A Soft Polydimethylsiloxane Liquid Metal Interdigitated Capacitor Sensor and Its Integration in a Flexible Hybrid System for On-Body Respiratory Sensing

Abstract

We report on the dual mechanical and proximity sensing effect of soft-matter interdigitated (IDE) capacitor sensors, together with its modelling using finite element (FE) simulation to elucidate the sensing mechanism. The IDE capacitor is based on liquid-phase GaInSn alloy (Galinstan) embedded in a polydimethylsiloxane (PDMS) microfludics channel. The use of liquid-metal as a material for soft sensors allows theoretically infinite deformation without breaking electrical connections. The capacitance sensing is a result of E-field line disturbances from electrode deformation (mechanical effect), as well as floating electrodes in the form of human skin (proximity effect). Using the proximity effect, we show that spatial detection as large as 28 cm can be achieved. As a demonstration of a hybrid electronic system, we show that by integrating the IDE capacitors with a capacitance sensing chip, respiration rate due to a human’s chest motion can be captured, showing potential in its implementation for wearable health-monitoring.

Solid–Liquid Composites for Soft Multifunctional Materials

“…SLCs can be used to create soft electronic components such as highly stretchable wires, resistors, and capacitors (e.g., Figure 9G-K). [12,112,156,232] These systems are based on electrically conductive liquids such as EGaIn LM or ionic conductors such as ionic liquids, [221,233] or water-containing salt ions. [233] These soft electronic materials have shown exceptional combinations of soft mechanical response with diverse electrical functionality.…”

Wearable Sensors for Remote Health Monitoring: Potential Applications for Early Diagnosis of Covid‐19

“…Such a high stretchability ensures that the sensors can be safely used without failure. [ 37 , 85 , 86 ] Sensors based on piezoresistive, [ 86 ] piezoelectric, [ 49 ] capacitive, [ 87 ] and triboelectric [ 88 ] effects have been demonstrated promises for this purpose. In contrast to rigid and nonconformable semiconductor‐based or silicon‐based sensors, these sensors employ flexible polymers coupled with various functional materials such as electrically conductive particles or piezoelectric nanomaterials or nanofibers.…”

Soft Material-Enabled Electronics for Medicine, Healthcare, and Human-Machine Interfaces

“…One such example of these wearable electronics is demonstrated in "A Soft Polydimethylsiloxane Liquid Metal Interdigitated Capacitor Sensor and Its Integration in a Flexible Hybrid System for On-Body Respiratory Sensing" [3]. The proposed sensor utilizes a soft material to form channels that are filled with conductive liquid metal.…”