Electrosurgical Generator Crest Factor Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current electrosurgical systems lack the ability to continuously and arbitrarily adjust the crest factor of electrosurgical waveforms, limiting the precision and effectiveness of energy delivery to tissue during procedures.
Innovation Solution
An electrosurgical generator with a non-resonant RF output stage, incorporating a DC-DC buck converter and a DC-AC boost converter, controlled by a controller that adjusts the duty cycles of both converters to dynamically adjust the crest factor of the electrosurgical waveform on a cycle-by-cycle basis, while maintaining the root mean square voltage and output power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fixed crest factor is used in electrosurgical waveforms, then the system is simpler to control, but the precision and effectiveness of energy delivery to tissue is limited
Solution Approach 1:
The patent implements dynamic crest factor adjustment by modifying the duty cycle of the RF waveform on a cycle-by-cycle basis. The controller dynamically changes the proportion of the cycle during which voltage is applied, allowing the crest factor to vary continuously from approximately 1.4 to 4.0 or higher. This dynamic control enables precise matching of waveform characteristics to specific tissue types and surgical requirements, directly improving energy delivery precision without requiring complex additional hardware beyond standard PWM control capabilities.
Solution Approach 2:
The patent changes the key parameter of crest factor by adjusting the duty cycle of the RF output stage. By varying the duty cycle parameter from fixed to variable, the system can continuously adjust the crest factor to optimize tissue interaction. This parameter change approach allows the same hardware to deliver different waveform characteristics (sinusoidal-like at low crest factors, more peaked at high crest factors) suitable for different surgical applications such as cutting versus coagulation.
2Adaptability or versatility
If conventional resonant RF output stages are used, then the circuit design is traditional and familiar, but the ability to adjust crest factor continuously is limited
Solution Approach 1:
The patent replaces the traditional resonant LC circuit approach with a modern switched-mode power converter architecture (buck-boost or four-switch bridge converter). This substitution eliminates the need for resonant tanks and associated tuning components, while providing inherent electronic control capability through PWM duty cycle adjustment. The converter-based approach uses solid-state switching devices controlled by a microprocessor or DSP, enabling continuous crest factor adjustment without mechanical or resonant constraints.
Solution Approach 2:
The converter-based RF output stage serves multiple functions simultaneously: it generates the RF voltage, controls the crest factor through duty cycle adjustment, regulates output power, and can adapt to various load conditions. The same converter circuitry that would normally only generate a fixed waveform can now produce a range of waveform shapes by varying the duty cycle, making the system universally applicable to different surgical needs without requiring separate circuits for different waveform types.
3Ease of operation
If the duty cycle is adjusted to change crest factor, then the crest factor control is simplified, but the root mean square voltage may change affecting output power
Solution Approach 1:
The patent implements feedback control where the controller (microprocessor or DSP) monitors the actual RF output voltage and current, calculates the resulting crest factor and power level, and adjusts the duty cycle accordingly. This closed-loop feedback ensures that when the duty cycle is changed to achieve a desired crest factor, the system simultaneously compensates to maintain the target RMS voltage and output power. The feedback mechanism uses sensed values from voltage and current sensors to continuously correct any deviations.
Solution Approach 2:
The controller pre-calculates or pre-determines the appropriate duty cycle adjustments needed to achieve both the desired crest factor and maintain constant power. Before applying the waveform change, the system computes the required duty cycle modification that will achieve the target crest factor while compensating for its effect on RMS voltage. This preliminary calculation allows the system to make coordinated adjustments that achieve multiple objectives simultaneously without trial-and-error.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution allows for precise control of energy delivery, reducing muscle stimulation, improving tissue effects, and enabling continuous adjustment of crest factors, thereby enhancing surgical control and outcomes.
Implementation Method 1
a DC-DC buck converter configured to output a DC waveform
Implementation Method 2
a DC-AC boost converter coupled to the DC-DC buck converter and including at least one second switching element operated at a second duty cycle, the DC-AC boost converter configured to convert the DC waveform to generate the substantially square electrosurgical waveform
Data Source
Figure 1
Figure 2
Figure 3
AI summary
An electrosurgical generator is provided. The electrosurgical generator includes: a non-resonant radio frequency output stage configured to output a substantially square electrosurgical waveform; and a controller coupled to the non-resonant radio frequency output stage, the controller configured to adjust a crest factor of the substantially square electrosurgical waveform on a cycle-by-cycle basis.