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Harmonic reduction in capacitive micromachined ultrasonic transducers by gap feedback linearization
Sarp Satir1, F Levent Degertekin
1School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA, USA. sarp.satir@gatech.edu
Summary
This study introduces a new method to improve harmonic imaging in capacitive micromachined ultrasonic transducers (CMUTs). By using gap feedback linearization, researchers significantly reduced harmonic distortion, enhancing CMUT performance.
Area of Science:
- Ultrasound technology
- MEMS devices
- Nonlinear acoustics
Background:
- Capacitive micromachined ultrasonic transducers (CMUTs) exhibit nonlinear behavior due to electrostatic force dependence on voltage squared, limiting harmonic imaging.
- Existing input shaping methods primarily address voltage-dependent nonlinearity, overlooking other significant factors.
- Understanding and mitigating nonlinearity is crucial for advancing CMUT applications, particularly in harmonic imaging.
Purpose of the Study:
- To analyze harmonic generation in CMUTs using a time-domain model.
- To investigate the role of gap-dependent electrostatic force nonlinearity.
- To propose and evaluate gap feedback linearization techniques for harmonic distortion elimination.
Main Methods:
- Developed a time-domain model to analyze harmonic generation in CMUTs.
- Investigated subharmonic ac-only excitation combined with gap feedback.
- Analyzed various series impedance feedback topologies (resistive, capacitive, inductive) for linearization.
- Experimentally validated the feedback method using a 3 MHz CMUT with series resistor feedback.
Main Results:
- The time-domain model identified both voltage-squared and gap-dependent nonlinearities.
- Subharmonic excitation with gap feedback effectively eliminated harmonic distortion.
- Series inductance and resistance feedback suppressed harmonic generation while increasing transmit sensitivity (Pa/V).
- Experimental results showed a 10 dB reduction in harmonic generation with simple series resistor feedback.
Conclusions:
- Gap feedback linearization, particularly with series inductance and resistance, is effective in mitigating CMUT harmonic distortion.
- The proposed methods enhance CMUT performance for harmonic imaging and high-intensity ultrasonic applications.
- This approach allows for full utilization of the CMUT gap, improving transmit operation.
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