Rapid technology advances have changed the ways we live and work; the way we consume entertainment and news, how we communicate with each other, and how we work and play. There are more computers in each person’s homes than there were in major corporations 50 years ago, and we have more computing and communication power in our pockets—in the form of smartphones—than anyone had even ten years ago.
Despite the change, what has remained constant over the decades is people’s basic concern for the well-being of themselves and their families. And so, not surprisingly, one of the fastest growing areas for smartphone applications is health and wellness. These apps rely on the ability of new sensor systems to gather information about our activities—everything from counting steps and measuring calorie burn to monitoring for heart arrhythmia.
Beginnings
Back in 2012, Plessey Semiconductors demonstrated one of the earliest prototypes of a wearable, personal health device: a heart-rate monitor in the form factor of a wristwatch (Figure 1). The reference design sensed electrocardiograph (ECG) signals using a sensor electrode on the rear of the device in permanent contact with the wrist; touching a second electrode on the front of the device with a finger from the opposite hand enabled the device to collect heart signals.
Figure 1: Plessey Semiconductors’ demonstrator for its EPIC sensor. (Source: Electronic Products)
The demonstrator was based on Plessey’s PS25x01 series EPIC (electric potential integrated circuit) sensor technology, developed in conjunction with the University of Sussex, UK. The sensors are the first to measure changes in an electric field much as a magnetometer detects changes in a magnetic field, requiring no physical or resistive contact to take readings. It works at normal room temperatures and functions as an ultra-high-input impedance sensor, using active feedback techniques to both lower the effective input capacitance of the sensing element and boost its input resistance. In effect, it is a near-perfect voltmeter, highly stable and able to measure tiny changes in an electric field down to millivolts.
Another health-related sensing system involving electric potential, albeit at a much higher level, was also introduced in 2012 by ams. A programmable, fully integrated lightning sensor, the ams AS3935 Franklin IC detects the approach of potentially hazardous lightning storms, estimating the distance to the head of the storm so that users can seek shelter well in advance of any danger (Figure 2).
Figure 2: The AS3935 Franklin lightning sensor from ams. (Source: Electronic Products)
The sensor is essentially a radio receiver with an embedded lightning algorithm that checks the incoming signal pattern for approaching lightning, while rejecting any false signals due to man-made disturbances. Like the Plessey device, ams envisioned this as a wristwatch-like device that could be worn by, say, golfers out on the fairway.
At Sensors Expo in 2014, ROHM/Kionix demonstrated a wearable key device. The demo device is designed to transmit data, using the Bluetooth Low Energy specification, from multiple sensors in the key to smartphones and tablets. The design integrates an ultra-high sensitivity magnetic-impedance (MI) sensor, accelerometer, gyroscope, barometric pressure sensor, proximity/ambient light sensor (ALS), and RGB/UV sensors in a compact, lightweight key-shaped enclosure (Figure 3).
Figure 3: A wearable key device demonstrator. (Source: ROHM)
The sensor complement makes possible a variety of functions and operations. For instance, it can serve as an activity monitor, not only estimating calories burned and counting steps taken, but even detecting when the wearer is riding in a vehicle (i.e. bus, train, car) or walking up/down stairs, and track time traveled. Wearing the key externally will allow a user to determine how much UV radiation they are receiving, and alert them if there’s a danger of sunburn or risk of melanoma.
Today’s Healthy Wrist
Jumping ahead to the current year, we find that there are a significant number of smartwatches available on the market. Consider the recently introduced Fitbit Surge as well as the Garmin vivoactive.
The Fitbit Surge contains a GPS, 3-axis accelerometers, a 3-axis gyroscope, a digital compass, an optical heart-rate monitor, an altimeter, an ambient light sensor, and a vibration motor. GPS tracking allows users to see distance, pace, and elevation climbed, as well as review routes and split times, while the PurePulse optical heart-rate monitor provides continuous, automatic, wrist-based heart rate and simplified heart-rate zones. Users can track steps, distance, calories burned, floors climbed, and active minutes, and the device can also monitor sleep and automatically set a silent alarm. The wearable can communicate with iOS, Android, and Windows mobile devices, as well as with a separate digital scale to record weight information.
Figure 4: The Fitbit Surge. (Source: Fitbit)
The Garmin vivoactive has been called “one of the best for true fitness types...” because of its data handling and presentation capabilities. In addition to being able to monitor running, walking, and cycling activities, its software can also evaluate golf and swimming sessions. It works with both mobile and desktop platforms, syncs quickly and supports Windows mobile. Heart-rate monitoring is optional, using Garmin’s ANT+ sensor accessories, and requires users to strap a separate device to their chest; the ANT+ sensor communicates wirelessly with the wrist device.
Figure 5: The Garmin vivoactive. (Source: The Verge)
Next Generation
While today’s focus is mainly on devices that strap onto the wrist, a new generation of printable, flexible sensors is in development. These will allow sensors to directly and continuously gather even more types of data.
For instance, Northeastern University’s Center for High-Rate Nanomanufacturing has developed a simple, highly sensitive multi-biosensor containing semiconductor single-walled carbon nanotubes (SWCNTs) printed on a flexible substrate (Figure 6). The SWCNTs are enzyme-immobilized for detecting D-glucose, L-lactate, and urea in sweat in real-time. The ability to print these materials results in low manufacturing costs.
Figure 6: A flexible biosensor, based on single-walled carbon nanotubes, created by researchers at Northeastern University’s CHN. (Source: Electronic Products)
At the University of California, San Diego’s Center for Wearable Sensors, a research team has developed a skin-worn “tattoo,” a wearable electrochemical device that includes electrolyte and metabolite sensors, a biofuel cell, and batteries (Figure 7). Sensors can be applied to subjects’ arms to monitor analytes —the chemical constituent of interest in an analytical procedure.
Figure 7: A printed, flexible, and stretchable “tattoo” of electrochemical sensors developed by researchers at UCSD’s Center for Wearable Sensors. (Source: Electronic Products)
Continuing advances in sensor design and packaging will one day make it natural for people to have their vital indicators constantly and comfortably monitored whenever warranted. The result will be less worry about our health and hopefully a longer and more enjoyable