Microfabricated Capacitive Ultrasonic Transducer Wide Bandwidth
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Solution Overview
Problem
Current microfabricated capacitive ultrasonic transducers face limitations in achieving high frequencies above 15 MHz due to physical and technological constraints, such as membrane size reduction, etching via scaling issues, and mechanical impedance, which hinder the production of transducers with wide bandwidths and high fractional bandwidths for applications like medical diagnostics and industrial non-destructive testing.
Innovation Solution
The transducer design involves arranging electrostatic micro-cells in homogeneous groups with different geometries, where micro-cells within each group resonate at frequencies above or below the operating frequency, allowing for a larger average transmit pressure bandwidth by optimizing membrane size and pitch, and using a silicon semiconductor substrate with metallized membranes to enhance acoustic coupling and mechanical impedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If membrane size is reduced to achieve higher resonant frequencies, then operating frequency increases, but bandwidth decreases
Solution Approach 1:
The transducer element is divided into multiple micro-cells with different membrane sizes (first group with smaller membranes for higher frequencies, second group with larger membranes for lower frequencies). This segmentation allows each group to contribute to different frequency ranges, achieving wide bandwidth while maintaining high operating frequencies through the combined response of multiple resonant elements.
2Speed
If membrane size is reduced to increase operating frequency, then frequency response shifts higher, but transmit pressure bandwidth decreases
Solution Approach 1:
Multiple micro-cells with different resonant frequency characteristics are merged into a single transducer element and electrically connected in parallel. The smaller membranes (first group) contribute to high-frequency response while larger membranes (second group) contribute to low-frequency response, creating a combined element with both high operating frequency and wide transmit pressure bandwidth exceeding 80%.
3Ease of manufacture
If single geometry micro-cells are used, then manufacturing is simplified, but bandwidth is limited
Solution Approach 1:
Different regions of the transducer element contain micro-cells with different geometrical characteristics (smaller membranes in first group, larger membranes in second group). This local variation in quality allows each region to be optimized for specific frequency ranges, achieving wide bandwidth while maintaining compatibility with standard microfabrication processes through systematic geometric variations.
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 the achievement of wide bandwidths exceeding 80% and fractional bandwidths of 100% at high frequencies, improving the axial resolution and versatility of ultrasonic transducers for applications requiring high-frequency operation, such as intravascular ultrasound and acoustic microscopy.
Implementation Method 1
These devices are based on the electrostatic attraction exerted on the membrane which is forced to flexurally vibrate when an alternate voltage is applied between it and the backplate
Implementation Method 2
during reception, when the membrane is set in vibration by an acoustic wave, incident on it, the capacity modulation due to the membrane movement is used to detect the wave
Data Source
AI summary
The invention relates to an electro-acoustic transducer, particularly an ultrasonic transducer, comprising a plurality of electrostatic micro-cells of the cMUT type. The electrostatic micro-cells are arranged in homogeneous groups of micro-cells having the same geometrical characteristics. The micro-cells of each group have geometries different from the geometry of the micro-cells of the other group or groups.