibliographical review of the finite-element methods (FEMs) applied to the analysis and simulation of smart materials and structures. The bibliography at the end of the paper contains references to papers, conference proceedings and theses/dissertations on the subject that were published between 1986-1997. The following topics are included: smart materials; smart components/structures; smart sensors and actuators; controlled structures technology; and other topics.

https://iopscience.iop.org/article/10.1088/0965-0393/6/3/007/pdf

Smart materials and structures - a finite-element approach: a bibliography (1986-1997)

This paper aims to report the results of an experimental study on the application of piezoelectric dynamic strain sensors for crack length measurement in fracture mechanics specimens. The performance of the piezoelectric sensors was assessed through fatigue crack propagation tests in compact tension (CT) specimens. Sensors of polarized polyvinilidene fluoride polymer (PVDF) were bonded to the back face of CT specimens, in the same manner as the electrical resistance strain gages installed for crack length measurement in the back face strain technique. The results showed that, mainly due to its high sensitivity to strain, the use of piezoelectric materials as dynamic strain sensors can contribute to the experimental investigation in the field of fracture mechanics.

Monitoring Fatigue Crack Growth in Compact Tension Specimens Using Piezoelectric Sensors

A unique acceleration transducer, using piezoelectric PVDF, has been developed for low-frequency vibration monitoring. The paper develops the theoretical model for this low-cost, robust sensor. The theoretical model is validated using experimental results from laboratory tests. The sensor was also installed in an underground potash mine alongside a commercial geophone for a three-month in-mine test producing results that show a close correspondence between the two transducers.

A PVDF transducer for low-frequency acceleration measurements.

This paper reviews wearable and unconstrained systems based on PVDF sensors in physiological signals monitoring. Since using wearable and unconstrained biomedical sensor systems for health monitoring is convenient and efficient, and piezoelectric polyvinylidene fluoride (PVDF) film has the advantages as flexibility, wide frequency response, low cost, easiness to fabricate, biocompatibility and light weight, many studies have focused on the PVDF film as sensors of wearable and unconstrained systems. Utilizing a modular design concept, the processing circuit of systems can be reorganized to implement different functions, so as to match different medical applications. This paper reviews key ideas and performance of the reported wearable and unconstrained systems based on PVDF sensors in physiological signals monitoring and the modular design concept. The various existing state of art practices of the wearable and unconstrained systems with PVDF sensors in measurement of physiological signals are also...

Wearable and unconstrained systems based on PVDF sensors in physiological signals monitoring: A brief review

Piezo-film sensors were employed in determining the dynamic response of [(0 deg/90 deg)4]s s-glass/epoxy laminates and 2024 aluminum specimens. Simple beam- and plate-type sensor equations were derived based on classical plate theory incorporating the linear piezoelastic constitutive relationship. A series of vibration and impact tests were conducted for the determination of structural dynamic response. Piezo-film sensors, with a thickness and area of 110 μm and 1×1 cm2, respectively, were connected directly to a voltage measurement device in these tests. The first three bending frequencies of the glass-fiber-reinforced plastic (GFRP) cantilever specimen were examined. Experimental results and those simulated by the MARC finite-element code were found to be in good agreement, with the difference between the two being less than five percent. At frequencies above 3 kHz, piezo-film transducers are capable of closely detecting structural dynamic response in the absence of charge amplification. At frequencies lower than approximately 3 kHz, however, the voltage measured directly from a piezo-film sensor underestimates structural response. A modified piezo-film sensor equation is thus proposed for lower frequency measurements. Effect of frequency and piezo-film's size on lower frequency attenuation is explicitly formulated based on a simple RC circuit analogy. Drop tests were also performed on clamped [(0 deg/90 deg)4]s GFRP laminates and aluminum targets, with nine piezo-film sensors being glued to the specimen's distal surface in order to determine the low-speed impact response. Specimen transient central deflection subjected to impact loading was identified based on test findings and the plate-type piezo-film sensor equation. The results were found to be in good agreement with the numerical solution obtained from the MARC finite-element code.

C. K. Chang

Papers

Characterization of piezo-film sensors for direct vibration and impact measurements