Download the PKGS-25NB-R datasheet PDF.
This datasheet also covers the PKGS-25MF-R variant, as both devices belong to the same (pkgs-xxxx) piezoelectric ceramics sensors family and are provided as variant models within a single manufacturer datasheet.
Note: The manufacturer provides a single datasheet file (PKGS-25MF-R_MurataManufacturing.pdf) that lists specifications for multiple related part numbers.