Liu Yuchen, Hafezi Mahshid, Feeney Andrew
Centre for Medical and Industrial Ultrasonics, University of Glasgow, James Watt School of Engineering, Glasgow, G12 8QQ, United Kingdom.
Centre for Medical and Industrial Ultrasonics, University of Glasgow, James Watt School of Engineering, Glasgow, G12 8QQ, United Kingdom.
Ultrasonics. 2024 Feb;137:107201. doi: 10.1016/j.ultras.2023.107201. Epub 2023 Nov 10.
Across power ultrasonics and sensing, piezoelectric ultrasonic transducers commonly experience degradation in mechanical, electrical, and dynamic performance due to the relatively high sensitivity of piezoelectric materials to changes in temperature. These changes, arising for example through high excitation voltages or environmental conditions, can lead to nonlinear dynamic behaviours which compromise device performance. To overcome this, the excitation signal to the piezoelectric material is often pulsed, mitigating the influence of temperature rises. However, there remain constraints on suitable candidate piezoelectric materials for power ultrasonic devices. As a novel approach to mitigating the influence of temperature on the properties of piezoelectric materials, the phase-transforming shape memory alloy Nitinol is incorporated into the piezoelectric stack of a Langevin power ultrasonic transducer, in a cascade formation. The underlying principle is that the nonlinear hardening response of Nitinol to rising temperature can be used to dynamically compensate for the nonlinear softening of the piezoelectric materials. Thus, the dynamic response of the transducer can be linearised at elevated excitation levels. In this study, two configurations of Langevin transducer are designed and characterised. One transducer incorporates a Nitinol middle mass, and in the second, titanium. A combination of electrical and thermomechanical characterisation is undertaken, where it is demonstrated that the nonlinear softening of the piezoelectric stack can be mitigated through control of the Nitinol microstructure. The vibration amplitudes of the Nitinol-middle cascaded transducer are higher and more stable when the Nitinol is austenite rather than a combination of martensite and austenite at room temperature. It has also been shown that the vibration amplitude and resonance frequency of Nitinol-middle cascaded transducer remain stable as temperature changes from 20 °C to 45 °C, dependent of the excitation voltage. Moreover, the self-heating experiment demonstrates the resonance stability of the Nitinol-middle cascaded transducer for continuous operation.
在功率超声和传感领域，由于压电材料对温度变化相对较高的敏感性，压电超声换能器通常会在机械、电气和动态性能方面出现退化。例如，通过高激励电压或环境条件引起的这些变化，可能会导致非线性动态行为，从而损害器件性能。为了克服这一问题，施加到压电材料上的激励信号通常采用脉冲形式，以减轻温度升高的影响。然而，对于功率超声器件而言，合适的候选压电材料仍然存在限制。作为减轻温度对压电材料性能影响的一种新方法，将相变形状记忆合金镍钛诺以级联形式并入兰姆波功率超声换能器的压电叠层中。其基本原理是，镍钛诺对温度升高的非线性硬化响应可用于动态补偿压电材料的非线性软化。因此，在较高的激励水平下，换能器的动态响应可以线性化。在本研究中，设计并表征了两种配置的兰姆波换能器。一种换能器包含镍钛诺中间质量块，另一种则包含钛。进行了电学和热机械特性的综合表征，结果表明，通过控制镍钛诺的微观结构，可以减轻压电叠层的非线性软化。当镍钛诺在室温下为奥氏体而非马氏体和奥氏体的组合时，含镍钛诺中间质量块的级联换能器的振动幅度更高且更稳定。研究还表明，含镍钛诺中间质量块的级联换能器的振动幅度和共振频率在温度从20℃变化到45℃时保持稳定，这取决于激励电压。此外，自热实验证明了含镍钛诺中间质量块的级联换能器在连续运行时的共振稳定性。
