Determining the state of our health has always been a matter of finding a way to monitor and measure the body’s most basic functions. Before instrumentation, visual indicators were used that allowed us to know, for example, what our body temperature should be, what a healthy pulse is, and what an acceptable respiration rate is.
Today, with an aging population more people now need some sort of portable health monitoring, which could take the form of devices that, among other things, dispense medication at regular intervals, stimulate the heart, or measure blood sugar levels and inject insulin. This article looks at medical- and fitness-sensor technology—contacted and contact-less, placed on the skin, subcutaneous, or internal—that now or soon will be available to design engineers. All parts, tools, and data referenced here can be found on the Digi-Key website.
The simplest form of a sensor is a transducer, which can be as basic as two different substances touching each other. The actual sensor element can be fabbed as a small discrete leaded component, or as part of a probe or electrode assembly. They can be as thin as a hair-like wire and can actually generate voltages themselves. Thermocouples are an example of voltage-generating sensor of dissimilar metals that creates voltages based on temperatures. Parts like the non-grounded Omron E52-CA15AYD32 4M, for example, measure temperatures using a K-type element with a 3.2 mm protective tube capable of skin mount or mounting in a stationary crevice.
Piezo effects can be taken advantage of to create energy from a tiny embeddable sensor when exposed to shock and vibration. A small, rather non-intrusive skeletal sensor could indicate too much physical trauma to a football player in real time to avert more serious injury. The miniaturizing of piezo sensors means they can now be weaved into textiles, bandages, or clothing. Sheet sensors like the TE Connectivity 2-1004347-0 are flexible, foldable, and can be cut to very specific states (Figure 1). A shoe insert for example, could determine if too much stress is being generated on downward steps to help diagnose back or joint issues.
While transducers are useful for picking up real-world conditions, they need to be calibrated, linearized, and compensated for drift and temperature effects. This is why transducer systems integrated with small, smart, and system-level electronics can make these devices into self-contained monitoring and reporting systems.
We are what we wear
Researchers and manufacturers are now looking at wearable medical and fitness devices for the masses. One place where active projects are underway is the University of Illinois where next-generation devices are being developed that can measure energy exertion, heart rate and variability, falls, skin temperature, and EEG/EKG signals (Figure 2). Worn like a disposable patch, these peel-and-stick sensors can wirelessly communicate to a hub or router that either performs the necessary processing or passes along data to a cloud or medical monitoring service. A local smartphone can be used as well.
Figure 2: Stick-on sensors are self-contained measurement systems specifically designed to monitor and alert the wearer and/or remote medical monitoring services anywhere in the world.
This is just one example of how transducers integrated with system electronics can result in small and compact medical devices that are not very intrusive. Weaving sensors into textiles can be used as a way of monitoring a physiological condition without surgery or without the need to carry around medical boxes. One such technology is in the form of smart socks where the textiles are infused with stress sensors and can track steps, speed, calories, and distance. However, they do more. These socks can also detect altitude so oxygen levels can be adjusted depending on the available oxygen density.
Still another benefit of these smart socks is the ability to monitor and measure foot-landing force. The distribution of weight as we walk and land can transfer force, shock, and stress through bones, joints, and vertebrae. A chronic back problem can be traced directly to the way someone is walking and remedies easily and quickly once the technology is in place to detect and quantify this, even in real time using a smartphone to alert a person if they are aggravating the situation (Figure 3).
Figure 3: Smart socks with embedded sensors woven into textiles can send data in real time to a smartphone to help people with chronic back and joint pain know when they are aggravating the situation and change their walking pattern.
Generating bytes from bites
A novel design, which has been on people’s minds for decades, is electronics implanted inside a tooth. Recently, researchers at the University of Taipei actually created an in- tooth smart sensor that can monitor, log, and send data when triggered by smoking, drinking, coughing, speaking, or cessation of breathing. Said to be up to 94 percent accurate, this tooth implant uses Bluetooth to communicate and can be placed inside a filling (Figure 4).
Figure 4: In-tooth sensors can detect chemical as well as physical activities and alert receivers locally when smoking, drinking, or cessation of breathing takes place.
Teeth are a special case because enough force and pressure can be generated and collected using energy-harvesting technologies (such as the piezo technology referenced earlier) to power sensors. Energy harvesting for on-body (or in-body) sensors is another center of focus for researchers at the University of Illinois. They have created a mechanical energy-harvesting patch that captures and stores energy from a beating heart (Figure 5). The bio-plastic substrate houses the sensor and energy-conditioning circuitry and is capable of measuring muscle-energy output or detecting when an athlete is warmed up or over-fatigued. It has been demonstrated that simple bending and unbending of the harvester was able to charge a 3.8 volt battery.
The ramifications of energy harvesting are huge for those requiring assistance in the form of a pacemaker. Instead of facing open-chest surgery at regularly scheduled intervals to replace batteries, the implanted regulating prosthetic could recharge itself continuously.
Figure 5: Energy-harvesting patches like this one can be inserted on a heart or lungs, and will use the energy generated from physical movement to charge and power other sensors and electronics on or inside the body.
Now more than ever implantable technology is poised to become a part of our daily existence. One example is the Digital Health Assistant developed in England. This is an implantable sensor used to detect when someone is “unwell” via detecting changes in movement, habits, diet, heart rate, mood, and other metabolic functions.
Note, in particular, mood detection. This opens up the possibility of technology solutions in the new (for sensors, anyway) territory of bio depression. Before too long we may see detectors that will actually dispense anti-depression medication when needed.
In a similar vein sensor technology may bring new relevance to the old saying “is nothing sacred.” Even connected intimacy can be monitored anywhere with devices like the Tactilu1 bracelet which is capable of transmitting touch between users. Imagine a digital chastity belt implanted in our exuberant youth.
Our understanding of medicine is allowing us to be more intrusive in our probing and monitoring of the internal processes that affect our health. This trend will continue as doctors find ways to add more sensors targeting specific metabolic indicators. As new and clever sensors are introduced for on- and in-body use, more of us will be walking, talking, eating, and sleeping while behind the scenes active sensors are monitoring our well-being. We are becoming wireless data nodes in our globally connected network. Let’s hope no one can hack into us.
For more information about the parts discussed in this article, use the links provided to access product pages on the Digi-Key website.