Wearable devices have gained popularity in the healthcare sector over the last decade, offering continuous tracking through devices such as smartwatches and, more recently, rings. Smart rings pack a variety of sensors into a compact, ring-sized form factor and are designed to be worn on the finger, enabling non-invasive monitoring and analysis of health and fitness parameters, such as heart rate, blood oxygen levels, sleep, physical activity, etc.
Understanding Smart Ring Technology
PPG sensors in smart rings detect and measure users’ heart rate and blood oxygen saturation using LEDs and photodetectors. The LEDs emit light at specific wavelengths (typically green and infrared), which then penetrate the skin and interact with blood vessels. The photodetectors measure the amount of light reflected or transmitted through the tissue, depending on the volume of blood in the vessels. As our heart pumps blood, the volume of blood in the vessels changes, causing periodic variations in the amount of light absorbed or reflected. By analyzing these variations, smart rings can measure the user’s heart rate.
Additionally, by comparing the absorption of green and infrared light, a smart ring can estimate the blood oxygen saturation, as oxygenated and deoxygenated hemoglobin have different absorption spectra. For example, the Iris Smart Ring uses PPG sensors that measure blood pressure, heart rate, blood oxygenation, etc., offering wearers a holistic picture of their cardiovascular health.
Accelerometers and gyroscopes, microelectromechanical systems (MEMS), in smart rings are used to detect and quantify motion and orientation. Accelerometers measure the acceleration forces acting on the smart ring, such as gravity, while gyroscopes measure angular velocity and rotation. These sensors are typically deployed in a 3-axis configuration that allows the device to determine a user’s motion and orientation in three-dimensional space. By analyzing patterns and the magnitudes of acceleration and rotation, smart rings monitor the user’s physical activity, e.g, steps taken, distance traveled, and calories burned.
Temperature sensors in smart rings measure the user’s skin temperature, providing insights into thermoregulation and their overall state of health. These sensors are based on thermistors or resistance temperature detectors (RTDs), components that exhibit a change in resistance with variations in temperature. By monitoring the skin temperature, smart rings detect changes that indicate the onset of fever, heat stress, or other health conditions. Additionally, skin temperature information can be used to assess a person’s body response to exercise and also monitor their circadian rhythm and sleep patterns.
Integrating health monitoring features into a smart ring can be challenging at the design phase. First, the ring must be small and comfortable enough to not cause discomfort or interfere with a wearer’s regular activities. The device must also be robust and waterproof to withstand the rigors of everyday use, such as exposure to sweat, moisture, and harsh/adverse environmental conditions. Given the limited space available in a smart ring, smart rings must be designed with power efficiency in mind. Since battery capacity is typically constrained by size, designers will need to utilize ultra-low power components and implement advanced power management techniques to extend battery runtime between charges. Moreover, data security and privacy is critical, as smart rings collect personal health information that needs to be stored, transmitted, and accessed only by authorized individuals.
Data Processing and Analysis
Overcoming the design challenges of smart rings requires powerful, low-power microcontrollers (MCUs) to handle on-device processing. MCUs perform a broad range of functions — from data analysis, signal processing and algorithm execution to power management, improving response times, and enhancing data security by minimizing the need for constant data transmission to external devices or the cloud. Microcontrollers comprise a range of peripherals, such as analog-to-digital converters (ADCs) and sensor interfaces for collecting raw data to process. MCUs with integrated AI accelerators go a step further, providing specialized hardware to accelerate ML workloads. These accelerators allow smart rings to execute AI algorithms in real-time, while consuming less power compared to general-purpose processors. Localized ML processing on the ring can perform sensor fusion in a very smart way to immediately recognize patterns, habits, behaviors, health markers, and signs or symptoms of dangerous conditions without delays related to connected devices or the cloud. When it’s time for the data to leave the ring, it’s more compact and relevant after ML-enhanced sensor fusion which saves power.
Wireless Connectivity
Bluetooth Low Energy (BLE) technology is the de-facto wireless protocol for smart rings due to its low power consumption and widespread compatibility with smartphones and other devices. It operates in the 2.4 GHz ISM band and works with short-range, low-bandwidth communication ideal for periodically transmitting small amounts of data, such as sensor readings and device status information. In a BLE-enabled smart ring, the ring acts as a peripheral device, advertising its presence and waiting for another device, such as a smartphone, to establish a connection. The smart ring will periodically send out advertising packets containing information about its capabilities and a smartphone within range can discover it and initiate a connection to exchange data.
Near-Field Communication (NFC)
NFC, a short-range, high-frequency wireless technology, allows a smart ring to transmit data to and from other NFC-enabled devices, such as payment terminals and smartphones, by bringing them into close proximity. NFC operates at a frequency of 13.56 MHz and has a typical range of a few centimeters, suitable for secure device-to-device communication.
In smart rings, NFC is primarily used for contactless payments, device pairing, and secure data exchange. For example, in contactless payments, the smart ring acts as a secure element that stores a user’s payment methods and communicates with the payment terminal using standard NFC protocols, such as ISO/IEC 14443 and EMV. When the user brings the smart ring close to a terminal, the terminal initiates the transaction, and the ring executes the payment. Samsung Galaxy Ring, for example, uses NFC for contactless payments as well to charge the device. This feature enhances the convenience and practicality of a smart ring in daily life.
Power Management
Power management is critical in smart rings to extend battery life and minimize the frequency of recharging the device. Smart rings utilize both hardware and software techniques to optimize power consumption, ensuring that energy is used only when necessary and in the most efficient manner possible. At the hardware level, smart rings use low-power components such as MCUs, sensors, and wireless radios designed to operate at lower voltages and currents. Additionally, smart rings are designed with advanced packaging techniques such as chip-scale packaging (CSP) and system-in-package (SiP), to reduce the physical size of components and the power usage associated with interconnects and signal routing.
Smart rings also benefit from power management techniques, such as DVFS, which allows the device to adjust its operating voltage and clock frequency based on the current workloads and performance requirements. A key power management technique employed is selective power gating — shutting down unused elements or subsystems when they are not required. Strategically controlling power supply to individual components, such as sensors, radios, and memory banks allows smart rings to systematically lower leakage current and power consumption.
At the software level, smart rings leverage algorithms and programming techniques to minimize any computational overhead and reduce power consumption. This includes techniques such as event-driven programming, where the device remains in a low-power state until triggered by an event, such as an internal timer set to trigger events at a given period of time, or external events that trigger with new sensor data, user interaction, or specific motions.
Alif Balletto B1 Wireless MCU Family for Smart Ring Applications
Block diagram of the operating regions and main internal components of the Alif Semiconductor Balletto B1 Wireless MCUs.
Alif Semiconductor’s Balletto™ family of wireless MCUs combine high performance, energy efficiency, and security features in a small-footprint package, making it suitable for wearables like smart rings. The Balletto B1 is built around the Arm® Cortex® -M55 CPU core, featuring a Helium vector processing extension for handling digital signal processing (DSP) functions. In smart rings, this enables faster and more efficient execution of complex algorithms, such as those used for heart rate and SpO2 calculations. In addition to the Cortex-M55 core, Alif’s B1 features an optional Ethos™-U55 neural processing unit (NPU) that delivers 46 Giga Operations Per Second (GOPS) of performance for advanced and machine learning features such as gesture recognition and fall detection. The B1 also integrates up to 2MB of tightly-coupled SRAM, providing memory for storage and processing without the need for external memory chips. To wirelessly transport all of that processed data off chip to a connected central device like a smartphone, the Balletto B1 integrates a power efficient BLE radio with its own processor running the wireless networking stack. It features high receive (Rx) sensitivity of -99dBm, and offers a choice of two power amplifiers for transmit (Tx) power of up to +10dBm or +4dBm optimizing for higher range or lower power consumption respectively. Additionally, the solution footprint including the external components and the RF antenna is compact enough for a ring form factor.
Key Features and Benefits
Optimized Smart Ring System Architecture
The Balletto B1 can be connected to miniaturized PPG sensors, accelerometers, gyroscopes, and other body function sensors to enable health and activity tracking capabilities. Optimized component placement and PCB layout optimization facilitated by the compact size of the B1 can enhance performance, improve overall design aesthetics, and maximize user comfort.
Lower Power Consumption and Improved Performance
The B1 uses Alif’s advanced power management system, known as aiPM™, intelligently managing the power states of areas of the chip based on the immediate demand of the application. This means that the MCU will dynamically power only necessary regions of the chip at any given time, reducing the overall power consumption. In the lowest power state of STOP mode for example, the B1 MCU consumes as low as 2.3uW. In RUN mode, the processor consumes as low as 0.55uW per CoreMark, where CoreMark is a standard measure of CPU computation output.
In addition to energy efficiency, the B1 delivers high performance for real-time processing of sensor data and execution of AI/ML workloads. The Arm Cortex-M55 CPU core, coupled with the optional Ethos-U55 NPU can provide the processing power for complex algorithms and data analysis on the ring. This enables enhanced data collection and processing capabilities such as heart rate and oxygen saturation measurements using the MCU’s integrated analog front-end and digital signal processing capabilities.
Data Security and Privacy
B1 provides a foundation for implementing secure data handling and protection mechanisms for protecting sensitive information. Alif’s secure enclave features a hardware root-of-trust as well as secure storage and processing. The root of trust enables processes like key generation and storage, secure boot, and cryptographic acceleration, ensuring that user data is protected from unauthorized access or tampering. To ensure that smart rings powered by the B1 are secure and compliant with evolving data protection regulations, Alif enables secure over-the-air (OTA) firmware updates. This allows device manufacturers to send security patches and feature enhancements wirelessly, ensuring that products remain protected against emerging threats.
Conclusion
By combining smart sensors, low-power processing capabilities and intuitive user interfaces, smart rings offer a convenient and comfortable means for users to track their vitals and make informed decisions about their health. However, the viability of smart rings lies in their ability to deliver reliable, precise, and secure health monitoring in small and energy-efficient packages. Alif’s Balletto family addresses these limitations with low power consumption, high-performance processing capabilities, and advanced security features, enabling manufacturers to design smart rings that are both highly functional and appealing to users.
To learn more about Alif Semiconductor’s Balletto B1 wireless MCUs and how they can be integrated into your smart ring applications, please contact Alif Semiconductor.