PSI - Issue 64

Donato Fiore et al. / Procedia Structural Integrity 64 (2024) 740–748 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Figure 1 - IBIS-FS composition: (a) & (b) radar system, (c) PC controller

The base-band section consists of a direct radiates at a central frequency of 16.75 GHz with a maximum bandwidth of 200 MHz. A final section of calibration provides the necessary phase stability; design specifications on phase uncertainty are suitable for measuring displacements with accuracy lower than 0.01 mm. The sensor module is installed on a tripod equipped with a rotating head, allowing the sensor to be oriented in the desired direction, as show in Fig. 1. The module has an USB interface for connection with the control PC and an interface for the power supply module. The control PC is provided with the software for configuring the acquisition parameters, storing the acquired signals, processing the data and viewing the result in real time. The ability to determine rage (i.e. distance) by measuring the time for radar signal to propagate to the target and back is surely the distinguishing and most important characteristic of radar system. Two a more targets, illuminated by the radar, are individually detectable if they produce different echoes. The resolution is measure of the minimum distance between two targets at which they can still be detected individually. The range resolution is a measure of the minimum distance between separation that can be detected along the radar’s line of sight. Differently from the system in Farrar et al. (1999), the IBIS-FS sensor is capable of providing range solution, i.e. to distinguish different targets in the scenario illuminated by the radar beam. This performance is obtained by using the Stepped-Frequency Continuous Wave either a burst of N single tones at uniform frequency step ∆f. Hence, the transmitted spectrum is a line spectrum with a frequency separation ∆f between the lines and the frequency response measured by the radar is sampled in the frequency domain with a sampling interval ∆f. In such instances and by applying a quadrature mixer in the receiver, unambiguous range measurement is obtained if the maximum distance of targets does not exceed: = 2∆ (1) with c being the speed of light in free space. The scenario is sampled with range resolution of: ∆ = 2 = 2 ( −1)∆ = ( −1) (2) The lBlS-FS sensor was designed in order to obtain a range resolution of 0.50 m; in other words, two targets can still be detected individually by the sensor if their relative distance is greater than 0.50 m. Each range resolution area is termed range bin (Fig.2).