# Effect of the Insulating Layer on the Properties of SMC Inductors
## 1 Introduction  
The magnetic materials world is vast, with applications spanning various industrial sectors [1]. In general, this world is split into two main groups: soft and hard magnetic materials. Hard magnetic materials play a central role in magnetic flux generation without requiring an external source to produce it. Permanent magnets are hard magnetic materials. They are subdivided into families, the most common of which are hard ferrite, AlNiCo, SmCo, and NdFeB. There are various types of manufacturing processes, but sintered and bonded are the most popular ones [2].  
Magnetic cores are made with soft magnetic materials [3, 4]. The great variety of materials depends on application types [5, 6, 7, 8, 9]. Silicon-iron electrical steel is used in transformers, electrical motors and generators, reactors, lamp ballasts, instrumentation, and shielding. Amorphous and nanocrystalline alloys are the favored materials for special transformers [10], power electronics, pulsed powers, and shielding. Instead, FeCo alloys are used in particular generators and power electronics. Soft magnetic compacted powder is used in electrical machines and, to top it off, soft ferrites are used in power transformers, electronic devices, chokes, and also pulsed power.  
For inductive applications within power electronics and electrical machines, there is a requirement for the ability to rapidly switch the magnetization of the material with an external magnetic field. Thus, soft magnetic materials are primarily used within these applications due to their high magnetic permeabilities. Furthermore, with the introduction of wide-bandgap semiconductors, power conversion electronics and motor controllers, forexample, can operate at higher frequencies. These components tend to reduce the size of the passive components, such as inductors and capacitors, and allow for higher efficiencies of electrical machines.  
For this reason, the selection of magnetic materials depends heavily on the application one is considering. Additionally, the frequency range determines some limitations in the use of soft magnetic materials for inductance applications. In particular, for MHz frequency intervals, the uses are related to oscillators and electromagnetic interference (EMI) filters [7]. However, the same EMI filters are also used for kHz ranges, where power electronics components find applications together with common-mode choke inductance. For low frequencies, audio applications and smoothing inductances represent the characteristic use of soft magnetic materials. Typical soft materials used at these frequency ranges are soft ferrites and amorphous and nanocrystalline alloys due to their respective permeability behavior and reduced losses.  
Nevertheless, these materials present some drawbacks: brittleness [11], low saturation for ferrites, non-constant permeability across a frequency range, and the manufacturing costs for amorphous and nanocrystalline alloys.  
This work investigates the possibility of adopting soft magnetic materials suitable for use in high-frequency applications, particularly analyzing soft magnetic composites (SMCs) [12]. SMC materials are commonly used in electrical machine magnetic cores; in some cases, they are also used in inductance applications [13; 14]. A wide investigation into this specific adoption is still being carried out, possibly leading to promising solutions.  
Different SMC materials are explored in this work, mainly considering the type of insulating layer for an inductance application. For a comprehensive inductance analysis, the magnetic permeability, the core power losses, and quality factor (Q) are examined for different frequency ranges [15; 16] using data from two different instruments and methods which complement each other: an RLC meter and a large-cycle hysteresisraph.