The performance and characteristics required of sensors vary greatly depending on the application area, and the types of sensors used also differ accordingly.
In particular, medical wearable devices are a representative field where high accuracy and reliability are required. I will explain the characteristics of each field and the sensors used in detail.

1. Fitness and Sports:

• Key Requirements: Focus is on measuring activity levels, identifying exercise types, gauging exercise intensity, tracking distance and speed, and estimating calorie expenditure. Real-time data and ease of use are prioritized over extremely high accuracy, though reasonable precision is still necessary. Durability is also crucial, as sensors must withstand vigorous movements and potentially harsh environmental conditions.
• Commonly Used Sensors:
  • Accelerometers: Measure steps taken, overall activity levels, and distinguish between different exercise types (walking, running, etc.). Typically, small, low-power MEMS (Micro-Electro-Mechanical Systems) based accelerometers are employed.
  • Gyroscopes: Analyze movement and estimate exercise posture. Often used in conjunction with accelerometers for more accurate motion tracking.
  • Heart Rate Sensors (PPG – Photoplethysmography): Measure exercise intensity and estimate calorie consumption. These optical sensors typically use green LEDs to illuminate the skin and measure changes in blood flow.
  • GPS (Global Positioning System): Tracks distance and speed, providing location data and movement paths during outdoor activities.
  • Altimeters: Measure changes in altitude (useful for activities like hiking and climbing). These often use barometric pressure to calculate altitude.

2. Health Management and Wellness:

• Key Requirements: Focus is on monitoring general health status, assessing sleep quality, measuring stress levels, and tracking circadian rhythms. Higher accuracy is required compared to fitness applications, along with the ability for continuous, long-term monitoring. Data reliability and the ability to provide actionable insights to the user are essential.
• Commonly Used Sensors:
  • Heart Rate Sensors (PPG): Measure heart rate and heart rate variability (HRV), which can be used to analyze stress and sleep quality. Techniques to enhance the accuracy of PPG signals are often implemented.
  • Accelerometers: Analyze activity levels and sleep patterns. They can detect movements during sleep, such as tossing and turning, which help in sleep stage analysis.
  • Skin Temperature Sensors: Measure changes in body temperature and contribute to sleep quality analysis. Analyzing temperature fluctuations during sleep can help estimate sleep stages.
  • Blood Oxygen Saturation Sensors (SpO2 – Pulse Oximetry): Measure blood oxygen levels, which can be useful for detecting conditions like sleep apnea. These sensors use red and infrared light to determine the oxygen saturation of the blood.
  • Bioimpedance Sensors (Bioimpedance Analysis): Analyze body composition, including body fat percentage and muscle mass. They measure the body’s electrical resistance by passing a small, imperceptible current through the body.

3. Medical Field:

• Key Requirements: Used for critical applications like disease diagnosis and monitoring, patient tracking, and evaluating the effectiveness of treatments. Extremely high accuracy, reliability, and data security are paramount. These devices must comply with stringent medical device certifications and regulations. Not only data accuracy but also secure storage and transmission of data are crucial.
• Commonly Used Sensors:
  • Electrocardiogram Sensors (ECG): Measure the electrical activity of the heart, enabling diagnosis of conditions like arrhythmias and myocardial infarction. ECG provides a much more accurate measurement of heartbeats and electrical signals compared to PPG.
  • Electromyogram Sensors (EMG): Measure the electrical activity of muscles, used in diagnosing muscle disorders and for rehabilitation therapy. They measure electrical signals related to muscle movement.
  • Continuous Glucose Monitoring Sensors (CGM): Provide real-time glucose measurements for diabetes management. These typically involve a small sensor inserted under the skin that measures glucose levels in interstitial fluid.
  • Pressure Sensors: Measure blood pressure and can be used for preventing pressure ulcers by detecting pressure on specific areas of the body.
  • Body Temperature Sensors: Measure precise body temperature using highly accurate temperature sensors.
  • Oxygen Sensors: Monitor respiratory conditions by measuring blood oxygen saturation and breathing patterns.
  • Impedance Sensors: Monitor changes in body fluid volume, which is important in managing conditions like heart failure.

4. Research Field:

• Key Requirements: The types of sensors used vary widely depending on the specific research goals. High precision and data reliability are crucial, as is the ability to collect, analyze, store, and share data according to strict research protocols.
• Commonly Used Sensors:
  • All of the above sensors: Used in various combinations depending on the research objectives.
  • Electroencephalogram Sensors (EEG): Measure brain activity by recording electrical activity in the brain.
  • Sweat Analysis Sensors: Analyze sweat composition to measure various chemical compounds, which can provide insights into stress levels, hydration status, and even certain medical conditions.
  • Motion Analysis Sensors (Motion Capture): Provide extremely precise movement analysis using various techniques, including optical and inertial systems.

Summary Table: