Liquid Testing with Smartphones

Like the idea that we are extending smartphone use as sensors. It provides another means for gathering and utilizing complex data.   Here a good example:

Liquid Testing with Your Smartphone

By Shichao Yue, Dina Katabi

Communications of the ACM, October 2021, Vol. 64 No. 10, Pages 75-83

10.1145/3481038

Surface tension is an important property of liquids. It has diverse uses such as testing water contamination, measuring alcohol concentration in drinks, and identifying the presence of protein in urine to detect the onset of kidney failure. Today, measurements of surface tension are done in a lab environment using costly instruments, making it hard to leverage this property in ubiquitous applications. In contrast, we show how to measure surface tension using only a smartphone. We introduce a new algorithm that uses the small waves on the liquid surface as a series of lenses that focus light and generate a characteristic pattern. We then use the phone camera to capture this pattern and measure the surface tension. Our approach is simple, accurate, and available to anyone with a smartphone. Empirical evaluations show that our mobile app can detect water contamination and measure alcohol concentration. Furthermore, it can track protein concentration in the urine, providing an initial at-home test for proteinuria, a dangerous complication that can lead to kidney failure.

1. Introduction

Mobile computing has recently seen a surge in research on inexpensive methods for measuring liquid properties and identifying liquid type.7, 12, 17, 21 The developed methods can detect water contamination and distinguish a variety of liquid types such as water, milk, oil, and different alcohol concentrations. The goal of this line of research is to enable liquid testing outside the lab environment and encourage ubiquitous applications. However, the proposed designs require a specialized setup (a robot,21 a special container,7 etc.) and use devices typically unavailable to the general population (e.g., UWB radios or RFID readers). Although they make an important step toward ubiquitous liquid testing, they are still difficult to use by lay users.

This paper asks whether it is possible to deliver such services to lay users without a specialized setup, and using only a device that almost everyone has: a smartphone. Answering this question is not simple. Typically, liquid testing is done by measuring a particular property, such as electric permittivity or optical absorption, and using the measurements to identify the liquid type and characteristics.7, 12, 17, 21 However, none of the properties used in past work can be measured with a smartphone. To address this problem, we explore an alternative liquid property, surface tension, and develop algorithms and system architectures that enable measuring surface tension using only a smartphone.

Surface tension characterizes the force that holds the surface molecules together and minimizes the surface area. Measuring surface tension can reveal water contamination and allow for distinguishing liquid types.19 Water has a relatively high surface tension, and when polluted with organic compounds such as bacteria, oil, petroleum or its derivatives, its surface tension decreases significantly.3, 19 Hence, one may use this property to detect water contamination. Further, lipids and proteins act as surfactants, that is, they reduce surface tension. Alcohol also reduces surface tension, a property that can be leveraged to measure alcohol concentration.20 Most interestingly, the ability to measure surface tension at home can enable early detection of medical problems. For example, low surface tension of urine may indicate the presence of excess protein, a dangerous complication in diabetes patients.8 Daily measurements of urine surface tension help detect diabetic nephropathy (the chronic loss of kidney functions) and monitor the effect of treatment.8

Today, measurements of surface tension require a device called tensiometer, which typically costs thousands of dollars.9 They are often conducted by dipping a platinum plate into the liquid and carefully measuring the force required to pull it out. The process is complicated and requires professional training.9 This high bar hampers the ubiquitous application of surface tension.

We introduce CapCam (Capillary Camera), the first mobile app that measures liquid surface tension using only a smartphone. To measure surface tension, the user places the smartphone on top of a lightweight container, such as a paper cup, and activates the app, as shown in Figure 1. The phone vibrates and forces the container's wall to vibrate. The vibration generates capillary waves on the liquid surface, that is, small waves whose wavelength characterizes the liquid's surface tension. Our app uses the flashlight camera to take a few photos of the liquid, which it processes to estimate the capillary wavelength and hence the surface tension. Our approach is accurate, simple, cheap, and accessible to any user with a smartphone.  .... '