CMUT Transducer Array with High Density Membrane Layers
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Solution Overview
Problem
Conventional ultrasound transducers, particularly those using PZT materials, face manufacturing complexity, high costs, and design limitations due to low yields, and struggle to achieve both high image resolution and depth-of-field in ultrasound diagnostic imaging systems, as CMUT transducers have limited bandwidth and are prone to premature failure when operated with varying spring constants.
Innovation Solution
A transducer array comprising CMUT cells with two groups of membranes, one with a standard layer stack and the other with a higher density layer stack, allowing for increased mass without significantly altering the spring constant, enabling safe collapse mode operation and enhanced bandwidth by tuning the spring constants to be no more than 20% different, thereby improving image quality and reducing the risk of premature cell failure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If PZT materials are used for ultrasound transducers, then high image resolution and sensitivity are achieved, but manufacturing complexity increases and cost rises due to low yields
Solution Approach 1:
The patent replaces PZT piezoelectric materials with CMUT (capacitive micromachined ultrasonic transducer) technology, substituting a mechanical piezoelectric system with an electromechanical capacitive system. This substitution enables batch manufacturing using semiconductor processes, dramatically reducing manufacturing complexity while maintaining high image resolution and sensitivity through precise control of capacitor geometry and electrical properties.
Solution Approach 2:
The patent changes the fundamental operating parameters of the transducer by transitioning from piezoelectric charge-based operation to capacitive voltage-based operation. By controlling the voltage applied to the CMUT capacitor plates and adjusting the capacitor geometry, the system achieves the desired acoustic output with simplified manufacturing processes compatible with standard semiconductor fabrication.
2Reliability
If PZT materials are used for ultrasound transducers, then high sensitivity is achieved, but acoustic impedance matching with biological tissue deteriorates
Solution Approach 1:
The patent changes the acoustic impedance parameters by replacing PZT ceramic material with a capacitive structure consisting of thin membrane and electrode layers. The effective acoustic impedance of the CMUT is determined by the membrane density, thickness, and tension, which can be engineered to closely match biological tissue impedance, thereby improving sensitivity and energy transfer efficiency without requiring complex matching layers.
3Adaptability or versatility
If CMUT transducers operate with varying spring constants to broaden bandwidth, then bandwidth is improved, but reliability deteriorates due to premature cell failure
Solution Approach 1:
The patent applies local quality by creating groups of CMUT cells with different membrane densities rather than varying spring constants across the entire array. Each local group has optimized membrane properties (different densities) that provide broadband response, while all cells operate within safe stress limits, ensuring uniform reliability and preventing premature failure.
Solution Approach 2:
The patent changes the membrane density parameter selectively in different cell groups to achieve broadband operation. By adjusting the density of the membrane material in specific groups rather than varying the spring constant, the system broadens the frequency response while maintaining uniform and safe operating conditions across all cells, thereby preserving reliability.
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
The solution allows for a transducer array with improved broadband characteristics and extended lifespan, achieving high image resolution and depth-of-field while maintaining structural integrity and flexibility, suitable for applications like catheter-based imaging.
Implementation Method 1
CMUT transducers are tiny diaphragm-like devices with electrodes that convert the sound vibration of a received ultrasound signal into a modulated capacitance
Implementation Method 2
For transmission the capacitive charge applied to the electrodes is modulated to vibrate/move the diaphragm of the device and thereby transmit an ultrasound wave
Implementation Method 3
the provision of a (thin) layer of a high density material to selected CMUT cells to significantly increase the mass of the membranes of the selected CMUTs without significantly increasing the spring constant of these membranes
Data Source
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AI summary
A transducer array (10) is disclosed comprising a plurality of CMUT cells (100, 100, 100"), each CMUT cell comprising a first electrode (110) supported by a substrate (101) and a second electrode (120) supported by a membrane suspended over a cavity (105) between the first electrode and the second electrode, the plurality of CMUT cells comprising a first group of CMUT cells (100) each having a membrane comprising a first layer stack (130); and a second group of CMUT cells (100') each having membrane comprising a second layer stack (130'), the second layer stack including a layer (135) of a material having a higher density than any of the layers in the first layer stack. Also disclosed is a device comprising such a transducer array, an ultrasound imaging system including such a transducer array and a method of operating such an ultrasound imaging system.