Untitled record

(54) Title: 'TRANSPONDER OVERMOLDED TO AN ELECTRONIC SYSTEM OF

IDENTIFICATION. E. METHOD FOR FORMING AN OVERMOLDED TRANSPONDER FOR AN ELECTRONIC IDENTIFICATION SYSTEM (73) Holder: AVID IDENTIFICATION SYSTEMS. INC .. North American Company. Address: 3179 Ilamner Avenue, Suite 5, Norco, California 91760, United States (US).

(72) Inventor: JAY YOAKUM, Engineer. Address: 3179 Ilamner Avenue, Norco. California 91760. United States.

Validity Term: 10 (ten) years from 12/02/2014, subject to legal conditions.

Issued: December 2, 2014.

Digitally signed by Júlio César Castelo Branco Reis Moreira Patent Director ^4tTRANSPONDER OVERMOLDING TO AN ELECTRONIC IDENTIFICATION SYSTEM, AND, METHOD FOR FORMING AN OVERMOLDING TRANSPONDER TO AN ELECTRONIC IDENTIFICATION SYSTEM ”

Field of invention

The present invention relates generally to products and materials in the field of overmoulding of electronic components and devices featuring ferrite cores, powder metal cores and high energy magnetic product cores, and, more particularly, materials for, and products prepared by overmoulding electronic components that incorporate such materials. The invention has particular applications in the field of electronic identification components and devices (EID: e / ec fore identificatiori) or (RFID: radio frequency Identification) manufactured through the process of 1 st age.

Fundamentals of the invention

Ferrite cores. powdered metal cores and high-energy product magnets, such as samarium cobalt and neodymium-ferroboro magnets, have certain advantageous magnetic and electric field properties that make them ideal for use in certain types of electronic components and circuits. These types of materials are frangible, although the materials can be manufactured in a variety of ways and generally have good mechanical characteristics under compression loads. However, these frangible materials are generally weak in terms of tensile strength, tending to crack or fracture when subjected to tensile loads, bonding loads or relatively modest impact loads. Cracks and fractures within manufactured frangible materials can substantially reduce the beneficial properties of magnetic and electric fields, negatively impacting their desirable characteristics. Thus, the maximum use of these types of frangible materials requires consideration of, and accommodation for, their limiting physical properties.

An exemplary application that can benefit from the use of a ferrite core as part of an electronic circuit is an electronic identification (EID) or radio frequency identification (RFID) transponder circuit used in EID or RFID systems. EID and RFID systems generally include an emitting signal or “reader” that is capable of emitting a high frequency signal in the kilohertz (kHz) frequency band or an ultra high frequency signal in the frequency band megahertz (MHz). The signal emitted from the reader is received by a transponder that is activated in some way when the reader detects or receives the signal. In EID and RFID systems, the transponder generates a signal or inductively engages the reading to allow the reader to obtain memory identification codes or data from the transponder.

Generally, the transponder of an EID or RFID system will include a signal processing circuit that is connected to an antenna, such as a coil. For certain applications, the coil can be wound around a core of ferrite, powdered metal, or magnetic. The signal processing circuit can include a number of different operating components including integrated circuits, as known in the art, and many, if not all, operating components can be manufactured in a single integrated circuit that the main component of the signal processing circuit EID and RFID devices.

For example, certain types of "active" RFID transponders may include a power source, such as a battery, which can also be connected to the circuit board and the integrated circuit. The battery is used to energize the signal processing circuit during the operation of the transponder. Other types of transponders, such as transponders

Half Duplex (HDX), include an element to receive energy from the reader, such as a coil, and elements to convert and store energy, for example a transformer / capacitor circuit.

In an HDX system, the signal emitted by the reader is cyclized, turned on and off, inductively coupling to the coil when in the emitter cycle to charge the capacitor. When the signal emitted by the reader is interrupted, the capacitor discharges to the transponder circuit in order to energize the transponder which can emit or generate a signal that is received by the reader.

A Full Duplex system (FDX), in comparison, includes a transponder that generally does not include neither a battery nor an element to store energy. Instead, in an FDX transponder, the energy in the field emitted by the reader is inductively coupled to the transponder's antenna or coil and passed through a rectifier to obtain power to drive the transponder's signal processing circuit and generate a response to the reader concurrently with the emission of the signal emitted by the reader.

Notably, many different circuit designs for active, HDX and FDX transponders are known in the art and have been described in a number of issued patents, and therefore are not described in more detail here. Many of the types of EID and RFID transponders presently in use have particular benefits resulting from their ability to be embedded or implanted within an object to be identified in such a way that they are hidden from detection or visual inspection. For these applications, the entire transponder can be encapsulated in a sealed component, for example to allow implantation in biological items to be identified, or to allow use in submerged, corrosive or abusive environments. Thus, several references, including US Patent Nos. 4,262,632; 5,211,129; 5,223,851, 5,281,855 and

5,482,008 describe the complete encapsulation of several transponders inside a ceramic, glass or metallic container.

For an encapsulated transponder, it is general practice to assemble the transponder circuit and then insert the circuit into the glass, ceramic or metallic cylinder, one end of which is already sealed. The open end of a glass-type cylinder is generally closed by fusion using a flame to create a hermetically sealed capsule. Other types of glass, ceramic or metallic containers use a lid to seal the open end, the lid being glued or mechanically connected to the open end of the cylinder, as discussed, for example, in US Patent No. 5,482,008. In addition, as discussed in the patent previously indicated, to prevent the transponder circuit from moving inside the capsule, it is also known to use an epoxy material to connect the transponder circuit to the inner surface of the capsule.

As shown, for example, in US Patent No. 4,262,632 (incorporated herein by reference) the potential advantages of using E1D and RFID devices in biological applications, such as livestock identification, have been the subject of research for several years. As discussed in patent 4,262,632, studies show that a bolus EID transponder suitable for placement in the reticulum of a ruminant animal will remain in the reticule for an indefinite period if the specific weight of the bolus transponder is two or greater, and / or the total weight of the bolus transponder exceeds sixty grams. Thus, for these applications, the bolus transponder generally requires a weight element because that of the EID circuit can generally be very small and even super-light, merely requiring the integrated circuit and antenna and a few other components. Therefore, it has been disclosed, for example in patent 4,262,632, how to incorporate a ferrite weight element into an encapsulant which also contains an EID transponder.

The design of a bolus transponder suitable for use in a ruminant animal can also benefit from the appropriate use of a magnet or ferrite core to increase the signal transmission characteristics of the transponder while providing the weight necessary to maintain the bolus transponder specific weight at two or greater, and / or to maintain the total bolus transponder weight exceeding sixty grams. However, to achieve widespread acceptance and use of bolus dc El D transponder devices for ruminant animals, devices also need to be designed and manufactured with an understanding of the physical and economic requirements of livestock application. Thus, although bolus transponders encapsulated in ceramics suitable for the reticle environment are being investigated, the cost of the fragile physical characteristics of ceramics impacts on their commercial acceptance. Thus, an encapsulant for making the capsule or involving transponders of

E1D that does not have the limitations of ceramic, glass or metallic encapsulants, particularly for bolus transponders, would be highly beneficial.

Summary of the invention

The present invention contemplates a method, apparatus and material for overmoulding electronic devices which may include ferrite core materials, powdered metal and magnetic cores and associated circuits, for example circuits for an EI D or RFID transponder, the encapsulant being a plastic, polymer or elastomer or other injection-moldable material compatible with the intended application environment. According to the invention, the wrapping material can be applied in an injection molding or extrusion molding process to overmould the transponder core and electronic circuits. In addition, the invention contemplates an unprecedented coating material, particularly useful for the protection of electronic components against environmental degradation.

Brief description of the drawings

Fig. 1 is a side cross-sectional view of a transponder including an overmoulded core manufactured in accordance with the present invention;

Fig. 2 is a cross-sectional view of the transponder of the

Fig. 1;

Fig. 3 shows a perspective view of the mold tool used for the overmolding process to manufacture the transponder of Fig. 1;

Fig. 4 shows a cross-sectional view through the mold tool of Fig. 3 during the initial stage of injection of overmoulding material into the mold tool;

Fig. 5 shows a second cross-sectional view of the mold tool of Fig. 3 showing a further stage in the molding process;

Fig. 6 illustrates another cross-sectional view of the tool of Fig. 3 showing a further stage in the molding process;

Fig. 7 illustrates another cross-sectional view of the tool of Fig. 3 showing the molding process in which core centering pins are retracted in the tool;

Fig. 8 shows a side view of an alternative configuration for a transponder that has not yet been coated with molding material:

Fig. 9 shows the front view of the transponder of Fig. 8; Fig. 10 illustrates the transponder of Figs. 8 and 9 placed inside the mold tool of Fig, 3 during the injection molding process at the same stage illustrated in Fig. 6;

Fig. 11 illustrates a frangible core element placed inside the tool of Fig. 3 during the injection molding process in the same stage as the step illustrated in Fig. 6;

Fig. 12 illustrates a cross-sectional view of a frangible core overmolded with an overmoulding material according to the process of the present invention;

Fig. 13 illustrates a perspective view of a transponder in an alternative design for the mold tool, and positioned on it by means of one or more centralizing elements during the overmolding process, Fig. 14 illustrates a perspective view of a centralizing element as shown in Fig. 13,

Detailed description of the preferred embodiment

Fig. 1 illustrates a side cross-sectional view of a transponder 10 prepared in accordance with the present invention, Fig. 2 illustrates a top view of transponder 10 of Fig. 1. Transponder 10 includes signal processing circuit, such as an integrated circuit 12, mounted on a circuit board 14 together with other circuit elements, such as a capacitor 16, The signal processing circuit can be an active transponder circuit, senii -duplexed (HDX) or fully duplexed (FDX).

The integrated circuit 12 and capacitor 16 are attached to the circuit board 14 and electrically coupled to a wire 18 formed into a coil 20, at the ends or ends 22 and 24 of the wire 18. In the embodiment illustrated in Figs. 1 and 2, the coil 20 is wound around a coil body 26 and then positioned on a core 30, the circuit board 14 being attached to one end of the core 30 to form a transponder assembly 10a. As discussed below, the transponder assembly 10a can preferably be overmoulded with an injection molding material 32, which can be a plastic, polymeric or epoxy material, to form the complete transponder 10.

The relative axial location of coil 20 around core 30 can be important for the optimal operation of transponder 10. Specifically, transponder 10 preferably includes a tuned combination of coil 20 and capacitor 16. Generally, on a transponder, the tuning is performed by matching the length of the wire 18 that forms the coil 20 with the capacitance of the capacitor 16. However, when the wire 18 needs to be wound around the coil body 26 and installed on the core 30, the exact length of the wire 18, as well as its inductance, cannot be advantageously controlled during design and manufacture in order to allow the matching of the inductance of the coil 20 with the capacitance of capacitor 16 in order to tune the circuit of transponder 10. It should be considered that if the transponder is not properly tuned, the reading and data transfer capacities may be reduced.

However, it was found that, through the appropriate axial arrangement of the core 30 inside the coil 20, the transponder 10 can be tuned even without the optimization of the length of the wire 18, since the inductance of the coil 20 changes due to the axial positioning of the ferrite core 30. For a given set of design parameters for a combination of ferrite core 30 and coil 20, including the circumference and length of the core, as well as the length of wire 18 and capacitance of capacitor 16, it is possible to manufacture a transponder set 10a tuned through the axial movement of the coil 20 along the longitudinal axis of the ferrite core 30 until a tuned inductor / capacitor system is established and then attaching the coil body 26 and the coil 20 to the ferrite core 30 during the manufacturing process.

After the transponder assembly 10a circuit is assembled, the transponder assembly 10a is transferred to an injection molding machine. Specifically, the transponder assembly 10a is placed within the mold tool 40, 42 shown in Figs. 3-7. Fig. 3 illustrates a perspective view of the mold tool 40, 42 without the transponder assembly 10a installed inside it. The mold tool 40, 42, when closed, defines a cavity sized to receive the transponder 10a in preparation for overmoulding with the plastic, polymeric or epoxy injection molding material 32. However, it should be noted that, although illustrated as cylindrical, the inner walls of the mold tool 40, 42 may have surface characteristics to define a variety of shapes or patterns on the outer surface of the complete transponder 10, as may be beneficial for particular applications. Potential variations for the design of the outer shape of the complete transponder, for example, can be cylindrical, projectile-shaped, tapered on opposite sides, or a flattened oval, and the outer walls can be smooth, rough or bumpy , depending on the intended application.

As illustrated in Fig. 3, the mold tool 40, 42 includes inwardly projecting pins 46, 48 which serve to position and secure the transponder assembly 10a inside the mold tool 40, 42 during the injection process. Pins 46, 48 are configured so that they can be retracted by pin retractors driven by pressure response 50, 52 on the mold tool 40, 42 near the end of the injection cycle. At one end of the mold tool 40, 42 is a sprocket 56 through which the injection molding material 32 is injected by means of an injection molding machine (not shown). As also seen in the perspective view of Fig. 3, the mold tool 40, 42 can include guide pins 60 in tool 42 that align and mate with guide pin receiving holes 62 in tool 40 when the mold tool is closed, so as to maintain alignment of the tool mold 40, 42 during the injection cycle.

Figs. 4-7 illustrate cross-sectional views of the mold tool 40, 42 and a transponder set 10a positioned inside it, illustrating in sequence the advance of the plasticized molding material 32 during the injection molding process. As illustrated, pins 46, 48 act by positioning coaxially and centralizing the transponder assembly 10a within the mold cavity 44. When the hot, plasticized molding material 32 is injected under pressure by the injection molding machine, the plasticized molding material 32 penetrates flowing through the sprue 56 and imposes on the end 64 of the core 30 as shown by arrow 70, and compresses axially. the core 30 against the pins 48 which are positioned to contact the opposite end 66 of the transponder assembly 10a.

The molding material 32 then flows radially outwardly along the end 64 of the ferrite core 30 as illustrated by the arrows 72 in Figs. 4 and 5. When sufficient impression material 32 has been injected to fill the end of cavity 44, then the advancing face of impression material 32 proceeds longitudinally along the radially outer surface 68 of transponder assembly 10a, as shown by arrows 74 in Fig. 6. This overmoulding injection process only subjects the core 30 to compression loads, and does not subject the core 30 to tensile loads at any time during the entire injection cycle. Thus, through the overmoulding injection process of the present invention, the core 30 will not be damaged in a way that could decrease the electrical or magnetic properties of the core.

When the mold cavity 44 is completely filled with plasticized molding material 32, the internal pressure inside the cavity 44 increases. The pins 46, 48, which position the transponder assembly 10a inside the cavity 44, are connected with pin retractors 50, 52, which are pressure sensitive. When the pressure in the mold cavity reaches a predetermined level, pins 46, 48 retract on the wall of the mold cavity as shown by arrows 76, 78, and the space vacated by pins 46, 48 is filled with the molding material 32 as shown in Fig. 7. However, as the impression material 32 has already encapsulated transponder 10, the impression material 32 will hold transponder 10 in place during the curing or hardening stage of the injection molding cycle. Once the overmolding process is complete, the mold tool 40, 42 is opened and the complete transponder 10 is ejected.

Figs. 8 and 9 illustrate a side view and a front view, respectively, of an alternative embodiment of a transponder 80 that does not include the core 30 of transponder 10 of Fig. 1. Instead, for transponder 80, the wire that forms the coil 20 is wound around circuit board 14 on which integrated circuit 12 and capacitor 16 are mounted. The coil 20 is interconnected with the circuit board Meo and the integrated circuit 12 on it, via wires 22 and 24 generally as discussed above with respect to Fig. 1. Transponder 80 of Figs. 8 and 9 is generally much smaller than the set in Fig. 1. in the fact that it does not particularly include the core 30 and the additional weight and size corresponding to the use of the core 30 as illustrated in Fig. 1. However, the transponder 80 of Figs. 8 and 9 can also be overmoulded by a process similar to the process described with respect to Figs. 4-7.

To briefly illustrate this process, transponder 80 is illustrated within the assembled mold tool as shown in Fig. 10, which is comparable to the mold tool 40 and 42 discussed above with respect to Figs. 3-7. In the illustration in Fig. 10, the injection of the plasticized impression material 32 progressed to essentially the same stage as shown in Fig. 6, in that the advancing face of the molding material 32 is proceeding longitudinally along the outer surface of the transponder 80 and the pins 46 and 48 are centrally positioning the transponder 80 within the mold tool 40, 42. Again, the Outer configuration of the resulting overmoulded transponder assembly 80 can have any desired shape, limited only by the moldability of the shape. It should be noted that transponder 80 can be encapsulated in glass prior to the overmoulding process, however the glass capsule is not shown.

Fig. 11 illustrates another application for the overmolding process according to the present invention in which a frangible core 110 is placed inside the mold tool 40 and 42 of Fig. 3 and positioned by means of pins 46 and 48 during the process overmoulding. The overmolding process generally proceeds in the same manner as discussed above with respect to Figs. 4-7. Thus, Fig. 11 illustrates the stage that generally corresponds to Fig. 6, wherein the feed face of the plasticized molding material 32 is proceeding longitudinally along the outer radial surface of the frangible core 110. After the overmolding process is completed, the encapsulated frangible core 110 is ejected from the mold tool. The complete assembly 100, as shown in the cross-sectional view of Fig. 12, is a frangible core 110 encapsulated in an overmoulding material 112. In this embodiment, the frangible core can consist of ferrite, powdered metals or high-energy product magnets, such as materials of samadium cobalt and neodymium-iron-boron.

Fig. 13 illustrates a cross-sectional view of a transponder within an alternative design for the mold tool, and positioned there by means of one or more centralizing elements 120 during the overmolding process to manufacture the transponder like that of Fig 1. Centering elements 120 are designed with a central portion in the form of a sleeve 122, designed to fit around core 30. The centralizing elements 120 can also include fins or pins that project radially outwardly 124, which will center the transponder inside the tool during the overmolding process, and with this, the need for retractable pins illustrated and described above will be eliminated.

The overmolding process of the present invention encapsulates the frangible core 110 in a protective shell, which allows the use of frangible core materials in applications that the frangible physical property of these materials would not otherwise permit. For example, it would be possible to use samarium cobalt and neodymium-iron-boron magnets encapsulated in a relatively thin coating of plastic or polymeric materials provided by the overmoulding process on objects subject to shock, impact or vibration loads that would otherwise lead cracking, fracture or other physical or magnetic degradation of the magnetic core.

Fig. 14 illustrates a perspective view of the centralizing element 120, showing the sleeve 122 and the radially projecting fins or pins 124. The centralizing element 120 can be made of plastic, or the same type of material used to overmould the transponder. It is also considered that the centralizing element can simply be part of, or be connected to, the coil body 26 of Fig. 1, pins 124 simply extending radially outward from one end or both ends of the coil.

The material selected for the overmoulding of the transponder set 10a, transponder 80 or frangible core 110, depends in part on the specific application for the completed component. Various types of thermoplastic materials are available for the injection molding of these components. As used here, thermoplastic should be interpreted broadly, including, for example, linear polymers and straight chain or branched chain macromolecules that soften or plastify when exposed to heat and return to a hardened state when cooled to room temperatures. The term polymer should be widely understood to include any type of polymer, such as random polymers, block polymers, and graft polymers.

A large number of thermoplastic polymeric materials are considered useful for the overmoulding of transponders and frangible cores of the present invention. Thermoplastic materials can be used alone or in combinations. Suitable thermoplastic materials include, but are not limited to, rubber modified polyolefins, metallocene, polyether ester block copolymers, polyether amide block copolymers, thermoplastic urethanes, ethylene butane copolymers and maleic anhydride, hydrogenated maleic anhydride , polycaprolactone polyester, polyadipate polyester, polytetramethylene glycol ether, thermoplastic elastomer, polypropylene, vinyl, chlorinated polyether, polybutylene terephthalate, polymethylpentene, silicone, polyvinyl chloride, thermoplastic polyurethane, polycarbonate, polyurethane, polyamide, polybutylene, polyethylene and mixtures thereof.

Preferred thermoplastic materials include rubber modified polyolefins, metallocenes, polyetheramide block copolymers, and polyether ester block copolymers. Preferred rubber-modified polyolefins are commercially obtainable under the trade names VISTAFLEX® from Advanced Elastomer Systems Corporation, KRTON® from Shell Corporation, HIFAX® from Montell Corporation, X1019-28® from MA Hanna, SARLINK® from DSM Corporation, and SANTOPRENE® from Advanced Elastomer Systems Corporation. Preferred metallocenes are available from Dow Corporation under the trade names ENGAGE® and AFFINITY®. Polyether-amide block copolymers are available under the trade name PEBAX® from EIG Auto-Chem. Preferred polyether ester block copolymers are commercially available from DuPont under the trade name HYTREL®.

The thermoplastic overmolded wrappers of the present invention may also include a filler or ballast material suitable for adjusting the properties of the finished wrapper and / or transponder. For example, the density or specific weight of the overmolded casing can be adjusted with the addition of a suitable material, such as barium sulfate, zinc oxide, calcium carbonate, titanium dioxide, carbon black, kaolin, magnesium aluminum silicate , silica, iron oxide, glass beads and wollastonite. The cargo or ballast material can be present in an amount that will adjust the specific weight of the overmolded casing and the resulting transponder. Thus, the ballast material can be added in a range of about 5 weight percent to about 70 weight percent. In addition, the overmoulding material for the wrappers of the present invention may also include a plasticizer or other suitable additives, in order to improve processability and physical properties, such as the flow and ejectability properties of the overmoulding material. The plasticizer can be present in an amount that will adjust the flow properties during the injection molding process as needed for various applications.

Notably, for many of the types of injection molding materials previously indicated, particularly those whose density is increased with the addition of a densifier, the material in its plasticized state for the injection process has a low viscosity. Thus, the injection molding of these materials requires high injection pressures, leading, in turn, to imposing high efforts on the core materials during the injection process. For these reasons, minimizing or eliminating any load other than the compressive load on the frangible cores during the injection process is highly preferred.

The overmolded casing of the present invention preferably has a wall thickness between about 0.03 cm to more than 2.54 cm, however, for most applications, the wall thickness will preferably be less than 1.27 cm. Depending on the desired exterior shape of the completed assembly and the shape of the core, the wall thickness of the enclosure can be uniform or can vary significantly at the various locations around the core.

For a bolus 10 transponder intended for use in ruminant animals, it is necessary to have specific physical properties for the overmolding casing material. Thus, the overmolding wrapping material must be able to withstand the acidic environment in the digestive tract of a ruminant animal, and must be impervious to the microbes and enzymes that are active within the digestive tract of the ruminant animal, and should preferably have certain physical properties to allow easy handling and transport of the bolus transponder 10 prior to administration to the ruminant animal. Additionally, it is preferable that the bolus transponder 10 has a specific weight of at least 1.7 and, preferably, at least 2. Thus, it is generally desirable to use a ballast material to increase the volumetric density or the specific weight of the material overmoulding so that the overmoulding material has a specific weight that contributes to maintaining the specific weight of the bolus transponder 10 manufactured in the desired range.

Therefore, for a 10 bolus transponder, it was determined that a preferred combination of a thermoplastic polyester elastomer sold by DuPont under the trade name HYTREL 3078®, combined with barium sulfate as a densifier provides an acceptable combination for use as overmoulding for a bolus, and, in appropriate proportions, provides an injection molding material in the range of 1.7 to 2.

In order to provide a specific example, an acceptable overmoulding material may consist of a mixture of HYTREL 3078®, or a similar thermoplastic polyester elastomer (TPE: thermoplastic polyester elastomer), mixed with barium sulfate in a ratio of between about 20 to 90% TPE and 80% to 10% barium sulfate. This combination provides a suitable overmoulding material to form the casing of the bolus transponder 10. USP grade purified barium sulphate or barite fines are preferred as thickening agents because these materials were previously mixed with a carnauba wax and a bolus forming agent for ruminant animals, as described, for example, in US Patent No. 5,322 .692 shipped to the American Cyanamid Company.

The advantages of the preceding method for use in making boluses have been shown to be significant. First, the elimination of the need for ceramic encapsulation resulted in a substantial reduction in material costs compared to the costs of manufacturing a ceramic encapsulated bolus. Additionally, manufacturing costs, ie the bolus manufacturing costs, separate from the component costs, are substantially reduced due to the efficiency and automation associated with the injection molding process. Consequently, the overall cost savings relative to the equivalent costs of manufacturing the bolus transponder encapsulated in ceramic material can exceed 50%. Whereas ceramic encapsulated boluses have been shown to be relatively fragile so that they can be damaged if dropped or even shaken with each other during transport, the boluses encapsulated with thermoplastic polyester elastomer (TPE) overmolding material with barium sulfate showed physical characteristics that eliminated these problems.

In addition, the bolus transponder 10 of the present invention can be packed in bulk with a minimum of packaging material because the vibrations between the respective boluses during transport do not cause breakage. Finally, the combination of TPE-barium sulfate provides the physical characteristics required for use in the stomach of a ruminant animal. The combination is not affected by acidic conditions, is neutral for biological fauna, microbes and enzymes, and has a specific weight sufficient to maintain its retention in the stomach of the ruminant animal.

For transponder 80 of Figs. 8-10 which is intended for implant applications, it may be preferable to use a grade 6 medical grade epoxy. Alternatively, transponder 80 can be encapsulated in a glass material by means of known processes, and then be overmolded with the plastic or polymeric materials discussed here to provide additional strength, impact resistance, and strength, properties that glass encapsulated transponders lack.

Those skilled in the art will find that, reviewing the foregoing description of the present invention, other alternatives and variations of the present invention will become apparent. Thus, the scope of the protection provided should be limited only by the attached claims.