Almost every person is in stress and feels anxious due to work, study, career, and relationships. This is the reason why in the age group of 30-40 years people going to die due to heart attacks.
Health is now a bigger challenge for people to maintain. Nowadays smartwatches are doing quite well in monitoring health data, where Information is quite accurate.
This creates more awareness inside a person regarding health, where you can check SPo2 level, daily calorie burns, heart rate, Blood pressure, and ovulation of women.
Before we jump on the topic of sensors, let’s start with a little bit of the history of Smartwatches and how they evolved.
History of Smartwatches
Smartwatch advancement began with the digital watch. So the first digital watch “Pulsar” was made by the Hamilton Watch organization in 1972. Later this company was possessed by Seiko a Japanese organization in 1978.
The first watch which has user-programmable memory that could store 24 digits was the NL C01 of the pulsar.
Astra is the first batch of advanced watches of the HMT organization sold like hot tea in the Indian market. Later numerous different organizations like Casio, and Seiko hopped into this advanced watch.
From now onwards advancement of smartwatches will happen and smartwatches had their memory and processor like PCs.
William Stephen George Mann a Canadian Specialist, Teacher, and Designer is known as the “Father of wearable registering” who built the world’s most memorable Linux wristwatch in 1998.
Later in 2010, other Smartwatch organizations like Amazefit, Fossil, Samsung, and different contenders bounced into this field.
1st Apple Smartwatch was launched in 2014 and became so popular for its performance and takes place in the market easily and now became one of the top 3 smartwatch company lists.
smartwatch sensors list
In today’s world smartwatches and mobile phones are alike.
You can call, text messages, listen to music, control the music devices, and monitor your health report like heart rate, spo2 level, calories burned, sleeping tracking, ovulation of women, blood pressure, etc.
Let’s talk about the sensors used in Smartwatches
Sensors like sense temperature, detect the direction in GPS, Heart rate, detect accidents, etc are called MEMS(Micro-Electrical-Mechanical-Sensors)
These sensors circuit is connected to the CPU of a device (Smartwatches) for further processing, they show digitally on the screen.
Some common sensors that are used in Smartwatches:
- Accelerometer: measures acceleration and tilt
- Gyroscope: measures angular velocity and orientation
- Heart rate monitor: measures the wearer’s heart rate
- GPS: determines the device’s location through the phone.
- Barometer: measures air pressure
- Ambient light sensor: it measures the amount of light in the environment and according to this smartwatch changes the screen’s glow.
- Microphone: enables voice commands and recording audio
- Compass: measures the direction of magnetic north
- Blood oxygen sensor: measures the oxygen saturation of the blood
- ECG (electrocardiogram): measures the electrical activity of the heart.
- Optical sensors and pressure sensors
Accelerometer
It is a device that measures the acceleration of the rate of change of velocity of an object. It detects the acceleration of an object and detects the magnitude of gravity and measures the vibration of an object.
Accelerometer uses in different areas:-
- Mobile screen rotation.
- Vibration of mobile
- Sportsman training time is used
- The trainer uses this device to check the body mass and heart rate of the trainee
- To prevent aircraft design LCA-5080 accelerometer is used.
- This device used to calculate the step, cycling, and different exercise were pre-installed in smartwatches. Through software, it estimates how many calories are burned.
3 Types of accelerometers
- MEMS accelerometer- This is Micro–Electro – a Mechanical – System. The most mobile is using this technology.
- Piezoresistive Accelerometer
- Piezoelectric Accelerometer
How does MEMS Accelerometer work?
In the above figure, a mass structure in black color is given. When this mass oscillates according to the movement of devices like mobile or Smartwatches a capacitance is created between mass and fixed plate( Green color).
Due to change in capacitance electricity also fluctuate.
Both end sprigs are connected which helps the mass to get back to its original place when the device is stationary position.
All these fluctuations go to the CPU of the device and show the result after processing and OS shows that result on your screen.
Gyroscope Used in Smartwatches
Gyroscope is a device that measures angular velocity and maintains orientation.
Angular velocity:- it means an object rotates or revolute within its axis with respect to time. Here displacement is denoted as θ.
This device has 4 major parts
- Gimble
- Gyroscope frame
- Spin axis
- Rotor
The Aim of this device is to maintain orientation and angular velocity. Here gimble is connected to the gyroscope frame. Whenever the rotor which is connected to the motor, rotates its own axis its rigidity force came into action.
Rigidity force is directly proportional to the rotation of the rotor
For example– whenever the bicycle wheel rotates more It is easy to balance but in case lower speeds it’s not.
The greater the rotor mass and diameter, decide the more rigidity/ balance in space.
For example – you can experience a small wheel bicycle creating less balance rather than a big wheel bicycle while moving.
Another thing is precession
Here when we applied force to tilt, the gyro will also tilt according to the applied force to balance the angular momentum.
Where gyroscope is used in Smartwatches?
- Tilt while gaming
- Playing PUBG in gyro mode
- Tilt your mobile to landscape mode
- Aerospace
- Satellite
- Fighter jet
MEMS gyroscope is also called a Gyro meter. It is basically used in mobile and Smartwatches.
How does a MEMS gyroscope work in your Phone/Smartwatch?
The above pic is showing about the simplified form of a MEMS gyroscope. Here Movable mass is black and Red in color and is connected to the springs.
The fixed plate is connected to the electricity, whenever exercise or running or any physical activity is done by you movable mass also moves.
Due to the movement of Movable mass, there is a capacitance created between the fixed plate, and after processing the data device shows the calories burn, and the steps you walk.
If any accident happens to you this sensor detects due to vibration detection, it makes a call to emergency no which is life-saving.
Optical And Pressure Snesors to Monitor Heart Rate
The optic is related to light. This is one of the important sensors for monitoring Heart rate and SPO2 level.
The heart is an important organ of your body and is the most sophisticated pump which supplies blood to different parts of your body.
What is Heart Rate?
The rate of the heart pump within a minute is called the heart rate. Your heart rate shows your health condition. It varies for different age people at normal conditions.
- Newborn babies below 4 weeks have a heart rate of 100-205 beats per minute
- Infants ( 4 weeks to 1 year) have a heart rate of 100-180 beats per minute.
- Toddlers (1 to 3 Years) have a heart rate of 98-140 beats per minute.
- Preschools (3 to 5 Years) have a heart rate of 80-120 beats per minute.
- School-age (5 to 12 Years) have a heart rate of 75-118 beats per minute
- Adolescents (13-18 years) have a heart rate of 60-100 beats per minute.
- Above 18 also have a heart rate between 60-100 bpm.
- Depending upon heart rate varies.
How smartwatches measure Heart rate
Optical sensor
Optics means related to sight and light. Light is a radiant energy form that passes from one point to another point in a waveform.
Here two types of color lead are used in Optical sensors that are red and green.
some fundamental rule of light is used in Optical sensors that is when an object is red in color that means it emits red color and absorbs another color.
For this reason, green light is used for heart rate measurement because human blood is red in color. that means your blood emits red color.
When light passes through your skin and contact with your blood, it absorbs the energy, and how much energy of light gets back to the sensor that decides the heart rate, after evaluation done by the software.
This is the way how all-optical sensor works in Smartwatches.
Another is a pressure sensor that is related to the pressure point of your body where you can calculate your heart rate. The easiest pressure point of your body is the Neck or Wrist where you can easily measure heart rate.
- you check your wrist by pressing your fingers and count for 15 secs then multiply by 4 which shows a heart rate of 60 secs.
- Otherwise, measure continuously for 60 secs.
How Spo2 level Checked Through Sensors?
saturation of pulse oximeter checks the oxygen level in our blood which shows your health condition. In covid period it plays a significant role for medical personnel.
If the SPo2 level of the human body is below 90 percent then it is an Emergency condition.
Before you know the working principle of the sensor, let’s know about oxygen and its importance.
Why oxygen is important for the human body?
Oxygen is an element that comes to your body through the respiration process. This oxygen comes through the first pharynx, larynx, and trachea which is called the windpipe, and goes to the lungs.
From here Deoxygenated blood( blood that contains Co2) is coming from the heart’s Right atrium. After dropping Co2 in the lungs it contains oxygen in Hemoglobin which is in RBC and passed through the Left Atrium of the Heart.
The Left Atrium of the Heart pumps that blood to the different parts of your body through Arota.
This oxygen goes to each cell of the body part and converts Glucose to Pyruvate and converts to ATP(which is a form of energy) inside the Mitochondria.
1 glucose molecule can produce 38 ATP maximum, but due to loss, it converts 29 to 32 ATP.
what happens if oxygen is absent in our body?
When you run or work on something you need the energy to perform. This energy comes through glucose which comes from food. To convert glucose to energy you need oxygen. When there is the absence of oxygen-glucose only produces 2ATP rather than 38 ATP and produces Lactic acid.
This creates stiffness in muscles and you aren’t able to do work. Without this energy your heart also becomes dead. This is the reason you need oxygen to survive.
How do SPo2 Sensors work in Smartwatches?
To calculate oxygen level in Smartwatches there is RED light LED and INFRARED light below the Smartwatches. When light passes through the skin and comes to contact with blood the reflection and absorption of light occur.
This infrared light helps to detect how much light reflects by Saturated hemoglobin (which contains Oxygen) and Unsaturated hemoglobin (which doesn’t contain Oxygen). This decides the saturation of Oxygen in your Blood or calculates the SPo2 level of your body.
How is ECG/EKG used in Smart Watches?
An electrocardiogram is used to monitor different types of common types of your heart problems like:-
irregular heartbeats called arrhythmias if the Arteries are blocked or getting narrow which causes heart attack and etc.
how to take readings of ECG https://oxfordmedicaleducation.com/ecgs/ecg-interpretation/
The Apple series watch 4,5,6,7,8, or Ultra all have single-lead ECG but in ECG/EKG machine there are 12 lead which shows more accuracy and take different angles to record the electrical signal of the heart in the waveform.
Single lead ECG only gives information like heart rate and heart rhythm and if the heartbeat is missing. Here it does not show which part of your heart is suffering but it gives 96 to 97 percent accurate reading in the Apple Watch series. This helps you to know about your health and consult a doctor.
How GPS works in our Smartwatches?
GPS means Global Positioning System. This technology is developed by U.S. Navy and is currently owned by U.S Government.
Your phone/ Smartwatch has a receiver and sender. GPS Satellite rotates around Earth twice a day in a very precise orbit of about 10900 nautical miles and transmits signals to Earth.
Smartwatches having GPS receiver sends a signal to the Satellite which nears. To more accuracy in location, this signal passes through 4 satellites.
This precision information gives info about the Longitude and Altitude of a person.
Why does it need 4 satellites to increase accuracy in location
Every satellite covers a specific area according to the satellite’s position in orbit. This circle area which is covered by 3 satellites and a common intersection point shows the exact location of the person having a GPS tracker.
Forth no satellite shows the exact time, according to Albert Einstein time runs faster if an object moves away from the gravitational force.
This is the reason why the atomic time clock of the satellite is 38 microseconds faster than Earth’s atomic time.
How does GPS connect with satellites?
AGPS is Assisted Global Positioning System. This is actually used for mobile or Smartwatches. whenever you are on your GPS tracker on your phone or Smartwatches it actually connects with the AGPS server and sends signals to the satellite.
AGPS plays a significant role in transmitting signal and receiving signals. A normal GPS tracker takes 10-15 minutes to receive a signal from the satellite. AGPS server solves this issue and gives an instant signal to the receiver.
How do Smartwatches/Mobile detect the atmospheric pressure of
Earth and altitude Through a Barometer?
A Barometer sensor is used to check atmospheric pressure and measure the altitude from the sea level. This feature helps you in Climbing Mountains to check atmospheric pressure.
Here a Micro Mechanical Sensor Chip is used to determine the pressure of the atmosphere. There is a processor and sensor which contains pressure sensitive membrane which is connected with Electric Resistors to form a Wheatstone bridge.
A change in pressure in the membrane causes a change in an electrical voltage proportionate to the amount of distortion created at the resistor.
So the change in voltage is a change in Ambient Pressure. After this change in voltage data is processed in the processor and shown to you digitally.
Conclusion
Every device getting more optimized day by day through sensors.
From my end Optical sensor forHeart Monitor getting updated day by day, which is a great innovation for human beings.
In 2023 Apple, Samsung, and Fitbit smartwatch companies can perform in Android and ios give quite a good accuracy about your health.
Which is your best sensor for humans necessary comment below.
