Ferromagnetic Glass-Coated Micro-and Nanowires for Medical Application

The properties of shielding made of a glass-coated amorphous magnetic micro- and nanowires have been studied by radio noise suppression experiments. This effect can be used also for contactless diagnostics of deformations in distant objects (including organs of the body) reinforced by cast magnetic microwires with the stress effect. The absorption parameter values observed are of (5-20) dB at (0,1-10) GHz. The losses profile is ascribed to the presence of natural ferromagnetic resonance in microwires. The natural ferromagnetic resonance (NFMR) reveals large residual stresses appearing in the microwire core in the course of casting. These stresses, together with the magnetostriction, determine the magnetoelastic anisotropy. Beside the residual internal stresses, the NFMR frequency is influenced by external stresses applied to the microwire or to the composite containing the latter (the so-called stress effect). The dependence of the NFMR frequency on the deformation of the microwires is proposed to be used in the distant diagnostics of deformations of medical objects (including organs of the body).

As this research has evolved, the need to control the magnetic anisotropy in components came into attention since the field absorption is related to natural ferromagnetic resonance (NFR) [5][6][7][8][9][10]. That glass-coated amorphous magnetic micro-and nanowires (GCAMNWs) possess very interesting high frequency properties due to the strong magnetoelastic anisotropy which is induced in the fabrication process [5]. By defining strictly, the geometric characteristics and the alloy composition the medical norms of electromagnetic field can be accurately controlled. Furthermore, the high production rate and high permeability feature of GCAMNWs without any rigid substrates are advantageous for use as noise absorbers of electromagnetic field. In this report, amorphous glasscoated microwire arrays in a sheet configuration are proposed for use as absorbers. High frequency characteristics of thin amorphous microwires will be presented and evaluated as radio noise absorbers and medical protection radio absorption shielding.
During the manufacturing, the GCAMNWs using the Ulitovsky-Taylor method the soften glass capillary is filled with a melted metal alloy with a further quenching [5]. The residual stresses, arising in metal core of GCAMNWs by during manufacturing, determine magnetic behavior of such GCAMNWs [5]. The metal is frozen into very thin GCAMNWs. Thus, a strong quenching stress (for example, 9 10 s Pa in ultrathin GCAMNWs) is introduced in the GCAMNWs [4][5][6][7][8][9][10][11][12]. The phenomenon of natural ferromagnetic resonance (NFMR) in CGCMMWs [5][6][7][8][9][10][11][12][13][14] is extremely interesting from the viewpoint of using it for non-contact diagnostics of distant objects (or organs of the body). The diagnostics become possible due to the stress effect on the NFMR, that is, the shift of the resonance frequency as a result of a deformation of the object (or organs of the body). Such a frequency shift can be measured by irradiating the object with microwaves emitted by radar at frequencies near the NFMR and detecting the reflected signal, thus revealing a deviation of the resonance frequency from the original value. The glass coating of the cast GCAMNWs induces strong mechanical stresses in the kernel [4][5][6][7][8][9][10][11][12]. In cylindrical coordinates, the residual tension is characterized by the axial, z σ , radial, r σ , and tangential, ϕ σ , components. The value of these stresses depends on the ratio of the radius, Rm, of the metallic kernel to the total microwire radius, Rc: Using the cylinder-shell model, we then obtain a formula for stresses in the metallic kernel of the cast GCAMNWs: , With additional longitudinal strain, which occurs when the microwire is embedded in a solid matrix that itself deforms under external influence, the following term is added to the expression for the residual axial tension: Where P o is the force applied to the composite; Sm= π (Rm) 2 is the microwire cross-sectional area. The theory of NFMR is presented in Refs. [5][6][7][8][9][10]. The NFMR frequency can be written as ( ) Where ( ) ( )

Design of Composites for Radio-Absorption Shielding
The Designs of Composites from GCAMNWs have

Following Configurations
However, for very thin GCAMNWs with negative, positive and zero magnetostriction the domain structure is far more complicated due to a complex stress distribution within the small diameter. The simplest domain structure reported so far for these GCAMNWs is obtained in [10,12]. As for the microwire array configuration    range of properties [6][7][8][9]. An important feature of cast microwires with an amorphous magnetic core is the dependence of the NFMR frequency from the deformation [7,8]. Therefore, this effect can be used for contactless diagnostics of deformations in distant objects (including organs of the body) reinforced by cast magnetic microwires with the stress effect. These objects are periodically scanned with floating-frequency radar to determine the deviation of the initial NFMR frequency due to potentially dangerous deformations of the monitored object.

Noise Absorption Experiments
Another principle of detecting mechanical strain is examined in [15,16]. This principle is based on the giant magnetoimpedance (GMI) effect. The GMI effect [15,16] demands external magnetization of the sample which is not required in the NFMR method [6][7][8][9].