# Contactless Detection of pH Change in a Liquid Analyte

## TL;DR

This paper introduces a new method to detect pH changes in a liquid without direct contact using a radiofrequency sensor and Fourier analysis.

## Contribution

The first use of Fourier analysis in contactless pH measurement using radio frequencies.

## Key findings

- A radiofrequency sensor can detect pH changes from outside a PVC pipe without contact.
- Linear Discriminant Analysis with inverse Fourier transform features effectively identifies pH changes.
- The method demonstrates potential for non-invasive chemical sensing.

## Abstract

We describe an experiment in which we employ a radiofrequency sensor to measure pH changes in a liquid solution. The experiment is novel in a few ways. First, the sensor does not have contact with the liquid but rather detects the change from the outside of a PVC pipe. Second, the change is detected using a Linear Discriminant Analysis model using values from an inverse Fourier transform of the frequency data as its features. We believe this to be the first use of Fourier analysis in contactless pH measurement using radio frequencies.