JAE, VOL. 15, NO.1, 2013 JOURNAL OF APPLIED ELECTROMAGNETISM 49 APPLICATION OF SPREAD SPECTRUM SIGNALS IN ULTRASONIC IMAGING L.Svilainis, V.Dumbrava, A. Chaziachmetovas, A.Aleksandrovas Kaunas University of Technology, Department of Signal Processing Studentu Str. 50-340, LT-51368, Kaunas, Lithuania linas.svilainis@ktu.lt Abstract Paper presents the initial investigation of spread spectrum signals application in ultrasonic imaging. Structure of the novel data acquisition system for ultrasonic imaging is presented. Application of Spread Spectrum signals in spectroscopy and direct correlation imaging is presented. It was shown that spread spectrum signals use for imaging offers some advantage over short duration pulses. Thanks to the high energy content produced by the spread spectrum signal, spectroscopy can be carried out well beyond the specified transducer bandwidth. Application of the spread spectrum signals is giving better performance in time of flight estimation. 1. INTRODUCTION Use of radar principle has received attention in imaging applications, when other than airborne targets have to be located. Imaging using optical waves on optical coherence tomography allows to achieve sub-micrometer resolution and is widely used in medicine or industry [1,2]. Radio waves imaging is gaining in medicine [3] and engineering [4]. For decades, application area of the ultrasonic systems is expanding: non-destructive testing and evaluation, robotic vision and navigation, measurements in production automation, medicine diagnostics and treatment, imaging in solid and liquid environments, food industry and agriculture [5-7]. Parameters of signal and antenna or sensor define the imaging quality. Essential parameter affecting the temporal resolution of image obtained is the envelope bandwidth. Propagation time estimate accuracy depend on signal energy, input noise and signal spectrum as defined by the Cramer-Rao lower bound (CRLB) [8, 9]. Latter dictates to use signals which have high energy and are wideband. Furthermore, in order to avoid going into region where abrupt Time of Flight (ToF) estimate errors can occur demands the use of wideband signals. Also, as mentioned above, temporal resolution of imaging calls for short, wideband signals. This creates the contradiction for conventional signals: duration has to be increased to gain the energy; bandwidth has to be improved to get