Overview
With rapid economic growth and a rising population, healthcare has become a prominent concern. In recent years, smart electronic health monitoring devices have become widespread. Wearable medical devices, the most representative category, have appeared widely in public spaces. They combine attention-grabbing designs with features that encourage users to track health metrics, and they are increasingly part of home health monitoring. This article examines the underlying aspects of wearable medical devices.
Behind this trend, in addition to advances in sensing, communication, and data analytics, highly integrated hardware architectures play a crucial enabling role. Modern wearable medical devices rely on HDI (High-Density Interconnect) PCB technology to integrate sensors, processors, wireless modules, and power management circuits into compact, lightweight, and wearable form factors. HDI PCBs support fine-pitch components, multilayer routing, and reliable signal transmission, making it possible to achieve continuous physiological monitoring without compromising comfort or device reliability. This article examines the underlying aspects of wearable medical devices from both technological and industry perspectives.
Behind Wearable Medical Devices
The history of wearable medical technology traces back to the 1960s, originating from a project at the MIT Media Lab. The concept embeds multimedia information, sensors, and wireless communication into everyday personal items. When worn correctly, these devices collect data rapidly and share recorded information; after processing and analysis by companion software, they produce health metrics. They also synchronize data with electronic displays to enable real-time monitoring of the wearer's health.
PCB Design Considerations in Wearable Medical Devices
Wearable medical devices must deliver consistent readings over long periods while staying in direct contact with the body. The medical PCB therefore has to support very low noise levels and high reliability without adding bulk or stiffness.
Designers start by choosing a thin or flexible board that can follow body contours and keep sensor connections short. Power delivery is arranged so the device can run for days on a small battery without frequent recharging.
Any heat from the processor or wireless circuits must stay minimal so it does not raise skin temperature or interfere with temperature sensitive measurements.
Careful trace layout and grounding help preserve the integrity of weak biosignals such as ECG or pulse oximetry even when the device moves with the patient.
Materials and protective layers are selected early to resist sweat, moisture, and repeated cleaning while maintaining stable electrical performance over months of continuous use.
Architectures and Design Challenges
Size Is Critical
Most wearable devices are lightweight and becoming smaller. Key considerations include:
- Smaller packages and component footprints
- Use of advanced packaging technologies to increase integration
- Minimizing external components
Ultra-Low Power
Power consumption is crucial for user experience and should be as low as possible. Because system size limits battery capacity, low quiescent current chips help achieve low overall power and extend standby time. Wearables generally require low-power microcontrollers and low-power connectivity technologies.
Ergonomics
- Design for ease of use
- Preventing accidental operation
- Sensor designs that provide high sensitivity and reliability
High Reliability
- Ability to operate across a range of environments
- Robust mechanical design to prevent damage
- Occasional requirements for water resistance
Sensor Technology
- Multi-sensor fusion
- Selection of sensor materials with good biocompatibility
- High sensitivity at low power consumption
Connectivity
- Low-power Bluetooth and Wi-Fi to connect with other smart devices
- Data synchronization and automatic application updates
Heart Rate Sensor Technologies for Wearables
In simple terms, PPG is a reflection-based optical method. It uses the pulsatile change in blood optical transmission to produce an electrical signal at a photodetector. That signal is then converted into heart rate by firmware or software algorithms.
When light of a certain wavelength illuminates the skin surface, it is transmitted or reflected to the photodetector. During this path, absorption by skin, muscle, and blood attenuates the detected light intensity. Absorption by skin and muscle tissue remains essentially constant over the cardiac cycle, while blood volume in the tissue varies pulsatilely under cardiac action. When the heart contracts, peripheral blood volume is at its maximum, producing the greatest light absorption and thus the lowest detected light intensity. During diastole, the opposite occurs and the detected light intensity is highest, so the photodetector signal shows a pulsatile variation.
Why is the LED color commonly green? In blood, green light is absorbed more strongly than red light, which tends to provide a clearer signal for pulse detection. When the heart beats, more blood flows past the wrist and green light absorption increases; between beats, blood flow decreases and green light absorption decreases accordingly.
For example, assume the LED emission level is 100, skin and muscle each absorb 10 (constant), and blood absorption is 15, so the reflected signal would be 100 - 10*2 - 15 = 65. When an arterial pulse arrives and red blood cell oxygenation increases, total blood absorption rises and the reflected signal may drop to about 50. The detector therefore observes a repeating pattern such as 65-50-65-50, and by counting how many pulses occur per second the device derives the heart rate.
This sensing principle also explains its limitations. If there is substantial sweat or other fluid between the band and the skin, the measured values will be inaccurate. Irregular motion introduces noise, producing sequences like 65-50-66-51-62-50-65 that make pulse detection less reliable.
Overall, PPG-based measurement is relatively accurate for resting heart rate and for regular activities such as running. For irregular sports movements, such as soccer or badminton, measurement accuracy can decline due to motion artifacts. For most nonprofessional users, the typical error is only a few beats per minute and is generally acceptable.
Safety and Radiation Concerns
Privacy and Data Risks
Dependence on the Internet is increasing, and wearable medical devices play a supporting role. The Internet continuously generates massive amounts of data, whether about company developments, individual consumption patterns, or identity features; these become stored in various forms. As health indices, activity traces, and habits are recorded everywhere, the risk of user privacy exposure increases. The more data uploaded, the greater the amount of sensitive information. With enough data, comparative analysis can reveal a wearer's life patterns. This is a major challenge for the future development of wearable medical devices.
Emissions and Safety
Do emissions from wearable medical devices affect the wearer's health? Research indicates that smart wristbands use sensors to convert pulse pressure, temperature, and other physiological information into electrical signals, which are then transmitted via electromagnetic waves to data terminals such as smartphones. Because transmission distances are short, signal strength is weaker than that of typical smartphone signals, and associated radiation is correspondingly lower. Therefore, wearable medical devices used in daily life operate within established safety limits.
Key Considerations for Medical Wearables Industry
From a short-term industry perspective, CCTV's reporting will certainly affect the wearable market. From a long-term perspective, regardless of the technical thoroughness of the exposure, it will to some extent push the industry toward greater standardization. More importantly, companies that are not pursuing opportunistic gains but instead have genuine technical competence and design products with children's needs in mind need not fear such exposures.
Given that the wearable device industry has not yet fully industrialized and the supply chain remains in an exploratory stage, many startups lack R&D and testing capabilities. Many are asset-light, outsourcing product design, parts procurement, assembly, algorithms, and cloud services to third parties while focusing internally on marketing and packaging. This approach reflects limitations in funding, talent, experience, and industry knowledge, and explains why some teams opt for a quicker path to revenue.
Some entrants may adopt an opportunistic mindset, hoping to capitalize on the IoT trend with low-priced products. In either case, products are constrained by the current supply chain and the capabilities of their creators, so resulting products often reveal various shortcomings.
By contrast, larger companies typically have advantages in technology, supply-chain integration, capital, and talent. Brand considerations also make the cost of errors higher for them, which tends to produce greater control during product development. Relative to existing communication standards, many established companies can meet, and in some cases already meet, relevant communication reference standards. It is difficult to judge whether the broadcaster's exposure reflects deliberate targeting or simple scrutiny; perhaps it indicates high expectations for a nascent industry.
From a regulatory standpoint, smart watches that include communication functions are generally required to obtain a network access license. In that process, products are obliged to meet current communication standards and obtain relevant regulatory testing and certification. Those requirements represent the basic baseline for children's wearables; if specific standards for children's wearable devices were to be introduced, radiation limits would likely need to be stricter than those for general mobile communication products. At present, some products exist in regulatory gaps, which has led to radiation issues being highlighted by the broadcaster.
