IEEE Trans Ultrason Ferroelectr Freq Control. 2017 Nov;64(11):1723-1734. doi: 10.1109/TUFFC.2017.2739692. Epub 2017 Aug 14.
Air-coupled capacitive micromachined ultrasonic transducers (CMUTs) with annular cell geometry have recently been reported to have a promising transmit sensitivity. This paper reports three optimization schemes, which further improve the transmit sensitivity and also help achieve a reasonable comparison between the novel annular and conventional circular cells. Lumped element models of both cell types with laminate plate structures are presented. Based on these models, a design optimization flowchart was constructed to facilitate analytical optimization on the three schemes. Circular and annular CMUTs with a common 97-kHz natural resonance frequency were fabricated and characterized to verify the efficacy of the optimization principle. Using the optimization flowchart, annular and circular cells with frequencies ranging from 100 to 300 kHz were analytically optimized and then compared. The comparison results demonstrate that, given the same dc bias and ac excitation voltage, the output power density at the plate surface of the optimized annular cell is double that of the optimized circular cell. Additionally, when generating the same surface power density, an optimized annular cell requires either half the dc bias or half the ac excitation voltage of an optimized circular cell. This paper provides a practical optimization framework for CMUT cell design and demonstrates the superiority of annular cells for air-coupled applications.
最近有报道称，具有环形单元几何形状的空气耦合电容式微机械超声换能器 (CMUT) 具有很有前途的发射灵敏度。本文报道了三种优化方案，这些方案进一步提高了发射灵敏度，并有助于在新型环形和传统圆形单元之间实现合理的比较。提出了具有层压板结构的两种单元类型的集总元件模型。基于这些模型，构建了设计优化流程图，以方便对三种方案进行分析优化。制造并表征了具有共同 97 kHz 自然谐振频率的圆形和环形 CMUT，以验证优化原理的有效性。使用优化流程图，对频率范围为 100 至 300 kHz 的环形和圆形单元进行了分析优化，并进行了比较。比较结果表明，在相同的直流偏置和交流激励电压下，优化后的环形单元的板表面输出功率密度是优化后的圆形单元的两倍。此外，当产生相同的表面功率密度时，优化后的环形单元所需的直流偏置或交流激励电压仅为优化后的圆形单元的一半。本文为 CMUT 单元设计提供了实用的优化框架，并展示了环形单元在空气耦合应用中的优势。
