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

https://reidscoolthoughtss.swiftnestly.com/posts/do-clinics-use-templates-for-ultherapy-or-map-your-anatomy-every-time

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