Capacitive Electrical Transfer (CET) and Resistive Electrical Transfer (RET) are the two primary energy delivery modes used in Monopolar Radiofrequency (RF) systems, often seen in 448kHz machines used for physical therapy and aesthetic treatments.
While they operate at the same frequency and use the same power source, the design of the handpieces—specifically, whether they are insulated or non-insulated—creates fundamentally different biological effects and heat distribution patterns in the body.
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CET (Capacitive Electrical Transfer) The Secret of Insulation
Why is it Insulated?
The CET handpiece is insulated, meaning there is no direct conductive contact between the electrode and the skin. This setup effectively creates a capacitor:
- The electrode is one plate.
- The insulating layer acts as the dielectric.
- The skin and superficial tissues act as the other plate.
The RF current passes through the insulating layer via Displacement Current to enter the body’s tissues.
Heating Principle and Depth
Because the energy is coupled and concentrated directly beneath the electrode and in the superficial tissues, the heat is primarily generated and focused on:
Shallow Skin and Subcutaneous Tissue: This promotes immediate collagen contraction and long-term stimulation, leading to tightening effects.
Water-Rich Layers (Muscle and Fat): This increases blood circulation and lymphatic drainage, promoting tissue metabolism.
Conclusion: Since CET mode concentrates energy in superficial, well-hydrated soft tissues, it is the ideal choice for aesthetic contouring, lymphatic drainage, and superficial muscle relaxation.
RET (Resistive Electrical Transfer) The Secret of Non-Insulation
Why is it Non-Insulated?
The RET handpiece is made of non-insulated metal and makes direct contact with the skin. In this mode, the body’s tissues behave primarily as a resistive element.
The Non-insulated mode can ensure the current bypasses the superficial, low-resistance fluid (muscle, blood) and concentrates its heating effect deep down at the sites of highest impedance, which are the target tissues for deep structural repair and chronic pain relief.
Heating Principle and Depth
According to Joule’s Law (Q = I2RT), heat generation is proportional to the square of the current (I), the resistance (R), and the time (T).
While the current flows through the path of least resistance (usually blood and muscle), the highest heat is generated in the areas of greatest resistance (impedance), where the current density is also concentrated.
RET mode, therefore, specifically focuses on heating dense, less-hydrated, high-impedance structures:
Tendons, Ligaments, and Joints: These deep structures have higher electrical resistance, causing them to generate and hold more heat when the current passes through.
Deep Fascia and Periosteum: This depth of heating is highly effective for treating chronic inflammation and deep-seated fibrosis.
Conclusion: RET mode’s characteristic of concentrating energy in high-impedance deep tissues makes it the preferred choice for pain management, deep structural repair, and chronic conditions.
