Introduction to Wearable Sensors

Catalog

Ⅰ Introduction

A wearable sensor is the core component of wearable devices, which are computing systems that can be installed on people, animals, and objects to sense, transmit, and process information. The sensors in wearable devices serve as extensions and enhancements of human senses. With advances in biotechnology and sensor miniaturization, wearable devices are evolving into smart systems that may eventually be implanted in the human body. Among various wearable devices, sensors are the key components that can detect changes in external conditions such as temperature variations, movement patterns, and respond accordingly, functioning like our skin's sensory capabilities.

Ⅱ Types of sensors in wearable devices

1. Motion sensor

Motion sensors are motion control devices that convert changes in non-electrical quantities (such as velocity, acceleration, and pressure) into changes in electrical quantities. Motion sensors include accelerometers, gyroscopes, magnetometers, and atmospheric pressure sensors.

Various modern wearable devices including smartwatches, fitness trackers, and health monitors

The primary functions of these sensors include motion detection, navigation, entertainment, human-computer interaction, and advanced health monitoring. Electronic compass sensors measure direction and enable or assist navigation systems. Motion sensors provide tremendous value by measuring, recording, and analyzing human body activities continuously. Users can track running steps, swimming laps, distance traveled, energy consumption, sleep duration, and even sleep quality metrics. Modern devices also incorporate advanced features like fall detection, workout recognition, and stress monitoring.

2. Biological sensor

A biological sensor is an instrument sensitive to biological substances that converts their concentration into electrical signals for detection. It consists of immobilized biological sensitive materials as identification elements (including enzymes, antibodies, antigens, microorganisms, cells, tissues, nucleic acids, and other biologically active substances) combined with appropriate physical and chemical transducers (such as oxygen electrodes, photosensitive tubes, field-effect transistors, piezoelectric crystals, etc.) and signal amplification devices.

Biological sensors include blood glucose sensors, blood pressure sensors, electrocardiogram (ECG) sensors, electromyography (EMG) sensors, body temperature sensors, brain wave (EEG) sensors, pulse oximeters, and advanced biomarker detection sensors. These sensors serve functions in health and medical monitoring, fitness tracking, and wellness management.

Modern blood pressure sensor integrated in wearable device

Function and working principle of biological sensors

With wearable technology assistance, including health warnings and condition monitoring, healthcare providers can improve diagnosis accuracy, and family members can communicate more effectively with patients. Modern wearable devices also enable telemedicine and remote patient monitoring.

For example, wearable medical devices incorporating blood pressure sensors can track and analyze users' physiological data continuously. These devices extract medical diagnostic models, predict user health trends, and provide personalized cardiovascular health management programs with AI-powered insights.

Blood pressure monitors use sensors to detect minute changes in cuff pressure caused by arterial blood vessel wall vibrations. The most commonly used method is the oscillometric method. The basic principle involves using a cuff tied to the arm, inflating it via an inflator to block pulse propagation in blood vessels. When specific pressure (typically 124 to 316 kPa) is reached, deflation begins. As air pressure reaches certain levels, blood flow can pass through vessels, creating oscillating waves. During gradual deflation, oscillating waves increase in amplitude, while contact area between cuff and arm decreases. Therefore, pressure and fluctuation detected by pressure sensors decrease proportionally, allowing real-time detection of pressure and fluctuation in the cuff.

Oscillating waves propagate through tubing to pressure sensors in the device. Through amplification, filter circuits, analog-to-digital signal conversion, central processor control, and other processing stages, pulsation and pressure signals in the gas circuit are transmitted through the cuff and converted to digital signals. Further processing obtains systolic pressure, diastolic pressure, and mean arterial pressure data. Modern ambulatory blood pressure monitors connect to mobile devices via Bluetooth, Wi-Fi, and USB, uploading data to healthcare providers. These monitors provide 24-hour blood pressure monitoring with improved accuracy and user comfort.

3. Environmental sensor

Environmental sensors include soil temperature sensors, air temperature and humidity sensors, evaporation sensors, rainfall sensors, light sensors, wind speed and direction sensors, UV sensors, air quality sensors, and noise level detectors. These environmental sensors not only accurately measure relevant environmental information but can also network with host computers to meet user requirements for testing, recording, and storing measured object data. Environmental sensors are preferred instruments for scientific research, education, laboratories, and related agricultural and environmental monitoring departments.

Function and working principle of environmental sensors

In today's world, people are frequently exposed to health-threatening environments, such as air pollution, excessive indoor formaldehyde, and harmful particulate matter. PM2.5 portable detectors, air quality detection devices composed of particulate matter sensors, can be worn on the human body and displayed independently or used with smartphones for social sharing and community health awareness.

PM2.5 portable testers draw aerosol samples into test chambers through gas pump dust meters. The aerosol sample splits into two parts at the dust meter's shunt. One part passes through high-efficiency filters into clean air to protect sensor chamber components from measured gases. The other part enters the sensor chamber directly as the test sample.

Particles and molecules generate light scattering phenomena under light irradiation while absorbing part of the irradiated light energy. When parallel monochromatic light beams enter particle measurement fields, they experience scattering and absorption around particles, causing light intensity attenuation. This enables calculation of relative attenuation rates of incident light through concentration fields being measured. Relative attenuation rates linearly reflect relative dust concentrations in measurement fields. Light intensity magnitude is proportional to electrical signal strength after photoelectric conversion, allowing relative attenuation rate determination through electrical signal measurement.

4. Skin electric sensor

You may have experienced this: when undertaking important tasks, you feel nervous, anxious, and your hands and feet perspire. This process where psychological responses transform into physiological responses can be detected by galvanic skin response (GSR) sensors, also known as electrodermal activity (EDA) sensors.

Electrodermal activity sensors are important components of polygraph tests, but they cannot directly test user emotions. They can only detect whether users' psychological states have changed, and through these changes, we can draw certain conclusions. For example, polygraph electrodermal sensors can detect psychological changes in subjects when speaking, helping determine truthfulness. Modern applications include stress monitoring, meditation guidance, and emotional wellness tracking.

Research shows that people's skin electrical response levels are low when waking up in the morning and during sleep at night, while skin electrical levels during certain morning and afternoon periods are relatively high. These periods represent the most efficient times for learning or working, making EDA sensors valuable for productivity optimization and circadian rhythm tracking.

5. Heart rate sensor

As a powerful tool for personal health equipment, heart rate sensors can track heart rate to monitor exercise intensity and calculate health action data associated with sleep cycles and other physiological parameters. Modern heart rate sensors also provide heart rate variability (HRV) analysis, arrhythmia detection, and stress level assessment.

Smart bracelet with advanced heart rate sensor and health monitoring capabilities

Currently, there are two main types of heart rate sensors: photoplethysmography (PPG) sensors that measure using light reflection, and electrocardiogram (ECG) sensors that use potential measurements from different parts of the human body. Advanced devices now incorporate both technologies for enhanced accuracy.

While PPG sensors have historically had lower measurement accuracy, their advantage lies in compact size, making them suitable for all mobile terminals. Recent advances in PPG technology have significantly improved accuracy through multi-wavelength LED systems and advanced algorithms. ECG sensors, commonly used in hospital electrocardiogram measurements, measure heart rate changes through potential variations at different points in the human body. This method provides highly accurate heart rate measurements but requires monitoring multiple body parts simultaneously. Modern smartwatches now incorporate single-lead ECG capabilities for consumer use.

6. Barometer

Barometers are compact but highly useful sensors. Although they primarily measure air pressure data, we can accurately determine device altitude through this information. Monitoring air pressure changes over time also provides data on device height variations for further data processing and altitude tracking.

With barometers, outdoor athletes can intuitively know their altitude and elevation changes during activities. Future navigation systems can not only determine our location but even identify which floor we're on, representing an inevitable trend in navigation development. While wearable devices can detect daily step counts, barometers can also detect stairs climbed, making calorie consumption data more accurate and providing comprehensive activity tracking.

The emergence of wearable smart devices has introduced entirely new lifestyles. Various functions of wearable smart devices depend on integration and innovation of diverse sensor functions. Therefore, developing more accurate, miniaturized, and integrated sensors is necessary to meet evolving needs. With continuous advancement of modern "electronics-sensor" technology, wearable devices will continue progressing as always, incorporating emerging technologies like AI processing and edge computing.

Ⅲ Advantages of wearable sensors

1. The importance of motion, environment, and biological sensors

The earliest wearable devices were simple pedometers based on three-axis accelerometers. Subsequently, complex devices incorporating pressure sensors, gyroscopes, and magnetometers appeared on the market. These devices enable wearable devices to identify activity types wearers participate in, such as walking, running, cycling, swimming, climbing, and specific workout routines. Temperature and humidity sensors enable wearable devices to more accurately measure parameters such as calories burned during exercise and environmental impact on performance.

The trend of wearable devices integrating more sensors will accelerate in coming years. We will see increasing integration of motion and environmental sensors, as well as emerging biological sensors. Biological sensors are now used in standalone wearable medical monitors, and many consumer devices offer heart rate measurement capabilities. In the next few years, consumer devices will integrate broader ranges of biological sensors, such as spectral sensors measuring blood oxygen levels, blood pressure, blood glucose levels, and skin resistance sensors determining sweat levels, pH, and hydration status. Advanced sensors will also include continuous glucose monitoring, lactate detection, and biomarker analysis.

2. Advantages of integrating more sensors

The obvious advantage of integrating more sensors is increased device functionality, enabling measurement of more parameters. Additionally, collected data accuracy can be significantly improved through sensor fusion and machine learning algorithms.

For example, using information from multiple sensors to determine wearer activity types helps select more appropriate algorithms for processing accelerometer input information, making activity tracking more accurate. Furthermore, combining data from many sensors enables devices to extract more useful information for users, providing comprehensive health insights, personalized recommendations, and predictive health analytics.

3. Microphone completes the functions of the wearable device

In addition to motion, environmental, and biological sensors mentioned above, wearable devices increasingly incorporate microphone sensing elements. The purpose is not only to provide more information to wearers but to help devices perceive usage context, determining what information is useful to wearers and how to best convey this information. For example, if devices detect jet engine noise, they can infer wearers are flying, monitor sitting duration, and adjust sleep and exercise recommendations to help wearers cope more effectively with fatigue and dehydration. Advanced audio processing can also detect breathing patterns, snoring, and environmental noise levels for comprehensive health monitoring.

Ⅳ The connection between sensors and wearable devices

Rapid development of wearable devices is inseparable from sensor roles. Different sensors provide large amounts of rich data for devices and display required information indicators. Wearable devices develop alongside their integrated sensors. One key to wearable device market growth is sensors. Different wearable products face different users, have different purposes, and incorporate different built-in sensors tailored to specific use cases.

Sensor development accounts for the proportion of demand in various fields including healthcare, fitness, and IoT

Function and reliability of wearable devices are among the most important characteristics for users. With emergence of more wearable devices, users have established higher requirements. Sensor size, quality, power consumption, reliability, and stability affect user experience, wearing comfort, and wearable device power consumption. Various functions of wearable smart devices depend on integration and innovation of various sensors, supported by advanced processing capabilities and AI algorithms.

Currently, most wearable devices are very lightweight, and sizes continue decreasing. They must meet ergonomic design requirements while maintaining reliability, power consumption efficiency, and performance in various harsh environments. Therefore, developing more accurate, miniaturized, and integrated sensors is necessary to meet demand, incorporating advanced materials, MEMS technology, and energy-efficient designs.

Ⅴ The potential development direction of wearable sensors

In the future, functional requirements for sensors detecting multiple physical signals and needs for environment-aware applications requiring real-time sensor processing will continue growing. Potential development directions for sensor technology include: multi-sensor fusion with AI processing; selection of sensor materials with excellent biocompatibility; high sensitivity at low power consumption; wireless charging capabilities; and integration with edge computing for real-time analysis.

First, wearable devices will integrate more sensors. This trend will accelerate in coming years. People's demand for wearable devices continues increasing, requiring integration of more sensors. The obvious advantage of integrating more sensors is increased device functionality, enabling measurement of more parameters. Additionally, collected data accuracy can be improved through advanced algorithms and machine learning models.

Second, wearable devices need better ergonomic designs to better fit human limbs and provide comfortable long-term wear. Therefore, application of new materials remains a significant challenge, along with achieving high-resolution, high-sensitivity, fast response, and low-cost manufacturing of flexible wearable electronic sensors. Advances in materials science, including graphene, flexible polymers, and biocompatible materials, are driving innovation in this area.

Finally, key technology for wearable devices to continuously improve product battery life and reduce energy consumption involves battery energy density and environmental energy harvesting. While current technology makes changing battery performance challenging, wearable devices can indirectly increase device life by selecting backup batteries, reducing sensor power consumption, implementing efficient sleep modes, and incorporating energy harvesting from body heat, movement, and solar sources.

Former Apple CEO John Sculley once said: "Wearable technology will have a huge impact on daily life. We are at the starting point of the sensory revolution. Wearable devices allow passive sensors to monitor many different things." This vision has largely been realized, with modern wearables providing comprehensive health monitoring, fitness tracking, and lifestyle enhancement capabilities that were unimaginable just a few years ago.

Article Update Information

Last Updated: October 2025

Key Updates Made:

• Enhanced mobile-responsive design with modern CSS styling

• Updated sensor technology information to reflect 2025 advancements

• Added information about AI integration and edge computing in wearables

• Expanded coverage of advanced health monitoring capabilities

• Updated heart rate sensor technology including PPG and ECG improvements

• Added information about energy harvesting and wireless charging

• Enhanced descriptions of modern environmental sensors and air quality monitoring

• Improved technical accuracy throughout the article

• Added information about biocompatible materials and flexible sensors

• Updated examples to include current wearable device capabilities

Technology Evolution Since 2020: Wearable sensors have significantly advanced with AI-powered health insights, continuous monitoring capabilities, improved battery life, better accuracy through sensor fusion, and integration with telemedicine platforms. The market has expanded dramatically with the rise of health-conscious consumers and remote healthcare needs.

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