Wearable devices continue to fuel a fast-growing drive toward more comprehensive services in health and fitness. Propelling this growth, the combination of market need and technological advances are encouraging the evolution of advanced wearables well beyond earlier heart monitors and simple fitness devices. At the heart of next-generation wearables, advances in sensors, microcontroller units (MCUs), and integrated connectivity technologies promise to enable more personalized, more sophisticated, and more effective capabilities.

Fig. 1 – Health and fitness enthusiasts are turning to more sophisticated apps tied to advanced activity trackers such as the Jawbone UP24. (Credit: Jawbone)

In providing healthcare, providers have found themselves caught between the need for complete data on patient health and the limitations inherent in applying that data to gain an understanding of a patient’s overall health. Accurate diagnosis and treatment depends on a clear picture of an individual’s health. Yet, healthcare providers rely on tests administered in physicians’ offices, clinics, or hospitals that offer, at best, a static snapshot of an individual’s ever-changing health dynamics. More long-term data that could reveal persistent sources of concern or eliminate transient conditions remain unavailable outside expensive extended stays in overbooked health facilities. For individuals themselves, the need to go to an office or even deal with at-home medical equipment becomes disruptive and too often translates into noncompliance with health treatment plans.

Remote Monitoring Advantages

Widespread use of wearables able to provide long-term health data can lead directly to measurable improvements in healthcare. The Continua Health Alliance, Beaverton, OR, a non-profit industry organization of healthcare and technology companies, sees remote monitoring, or telehealth, as a key enabler for healthcare solutions needed to address skyrocketing spending on chronic disease already surpassing $500 billion/yr. In fact, the international Groupe Speciale Mobile Association (GSMA), London, UK, sees specific measurable advantages. According to the GSMA, a study of patients in the US with chronic heart failure found that remotely monitored patients had fewer and shorter hospital stays than a control group. In fact, a separate study noted that remote monitoring of patients with chronic heart failure could reduce re-hospitalizations by 72 percent.

Wearable electronic devices promise to directly address growing concerns about healthcare cost and effectiveness. By providing a steady stream of health data, these devices can offer individuals and their healthcare providers a better understanding of the individual’s health than available in the past. Instead of isolated snapshots taken in physicians’ offices or hospitals, wearable health and wellness products can offer a more accurate history for interpreting health incidents and for assessing overall health trends. In fact, more advanced wearables will even provide instant response to health events or allow physicians to perform remote diagnostics and limited treatment.

Trends in Health Wearables

Fig. 2 – Powered by a user-replaceable CR2032 Li-ion battery, the Misfit Shine activity monitor is based on an ultra-low-power ARM Cortex-M3-core based MCU from Silicon Laboratories. (Credit: Silicon Laboratories)

Personal activity trackers continue to evolve well beyond the simple devices that for years have helped individuals monitor their heart rates during exercise. Manufacturers are shrinking these devices in size, allowing users to wear them continuously, comfortably, and inconspicuously. Next-generation fitness wearables such as the Jawbone UP24™, LG Lifeband Touch, and Sony Core are becoming more powerful, providing more comprehensive data to sophisticated apps able to offer better guidance on fitness and overall wellness trends (See Figure 1).

At the same time, a new wave of more sophisticated wearables promises to elevate the nature of monitored data to offer continuous updates of important diagnostic data. For example, iHealth Lab’s ambulatory blood pressure monitor, wireless ambulatory ECG, and wearable pulse oximeter all combine wearable sensor systems that transmit data wirelessly to smartphones using Bluetooth® technology. The ambulatory blood pressure monitor is designed to be worn inside a vest to provide 24-hour monitoring without changing a user’s normal daily routine. The ECG device’s electrodes and monitor are combined in a lightweight unit that attaches directly to the user’s chest and can be worn under clothing, pushing data to the cloud for access by healthcare providers. Similarly, the pulse oximeter uses a fingertip sensor attached to a comfortable wristband, enabling oxygen saturation (SpO2) measurements 24 hours/day.

Embedded Sensors

Fig. 3 – The SD-card-size Intel Edison development board features a two-core Quark with on-board memory and both Wi-Fi and Bluetooth Low Energy. (Credit: Intel®)

Underlying the rapid emergence of advanced health wearables, advances in key technologies are providing wearables designers with more flexible sensors, ultra-low-power processors, integrated wireless communications, flexible electronics, and innovative packaging. In fact, one of the key breakthroughs in the past few years has been the ability of manufacturers to weave sensor arrays into clothing, enabling development of diagnostic instruments that can be worn comfortably and unobtrusively.

For example, AiQ Smart Clothing embeds tiny stainless steel threads into fabric, providing a conductive mesh for embedded sensors able to monitor skin temperature and moisture, as well as bioelectric measurements including electrocardiograms, electroencephalograms, and electromyograms, among others. Embedded unobtrusively in clinical garb such as patient gowns and blankets, this sensor array could noninvasively and continuously provide healthcare providers with an ongoing source of vital statistics.

Looking to reduce misdiagnosis in current screening procedures, First Warning Systems, Inc., is using its own embedded sensor technology in its smart bra, designed to deliver non-radiogenic, noninvasive diagnostic data while being worn like any other bra. The company’s smart bra embeds multiple sensors to collect data for predictive analysis by software that can actually alert physicians to possible abnormalities. Confirmed in clinical trials, First Warning Systems’ technology monitors tissue changes that occur before tumors appear, offering an affordable early warning that helps make current screening practices more effective.

Active Wearables

While delivering more sophisticated healthcare data, wearables are even moving beyond passive monitoring devices. Soon, healthcare providers will be able to fit patients with active wearables designed to deliver specific treatments. For example, Thimble Bioelectronics is developing a small patch designed to offer mobile treatment for localized pain using transcutaneous electrical nerve stimulation (TENS) and electromyostimulation (EMS). In the past, bulky TENS/EMS devices have tethered individuals to at-home equipment or equipment installed in physical therapists’ treatment rooms. Instead, these new wearables can offer the kind of long-term, immediate treatment needed to deliver extended relief from chronic pain.

Insulet’s OmniPod® provides a wearable insulin delivery system in tandem with its Personal Diabetes Manager (PDM). The PDM combines a built-in blood glucose meter with wireless control of insulin injections administered by the small wearable insulin-delivery pod. Unlike conventional insulin injection systems, the waterproof OmniPod can be worn continuously—even while swimming and showering—without risking noncompliance or compromising an active lifestyle.

Creating a wearable product for medical, health, and fitness applications presents new and unique design challenges. Engineers must combine advanced sensor systems, low-power embedded systems, and wireless communications into the smallest possible biocompatible packages. At the same time, wearables like wristbands or others likely to be visible must offer the form and fit of an attractive fashion accessory, while still providing extended running time between infrequent charges.

Ultra-Low-Power MCUs

With the demand for both extended wear time and greater functionality, designers face conflicting requirements of power and performance. The emergence of highly integrated ultra-low-power MCUs has helped developers address these challenges in the design of next-generation wearables. For example, Insulet based its OmniPod on Freescale Semiconductor’s ultra-low-power S08 core architecture. These highly integrated MCUs combine on-chip RAM, flash, timers, ADCs, and multiple interface options while providing multiple low-power modes featuring only 20 nA in power-down mode. With the MCU’s very low power requirements, Insulet can remain confident that energy from the OmniPod’s two AA batteries remains largely reserved for running the relatively power-hungry insulin pump.

For its Shine wearable wireless activity monitor, Misfit faced even greater power constraints. Misfit decided that requiring users to frequently recharge the Shine would interfere with its role as a continuously worn monitor. Consequently, Misfit powers its Shine™ activity monitor from a user-replaceable CR2032 Li-ion battery expected to provide at least four months of power for a feature-rich wireless application.

With this limited power budget, the Shine must process data from its three-axis accelerometer using a series of sophisticated algorithms while driving an LED-based user interface and communicating wirelessly with the Shine app on smartphones. In this case, Misfit designed the Shine around the Leopard Gecko MCU—Silicon Laboratories’ ultra-low-power implementation of the ARM Cortex-M3 core (See Figure 2). Features like the Gecko’s low-energy sensor interface (LESENSE) and peripheral reflex system (PRS) help minimize power by allowing the MCU core to sleep while still collecting sensor data with LESENSE and allowing autonomous peripheral operations with PRS.

Fig. 4 – The Wearable Reference Platform (WaRP) combines a main board (top) with daughter board to offer complete hardware complement for a wearable design. (Credit: WaRPboard.org)

Intel® designed its Quark MCU specifically to target wearable and similar deeply embedded applications where low power and small footprint are more critical than raw performance. The initial Quark device, the X1000, integrates a 400MHz 32-bit core with 512KB SRAM, a DDR3 memory controller and multiple connectivity options. Recognizing the growing need for security in wearable applications, the X1000 includes an on-chip boot ROM that provides a hardware root of trust used in authentication.

MCU manufacturers are integrating more memory and features into faster devices. Among those features, on-chip wireless transceivers simplify design and allow developers to squeeze their systems into smaller packages. In fact, integrated support for Bluetooth Low Energy (BLE) allows wearables designers to leverage BLE support available in the extensive existing base of smartphones, tablets, and other mobile devices. For example, the Texas Instruments (TI) CC2540 and CC2541 SoCs each combine an 8051-based MCU core with on-chip 2.5 GHz transceiver. Both TI devices are BLE compliant, while the CC2541 also adds support for proprietary protocols.

Nordic Semiconductor’s nRF51422 MCU allows designers to support both BLE as well as the ANT/ANT+ protocol commonly used for connectivity in fitness markets. Based on the 32-bit ARM Cortex-M0 core, the nRF51422 integrates an embedded 2.4GHz transceiver that supports BLE, ANT, and proprietary 2.4GHz protocols.

Accelerated Development

Even as more effective electronic components and packaging methods emerge, designers face greater complexity in fashioning hardware and software components into practical wearable system designs. For the fast-moving health market, wearable device manufacturers find themselves caught be tween this growing design complexity and increasingly short market windows.

To help accelerate development, manufacturers are offering reference designs, design kits and development frameworks. For example, Intel offers its Edison development board, which provides wearable designers with a very small (SD card form) platform that combines a 400MHz Quark with two cores, LPDDR2 and NAND flash storage, and both Wi-Fi and BLE connectivity (See Figure 3).

Beyond development aids such as Intel’s Edison board, designers can find development frameworks tailored for wearables. For example, a group of collaborating companies led by Freescale Semiconductor offers a comprehensive wearables reference platform (WaRP). Intended as a comprehensive open source, scalable solution for wearable design (See Figure 4), WaRP combines the Freescale i.MX 6SoloLite ARM Cortex-A9 application processor, Xtrinsic MMA955xL Intelligent Motion-Sensing Platform, and Freescale FXOS8700CQ 6-Axis digital sensor with Kynetics software and Revolution Robotics hardware.

Texas Instruments offers its own Chronos Personal Area Network (PAN) and sensor node reference design based on an MSP430 MCU with integrated sub-GHz wireless transceiver. Offered in a sports watch format, the Chronos platform can be paired wirelessly with heart-rate monitors, pressure sensors, and other measurement units.

Movea partnered with TI and Xm-Squared to offer its G-Series wearable wristband reference design to mon itor a wide range of health characteristics including activity, posture, and sleep as well as movement speed and cadence. The reference design combines Movea’s Motion sport embedded library and a wristband design from Xm-Squared with TI’s low-power CC2541 SoC, which provides both BLE and proprietary 2.4-GHz wireless communications. For medical applications, one of the reference design’s distinguishing features is its support for sleep analysis, able to deliver results close to the polysomnography methods used in hospital sleep studies.

Conclusion

Wearables promise to address ongoing concerns in the healthcare industry about the quality and immediacy of vital statistics. By providing ready access to the results of long-term monitoring, wearable technologies can deliver data that healthcare providers need to diagnosis health problems more quickly and accurately—and begin to address skyrocketing costs for treatment of chronic disease and pain.

With the continued emergence of more advanced sensors, ultra-low-power MCUs, flexible electronics and packaging, wearables are finding application in medical, fitness, and health arenas once the sole domain of expensive hospital equipment or at-home units.

For developers, a growing list of reference designs and design kits offer a ready starting point for venturing into wearable products.

This article was written by Dr. Stephen Evanczuk, Principal, WebPatter LLC, for Mouser Electronics, headquartered in the DFW Metroplex, TX. For more information about Mouser Electronics, visit http://info.hotims.com/49749-165 .


Medical Design Briefs Magazine

This article first appeared in the September, 2014 issue of Medical Design Briefs Magazine.

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