Patent Publication Number: US-6911889-B2

Title: High frequency filter device and related methods

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of U.S. Provisional Application No. 60/313,639, filed Aug. 20, 2001, which is hereby incorporated herein in its entirety by reference. 

   FIELD OF THE INVENTION 
   The present invention relates to the field of electronic devices, and, more particularly, to filters for use in electronic circuits and related methods. 
   BACKGROUND OF THE INVENTION 
   Electromagnetic interference (EMI) or radio frequency (RF) interference from electrical devices, signal sources, etc., can interrupt or otherwise degrade the effective performance of certain telecommunication, computer, and other electrical/electronic equipment. As a result, filters are commonly used in numerous types of electronic circuits to allow signals of a desired frequency to pass along a signal path, for example, while reducing the propagation of other undesired frequencies. 
   One particular type of filter commonly used in electrical and electronic devices is the ferrite filter. Ferrite filters act as chokes which attenuate signals to a desired frequency range. One basic type of ferrite filter is the so-called ferrite “bead” which typically includes a single, “soft” ferrite material having a particular attenuation range that depends upon the type of ferrite used. 
   A somewhat more sophisticated ferrite shield is disclosed in U.S. Pat. No. 4,796,079 to Hettiger entitled “Chip Component Providing RF Suppression.” The ferrite shield is formed by surrounding an electrical conductor with ferrite material and is made in the shape of a leadless chip to permit placement on a circuit board by chip insertion machines. In one embodiment, different shield elements are disposed along the lateral conductor signal path, where each shield element includes a different type of ferrite material having different impedance-frequency characteristics. Each shield element thus contributes to the overall impedance-frequency characteristics of the shield. 
   EMI can be a particular problem between about 800 MHz and about 15 GHz, for example. However, soft ferrites based on a spinel crystal structure are not traditionally used over 1 GHz or so because the ferromagnetic frequency response thereof decays rapidly in this frequency range. More particularly, most prior art surface mount EMI filters, such as those noted above, typically use soft ferrites which exhibit an impedance maximum below 2 GHz. While other types of ferrite are used in microwave frequencies in devices such as monolithic microwave integrated circuits (MMICs) and in elements of radar devices that operate in the low to high GHz frequency range, such devices may not readily lend themselves to relatively small-scale applications. 
   SUMMARY OF THE INVENTION 
   In view of the foregoing background, it is therefore an object of the present invention to provide a filter device and related methods which provide desirable impedance versus frequency characteristics over a relatively broad attenuation frequency band. 
   This and other objects, features, and advantages in accordance with the present invention are provided by a filter device which may include a plurality of ferrite filters laminated together in vertically stacked relation, where each ferrite filter may include a pair of ferrite layers laminated together in vertically stacked relation and a lateral conductor extending therebetween. The filter device may also include at least one vertical conductor connecting the lateral conductors together in series. Moreover, at least some of the ferrite filters may have different operating characteristics. 
   In particular, the different operating characteristics may be different impedance versus frequency characteristics to thereby broaden an attenuation frequency band of the filter device. For example, at least one of the ferrite layers may include iron deficient zinc ferrite to provide desired impedance characteristics at higher frequencies, and at least one other of the ferrite layers may include copper nickel zinc ferrite to provide desired impedance characteristics at lower frequencies. Specifically, the iron deficient zinc ferrite may include about 30-40 percent by weight ZnO and about 60-70 percent by weight Fe 2 O 3 . 
   The filter device may also include a first end conductor on a bottom one of the ferrite filters and connected to the lateral conductor thereof, and a second end conductor on a top one of the ferrite filters and connected to the lateral conductor thereof. Moreover, the first and second end conductors may be on a same side of the filter device. Additionally, the at least one vertical conductor may be at least one via extending between adjacent ferrite filters. Also, in some embodiments the lateral conductors may extend to opposing ends of their respective ferrite filters, in which case the at least one vertical conductor may be at least one vertical end conductor. 
   A method aspect of the invention is for making a filter device and may include arranging a plurality of ferrite layers in vertically stacked relation with a respective lateral conductor extending between adjacent pairs of ferrite layers. Furthermore, the lateral conductors may be connected in series using at least one vertical conductor, and the plurality of ferrite layers laminated together. This is done such that each adjacent pair of ferrite layers and respective lateral conductor defines a ferrite filter. Moreover, at least some of the ferrite filters may have different operating characteristics, as noted above. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a filter device in accordance with the present invention. 
       FIG. 2  is a perspective exploded view of the filter device of FIG.  1 . 
       FIG. 3  is a perspective view of the filter device of  FIG. 1  showing a back side thereof. 
       FIG. 4  is a graph illustrating impedance versus frequency characteristics of the high frequency ferrite filter of the filter device of FIG.  1 . 
       FIG. 5  is a graph illustrating the combined impedance versus frequency characteristics of both the high and low frequency ferrite filters of the filter device of FIG.  1 . 
       FIG. 6  is a perspective view illustrating the assembly of an alternate embodiment of the filter device in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. 
   Referring initially to  FIGS. 1-3 , a filter device  20  in accordance with the present invention includes a bottom ferrite filter  21  and a top ferrite filter  22  laminated together in vertically stacked relation. More particularly, each ferrite filter  21 ,  22  includes a pair of ferrite layers  23   a ,  23   b  and  24   a ,  24   b  laminated together in vertically stacked relation and a lateral conductor  25 ,  26  extending therebetween, respectively. 
   The filter device  20  also includes a vertical end conductor  27  connecting the lateral conductors  25 ,  26  together in series. That is, as may be seen in  FIG. 2 , the lateral conductors  25 ,  26  extend to opposing ends of their respective filters  21 ,  22 . Thus, by positioning the vertical end conductor  27  on one end of the filters  21 ,  22 , the lateral conductors  25 ,  26  are connected in a series path. The lateral conductors  25 ,  26  may be formed by screen printing with a conductive ink, for example. More particularly, the vertical conductors  25 ,  26  and layers of ceramic slurry may be directly screen printed onto a plastic carrier to build up a complete three-dimensional unfired (i.e., “green”) part one layer at a time. 
   Another approach is to use one or more layers of pre-formed ferrite tape for the ferrite layers  23   a ,  23   b ,  24   a ,  24   b  and print conductive patterns for their respective lateral conductors  25 ,  26  on (or both) of the adjoining surfaces of the tape layers. In particular, the lateral conductors may be formed by directly printing conductive paths of polymer-based ink including a large percentage of silver, or silver alloyed with a higher melting metal such as palladium, for example. Of course, other suitable conductive materials known to those of skill in the art may also be used. Furthermore, multiple layers of tape may have conductive paths printed on them for specific geometric paths for the conductor, as will be appreciated by those of skill in the art. The tape layers are then laminated, which forms the series conductive path between the lateral conductors  25 ,  26  and the vertical end conductor  27 . 
   In both of the above noted cases, many individual parts may be printed simultaneously on the tape or substrate. The laminated array or the slurry printed array may be dried and then cut into desired individual parts and fired in a kiln using processing methods widely known to the ferrite industry. The vertical end conductor  27  may be similarly formed by applying a conductive paste on the appropriate side of the filter device  20  prior to laminating the layers together, as will be understood by those skilled in the art. Of course, other suitable conductors may also be used. 
   Additionally, the filter device  20  may also include a first end conductor  28  on the bottom ferrite filter  21  which is connected to the lateral conductor  25  thereof. Further, a second end conductor  29  is on the ferrite filter  22  and connected to the lateral conductor  26  thereof. The first and second end conductors  28 ,  29  advantageously provide input and output terminals for connecting the filter device  20  with other circuit components, as will be appreciated by those of skill in the art. 
   The first and second end conductors may similarly be formed using conductive paste, as with the vertical end conductor  27 , and all of these end conductors may also be plated following lamination, if desired. In the illustrated example, the first and second end conductors  28 ,  29  are on a same side of the filter device, but it will be appreciated that in other embodiments one or both of the first and second end conductors could be located on a different side of the filter device  20  to provide various connection configurations. In such case, the lateral conductors  25 ,  26  may be formed to terminate at the appropriate side of the filter device  20 , as will be understood by those skilled in the art. 
   In accordance with the invention, the ferrite filters  21 ,  22  preferably have different operating characteristics, i.e., impedance versus frequency characteristics to broaden an attenuation frequency band of the filter device  20 . That is, when different ferrite materials are used in one or more of the layers  23   a ,  23   b ,  24   a ,  24   b  of the ferrite filters  21 ,  22 , these filters exhibit different impedance versus frequency characteristics. Stated alternately, by using different type of ferrite materials in the filters  21 ,  22 , the resonance points or insertion loss nulls of these filters will be different, which when combined provides for a wider attenuation frequency band. 
   In particular, one important aspect in accordance with the present invention is that zinc ferrite, a material which with proper adjustments of the zinc content can be made to have nearly paramagnetic properties at or about operating temperatures of the device to adjust its resonance point well into the microwave range. Accordingly, by using zinc ferrite in one of the layers  23   a ,  23   b ,  24   a ,  24   b , one or both of the ferrite filters  21 ,  22  advantageously provide desired impedance characteristics at higher frequencies than in typical soft ferrite filters. 
   Specifically, it has been found that a somewhat iron deficient zinc ferrite is well suited for this purpose, which may include about 30-40 percent by weight ZnO and about 60-70 percent by weight Fe 2 O 3 , for example, though other percentages may also be used. It will be appreciated that the amount of ZnO used will affect both the resonance point of the filter device as well as the magnetic characteristics thereof. The impedance versus frequency characteristics for a single ferrite filter in which both ferrite layers include such iron deficient zinc ferrite are shown in the plot  40  of the graph of FIG.  4 . As may be seen, the resonance point of this filter is between 11 and 12 GHz, well beyond the attenuation range possible with typical prior art ferrite filters. 
   Regarding the advantageous high frequency attenuation, or insertion loss, of the iron deficient zinc ferrite material, applicants theorize, without wishing to be bound thereto, that this insertion loss is caused by a destructive interference of propagation and internally reflected electromagnetic waves in the ferrite filter, or as surface waves operating on the “skin” or near surface volume of the ferrite filter which may be adjacent to the conductor path  25 ,  26 ,  69 ,  70  or  71 . With this in mind, prototype ferrite filters made as described above with iron deficient zinc ferrite which have insertion losses in the 10-12 GHz and 15 GHz range were constructed and analyzed, and some general design considerations may be made based upon the operational characteristics thereof. 
   First, it will be appreciated by those of skill in the art that the wavelength in a medium in which an electromagnetic wave is propagating is related to the permeability and permittivity of the medium. Accordingly, the insertion loss null of a given filter will depend on the permeability and permittivity of the ferrite materials used. Moreover, the insertion loss null will also be dependent on conductor length and part size, as will also be appreciated by those of skill in the art. 
   Thus, for a given application, it will be important to select an initial combination of ferrite materials, conductor lengths, and part sizes to achieve nulls near the desired frequencies. Other ferrite materials with slight changes in permeability and/or permittivity may then be used to further refine the position of these nulls since the wavelength will change. Performance curves may then be constructed for candidate ferrites and the position of a null may be selected therefrom, as will be understood by those skilled in the art. 
   If one of the ferrite filters  21 ,  22  includes the above noted iron deficient zinc ferrite material, one or more layers of the other ferrite filter may include a ferrite material with impedance versus frequency characteristics which are complementary to those of the iron deficient zinc ferrite filter (e.g., lower than) to thus provide a broadened attenuation frequency range. By way of example, the other ferrite material may include copper nickel zinc ferrite, which provides desired impedance characteristics at lower frequencies. 
   The impedance versus frequency characteristics for a filter device  20  in which the layers  23   a ,  23   b  or  24   a ,  24   b  of one filter device  21 ,  22  include the above described iron deficient zinc ferrite and the layers of the other filter device include copper nickel zinc ferrite are shown in the plot  50  of the graph of FIG.  5 . As may be seen, the filter device  20  has nulls between 6 and 7 GHz and between 17 and 18 GHz. Of course, those of skill in the art will appreciate that various types, amounts, and/or compositions of ferrite materials may be used to provide desired impedance versus frequency characteristics in different applications, as noted above. Specific examples including process details for making various iron deficient zinc ferrite and copper nickel zinc ferrite materials are provided below. 
   An alternate embodiment of a filter device  60  in accordance with the present invention is now described with reference to FIG.  6 . The filter device  60  includes three ferrite filters  61 ,  62 ,  63 , each of which includes respective pairs of ferrite layers  65   a  and  65   b ,  66   a  and  66   b , and  67   a  and  67   b  and lateral conductors  69 - 71  extending therebetween. Moreover, rather than using vertical end conductors  27  to provide the series connection between the vertical end conductors as in the filter device  20  noted above, vias  72 ,  73  are used for this purpose. That is, the via  72  (illustratively shown in lower and upper portions  72   a ,  72   b  in the unassembled view of  FIG. 6 ) extends between the ferrite filters  61 ,  62  to connect the lateral conductors  69 ,  70  in series. Similarly, the via  73  (illustratively shown as lower and upper portions  73   a ,  73   b ) extend between the filters  62 ,  63  to connect the lateral conductors  70 ,  71  in series. 
   The vias  72 ,  73  may be formed using known fabrication techniques, as will be understood by those of skill in the art. One approach is to form holes in the appropriate locations of the green layers  65   b ,  66   a ,  66   b , and  67   a  and then fill these holes with the conductive ink used for screen printing the lateral conductors  69 - 71 . Of course, the filter  60  may also include end conductors similar to the first and second end conductors  28 ,  29  described above to provide connection with other circuit elements. 
   The ferrite filters  61 - 63  may all include different ferrite materials to provide different impedance versus frequency characteristics, or two or more of the ferrite filters may include the same material. By way of example, the filters  61  and  63  may include the above noted iron deficient zinc ferrite material, while the filter  62  may include the copper nickel zinc ferrite material. Other zinc ferrites and conductor material types, arrangements, etc. are also possible and are contemplated by the present invention, as will be appreciated by those skilled in the art. 
   A method aspect of the invention for making the above described filter device  20  includes arranging the ferrite layers  23   a ,  23   b ,  24   a ,  24   b  in vertically stacked relation with the respective lateral conductors  25 ,  26  extending between adjacent pairs of the ferrite layers, as previously noted above. As noted above, the ferrite layers may be ferrite tape layers cut to a predetermined size, and the lateral conductors  25 ,  26  may be screen printed thereon. Furthermore, conductive paste may be applied to the appropriate locations on the ends of the ferrite filters  21 ,  22  to form the vertical end conductor  27  and first and second end conductors  28 ,  29 . The ferrite layers  23   a ,  23   b ,  24   a ,  24   b  may then be laminated together, and the laminated assembly sintered to form the filter device  20 . 
   Of course, it will appreciated that various other steps may be included in place of, or in addition to, those briefly described above. For example, openings may be formed in the various ferrite layers and conductive paste placed therein to make the conductive vias  72 ,  73 , as in the embodiment illustrated in FIG.  6 . Other method aspects of the invention will also be appreciated based upon the foregoing description, and in view of the exemplary zinc ferrite material formation process details provided below. 
   EXAMPLE 1 
   Iron Deficient Zinc Ferrite Material Made from Raw Materials 
   1.0 Product Formulation and Mixing Requirements for ZF10 Calcine. 
   1.1 Mix the following materials using an Elrich model R-07 (or other suitable mixer): 
   
     
       
         
             
             
             
             
             
           
             
                 
                 
             
             
                 
               Raw 
                 
                 
                 
             
             
                 
               Material 
               Supplier 
               Grade 
               Weight 
             
             
                 
                 
             
           
          
             
                 
               Iron 
               Thyssen 
               Premium 
               110.2 ± 
             
             
                 
               Oxide 
               Krupp 
               Ground 
               1.0 lbs. 
             
             
                 
                 
               Stahl 
               Thyssen 
             
             
                 
               Zinc 
               Zochem 
               Zoco 103 
               81.9 ± 
             
             
                 
               Oxide 
                 
                 
               0.6 lbs. 
             
             
                 
                 
             
          
         
       
     
   
   1.2 Pull sample for x-ray on the first two mixes of each lot to ensure proper mixture, consistency, etc. Mixing times are as follows: 
                                               Step   Time/Quantity   Comment                          1. Pre-mix on   ˜1 minute               high speed:           2. Add water:   ˜3.5 gallons   Adjust as necessary                   to achieve pellet                   integrity.           3. Mix on high   ˜6 minutes   Adjust as necessary           speed:       to achieve pellet                   integrity.           4. Mix on low   ˜4 minutes   Adjust as necessary           speed:       to achieve pellet                   integrity.           5. Pan on:   As needed to               achieve ˜0.1-               .02″ pellet                        
2.0 Drying.
 
   2.1 Dry in suitable dryers under the following condition: 
   
     
       
         
             
             
             
           
             
                 
                 
             
           
          
             
                 
               Temp: 
               425° F. 
             
             
                 
               Time: 
               24 hours (minimum) 
             
             
                 
                 
             
          
         
       
     
   
   2.2 Another option is to allow the material to dry next to a kiln, for example. 
   3.0 Calcining. 
   3.1 Perform Calcining using a rotary calciner as follows: 
   
     
       
         
             
             
             
           
             
                 
                 
             
             
                 
               Tolerance 
               Test Frequency 
             
             
                 
                 
             
           
          
             
                 
             
          
         
         
             
             
             
             
          
             
                 
               Bulk Density: 
               1.50 g/cc 
               1 time per barrel 
             
             
                 
               (g/cc) : 
               min 
             
             
                 
               Temp. (Zone 1): 
               *1050 ±5 ° C. 
               Every two hours 
             
             
                 
               Temp. (Zone 2): 
               *1050 ±5 ° C. 
               Every two hours 
             
             
                 
               Temp. (Zone 3): 
               *1050 ±5 ° C. 
               Every two hours 
             
             
                 
               Feed Set: 
               TBD 
               Every two hours 
             
             
                 
               Feed Rate 
               25-35 lbs/hr 
               Every two hours 
             
             
                 
               (Exit): 
             
             
                 
               RPM (tube) : 
               2 
               Once per shift 
             
             
                 
               Angle 
               2° 
               Once per shift 
             
             
                 
               Draft/Baghouse 
               TBD 
               Every two hours 
             
             
                 
               (inches water 
             
             
                 
               column) 
             
             
                 
               EMU/g 
               *&lt;3 
               Every two hours 
             
             
                 
                 
             
             
                 
               *Critical Parameter  
             
          
         
       
     
   
   EXAMPLE 2 
   Iron Deficient Zinc Ferrite Made from Pre-Processed Zinc Ferrite Material 
   1.0 Lot Make-Up 
   ZF-10 Calcine—99% 
   Bi 2 O 3 —1% 
   2.0 Mill with Attritor (Model S100) 
   2.1 Rinse attritor thoroughly prior to use. 
   2.2 Calcine Charge: 
   
     
       
         
             
             
             
           
             
                 
                 
             
           
          
             
                 
               ZF-10 Calcine Wt. 
               800 lbs 
             
             
                 
               Bi 2 O 3 : 
                8 lbs 
             
             
                 
               Water: 
               33 gallons 
             
             
                 
               Colloid 102: 
               1000 cc 
             
             
                 
               Foamblast 338 
                80 cc 
             
             
                 
               (RossChem): 
             
             
                 
                 
             
          
         
       
     
   
   2.3 Up to 4 gallons of water may be added to aid unloading (as pulp density permits). Also, 500 cc of colloid may also be added to each mill to aid in unloading. 
   
     
       
         
             
             
             
           
             
                 
                 
             
           
          
             
                 
               Mill 
               As necessary to achieve BET target 
             
             
                 
               Time: 
             
             
                 
               BET 
               *2.15-2.35 m 2 /g 
             
             
                 
               Target: 
             
             
                 
               Pulp 
               2450-2500 
             
             
                 
               Density: 
             
             
                 
                 
             
             
                 
               *Critical Parameter  
             
          
         
       
     
   
   2.4 Check pH on each attritor mill when the BET target has been achieved, and record results on attritor mill log. 
   3.0 Slurry Screening. 
   3.1 Screen all slurry transferred to the tank(s) with Sweco 30″ or other suitable screener. 
   Screen size: 150 MG (with backing wire) 
   4.0 Slurry Tanks. 
   4.1 Clean all slurry tanks thoroughly prior to use. All slurry transferred to tanks should have accurate weight and pulp density measurements. 
   4.2 Perform x-ray analysis on slurry samples. BET measurements are preferably performed on one sample (for reference purposes). 
   5.0 Tank Adjustments. 
   5.1 Raw Materials (tank adjustments): 
   
     
       
         
             
             
             
           
             
                 
                 
             
           
          
             
                 
               Iron Oxide 
               Premium Ground 
             
             
                 
               (Fe2O3) 
               Thyssen (see 1.1 
             
             
                 
                 
               above) 
             
             
                 
               Zinc Oxide 
               Zoco 103 (Zochem) 
             
             
                 
               (ZnO) 
             
             
                 
                 
             
          
         
       
     
   
   5.2 Water Addition: total adjustment lbs×0.04=gallons of water. 
   5.3 Perform pH check on “dry as is” slurry (before binder addition). 
   6.0 Binder Addition: 
   
     
       
         
             
             
             
           
             
                 
                 
             
             
                 
                 
               Part 
             
             
                 
               Vendor 
               Number 
             
             
                 
                 
             
           
          
             
                 
             
          
         
         
             
             
             
             
          
             
                 
               Binder: 
               Southern 
               SCT-227 
             
             
                 
                 
               Chemicals 
             
             
                 
               Plasticizer: 
               Southern 
               SCT-471 
             
             
                 
                 
               Chemicals 
             
             
                 
                 
             
          
         
       
     
   
   6.1 Mix binder in a clean PVA tank or a clean barrel using a portable mixer. 
   6.2 Add Colloid  102  to tank while the binder/plasticizer is mixing (at least 30 minutes before the binder is added). Colloid addition is calculated by multiplying the calculated tank weight of the calcine mills by 0.50, which is rounded to the nearest 50 cc. 
   6.3 Binder/plasticizer should be added to the PVA tank or barrel in the specified amount. 
   6.4 Agitate binder/plasticizer for 30 minutes before unloading into the slurry tank. 
   6.5 Agitate the slurry in the tank for 1 hour after the binder has been added. 
   6.6 Record binder/plasticizer weights, lot # and barrel number on attritor log. 
   7.0 Spray Drying. 
   7.1 Clean spray dryer and cyclone thoroughly prior to use. 
   7.2 Add 200 cc of Foamblast before spray drying. 
   7.1 Material conditions, dryer conditions and in process testing. 
   
     
       
         
             
             
             
             
           
             
                 
                 
             
             
                 
                 
                 
               Test 
             
             
                 
               Parameter 
               Value 
               Frequency 
             
             
                 
                 
             
           
          
             
                 
               Pump Pressure: 
               800-950 
               Each 
             
             
                 
                 
                 
               Barrel 
             
             
                 
               Pulp Density (g/1000 
               2100-2200 
               Each 
             
             
                 
               cc): 
                 
               Barrel 
             
             
                 
               Product Temperature 
               *95-105 
               Each 
             
             
                 
               (C): 
                 
               Barrel 
             
             
                 
               Orifice: 
                    0.047-0.051″ 
               Every Lot 
             
             
                 
                 
               (0.049° nom.) 
             
             
                 
               Swirl Chamber: 
               SG 
               Every Lot 
             
             
                 
               Draft/Cyclone (#2 
               0.1-1.2 
               Each 
             
             
                 
               dryer): 
                 
               Barrel 
             
             
                 
               Draft/Baghouse: 
               6.0 Max 
               Each 
             
             
                 
                 
                 
               Barrel 
             
             
                 
               Inlet Temperature 
               *500-525  
               Each 
             
             
                 
               (F): 
                 
               Barrel 
             
             
                 
               Outlet Temperature 
               230-280 
               Each 
             
             
                 
               (F): 
                 
               Barrel 
             
             
                 
               pH (Slurry): 
               TBD 
               Each 
             
             
                 
                 
                 
               Barrel 
             
             
                 
               Bulk Density: g/cc: 
               0.75-1.00 
               Each 
             
             
                 
                 
                 
               Barrel 
             
             
                 
               60 Mesh Sleeve (5 
                3-10% 
               Each 
             
             
                 
               minute tap): 
                 
               Barrel 
             
             
                 
                 
             
          
         
       
     
   
   7.2 Screen slurry via slurry filter (mesh size=20 MG) 
   8.0 Screening. 
   8.1 Exemplary screener—Rotex (Model 12A)
         Top Screen: HC-7 212/70   Bottom Screen: None       

   8.2 Coarse material should be re-screened 2 times. 
   8.3 Unload product into barrels and check samples for moisture. If product passes moisture test, package in bulk bags per print specifications. 
   8.4 If product fails moisture test, place barrels in dryers for two hours. Set temperature to 150° F. The operator should use his best judgment to determine necessary drying time. 
   8.5 Final analysis may be performed on dried samples. 
   EXAMPLE 3 
   Copper Nickel Zinc Ferrite Material Made from Raw Materials 
   1.0 Dry Mix Composition (Raw Pellets). 
   1.1 Normalize elements below to composition specified. 
                                       Nominal EXZN           FE-235 final                                                    MnO:    0.15 wt. %           Fe 2 O 3     64.91 wt. %           NiO    0.11 wt. %           CuO    0.02 wt. %           ZnO   34.81 wt. %           Bi 2 O 3      0.00%           SiO 2      0.00%                        
2.0 Final Composition Adjustment.
 
   2.1 Maximum tank adjustment percentage on final composition adjustment: 3.00%. 
   2.2 Re-normalize elements below to composition specified. 
                                       Nominal EXZN           FE-235 final                                                    MnO:    0.15 wt. %           Fe 2 O 3     64.91 wt. %           NiO    0.11 wt. %           CuO    0.02 wt. %           ZnO   34.81 wt. %           Bi 2 O 3      0.00%           SiO 2      0.00%                        
3.0 Water Addition.
 
   3.1 Total adjustment (lb.)×0.04=gallons of water. 
   4.0 Mill Time. 
   4.1 Additions&lt;1.0%=15 minutes. 
   4.2 Additions&gt;1.0%=30 minutes. 
   5.0 BET Measurement (#2 Quantasorb). 
   5.1 Calcine Mills: 2.15-2.36 m 2 /g (once Coulter reaches 2.80 microns (ferrite)). 
   6.0 Reference Part Print for Final Product Specifications. 
   It will therefore be appreciated that filter devices in accordance with the invention which provide attenuation well above 2 GHz may be constructed in a convenient leadless chip that may easily be used in circuit applications. In particular, it is anticipated that device footprint sizes as low as 0.25 inches square by 0.25 inches in height or smaller may be achieved in accordance with the present invention. 
   Many modifications and other embodiments of the invention will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is understood that the invention is not to be limited to the specific embodiments disclosed, and that modifications and embodiments are intended to be included within the scope of the appended claims.