Despite the body's signals about our well-being, we often realize too late that the daily stress and exertion have led us to exhaustion, physical injuries, or even mental illnesses. And, the best-intended workout is ineffective if we don't allow ourselves enough time to rest and recover. Data enables us to make more informed decisions to keep ourselves healthier.
Wearable technology has made significant strides in the past decade, largely due to the proliferation of smartwatches. Now, dedicated sensors capable of continuously monitoring our well-being are available in devices as small as fashionable rings. These smart rings can be worn comfortably 24/7 and operate for multiple days on a single charge. They provide valuable data not only about the strain we experience but also about our recovery efficiency during rest. This data allows us to make informed decisions about when to work out, how intensely to exercise when to go to sleep, and when to wake up to optimize recovery. With this wealth of information at our fingertips, we can enhance habits that improve our well-being while identifying and reducing negative impacts.
The heart acts as our central engine, driving the body by pumping blood and distributing oxygen and nutrients where they are needed, regulating body temperature, and performing many other vital functions. Monitoring the heart's activity provides direct insight into our overall well-being. While pulse rate has long been used as a health indicator in medicine, blood oxygen saturation measurements are a more recent development. Today, highly integrated devices are available that use LED light to measure these physiological markers and more. However, integrating this functionality into a device as small as a ring is still no easy feat.
Design Challenges
The high-level requirements for a smart ring include form factor, robustness, visual appeal, comfort, and battery runtime. Since the intention is that the ring is worn continuously, it must withstand various environments and conditions just as our hands do. This includes regular hand washing with soap, exposure to acids and other substances when cooking, salt water when swimming in the ocean, hot temperatures when in the sauna, and the list goes on.
At the same time, the ring is worn on the hand and must be comfortable and non-intrusive, avoiding any hindrance or clunky appearance. If the ring must be removed too often to charge, it will become a burden to the user, charging overnight is not an option since it needs to be worn to assess recovery during sleep.
To translate these high-level requirements into design specifications means the physical space for components is extremely limited, the overall thickness is very limited, and encapsulation in waterproof yet skin-compatible material is necessary. The average power consumption needs to be low enough to allow operation for multiple days on a minuscule battery while keeping a high enough measurement frequency for accurate data collection. The connectivity interface must be secure to ensure that only authorized users can access the data. All these features must fit into a circular object with varying radii to accommodate different ring sizes.
System Setup
This is where Renesas' Smart Ring winning combination (see diagram below) helps smart ring designers achieve their targets. The ring's core is designed around the DA14592, a Bluetooth® Low Energy SoC offering the lowest power consumption and smallest solution footprint in its class. With an ultra-low active current of 34µA/MHz, 2.3mA at 0dBm transmit power, and 1.2mA when receiving, the SoC provides significant processing power with its multi-core processing architecture, which together with Reality AI can implement edge AI applications to optimize the power consumption while maximizing the data analysis. The PTX30W, a single-chip solution for NFC-based charging, integrates an NFC tag, rectifier, Li-ion battery charger, and charging protocol controller all in a WL-CSP of 1.78mm x 1.78mm. Using the NFC-based technology offers the advantage of relatively simple antenna technology based on ultra-thin flexible circuit boards that can reuse the space required by the battery. Combined with the PTX130W NFC Poller on the charger side it allows simple, yet effective wireless charging based on the NFC technology. Combined with the highly integrated yet efficient ISL9120 buck-boost regulator this leaves the designer with as much space as possible to integrate the sensing functionalities.
To learn more about this winning combination and others please visit us at https://renesas.com/win.