Nickel zinc copper ferrite for VUHF antenna applications

Abstract

The present invention relates to a nickel zinc copper ferrite for VUHF antenna applications. In particular to a composition and solid material particularly suitable for the manufacture of antennas suitable for operation in the very high frequency (VHF) band and the ultra high frequency (UHF) band or V / UHF, and to a method of manufacture and use thereof. The composition has the formula Ni a Zn b Cu c Co d Fe 2‑δ O4, wherein: 2(a+b+c+d)+3(2-δ)=80.05

Description

TECHNICAL FIELD

[0001] The present invention relates to a composition and a solid material particularly suitable for the manufacturing of antennas adapted to operate in the very high frequency (VHF) band, between 30 MHz and 300 MHz, and in the ultra high frequency (UHF) band, between 300 MHz and 3 GHz, or V / UHF, and to the manufacturing method and uses thereof. PRIOR ART

[0002] The miniaturization of antennas is a major issue, especially for antennas operating below GHz. Indeed, the size of an antenna is directly proportional to the wavelength of the transmitted / received signal, which is the order of magnitude of the VHF / UHF frequencies (VHF: 30 MHz to 300 MHz; UHF: 300 MHz to 3000 MHz). Nowadays, one of the strategies commonly used to reduce the antenna geometry is the use of dielectric materials with high permittivity (ε'). However, the use of such materials leads to a decrease in the antenna performance (gain, bandwidth).

[0003] This limitation can be overcome by using magnetic-dielectric materials such as ferrites. Indeed, the use of materials with high magnetic permeability (μ') would make it possible to reduce the size of the antenna while maximizing its efficiency. Indeed, while ε' has a positive impact on dielectric losses and the amount of stored energy, it has been shown that: (i) ε' has a negative impact on the bandwidth as well as on the antenna efficiency, and (ii) μ' has the opposite effect, thus having a positive impact on both parameters. Moreover, if the antenna remains iso-dimensional, such materials would improve its performance (M.A.C Niamien, S. Collardey, A. Sharaiha, K. Mahdjoubi, "Compact Expressions for Efficiency and Bandwidth of Patch Antennas Over Lossy Magneto-Dielectric Materials," IEEE antennas and wireless propaga. letters, 10 (2011) 63-66).

[0004] It is well known that the addition of low concentrations of cobalt to ferrites, in particular to nickel-zinc ferrites, can have a positive influence on the magnetic losses of the compounds. An example is the study of Lau and Stuijts (J.G.M. Lau and A.L. Stuijts, Chemical Composition and High-Frequency Properties of Ni-Zn-Co Ferrites, Philips Res. Repts, 21 (1966) 104-112) which describes the addition of cobalt to (Ni 0.8 Zn 0.2 ) 0.97-X Co 0.03 Fe2O 4+γ The mechanism of the cobalt ion behavior in the crystal structure. There is a large number of studies focused on nickel-zinc ferrites with cobalt substitution. However, the compositions discussed do not contain copper and perform much worse in terms of magnetic losses at high frequencies (frequencies F > 100 MHz) than the present invention prescribes. Some compositions manage to perform a stable behavior in terms of magnetic permeability. However, they have the problem of the occurrence of a ferrimagnetic resonance at too low frequencies and cause an increase in magnetic losses from about 10 MHz.

[0005] There are some laboratory grade nickel-zinc ferrite materials with similar properties to the present invention. For example, the team of Mathur et al. published in 2010 a ferrite composition that allows high frequency use (P. Mathur, A. Thakur, J.H. Lee, M. Singh, Sustained electromagnetic properties of Ni-Zn-Co nanoferrites for the high-frequency applications, Materials Letters, 64 (2010) 2738-2741). In fact, the resulting material has low magnetic losses (tangent loss of about 0.05) at a frequency range of 10 to 200 MHz and a magnetic permeability μ' of about 9. The composition of the material presented is as follows: Ni 0.49 Zn 0.49 Co 0.02 Fe2O4. Due to the low cobalt content (0.02 mol), the authors used another method to push the resonance beyond 200 MHz. They used a co-precipitation method to synthesize the compound as particles of about 50 nm and sintered their material at lower temperatures to avoid excessive crystal growth. Thus, the material has a fine microstructure which allows to change the dynamics of the movement of the magnetic domain walls to a repulsive resonance. The co-precipitation synthesis method is very different from the traditional synthesis method. From an industrial point of view, it is also expensive and difficult to implement.

[0006] Saini et al. (A. Saini, A. Thakur, P. Thakur, Matching permeability and permittivity of Ni 0.5 Zn 0.3 Co 0.2 In 0.1 Fe 1.9 O4 ferrite for substrate of large bandwidth miniaturized antenna, J Mater Sci: Mater Electron, 27 (2016) 2816-2823) showed interest on the composition Ni 0.5 Zn 0.3 Co 0.2 In 0.1 Fe 1.9 O4 for miniaturization of UHF antennas with gain in bandwidth if compared to antennas loaded with simple dielectric materials. The material was synthesized by co-precipitation and has a high cobalt content (0.2 mol). It has a magnetic permeability of about 5-6 and low magnetic losses up to at least 500-600 MHz.

[0007] Finally, we can also mention the work carried out in the Lab-STICC laboratory in Brest (France) which focuses on the manufacture of magnetic-dielectric materials by co-precipitation which can meet the requirements of antennas in the V / UHF frequency band. Several results have been published demonstrating the interest of using the co-precipitation method on compounds such as Ni 0.5 Zn 0.3 Co 0.2 Fe 1.98 O 4-δ to achieve low magnetic losses at high frequencies while maintaining a relatively high magnetic permeability.

[0008] Nickel-zinc-copper ferrites are widely used for inductors. Manufacturers take advantage of the low sintering temperature of this compound (<1000°C) provided by a large degree of copper (typically between 0.2 and 0.25 mol) to co-sinter the ferrite directly with the electrodes or windings. It is reported that when copper is added to compounds such as Ni 0.8-x Zn 0.2 Cu xFor values of copper addition higher than 0.2 mol, copper forms a second CuO / CuFe04phase and the properties of the material deteriorate (J. J. Shrotri, S. D. Kulkarni, C. E. Deshpande, A. Mitra, S. R. Sainkar, P. S. Anil Kumar, S. K. Date, Effect of Cu substitution on the magnetic and electrical properties of Ni-Zn ferrite synthesised by soft chemical method, Materials Chemistry and Physics, 59 (1999) 1-5).

[0009] Many studies have shown that Ni-Zn-Cu ferrites have interesting high frequency behavior. However, for the applications covered by the present invention, the frequencies considered are generally too low. Materials of this type generally have a ferrimagnetic resonance between 1 and 100 MHz. In addition, the occurrence of the resonance is accompanied by an increase in magnetic losses (represented by the value μ" or tan δ μ ) such that the material cannot be used as an antenna material above this frequency band.

[0010] Object of the invention

[0011] The present invention aims to solve the technical problem of providing a composition usable as a VHF or V / UHF antenna.

[0012] In particular, the present invention aims to solve the technical problem of providing a composition usable as a small VHF or V / UHF antenna.

[0013] In particular, the present invention aims to solve the technical problem of providing a nickel-zinc-copper ferrite composition suitable for use as an (preferably miniaturized) antenna material in the VHF and / or UHF frequency band.

[0014] In particular, the present invention aims to solve the technical problem of providing a composition usable as an (preferably miniaturized) antenna, for which the resonance occurs at a frequency higher than 50 MHz, preferably higher than 70 MHz, preferably higher than 100 MHz, or even more preferably at a higher frequency.

[0015] In particular, the present invention aims to solve the technical problem of providing a magnetic-dielectric composition preferably having a magnetic permeability μ' > 5 and a dielectric constant ε' > 10, the composition preferably having a magnetic permeability close to the dielectric constant.

[0016] The present invention also aims to solve the technical problem of providing a method of manufacturing such a composition, preferably manufactured by the conventional industrial method of preparing ceramic materials by milling / hammering. SUMMARY

[0017] The inventors have found that the use of the present composition having a high level of cobalt and a high level of copper in a nickel-zinc ferrite composition solves at least one, preferably all, of the above technical problems.

[0018] The inventors have found that the use of the composition according to the present invention provides a composition that advantageously solves at least one, preferably all, of the above technical problems by increasing the Ni / Zn ratio.

[0019] Advantageously, such a composition can be obtained by introducing cobalt partially replacing nickel in a ferrite composition of the alloy of formula Ni a Zn b Cu c Co d Fe 2-δ O4.

[0020] The present invention relates to a composition of formula Ni a Zn b Cu c Co d Fe 2-δ O4, wherein:

[0021] 2(a+b+c+d)+3(2-δ) = 8

[0022] 0.05 < b < 0.5, for example 0.1 < b < 0.5, for example 0.1 < b < 0.4.

[0023] 0.10 < c < 0.25, preferably 0.15 < c < 0.25, or c is 0.20,

[0024] 0.04 < d < 0.25, preferably 0.06 < d < 0.25, more preferably 0.07 < d < 0.25, and

[0025] δ < 0.05.

[0026] Advantageously, the composition is a nickel zinc copper ferrite, preferably having a Ni / Zn ratio of 1 to 15.

[0027] Advantageously, the composition has a spinel structure.

[0028] The present invention relates to a nickel-zinc-copper ferrite material having a spinel structure, which can be used as an antenna material in the VUHF frequency band.

[0029] In one embodiment, "b" is greater than or equal to 0.05.

[0030] In one embodiment, "b" is greater than or equal to 0.1.

[0031] In one embodiment, "b" is less than or equal to 0.5.

[0032] In one embodiment, "b" is less than or equal to 0.4.

[0033] In one embodiment, "b" is less than or equal to 0.35.

[0034] Advantageously, any of the lower limits can be combined with any of the upper limits.

[0035] In one embodiment, 0.05 < b < 0.5.

[0036] In one embodiment, 0.1 < b < 0.5.

[0037] In one embodiment, 0.1 < b < 0.4.

[0038] In one embodiment, 0.15 < b < 0.35.

[0039] In one embodiment, "c" is greater than or equal to 0.10.

[0040] In one embodiment, "c" is greater than or equal to 0.15.

[0041] In one embodiment, "c" is less than or equal to 0.25.

[0042] Advantageously, any of the lower limits can be combined with any of the upper limits.

[0043] According to one embodiment, 0.10 < c < 0.25, preferably 0.15 < c < 0.25, according to a variant c is 0.20.

[0044] In one embodiment, "d" is greater than or equal to 0.04.

[0045] In one embodiment, "d" is greater than or equal to 0.05.

[0046] In one embodiment, "d" is greater than or equal to 0.06.

[0047] In one embodiment, "d" is greater than or equal to 0.07.

[0048] In one embodiment, "d" is 0.10.

[0049] In one embodiment, "d" is less than or equal to 0.25.

[0050] Advantageously, any of the lower limits can be combined with any of the upper limits.

[0051] In one embodiment, 0.04 < b < 0.25.

[0052] Preferably, 0.06 < d < 0.25.

[0053] Advantageously, 0.07 < d < 0.25.

[0054] Advantageously, 0.09 < d < 0.25.

[0055] In one embodiment, "a" is greater than or equal to 0.3.

[0056] In one embodiment, "a" is greater than or equal to 0.35.

[0057] In one embodiment, "a" is greater than or equal to 0.4.

[0058] In one embodiment, "a" is less than or equal to 0.8.

[0059] In one embodiment, "a" is less than or equal to 0.7.

[0060] In one embodiment, "a" is less than or equal to 0.6.

[0061] Advantageously, any of the lower limits can be combined with any of the upper limits.

[0062] In one embodiment, 0.3 < a < 0.7.

[0063] In one embodiment, 0.4 < a < 0.7.

[0064] Advantageously, the composition is selected from the group of compositions of the following formulae:

[0065] Ni 0.5005 Zn 0.3195 Cu 0.20 Co 0.04 Fe 1.96 O4,

[0066] Ni 0.4805 Zn 0.3195 Cu 0.20 Co 0.06 Fe 1.96 O4,

[0067] Ni 0.4405 Zn 0.3195 Cu 0.20 Co 0.10 Fe 1.96 O4,

[0068] Ni 0.4347 Zn 0.3153 Cu 0.20 Co 0.11 Fe 1.96 O4,

[0069] Ni 0.4231 Zn 0.3069 Cu 0.20 Co 0.13 Fe 1.96 O4,

[0070] Ni 0.4115 Zn 0.2985 Cu 0.20 Co 0.15 Fe 1.96 O4, and

[0071] Ni 0.6 Zn 0.2 Cu 0.20 Co 0.06 Fe 1.96 O4,

[0072] In one embodiment, the ratio of Ni / Zn is between 1 and 15, preferably between 1 and 10, even more preferably between 1.2 and 7.

[0073] Advantageously, the ratio of Ni / Zn is greater than 2.

[0074] In one variant, the ratio is 1.38, in another variant, the ratio is 3.

[0075] The present application also relates to a solid material having a composition according to the definition of the present application.

[0076] According to one embodiment, the material according to the present application forms a magnetic-dielectric material preferably having a magnetic permeability μ' > 1 and a dielectric constant ε' > 1, and preferably μ' > 5 and ε' > 10.

[0077] According to one embodiment, the material according to the present application has a magnetic permeability μ' between 10 and 20 for the VHF range (1 MHz to 300 MHz) range, or μ' between 5 and 15 for the V / UHF range (200 MHz to 600 MHz).

[0078] According to one embodiment, the material according to the present application has a magnetic loss tan(δμ) < 0.06, and preferably a dielectric loss tan(δε) < 0.02 over the frequency band between 100 and 200 MHz.

[0079] According to one embodiment, tan(δε) < 0.006.

[0080] The present invention also relates to a VHF or V / UHF antenna having a composition or a solid material according to the present invention.

[0081] According to one embodiment, the antenna is a printed antenna or a microstrip or "patch" type VHF or V / UHF antenna comprising one or more substrate layers adhered to a radiating element, wherein the one or more substrate layers comprise or consist of a composition according to the present invention or a solid material according to the present invention.

[0082] In one embodiment, the antenna is miniaturized. Typically, the antenna has a larger dimension of less than 300 mm.

[0083] The present invention also relates to the use of a composition according to the present invention or a solid material according to the present invention as a VHF or V / UHF antenna.

[0084] Advantageously, the present invention relates to an antenna for aeronautics.

[0085] In one embodiment, the antenna is adapted for operation between 118 MHz and 156 MHz, and preferably between 118 and 137 MHz.

[0086] The present invention also relates to a method of manufacturing a composition as defined according to the present invention.

[0087] In particular, the present invention relates to a method of manufacturing a composition according to the present invention or a solid material according to the present invention, the method comprising:

[0088] milling a raw material providing Ni, Zn, Cu, Co, Fe and O, typically NiO; ZnO; CuO; Co304 and Fe203,

[0089] After milling, the powder is dried and then sieved, preferably with a 400 pm sieve,

[0090] After sieving, the powder is heat treated, preferably at a temperature of at least 600 °C, such as 800 °C, for example for 1 to 10 hours, typically 2 hours,

[0091] After heat treatment, the powder is subjected to a second milling, for example with an aqueous solution,

[0092] The powder is then shaped into a solid material.

[0093] In one embodiment, prior to shaping, the method comprises coating the powder with a binder to provide a shaped material.

[0094] In one embodiment, after shaping, the method comprises sintering the shaped material.

[0095] Advantageously, the material is synthesized according to a method of preparing a ceramic material.

[0096] In one embodiment, the step of milling the raw materials comprises or consists of weighing the different oxides to make the composition: NiO; ZnO; CuO; Co304 and Fe203. Iron oxide defects are introduced in this weighing taking into account the iron impurities introduced during the milling. According to one embodiment, the raw materials are then mixed and then milled (typically jar milling for 20 hours) in an aqueous process with a milling device such as a ball mill, attritor, jar blender, etc.

[0097] In one embodiment, after milling, the powder is dried and then sieved to 400 pm. It is then heat treated ("clinkered") in a kiln at 800°C for 2 hours.

[0098] In one embodiment, the powder is subjected to a second milling. For example, the powder is sieved and then put in an aqueous slurry, i.e. diluted in an aqueous solution (typically water) for re-milling (typically jar milling for 36 hours).

[0099] In one embodiment, the powder is coated with a binder and then shaped by pressing.

[0100] Advantageously, the powder receives a coating to allow the shaping of the powder. The addition of the binder can be done during the second milling by adding the binder to the powder slurry or once the powder is dried and sieved after milling. In each case, the powder is preferably dried and then sieved between 200 and 400 pm before shaping.

[0101] Advantageously, the shaping is performed in the form of a tablet, a disc or a core by pressing (typically uniaxial) as needed.

[0102] Advantageously, the shaped material is sintered.

[0103] Sintering is typically performed at a temperature higher than 800°C, preferably between 850 and 1000°C.

[0104] Typically, sintering is performed in an oxidizing atmosphere such as air.

[0105] In one embodiment, the pressed material is sintered at 950°C in air for 2 hours. Preferably, before the kiln temperature is raised to for example 950°C, the material is debonded with a slow temperature ramp at 500°C. The duration of the debonding depends on the size of the part and its mass and can be for example 1 h to 48 h. Sintering according to the application at a temperature lower than 1200°C, advantageously at 950°C, has a significant technical advantage. Typically, sintering at 1200-1400°C for 4 to 12 hours for ferrites with spinel structure. Thus, the present application saves time and cost on the kiln (size at temperature < 1000°C) and power needed for heating.

[0106] Advantageously, the composition or material according to the application constitutes a magneto-dielectric material having a magnetic permeability close to (e.g. + / - 10 units, preferably + / - 5 units) its dielectric constant (magneto-dielectric material: ε' > 1 and μ' > 1).

[0107] Advantageously, the composition or material according to the application exhibits a ferromagnetic resonance higher than 50 MHz, preferably higher than 70 MHz, most preferably higher than 100 MHz.

[0108] A ferromagnetic resonance higher than a certain value means that a peak of magnetic permeability appears at a frequency higher than this value.

[0109] Advantageously, the composition or material according to the application exhibits a ferromagnetic resonance higher than 120 MHz, preferably higher than 140 MHz, most preferably higher than 150 MHz.

[0110] Even more advantageously, the composition or material according to the application has a ferromagnetic resonance higher than 200 MHz.

[0111] This advantage is in particular related to the composition of the alloy formulation according to the application.

[0112] Advantageously, for the VHF range (1 MHz to 300 MHz), the composition and material according to the application have a magnetic permeability μ' greater than 10, preferably greater than 15, even more preferably greater than 20.

[0113] Advantageously, for the V / UHF range (200 MHz to 600 MHz), the composition and material according to the application have a magnetic permeability μ' greater than 5, preferably greater than 10, even more preferably greater than 15.

[0114] Advantageously, the composition and material according to the application have a low magnetic loss at VHF / UHF, tan δ < 0.05 in the frequency band of 1 to 50 MHz, preferably 1 to 70 MHz, more preferably 1 to 100 MHz. μ

[0115] Advantageously, according to one embodiment, the composition and material according to the application have a low magnetic loss at VHF / UHF, tan δ < 0.06, preferably < 0.05, even more preferably < 0.04, in the frequency band of 100 to 200 MHz. μ

[0116] Advantageously, the composition and material according to the application have a medium magnetic permeability (typically μ' of 5 to 20, preferably 10 to 20) and a low magnetic loss at VHF / UHF (tan δ < 0.05) in the frequency band of 100 to 200 MHz. μ <0.05).​​

[0117] In the diagram:

[0118] Figure 1 This displays conventional nickel-zinc ferrite (NZ50 where Ni / Zn is 1.77 and Co is 0.008) and nickel-zinc-copper ferrite (Ni... 0.5005 Zn 0.3195 Cu 0.20 Co 0.04 Fe 1.96 A graph showing the permeability and magnetic loss of O4 (where Ni / Zn is 1.57 and Co is 0.04) relative to frequency.

[0119] Figure 2 This is a graph showing the permeability and magnetic loss of NZC ferrite relative to frequency. Ni 0.5005 Zn 0.3195 Cu 0.20 Co 0.04 Fe 1.96 O4 (Ni / Zn ratio is 1.57 and Co ratio is 0.04) and Ni 0.4805 Zn 0.3195 Cu 0.20 Co 0.06 Fe 1.96 O4 (Ni / Zn ratio is 1.50 and Co ratio is 0.06).

[0120] Figure 3 This is a graph showing the permeability and magnetic loss of NZC ferrite as a function of frequency, where Ni 0.4805 Zn 0.319 5Cu 0.20 Co 0.06 Fe 1.96 O4 (Ni / Zn ratio is 1.50 and Co ratio is 0.06); Ni 0.4405 Zn 0.3195 Cu 0.20 Co 0.10 Fe 1.96 O4 (Ni / Zn ratio of 1.38 and Co ratio of 0.1) and Ni 0.6 Zn 0.2 Cu 0.20 Co 0.06 Fe 1.96 O4 (Ni / Zn is 3 and Co is 0.06).

[0121] Figure 4 This is a graph showing the permeability and magnetic loss of NZC ferrite as a function of frequency, where Ni 0.4347 Zn 0.315 3Cu 0.20 Co 0.11 Fe 1.96O4 (Ni / Zn is 1.38 and Co is 0.11); Ni 0.4231 Zn 0.3069 Cu 0.20 Co 0.13 Fe 1.96 O4 (Ni / Zn is 1.38 and Co is 0.13) and Ni 0.4115 Zn 0.2985 Cu 0.20 Co 0.15 Fe 1.96 O4 (Ni / Zn is 1.38 and Co is 0.15).

[0122] Figure 5 is a graph showing the magnetic permeability and magnetic loss of the material Ni 0.4405 Zn 0.3195 Cu 0.20 Co 0.10 Fe 1.96 O4 as a function of frequency.

[0123] Figure 6 is a graph showing the magnetic permeability and magnetic loss of the material Ni 0.6 Zn 0.2 Cu 0.20 Co 0.06 Fe 1.96 O4 as a function of frequency.

[0124] Figure 7 is a graph showing the dielectric constant and dielectric loss of the material Ni 0.4405 Zn 0.3195 Cu 0.20 Co 0.10 Fe 1.96 O4 as a function of frequency.

[0125] Figure 8 is a graph showing the dielectric constant and dielectric loss of the material Ni 0.6 Zn 0.2 Cu 0.20 Co 0.06 Fe 1.96 O4 as a function of frequency. Example

[0126] To evaluate the potential of the materials according to the present application, we are mainly interested in the variation of the magnetic permeability versus the magnetic loss as a function of frequency. This means monitoring the moment when the loss increases (which coincides with the beginning of the ferromagnetic resonance) and the value of the magnetic permeability before the resonance.

[0127] Measurements of magnetic permeability, dielectric constant, magnetic and dielectric loss were performed between 1 MHz and 1 GHz using a HP4291A impedance analyzer.

[0128] To measure the magnetic permeability and the magnetic losses, samples in the form of cylindrical sintered toroids of the APC7 type (Ni thickness < 3 mm) were manufactured. The measurements were made in a Keysight 16454A Magnetic Material Test Fixture. The reference for this test can be found on the manufacturer's website (reference document: 16454A Magnetic Material Test Fixture Operation and Service Manual and Materials Measurement: Magnetic Materials - Application Brief at https: / / www.keysight.com / en / pd-1000000509%3Aepsg%3Apro-pn-16454A / magnetic-material-test-fixture?pm=PL&nid=-536902475.536879639&cc=FR&lc=fre).

[0129] To measure the dielectric constant and the dielectric losses, samples in the form of 10 mm square plates of varying thickness (1 ; 0.5; 0.3 mm) were manufactured. The capacitance and the loss factor were then measured in an impedance analyzer (HP 4291 A) using an HP Agilent Keysight 16092A Spring Clip Test Fixture (allowing measurements between 1 and 500 MHz).

[0130] Figure 1 This curve is shown. The dotted line shows a classic spinel ferrite (NZ50, sold by EXXELIA) and the appearance of a resonance can be observed before 50 MHz (peak of magnetic permeability at about 20 MHz). The losses increase and make the material unusable as a VHF and / or UHF antenna material. As Figure 1 shown, the use of a nickel-zinc-copper ferrite (Ni 0.5005 Zn 0.3195 Cu 0.20 Co 0.04 Fe 1.96 O4) with a copper content of 0.2 allows the resonance to be shifted to higher frequencies, above 50 MHz (peak at about 100 MHz).

[0131] Figure 2 The composition Ni 0.4805 Zn 0.3195 Cu 0.20 Co 0.06 Fe 1.96O4. For a Ni / Zn ratio of 1.5 and an increased cobalt content of 0.06, the resonance is pushed to higher frequencies, allowing for low loss (tan δ μ <0.04). This gives a material that can be used as an antenna material between 1 and 100 MHz, while μ' is about 29.

[0132] Figure 3 The two new materials are compared with Figure 2 the material shown in thin solid line / grey (Ni 0.4805 Zn 0.3195 Cu 0.20 Co 0.06 Fe 1.96 O4). The first material shown in thick solid line / black has the following composition: Ni 0.4405 Zn 0.3195 Cu 0.20 Co 0.10 Fe 1.96 O4. In contrast, the Ni / Zn ratio is slightly reduced (due to a strong addition of cobalt by replacing nickel), but the proportion of cobalt is greatly increased to 0.1 mole. This shows the direct effect of cobalt to push the resonance back after 200 MHz. In Figure 3 The material shown in dashed line: Ni 0.6 Zn 0.2 Cu 0.20 Co 0.06 Fe 1.96 O4, observes a similar effect. The cobalt content remains the same compared to the material shown in thin / grey solid line, but the Ni / Zn ratio is doubled. It can be seen that the resonance is also pushed back after 200 MHz.

[0133] Figure 4 Three compositions (Ni 0.4347 Zn 0.3153 Cu 0.20 Co 0.11 Fe 1.96 O4; Ni 0.4231 Zn 0.3069 Cu 0.20 Co 0.13 Fe 1.96 O4; and Ni 0.4115 Zn 0.2985 Cu 0.20 Co 0.15 Fe 1.96 O4) are shown, each with a Ni / Zn ratio set to 1.38. The cobalt content of these compositions is set to 0.11, 0.13 and 0.15, respectively. The effect of cobalt can be clearly seen, allowing the use of the material at higher frequencies (above 300 MHz for the composition with a cobalt content of 0.15).

[0134] Figure 5 and 6 Focus on the frequency range between 100 and 200 MHz. Due to the many VHF applications operating in this range, there is a great interest in this frequency band, in particular for aviation applications (use band between 118 and 156 MHz, more particularly between 118 and 137 MHz for aviation traffic). In these specific frequency bands, it is observed in Figure 4 and 5 that the material Ni 0.440 5Zn 0.3195 Cu 0.20 Co 0.10 Fe 1.96 O4and Ni 0.6 Zn 0.2 Cu 0.20 Co 0.06 Fe 1.96 O4show advantageous properties with a magnetic loss tan(δ μ )<0.02 and a magnetic permeability μ'≈15.

[0135] Figure 7 and 8 show the relative permittivity and dielectric loss of Ni 0.4405 Zn 0.3195 Cu 0.20 Co 0.10 Fe 1.96 O4and Ni 0.6 Zn 0.2 Cu 0.20 Co 0.06 Fe 1.96 O4in the frequency range 100-200 MHz. They show advantageous properties with a dielectric loss tan(δ ε )<0.006 and a permittivity ε'≈13-14.

[0136] These results support the scope of the invention in their generality. In particular, the examples support the Ni / Zn ratio defined according to the invention, and the cobalt content defined according to the invention makes it possible to adapt the targeted behavior. Starting from one of the compositions according to the examples of the invention and varying one parameter in one direction and the other in the opposite direction, similar results are achieved in terms of magnetic permeability μ', permittivity ε' and magnetic-dielectric loss tan(δ μ )+tan(δ ε ). Thus, there is a large number of possible compositional variants with similar properties to those shown in the examples.

Claims

1. A composition selected from the group of formulae: Ni 0.4805 Zn 0.3195 Cu 0.20 Co 0.06 Fe 1.96 O4, Ni 0.4405 Zn 0.3195 Cu 0.20 Co 0.10 Fe 1.96 O4, Ni 0.4347 Zn 0.3153 Cu 0.20 Co 0.11 Fe 1.96 O4, Ni 0.4231 Zn 0.3069 Cu 0.20 Co 0.13 Fe 1.96 O4, Ni 0.4115 Zn 0.2985 Cu 0.20 Co 0.15 Fe 1.96 O4; and Ni 0.6 Zn 0.2 Cu 0.20 Co 0.06 Fe 1.96 O4.

2. The composition of claim 1, wherein, It forms a magnetic-dielectric material.

3. The composition of claim 1, wherein It has a magnetic permeability μ' of 10-20 for the VHF range (1 MHz to 300 MHz) and a μ' of 5-15 for the V / UHF range (200 MHz to 600 MHz).

4. The composition of claim 1, wherein It has a magnetic loss tan(δ μ )<0.

06.

5. A VHF or V / UHF antenna characterised in that It comprises or consists of a composition according to claim 1.

6. A VHF or V / UHF antenna of printed or microstrip type, characterized in that It comprises or consists of one or more substrate layers adhered to the radiating element, wherein the one or more substrate layers comprise or consist of a composition according to claim 1.

7. The VHF or V / UHF antenna according to claim 5, characterized in that It has a larger dimension of less than 300 mm.

8. Use of a composition according to claim 1 as a VHF or V / UHF antenna.

9. Process for the preparation of a composition according to claim 1, characterized in that, The method comprises: milling a feedstock that provides Ni, Zn, Cu, Co, Fe and O to provide a powder, after milling, drying the powder and then sieving, after sieving, heat treating the powder, after heat treating, subjecting the powder to a second milling, then shaping the powder into a solid material.

10. The method of claim 9, wherein, Before shaping, the method comprises coating the powder with a binder.

11. The method of claim 9, wherein, After shaping, the method comprises sintering the solid material.

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