A review of materials, applications, and technological breakthroughs in wearable acoustic sensing

Sound plays a vital role in our perception of the world. It enables us to communicate, learn, detect potential dangers, diagnose diseases, and more. However, conventional acoustic sensors are limited in their potential applications due to their shape and size constraints, rigidity, and bulkiness. Flexible wearable acoustic wave technology has attracted great attention in recent years due to its advantages such as low power consumption, small size, ease of manufacturing, and passive/wireless capabilities, and has a wide range of applications in wearable electronics, sensing, acoustofluidics, and lab-on-a-chip. In recent years, the scientific research community has made great efforts and fruitful work in the technical development, fabrication, and characterization of the rationally designed structures of the next generation of acoustic wave-based flexible sensors and electronics.

Academician Zhu Meifang and Professor Yan Wei of Donghua University published a review paper titled "Insights into Materials, Physics and Applications in Flexible and Wearable Acoustic Sensing Technology" in Advanced Materials, which comprehensively discussed the latest scientific and technological breakthroughs in materials, physics, design principles, manufacturing strategies, functions and applications of flexible and wearable acoustic sensing technology, and conducted corresponding in-depth analysis.

The research team highlighted a new generation of acoustic sensors that can recognize sounds, interact with machines, control robots, monitor structural health, diagnose vital signs of human biological tissue, and perform organ imaging. These innovations provide innovative and unique solutions to major challenges in healthcare, biomedicine, wearable devices, robotics, and the metaverse. This review also discusses existing challenges and future opportunities in the field and provides strategies to advance acoustic sensing technology to attract real-world applications and inspire new research directions.

Sound detection has always attracted much attention due to its scientific and technological importance. The fusion of acoustics with material science, electronics, and information science is producing a new generation of flexible and wearable acoustic sensors that are characterized by high flexibility, ultra-light weight, excellent conformality, and imperceptibility.

This radically different class of acoustic sensing technologies includes unusual form factors such as skin patches and films, nanomembranes, pyramid tattoos, nanowebs, complex fibers and yarns, and everyday clothing. Innovations in material architecture, device configuration, system integration, and manufacturing methods give this platform broad applicability across a wide range of acoustic frequencies, as well as sensing accuracy and reliability comparable to traditional counterparts.

By synergistically harnessing the power of machine learning and artificial intelligence, flexible, wearable acoustic sensing is emerging as a transformative technology, powering the burgeoning Internet of Things, augmented reality, the metaverse, and personalized and precision medicine.

Acoustic sensing



Key manufacturing methods for acoustic sensors



Electromagnetic and piezoresistive acoustic sensors



with various designs Capacitive acoustic sensors with various designs Piezoelectric



acoustic sensors with various designs



Triboelectric and optical acoustic sensors with various designs



Optical acoustic sensors with various designs Acoustic sensors



for acoustic detection, communication and control applications Acoustic sensors



for underwater listening Acoustic sensors



for structural health monitoring



Applications of wearable acoustic devices in healthcare Applications



combining acoustic sensors and artificial intelligence



Development and future trends of acoustic sensors

Summary and Outlook

Driven by application demands, acoustic devices have made remarkable progress. They have evolved from the earliest carbon fiber microphones and more recently handheld audio electronic microphones (rigid and bulky) to the most advanced membrane and textile-shaped acoustic sensors (flexible and wearable). This evolution represents a major leap in sophistication to meet the ever-changing needs of a wide range of applications.

Over the past decade, advances have been made in sensing mechanisms, new materials and structural designs, and fabrication strategies for flexible wearable acoustic sensors, which have greatly improved the sensing performance of this emerging technology. Despite the tremendous progress made in the past decade, many scientific and technological challenges remain. In light of this, we offer our insights to promote continued progress and development in this field:

1

Various advanced materials including polymers, carbon materials, living materials, and composites should be developed to expand acoustic sensing capabilities.

2

Future acoustic sensors need to be used in complex environments, such as inside the human body, on the body, or in machines, and should be portable, wearable, or implantable. To meet these requirements, they should be miniaturized, lightweight, and highly integrated. In addition, given the need to integrate devices onto curved or stretchable surfaces in various applications, these acoustic sensors should have a variety of form factors, from wires and patches to films and textiles.

3

When using acoustic sensors in various applications, several factors need to be considered to ensure their use and performance, including stability to water, heat or salt during long-term operation, power consumption, cost and mass production. Therefore, durable materials and effective packaging design should be used to enable long-term stable operation.

4

Developing low-power acoustic sensor systems remains a technical challenge, requiring optimization of sensor and system design from multiple aspects, including mechanisms, materials, devices, systems, communications, computing, and power. In addition, to ensure economic benefits, cost reduction is essential for industrial-compatible large-scale production. In addition, some feasible solutions to improve the innovation capabilities of acoustic sensors include: developing test standards, improving durability and integration, adopting computer-aided design, exploring green and sustainable manufacturing routes, and adopting smart manufacturing.

5

The multidisciplinary integration of acoustic sensing with other advanced technologies can achieve significant progress in high-tech fields such as robotics, space exploration, precision medicine, and the metaverse.

For robots, acoustic sensors enable them to have hearing capabilities, thereby achieving advanced human-machine interaction and robot environmental perception capabilities. For example, acoustic sensors worn on robots can achieve speech recognition and speech generation, thereby achieving more efficient human-machine interaction. In addition, acoustic sensors can also help robots identify obstacles and avoid collisions.

In the healthcare sector, wearable acoustic sensors enable effective medical diagnosis and monitoring, such as deep heart monitoring. By introducing acoustic sensors, the accuracy of diagnosis is greatly improved and health problems can be detected at an early stage.

In the field of space exploration, acoustic sensors are expected to give space probes acoustic perception capabilities, help better understand the space environment, and provide better guarantees for future space exploration. Acoustic sensors can also detect dust, gas, and matter in space, which is conducive to assessing the safety of the space environment and designing safer routes for space travel.

Additionally, acoustic sensors play a key role in augmenting reality by allowing users to perceive and interact with their environment in a more immersive and enhanced way. Combining acoustic sensors with augmented reality technology has great potential to enhance the user experience and expand the possibilities of augmented reality applications. With the capabilities of flexible and wearable acoustic sensors, augmented reality can become more immersive, interactive, and context-aware, opening up new avenues for entertainment, education, training, and a variety of other industries.

In short, acoustic sensing will have a significant impact on many key areas in the future and become a huge driving force for technological progress.