## 2 Materials and Methods
### AID Tag Generation Workflow  
As shown in Figure 3, comparative analysis reveals that for multilayer shell structures of varying materials, the theoretical analytical solutions and numerical simulation results for far-field target strength (TS) exhibit remarkable consistency in spatial distribution characteristics across the reduced frequency range \(kr\in[1,20]\), where \(k\) is the wavenumber and \(r\) the shell radius.  
Based on the frequency-domain indirect method [22], a Gaussian-windowed tone burst with a center frequency \(f_{c}=500\) kHz and fractional bandwidth \(\text{FBW}=0.7\) was employed as the excitation signal. The frequency-domain backscattered sound pressure \(p_{s}(f)\) of the multilayer cylindrical shell was calculated, and the time-domain echo \(p_{s}(t)\) was obtained via inverse Fourier transform. The governing equations are as follows:  
\[p_{s}(f)=\mathcal{F}\{p_{inc}(t)\}\cdot H(f), \tag{12}\]  
\[p_{s}(t)=\frac{1}{2\pi}\int_{-\infty}^{\infty}p_{s}(f)e^{i2\pi ft}df, \tag{13}\]  
where \(H(f)\) represents the theoretical transfer function derived from the Normal Mode Series (NMS) scattering model.  
The Gaussian-windowed tone burst is given by the following equation:  
\[p_{inc}(t)=A\cdot e^{-\left(\frac{t-t_{0}}{\sigma}\right)^{2}}\sin(2\pi f_{c} t), \tag{14}\]  
where  
\(\sigma\) = Bandwidth control parameter.  
\(t_{0}\) = Time center of pulse.  
\(f_{0}\) = Center frequency.  
To extract the time-domain echo peak features from the acoustic backscatter signals of cylindrical shells under different stratification strategies, a matched filtering technique is employed by convolving the echo signal with the incident signal. Simultaneously, positional information of distinct peak points and peak interval sequence information are extracted, quantized, and encoded into a 1D barcode. The detailed workflow is illustrated in Figure 4.  
Figure 3: Target Strength (TS) comparison between Normal Mode Series (NMS) analytical solutions and Finite Element Method (FEM) results for four multilayer cylindrical shells (radius \(r\) = 0.25 m reference distance 1000 m). Subfigures (**a–d**) correspond to material combinations Al-AA, PMMA-PVC-PETG, LDPE-PTFE-PVC-STEEL, and LDPE-PTFE-PVC-PETG-STEEL, respectively (the thickness of the steel is 0.002 m).  
For a three-layer cylindrical shell with an outermost radius of 0.25 m and a uniform shell thickness of 0.01 m per layer, optimized stratification strategies enable the generation of distinct time-domain echo characteristics. These features are encoded into corresponding AID tags, demonstrating unique acoustic fingerprints for material-layer configurations.  
[PERSON] [23] systematically classified the ocean noise spectrum for the first time, delineating the frequency distributions of natural sources (wind, waves, marine life) and anthropogenic sources. High-frequency noise is predominantly thermal noise generated by molecular thermal motion (Brownian motion) in seawater, with noise level decreasing as frequency increases. To validate the effectiveness of AID tags, this study added Gaussian white noise (uniformly distributed across all frequencies, signal-to-noise ratio (SNR) = 3 dB) to the echo signals and performed the Shapiro-Wilk normality test [24]. The results confirmed that the added noise followed a normal distribution. The signal-to-noise ratio [25] (SNR) is defined as the ratio of signal power to noise power (in decibels, dB):  
\[\text{SNR}_{\text{dB}}=10\ \text{log}_{10}\bigg{(}\frac{P_{\text{signal}}}{P_{ \text{noise}}}\bigg{)}, \tag{15}\]  
where \(P_{\text{signal}}\) denotes the signal power and \(P_{\text{noise}}\) represents the noise power.