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Wearable Shirt SOC Transmits Cardiac Signals to Remote Smartphone

12 June 2014

University of Washington researchers have developed and integrated an electrocardiography SoC into a shirt along with electrodes, battery and antenna for constant remote monitoring of active cardiac patients.

The "smart shirt" records clinically standard 12-lead ECGs, encrypts the data and wirelessly transmits the data via an on-chip ISM band radio and flexible antenna for secure, continuous cardiac monitoring by a remote smartphone. The SOC dissipates less than 1mW.

The flexible electronics package of chip, antenna and battery is less than 2.3mm thick, allowing easy integration into various textiles. The goal is to make the technology inexpensive enough for incorporation into consumer-grade clothing with continuous and secure connectivity to smartphones.

Up to now, wired systems make patients be tethered to equipment or have them log data for later download, limiting mobility or delaying alerts. While advances in textile electrodes have allowed for the development of highly integrated smart shirts, the size of the electronics has limited their use.

The researchers’ wireless ECG single chip enables low profile textile integration. Dry electrodes couple human heart potentials from their clinically relevant positions to the chip via twelve independent, fully differential digitized channels thru which encrypted data is transmitted wirelessly using an on-chip low power 433MHz FSK transmitter.

The gain of each of the 12 channels is programmable between 40-80dB independently to allow each channel to use the full dynamic range of the 8-bit SAR ADC for various signal levels. Total chip power consumption of less than 1mW enables all-day transmission of data using a rechargeable coin cell battery, according to the researchers.

The researchers integrated a 128-bit Advanced Encryption Standard cypher into the SOC for securing the sensitive data.

Commercial electrodes attached to shielded, 810μm coaxial wires which were sewn into the shirt to connect the IC to the electrodes. The IC was placed on a flexible PCB and together with battery and flexible 433MHz patch antenna was housed in a 2mm thick pouch on the chest.

The prototype shirt was constructed as a proof of concept demonstrating the potential of the low-power SoC, according to the researchers.

The technical details for this work is being presented this week at the 2014 Symposia on VLSI Technology and Circuits held in Honolulu.

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