Modeling thin-film piezoelectric polymer ultrasonic sensors

Abstract

This paper presents a model suitable to design and characterize broadband thin film sensors based on piezoelectric polymers. The aim is to describe adequately the sensor behavior, with a reasonable number of parameters and based on well-known physical equations. The mechanical variables are described by an acoustic transmission line. The electrical behavior is described by the quasi-static approximation, given the large difference between the velocities of propagation of the electrical and mechanical disturbances. The line parameters include the effects of the elastic and electrical properties of the material. The model was validated with measurements of a poly(vinylidene flouride) sensor designed for short-pulse detection. The model variables were calculated from the properties of the polymer at frequencies between 100 Hz and 30 MHz and at temperatures between 283 K and 313 K, a relevant range for applications in biology and medicine. The simulations agree very well with the experimental data, predicting satisfactorily the influence of temperature and the dielectric properties of the polymer on the behavior of the sensor. Conversely, the model allowed the calculation of the material dielectric properties from the measured response of the sensor, with good agreement with the published values.

Reducing the capacitance of piezoelectric film sensors

“…The measured impulse response was analyzed using the model presented in Ref. 7, where the mechanical variables are considered as an acoustic transmission line and the electrical behavior by the quasi-static approximation. It is important to remark that, from the electrical point of view, the quasistatic description is still appropriate given the large difference between the velocities of propagation of the electrical and mechanical disturbances.…”

High-speed real-time heterodyne interferometry using software-defined radio

“…Compared to inorganic piezoelectric materials, the internal losses (both mechanical and electrical) are much larger in polymers [33]. In consequence, it is very important to measure the frequency dependence of the electromechanical response for the validation of design models and fabrication of transducers based on piezoelectric polymers [34,35].…”

“…At point B (center of the PVDF film) the displacement per unit volt has a higher value than at the other two points at the edges (that are practically the same). These differences are due to the interaction between higher vibration modes over the surface of the piezoelectric film and in-plane displacements [34,35]. To highlight the difference between the device response and the intrinsic properties of the polymer, in Fig.…”

Caracterización de Líquidos por Técnica Fotoacústica: Estudio de Sensores Piezoeléctricos de Banda Ancha

“…Los polímeros piezoeléctricos, como el polifluoruro de vinilideno (PVDF) y sus copolímeros, son muy usados en la construcción de sensores debido a sus propiedades físicas que permiten su utilización en gran cantidad de aplicaciones. Estos materiales son flexibles, están disponibles como películas delgadas, tienen un gran ancho de banda acústica, y sus valores de impedancia acústica están próximos al del agua lo que los vuelve interesantes para su aplicación en el estudio de líquidos [7], [8]. Las propiedades aquí detalladas dependen, entre otras cosas, fuertemente de cómo el film es adherido al substrato o cuerpo del sensor.…”