cMUT Charge Drift Calibration via Polarity Inversion
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Solution Overview
Problem
Capacitive micro-machined ultrasound transducers (cMUTs) experience sensitivity drift and distortion due to charge accumulation in insulating portions between electrodes when a DC bias is applied, leading to increased harmonic components and inability to suppress transmission-reception sensitivity distortion.
Innovation Solution
An ultrasound diagnostic apparatus with a discharge mechanism that applies a voltage with inverted polarity between the electrodes to quickly discharge accumulated charge, utilizing the collapse phenomenon to reduce impedance and accelerate charge discharge, thereby calibrating transmission-reception sensitivity drift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a DC bias is applied between the electrodes to generate an electric field and enable ultrasound transmission, then the transmission-reception sensitivity is improved, but charge accumulates in the insulating portion between the electrodes causing sensitivity drift and distortion
Solution Approach 1:
The patent applies periodic reverse-polarity voltage pulses to discharge accumulated charge in the insulating portion. The control unit periodically switches the voltage polarity between positive and negative, creating alternating electric fields that enable continuous discharge of trapped charge, thereby maintaining sensitivity stability over time
Solution Approach 2:
The patent changes the voltage polarity parameter from a constant DC bias to an alternating bipolar signal. By inverting the voltage polarity periodically, the electric field direction reverses, enabling charge to be discharged through the insulating portion in the opposite direction, thus eliminating accumulation and maintaining stable sensitivity
2Duration of action of stationary object
If a DC bias is applied for a long period to maintain the electric field, then the ultrasound transmission function is sustained, but charge accumulates in the diaphragm causing transmission-reception sensitivity drift
Solution Approach 1:
The control unit implements periodic voltage polarity inversion during the DC bias application period. By alternating the voltage direction at regular intervals, the system maintains continuous electric field presence for ultrasound transmission while simultaneously discharging accumulated charge through the reversing field, preventing sensitivity drift over extended operation
Solution Approach 2:
The patent ensures continuous useful action by maintaining the DC bias application for prolonged periods while integrating periodic discharge pulses. The alternating voltage polarity continues to discharge charge throughout the bias application duration, ensuring that the transmission-reception sensitivity remains stable without interruption to the ultrasound transmission function
3Quantity of substance
If charging or discharging is performed at the electrodes to remove charge, then the charge accumulation is reduced, but charge remains in the insulating portion between the electrodes causing sensitivity distortion
Solution Approach 1:
The patent applies reverse-polarity voltage pulses that invert the electric field direction compared to the normal DC bias. This inversion creates a force that pulls charge out of the insulating portion in the opposite direction, effectively discharging trapped charge that cannot be removed by conventional same-direction charging/discharging methods
Solution Approach 2:
The patent changes the voltage polarity parameter from unidirectional to bidirectional. By allowing the voltage to switch between positive and negative polarities, the electric field can exert force in both directions, enabling complete discharge of charge from the insulating portion and eliminating sensitivity distortion caused by residual charge
4Reliability
If the insulating portion has high conductivity to reduce charge accumulation, then the leak current increases, but the sensitivity drift is reduced
Solution Approach 1:
The patent uses periodic reverse-polarity pulses to actively discharge charge from the insulating portion. This periodic action prevents charge accumulation without requiring the insulating portion to have higher conductivity, as the discharge mechanism operates independently of the leak current path, thus maintaining low energy loss while ensuring sensitivity stability
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 apparatus effectively calibrates transmission-reception sensitivity drift by rapidly discharging accumulated charge, minimizing sensitivity distortion and harmonic components, and maintaining sensitivity offset close to zero.
Implementation Method 1
discharge means for discharging a charge accumulated in the insulating portion between the electrodes
Implementation Method 2
utilizing the collapse phenomenon to reduce impedance and accelerate charge discharge
Implementation Method 3
a DC bias and AC pulses are applied between the electrodes so as to modulate a capacitance charge to thereby generate an electric field, so that a diaphragm vibrates and thus an ultrasound wave is generated
Implementation Method 4
reception means for receiving an ultrasound echo from the subject
Data Source
AI summary
An ultrasound diagnostic apparatus 1 causes discharge means 4 to apply a discharge pulse (having a peak value equal to or greater than a collapse voltage) between electrodes of an ultrasound transducer 20 a plurality of time while inverting the polarity of the discharge pulse each time, to thereby accelerate discharge of the charge accumulated in the diaphragm of the ultrasound transducer 20, so that a transmission-reception sensitivity offset can be caused to quickly approach zero. The charge is discharged instantaneously. That is, it is possible to quickly calibrate a transmission-reception sensitivity drift stemming from time-course accumulation of charge flowing into the diaphragm between the electrodes upon application of a DC bias thereto.