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The physics of RF, ultrasound and HIFU.

What each technology does, where it works in the skin and how to compare devices on evidence, not brand names.

A cross-section of skin in glass, its layers from the epidermis to the SMAS. Marked on it: radiofrequency heating the dermis, unfocused ultrasound spreading through the deep dermis and the fat, and the HIFU focal points at 1.5, 3.0 and 4.5 mm.
Schematic cross section of facial skin, not to scale. Depths vary by area and by patient.

Radiofrequency

RF passes an alternating current through tissue. Resistance turns it into heat, and controlled heating in the dermis triggers collagen remodeling. Monopolar RF sends current from one electrode to a return pad and heats deeper. Bipolar and multipolar RF run current between electrodes on the handpiece and heat more superficially and predictably. Fractional and microneedle RF deliver the heat through needles or pins at a chosen depth.

Micrograph of a skin section, toned in blue, with a wavy border between the epidermis and the dermis
Skin under the light microscope: the dense epidermis meets the fibrous dermis along a wavy border.

Monopolar

Deeper heating; needs cooling and impedance control.

Bipolar

Shallower, more predictable, less discomfort.

Microneedle RF

Depth set mechanically. Check which skin types the device is indicated for.

Schematic cross section of facial skin, not to scale. Depths vary by area and by patient.

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Ultrasound and HIFU

HIFU focuses ultrasound energy at a precise depth, typically 1.5, 3.0 or 4.5 mm, creating small thermal coagulation points without harming the surface. It is used for lifting and tightening. Non-focused ultrasound is used for body contouring and for drug delivery.

  • Focal depth is set by the transducer, so cartridges matter
  • Imaging-guided systems show the layer being treated
  • Energy per line and line spacing define both result and risk

HIFU

Focused ultrasound stops at one depth, 1.5, 3.0 or 4.5 mm, set by the transducer.

Ultrasound

Unfocused ultrasound spreads through the deep dermis and the fat. It is used for body contouring.

Schematic cross section of facial skin, not to scale. Depths vary by area and by patient.

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How to compare devices

A device is a long relationship, not a purchase. Compare on these points and write the answers down.

  • Energy delivery and control

    How depth, power and cooling are set and measured.

  • Evidence

    Peer-reviewed studies on the actual device, not the category.

  • Safety

    Skin-type range, contraindications, built-in protections.

  • Service

    Local technician, response time, spare parts, consumables cost.

  • Total cost of ownership

    Over five years, including consumables and downtime.

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