Wood-based 3D-printed sensors include wireless access

September 17, 2019 //By Bill Schweber
Leveraging a previously developed technique, researchers developed sensors that are printed on cellulose and can be read wirelessly using a VNA.

Using wood—or to be more precise, cellulose derived from wood—is a hot R&D material, perhaps due to its biocompatibility and sustainability potential. A joint research team from Simon Fraser University (BC, Canada), and the Applied Wood Materials Laboratory at the Swiss Federal Laboratories for Materials Science and Technology (EMPA, Zurich) has developed 3D-sensor systems printed on cellulose that are disposable, ion-selective, and can be interrogated wirelessly. These sensors offer what the researchers maintain are a unique combination of form factor, high sensitivity, and flexibility.

Simon Fraser University Mechatronic Systems Engineering
professor Woo Soo Kim holds one of the sensors developed
by the multi-institute team (Source: Simon Fraser University).

The goal is to replace the plastic of common printed circuit boards (PCBs) with eco-friendly and disposable chemical sensors. “If we are able to change the plastics in PCB to cellulose composite materials,” noted project leader Professor Woo Soo Kim (SFU professor at FSU’s School of Mechatronic Systems Engineering), then “recycling of metal components on the board could be collected in a much easier way.”

These three 3D-printed inductor-capacitor (LC) circuit
samples have different thicknesses with different printing
paths; for example, 2L8C contains a double-layered inductor
and 8-layered capacitor. (Source: Simon Fraser University).

To achieve this, they used a printable conductive ink that’s designed and optimized for cellulose nanofibers (CNFs) by adding silver nanowires (AgNWs). For better resolution of the printing, they used a polyimide film that has high surface hydrophobicity as a substrate. They were able to create 3D-printed sensor circuits that included inductor–capacitor (LC) circuits along with ion-selective membrane electrodes. These electrodes can be tailored to selectively detect quantitative ion concentrations.

The equivalent circuit of the sensor system consists
of an ion selective membrane electrode (ISME) for
the sensing part and an inductor-capacitor (LC) circuit.
(Source: Simon Fraser University).

The change of ion concentrations is reported wireless by measuring the magnitude of S11 (the reflective coefficient S-parameter, also known as gamma or Γ, the return loss) at the resonant frequency of 2.36 GHz using a vector network analyzer (VNA) and loop antenna (Fig. 4). Among their many tests, Figure 5 shows the change in magnitude of S11 for the ion-selective membrane electrode (ISME) with four different concentrations of NH4Cl solution.


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