Wyniki wyszukiwania - BazTech

1

Influence of process-material conditions on the structure and biological properties of electrospun polyvinylidene fluoride fibers

Zaszczyńska A., Sajkiewicz P. Ł., Gradys A., Tymkiewicz R., Urbanek O., Kołbuk D.

Bulletin of the Polish Academy of Sciences. Technical Sciences

|

2020

|

Vol. 68, nr 3

627--633

EN

Polyvinylidene fluoride (PVDF) is one of the most important piezoelectric polymers. Piezoelectricity in PVDF appears in polar b and ɣ phases. Piezoelectric fibers obtained by means of electrospinning may be used in tissue engineering (TE) as a smart analogue of the natural extracellular matrix (ECM). We present results showing the effect of rotational speed of the collecting drum on morphology, phase content and in vitro biological properties of PVDF nonwovens. Morphology and phase composition were analyzed using scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR), respectively. It was shown that increasing rotational speed of the collector leads to an increase in fiber orientation, reduction in fiber diameter and considerable increase of polar phase content, both b and g. In vitro cell culture experiments, carried out with the use of ultrasounds in order to generate electrical potential via piezoelectricity, indicate a positive effect of polar phases on fibroblasts. Our preliminary results demonstrate that piezoelectric PVDF scaffolds are promising materials for tissue engineering applications, particularly for neural tissue regeneration, where the electric potential is crucial.

2

Thick Film Transducers for High Frequency Coded Ultrasonography

Nowicki A., Lewandowski M., Wójcik J., Tymkiewicz R., Lou-Moller R., Wolny W., Zawada T.

Archives of Acoustics

|

2011

|

Vol. 36, No. 4

945-954

EN

Recently a new technology of piezoelectric transducers based on PZT thick film has been developed as a response to a call for devices working at higher frequencies suitable for production in large numbers at low cost. Eight PZT thick film based focused transducers with resonant frequency close to 40 MHz were fabricated and experimentally investigated. The PZT thick films were deposited on acoustically engineered ceramic substrates by pad printing. Considering high frequency and nonlinear propagation it has been decided to evaluate the axial pressure field emitted (and reflected by thick metal plate) by each of concave transducer differing in radius of curvature – 11 mm, 12 mm, 15 mm, 16 mm. All transducers were activated using AVTEC AVG-3A-PS transmitter and Ritec diplexer connected directly to Agilent 54641D oscilloscope. As anticipated, in all cases the focal distance was up to 10% closer to the transducer face than the one related to the curvature radius. Axial pressure distributions were also compared to the calculated ones (with the experimentally determined boundary conditions) using the angular spectrum method including nonlinear propagation in water. The computed results are in a very good agreement with the experimental ones. The trans- ducers were excited with Golay coded sequences at 35–40 MHz. Introducing the coded excitation allowed replacing the short-burst transmission at 20 MHz with the same peak amplitude pressure, but with almost double center frequency, resulting in considerably better axial resolution. The thick films exhibited at least 30% bandwidth broadening comparing to the standard PZ 27 transducer, resulting in an increase in matching filtering output by a factor of 1.4–1.5 and finally resulting in a SNR gain of the same order.

3

Annular Array Transducer and Matched Amplifier for Therapeutic Ultrasound

Secomski W., Nowicki A., Wójcik J., Lewandowski M., Walczak M., Tymkiewicz R.

Archives of Acoustics

|

2010

|

Vol. 35, No. 4

653-660

EN

The use of therapeutic ultrasound continues to grow. A focused ultrasonic wave can increase the tissue temperature locally for the non-invasive cancer treatment or other medical applications. The authors have designed a seven-element annular array transducer operating at 2.4 MHz. Each element was excited by sine burst supplied by a linear amplifier and FPGA control circuits. The acoustic field, generated by a transducer was initially numerically simulated in a computer and next compared to water tank hydrophone measurements performed at 20, 40 and 60 mm focal depth. The results showed good agreement of the measurements with theory and the possibility to focus the ultrasound in the preselected area. The total acoustic power radiated by the annular array was equal to 2.4 W.

4

Scattering of ultrasonic wave on a model of the artery

Wójcik J., Powałowski T., Tymkiewicz R., Lamers A., Trawiński Z.

Archives of Acoustics

|

2006

|

Vol. 31, No. 4

471-479

EN

The study was aimed at elaboration of a mathematical model to describe the process of acoustic wave propagation in an inhomogeneous and absorbing medium, whereas the wave is generated by an ultrasonic probe. The modelling process covered the phenomenon of ultrasonic wave backscattering on an elastic pipe with dimensions similar to the artery section. Later on, the numerical codes were determined in order to calculate the fields of ultrasonic waves, as well as backscattered fields for various boundary conditions. Numerical calculations make it possible to define the waveforms for electric signals that are produced when ultrasonic waves, being reflected and backscattered by an artery model, are then received by the ultrasonic probe. It is the signal which pretty well corresponds with the actual RF signal that is obtained during measurements at the output of an ultrasonic apparatus.

5

Numerical and experimental pressure determination in the very near field of a piezoelectric transducer

Filipczyński L., Kujawska T., Wójcik J., Tymkiewicz R.

Archives of Acoustics

|

2001

|

Vol. 26, no. 3

223-233

EN

Measurements in the very near field of piezoelectric transducers are fundamental for many ultrasonic problems. In such cases also the transducer vibrations should be known to perform mathematical models of radiated beams. Acoustic pressure measurements near to the transducer surface can give the necessary information. The pressure of the radiated wave at the transducer surface corresponds to its normal vibration velocity multiplied by the ?c value of the medium. However, this is valid only for the central wave, when the edge wave of the transducer can be ignored. On the other hand, pressure measurements on and very near to the transducer surface are not possible because of the voltage leakage between the electronic transmitter and the PVDF hydrophone used in such measurements. By means of a numerical model, central and edge waves were found for a plane PZT transducer 7.5mm in radius, with the applied 2.7MHz voltage pulse composed of 3 cycles. Two types of boundary conditions of Dirichlet and Neumann were considered showing a negligible difference in the case of short pulses. Basing on numerical and experimental results, practical conditions were determined which make it possible to carry out pressure measurements in the very near field of the transducer, and hence to determine the transducer vibrations which are important for modeling ultrasonic pulse beams.

6

Ilościowa ocena nieliniowej propagacji w wodzie i w tkance

Filipczyński L., Kujawska T., Tymkiewicz R., Wójcik J.

Hydroacoustics

|

2000

|

Vol. 3

53--56

EN

Nonlinear propagation effects were investigated numerically and experimentally u wate r and In blood from the point of view of ultrasonic diagnostic applications in cardlology. Pressure distributions of short and long pulses with the frequency of 3 and 3.5 MHz, radiated by a typical cardiological probe, were found along the ultrasonic beam axis. The numerial results were obtained by means of the numerical code Wf developed previously. The experimental pressure distributions were measured by memu of a membrane PYDF hydrophone. The obtained numerical and experimental results show ing the distributions of the 2-nd and I -st harmonics have shown good agreement allowing us to determine some diagnostic conclusions.

7

Computing and measuring nonlinear and linear propagation by two independent methods

Filipczyński L., Kujawska T., Secomski W., Tymkiewicz R., Wójcik J.

Archives of Acoustics

|

1999

|

Vol. 24, no. 3

269-288

EN

Nonlinear effects, caused by propagation of ultrasonic pulses with finite amplitudes, were computed and measured in water in the case of pulses with pressures up to 1.5MPapp used in diagnostic devices. An electronic transmitter generated high (280Vpp) and low (47Vpp) voltages, applied to a plane PZT transducer causing in this way nonlinear and linear propagation effects. The carrier frequency of the pulse was 2MHz, while its time duration was 2.5\,ms. The measurements were carried out by means of a typical calibrated PVDF membrane hydrophone and by an electromagnetic (EM) hydrophone, prepared for this study. The pulse measurements by means of the PVDF hydrophone showed a higher number of spectral components than those by means of the EM hydrophone. This effect was explained by sensitivity characteristics that increased in the PVDF and decreased in the EM hydrophone as a function of frequency. Previously, it was shown that the effective frequency band used in measurements by means of the PVDF hydrophone is situated below the resonance, on the increasing slope of the resonanse curve. The properties of the EM hydrophone were analysed on the basis of the plane wave assumption. A procedure was developed to correct distortions of the pulse spectrum and its pressure measured by PVDF and EM hydrophones. In the first case the maximum peak-to-peak pulse pressure should be decreased by 27%, while in the second case it should be increased by only 0.7%, and by 3% if an additional amplifier was used. The sensitivities of PVDF and EM hydrohones were very different and equal for the frequency of 2MHz to 28mV/MPa and 0.10mV/MPa, respectively. The calibration of the EM hydrophone was carried out by means of only two simple: electrical and magnetic independent measurements, although in the EM hydrophone there occured external interferring signals. For the theoretic-numerical detemination of the acoustic fields and their spectra generated in the case of nonlinear and linear propagation the numerical procedure called the WJ Code was applied. It was developed recently by the last-named author of this paper. In calculations absorption in water was taken into account. The critical distance, where distortions caused by nonlinear propagation in water were maximum, was determined by a number of computations of the ultrasonic field as a function of the distance from the transducer. A good agreement between computed results and those measured by two different methods, showing the pulse pressure distribution along the whole beam axis, was confirmed. In this case it was shown that the ?/4 matching layer covering the transducer surface influenced the edge wave radiated by the transducer.

8

A multilayer method for linearity determination of the PVDF hydrophone for pressures up to 2.3MPa

Filipczyński L., Etienne J., Kujawska T., Tymkiewicz R., Wójcik J.

Archives of Acoustics

|

1998

|

Vol. 23, no. 4

513-520

EN

A new method of linearity measurements of a PVDF membrane hydrophone was elaborated. High pressure pulses up to 6MPa were obtained in the focus of a concave PZT transducer with the frequency of 3MHz. The method is based on the pressure decrease of these pulses transmitted through metal layers with known acoustic impedances, immersed in water. In this way one obtained pressure changes at constant shapes (spectrum) of the pulses which were measured by means of the hydropbone under investigation. The measurement results confirmed the linearity of the hydrophone up to pressures equal to 2.3MPa. Correlation coefficients of 5 measured relations were in average equal to r=0.994.

9

Possible temperature increases in soft tissues in the case of nonlinear and linear wave propagation

Filipczyński L., Kujawska T., Tymkiewicz R., Wójcik J.

Hydroacoustics

|

1997

|

Vol. 1

329--332

EN

It is well known that the nonlinear propagation increases the absorption of acoustic waves in the medium thus increasing the temperature effects. According to the recently developed new theoretical approach it is possible to determine in a simple way the effective absorption in the case of nonlinear propagation basing on the pulse spectrum analysis [Wójcik, 1996]. In this way it was possible to find the corresponding absorption values occuring in ultrasonography. In this case a classical PVDF membrane hydrophone was used to demonstrate and to measure nonlinear effects. Analysing the obtained wave spectra it was possible to determine the increase of the effective tissue absorption and hence to find the rate of heat generation per unit volume which is crucial for temperature elevations In this way possible temperature increases for the case of nonlinear and linear propagation can be determined.