Nickel zinc copper ferrite for VUHF antenna applications

Abstract

Nickel zinc copper ferrite for VUHF antenna application The present invention relates to a composition and a solid material, specially adapted for the manufacture of an antenna adapted to operate in the very high frequency and ultra high frequency or V / UHF band, as well as a manufacturing process and their uses. The composition has the formula NiaZnbCucCodFe2-δO4, in which: 2(a+b+c+d) + 3(2-δ) = 8. 0.05 < b < 0.5, for example, 0.1 < b < 0.5, for example, 0.1 < b < 0.4, for example, 0.15 < b < 0.35, 0.10 < c < 0.25, preferably 0.15 < c < 0.25, according to one variant c is 0.20, 0.04 < d < 0.25, preferably 0.06 < d < 0.25, and even more preferably 0.07 < d < 0.25, and δ < 0.05. Figure for the abbreviation: NONE

Description

Title of the invention: Nickel-zinc-copper ferrite for VUHF antenna application

[0001] The present invention relates to a composition and a solid material, specially adapted for the manufacture of an antenna adapted to operate in the very high frequency (VHF) band, between 30 MHz and 300 MHz, and ultra high frequency (UHF) band, between 300 MHz and 3 GHz, or V / UHF, as well as a manufacturing process and their uses. State of the art

[0002] The miniature size of an antenna is a major consideration, especially for antennas operating below 1 GHz. Indeed, the size of an antenna is directly proportional to the wavelength of the transmitted / received signal, which is on the order of a meter for VHF / UHF frequencies (VHF: 30 MHz to 300 MHz; UHF: 300 MHz to 3000 MHz). Currently, one of the strategies commonly used to reduce the geometric dimensions of an antenna is to use a dielectric material with a high dielectric constant (e'). However, the use of such materials leads to a decrease in antenna performance (gain, bandwidth).

[0003] This limitation can be overcome by using magnetodielectric materials such as ferrites. Indeed, the use of materials with high permeability (p') would allow for a reduction in antenna size while maximizing their efficiency. In fact, although e' has a positive impact on dielectric losses and the amount of stored energy, it has been shown that: (i) e' has a negative impact on bandwidth and antenna efficiency, and (ii) p' has the opposite effect and therefore a positive impact on both of these parameters. Moreover, if the antenna is kept at the same dimensions, such a material would increase its performance (MAC 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 propagation letters, 10 (2011) 63-66).

[0004] It has long been generally known that adding low concentrations of cobalt to ferrites, and in particular to nickel-zinc ferrites, has a positive effect on the magnetic losses of the compound. For example, the study by Lau and Stuijts (JGM Lau and AL Stuijts, Chemical Composition and High-Frequency Properties of Ni-Zn-Co Ferrites, Philips Res. Repts, 21 (1966) 104-112) presents mechanisms of cobalt ion behavior. in the crystal structure of (Nio,8Zno,2)o,97-xCoo,o3Fe2O4+Y. A large number of studies focus on cobalt-substituted nickel-zinc ferrites. However, these compositions do not contain copper and exhibit magnetic loss performance at high frequencies (Frequency F > 100 MHz) that is significantly lower than that targeted by the present invention. Some compositions manage to exhibit stable magnetic permeability. However, they present the problem that ferrimagnetic resonance appears at too low a frequency and causes an increase in magnetic losses starting at around tens of MHz.

[0005] There are certain nickel-zinc basic ferrite materials available at the laboratory scale that exhibit performance similar to the invention. For example, the team of Mathur et al. published in 2010 a ferrite composition suitable for high-frequency applications (P. Mathur, A. Thakur, JH Lee, M. Singh, Sustained electromagnetic properties of Ni-Zn-Co nanoferrites for the high-frequency applications, Materials Letters, 64 (2010) 2738-2741). Indeed, the developed material exhibits low magnetic losses (loss tangent of approximately 0.05) over a frequency band ranging from 10 to 200 MHz, as well as a magnetic permeability p' of approximately 9. The composition of the material presented is as follows: Ni0.49Zno.49Coo.o2Fe2O4. Since the cobalt level was low (0.02 mol), the authors used another method to push back the resonance beyond 200 MHz.They used a co-precipitation synthesis method to synthesize particles on the order of approximately 50 nm and sintered their material at a lower temperature to prevent excessive crystal growth. The material thus possesses a fine microstructure that allows the movement kinetics of the magnetic domain walls to be altered in order to suppress resonance. The co-precipitation synthesis method is very different from the conventional synthesis method. It is also more expensive and complex to implement on an industrial scale.

[0006] The team of Saini et al. (A. Saini, A. Thakur, P. Thakur, Matching permeability and permittivity of Ni0.5Zn0.3Co0.2In0.1Fe19O4 ferrite for substrate of large bandwidth miniaturized antenna, J Mater Sci: Mater Electron, 27 (2016) 2816-2823) demonstrates the advantages of the Ni0.5Zn0.3Co0.2In0.1Fe19O4 composition for the miniaturization of UHF antennas with a bandwidth gain compared to an antenna loaded with a simple dielectric material. This material is synthesized by co-precipitation and has a high cobalt content (0.2 mol). It exhibits a magnetic permeability of approximately 5–6 and low magnetic losses up to at least 500–600 MHz.

[0007] Finally, we can also mention the work carried out at the Lab-STICC laboratory in Brest (France), which focuses on the fabrication of a magneto-dielectric material by co-precipitation that can meet antenna requirements on the bands V / UHF frequency. Several results have been published which demonstrate the interest of using the co-precipitation method on compounds such as Nio.5Zno.3Coo,2 Fei 98O4 ô to achieve low magnetic losses at high frequency while maintaining a relatively high permeability.

[0008] Nickel-zinc-copper ferrites are widely used for inductors. Manufacturers take advantage of the low sintering temperature of this compound (< 1000 °C) afforded by the high percentage of copper (generally between 0.2 and 0.25 mol) to co-sinter the ferrite with the electrodes or the winding directly. It has been reported that when copper is added to a compound such as NiO.8-xZNO.2CuxFe2O4, an optimum exists for a copper addition of 0.2 mol (JJ Shrotri, SD Kulkami, CE Deshpande, A. Mitra, SR Sainkar, PS Anil Kumar, SK Date, Effect of Cu substitution on the magnetic and electrical properties of Ni-Zn ferrite synthesized by soft chemical method, Materials Chemistry and Physics, 59 (1999) 1-5). For values ​​that are too high (x > 0.3 mol), copper forms a second phase CuO / CuFeO4 and the properties of the material degrade.

[0009] Many studies present Ni-Zn-Cu ferrites with interesting high-frequency behavior. However, the frequencies considered are often too low for the applications targeted by the invention. This type of material generally exhibits ferrimagnetic resonance between 1 and 100 MHz. Moreover, the onset of resonance is accompanied by an increase in magnetic losses (represented by the value / j” or tan), rendering the material unusable as an antenna material over frequency bands extending beyond this resonance. Objectives of the invention

[0010] The present invention aims to solve the technical problem of providing a useful composition as a VHF or V / UHF antenna.

[0011] In particular, the present invention aims to solve the technical problem of providing a useful composition as a miniaturized VHF or V / UHF antenna.

[0012] The present invention aims in particular to solve the technical problem of providing a nickel-zinc-copper ferrite composition that can be used as an antenna material, preferably miniaturized, on VHF and / or UHF frequency bands.

[0013] The present invention aims in particular to solve the technical problem of providing a useful antenna composition, preferably miniaturized, for which resonance appears above 50 MHz, preferably above 70 MHz, and preferably above 100 MHz, or even preferably at a higher frequency.

[0014] The present invention aims in particular to solve the technical problem consisting of providing a magneto-dielectric composition preferably having a magnetic permeability p' > 5 and a dielectric permittivity e' > 10, with preferably a magnetic permeability close to the dielectric permittivity.

[0015] The present invention also aims to solve the technical problem of providing a method for manufacturing such a composition, preferably by a conventional industrial process of preparing ceramic material by grinding / chamotting. Detailed description of the invention

[0016] The inventors discovered that the use of a composition according to the present invention, having a high cobalt content combined with a high copper content in a nickel-zinc ferrite composition, made it possible to solve at least one, and preferably all, of the aforementioned technical problems.

[0017] The inventors discovered that using a composition according to the present invention by increasing the Ni / Zn ratio made it possible to provide an advantageous composition for solving at least one, and preferably all, of the aforementioned technical problems.

[0018] Advantageously, such a composition can be obtained by introducing cobalt as a partial substitution for nickel in a ferrite alloy composition of formula NiaZnbCucCodFe2ôO4.

[0019] The invention relates to a composition of formula NiaZnbCucCodFe20O4, in which:

[0020] 2(a+b+c+d) + 3(2-ô) = 8

[0021] 0.05 < b < 0.5, for example 0.1 < b < 0.5, for example 0.1 < b < 0.4.

[0022] 0.10 < c < 0.25, preferably 0.15 < c < 0.25, according to a variant c is 0.20,

[0023] 0.04 < d < 0.25, preferably 0.06 < d < 0.25, and even more preferably 0.07 < d < 0.25, and

[0024] ô < 0.05.

[0025] Advantageously, the composition is a nickel zinc copper ferrite, preferably having a Ni / Zn ratio of 1 to 15.

[0026] Advantageously, the composition has a spinel structure.

[0027] The invention relates to a nickel-zinc-copper ferrite material with a spinel structure that can be used as an antenna material on VUHF frequency bands.

[0028] According to one embodiment, “b” is greater than or equal to 0.05.

[0029] According to one embodiment, “b” is greater than or equal to 0.1.

[0030] According to one embodiment, “b” is less than or equal to 0.5.

[0031] According to one embodiment, “b” is less than or equal to 0.4.

[0032] According to one embodiment, “b” is less than or equal to 0.35.

[0033] Advantageously, any one of the stated lower bounds can be combined with any one of the stated upper bounds.

[0034] According to one embodiment, 0.05 < b < 0.5,

[0035] According to one embodiment, 0.1 < b < 0.5.

[0036] According to one embodiment, 0.1 < b < 0.4.

[0037] According to one embodiment, 0.15 < b < 0.35.

[0038] According to one embodiment, “c” is greater than or equal to 0.10.

[0039] According to one embodiment, “c” is greater than or equal to 0.15.

[0040] According to one embodiment, “c” is less than or equal to 0.25.

[0041] Advantageously, any one of the stated lower bounds can be combined with any one of the stated upper bounds.

[0042] According to one embodiment, 0.10 < c < 0.25, preferably 0.15 < c < 0.25, according to another variant c is 0.20.

[0043] According to one embodiment, “d” is greater than or equal to 0.04.

[0044] According to one embodiment, “d” is greater than or equal to 0.05.

[0045] According to one embodiment, “d” is greater than or equal to 0.06.

[0046] According to one embodiment, “d” is greater than or equal to 0.07.

[0047] According to one embodiment, “d” is equal to 0.10.

[0048] According to one embodiment, “d” is less than or equal to 0.25.

[0049] Advantageously, any one of the stated lower bounds can be combined with any one of the stated upper bounds.

[0050] According to one embodiment, 0.04 < d < 0.25.

[0051] Preferably, 0.06 < d < 0.25.

[0052] Advantageously, 0.07 < d < 0.25.

[0053] Advantageously, 0.09 < d < 0.25

[0054] According to one embodiment, “a” is greater than or equal to 0.3.

[0055] According to one embodiment, “a” is greater than or equal to 0.35.

[0056] According to one embodiment, “a” is greater than or equal to 0.4.

[0057] According to one embodiment, “a” is less than or equal to 0.8.

[0058] According to one embodiment, “a” is less than or equal to 0.7.

[0059] According to one embodiment, “a” is less than or equal to 0.6.

[0060] Advantageously, any one of the stated lower bounds can be combined with any one of the stated upper bounds.

[0061] According to one embodiment, 0.3 < a < 0.7

[0062] According to one embodiment, 0.4 < a < 0.7.

[0063] Advantageously, the composition is chosen from among the following formula compositions:

[0064] Nio,5oo5Zno3i95Cuo,2oCoOMFeij9604,

[0065] Nio,48o5Znoj3i95Cuoj2oCo0jo6Felj9604,

[0066] Nio,44o5Znoj3i95Cuoj2oCo0jioFelj9604,

[0067] Nioj4347Znoj3i53Cuoj2oCoojnFelj9604,

[0068] Nioj423iZnoj3o69Cuoj2oCooji3Fe1>9604,

[0069] Nio,4ii5Zno,2985Cuo,2oCoo,i5Felj9604, and

[0070] Nioj6Znoj2Cuoj2oCoojo6Fe1>9604.

[0071] According to one embodiment, the Ni / Zn ratio is from 1 to 15, preferably from 1 to 10, and even more preferably from 1.2 to 7.

[0072] Advantageously, the Ni / Zn ratio is greater than 2.

[0073] According to one variant this ratio is 1.38 and according to another variant this ratio is 3.

[0074] The invention also relates to a solid material having a composition such that defined according to the present invention.

[0075] According to one embodiment, the material according to the present invention forms a magneto-dielectric material, preferably having a magnetic permeability p' > 1 and a dielectric permittivity e' > 1, and preferably p' > 5 and e' > 10.

[0076] According to one embodiment, the material according to the present invention has a magnetic permeability p' of 10 to 20 for the VHF range (1 MHz to 300 MHz) or p' of 5 to 15 for the V / UHF range (200 MHz to 600 MHz).

[0077] According to one embodiment, the material according to the present invention has magnetic losses tanfbj < 0.06, and preferably dielectric losses tan(ôE) < 0.02 over the frequency band between 100 and 200 MHz.

[0078] According to one embodiment, tan(ôE) < 0.006.

[0079] The invention further relates to a VHF or V / UHF antenna having a composition or solid material as defined according to the present invention.

[0080] According to one embodiment, the antenna is a VHF or V / UHF antenna of the printed antenna or micro-strip or "patch" type comprising one or more layers of a substrate attached to a radiating element, one or more layers of the substrate being made up of or comprising a composition according to the invention or a solid material according to the invention.

[0081] According to one embodiment, the antenna is miniaturized. Typically, the antenna has a largest dimension of less than 300 mm.

[0082] The invention also relates to the use of a composition according to the invention or of a solid material according to the invention, as a VHF or V / UHF antenna.

[0083] Advantageously, the invention relates to an antenna for aeronautics.

[0084] According to one embodiment, the antenna is adapted for operation between 118 MHz and 156 MHz, and preferably between 118 and 137 MHz.

[0085] The invention further relates to a method of manufacturing a composition as defined according to the present invention.

[0086] In particular, the invention relates to a method for manufacturing a composition according to the invention or a solid material according to the invention, said method comprising:

[0087] grinding of raw materials yielding Ni, Zn, Cu, Co, Fe and O, typically NiO; ZnO; CuO; Co3O4 and Fe2O3,

[0088] After grinding, the powder is dried and then sieved, preferably with a 400 µm sieve,

[0089] after sieving, the powder is heat-treated, preferably at a temperature of at least 600 °C, and for example 800 °C, for example for 1 to 10 h, typically 2 h,

[0090] after heat treatment, the powder undergoes a second grinding, for example with aqueous dissolution,

[0091] then the powder is shaped to obtain a solid material.

[0092] According to one embodiment, prior to shaping the process includes coating the powder with a binder to provide a shaped material.

[0093] According to one embodiment, after shaping the process includes sintering the shaped material.

[0094] Advantageously, the material is synthesized according to a process for preparing a ceramic material.

[0095] In one embodiment, the raw material grinding step includes or consists of weighing the various oxides required to achieve the composition: NiO, ZnO, CuO, Co3O4, and Fe2O3. To account for the introduction of iron impurities during the grinding process, an iron oxide deficiency is introduced at this weighing stage. In one embodiment, the raw materials are then mixed and subsequently ground in aqueous solution (typically for 20 hours for jar grinding) using grinding equipment, such as, for example, a ball mill, an attrition mill, a jar turner, etc.

[0096] According to one embodiment, after grinding, the powder is dried and then sieved at 400 µm. It is then heat-treated ("chamotte") in an oven at 800 °C for 2 h.

[0097] According to one embodiment, the powder undergoes a second grinding. For example, the powder is sieved and then put into an aqueous slip, i.e. diluted in an aqueous solution, typically water, for regrinding (typically for a period of 36 h for grinding in a jar).

[0098] According to one embodiment, the powder is coated with a binder and then shaped by pressing.

[0099] Advantageously, the powder is coated to allow for shaping. The binder can be added during the second grinding by adding it to the slip, or after grinding once the powder is dry and sieved. In each In some cases, the powder is preferably dried and then sifted between 200 and 400 pm before shaping.

[0100] Advantageously, the shaping is carried out by pressing (typically uniaxial) in the form of plates, discs or tori as required.

[0101] Advantageously, the shaped material is sintered.

[0102] Sintering typically takes place at a temperature above 800°C, and preferably between 850 and 1000°C.

[0103] Typically, sintering is carried out under an oxidizing atmosphere, for example air.

[0104] According to one embodiment, the pressed material is sintered at 950 °C for 2 h under air. Preferably, before raising the furnace temperature, for example to 950 °C, the materials are debinded with a slow temperature increase when the temperature is below 500 °C. The debinding time depends on the dimensions and mass of the parts and can, for example, range from 1 to 48 hours. Sintering according to the invention at a temperature below 1200 °C, and advantageously at 950 °C, offers a significant technical advantage. Generally, spinel-structured ferrites sinter between 1200 and 1400 °C for 4 to 12 hours. The invention thus allows for savings in time and furnace cost (sizing for temperatures < 1000 °C) and in the power required for heating.

[0105] Advantageously, the composition or material according to the present invention constitutes a magneto-dielectric material having a magnetic permeability close (for example + / - 10 units, preferably + / - 5 units) to its dielectric permittivity (magneto-dielectric materials: e' > 1 and p' > 1).

[0106] Advantageously, the composition or material according to the present invention exhibits a ferrimagnetic resonance above 50 MHz, preferably above 70 MHz, and preferably above 100 MHz.

[0107] Ferrimagnetic resonance beyond a certain value means that the magnetic permeability peak occurs at a frequency greater than that value.

[0108] Advantageously, the composition or material according to the present invention exhibits a ferrimagnetic resonance above 120 MHz, preferably above 140 MHz, and preferably above 150 MHz.

[0109] Even more advantageously, the composition or material according to the present invention exhibits a ferrimagnetic resonance beyond 200 MHz.

[0110] Such an advantage is linked in particular to the composition of the alloy formula according to the invention.

[0111] Advantageously, the composition and material according to the invention have a magnetic permeability p' greater than 10, preferably greater than 15, and even more preferably greater than 20, for the VHF range (1 MHz to 300 MHz).

[0112] Advantageously, the composition and material according to the invention have a per magnetic measurability p' greater than 5, and preferably greater than 10, and even more preferably greater than 15, for the V / UHF range (200 MHz to 600 MHz)

[0113] Advantageously, the composition and material according to the invention exhibit low magnetic losses in VHF / UHF with tan less than 0.05 over the frequency band from 1 to 50 MHz, preferably from 1 to 70 MHz, and preferably from 1 to 100 MHz.

[0114] Advantageously, according to one embodiment, the composition and material according to the invention exhibit low magnetic losses in VHF / UHF with tan less than 0.06, and preferably less than 0.05, and even more preferably less than 0.04, over the frequency band from 100 to 200 MHz.

[0115] Advantageously, the composition and material according to the invention exhibit moderate magnetic permeability (typically q' of 5 to 20, preferably of 10 to 20) and low magnetic losses in VHF / UHF (tan < 0.05) over the frequency band of 100 to 200 MHz. In the figures:

[0116] [Fig. 1] The [Fig. 1] is a graph representing the magnetic permeability and magnetic losses of a conventional nickel zinc ferrite (NZ50 where Ni / Zn is 1.77 and Co is 0.008) and of a nickel zinc copper ferrite (Nio.sœsZno^içsCuo.ioCoo.MFei^C^ where Ni / Zn is 1.57 and Co is 0.04) as a function of frequency.

[0117] [Fig.2] Fig.2 is a graph representing magnetic permeability and losses magnetic properties of NZC ferrites as a function of frequency. Nio,5oo5Zno>3i95Cuoj2oCoojo4Fe 1.9604 (Ni / Zn is 1.57 and Co is 0.04) and Nio,4805Zno,3i95Cuo,2oCoo,o6Fei,9604 (Ni / Zn is 1.50 and Co is 0.06).

[0118] [Fig.3] Fig.3 is a graph representing magnetic permeability and losses magnetic properties of NZC ferrites as a function of frequency; with Nio,4805Zn0,3i95Cu0,2oCo o,o6Fei>9604 (Ni / Zn is 1.50 and Co is 0.06); Nioj44o5Znoj3i95Cuoj2oCoojioFeij9604 (Ni / Zn is 1.38 and Co is 0.1) and Nio>6Znoj2Cuoj2oCoojo6Feij9604 (Ni / Zn is 3 and Co is 0.06).

[0119] [Fig.4] Fig.4 is a graph representing magnetic permeability and losses magnetic properties of NZC ferrites as a function of frequency; with Nioj4347Zn0j3i53Cuoj2oCo o,iiFei>9604 (Ni / Zn is 1.38 and Co is 0.11); Nioj423iZn0j3069Cuoj2oCooji3Feij9604 (Ni / Zn is 1.38 and Co is 0.13) and Nioj4ii5Znoj2985Cuoj2oCooji5Feij9604 (Ni / Zn is 1.38 and Co is 0.15).

[0120] [Fig.5] Fig.5 is a graph representing magnetic permeability and losses magnetic properties of the Nioj44o5Znoj3i95Cuoj2oCoojioFeij9604 material as a function of frequency.

[0121] [Fig.6] Fig.6 is a graph representing magnetic permeability and losses magnetic properties of the Nioj6Znoj2Cuoj2oCoojo6Feij9604 material as a function of frequency.

[0122] [Fig.7] Fig.7 is a graph representing permittivity and dielectric losses of the Nioj44o5Znoj3i95Cuoj2oCoojioFeij9604 material as a function of frequency.

[0123] [Fig.8] The [Fig.8] is a graph representing the permittivity and dielectric losses of the Nio,6Zn0,2Cuo,2oCoo,o6Fei,9604 material as a function of frequency. Examples

[0124] To evaluate the potential of the materials according to the invention, one is primarily interested in the evolution of permeability and magnetic losses with frequency. One thus considers the point at which the losses increase (this coincides with the onset of ferri-magnetic resonance) and the value of the permeability before resonance.

[0125] Measurements of permeability, permittivity, magnetic and dielectric losses are carried out between 1 MHz and 1 GHz using an HP4291A type impedance analyzer.

[0126] For the measurement of permeability and magnetic losses, samples in the form of as-cast cylindrical toroids of type APC7 are manufactured (ext < 7 mm; oint > 3.05 mm; thickness < 3 mm). The measurements are performed in the Keysight 16454A Magnetic Material Test Fixture. References for this measurement 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.eom / en / pd-1000000509%3Aepsg%3Apro-pn-16454A / magnetic-material-test-fixture?pm=PL&nid=-536902475.536879639&cc=FR&lc=fre).

[0127] For the measurement of permittivity and dielectric losses, samples in the form of 10 mm square plates of varying thickness (1; 0.5; 0.3 mm) are fabricated. A measurement of the capacitance and loss factor is then performed on the impedance analyzer (HP4291A) using the HP Agilent Keysight 16092A Spring Clip Test Fixture, which allows measurement between 1 and 500 MHz.

[0128] Figure 1 shows such curves. A conventional spinel ferrite (NZ50, marketed by EXXELIA) is shown in dashed line, and the onset of resonance can be observed before 50 MHz (permeability peak at approximately 20 MHz). Losses increase, rendering the material unusable as a VHF and / or UHF antenna material. The use of a nickel-zinc-copper ferrite with a copper content of 0.2, as shown in solid line in Figure 1 (NiO₂ZNO₂₃CuO₂CotyMFei geCL), makes it possible to push the resonance to higher frequencies, above 50 MHz (peak at approximately 100 MHz).

[0129] Figure 2 shows the composition Nio,4805Zn0,3195Cu0,20Cu0,06Fe1,9604. With a ratio A Ni / Zn ratio of 1.5 and a cobalt content increased to 0.06 pushes the resonance to a higher frequency, resulting in low losses (tan < 0.04) up to 100 MHz. This yields a material usable as an antenna material between 1 and 100 MHz with a p' value around 29.

[0130] Figure 3 compares two new materials to the one already shown as a thin solid gray line in Figure 2 (Nio / tëosZno^içsCuo.ioCoo.oeFei^C^). The first material, shown as a thick solid black line, has the following composition: Nio^osZno^sCuo^oCoojoFei^CL. In comparison, the Ni / Zn ratio has been slightly decreased (due to the fact that the large addition of cobalt was achieved by substituting nickel), but the proportion of cobalt has been significantly increased to 0.1 mol. The direct effect of cobalt, which has allowed the resonance to be pushed back beyond 200 MHz, is thus observed. A similar effect is observed in the material shown as a dashed line in Figure 3: Nioj6Zn0j2Cuoj2oCoojo6Feij9604. Compared to the material shown in the thin / grey solid line, the cobalt content remained the same, but the Ni / Zn ratio was doubled. This shows that the resonance is also pushed beyond 200 MHz.

[0131] Figure 4 shows three compositions (NiO4347ZnO3153CuoJ2OCoojiiFeij96O4; NiO423iZnO3069CuO2OCoOji3Felj96O4 and NiO415ZnO2985CuoJ2OCoOji5Felj96O4 and NiO415ZnO2985CuoJ2OCoOji5Felj96O4), each with a Ni / Zn ratio of 1.38. The cobalt content of these compositions is set at 0.11, 0.13 and 0.15 respectively. The effect of cobalt is clearly observed, allowing higher frequency use of the material (above 300 MHz for the composition with a cobalt content of 0.15).

[0132] Figures 5 and 6 focus on the frequency range between 100 and 200 MHz. This frequency band is of great interest due to the numerous VHF applications operating in this range, and in particular for aeronautical applications (the operating band is between 118 and 156 MHz, and more specifically between 118 and 137 MHz for aeronautical traffic). Figures 4 and 5 show that the materials NiO₄₄O₅ZNO₃₁₀O₅COO₂O₅COO₂O₅Fe₁₀O₄ and NiO₃₆ZNO₃₁₀ ... exhibit advantageous performance with magnetic losses tanfbj < 0.02 and a magnetic permeability p' ~ 15.

[0133] Figures 7 and 8 show the relative permittivity and dielectric losses of the materials Nioj44o5Znoj3i95Cuoj2oCoojioFelj9604 and Nioj6Zn0j2Cuoj2oCoojo6Felj9604 over the frequency range of 100 - 200 MHz. They exhibit advantageous performance with dielectric losses tan(θE) < 0.006 and a dielectric constant e' ~ 13-14.

[0134] These results support the general scope of the invention. In particular, the examples demonstrate that the Ni / Zn ratio and the cobalt content defined according to the invention allow for the adaptation of the desired behavior. Starting with one of the compositions in the examples according to the invention and varying one parameter in one direction and the other in the opposite direction, a similar result can be achieved in terms of magnetic permeability p', dielectric permittivity e', and magnetodielectric losses tan(θ) + tan(θE). Thus, there are a large number of possible composition variants with performance similar to that presented in the examples.

Claims

Demands

1. Composition of formula NiaZnbCucCodFe2 ôO4, in which: 2(a+b+c+d) + 3(2-ô) = 8 0.05 < b < 0.5, for example 0.1 < b < 0.5, for example 0.1 < b < 0.4, for example 0.15 < b < 0.35 0.10 < c < 0.25, preferably 0.15 < c < 0.25, according to a variant c is 0.20, 0.04 < d < 0.25, preferably 0.06 < d < 0.25, and even more preferably 0.07 < d < 0.25, and ô < 0.

05.

2. Composition according to claim 1, having a Ni / Zn ratio of 1 to 15.

3. Composition according to claim 1 or 2, characterized in that the composition has a spinel structure.

4. Composition according to any one of claims 1 to 3, characterized in that the composition is selected from the compositions of the following formulas: Nio,48O5Zno,3195Cu0.20Co0.06Fe 1.96O4. Nio^osZno.s 195CU0.20CO0.1 oFe ! .ç6O4, Nio.4347Zno.3153CU0.20CO0.1 iFe i.96O4, Nio.423 lZn0,3069CU0,20Co0,13Fe ! .96O4, Nio,4115Zno,2985CUo,2oCOo,15Fei,96O4 ; and Nio,6Zno.2Cuo.2oCoo.06Fe1.96O4.

5. Solid material characterized in that it has a composition as defined according to any one of claims 1 to 4.

6. Solid material according to claim 5, characterized in that it forms a magneto-dielectric material, preferably having a magnetic permeability p' > 1 and a dielectric permittivity e' > 1, and preferably p' > 5 and e' > 10.

7. Solid material according to claim 5 or 6, characterized in that it has a magnetic permeability p' of 10 to 20 for the VHF range (1 MHz to 300 MHz) or p' of 5 to 15 for the V / UHF range (200 MHz to 600 MHz).

8. Solid material according to any one of claims 5 to 7, characterized in that it has magnetic losses tanfbj < 0.06, and preferably dielectric losses tan(ôE) < 0.02 over the frequency band between 100 and 200 MHz.

9. VHF or V / UHF antenna characterized in that it comprises or is made of a composition according to any one of claims 1 to 4 or of a solid material according to any one of the CAD claims

10. J a O. VHF or V / UHF antenna of the printed antenna or microstrip type, characterized in that it comprises one or more layers of a substrate attached to a radiating element, one or more layers of the substrate being made up of or comprising a composition according to any one of claims 1 to 4 or a solid material according to any one of claims 5 to 8.

11. VHF or V / UHF antenna according to claim 9 or 10, characterized in that it has a largest dimension less than 300 mm.

12. Use of a composition according to any one of claims 1 to 4 or of a solid material according to any one of claims 5 to 8, as a VHF or V / UHF antenna.

13. A method for manufacturing a composition according to any one of claims 1 to 4 or a solid material according to any one of claims 5 to 8, characterized in that said method comprises: grinding the raw materials providing Ni, Zn, Cu, Co, Fe and O, typically NiO; ZnO; CuO; Co3O4 and Fe2O3, after grinding, the powder is dried and then sieved preferably with a 400 µm sieve, after sieving, the powder is heat-treated, preferably at a temperature of at least 600 °C, and for example 800 °C, for example for 1 to 10 h, typically 2 h, after heat treatment, the powder undergoes a second grinding, for example with aqueous solution, and then the powder is shaped to obtain a solid material.

14. A process according to claim 13, characterized in that prior to shaping the process comprises coating the powder with a binder to provide a shaped material.

15. A process according to claim 13 or 14, characterized in that after shaping the process includes sintering the shaped material.

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