Ultherapy uses ultrasound targeting the 4.5mm SMAS layer to stimulate collagen...

https://cruzqmfp756.theburnward.com/what-age-is-best-for-rf-tightening-focus-on-your-30s-to-early-40s

Ultherapy uses ultrasound targeting the 4.5mm SMAS layer to stimulate collagen deep under the skin, with results peaking around 3 to 6 months. RF heats tissues to 40-45°C for surface tightening but doesn’t reach as deep