CMUT Cavity Height Measurement Using Reference Cell Parasitic Correction
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Solution Overview
Problem
Current methods for measuring the precise cavity height in capacitive micromachined ultrasonic transducers (CMUTs) are inadequate, leading to insufficient precision in determining maximum transmission sound pressure, especially when parasitic capacity is included in electrostatic capacity measurements.
Innovation Solution
Incorporating a reference cell with a conductive material into the ultrasonic probe, allowing for the separation and correction of parasitic capacity in electrostatic capacity measurements to accurately calculate the cavity height of the ultrasonic cell.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a method of estimating cavity height on the basis of a shape of a membrane is used, then the measurement process is simple, but the precision of cavity height measurement is insufficient
Solution Approach 1:
The patent replaces mechanical/optical measurement methods (membrane shape observation) with electrical measurement methods (electrostatic capacity measurement). By measuring the electrostatic capacity between the upper and lower electrodes, the cavity height can be calculated with high precision using the relationship C = εS/d, where d is the cavity height. This substitution of measurement principle resolves the contradiction between simplicity and precision.
2Measurement precision
If a method of calculating cavity height on the basis of electrostatic capacity is used, then the precision of cavity height measurement is improved, but parasitic capacity interferes with the measurement accuracy
Solution Approach 1:
The patent extracts and separates the parasitic capacity component from the total measured electrostatic capacity. By measuring the electrostatic capacity of only the lower electrode and surrounding structures (excluding the cavity contribution), the parasitic capacity is isolated and can be subtracted from the total measurement. This extraction approach eliminates the harmful interference while preserving the precision benefit.
Solution Approach 2:
The patent applies different measurement approaches to different parts of the electrode structure. The electrostatic capacity measurement is specifically targeted at the cavity region between upper and lower electrodes, while the parasitic capacity measurement focuses on the lower electrode and surrounding structures. This localized measurement strategy ensures that each measurement captures only the intended component, resolving the interference issue.
3Adaptability or versatility
If multiple transducer units are arrayed in a two-dimensional array, then the imaging capability is enhanced, but it becomes difficult to ensure uniform ultrasonic wave generation across all units
Solution Approach 1:
The patent implements self-diagnosis and self-calibration capability for each transducer unit in the array. By measuring the electrostatic capacity of each individual unit, the system can automatically detect variations in cavity height and other parameters. This self-service measurement approach enables quality control without requiring external intervention, ensuring uniform performance across all array elements while maintaining the enhanced imaging capability.
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 precise measurement of cavity height, thereby accurately determining maximum transmission sound pressure and ensuring uniform sound pressure generation across transducer units in a two-dimensional array.
Implementation Method 1
a piezoelectric transducer making use of electrostatic force generated on a membrane on the upside of the cavity by applying voltage between the upper electrode and the lower electrode
Implementation Method 2
the reception of an ultrasonic wave is performed by detecting displacement of the membrane as voltage variation or current variation
Data Source
AI summary
Technique that enables precisely measuring cavity height and precisely grasping maximum transmission sound pressure in an ultrasonic probe is provided to the ultrasonic probe using CMUT. The ultrasonic probe according to the present invention includes plural cells each of which includes a lower electrode and an upper electrode arranged via a gap with respect to the lower electrode, and the plural cells include an ultrasonic cell the gap of which is void and which transmits/receives an ultrasonic wave and a reference cell the gap of which is filled with a conductive material. Electrostatic capacity of the ultrasonic cell and the reference cell is measured, parasitic capacity included in the measured electrostatic capacity as to the ultrasonic cell is corrected using parasitic capacity included in the measured electrostatic capacity as to the reference cell, and cavity height is calculated on the basis of the corrected electrostatic capacity of the ultrasonic cell.