P.A. Sorichetti

Modeling thin-film piezoelectric polymer ultrasonic sensors.

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

We present a novel design for large area, wideband, polymer piezoelectric sensor with low capacitance. The large area allows better spatial resolution in applications such as photoacoustic tomography and the reduced capacitance eases the design of fast transimpedance amplifiers. The metalized piezoelectric polymer thin film is segmented into N sections, electrically connected in series. In this way, the total capacitance is reduced by a factor 1/N(2), whereas the mechanical response and the active area of the sensor are not modified. We show the construction details for a two-section sensor, together with the impedance spectroscopy and impulse response experimental results that validate the design.

A Bayesian method for analysing relaxation spectra

Abstract The knowledge of electrical and mechanical properties of material, relies on a precise analysis of the relaxation spectra. We explore the ability of a Bayesian method to achieve an accurate estimation of spectral parameters. We implemented a parallel-tempering Markov-chain Monte Carlo algorithm and used it to fit simulated and measured spectra. An exhaustive testing of the code shows that it presents an extremely good performance, accurately fitting complex spectra under strong noise and overlapping components. We conclude that this technique is quite suitable for relaxation spectra analysis, complementing classical methods.

Pulsed chemical HF laser using graphite continuous electrodes for transverse discharge stabilization

We report results obtained in the operation of a chemical HF laser using a mixture of SF6 and technical grade C3H8 reacting in a transverse high‐voltage discharge in which a pair of inexpensive continuous electrodes of polycrystalline graphite are used as the only means for stabilizing the discharge and avoiding the formation of arcs during excitation of the laser medium. Energies of up to 60 mJ per pulse in stable operation are obtained from a 0.1‐l volume.

Introduction to Biodiesel Production

Biodiesel [1, 2, 3, 4, 5] is a liquid biofuel obtained by chemical processes from vegetable oils or animal fats and an alcohol that can be used in diesel engines, alone or blended with diesel oil.

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

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.

Wideband quad optical sensor for high-speed sub-nanometer interferometry

This paper describes the design and performance of a low-noise and high-speed optical sensor that provides two output signals in quadrature from the simultaneous detection of four phase-shifted interferograms. The sensor employs four high-speed photodiodes and high-speed, low-noise transimpedance amplifiers. The optical and electronic design was optimized for high-speed displacement measurement interferometry, over a broad range of operating frequencies. Compared to other experimental schemes, the sensor is simpler and of lower cost. The performance of the sensor is demonstrated by characterizing a piezoelectric transducer for ultrasonic applications. We measured displacements between 38 pm and 32 nm with 6% relative uncertainty, in the frequency range from 1 to 2 MHz.

Sensores piezoeléctricos para aplicaciones optoacústicas: Efectos de los procesos de relajación

This work presents the theoretical analysis of the effects of dielectric relaxation on the response of polymer piezoelectric sensors. In systems that obtain spatial information from temporal signals, such as optoacoustic tomography, the accurate characterization of transducers is very important. There are many works in the literature about reconstruction algorithms assuming ideal piezoelectric sensors. However, the distortions introduced by polymeric broadband ultrasonic sensors have been less treated. In consequence, a model is necessary to assess the relative importance of these effects in comparison to other factors that limit the resolution of the image.

Interferometría óptica dinámica para la determinación del coeficiente piezoeléctrico en polímeros

Piezoelectric polymers are of great interest due to their physical properties that allow their use in many applications. Their are particularly important for biomedical applications. Moreover, broadband sensor development requires a reliable system to measure the piezoelectric coefficient of these materials. In this work, we propose an interferometric scheme to measure this coefficient on a polyvinylidene fluoride sample in the frequency range between 100 Hz and 10 kHz using a Michelson interferometer with quadrature detection. The results were compared with an indirect method based on dielectric spectroscopy.

Laser-induced bubble generation on a gold nanoparticle: A nonsymmetrical description.

The modeling of bubbles initiated by laser-irradiated nanoparticles is of interest for many applications. There is at present no comprehensive physical picture for all the stages of the process. We present an alternative approach with a key assumption: the vapor bubble evolves adjacent to the nanoparticle. To take into account the irreversible evolution, the statistical rate theory was used, thus avoiding the introduction of extra ad hoc parameters. Model results agree well with published data and our measurements. The only free parameter, the thermal boundary conductance, can be obtained by adjusting the model to the experimental data.