Last Updated on June 30, 2023 by You Ling
Wearable electronic devices are changing people’s lifestyles, and related new materials and technologies have become important research areas in the 21st century. With the assistance of wearable devices, the future intelligent world can operate with a focus on human beings. In an active manner, we can use wearable devices to communicate instructions to the intelligent world, while in a passive manner, wearable devices can collect our physiological information for healthcare purposes. Many wearable devices have been proposed, focusing on human energy harvesting, human-computer interaction, human motion detection, artificial nerves, and personalized health monitoring. In these operational scenarios, wearable electronic devices should meet some basic requirements, including high efficiency, biocompatibility, flexibility, durability, lightweight, and low power consumption. Although the power required to drive wearable electronic devices needs to be in the range of milliwatts or even microwatts, providing continuous energy supply remains a major challenge. Typically, wearable electronic devices are powered by rigid batteries. However, this may not be a good choice as these batteries bring some issues such as large size, limited lifespan, difficult replacement, and adverse environmental impact. To address this challenge, wearable electronic devices that can harvest energy from human activities have been developed.
What is wearable technology?
Wearable technology refers to any electronic device or computer that is embedded in clothing or compact accessories and can be worn on or integrated into the body. Many of these devices collect and communicate information wirelessly through applications or the devices themselves.
Wearable devices include:
Fitness wristbands and activity trackers
Smartwatches that can manage messages, calls, and emails
Smart clothing that can monitor vital signs, sleep patterns, and body movements
Smart glasses that can capture photos and videos and connect to the internet
Medical devices that monitor vital signs, medication, blood glucose, etc.
Their small size, portability, and ability to perform multiple functions make wearable devices highly popular among consumers. The market for wearable devices is not expected to decline soon.
The development history of piezoelectric components in wearable technology?
Piezoelectricity is a direct method of converting mechanical energy into electrical energy, which means piezoelectric nanogenerators do not require two moving components like electrostatic or triboelectric nanogenerators. In principle, a piece of piezoelectric material can accomplish the energy conversion process. This characteristic allows piezoelectric electronic devices to be easily miniaturized and manufactured/integrated into complex shapes/structures. With their excellent energy conversion performance, piezoelectric nanogenerators have attracted the greatest attention from engineers and researchers in the field of wearable electronics, with nearly 5000 publications in the past decade (accounting for approximately 52% of the total publications on mechanical energy harvesting and self-powered physical sensors). However, for piezoelectric nanogenerators, there seems to be a conflicting trade-off between mechanical flexibility and piezoelectric performance. Inorganic piezoelectric materials such as piezoelectric ceramics or single crystals exhibit good piezoelectricity (with large piezoelectric coefficients, d33 = 200-500 pC/N) but are always rigid and brittle. On the other hand, piezoelectric polymers such as polyvinylidene fluoride (PVDF) and its derivatives have good flexibility and durability but have piezoelectric coefficients (d33 = 20-40 pC/N) an order of magnitude lower than inorganic materials. Some researchers have attempted to blend inorganic piezoelectric nanomaterials into organic elastomers to form flexible piezoelectric nanocomposites, but the large stiffness difference and spatial discontinuity of the nanoparticles result in poor stress transfer from the polymer to the nanoparticles, greatly limiting the piezoelectric performance of the nanocomposites. In light of this background, a type of polymer filled with elliptical air cavities has caught the attention of researchers. These polymers exhibit strong piezoelectricity after charging, with piezoelectric coefficients as high as 200-400 pC/N, several times higher than PVDF. Therefore, with proper manufacturing, these polymers can offer competitive piezoelectric coefficients similar to piezoelectric ceramics. Additionally, due to their inflated structure, they are lightweight, flexible, and highly elastic. As a result, these polymers have become one of the best candidate materials for wearable electronic products.
Piezoelectric components used in wearable technology
Piezoelectric components can be used in wearable technology and other emerging technologies, bringing tremendous possibilities to many industries. With the availability and usage of products incorporating piezoelectric components, human comfort, convenience, health, and safety can be greatly improved. Many of these functionalities and products have already emerged in today’s society.
These include:
Piezoelectric pacemakers powered by the pulsation of the heart rhythm. This eliminates the need for invasive and risky surgeries to replace batteries.
Sidewalk lighting powered by energy-absorbing tiles that are impacted by footsteps.
Powering monitoring and sensor devices in remote and hazardous locations such as bridges and pipelines. This eliminates the risks to humans when batteries need recharging or replacement.
Car driver seats using piezoelectric sensors to monitor and sense the driver’s heart rate and breathing. It employs vibration sensors that automatically activate the seat’s ventilation and massage functions upon detecting driver pressure.
Wearable devices that can be charged through walking, running, or other physical activities.
Some of the wearable sensors available in today’s market include fitness and activity wristbands as well as monitors that track distance, respiration, heart rate, and even sleep patterns. Wireless blood pressure cuffs measure patients’ blood pressure through smartphone applications. Quartz watches have been around for a long time, utilizing the natural piezoelectric properties of quartz to maintain accurate time. Monitors detecting and measuring fetal heartbeat use piezoelectric components to convert vibrations into readable signals.
The use of “smart” fabrics is also gaining popularity. Flexible textiles are infused with piezoelectric materials as sensors to measure, monitor, and harvest energy. A single piezoresistive layer is sandwiched between two conductive layers. These sensors are currently under development and used in insoles, clothing, and wearable devices to measure pressure, steps, energy consumption, and other information. The energy generated by the fabric depends on the type of piezoelectric material used and the user’s movement.
In conclusion, the integration of piezoelectric components in wearable technology has the potential to revolutionize various aspects of our lives, from healthcare to energy harvesting. Ongoing research and advancements in materials and design will continue to drive innovation in this exciting field.
