## 2 Materials and Methods
### Scanning Methodology  
The fundamental property of CFRP that enables our method of detecting fiber directionality is its anisotropic conductivity. A unidirectional CFRP has a significantly higher conductivity in the direction of the fiber than in the transverse direction, by as much as several orders of magnitude [16]. To test and observe this basic principle, we perform an ECT rotational scan (herein referred to as an \"r-scan\" for brevity). An r-scan is simply a rotational sweep of the eddy current probe over the surface of the part while recording coil response as a function of angle, as depicted in Figure 4. A greater response is produced in the receiver coil when the coils are aligned with the fiber direction, i.e., when \(\theta=0^{\circ},180^{\circ}\) in Figure 4a, as compared to when the coil orientation is transverse to the fiber alignment, such as when \(\theta=90^{\circ},270^{\circ}\) for the configuration shown in Figure 4a. This observation is similar to that shown by [PERSON] in [17]. In such a configuration, it is common to plot angular data on polar axes, as shown in Figure 4b, where the radial axis is the magnitude of the complex ECT response on the receiver coil, \(r\), normalized between 0 and 1. When the fiber direction is constant throughout the entire part, this method can be used to determine the dominant fiber orientations quickly and accurately in the laminate [5]. When the fiber direction changes throughout the part (as is the case when in-plane waviness is present), the process of rotating the probes to obtain the local alignment is performed at multiple locations. For repeatability and standardization, we create a grid over the surface of the part where angular \"r-scan\" data are collected at each vertex. The resulting data take the form of a 3D matrix representing the coil response in the spatial dimensions \((x,y)\) and the rotation \(\theta\) space. The time required to perform the scan depends on both the desired resolution in the rotational space \(\theta\) and the spatial resolution of the \((x,y)\) grid. These resolutions also determine the optimal scanning order of operations. For example, for high rotational resolution and low spatial resolution, it is optimal to sweep the rotational axis (i.e., \"r-scan\") first, and then move to the next (x, y) point. Conversely, if low angular resolution and high spatial resolution are desired, the optimal order is to scan the entire surface of the part (i.e., \"c-scan\") before incrementing the probe angle. When scanning for in-plane waviness, as is the case in this study, a high spatial resolution is desired to properly quantify the wrinkle parameters. Furthermore, we show here that it is possible to increase the effective angular resolution of the scan by signal processing against the known rotational pattern in Figure 4b. Figure 4: Illustration of ECT r-Scan, (**a**) rotating TR probe (orange), consisting of transmit (Tx) and receive (Rx) coils, versus fiber orientation (blue), and (**b**) ECT normalized response of signal amplitude \(|r|\) as a function of rotation angle \(\theta\). Given a single high-resolution (e.g., \(\leq 1^{\circ}\)) r-scan \(r_{h}\), we can calculate the angular offset of low-resolution data \(r_{l}\) to determine the dominant fiber orientation. In the present study, a final angular resolution of \(\leq\)\(1^{\circ}\) can be obtained from a rotational resolution of \(15^{\circ}\). The offset calculation is accomplished using circular cross-correlation of a high-resolution zero-centered angular scan data \(r_{h}[n]\) against the up-sampled low-resolution data \(r_{l,up}[n]\) with \(n\in\{1,2,\ldots,N\}\) according to Equation (9). The up-sampled low-resolution data \(r_{l,up}[n]\) is obtained by zero-stuffing the low-resolution data \(r_{l}[m]\) where \(m\in\{1,2,\ldots,M\}\) and \(M<N\). The fiber offset is simply the angle corresponding to the maximum of the cross correlation, as shown in Equation (10).