Wearable RFID sensor for monitoring Sweat Electrolytes Ashok

Wearable RFID sensor for monitoring
Sweat Electrolytes

 

Ashok Kumar Pasumarthi

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Department of Engineering
Technology, Middle Tennessee State University

 

 

Abstract

Wearable
digital health gadgets overwhelmingly found in watches and bracelets. They have
a great significance in games and marathons as they empower physiological
signals and enzymes such as human sweat, to be continuously monitored. In this
paper a commercial RFID chip is adopted for demonstrating the sensing of
solutes in sweat and body surface temperature. These results can be read in an
android app with 96% accuracy at 50mM NA+. Paper microfluidics wick
sweat and allows them to flow to the sensors. This patch comes can be easily
worn like a regular band aid, which is similar in appearance.

 

I.
Introduction

When
compared to Urine and Saliva, sweat is easily accessible bio-fluid, to get
chronological readings of biomarker concentrations. An attractive application
includes heat-stress monitoring and hydration through electrolyte balance (Na+,
K+, etc.) for athletes, military personnel. High salinity
of sweat may prove readings of other bio-markers wrong, hence these
electrolyte concentrations are base-lined. Not only in band-aid patches but
also these sweat sensors are used in textiles, and digital health sensing
products like Nike+ and Fitbit. A commercial passive RFID chip senses both
electrolytes in sweat and reads body temperature. They both considered gives
information like how much fluid is needed by body and estimate body hydration
levels.

 

II.
Design of Patches

Patch
size

Two patch
sizes were demonstrated first one is a regular type (25*60mm2) and second one is big size of
70*40mm2 which can be placed under knee. It
got 10 to 20 loops of coiled antenna to power the electronics.

Communication

The ubiquity
of smartphones helps easily accessing of these electronic patches, and
eliminates the complexity in data storage of RFID patches, which further
reduces cost of making the patch.

 

Flexible
and Wearable

The thin
slice like patch without any sharp protrusions helps to wear the patch barely
on skin, with adhesive on it. We can feel like a regular band-aid.

Fig1.

III.
Basic Electronics and Programming Functionality

The diagram
illustrates the working of the patch from reading device to patch. The reading
device first requests for identification from patch. Then the patch responds by
load modulating the inductive coupling between itself and RFID reader. The
programming includes reading writing to memory registers, sensor configuration and
power management. The primary chip has both sweat sensor and energy harnessing
capabilities. To enable smartphones to turn the chip it needed to be
programmed. There are internal and external sensors. The four-pin input provide
the potential for measuring the electrolyte concentration, they are called
ion-selective electrodes(IES). Two internal connections can enable the output
of the on-board temperature sensors to be used as input into the multiplexer.
Configuration of the multiplexer determines which inputs are passed to the gain
amplifier. Digital to analog converter offsets the data in second amplifier.

Fig2.

IV.
Performance

In general
perspective the function of a RFID sweat sensor is analogous to the functioning
of an electrolyte battery. Here sweat is electrolyte and ion sensors are
electrodes. The potential produced due to ions in sweat is sent to the
amplifier in chip and compared to storage data in storage.

The RFID
circuit was tested to make sure that resonate frequency was fair enough to
target frequency, so that it communicates with reader. Contactless frequency
test is done for patch’s frequency response.

Sensors were
tested with different concentration solutions of NaCl. This involves both
Calibration and comparison of available ion selective electrodes. Accuracy is
96% of the sensor when the precision is 28%. The sensor exhibits good
repeatability and stability during this measurement.

 

V.
Conclusion 

The paper
demonstrates the complete integration of the components and functioning for a
low price and user-friendly passive RFID chip.

 

 

VI. References

1.       The
Possibilities of Passive UHF RFID Textile Tags as Comfortable Wearable Sweat
Rate Sensors click  

2.       A
Wearable Sensor for Measuring Sweat Rate click

3.       Adhesive
RFID Sensor Patch for Monitoring of Sweat Electrolytes click here

4.       System-Level
Design of an RFID Sweat Electrolyte Sensor Patch  click here

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