Smart Sock for Diabetic Patients

 

Diabetic foot is one of the most serious complications of diabetes mellitus (DM). Even in the early stages of DM, there is a significant pressure difference between non-diabetic and diabetic foot. This project designed and prototyped a type of smart diabetic sock for early-stage diabetic foot detection to alert patients about abnormal pressures. The designed sock has the following advantages:

 

1.  Battery-free operation

2.  High sensitivity to small pressure changes

3.  Textile sensors integrally embedded in regular fabrics

4.  Smartphone-based monitoring

5.  Detachable circuitry

 

Figure 1 shows a system overview of the sock. The radio-frequency (RF) energy radiated by an RFID (RF identification) reader is collected by an RF energy harvesting chip through antennas. The harvested energy generates a 3.3V voltage pulse to boot a pre-programmed microcontroller unit (MCU) and provides a reference voltage level to the sensor matrix. Analogue pressure values are digitalised by the MCU, and sent to an ultra-high frequency (UHF) RFID tag via I2C bus. These digitalised pressure values are stored in the serial number field of the RFID tag and therefore can be read by the RFID reader and displayed on a smart phone (Figure 2).

 

 

Figure 2. Digitalised pressure values
 

Figure 1. System overview

 
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The textile pressure sensor (Figure 3) is fabricated of piezo-resistive polymer and conductive yarns. It is well-hidden and integrated within regular fabrics by using intarsia knitted technique. The developed sensor can measure a pressure of up to 1,000 kPa with a relatively linear response to the applied force.

 

The central control unit (Figure 4) and antennas (Figure 5) are mounted on flexible printed circuit boards (FPCs). Each antenna is tuned to resonate at 868 MHz while close to human bodies and they are connected to the central control unit by U.FL cables (Figure 6). An interface fabric with snap-button connectors is used to electrically attach/detach the FPC to/from the textile sensors on the sock (Figure 7). The interface fabric is also stretchable so as to suit different perimeters of legs.

 

Figure 5. Antenna board
 

Figure 3. Textile pressure sensor
 
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Figure 4. Central control unit board
 
                                                                                          

 

 

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Figure 6. Antennas with central control unit
 

Figure 7. Interface fabric with snap-button connectors
 
                   

 

 

Figure 8 shows an open-view of the knitted sock prototype. Four sensors are positioned at locations where abnormal peak pressure could be best detected. These positions are: 1st metatarsal head (MTH), between 2nd and 3rd MTH, between 4th and 5th MTH, and under the heel (Figure 9). The final working prototype of the sock on a foot model is shown in Figure 10.

                                                           

Figure 10. Final prototype
 

Figure 9. Sensor locations
 

Figure 8. Open-view of sock prototype
 
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Click here for a short video demonstration of the sock’s RF energy harvesting and pressure sensing functions. Details of our work can be found here in the IEEE Transactions on Biomedical Circuits and Systems.

 

We gratefully acknowledge Amit Gupta, Gordon Fraser, Mandy Smith, Peter Heslop, and Frances Joseph from the Textile Design Lab of Auckland University of Technology for the support rendered in knitting the sensor and sock prototype.

 

For further information, please contact: Dr. Boon-Chong Seet (boon-chong.seet@aut.ac.nz)