## 5 Conclusions  
This study provides insight into the acoustic radiation generated during the squeal phenomenon in a brake system. Firstly, the acoustic phenomena during squeal events are investigated and, more specifically, their characteristics versus squeal frequencies are determined by analyzing the acoustic pattern (in terms of both directivity and sound level) per disc revolution. The reproducibility of the radiated acoustic field of each squeal frequency is highlighted for a given set of operational parameters. The squeal noise of the braking system is mainly characterized by a fundamental frequency and its harmonic components. Frequency contributions of lower acoustic intensity are also detectable. The squeal frequencies detected via acoustic measurements are similar to the squeal frequencies previously observed on vibrations during braking tests, which unambiguously demonstrates the potential links between the emergence of friction-induced vibrations and the squeal noise in far field. It is also shown that the radiated acoustic field emanating from each squeal frequency has its own directivity and intensity characteristics with eventual evolution per revolution of the disc.  
In addition, a method for reconstructing the acoustic field radiated in all the surrounding space is implemented. This approach is validated by reconstructing the pressure field at the location of the 117 measurement points of the microphone antenna and using a similarity criterion that allows verifying the correlation between the measured data and the output data of the reconstruction of the measurement points. We note that this similarity criterion is also used to highlight the temporal evolution of the acoustic pattern specific to each frequency of the squeal noise and thus obtain understanding of the radiated acoustic patterns as a function of disc rotation. Finally, the method implemented is applied to illustrate the method's capability of reconstructing the radiated acoustic field everywhere in the surrounding space of the brake system.  
It would be interesting in the next step of the study to use the pressure measurements to identify, locate and characterize the vibratory sources responsible for acoustic radiation and hence the problem of friction-induced vibration. This would provide additional insight into the problem of the origin of squeal noise in brake systems.  
Conceptualization, S.B., D.L. and J.-J.S.; Investigation, S.B., D.L. and [PERSON]; Methodology, S.B., D.L. and [PERSON]; Validation, [PERSON], D.L. and [PERSON]; Wirting--original draft, S.B.; Writing--review and editing, D.L. and [PERSON]. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The participants of this study did not give written consent for their data to be shared publicly, so due to the sensitive nature of the research supporting data is not available.  
The authors would like to thank [PERSON] for his work and contribution during the manufacturing and handling of the test bench, and [PERSON] for his work and contribution during its handling and instrumentation. [PERSON] acknowledges the support of the Institut Universitaire de France. The raw experimental data from pressure measurements that were analyzed and discussed in this study were collected in collaboration with the company MicrodB.  
The authors declare no conflict of interest.