Wearable device is a kind of computing equipment that can be installed on people, animals and objects, and can sense, transmit and process information. Sensor is the core device of wearable device, and the sensor in wearable device is the extension of human senses, which strengthens the function of human’s “sixth sense”, and it is the “core” tool for people/objects to communicate with the world, which opens the door to the “Perception Era”.
Table of Contents
What are the sensors in a wearable device?
Generally speaking, the sensors in a wearable device can be categorized into the following major groups.
1. Motion Sensor
Motion sensor motion control sensor is a kind of non-electricity (such as speed, pressure) changes into electricity changes in the original. Including: acceleration sensor, gyroscope, geomagnetic sensor or electronic compass sensor, atmospheric pressure sensor (through the measurement of atmospheric pressure can be calculated altitude) and so on.
These sensors mainly realize the functions of motion detection, navigation, entertainment, human-computer interaction, etc., of which the electronic compass sensor can be used to measure the direction, realize or assist navigation. Life is all about movement, and movement is an important and indispensable part of life. Therefore, through the motion sensor at any time and anywhere to measure, record and analyze human activity has a significant value, the user can know the number of running steps, swimming laps, cycling distance, energy consumption and sleep time, and even analyze the quality of sleep and so on.
Functions and Realization Principle of Motion Sensors
By measuring, recording and analyzing the human body’s activity anytime, anywhere, the motion sensor allows the user to know the number of running steps, swimming laps, cycling distance, energy consumption and sleep time, etc., and at the same time it can be used for navigation, entertainment, and human-machine interaction (HMI).
Take a wearable human motion capture system function as an example, in order to be able to capture the human body movement in real time, a wearable human motion capture system needs to be designed. It obtains real-time human posture information through inertial measurement units distributed on the human body. Each inertial measurement unit is composed of a miniature MEMS 3-axis gyroscope, a MEMS 3-axis accelerometer, a MEMS 3-axis magnetometer, and an MCU, which obtains the data from the sensors and solves the posture angle of the corresponding part by using the quaternion-based extended Kalman filter, and then sends the data to the MCU via CAN bus and Bluetooth module. Through the CAN bus and Bluetooth module, the data are uploaded to the computer in real time, and the computer drives the virtual human body movement through VC++ and OpenGL programs to realize the real-time human body movement reproduction.
The functions to be realized by the motion sensor include the acquisition of sensory data from three different types of inertial devices, attitude angle calculation and wired communication. The motion sensor consists of five main components: MCU, acceleration sensor, gyroscope sensor, magnetometer and CAN interface. The MCU contains modules such as synchronous sequence communication bus (I2C), asynchronous receiver-transmitter (UART), and pushbuttons, which control a series of operations of the node. The node is powered by wires, and the MCU controls data acquisition, attitude angle solving, and CAN transmitting and receiving for the three sensors.
2.Bio-sensors
Biosensors are instruments that are sensitive to biological substances and convert their concentration into telecommunication signals for detection. It is an analytical tool or system that consists of an immobilized biosensitive material as a recognition element (including enzymes, antibodies, antigens, microorganisms, cells, tissues, nucleic acids, and other biologically active substances), an appropriate physicochemical transducer (such as oxygen electrodes, photosensitive tubes, field-effect tubes, piezoelectric crystals, and so on), and signal amplification devices. Biosensors have both receiver and transducer functions.
Biosensors include glucose sensors, blood pressure sensors, cardiac sensors, myoelectric sensors, temperature sensors, brainwave sensors, т.б. These sensors mainly fulfill functions such as health and medical monitoring, and entertainment.
Functions of Biosensors and Implementation Principles
With the help of wearable technology, doctors can improve diagnosis and family members can communicate better with patients.
For example, the wearable medical equipment composed of blood pressure sensors can track and monitor the user’s body data, analyze and refine the medical diagnostic model, predict and shape the user’s health development, provide the user with personalized cardiovascular projects and health management solutions, and at the same time, help family members to care for their loved ones’ health conditions.
Blood pressure monitor is through the sensor to detect the human body arterial blood vessel wall vibration caused by the cuff pressure small changes, the most commonly used method is the oscillatory method, the basic principle is to use the cuff tied to the arm, through the inflatable pump to the cuff inflatable to block the propagation of blood vessels in the veins of the veins of pulsation, to reach a certain pressure (generally 124 ~ 316kPa) began to deflate, when the air pressure reaches a certain level, the blood flow through the blood vessels, and a certain amount of oscillatory wave, gradually deflate, and then deflate, as the pressure sensor detected by the contact with the arm is becoming more and more loose, therefore, the pressure sensor detected by the pressure sensor is small changes. When the air pressure reaches a certain level, the blood can pass through the blood vessel and there is a certain amount of oscillating wave, gradually deflate, the oscillating wave becomes bigger and bigger, then deflate again, because the contact between the cuff and the arm becomes looser and looser, therefore, the pressure and fluctuation detected by the pressure sensor becomes smaller and smaller, and the pressure sensor can detect the pressure and fluctuation inside the cuff instantly. The oscillating wave is transmitted to the pressure sensor in the machine through the air tube, and through the corresponding amplification, filtering circuit, analog/digital signal conversion, central processor control and other processing links, the pulsed signal and pressure signal transmitted to the airway through the cuff is converted into a digital signal, which is further processed to obtain the systolic, diastolic, and mean blood pressure data. This dynamic blood pressure monitor can be connected to a mobile device via Bluetooth and USB to upload the data to healthcare professionals, and is usually worn outside by the user to provide 24-hour blood pressure monitoring.
In addition, wearable devices that sense changes in human emotions through sensors such as EEG and ECG can realize entertainment and interaction. For example, the Idea Cat Ear uses NeuroSky’s advanced TGAM EEG chip, which can read human brain waves. Different patterns of brainwaves represent different moods and states. The TGAM chip will convert the brain signals that represent the emotional state of a person into digital signals that can be recognized by the cat’s ears, so as to execute corresponding commands and complete different actions. For example, when a person is in a state of concentration, it will stand up high, and when he is relaxed, it will shrug down.
3.Environmental Sensors
Environmental sensors include: soil temperature sensor, air temperature and humidity sensor, evaporation sensor, rain sensor, light sensor, wind speed and direction sensor, etc., not only can accurately measure the relevant environmental information, but also and the host computer to achieve networking, to maximize the satisfaction of the user on the test of the measured object data testing, recording and storage, is the scientific research, teaching, laboratories, and agricultural departments of the Soil Fertilizer Station, Agricultural Institute and the relevant agricultural environment monitoring department of choice for high quality instruments. It is the first choice of high quality instrument for scientific research, teaching, laboratory and agricultural department soil fertilizer station, agricultural science institute and related agricultural environment monitoring department.
Functions and Principles of Environmental Sensor Implementation
In today’s world, people are constantly exposed to health-threatening environments such as air/water pollution, noise/light pollution, electromagnetic radiation, extreme weather, т.б. Worse still, we are often unaware of the fact that we are in such environments, such as pm2.5 pollution, which can lead to various chronic diseases. What is even more frightening is that we are often unaware of the fact that we are in such environments, such as pm2.5 pollution, which can lead to various chronic diseases. The air quality detection device – pm2.5 Portable Sensor, which is made up of particulate sensors, can be worn on the human body and can be displayed alone or combined with a cell phone and shared with friends.
The WF200DP test draws the aerosol to be tested into the chamber by means of an air-pumping dust meter. The aerosol to be tested is split into two parts at the dust meter manifold, one of which passes through a high-efficiency filter and is filtered into clean air, which acts as a protective sheath to protect the components of the sensor chamber from contamination by the gas to be tested. The other part, the aerosol, enters directly into the sensor chamber as the sample to be measured.
Particles and molecules scatter light when illuminated and absorb some of the light’s energy. When a parallel beam of monochromatic light is incident on the particle field under test, it is scattered and absorbed by the surrounding particles, and the intensity of the light decreases. In this way, the relative attenuation rate of the incident light through the concentration field to be tested can be obtained. The magnitude of the relative attenuation rate is basically a linear reflection of the relative concentration of dust in the field to be measured. The magnitude of light intensity is directly proportional to the strength of the signal of the photoelectric conversion, and the relative attenuation rate can be obtained by measuring the signal.
The Little-Known Sensors in Wearable Devices
Picoelectric Sensors
I am sure every reader has had the experience of feeling so nervous and anxious that your hands and feet are sweating just before you have to undertake a very important task. This psychological response is translated into a physiological response that can be detected with the use of an electrocorticograph.
Utilizes electrodermal response to sense people’s moods and expresses feedback with different messages
The piezoelectric sensor is an important component of polygraph instruments.
Polygraphs work together with piezoelectric sensors, respiratory rate sensors and heart rate sensors.
It is important to note that the piezoelectric sensor cannot detect the user’s happiness, anger, sadness, or joy, but can only sense changes in the user’s psychological state, and through such changes, we can draw some conclusions.
For example, through the polygraph’s PEEK sensor to sense the psychological changes in the subject’s speech to determine whether or not he or she is lying.
For example, studies have shown that during a day’s activities, the human body’s electrodermal response level is lower in the morning when people wake up and in the evening when they go to sleep, while the electrodermal level is higher in the morning and in the afternoon at a certain time of the day, which is precisely the time when we are most productive in our studies or at work.
If we use a piezoelectricity detector to measure the level of our body’s piezoelectric response over several days, we will be able to find out which period of the day we are most productive through the level of the piezoelectricity waveform.
For piezoelectric sensors, we must understand things:
1, the human skin electric response is affected by three factors: temperature, human activity and psychological response, so the skin electric sensor will be affected, and the accuracy is yet to be tested.
2, people will have many emotions a day, each day the time of the emotions generated by the emotions, emotional categories are different, even if we accurately measure the skin electric response, categorization and organization of these data and to give scientific advice is still the manufacturer’s biggest headache.
Heart Rate Sensor
As a super weapon for personal health devices, the heart rate sensor can monitor heart rate to track exercise intensity, different exercise training modes, etc., and can be used to extrapolate sleep cycles and other health actions associated with this data.
The relationship between heart rate change and sleep state during sleep.
Since the pulse rate changes with the sleep cycle and decreases during deeper sleep, we can monitor the sleep quality by the change of heart rate during sleep time. However, since the accuracy of heart rate sensors on mobile devices is low, the reliability of these sensors has yet to be considered. It is rumored that to ensure the reliability of heart rate measurement, Apple Watch has designed four heart rate sensors to accurately measure heart rate.
Currently, electrodes are commonly used in hospitals, which are more accurate.
Currently, there are two types of heart rate sensors, the photoelectric heart rate sensor that measures by light reflection and the electrode heart rate sensor that utilizes electrical potentials from different parts of the body. Although the former is not as accurate, it has the advantage of being small in size, so all mobile terminals currently use this type of measurement. The latter, which we often see in hospitals when measuring ECG, measures changes in heart rate by measuring potential changes at different points of the body. This method is accurate, but it must monitor both parts of the body at the same time, and we usually use cell phones and watches with one hand to touch the product, so it is not possible to do continuous monitoring.
There are some things we must understand about heart rate sensors:
1. Simply giving out the heart rate value is not very meaningful to you, if you can keep measuring and giving out health advice such as sleep quality/resting time through the heart rate data for a period of time, it will be very helpful to the user.
2… Currently, most mobile terminals use optoelectronic heart rate sensors, which have a higher error rate than electrode heart rate sensors.
3. Electrode heart rate sensors can not be applied to smaller wearable devices, but there are already manufacturers working for this. I believe that in the future, it will become a standard accessory for high-end devices.
Barometer
The barometer sensor is a little buried but very useful item. Although it can only measure the air pressure data, but through this data we can accurately know the altitude of the machine. If we monitor the air pressure changes over a period of time, we can also get data on the machine’s altitude changes, which can be used to prepare for further data processing.
With a barometer to measure the altitude, you don’t have to worry about not being able to navigate on a double-decker road like this.
Athletic watches equipped with barometer sensors can measure altitude data for athletes.
What benefits does the barometer sensor bring to the user through the measured altitude data? Outdoor athletes can intuitively understand their own altitude; future navigation maps can not only know where we are located in the plane, and even know where we are on the floor, and this is definitely the inevitable trend of the future development of navigation; wearable devices can only detect the number of steps people walk every day, but with a barometer can also detect the number of stairs walked, thus making the calorie consumption data more accurate.
Things we must understand about barometer pressure sensors:
1. Since it is a component for measuring air pressure, abnormal air pressure changes will definitely affect the validity of the information obtained by the user. For example, in the aircraft flight, for the comfort of passengers will be pressurized for the cabin, the aircraft’s internal air pressure value is different from the outside, we will not be able to get the correct height information.
2. At present, barometric pressure sensors have been widely used in mobile terminals, but due to the lack of application software support, they are often left out by users.
3. Barometer pressure sensors are very practical components that can be used to read altitude information from equipment equipped with them while hiking.
Conclusion
The emergence of wearable smart devices has brought us a brand new way of life, but due to the limitations of other factors such as the level of technology and cost, the maturity of wearable smart devices is still not mature enough to meet the satisfactory expectations. However, as a very important part of the sensor, especially the various functions of wearable smart devices, all rely on the functional integration of various types of sensors and innovation to achieve, therefore, to develop more accurate, miniaturized, integrated sensors to meet the demand.
In the future, as modern “electronic-sensor” technology continues to advance, wearable devices will continue to develop. In the meantime, a variety of new pressure sensors will emerge, and the application of sensors will enter into even greater splendor.
