Papers by Linas Svilainis
IEEE sensors journal, 2024
The air-coupled resonance ultrasound spectroscopy (RUS) of thin plate thickness, density, ultraso... more The air-coupled resonance ultrasound spectroscopy (RUS) of thin plate thickness, density, ultrasound velocity and attenuation measurement are affected by air parameters. If air parameters are left unaccounted errors will occur. Conventional thermometer measurements are not efficient because temperature can vary faster than temperature sensor response. Technique for air parameters estimation and compensation of the RUS inverse solution results is proposed. The ultrasound delay over known distance is used for velocity in air estimation. There is no need for the additional measurement: the propagation time between transducers can be obtained from RUS calibration measurement. Ultrasound velocity in air is then used for temperature estimation. These measurements are augmented by pressure sensor measurement for air density estimation. Evaluation of the attainable measurement errors and analysis of uncertainties under such compensation was carried out using simulated signals. Sensitivity coefficients for every parameter were derived and attainable errors evaluated for temperature range from-5 °C to +40 °C and atmospheric pressure range from 94 kPa to 105 kPa. It was concluded that the relative uncertainty of sample attenuation, ultrasound velocity attenuation, density and thickness could be reduced approximately 22 times compared to case when air parameters are assumed to be equal to those in normal conditions. Experimental verification used 2 mm polycarbonate plate, measured values were compared against reported data. Experiment confirmed the efficiency of the proposed compensation: thickness estimation bias errors were reduced 17 times, bias errors for density were reduced 15 times and velocity estimation bias errors were reduced 5 times.
Social Science Research Network, 2023
Ferroelectret films are soft cellular solids capable to trap dielectric dipoles within the pores.... more Ferroelectret films are soft cellular solids capable to trap dielectric dipoles within the pores. These dipoles together with the large material compressibility give rise to a measurable piezoelectric response. They have been used to produce air-coupled ultrasonic transducers (200 kHz to 600 kHz) and recent works have shown the possibility to use them in water immersion. The main advantage is the large bandwidth and the main drawback is the poor sensitivity. This suggests the possibility of using these materials for wide-band reception, in particular, to make hydrophones. Due to the very low acoustic impedance of ferroelectret films (about 0.08 MRayl), thickness resonances under water immersion are completely damped out. Therefore, unlike conventional PVDF hydrophones, no upper frequency limit in the frequency band of the FE film hydrophone is expected due to these resonances, being the only limit the attenuation in the material. Present work is aimed to study the response of FE film as hydrophone and to explore the frequency range of the reception band in water immersion operation.
Sensors, Oct 18, 2022
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Informatica (lithuanian Academy of Sciences), 1991
The paper is devoted to analysis of the software peculia.rities of the comput.er based ultrasonic... more The paper is devoted to analysis of the software peculia.rities of the comput.er based ultrasonic imaging syst.em for non-destructivE) testing (NDT) applications. The developed software enables 1; 2, and 3-dimensiona.l ima.ging of the intrinsic structure of the mdterials and measurement of their para.meters.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, Nov 1, 2019
Time delay or the time-of-flight is a most frequently used parameter in many ultrasonic applicati... more Time delay or the time-of-flight is a most frequently used parameter in many ultrasonic applications. Delay estimation is based on sampled signal, so resolution is limited by sampling grid. Higher accuracy is available if signal-to-noise ratio is high, then subsample estimate is desired. Techniques used for subsample interpolation suffer from bias error. Time of flight estimation that is free from bias errors is required. Proposed subsample estimation works in frequency domain, it is based on crosscorrelation peak temporal position. Phase of the cross-correlation frequency response becomes linear thanks to multiplication by the complex conjugate, and its inclination angle is proportional to the delay. Then subsample interpolation becomes free from the bias error. Twelve algorithmic implementations of this technique have been proposed in this paper. All algorithmic implementations have been analyzed for bias and random errors using simulation and Matlab codes are given as supplementary material. Comparison with best-performing interpolation techniques (spline approximation, cosine interpolation, carrier phase) is given for both bias and random errors. It was demonstrated that frequency domain interpolation has no bias errors and noise performance is better or comparable to other subsample estimation techniques. Weighted regression using L2 norm minimization has the best performance: total errors (bias and random) are within 3 % of theoretical lower bound.
Elektronika Ir Elektrotechnika, Dec 19, 2016
Ultrasonics, Aug 1, 1997
A multi-frequency ultrasonic method was proposed to detect and characterize delamination and rich... more A multi-frequency ultrasonic method was proposed to detect and characterize delamination and rich resin in thick composites with waviness. Addressing the challenges for ultrasonic inspection caused by waviness, multilayer structure, and multiple defect types, ultrasound propagation in thick wavy composite was investigated through a dedicated numerical model built in OnScale®. Key features of ultrasonic testing and composite sample, including water immersion environment, fiber waviness, uneven inter-ply resin distribution, and side-drilled hole (SDH)-simulated delamination, were embraced in the model. Via this model, waviness and thick resin layers were found to cause disturbance and wave vector deviation to inter-ply reflection signal and thus introduce difficulties for delamination detection based just on the signal to noise ratio. In addition, reflections from interply resin and SDH were revealed with different reliance on probe frequencies. Using a 5 MHz probe with time corrected gain, ultrasonic testing in wavy composite was performed experimentally. Based on the reliance of defect characterization on frequency, SDHs and rich resin were differentiated experimentally in the B-scan images with various filtering frequencies, demonstrating the effectiveness of the proposed method for detection and characterization of delamination and rich resin in thick wavy composite structures.
Applied sciences, Aug 19, 2022
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Air-coupled ultrasonic transducers working at frequencies over 100 kHz have been widely used in t... more Air-coupled ultrasonic transducers working at frequencies over 100 kHz have been widely used in the past for NDT applications and are a very attractive alternative when test specimens cannot enter in contact with water. In these cases, and in order to determine transducer performance it is sufficient to measure transducer two-way insertion loss and signal to noise ratio. However, in the recent years, new applications are being developed for different fields. In these novel uses, the precise knowledge of the actual amplitude of the pressure field is demanded. However, such measurements are not simple nor straightforward. This work presents a simple procedure to measure the transducer sensitivity in transmission mode (Pa/V) and in reception mode (V/Pa) using mixed water-coupled air-coupled procedure that can be easily implemented in any ultrasonic lab. As an application example, the procedure is applied to 0.65 MHz wide band transducers. The transmission and reception sensitivities are presented here. As verification of the technique, the combined transmission-reception sensitivity is then calculated and compared with direct measurements
Elsevier eBooks, 2018
Abstract Large-scale LED displays proved as valuable information presentation device for decades.... more Abstract Large-scale LED displays proved as valuable information presentation device for decades. Much development had taken place until LED control settled to some driving circuitry standard. Today, thousands of manufacturers offer LED displays in numerous types, shapes, and quality. According to study provided by Persistence Market Research, the global outdoor LED displays market was 5 billion USD in 2014, and it was anticipated to grow to 15 billion USD by 2021. LED billboard segment was valued at 2.5 billion USD, the LED video walls—807 million USD, rental outdoor LED billboards—2.2 billion USD, rental outdoor—1.5 billion USD, indoor surface mounted rental—2.6 billion USD with growth forecast for all markets up to 18%. Increasing demand for advertisement, use of LED displays at stage, shopping malls, and conference rooms is driving the market growth. Demand for better image quality (resolution and contrast) for large audience and display price reduction are the primary factors increasing the market adoption of LED displays. The luminous performance of LEDs can now satisfy the most demanding LED screens. Color gamut of LED screen is larger than that of conventional displays. Although being capable of displaying many colors, LED displays are mainly intended for large audience imaging due to their price. LED displays have a long life; can provide the unbeatable luminance allowing for clear visibility outdoor even under the direct sun light; and can work under harsh environmental conditions. LED displays can satisfy any need for large-scale text, graphics, or video information and are used in street billboards, traffic signage, stage decorative illumination, and imaging. This chapter discusses LED video display types, structure, operation, quality parameters, and issues encountered.
Elektronika Ir Elektrotechnika, Feb 12, 2019
Estimation of the output impedance of ultrasonic transducers is required for electrical matching ... more Estimation of the output impedance of ultrasonic transducers is required for electrical matching circuits design and for receiving amplifiers noise optimization. This paper presents a simple technique for transducer output impedance estimation using the same data acquisition system and signals that are conventionally used in non-destructive testing. A pair of ultrasonic transducers is used: one for transmission, one for reception. Received signal is recorded under low and high resistance load and transducer output impedance is then obtained from these two signals. Hence, this technique requires only one measurement channel and bias errors are low (no need for calibration). In addition, it is ground referenced and does not require the transducer to be removed from the positioning fixture. Experimental results obtained using different probing signals have been compared against conventional measurements obtained by an impedance analyser.
Elektronika Ir Elektrotechnika, Feb 1, 2006
The noise model for first stages of ultrasonic system is developed. The aim is to obtain low nois... more The noise model for first stages of ultrasonic system is developed. The aim is to obtain low noise factor for input stages, particularly for preamplifier. The air-coupled composite ultrasonic transducer is used as the signal source. The transducer impedance is measured experimentally and equivalent Butterworth-Van Dyke dual-circuit model generated. The last have been merged with the preamplifier noise model and equations for noise spectral density and noise factor calculation developed. Analysis has indicated that lowest noise factor (NF=1,9 dB) for transducer used is obtained for operational amplifier LMH6624 at frequency f=500 kHz and input termination resistance RT=10 kΩ. Simulation results indicate increase of noise factor if input termination resistance RT is reduced.Ill.8, bibl.8 (in Lithuanian; summaries in English, Russian and Lithuanian).
Physics Procedia, 2015
Replacement of a single ultrasonic pulse to the spread spectrum signals allows higher energy with... more Replacement of a single ultrasonic pulse to the spread spectrum signals allows higher energy without losing the bandwidth and it also means higher requirements for energy delivery to test object. Pulser efficiency for single pulse is not essential comparing to high energy signals. Pulser stress is large if power delivery efficiency to transducer is low. In narrowband case the solution is to use the matching network, but matching circuit effect will be different in case of wideband excitation. Aim of the investigation was to evaluate the matching techniques for spread spectrum signals.
2022 IEEE International Ultrasonics Symposium (IUS), Oct 10, 2022
Pharmaceutics
Microbubble (MB)- and ultrasound (US)-facilitated intracellular Ca2+ delivery, known as sonoporat... more Microbubble (MB)- and ultrasound (US)-facilitated intracellular Ca2+ delivery, known as sonoporation (SP), is a promising anticancer treatment modality, since it allows a spatio-temporally controllable and side-effect-free alternative to conventional chemotherapy. The current study provides extensive evidence that a 5 mM concentration of Ca2+ in combination with US alone or US and Sonovue MBs can be an alternative to the conventional 20 nM concentration of the anticancer drug bleomycin (BLM). Ca2+ application together with SP induces a similar level of death in Chinese hamster ovary cells to the combination of BLM and SP but does not cause systemic toxicity, as is inherent to conventional anticancer drugs. In addition, Ca2+ delivery via SP alters three vital characteristics essential for viable cells: membrane permeability, metabolic activity and proliferation ability. Most importantly, Ca2+ delivery via SP elicits sudden cell death—occurring within 15 min—which remains similar duri...
2022 IEEE International Ultrasonics Symposium (IUS), Oct 10, 2022
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
Miniature microphones suitable for measurements of ultrasonic wave field scans in air are expensi... more Miniature microphones suitable for measurements of ultrasonic wave field scans in air are expensive or lack sensitivity or do not cover the range beyond 100 kHz. It is essential that they are too large for such fields measurements. The use of a ferroelectret (FE) film is proposed to construct a miniature, needle-style 0.5-mmdiameter sensitive element ultrasonic microphone. FE has an acoustic impedance much closer to that of air compared with other alternatives and is low cost and easy to process. The performance of the microphone was evaluated by measuring the sensitivity area map, directivity, ac response, and calibrating the absolute sensitivity. Another novel contribution here is that the sensitivity map was obtained by scanning the focused beam of a laser diode over the microphone surface, producing thermoelastic ultrasound excitation. The electroacoustic response of the microphone served as a sensitivity indicator at a scan spot. Micrometer scale granularity of the FE sensitivity was revealed in the sensitivity map images. It was also demonstrated that the relative ac response of the microphone can be obtained using pulsed laser beam thermoelastic excitation of the whole microphone surface with a laser diode. The absolute sensitivity calibration was done using the hybrid three-transducer reciprocity technique. A large aperture, air coupled transducer beam was focused onto the microphone surface, using the parabolic off-axis mirror. This measurement validated the laser ac response measurements. The FE microphone performance was compared with biaxially stretched polyvinylidene difluoride (PVDF) microphone of the same construction.
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Papers by Linas Svilainis