Vaishnavi Nattar Ranganathan
Published: 2018
Total Pages: 107
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This work addresses challenges in power delivery, efficient computation and communication to power-constrained wearable and implantable devices. We are surrounded today by over 25 billion smart devices, and this number is constantly increasing. Owing to the shrinking CMOS technology, some of these devices are so small that they can even be worn on the human body or implanted inside it. The sheer number of devices and their drastic minia- turization and integration into the human body posit two major challenges. First, how do we communicate with these numerous small devices? Second, how do we deliver power to them? The wearable or implantable nature of these smart devices only exacerbates these challenges. Since these devices are designed to be worn or implanted, they must be small, comfortable and, most importantly, safe to use. They must be small so that they are dis- crete when worn or can be implanted easily. They must be comfortable so that people can use them for extended periods of time for physiological monitoring, without the devices in- terfering with their normal lifestyle. Finally, they must not cause discomfort by overheating and operate at low power consumption so that they are safe to use. Traditionally, cables were used to power or communicate. However, with the proliferation of smart devices, tethering to communicate with or to recharge them is no longer a practical solution. Bluetooth technology allows some degree of wireless communication with smart devices, but it is a power-hungry technology and thus unsuited for implanted devices. Hence there is a need for reliable communication of data at low power levels. Batteries are currently the most prevalent option for power delivery, but are a less-than-ideal solution. While progress in CMOS technology has reduced size and power consumption of smart devices, the batteries used to power them are still large. With higher energy requirements, larger these batteries become. Even when rechargeable, these batteries have a diminishing eciency over their lifetime of about two to three years. Hence, they are not the best option for powering these billions of devices, especially when they are implanted in the body and need surgery for replacement. One of the solutions to make these devices untethered and battery free is to use wireless power transfer and low-power wireless communication. However, these smart devices used in diverse application have vastly dierent power requirements and communication data rates. Hence, it becomes dicult to standardize ways to wirelessly power and communicate with them. The wireless solutions presented here are applied to two different applications, one wearable and the other implantable, demonstrating the ability to serve diverse requirements. The first application includes a wearable sensing platform that operates with ultra-low power consumption to perform analog sensing of physiological signals and use backscatter communication, which is an ultra-low power communication method, to transmit sensed data. The total power consumption for sensing and communicating data to an external base station is as low as 35 [micro]W to 160 [micro]W. This modular wireless platform is battery- free and can be made in the form of an adhesive bandaid that can sense physiological parameters like heart rate, breathing rate and sense sounds to monitor health conditions. Thus it enables simple, continuous and seamless monitoring of health parameters while a person goes about their everyday tasks. The second application is an implantable platform that can record neural signals from the brain and process them locally to identify events in the signals that can trigger neural stimulations. The requirements for this implantable device are far more complex than the simple wearable application. The implants operate with several 100 mW of power consumption and need several Mbps data rates to transmit the recorded and processed data out to the user. To address the high power and high data rate requirements, this work presents a novel dual-band approach that supports wireless power delivery at high frequency (HF) and backscatter communication at ultra-high frequency (UHF). At the smart implantable device, the dual-band wireless system harvests energy from HF wireless signals while simultaneously communicating data using UHF backscatter. To localize the implant and deliver power to it, a novel low-overhead echolocation method is presented in this work. This method uses reflected parameters on a phased array of wireless power transmitters to locate the wireless device and deliver focussed power to it. The implantable platform is intended for use in two different application domains. First, in neural engineering research where neural interface devices are used to understand, record and map the brain function and to leverage them and develop brain-controlled technology like prosthetic limbs. Second, for treatment and rehabilitation of people suffering from spinal cord injury and chronic neural disorders. An implantable brain-computer-spinal interface (BCSI) is presented in this work, that records neural signals and processes them locally to extract intent. The decoded action intention can be used to trigger stimulation in the spinal cord to reanimate the paralyzed limb and perform the action. In addition, this device is developed as a low-power FPGA-based platform so that it is reconfigurable to enable research in closed-loop algorithms to understand and treat several other neural disorders. We expect that such wireless biomedical sensing can provide a better understanding of physiological parameters and enable treatment for chronic disorders.
