CMUT Array Bias Segmentation for Short Circuit Isolation
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Solution Overview
Problem
Ultrasonic transducer probes using capacitive micromachined ultrasonic transducers (CMUTs) face operational failures due to a single cell shorting out, causing the entire transducer array to become inoperative, which is complex and reduces sensitivity and performance.
Innovation Solution
An ultrasound system with a drive circuit and intermediate coupling circuits, including a buffer element and series capacitor, prevents low-impedance shorts between CMUT cell bias nodes and counter electrodes, allowing individual cell failures without affecting the entire array's operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single CMUT cell fails by collapsing the membrane onto the opposing electrode, then the failed cell shorts out, but this causes all hundreds or thousands of other cells with which it is commonly biased to short out as well, rendering the entire transducer probe inoperative
Solution Approach 1:
The patent divides the single common bias voltage distribution into multiple independent bias voltage lines, with each line serving a specific subset of CMUT cells. This segmentation ensures that a failure in one cell only affects cells on the same bias voltage line, not the entire array. The bias voltage distribution network is segmented into multiple independent channels, isolating failures to minimal regions.
Solution Approach 2:
The patent introduces intermediate bias voltage distribution nodes and isolation structures between the common bias voltage source and individual CMUT cells. These intermediary elements act as barriers that prevent failure propagation, allowing the system to maintain operation even when individual cells or small groups of cells fail.
2Productivity
If hundreds or thousands of CMUT cells are connected together and operated in unison as a single transducer element, then the acoustic efficiency is improved, but a single cell failure can render a vast number of cells inoperative
Solution Approach 1:
The patent segments the large array of CMUT cells into multiple independent operational groups, each fed by its own bias voltage line. This allows the array to maintain high acoustic efficiency through the combined operation of many cells while limiting the impact of failures to small segments, preserving the overall productivity and reliability of the transducer probe.
3Reliability
If the membrane is brought into close proximity to the opposing electrode by DC bias voltage to increase sensitivity, then the acoustic power output is optimized, but the risk of membrane collapse and shorting increases
Solution Approach 1:
The patent segments the bias voltage application into multiple independent lines, which allows for better control and monitoring of the electric field distribution across the CMUT array. This segmentation reduces the risk of catastrophic membrane collapse by isolating voltage stress to specific regions and enabling faster detection and response to developing failures.
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 solution maintains the functionality of the ultrasound system even when individual CMUT cells fail, reducing the impact of cell failures and enhancing the overall performance and sensitivity of the transducer array.
Implementation Method 1
Each coupling circuit comprises a buffer element (preferably a resistor) connected between a bias voltage and a device terminal and a series capacitor
Implementation Method 2
Each coupling circuit comprises a buffer element (preferably a resistor) connected between a bias voltage and a device terminal
Data Source
Figure 1~2a
Figure 2b~3b
Figure 4
AI summary
An ultrasound system has a set of CMUT ultrasound transducer devices and a drive circuit for operating the ultrasound transducer devices, for delivering an AC drive signal and receiving a reflected signal. An intermediate circuit is between the drive circuit and the set of ultrasound devices in the form of an array of coupling circuits, each coupling circuit between the drive circuit and an associated at least one ultrasound transducer device. Each coupling circuit comprises a buffer element connected between a bias voltage and a device terminal and as series capacitor. The intermediate circuit serves as a connection link between the set of CMUT transducer elements and the driving/sensing electronics, and is for example formed as a passive integrated technology circuit. The buffer element prevents a low-impedance short between the CMUT cell bias node and the counter electrode in the case of a CMUT cell drum short circuit. In this way, failure of an individual cell will not cause a breakdown of the whole CMUT array nor a breakdown of the driving electronics.