By Laura Shumaker, mechanical engineer & member of the informal freelance collective
Why this crossed our desks: I tore down a set of smart textile sensors while writing a state-of-the-industry report, “Smart Textiles: A Guide to Designing with Their Complexity.”
I assumed that these smart textile sensors would be simple — using as few different soft goods materials as possible. Perhaps the electrical leads would be embroidered using conductive thread, and then metal snaps would be riveted through the conductive thread to make a solderable connection.
To my surprise, some of these sensors were quite complex. For example, the silicone sensor architecture used a plethora of soft goods materials: conductive film coatings, conductive yarns in a knit, conductive and nonconductive adhesives, isolating foams, and conductive embroidery that directly captured the stranded wire of electrical leads.
This teardown documents the complexity and surprises of the silicone sensor from Softmatter.
Softmatter recommends this sensor for monitoring ECG and EMG signals.
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Two pads (1 and 2), covered with black film, are spaced ~13 mm apart. The pads measure ~10 mm x ~25 mm.
They’re sandwiched between layers of soft, brushed knit (3).
This is referred to as the “carrier fabric” in further slides.
The thickness of the assembly over the sensors is ~3.5 mm. The thickness of the assembly next to the sensors (in location C) is ~1.3 mm.
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Both of the carrier fabrics are fully laminated with thermal bonding film (TBF, 1).
The TBF easily pulled apart, without application of heat. However, it could be reactivated with heat. While the TBF was sufficiently bonded to both fabrics, its visibly glossy surface indicates that it wasn’t properly activated through heat and pressure when it was time to bond the whole sandwich together.
(Surprise) Stranded wire leads are embroidered to the sensor pads (2).
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The sensor pads are taco-shaped, with the side that faces the outside world larger than the side with the wire leads. Nonconductive foam separates the two sides. This increases the electrical resistance between the outside world and the wires.
Die-cut holes act as location features for the wire embroidery (1).
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Sensor unit is conductive fabric folded around foam.
Embroidered connection to wire leads under the foam.
