Imec and Holst Centre have demonstrated a body patch that integrates an ultra-low power electrocardiogram (ECG) chip and a Bluetooth Low Energy radio.
Intended to open up the potential of low power radio technology for long term healthcare monitoring, the ECG patch measures up to three lead ECG signals, tissue-contact impedance and includes a 3D-accelerometer for physical activity monitoring.
The data is processed in the device before information is transmitted through Bluetooth Low Energy.
The patch is designed for a very low power budget. When computing and transmitting the heart rate, the entire system consumes a mere 280µA at 2.1V, running continuously for one month on a 200mAh Li-Po battery.
When transmitting accelerometer data (at 32Hz) on top of the heart rate, the power consumption remains below 1mA in continuous operation, giving about 1 week of autonomy.
It is expected that Bluetooth Low Energy (Bluetooth 4.0) will be integrated as standard in smartphones and tablets next year, opening the way for new healthcare monitoring applicatiiuons.
At the heart of the patch is an ECG System-On-Chip (SoC), a mixed signal Asic.
Next to monitoring 1- to 3-lead ECG, the ECG SoC also monitors the contact impedance, providing real-time information on the electrode contact quality. This can be used to evaluate the quality of the ECG measurement and to filter motion artifacts. The ECG SoC has been designed to run algorithms for motion artifact reduction (based on adaptive filtering or principal component analysis) and beat-to-beat heart rate computation (based on discrete or continuous wavelet transforms).
It has additional computation power to run application-specific algorithms such as epileptic seizure detection, energy expenditure estimation or arrhythmia monitoring. The built-in 12-bit ADC is capable of adaptive sampling – sampling QRS waves at high frequency, and the other waves at a lower frequency – achieving a compression ratio of up to 5.
The monitor is part of the Human++ program being carried out at Imec and Holst Centre addressing healthcare technology.
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