Project is dedicated to summarize and expand the scientific competence and „know-how“ of spread spectrum digital ultrasonic systems design. Goal is to develop and investigate the novel spectrum spreading technique, based on discrete time and amplitude excitation signal. Technique is intended for new generation ultrasonic systems. Resolution requirements for non-destructive testing and biomedical imaging systems are growing, greater flexibility is demanded. Resolution and flexibility depend on possibilities to control the properties of the excitation signal. Ultrasonic flow rate, temperature, material properties measurements accuracy is influenced by signal bandwidth and signal-to-noise ratio. But for conventional signals bandwidth increase reduces signal energy. In such case complex, spread spectrum, excitation signals are used which posses both long duration (high energy) and wide bandwidth. Most popular, arbitrary waveform signals are complicated to excite, hard to deliver high power, equipment is inefficient and expensive. Phase manipulated sequences do not allow to control the shape of the correlation function and spectrum. We suggest new technique – use specially formed square pulse sequences, applying specific duration and position in time combinations; use discreet time: this would increase temporal stability and save system resources. Development is planned of theoretical background and procedure for straightforward signal construction in time basing the predefined spectral or correlation shape. Efficiency of excitation electronics would increase, maintaining small size, cost of the spread-spectrum equipment can be reduced. Such signals would allow to increase imaging resolution and quality, increase the sensitivity of the measurements.Results are applicable in imaging systems and high accuracy measurements: liquid, gas flowmeters, temperature measurements, chemistry research.
Project funding:
Projects funded by the Research Council of Lithuania (RCL), Projects carried out by researchers’ teams
Project results:
An ultrasonic signal acquisition system suitable for spread spectrum experiments was designed, a high-voltage pulse sequence generator, signal receiving, filtering and digitization equipment, a digital signal processing FPGA tract and a data transmission interface were designed and manufactured. According to the technical documentation prepared in previous years, a system for collecting ultrasonic signals of the spread spectrum was made, enabling the generation of arbitrary position and width pulse (APWP) sequences of high-voltage, the reception, filtering and digitization of signals. Up to 100 different signals can be used for the study at the same time: APWP, rectangular pulses, constant frequency radio pulses, frequency modulated signals. Thanks to this unique feature, signals can be reliably compared with each other. Equipment for positioning the ultrasonic transducer in three-dimensional space has been produced. The parameters of the system nodes were studied and suggestions for improvement were presented. A new methodology for estimating interpolation errors in signal propagation time estimation is proposed (Measurement journal). The determined regularities are extremely important when choosing the sampling frequency of the signal received by any system using a time interval (not only ultrasound, but also radar or lidar). An analysis of the effect of adjacent reflections on the propagation time estimate of conventional and spread spectrum signals was performed. Such a situation often exists when measuring the thickness of thin or multi-layered materials, so reducing the error is extremely important. It has been shown that spread spectrum signals, especially APWP, have a lower influence of adjacent reflections on the distribution of the propagation time estimate compared to conventional ones (short pulse, radio pulse).
Published 8 publications in WoS journals instead of the planned 6. Published 6 publications in other peer-reviewed scientific periodicals. 14 conference papers were published instead of the planned 8.
Project coordinator: Kaunas University of Technology
Project partners: Kaunas University of Technology
