A magnetic energy storage sheet (also called a magnetic storage film or magnetic energy sheet) is a thin, flexible sheet made of ferromagnetic or ferrimagnetic materials that stores electrical energy in the form of a magnetic field. Unlike bulk magnetic energy storage devices (e.g., inductors or flywheels), magnetic energy storage sheets are lightweight (thickness ranging from 10μm to 1mm), flexible, and can be integrated into thin electronic devices like wearable sensors, flexible displays, and IoT (Internet of Things) devices. They offer high energy density (compared to traditional capacitors), fast charge/discharge rates (millisecond-level), and long cycle life (100,000+ cycles), making them suitable for applications requiring compact, temporary energy storage.

The core composition of a magnetic energy storage sheet includes magnetic particles, polymer matrix, and conductive additives. Magnetic particles (e.g., ferrite nanoparticles, iron-cobalt alloy particles, or neodymium-iron-boron micro-particles) are the active components that store magnetic energy—they have high saturation flux density and permeability, enabling efficient energy storage. The polymer matrix (e.g., polyimide, polyurethane, or epoxy resin) binds the magnetic particles together, providing flexibility and mechanical strength—polyimide matrices are preferred for high-temperature applications (up to 200°C), while polyurethane matrices offer better flexibility for wearable devices. Conductive additives (e.g., carbon nanotubes or graphene) are added to improve electrical conductivity, reducing eddy current loss and enabling faster charge/discharge.

The working principle of a magnetic energy storage sheet is based on magnetic domain alignment: when an external magnetic field (generated by an adjacent coil or current-carrying conductor) is applied, the magnetic domains in the sheet align with the field, storing energy in the magnetic field. When the external field is removed or reversed, the domains return to their random state, releasing the stored energy as electrical energy (via electromagnetic induction in a nearby coil). This process is similar to inductors but in a thin, flexible form factor—magnetic energy storage sheets can be integrated into the PCB or wrapped around components, saving space.

Magnetic energy storage sheets are classified based on their magnetic properties and applications. Ferrite-based sheets have low eddy current loss and are suitable for high-frequency energy storage (10kHz-1MHz), used in flexible wireless chargers for smartwatches. Alloy-based sheets (e.g., iron-cobalt) have high saturation flux density and are used for high-energy storage applications (e.g., backup power for wearable health monitors). Composite sheets (combining ferrite and alloy particles) balance high energy density and low loss, suitable for IoT devices that require both energy storage and EMI shielding.

Key performance parameters of magnetic energy storage sheets include energy density (J/cm³), charge/discharge efficiency (η), cycle life (N), and flexibility (bending radius). Energy density measures the amount of energy stored per unit volume—higher density means more energy storage in a small space. Charge/discharge efficiency is the ratio of released energy to stored energy—high efficiency (90%+) minimizes energy loss. Cycle life is the number of charge/discharge cycles before performance degrades—long cycle life reduces replacement frequency. Flexibility (measured by bending radius, e.g., 5mm) determines the sheet’s ability to bend without damage—critical for wearable devices that conform to the body.

In applications, magnetic energy storage sheets enable compact, flexible energy solutions. For example, in a flexible wearable fitness tracker, a magnetic energy storage sheet integrated into the band stores energy from a small solar cell during the day, releasing it to power the tracker’s sensors and display at night—its thin, flexible design ensures comfort for the user. In a foldable smartphone, a magnetic energy storage sheet placed under the display provides temporary power during folding/unfolding, preventing voltage drops that could damage the screen. In IoT sensors (e.g., smart home temperature sensors), magnetic energy storage sheets store energy harvested from ambient vibrations, eliminating the need for replaceable batteries and reducing maintenance. As flexible and wearable electronics continue to grow, magnetic energy storage sheets are becoming a key enabling technology for compact, long-lasting energy storage.