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Local pulse-wave velocity (PWV) is an accurate indicator of the degree of arteriosclerosis (stiffness) in an artery, providing a direct characterization of the properties of its wall. Devices currently available for local PWV measurement are mainly based on ultrasound systems and have not yet been generalized to clinical practice since they require high technical expertise and most of them are limited in precision, due to the lack of reliable signal processing methods. The present work describes a new type of probe, based on a double-headed piezoelectric (PZ) sensor. The principle of PWV measurement involves determination of the pulse transit time between the signals acquired simultaneously by both PZs, placed 23 mm apart. The double probe (DP) characterization is accomplished in three main studies, carried out in a dedicated test bench system, capable of reproducing a range of clinically relevant properties of the cardiovascular system. The first study refers to determination of the impulse response (IR) for each PZ sensor, whereas the second one explores the existence of crosstalk between both transducers. In the last one, DP time resolution is inferred from a set of three different algorithms based on (a) the maximum of cross-correlation function, (b) the maximum amplitude detection and (c) the zero-crossing point identification. These values were compared with those obtained by the reference method, which consists of the simultaneous acquisition of pressure waves by means of two pressure sensors. The new probe demonstrates good performance on the test bench system and results show that the signals do not exhibit crosstalk. A good agreement was also verified between the PWV obtained from the DP signals (19.55 ± 2.02  ms(-1)) and the PWV determined using the reference method (19.26 ± 0.04  ms(-1)). Although additional studies are still required, this probe seems to be a valid alternative to local PWV stand-alone devices.

Electrical Impedance Spectroscopy, EIS, is widely used in the study of electrical properties and structure of biological tissues, namely in quality control of fruits and the characterization of specific botanical tissues. The present work aims to extend the EIS concept to identify structure damaging pathologies for in vivo vegetal tissue. This allows for the early detection of specific plant diseases with economic and environmental impact. Moreover, the commercially available EIS solutions miss a true frequency bandwidth analysis and, despite the general good performance, are unspecified for bioimpedance measurements and are often quite expensive. Consequently, these limitations are the main reason for erroneous interpretations and inaccurate results. Therefore, this work proposes the development of a dedicated bioEIS system, characterized by an appropriated frequency range (1kHz to 1MHz), suitable for biological applications, in such a way that it becomes possible to compensate the influence of potential errors in off-line analysis.

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