Multifunction biosensor/vital signs monitor for wearables, from ams
AS7000 is the first in what is to be a family of health/fitness solutions from ams, for wearable devices. The AS7000 solution incorporates a highly integrated optical sensor module accompanied by software to provide the highest accuracy optical heart rate measurements (HRM) and heart rate variation (HRV) readings, backed by opto-mechanical design-in support. The 24/7 reference is to indicate that ams intends the device for products that are worn continuously, rather than (for example) only during periods of exercise.
In a 6.1 x 4.1 x 1.0 mm package, ams presents the AS7000 as the first complete integrated health and fitness solution for wearables; it may enable devices such as fitness bands as well as sports and smart watches to replace cumbersome, uncomfortable electro-cardiogram (ECG) chest straps as the source of HR measurements in fitness and health monitoring applications. The device delivers a processed output in beats per minute, updated once per second.
The module includes the LEDs, photo-sensor, analogue front end (AFE) and controller as well as application software required to implement an accurate optical HRM/HRV fitness band product. The module also accommodates skin temperature and skin resistivity measurements by providing interfaces to external sensors.
The operation of the AS7000 is based on photoplethysmography (PPG), an HRM method which measures the pulse rate by sampling light modulated by the blood vessels, which expand and con-tract as blood pulses through them. Unlike existing optical AFEs, which produce raw PPG readings, the AS7000 integrates a digital processor which implements algorithms developed by ams. These convert the PPG readings into digital HRM and HRV values.
ams observes that deriving accurate and reliable data from the raw measurements in this domain is far from simple. The variation in returned light that is due to expansion and contraction of blood vessels is, in effect, a small AC signal superimposed on a large DC components: around two orders of magnitude difference. Motion, including that due to the heartbeat itself, introduces a further “error” source of motion artifacts, that can be removed by adding an accelerometer (external to the AS7000).
At its introduction, the AS7000 outputs heart rate data; software can follow trends in the HRM data to derive HRV parameters. Skin temperature and resistivity (GSR, galvanic skin resistance) parameters will be added (via software), and ams also has a feasibility study looking at blood pressure monitoring. This can, in principle, be derived from the transcutaneous optical measurement, the company says, but is an even more challenging signal processing task. The same is true for SPO2, or (reflective) oxygen saturation measurement, and that, too, is on the company’s roadmap for the product range.
Devices in this domain are rated, ams adds, by observing their deviation from the signal produced by a reference, multi-lead ECG. Under treadmill test conditions, the AS7000 tracks the ECG HR figure closely.
With past expertise in optical sensing in mobile devices, ams provides design teams with electrical, mechanical and optical design guidelines to enable them to quickly realise a successful implementation. These guidelines address critical opto-mechanical challenges such as the design and material of the wrist strap and housing, and specific optical design considerations such as the air gap and glass thickness.
The AS7000’s low-power design is aimed application in fitness bands, smart watches, sports watches, and devices in which board space is limited and in which users look for extended, multi-day intervals between battery recharges. The processor core is an ARM Cortex M0.
A complete HRM/HRV wristband demonstration kit contains a fitness band-mounted AS7000, that uploads its HRM and HRV readings via a Bluetooth interface board to any smartphone or tablet running Android. An ams-developed heart rate app presents HRM and HRV readings and allows for real time logging of all the data.
The AS7000 is priced at $6.00 (1,000)
ams; www.ams.com/Biosensor/AS7000
