Polymer based MEMS and microfluidic devices have the advantages of mechanical flexibility, lower fabrication cost and faster processing over silicon based ones. Also, many polymer materials are considered biocompatible and can be used in biological applications. A valuable class of polymers for microfabricated devices is piezoelectric functional polymers. In addition to the normal advantages of polymers, piezoelectric polymers can be directly used as an active material in different transduction applications. This paper gives an overview of piezoelectric polymers based on their operating principle. This includes three main categories: bulk piezoelectric polymers, piezocomposites and voided charged polymers. State-of-the-art piezopolymers of each category are presented with a focus on fabrication techniques and material properties. A comparison between the different piezoelectric polymers and common inorganic piezoelectric materials (PZT, ZnO, AlN and PMN?PT) is also provided in terms of piezoelectric properties. The use of piezopolymers in different electromechanical devices is also presented. This includes tactile sensors, energy harvesters, acoustic transducers and inertial sensors.

https://iopscience.iop.org/article/10.1088/0964-1726/23/3/033001/pdf

A review of piezoelectric polymers as functional materials for electromechanical transducers

This paper provides a detailed overview of developments in transducer materials technology relating to their current and future applications in micro-scale devices. Recent advances in piezoelectric, magnetostrictive and shape-memory alloy systems are discussed and emerging transducer materials such as magnetic nanoparticles, expandable micro-spheres and conductive polymers are introduced. Materials properties, transducer mechanisms and end applications are described and the potential for integration of the materials with ancillary systems components is viewed as an essential consideration. The review concludes with a short discussion of structural polymers that are extending the range of micro-fabrication techniques available to designers and production engineers beyond the limitations of silicon fabrication technology.

/pdf/new-materials-for-micro-scale-sensors-and-actuators-an-21qnaonn0l.pdf

New materials for micro-scale sensors and actuators An engineering review

The market for piezoceramic components is dominated by lead-based PZT materials containing more than 60 wt.% lead. Since lead is a toxic heavy metal, it has become a great concern how to eliminate the use of PZT by replacing it with non-harmful materials while maintaining comparable piezoelectric properties. This was the objective of the European LEAF project within the GROWTH programme, ending in February 2004. In this project, alkali niobates were proposed as alternative piezoceramic materials, and special emphasis was given to potassium sodium niobate, (K, Na)NbO3. The partners of the project have developed lead-free ceramics that can be a competitive alternative to PZT for certain applications. Considerations on powder synthesis and ceramic processing, obtained properties and examples of industrial applications will be presented.

Lead-free piezoceramics based on alkali niobates

Ultrasonics in food processing

Piezoelectric microelectromechanical systems (MEMS) offer the opportunity for high-sensitivity sensors and large displacement, low-voltage actuators. In particular, recent advances in the deposition of perovskite thin films point to a generation of MEMS devices capable of large displacements at complementary metal oxide semiconductor-compatible voltage levels. Moreover, if the devices are mounted in mechanically noisy environments, they also can be used for energy harvesting. Key to all of these applications is the ability to obtain high piezoelectric coefficients and retain these coefficients throughout the microfabrication process. This article will review the impact of composition, orientation, and microstructure on the piezoelectric properties of perovskite thin films such as PbZr1−xTixO3 (PZT). Superior piezoelectric coefficients (e31, f of −18 C/m2) are achieved in {001}-oriented PbZr0.52Ti0.48O3 films with improved compositional homogeneity on Si substrates. The advent of such high piezoelectric responses in films opens up a wide variety of possible applications. A few examples of these, including low-voltage radio frequency MEMS switches and resonators, actuators for millimeter-scale robotics, droplet ejectors, energy scavengers for unattended sensors, and medical imaging transducers, will be discussed.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/AC28E0B7FC52ADDE14E1F58F59416494/S0883769400003614a.pdf/div-class-title-piezoelectric-thin-films-for-sensors-actuators-and-energy-harvesting-div.pdf

Piezoelectric Thin Films for Sensors, Actuators, and Energy Harvesting

Effects of high-intensity high-frequency ultrasound on ageing rate, ultrastructure and some physico-chemical properties of beef

A model is proposed to predict the electroelastic moduli of 0-3 connectivity piezo-composites from which parameters such as longitudinal wave velocity and thickness mode coupling factor can be deduced. The composite, a polymer loaded with ceramic particles, is represented by a unit cell, and a matrix manipulation is shown to be a practical way to perform a generalization of the series and parallel analysis used for 2-2 connectivity composites. The anisotropy of the ceramic phase is taken into account, and its effect on the properties of the composite is shown. The model is then used to optimize composite performance and to choose the two constituents through comparison of results obtained using several commercial polymers and ceramics.

A matrix method for modeling electroelastic moduli of 0-3 piezo-composites

A screen-printed PZT thick film with a final thickness of about 40 mum was deposited on a porous PZT substrate to obtain an integrated structure for ultrasonic transducer applications. This process makes it possible to decrease the number of steps in the fabrication of high-frequency, single-element transducers. The porous PZT substrates allow high acoustic impedance and attenuation to be obtained, satisfying transducer backing requirements for medical imaging. The piezoelectric thick films deliver high electromechanical performance, comparable to that of standard bulk ceramics (thickness coupling factor over 45%). Based on these structures, high-frequency transducers with a center frequency of about 25 MHz were produced and characterized. As a result, good sensitivity and axial resolution were obtained in comparison with similar transducers integrating a lead titanate (PT) disk as active material. The two transducers were integrated into a high-frequency imaging system, and comparative skin images are shown

High-frequency transducers based on integrated piezoelectric thick films for medical imaging

Ferroelectric ceramics based on a solid solution between a PZT ferroelectric phase and a relaxor phase from the lead–nickel–niobium system are characterised. Two different mixed-oxide routes have been used in order to compare the dielectric, piezoelectric and elastic properties of the two ceramics obtained. The characterisation method is based on measurements of the electrical impedance of samples as a function of frequency and allows the determination of the thickness mode resonance parameters. Results are given as a function of frequency (5 to over 25 MHz) and temperature (ambient to over 230°C). Finally, several simulations, using a K.L.M. model, of medical transducers are performed. The results show that the ceramic is well adapted for medical imaging applications, in particular for array transducer configurations.

High-frequency and high-temperature electromechanical performances of new PZT–PNN piezoceramics

A model previously developed for pure 0-3 connectivity piezocomposites has been extended to 3-3 connectivity. This matrix method allows the prediction of the effective electroelastic moduli of a piezocomposite according to its connectivity. It is used to optimize composite performance by choosing the optimal constituents for each phase. A simple combination of the results for 0-3 and 3-3 connectivities allows the effective proportion of 3-3 connectivity to be defined in highly loaded 0-3 piezocomposites. This theoretical analysis has been used to evaluate effective proportions of 3-3 connectivity in five composite samples. The values obtained are shown to be a function of the ceramic volume fraction and fabrication process. The results of this study were used to optimize the fabrication process.

Marc Lethiecq

Papers

Effects of high-intensity high-frequency ultrasound on ageing rate, ultrastructure and some physico-chemical properties of beef

A matrix method for modeling electroelastic moduli of 0-3 piezo-composites

High-frequency transducers based on integrated piezoelectric thick films for medical imaging

High-frequency and high-temperature electromechanical performances of new PZT–PNN piezoceramics

Modeling of highly loaded 0-3 piezoelectric composites using a matrix method