Research Progress on Electrically Heated Wearable Products

As temperatures drop, wearing more layers or thicker clothing helps trap heat and keep the body warm. However, bulky clothing can restrict movement and make it uncomfortable. This is where electrically heated wearables come in, offering a practical solution that combines warmth with portability.

These products use various methods to generate heat, such as chemical oxidation (like iron powder hand warmers), solar energy absorption by materials like ceramics, and electric heating elements that convert electricity into heat. Of these, electric heating stands out as the most efficient, controllable, and convenient solution. Electrically heated wearables have become a significant area of research and are expected to play a big role in the growing smart wearables market.

1. Development of Flexible Heating Elements

The heating element is the heart of any electrically heated wearable. There are two primary methods for creating these elements: direct weaving and coating.

1.1 Direct Weaving

• How it works: This method uses conductive and heat-generating materials, such as metal wires, alloy fibers, or carbon fibers, which are woven into fabrics using techniques like knitting, weaving, or embroidery.
• Advantages: It is simple, flexible, and produces lightweight, thin textiles that can be easily customized and offer uniform heat distribution.
• Materials:
  • Metal wires: Durable but rigid, and can be uncomfortable for everyday wear.
  • Metal-coated fibers: Softer and more suitable for knitted fabrics.
  • Carbon fibers: Strong, heat-resistant, washable, and bendable, although they can feel rough to the touch.

1.2 Coating

• How it works: Conductive materials are applied to the fabric surface through methods like dip-coating, in-situ polymerization, or screen printing.
• Advantages: These elements are lightweight and flexible.
• Drawbacks: The heating layer may not adhere well to the fabric, which could lead to uneven heat distribution.

2. Electrically Heated Clothing and Accessories

Electrically heated clothing was first introduced in the early 20th century, mainly to help soldiers during World War I and II stay warm in high-altitude environments. Over time, these products have expanded into civilian markets, thanks to advancements in smart wearable technology.

Design Approaches

1. Integrated Heating Units:
   Heating elements are directly woven or sewn into fabrics.

   • Pros: The product is lightweight, compact, and visually appealing.
   • Cons: It can be challenging to simplify production and reduce costs.

2. Detachable Heating Units:
   The heating system is placed inside pockets or between layers of fabric, making it removable.

   • Pros: It’s easy to clean and allows for flexibility with temperature controls or added sensors.
   • Cons: The heat tends to concentrate in one area, which could lead to uneven warmth or discomfort.

3. Evaluation Methods and Standards

Before electrically heated wearables can be released to consumers, they need to be thoroughly tested for comfort and functionality.

3.1 Performance Testing

Thermal Protection and Comfort are key areas of testing:

• Thermal Manikin Tests: These simulate skin temperature and sweating in controlled environments to measure how heat and moisture are exchanged.
• Human Wear Trials: These tests track skin temperature, core body temperature, blood flow, and subjective comfort when worn by real people in normal conditions.
• Numerical Simulations: These model airflow and heat transfer between the body and the wearable to predict comfort and performance.

Comparison of Methods:

• Thermal manikin and simulation tests are more repeatable and not affected by environmental variables, but they tend to be less precise.
• Human wear trials are more accurate in reflecting real-world performance, but they are influenced by individual differences and cannot simulate extreme environments.
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3.2 Standards Development

Currently, no global standard exists specifically for electrically heated wearables. However, as these products gain popularity, researchers and businesses are working together to establish performance evaluation standards.

• Existing Standards: Some standards, like GB 4706 (for household electrical appliances) and T/CNTAC 24-2018 (a group standard for heated clothing in China), focus on safety, moisture resistance, heat resistance, and protection against electromagnetic radiation.
• Future Focus: There is an increasing need to expand these standards to include comfort and smart functionality for a more comprehensive evaluation.

Conclusion

Electrically heated wearables are a promising area of innovation in smart clothing. Moving forward, efforts should focus on:

• Improving the flexibility and durability of heating elements.
• Striking a balance between comfort, functionality, and design.
• Establishing more comprehensive industry standards that cover both safety and user comfort.

With continued advancements in these areas, electrically heated wearables can meet the growing demand for smart, functional, and comfortable clothing solutions that provide both warmth and convenience.