Huang Xuechen, Denprasert Petcharat May, Zhou Li, Vest Adriana Nicholson, Kohan Sam, Loeb Gerald E
Department of Biomedical Engineering, University of Southern California, Los Angeles, CA, USA.
General Stim Inc., Los Angeles, CA, USA.
Biomed Microdevices. 2017 Sep;19(3):46. doi: 10.1007/s10544-017-0189-9.
We have developed and applied new methods to estimate the functional life of miniature, implantable, wireless electronic devices that rely on non-hermetic, adhesive encapsulants such as epoxy. A comb pattern board with a high density of interdigitated electrodes (IDE) could be used to detect incipient failure from water vapor condensation. Inductive coupling of an RF magnetic field was used to provide DC bias and to detect deterioration of an encapsulated comb pattern. Diodes in the implant converted part of the received energy into DC bias on the comb pattern. The capacitance of the comb pattern forms a resonant circuit with the inductor by which the implant receives power. Any moisture affects both the resonant frequency and the Q-factor of the resonance of the circuitry, which was detected wirelessly by its effects on the coupling between two orthogonal RF coils placed around the device. Various defects were introduced into the comb pattern devices to demonstrate sensitivity to failures and to correlate these signals with visual inspection of failures. Optimized encapsulation procedures were validated in accelerated life tests of both comb patterns and a functional neuromuscular stimulator under development. Strong adhesive bonding between epoxy and electronic circuitry proved to be necessary and sufficient to predict 1 year packaging reliability of 99.97% for the neuromuscular stimulator.
我们已经开发并应用了新方法来估算微型、可植入式无线电子设备的功能寿命，这些设备依赖于诸如环氧树脂之类的非气密、粘性密封剂。具有高密度叉指电极（IDE）的梳状图案板可用于检测因水蒸气凝结导致的早期故障。利用射频磁场的电感耦合来提供直流偏置，并检测封装梳状图案的劣化。植入物中的二极管将部分接收能量转换为梳状图案上的直流偏置。梳状图案的电容与电感器形成谐振电路，植入物通过该电路接收功率。任何水分都会影响电路谐振的谐振频率和品质因数，通过其对放置在设备周围的两个正交射频线圈之间耦合的影响来进行无线检测。在梳状图案设备中引入了各种缺陷，以证明对故障的敏感性，并将这些信号与故障的目视检查相关联。在梳状图案和正在开发的功能性神经肌肉刺激器的加速寿命测试中，验证了优化的封装程序。事实证明，环氧树脂与电子电路之间的强粘合对于预测神经肌肉刺激器1年99.97%的封装可靠性是必要且充分的。
