Ultrasound Generation with Dynamic Pulse Width Modulation
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Solution Overview
Problem
Current ultrasound generator technologies face challenges in controlling ultrasound output pressure and reducing harmonic distortion, particularly in high-frequency applications, where MOSFET switched excitation results in fixed amplitude output and introduces undesirable harmonics, limiting the ability to accurately generate linear frequency modulated signals and control axial resolution and penetration.
Innovation Solution
The development of a method to generate pulsed drive signals using a carrier comparison technique, which adjusts switching angles and pulse positioning to match the modulating signal, allowing for increased linearity of ultrasound output power and selective reduction of harmonic content, while maintaining control over output pressure, using a MOSFET-based transmitter circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If MOSFET switched excitation is used to generate ultrasound drive signals, then high power and high voltage excitation can be achieved with reduced component count, but the output amplitude becomes fixed and harmonic distortion increases
Solution Approach 1:
The patent applies dynamics by making the pulse width variable rather than fixed. The pulse width modulation technique dynamically adjusts the duration of each excitation pulse based on the desired output amplitude, allowing continuous control of ultrasound output power while maintaining the high efficiency benefits of MOSFET switched excitation. This resolves the contradiction by introducing dynamic adaptability to the previously static switched excitation system.
2Device complexity
If MOSFET switched excitation is used, then component count is reduced and cost is minimized, but harmonic distortion increases and linearity of output power decreases
Solution Approach 1:
The patent implements feedback through a lookup table that stores pre-calculated pulse width values corresponding to desired output power levels. The microprocessor queries this table to determine the appropriate pulse width for each desired amplitude level, ensuring linear relationship between control signal and output power. This feedback mechanism compensates for the non-linear characteristics of switched excitation without adding complex analog circuitry.
3Ease of manufacture
If fixed DC levels are used in switched excitation, then circuit design is simplified, but amplitude control capability is lost
Solution Approach 1:
The patent employs periodic pulse width modulation where the excitation is delivered as a series of periodic pulses with variable widths. Each pulse maintains the simple fixed DC level characteristics easy to generate, but the variable pulse width within each periodic cycle enables precise amplitude control. This approach preserves the simplicity of fixed voltage levels while adding the adaptability needed for amplitude modulation through temporal variation.
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 approach enables improved control over ultrasound output pressure and reduced harmonic distortion, enhancing axial resolution and penetration, and is applicable to both medical and industrial ultrasound applications, particularly in high-frequency imaging and portable systems.
Implementation Method 1
An ultrasound generator uses a transducer to convert an electrical drive signal into ultrasound pressure waves
Implementation Method 2
The reflected pressure waves are converted back to electrical signals by the transducer
Data Source
AI summary
An ultrasound generator having a signal generator; and to generate a pulsed drive signal from a modulating signal, the pulsed drive signal having at least a zero output level, a positive output level and a negative output level. The position and width of pulses are defined by at least first and second switching angles per half cycle of the modulating signal. In part of the range of the modulating signal one switching angle increases while the other switching angle decreases simultaneously such that the fundamental frequency of the pulsed drive signal increases or decreases with the modulating signal and such that a selected harmonic component of the generated pulsed drive signal is maintained below a first threshold. A transducer is arranged to generate ultrasound in response to the pulsed drive signal.