Fig. 1.
Schematic of the transmitted laser pulse sequence for PPM.
Fig. 2.
The diagram shows the process of the denoising autoencoder.
Fig. 3.
The combination of the coded excitation technique and the denoising autoencoder neural network.
Fig. 4.
The graph shows a sample of the simulation setup.
Fig. 5.
(a) The original PA signal, (b) The coded PA signal from PPM with a code length of 2, (c) 14, and (d) 56.
Fig. 6.
(a) Original PA signal with a −10 dB (rms) SNR, (b) Decoded PA signal from PPM-coded signals with code lengths of 2, (c) 14, and (d) 56, after introducing noise to the generated PA sequence (−10 dB SNR (rms)).
Fig. 7.
The graph illustrates the structure of the denoising autoencoder training process.
Table 1.
Denoising autoencoder model summary.
| Layer (type) | Output shape | Param #1 |
|---|---|---|
| Encoder (sequential) | (None, 1, 233, 8) | 6456 |
| Decoder (sequential) | (None, 1, 1864, 1) | 12209 |
Fig. 8.
(a) The first simulation setup for testing PPM with denoising autoencoder models; (b) the ROI of the PA signal used to calculate SNR.
Fig. 9.
(a) The second simulation setup for testing PPM with denoising autoencoder models. (b) The ROIs of the PA signal are used to calculate SNR. The red dashed boxes and black boxes in this figure indicate the signal and noise regions, respectively.
Table 2.
The specifications for absorbent points.
| Absorbent point | Radius [mm] | Initial pressure [Pa] |
|---|---|---|
| 1 | 1 | 2 |
| 2 | 1 | 1 |
| 3 | 0.5 | 4 |
| 4 | 1 | 2 |
| 5 | 1.5 | 5 |
| 6 | 2 | 1 |
Fig. 10.
The relationship between code length and SNR of PPM and PPM with denoising autoencoder for the signal absorber.
Fig. 11.
The relationship between code length code gain for PPM-coded excitation and PPM-coded excitation with denoising auto-encoder for the signal absorber.
Fig. 12.
(a) The original PA signals, a PA signal resulting from (b) Time-equivalent averaging, (c) PPM (N = 10) coded excitation, and (d) PPM (N = 10) coded excitation with denoising autoencoder.
Fig. 13.
(a) The original PA signals, a PA signal resulting from (b) Time-equivalent averaging, (c) PPM (N = 56) coded excitation, and (d) PPM (N = 56) coded excitation with denoising autoencoder.
Fig. 14.
The relationship between code length and SNR of PPM and PPM with a denoising autoencoder for (a) ROI-1 and (b) ROI-2.
Fig. 15.
(a) Original PA signals; (b) PA signals from time equivalent averaging; (c) PA signals from PPM (N = 10) coded excitation; (d) PA signals from PPM (N = 10) coded excitation with denoising autoencoder.
Fig. 16.
(a) Original PA signals; (b) PA signals from time-equivalent averaging; (c) PA signals from PPM (N = 56) coded excitation; (d) PA signals from PPM (N = 56) coded excitation with denoising autoencoder.
Fig. 17.
Effect of code length on the performance of the denoising autoencoder.