Bio-impedance is a method to assess the body composition safely, non-invasively and inexpensively. This method finds application for assessing body fluid and body composition for multiple disease scenarios in clinical environments and for at-home monitoring of chronic ailments. Bio-impedance sensors require higher power than most other bio-signal acquisition systems due to need of high frequency current and voltage management. Currently used bio-impedance devices are bulky due to incorporation of large batteries and cannot be used for long term monitoring, especially for wearable applications. This limits the widespread implementation of bio-impedance measurement devices. We present the design and implementation of a wireless wearable bio-impedance sensor node, ImpediSense, which has a low power system design that achieves long duration operability without compromising on sensor measurement accuracy and precision. Experimental evaluation show a battery life of several months for measuring bio-impedance with power duty cycling every 1 min over ten frequencies in the range of 10 kHz–100 kHz, using a small form factor 250 mA h Li-ion battery. The lifetime is achieved due to several power optimization implemented in system design of hardware and firmware resulting in active power of 53 mW and idle power of 15.7 μW. Additionally, the presented sensor node shows high performance in terms of accuracy of impedance measurement with an error less than 1.5 % and precision of 0.6 Ω when measuring tetrapolar bio-impedance of the human body. With the inclusion of a small sized battery, ImpediSense has a compact form factor with dimensions 3 cm × 1.8 cm × 0.6 cm, making it more conducive for incorporation in wearable systems.

生物阻抗是一种安全，无创且廉价地评估人体成分的方法。此方法可用于评估临床环境中多种疾病场景的体液和身体成分，以及在家中监测慢性病。由于需要高频电流和电压管理，生物阻抗传感器比大多数其他生物信号采集系统需要更高的功率。当前使用的生物阻抗设备由于内置了大型电池而体积庞大，因此无法用于长期监控，尤其是在可穿戴应用中。这限制了生物阻抗测量设备的广泛实施。我们介绍了无线可穿戴生物阻抗传感器节点ImpediSense的设计和实现，它具有低功耗系统设计，可在不影响传感器测量精度和精度的情况下实现长时间的可操作性。实验评估表明，使用小型250 mA h锂离子电池，在10 kHz至100 kHz范围内的十个频率上，每1分钟测量一次功率循环，可测量生物阻抗的电池寿命为数月。由于在硬件和固件的系统设计中实现了几次功率优化，从而实现了使用寿命，从而使有功功率为53 mW，空闲功率为15.7μW。此外，在测量人体的四极生物阻抗时，提出的传感器节点在阻抗测量的精度方面表现出很高的性能，误差小于1.5％，精度为0.6Ω。加上小型电池，