Find the Gap: Multiband, Remote Measurement System to Quantify the Fit of Wearable Systems

We propose a technique for remotely measuring the gap between an external wearable device/clothing surface and the underlying (visually obstructed) body surface—which we refer to as the garment-body “air gap”—that commonly occurs in positive ease garments (i.e., garments that are larger in dimension than the underlying body dimension). To achieve this, we developed a triple-frequency band remote measurement system based on a 77–81-GHz frequency-modulated continuous wave (FMCW) radar, a 40-kHz ultrasound sensor, and an infrared 344-GHz proximity sensor. When used synergistically, these sensors allow for remote measurement of the uniaxial distances to multiple layered surfaces simultaneously. To validate this approach, a test setup was developed to mount multiple surfaces at variable distances from the sensor suite. The sensor suite, when activated, can provide measurements at different configurations and distances from 3 to 60 cm. To provide a single measurement for the infrared/ultrasonic sensors, a logistic regression-based model was used, reducing the surface estimation error (RMSE) from 1.610 and 4.728 mm for the ultrasonic and infrared sensors, respectively, to 0.41 mm. Results show that the current first-generation multisensor system is able to find the air gap between a fabric surface and an underlying body-like surface with an accuracy of 2.6 mm (measured in RMSE). The developed system shows potential to allow noninvasive assessment of functional garments such as hazmat suits, personal protective equipment (PPE), space suits, and everyday clothing, offering valuable wearer interaction insights without relying on post hoc simulations or physical sensors, enabling better design and evaluation of garments.