# Effects of sensor geometry, placement, and cycle detection on wearable respiration monitoring with textile printed strain sensors

## TL;DR

This study explores how sensor design and placement affect the accuracy of wearable respiration monitors using printed strain sensors on elastic chest belts.

## Contribution

The paper introduces a new elastic chest belt with printed strain sensors and evaluates the impact of sensor geometry, placement, and detection methods on respiration-rate accuracy.

## Key findings

- The peaks-and-valleys (PV) detector outperformed the power spectral density (PSD) method in respiration-rate accuracy.
- A vertical serpentine sensor on the lateral thorax showed the highest agreement with reference measurements.
- Circular sensors achieved their best accuracy on the left thorax.

## Abstract

Wearable respiration monitors often struggle with motion artifacts and variable skin–sensor coupling. We present an elastic chest belt with digitally printed piezoresistive strain gauges and a multi-channel bridge front-end, and we evaluate how sensor geometry, placement, and simple respiration cycle detectors affect minute-scale respiration-rate (RR) accuracy. Three printed sensor layouts (circular and serpentine/“linear”) were placed at three thoracic locations (left, center, right); for the serpentine layout, we also tested horizontal vs. vertical orientations. RR from (i) a time-domain peaks-and-valleys (PV) detector and (ii) a power spectral density (PSD) method were compared to a thermistor reference across 4-min trials in healthy volunteers (n = 3), analyzed per minute. PV achieved a larger share of minutes within ± 2 RPM than PSD (≈ 70% vs. ≈37%) and within ± 1 RPM (≈ 44% vs. ≈33%). Geometry and placement mattered: a vertical serpentine on the lateral thorax showed the highest minute-level agreement within this pilot cohort and under quiet-breathing conditions (left-lateral vertical: 100% of minutes within ± 2 RPM; right-lateral vertical/horizontal: 91.7%), while circular sensors showed their highest accuracy on the left thorax (83.3% within ± 2 RPM). These pilot findings suggest preliminary design guidance for e-textile RR monitors and indicate that PV detection may be a practical option for minute-scale RR estimation under the tested conditions.

The online version contains supplementary material available at 10.1007/s44397-026-00054-0.