Ultherapy uses focused ultrasound targeting the 4.5 mm layer beneath the skin...

https://trulyexpatlifestyle.com/non-surgical-skin-tightening-in-singapore/

Ultherapy uses focused ultrasound targeting the 4.5 mm layer beneath the skin called SMAS, which few treatments reach. It triggers collagen buildup over 3 to 6 months for natural lift