L. Ciocci Brazzano

Bio: L. Ciocci Brazzano is an academic researcher from University of Buenos Aires. The author has contributed to research in topics: Piezoelectricity & Monte Carlo method. The author has an hindex of 5, co-authored 7 publications receiving 59 citations. Previous affiliations of L. Ciocci Brazzano include National Scientific and Technical Research Council.

Electromechanical characterization of piezoelectric polymer thin films in a broad frequency range

Abstract: Piezoelectric materials are usually characterized using resonant methods. However, piezoelectric polymers are used in broadband devices, thus requiring characterization over a wide range of frequencies. In this work, we present a non-resonant method for the broadband electromechanical characterization of piezoelectric polymer thin films. The procedure is based on measuring the complex capacitance of a sample of known geometry under three conditions: free, blocked and immersed in a fluid of known acoustic properties. The behaviour of the sample under study is modelled as a one-dimensional transducer and treated as a two-port network that relates the measurable electrical and mechanical variables. Also, the sample is considered as a free-space radiator when immersed in a fluid. The method determines the intensive and the equivalent circuit parameters of piezoelectric polymer films, allowing the characterization of elastic and electrical properties in a broad frequency range. In order to test the method, we performed isothermal capacitance measurements on a sample of poly(vinylidene fluoride) at a temperature of 298 K. The sample was measured along the direction of the poling field and in the frequency range from 10 Hz to 10 MHz. The results given by the method agree with those reported by other authors.

Parametric modeling of wideband piezoelectric polymer sensors: Design for optoacoustic applications.

Abstract: In this work, we present a three-dimensional model for the design of wideband piezoelectric polymer sensors which includes the geometry and the properties of the transducer materials. The model uses FFT and numerical integration techniques in an explicit, semi-analytical approach. To validate the model, we made electrical and mechanical measurements on homemade sensors for optoacoustic applications. Each device was implemented using a polyvinylidene fluoride thin film piezoelectric polymer with a thickness of 25 μm. The sensors had detection areas in the range between 0.5 mm2 and 35 mm2 and were excited by acoustic pressure pulses of 5 ns (FWHM) from a source with a diameter around 10 μm. The experimental data obtained from the measurements agree well with the model results. We discuss the relative importance of the sensor design parameters for optoacoustic applications and we provide guidelines for the optimization of devices.

Broadband dielectric characterization of piezoelectric poly(vinylidene fluoride)thin films between 278 K and 308 K

Abstract: This work describes the dielectric properties of piezoelectric poly(vinylidene fluoride) (PVDF) thin films in the frequency and temperature ranges relevant for usual applications. We measured the isothermal dielectric relaxation spectra of commercial piezoelectric PVDF thin films between 10 Hz to 10 MHz, at several temperatures from 278 K to 308 K. Measurements were made for samples in mechanically free and clamped conditions, in the direction of the poling field (perpendicular to the film). We found that the imaginary part of the dielectric relaxation spectra of free and clamped PVDF samples is dominated by a peak, above 100 kHz, that can be characterized by a Havriliak-Negami function. The characteristic time follows an Arrhenius dependence on temperature. Moreover, the spectra of the free PVDF samples show two additional peaks at low frequencies which are associated with mechanical relaxation processes. Our results are important for the characterization of piezoelectric PVDF, particularly after the stretching and poling processes in thin films, and for the design and characterization of a broad range of ultrasonic transducers.

Generation of sub-microsecond quasi-unipolar pressure pulses.

Abstract: We present a method to generate sub-microsecond quasi-unipolar pressure pulses. Our approach is based on the laser irradiation of a thin copper wire submerged in water. The acoustic waveforms were recorded using two different, well characterized, wideband detection techniques: piezoelectric and optical interferometry. The results show that the irradiated target behaves as an omnidirectional source. Moreover, the peak pulse pressure linearly depends on the laser fluence and the source size. From the results, we propose an empirical equation for the spatial and temporal profile of the pressure pulse. The method has several advantages: ease of implementation, high repeatability, wide ultrasonic bandwidth and quasi-unipolar time profile. These features lead to potential applications of this acoustic source in ultrasonic characterization such as transducer systems, materials or passive devices.

Linear piezoelectric sensor for optoacoustic tomography: electroacoustic characterization

Abstract: In previous work we presented the implementation and electric characterization of a broadband piezoelectric polymer sensor with linear geometry, based on a thin film of polyvinylidene fluoride. In this paper we performed the electroacoustic characterization of the same sensor through the measurement of its response to short acoustic pulses (<50 ns), using a parametric model. We determined the polymer properties (relaxation time and acoustic attenuation), the reflexion coefficients of the water-polymer and polymer-substrate interfaces, the ultrasonic beam pattern and the sensitivity of the detector. The results of this work show that the implemented sensor is suitable for optoacoustic tomography detection systems.

Photoacoustic imaging in biomedicine

Abstract: Photoacoustic imaging is a promising method for visualizing biological tissues with optical absorbers. This article provides an overview of the rapidly developing field of photoacoustic imaging. Photoacoustics, the physical basis of photoacoustic imaging, is analyzed briefly. The merits of photoacoustic technology, compared with optical imaging and ultrasonic imaging, are described. Various imaging techniques are also discussed, including scanning tomography, computed tomography and original detection of photoacoustic imaging. Finally, some biomedical applications of photoacoustic imaging are summarized.

Towards the sEMG hand: internet of things sensors and haptic feedback application

Abstract: With the trend going on in ubiquitous computing, everything is going to be connected to the Internet and its data will be used for various progressive purposes, creating not only information from it, but also, knowledge and even wisdom. Internet of Things (IoT) is becoming important because the amount of data could make it possible to create more usefulness and develop smart applications for the users. Meanwhile, it mainly focuses on how to enable general objects to see, hear, and smell the physical world for themselves, and make them connected to share the observations. In this paper, we focus our attention on the integration of artificial sensory perception and haptic feedback in sEMG hands, which is an intelligent application of the IoT. Artificial sensory perception and haptic feedback are essential elements for amputees with myoelectric hands to restore the grasping function. They can provide information to users, such as forces of interaction and surface properties at points of contact between hands and objects. Recent advancements in robot tactile sensing led to development of many computational techniques that exploit this important sensory channel. At the same time, Surface electromyography (sEMG) is perhaps most useful for providing insight into how the neuromuscular system behaves. Therefore, integration of sEMG technology, artificial sensation and haptic feedback plays an important role in improving the manipulation performance and enhancing perceptual embodiment for users. This paper provides sEMG technologies that involve Multichannel sEMG electrodes array and processing methods, and then reviews current state-of-the-art of artificial sensation and haptic feedback. Drawing from advancements and taking into design considerations of each feedback modality and individual haptic technology, the paper outline challenging issues and future developments.

Investigation on crystalline structure and dielectric relaxation behaviors of hot pressed poly(vinylidene fluoride) film

Abstract: The dielectric relaxation behaviors of hot pressed poly(vinylidene fluoride) (PVDF) film have been studied using dielectric spectroscopy in the frequency domain from 20 Hz to 5 MHz at temperatures between 20 °C and 200 °C. Crystalline/amorphous interphase is suggested with methods of FTIR, XRD, and DSC. Frequency and temperature dependence of dielectric spectroscopy reveals the relaxation behavior and structural dynamics of the samples, and three types of relaxation processes are suggested, α Ac relaxation process contributed by the hopping transport process near the periphery of conduction band or valence zones at Fermi energy, α c relaxation process related to the structure change of crystal lattice trapped dipoles in crystalline regions, and α a relaxation process arising from segmental dipole rearrangement of interphases in amorphous regions. Cole-Cole and Havriliak-Negami experimental equations were utilized to analyze these relaxation processes, and differences of Arrhenius parameters for α Ac and α c relaxation processes obtained from Cole-Cole and Havriliak-Negami equations were discussed in detail. Activity energy of different relaxation processes obtained from Arrhenius equation and VFT equation indicates non-single thermal activation mechanism for hot pressed PVDF film.

Electromechanical characterization of piezoelectric polymer thin films in a broad frequency range

Abstract: Piezoelectric materials are usually characterized using resonant methods. However, piezoelectric polymers are used in broadband devices, thus requiring characterization over a wide range of frequencies. In this work, we present a non-resonant method for the broadband electromechanical characterization of piezoelectric polymer thin films. The procedure is based on measuring the complex capacitance of a sample of known geometry under three conditions: free, blocked and immersed in a fluid of known acoustic properties. The behaviour of the sample under study is modelled as a one-dimensional transducer and treated as a two-port network that relates the measurable electrical and mechanical variables. Also, the sample is considered as a free-space radiator when immersed in a fluid. The method determines the intensive and the equivalent circuit parameters of piezoelectric polymer films, allowing the characterization of elastic and electrical properties in a broad frequency range. In order to test the method, we performed isothermal capacitance measurements on a sample of poly(vinylidene fluoride) at a temperature of 298 K. The sample was measured along the direction of the poling field and in the frequency range from 10 Hz to 10 MHz. The results given by the method agree with those reported by other authors.

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.