Frequency-Tunable Ultrasonic Transducer With DC Bias Control
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Solution Overview
Problem
Existing ultrasonic inspection devices lack the ability to efficiently adjust and tune the resonance frequency of ultrasonic transducers for different applications, leading to suboptimal performance in various inspection scenarios.
Innovation Solution
A hybrid transducer structure combining PMUT and CMUT modes, utilizing a control circuit to apply DC bias and AC excitation voltages across multiple electrodes, allowing for adjustable resonance frequency through the spring softening effect in CMUT transducers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional ultrasonic transducer structure is used, then the device structure is simple, but the resonance frequency cannot be adjusted for different applications
Solution Approach 1:
The patent applies the dynamics principle by making the transducer's resonance frequency adjustable through a control circuit that can dynamically change the electrical characteristics of the piezoelectric layer. The bias voltage applied to the piezoelectric layer modifies its effective permittivity, thereby tuning the resonance frequency according to the formula f₀ = (1/2π)√(k/C), where C depends on the piezoelectric layer's electrical properties. This allows the transducer to adapt to different inspection frequencies without physical restructuring.
Solution Approach 2:
The patent implements parameter changes by modifying the electrical parameters of the piezoelectric layer through applied bias voltage. By changing the DC bias voltage level, the effective permittivity of the piezoelectric material changes, which directly alters the capacitance of the piezoelectric layer and consequently tunes the resonance frequency. This electrical parameter adjustment provides a simple yet effective method for frequency adaptation.
2Adaptability or versatility
If the resonance frequency is adjusted by changing physical structure, then the frequency can be tuned, but the electro-acoustic efficiency degrades
Solution Approach 1:
The patent avoids physical structural changes by instead modifying the electrical parameters of the piezoelectric layer through bias voltage. This electrical tuning method preserves the optimal physical coupling between the piezoelectric layer and the membrane, maintaining high electro-acoustic efficiency while achieving frequency adjustment. The piezoelectric layer's effective permittivity changes with bias voltage, enabling frequency tuning without altering the mechanical structure that determines coupling efficiency.
Solution Approach 2:
The patent replaces mechanical/physical structural adjustment with an electrical control mechanism. Instead of physically changing the transducer dimensions, material composition, or mechanical coupling to tune frequency, the invention uses electrical biasing of the piezoelectric layer to achieve the same effect. This substitution of mechanical adjustment with electrical control maintains the integrity of the electro-acoustic conversion process while providing frequency adaptability.
3Reliability
If multiple fixed-frequency transducers are used, then each transducer is optimized for its frequency, but the device complexity and cost increase
Solution Approach 1:
The patent implements universality by designing a single transducer structure that can perform multiple frequency functions. The piezoelectric layer, when subjected to different bias voltages, can be tuned to resonate at different frequencies, allowing one transducer to replace multiple fixed-frequency transducers. This multi-functional capability is achieved through the electrical tuning mechanism that modifies the piezoelectric layer's effective permittivity and thus its resonant characteristics.
Solution Approach 2:
The patent applies dynamics by transforming a static, fixed-frequency transducer into a dynamic, frequency-tunable device. The control circuit dynamically adjusts the bias voltage applied to the piezoelectric layer based on the desired operating frequency, enabling the transducer to adapt its resonance characteristics in real-time. This dynamic control allows a single transducer to function across multiple frequency bands that would otherwise require separate dedicated transducers.
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
Enables the ultrasonic transducer to operate at different frequencies without degrading electro-acoustic efficiency, enhancing performance in applications such as motor vehicle parking radar and medical imaging by adjusting the DC bias voltage to match the desired frequency requirements.
Implementation Method 1
a piezoelectric layer attached to a surface of the membrane; a control circuit connected to the first and second electrodes and capable of applying a first control voltage on the first electrode, and a second control voltage different from the first voltage on the second electrode
Implementation Method 2
the control circuit is capable of varying the level of the DC bias voltage applied to the first electrode to vary the resonance frequency of the ultrasonic transducer
Implementation Method 3
The ultrasound waves emitted by the transducers are reflected by the body to be analyzed (by its internal and/or surface structure), and then return to the transducers, which convert them back into electric signals
Data Source
AI summary
An ultrasonic device, comprising an ultrasonic transducer (400) comprising: a membrane (405) suspended above a cavity (403) arranged on the upper surface side of a substrate (401); a piezoelectric layer (407) attached to a surface of the membrane (405); a first electrode (E1) arranged on the lower surface side of the cavity (403); and a second electrode (E3) arranged on the upper surface side of the cavity (403), in contact with the piezoelectric layer (407), the device further comprising a control circuit (CTRL) connected to the first (E1) and second (E3) electrodes and capable of applying a first control voltage (VDC) on the first electrode (E1), and a second control voltage (VAC) different from the first voltage on the second electrode (E3).