**7. Conclusions**

In this work, a flexible and low-cost piezoelectric diaphragm was applied for surface quality monitoring in grinding of ceramic materials. The PZT diaphragm was also compared to an AE sensor, which is widely used for monitoring in several machining fields. In addition, a new time-domain ROP metric, based on the short-time Fourier transform, was proposed with the objective of estimating the surface quality of the workpieces. Therefore, the following conclusions can be drawn from this work:


The use of the PZT diaphragm in the monitoring of the surface quality of ground ceramic components, together with time–frequency domain analysis techniques, is new, and there are several possibilities for future applications and studies. Future work can be performed with new signal analysis methods and grinding parameters. The use of neural networks of classification or even estimation can be studied further.

**Author Contributions:** Conceptualization, M.A.A.V. and P.R.A.; Data curation, P.O.J.; Formal analysis, F.A.A. and W.N.L.; Investigation, M.A.A.V. and P.O.J.; Methodology, F.A.A.; Supervision, P.R.A.; Writing—original draft, M.A.A.V.; Writing—review & editing, P.R.A., E.C.B., R.B.d.S., D.D. and A.A.

**Funding:** This research was funded by the São Paulo Research Foundation—FAPESP, grant number #2018/07292-0 and National Council for Scientific and Technological Development (CNPQ), under grant 306435/2017-9 for supporting this research work.

**Acknowledgments:** The authors are grateful to the São Paulo Research Foundation—FAPESP for the financial support.

**Conflicts of Interest:** The authors declare no conflict of interest.
