Wearable Device to Monitor Back Movements Using an Inductive Textile Sensor

Abstract

Low back pain (LBP) is the most common work-related musculoskeletal disorder among healthcare workers and is directly related to long hours of working in twisted/bent postures or with awkward trunk movements. It has already been established that providing relevant feedback helps individuals to maintain better body posture during the activities of daily living. With the goal of preventing LBP through objective monitoring of back posture, this paper proposes a wireless, comfortable, and compact textile-based wearable platform to track trunk movements when the user bends forward. The smart garment developed for this purpose was prototyped with an inductive sensor formed by sewing a copper wire into an elastic fabric in a zigzag pattern. The results of an extensive simulation study showed that this unique design increases the inductance value of the sensor, and, consequently, improves its resolution. Furthermore, experimental evaluation on a healthy participant confirmed that the proposed wearable system with the suggested sensor design can easily detect forward bending movements. The evaluation scenario was then extended to also include twisting and lateral bending of the trunk, and it was observed that the proposed design can successfully discriminate such movements from forward bending of the trunk. Results of the magnetic interference test showed that, most notably, moving a cellphone towards the unworn prototype affects sensor readings, however, manipulating a cellphone, when wearing the prototype, did not affect the capability of the sensor in detecting forward bends. The proposed platform is a promising step toward developing wearable systems to monitor back posture in order to prevent or treat LBP.

Keywords: E-textiles; inductance; low back pain; monitoring; nurses; smart garment; textile sensors; trunk posture; wearable device.

Figure 1

Zigzag pattern evaluation in Ansys. (a) Single loop inductive textile sensor; (b) definition of zigzag characteristics.

Figure 2

Inductance vs. zigzag width. Inductance values simulated in Ansys for a single-loop inductive sensor with changing the zigzag width.

Figure 3

Placement of optical markers around the proposed shape for the inductive sensor. Markers are shown as grey circles.

Figure 4

Ansys simulation of the inductive sensor: dimensions of the (a) box, (b) inductive sensor.

Figure 5

Simulation of the electromagnetic field created by the sensor.

Figure 6

Smart garment prototype. Rear view of the smart garment with the inductive sensor affixed to the part that goes on the lumbar section.

Figure 7

Inductance values (µH) recorded from the designed sensor and actual forward bending angles (degrees) recorded by inertial measurement units (IMUs) during the considered trunk movements: (a) forward bending; (b) forward and lateral bending; (c) forward bending and trunk rotation. In each case, the periods of forward bending are highlighted in grey shade.

Figure 8

Inductance values (µH) recorded from the interference test, where a copper spool, a metallic element, a magnet, a cellphone, and a human hand were moved towards the inductive sensor’s coil. In each case, the periods of moving objects toward the coin are highlighted in grey shade.

Figure 9

Inductance values (µH) recorded from the interference test, where a single participant was wearing the prototype and performed forward bending. In the second set of forward bend, the participant had the cellphone inside the jeans’ back pocket. In each case, the periods of forward bending are highlighted in grey shade. The red circle shows when the cellphone was put inside the back pocket.