Such kinds of LHMs are easy to design but have disadvantages such that ferrite-based tunability requires big

magnetic bias and liquid crystal-based tunability has a finite tunable range [2].

However, when longer and thicker GMM rods are used, significant phenomena such as saturation and end effects are likely to occur [12]; the

magnetic bias may be subject to conditions outside of the transducer.

For eddy current there are traditional EC methods, pulsed EC and lately

magnetic bias EC, for latter see Asher et.al.

The frequency of operation for a ferrite material largely depends upon the external DC

magnetic bias that is applied on it.

Recalling the Terfenol-D strain characteristic from Figure 2(a), one can see that a negative magnetic field produces the same elongation in the magneostrictive material as a positive magnetic field would; thus, a rectified output response is obtained; if a nonrectified response is desired a permanent

magnetic bias scheme must be provided.

Differential phase shifts, calculated by subtracting phase spectra at different values of

magnetic bias field at some reference frequency, [DELTA][phi](H) = arg [S.sub.21](H) - arg [S.sub.21]([H.sub.0]) for Sample-A and Sample-B are compared with theoretical calculations in Fig.

With application of external

magnetic bias, at some value of [[mu].sub.0][H.sub.0], the magnetization of the magneto-dielectric composite system reaches the saturation level.

Orthogonal Helmholtz coils provide the

magnetic bias and saturating fields required for the measurement.

To account for the dependence of the ferrite's permeability tensor on the externally applied static

magnetic bias field, the magnetostatic field must first be computed.

The exchange coupling between a ferromagnet (FM) and an antiferromagnet (AF) creates a

magnetic bias field on the ferromagnet and thereby controls its magnetization characteristics.

Ferrite material will exhibit resonance absorption when [omega.sub.r] = [gamma] [H.sub.i] (1) where [omega.sub.r] is the electron precession frequency in MHz, [gamma] is the gyromagnetic ratio in MHz/per, and [H.sub.i] is the internal

magnetic bias field within the ferrite material.

Further, ferrite phase shifters may be latching or nonlatching, depending upon whether continuous holding current must be supplied to sustain the

magnetic bias field.