A stretchable strain sensor for on-the-skin posture monitoring

Abstract

Everyone has heard it, “sit up straight!” Probably from a mother figure or teacher. Why is bad posture so bad, and what problems does it create?

Bad posture is a prolific problem across the globe. Poor posture is highly linked to interaction with technology. In today’s society, that means nearly everyone is likely to suffer from poor posture. Positioning in miss aligned postures for extended periods of time create muscular imbalances. These imbalances strengthen certain muscles, while the opposing muscles weaken. Because of this, imbalances are cyclical, once created, you are more likely to continue the imbalance due to the strength/weakness of your musculature.

Consistent poor posture, and the imbalances that come with it, can make it difficult to perform active activities such as sports or hobbies. These imbalances alter the way the body moves and puts people at a higher risk of injury. Specifically, users who have a 9-5 mostly sedentary job interacting with technology, but also have an active hobby are at the most risk. Therefore, the target demographic of this thesis is the ‘active hobbyist.’

Today’s solutions available to users trying to fix their posture focus on fixing the symptoms, not the incredible amount of time a day we spend in compromising postures. The issue with this tactic is that no matter how much stretching or strengthening you do, nothing can counteract the 75+ hours a week spent sitting in awkward positions in front of your computer. These solutions also include hard electronics that impede the natural movement of the body and interfere with clothes and other daily interactions.

Changing one’s posture is hard. Most people sit up straight, but soon become distracted by Netflix, their phone, or work and slouch down again. In fact, a study done in this thesis found that the average user will need reminding about their posture about once every 2.5 minutes. This is because our brains actively work against us maintaining postural awareness.

Therefore, a solution to help users to maintain awareness of their posture is needed.

The skin of a person’s back stretches in a way that correlates to the posture of that person. A sensor that monitors stretch could be used to measure posture.
An on-the-skin sensing mechanism is made from a conductive, stretchable silver ink printed onto a plaster-like platform. The sensor functions by measuring the change in resistance as the sensor is stretched. This sensor is the first disposable sensor skin concept for its market. Its functionality is improved over the course of this thesis to become more robust and resilient.

Five concepts are developed to demonstrate how this sensor could be designed and implemented as a product for the market. These concepts are optimized to show the qualities of the stretchable ink printed sensor.