Operator that determines whether a substring belongs to a string

There is a line IRBIS MB2380 Monoblock, 23.8", Intel Celeron N3350, 4GB, 500GB, Intel HD Graphics 500, Windows 10 Home, black or IRU Office P2121 Monoblock, 21.5", Intel Celeron G4900, 4GB, 120GB SSD, Intel UHD Graphics 610, FreeDOS, black [1200026]. The 4th substring between the 4th and 5th commas is selected. It is necessary to find out whether the string SSD belongs to the selected string (php statement), and also to determine the location of the substring SSD in the selected string.