Ultrasonic backscatter communication has gained popularity in recent years with the advent of deep-tissue sub-mm scale biosensing implants in which piezoceramic (piezo) resonators are used as acoustic antennas. Miniaturization is a key design goal for such implants to reduce tissue displacement and enable minimally invasive implantation techniques. Here, we provide a systematic design approach for the implant piezo geometry and operation frequency to minimize the overall volume of the implant. Optimal geometry of the implant piezo for backscatter communication is discussed and contrasted with that of power harvesting. A critical design aspect of an ultrasonic backscatter communication link is the response of the piezo acoustic reflection coefficient $\Gamma$ with respect to the variable shunt impedance, $Z_E$ , of the implant uplink modulator. Due to the complexity of the piezo governing equations and multi-domain, electro-acoustical nature of the piezo, $\Gamma (Z_E)$ has often been characterized numerically and the implant uplink modulator has been designed empirically resulting in sub-optimal performance in terms of data rate and linearity. Here, we present a SPICE friendly end-to-end equivalent circuit model of the channel as a piezo-IC co-simulation tool that incorporates inherent path losses present in a typical ultrasonic backscatter channel. To provide further insight into the channel response, we present experimentally validated closed form expressions for $\Gamma (Z_E)$ under various boundary conditions. These expressions couple $\Gamma$ to the commonly used Thevenin equivalent circuit model of the piezo, facilitating systematic design and synthesis of ultrasonic backscatter uplink modulators.

中文翻译：

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优化生物传感超声植入物中的容积效率和反向散射通信

近年来，随着深组织亚毫米级生物传感植入物的出现，其中压电陶瓷（压电）谐振器用作声学天线，超声波反向散射通信越来越受欢迎。小型化是此类植入物的关键设计目标，以减少组织位移并实现微创植入技术。在这里，我们为植入物压电几何形状和操作频率提供了一种系统的设计方法，以最大限度地减少植入物的整体体积。讨论了用于反向散射通信的植入压电的最佳几何形状，并与功率收集的几何形状进行了对比。超声波反向散射通信链路的一个关键设计方面是压电声反射系数的响应$\伽玛$ 关于可变分流阻抗， $Z_E$ ，植入上行链路调制器。由于压电控制方程的复杂性和压电的多域电声性质，$\伽玛 (Z_E)$经常以数字方式表征，并且根据经验设计了植入上行链路调制器，导致数据速率和线性度方面的性能欠佳。在这里，我们提出了一个 SPICE 友好的通道端到端等效电路模型，作为压电 IC 协同仿真工具，它结合了典型超声反向散射通道中存在的固有路径损耗。为了进一步了解通道响应，我们提出了经过实验验证的封闭形式表达式$\伽玛 (Z_E)$在各种边界条件下。这些表达结合$\伽玛$ 与常用的压电戴维南等效电路模型相结合，便于超声反向散射上行调制器的系统设计和合成。