Application of Arbitrary Position and Width Pulse Trains Signals in Ultrasonic Imaging: Correlation Performance Study

Abstract

Ultrasonic imaging requires both the accuracy and the resolution. Conventional imaging systems use the pulse signals to accomplish the task. But the energy attainable with such signals is limited. Spread spectrum, compressible signals allow to achieve the wide bandwidth even using long durations. Conventional signals do not offer full flexibility or, like nonlinear frequency modulation signals, lack the ease of properties control. We suggest using novel spread spectrum signals generation technique: trains of pulses of arbitrary pulse width and position (APWP). It is expected that APWP should have properties similar to chirp (wide, controllable bandwidth) and both the single pulse (low correlation sidelobes) signals. Study presented here was aimed at evaluating the correlation properties of APWP signals. It indicates that application of APWP signals allows obtaining the properties better or close to those of the conventional signals. It can be concluded that APWP signals offer a new perspective in imaging applications.

Ultrasonic System Models for Pulse Trains Excitation Tuning

“…APWP signals offer the possibility to match the bandwidth of the ultrasonic transducer or even the whole signal transmission channel. Investigation presented in [13] has indicated that APWP signals can be optimized to produce correlation sidelobes that are lower than those of the pulse signal (Fig. 3).…”

“…Then, this signal is used to obtain the auto-correlation function (AKF), submitted to analysis block to extract correlation properties discussed in section II and is stored in codes data base if it produces better correlation parameter than previous signal. The selected APWP codes can be used later in imaging applications [14] as optimal for a particular system-transducer combination.…”

“…Multiple spread spectrum techniques can be used: phase manipulated sequences [7], linear frequency modulation signals (chirp) [8]- [10], or arbitrary waveform signals [11], [12]. The phase-coded sequences do not offer flexibility in spectral content management [9], [13]. Arbitrary waveform excitation needs more complex electronics [11].…”

“…Chirp [8] excitation is considered the best choice but in its simplest form it generates high correlation sidelobes [7]. Trains of the arbitrary position and width pulses (APWP) [14] are a novel SS signal generation technique, offering both simple generation and adaptability to the transducer and the system frequency response. It requires multiple measurements to achieve the optimal response of the system.…”

Comparison of Conventional and Spread Spectrum Signals Time of Flight Error Caused by Neighboring Reflections

“…Most widely used signals are chirp, linear frequency modulation and coded sequences [12]. New class of SS signals was suggested recently [15]: trains of pulses of arbitrary pulse width and position (APWP). For single reflection the SS signals have clear advantage: both sharp main correlation lobe and high energy increase the estimation accuracy.…”