TY - JOUR

T1 - Physics-based circuit modeling of the impedance characteristics of a smart hydrogel-actuated bending sensor

AU - Ahmed, Benozir

AU - Reiche, Christopher F.

AU - Solzbacher, Florian

AU - Magda, Jules

AU - Körner, Julia

N1 - Funding Information: This work was performed in part at the Utah Nanofab, which is sponsored by the College of Engineering, Office of the Vice President for Research , and the Utah Science Technology and Research (USTAR) initiative of the State of Utah. The authors appreciate the support of the staff and facilities that made this work possible. Research reported in this publication was supported by the Joe W. and Dorothy Dorsett Brown Foundation , the Olive Tupper Foundation as well as the National Institute of General Medical Sciences (NIGMS) of the National Institutes of Health (NIH) under award number 1R41GM130241 awarded to Sentiomed, Inc. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.

PY - 2022/11/1

Y1 - 2022/11/1

N2 - Smart hydrogels are stimuli-responsive polymers which exhibit a volume-phase transition in response to external influences. This makes them promising candidates for sensing elements, especially in a biomedical context due to their easily achievable biocompatibility. The main challenge in harnessing the smart polymer's potential for sensor applications lies in a reliable transduction of the swelling change into an electrical signal. A novel platform approach is based on a bending sensor where the smart hydrogel acts as an actuator on a thin film with embedded metal traces. Mechanical deformation due to the hydrogel volume change alters the traces’ electric impedance. However, besides deformation, the medium surrounding the sensor structure will also affect the impedance. For sensor design it is therefore crucial to understand the complex interdependencies between electric sensor properties, influences of the surrounding medium and mechanical deformation. Here, an electric circuit model is presented which considers all these contributions through a minimum number of lumped elements and is strictly based on physical considerations. By employing measured impedance spectra from an experimental sensor implementation subjected to different surrounding media and mechanical deformation, the validity of the simplified model is demonstrated. A detailed analysis and discussion give insights into the determination of the different model parameters and how external influences can clearly be attributed to specific circuit elements. This work provides a general approach for deducing minimalistic but strictly physics-based circuit models which can still adequately replicate the actual behavior of such types of impedance-based bending sensors.

AB - Smart hydrogels are stimuli-responsive polymers which exhibit a volume-phase transition in response to external influences. This makes them promising candidates for sensing elements, especially in a biomedical context due to their easily achievable biocompatibility. The main challenge in harnessing the smart polymer's potential for sensor applications lies in a reliable transduction of the swelling change into an electrical signal. A novel platform approach is based on a bending sensor where the smart hydrogel acts as an actuator on a thin film with embedded metal traces. Mechanical deformation due to the hydrogel volume change alters the traces’ electric impedance. However, besides deformation, the medium surrounding the sensor structure will also affect the impedance. For sensor design it is therefore crucial to understand the complex interdependencies between electric sensor properties, influences of the surrounding medium and mechanical deformation. Here, an electric circuit model is presented which considers all these contributions through a minimum number of lumped elements and is strictly based on physical considerations. By employing measured impedance spectra from an experimental sensor implementation subjected to different surrounding media and mechanical deformation, the validity of the simplified model is demonstrated. A detailed analysis and discussion give insights into the determination of the different model parameters and how external influences can clearly be attributed to specific circuit elements. This work provides a general approach for deducing minimalistic but strictly physics-based circuit models which can still adequately replicate the actual behavior of such types of impedance-based bending sensors.

KW - Bending sensor

KW - Circuit model

KW - Impedance spectrum

KW - Smart hydrogel

UR - http://www.scopus.com/inward/record.url?scp=85141533982&partnerID=8YFLogxK

U2 - 10.1016/j.sna.2022.113954

DO - 10.1016/j.sna.2022.113954

M3 - Article

AN - SCOPUS:85141533982

VL - 347

JO - Sensors and Actuators A: Physical

JF - Sensors and Actuators A: Physical

SN - 0924-4247

M1 - 113954

ER -