Transponder including a fluid cushioning medium and a method for its production

Transponder A,B! formed of a bottom-closed elongate tubular enclosure 12! having a mouth 12'! at an upper end and circuit-receiving space within the enclosure for fully receiving an electronic transponder circuit assembly 15!. A cap 14,114! closes the mouth, the enclosure and cap each being of tough synthetic resin material which will not be damaged by being dropped and is intrinsically capable of absorbing shock to a substantial degree when so dropped. The circuit assembly is completely immersed in silicone oil or gel cushioning medium 16! so that it completely surrounds the circuit assembly in all directions, the cushioning medium providing absorption of impact energy. The silicone cushioning medium when within the closure has its fluid level extending above the seal and above an upper end 15'! of the circuit assembly. The cap is hermetically joined to the enclosure by ultrasonic welding. The transponder repeatedly survives a 2-meter drop test without failure of the circuit assembly. Method for assembling the transponder involves introducing silicone fluid is introduced into the enclosure using a dispensing needle having a tip placed at a closed bottom of the enclosure in order to minimize the creation of air pockets in the silicone, and the predetermined volume of silicone fluid so dispensed is slightly greater than volume available for the silicone fluid after introduction of the circuit assembly.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to compact radio frequency transponders of the type 
known to be useful for security and information storage, access control, 
validation, identification, for example, and comparable other purposes. 
Such transponders may for such purposes be carried by a person or animal 
(as by tissue implantation) or on or within or about a vehicle for and 
thus typically require a miniaturized construction which incorporates 
transmitting/receiving circuits in a compact case. 
2. Related Art 
A compact RF transponder of the foregoing type and method for its 
production will be found disclosed in co-assigned U.S. Pat. No. 4,992,794, 
which is hereby incorporated by reference. Salient features of such prior 
transponder are represented in FIG. 3 of the present drawings. Any such 
compact RF transponder of this and related kinds used for purposes of the 
foregoing exemplary type are herein referred to simply by the term 
transponder. The transponder may include a hybridized electronic circuitry 
capable of transmit/receive operation, as by using FSK modulation, to 
transmit/receive digital information carrying the necessary intelligence, 
and may be an active or passive device. 
When the transponder circuity is housed in an enclosure made of glass, the 
transponder may not be able to survive a drop, such as determined by 
2-meter drop test wherein the unit is dropped from a height of 2 m to 
concrete. Glass cracking or shattering is one possible failure mode. 
Another possible failure mode is damaging transfer of impact shock through 
rigid glass or other material of the enclosure to the fragile electronics 
circuitry within the enclosure, which may be referred to as the package. 
This shock may damage or destroy the circuitry, particularly the antenna, 
and thus prevent or interfere with transponder operation, such as making 
the transponder unreadable by interrogation devices or circuits. 
Although the transponder circuity could be housed in an enclosure made of 
plastic, as in said U.S. Pat. No. 4,992,794, 
Referring to FIG. 3, such transponder according to said U.S. Pat. No. 
4,992,794 is generally designated 1 and has a plastic tube 2 closed with a 
bottom and shut off at the opposite end by a cap 4. Tube 2 has an 
electronic circuit element 5, e.g., as a chip, and other elements shown in 
said U.S. Pat. No. 4,992,794 but not shown in FIG. 3, viz., connected as 
by wire leads to windings of a ferrite core and to a capacitor. It is 
noted that the transponder may still be subject to breakage even when the 
plastic enclosure is partially filled with a filler material 6 such as 
polysiloxane. 
SUMMARY OF THE INVENTION 
It is in view of the above problems that the present invention was 
developed. Accordingly, the present invention is intended for such a 
technical application by providing an improved transponder having a 
package formed of so-called plastic, i.e., synthetic resin material, 
namely a suitable polymerized composition, which polymer is tougher than 
glass; which will absorb impact energy; which is resistant to cracking; 
which will be less likely to transfer shock to the electronics within the 
package; and which incorporates a cushioning medium, as in the form of 
silicone oil or gel, within the package for surrounding the electronics 
and protecting it and immobilizing it by submergence of the electronics 
within the cushioning medium. 
The present invention also involves an advantageous specifically preferred 
process for preparing and assembling the transponder. 
A specific polymer is preferred, and so constructed thereof, the 
transponder is found to be able to repeatedly tolerate 2-meter drop 
testing. 
These and other objects and of the invention will be apparent or are 
pointed out in the following columns.

DETAILED DESCRIPTION OF PRACTICAL EMBODIMENTS 
Referring to FIG. 1, a transponder in accordance with the proposed 
construction is designated generally by reference character A and has a 
tubular enclosure 12 having generally cylindrical wall configuration and 
referred to in this description as tube 12, which is formed of synthetic 
resin material, namely a suitable polymerized composition, which polymer 
is tough and resilient and will not be damaged by being dropped, as well 
as being intrinsically capable of absorbing shock to a substantial degree. 
A specific polymer is preferred to provide requisite toughness, namely a 
synthetic resin commercially available under the tradename VECTRA. 
The main body of such material, as may be formed according to preference by 
being injection molded, extruded, thermoformed or injection molded, and 
thereafter machined if necessary, is preferably in the form of an elongate 
closed tube as shown in said U.S. Pat. No. 4,992,794, being exemplary of 
circular cross section, and having a rounded closed bottom as therein 
illustrated, but closed at the opposite end by a cap 14, so that both ends 
may be of the same or similar rounded configuration as that shown in FIG. 
1 for the end having cap 14, or the opposite end may be squared off in 
accordance with preferred usage for the ultimate technical application of 
the transponder. 
Tube 12 has within its elongate interior space, which space is of 
cylindrical configuration, an RF transponder circuit assembly 15 as of 
integrated circuit chip type, in accordance with the latter patent 
reference, which is hybridized electronic circuitry capable of 
transmitting or receiving or both transmitting or receiving signal 
information as in digital form for carrying or conveying or signifying the 
necessary intelligence, it being thus desired to protect the elongate 
circuit assembly 15 and its related elements, such as an antenna within 
tube 12 and other elements as shown in said U.S. Pat. No. 4,992,794 but 
not shown in FIG. 3, viz., connected as by wire leads to windings of a 
ferrite core and to a capacitor. That is, it is desired to protect the 
electronic circuit and any circuit elements in their position extending 
along and within tubular enclosure 12 against damage by shock transmitted 
to the transponder, for example, as when dropped such as might jeopardize 
or interfere with or otherwise affect operation. 
Circuit assembly 15 terminates within tube 12 with an upper end 15' of the 
circuit assembly located proximally of a corresponding peripheral end face 
12' of the lip or opening of tube 12, and thus circuit end 15' will not 
project beyond tube edge 12', for reasons presently appearing. 
According to one embodiment, cap 14 is formed of the same material as tube 
12 but of greater thickness to provide a dome-shaped interior 14a and a 
peripheral inner flange lab defining an L-shaped seat 14c including a flat 
portion 14c', whereby seat 14c may receive a corresponding portion of tube 
12 and with peripheral end face 12' of the tube opening being tightly 
fitted against seat portion 14c', to which it will be sealed as described 
below. 
Surrounding circuit assembly 15 is silicone oil or gel 16 which serves as a 
surrounding cushioning for the circuit assembly which is completely 
immersed therein. Thus, the fully submerged electronic assembly is 
surrounded in all directions by this fluid cushioning medium of silicone 
oil or gel, hereinbelow referred to simply as silicone, which will provide 
absorption of impact energy. 
Transponder version A is prepared in the following manner. Tube 12, which 
is of bottom-closed character, is filled with a predetermined volume of 
the silicone less than the volume of tube 12. Such predetermined volume of 
the fluid silicone, whether oil or gel, is such than when the electronic 
assembly 15 is inserted within the tube, the upper end 15' of the circuit 
assembly will be below the mouth of tube 12, and so that circuit assembly 
15 will not only be completely submerged but also will cause the surface 
of the silicone to be at or a point slightly above the lip surface 12' of 
the tube. Thus, as shown, the upper end 15' of the circuit assembly is 
located proximally of the peripheral end face 12' of the tube lip, i.e., 
the open mouth of the tube, being in any event not higher than or at or 
most preferably slightly below the level of the mouth or tube lip, to 
prevent contact of cap 14 with end 15' of the circuit assembly during 
subsequent sealing. 
The predetermined volume of silicone introduced into the tube, preferably 
by method using a dispensing needle having a tip placed at the closed 
bottom of tube 12 in order to minimize the creation of air pockets in the 
silicone, may be slightly greater than the volume available for the 
silicone after introduction of circuit assembly 15, so that silicone can 
exude onto lip 12' of the tube. Cap 14 is then placed in contact with tube 
12 in the orientation depicted in FIG. 1, with volume of the fluid in tube 
12 being such that inserting the cap may cause fluid to be exuded from the 
enclosure from the tube mouth, i.e., onto the tube lip 12'. Then, cap 14 
is ultrasonically welded to tube 12 to bring about a hermetic seal between 
faces 12' and 14c'. Such ultrasonic welding can be done through any 
silicone on the tube lip 12', and such maximizes the amount of silicone in 
the enclosure. 
If cap 14 is of material different from the material constituting tube 12, 
it must similarly be of tough synthetic resin material resin material 
which will not be damaged by being dropped and will be intrinsically 
capable of absorbing shock to a substantial degree when so dropped; and it 
must be capable of being ultrasonically welded to tube 12 for closure to 
bring about requisite hermeticity. 
From the foregoing it is seen that the silicone cushioning medium when 
within the closure having an upper fluid level, i.e., after insertion of 
the circuit assembly, the meniscus of the silicone extending above the 
seal and also above upper end 15' of the circuit assembly. 
Although cap 14 includes internal dome 14a, to provide a dead space 18 over 
a meniscus-forming surface 17 of the silicone in which space air (or other 
fill gas) may remain, as for expansion, a different cap configuration may 
be used, as shown in the embodiment of FIG. 2. 
Referring to FIG. 2, a version generally designated by reference character 
B includes tubular package 12 with circuit assembly 15 to be fitted a cap 
114 with flat configuration. Cap 114, formed of the same material as cap 
14, thus comprises a disc 114a from which depends an annular flange 114b 
fitted within the mouth of tube 12 in the same manner as the version of 
FIG. 1. The flat cap configuration eliminates a void or space over the 
surface of silicone 16. 
Transponder version B is prepared in the same manner as version A, it being 
understood that the volume of silicone 16 introduced into tube 16 is again 
slightly greater than the volume available for the silicone after 
introduction of circuit assembly 15, so that silicone will exude onto lip 
12' of the tube and, by observing precautions, cap 114 is placed in 
contact with tube 12 in the orientation depicted in FIG. 2 and 
ultrasonically welded to tube 12 to bring about a hermetic seal between 
face 12' and flange 114b by ultrasonic welding through any silicone on 
face 12', and leaving substantially no void or dead space. 
From the foregoing it is seen that the silicone cushioning medium when 
within the enclosure has an upper fluid level, i.e., after insertion of 
the circuit assembly, the meniscus of the silicone extending above the 
seal and also above upper end 15' of the circuit assembly, and any excess 
silicone being thus exuded during insertion of the cad flange 114b into 
the mouth of tube 12. 
The materials for tube 12 and cad 114 are of the same character as 
described for embodiment A. 
Preferably, as to each version, the plastic tube and cap are all of the 
same material as described above, which need not have a rough surface, the 
toughness of the material being a desirable mechanical property and 
capability of being dropped without damage and of absorbing shock being in 
any event being comparably important. 
Accordingly, various plastics having requisite toughness might be employed 
other than that described above. 
Circuit assembly 15 may be coated with a layer of polyxylylene as an 
additional barrier to compounds or plastics that might tend to interfere 
with electrical performance. 
Referring now to FIGS. 4 and 5, there is shown two alternate cap 
configurations which were successfully welded to a receiving tube such as 
tube 12 shown in FIGS. 1 and 2. The resulting configuration of the tube 12 
and the alternate cap embodiments is shown in FIG. 6. As shown, using the 
cap configurations of FIGS. 4 and 5 may result in an offset lip portion 
116 which extends into tube 12 and is slightly spaced from the wall of 
tube 12. 
The following example illustrates the effectiveness of the invention. 
EXAMPLE 
Two transponders with tubes and caps made in accordance with the foregoing 
teachings were assembled as described, the transponder circuits being of 
the type noted hereinabove. The units were tested for performance by a 
2-meter drop to concrete. During each drop, the transponders typically 
bounced two to four times upon dropping to concrete. Both units were 
readable, i.e., exhibiting satisfactory RF performance, after 10 such 
drops each, with no damage to the plastic package, and thus repeatedly 
survived a 2-meter drop test without failure of the circuit assembly. 
In view of the foregoing description of the present invention and 
embodiments and methods it will be seen that the several objects of the 
invention are achieved and other advantages are attained. 
All matter contained in the foregoing description or shown in the 
accompanying drawings shall be interpreted as illustrative rather than 
limiting. Thus, the breadth and scope of the present invention should not 
be limited by any of the above-described exemplary embodiments, but should 
be defined only in accordance with the following claims appended hereto 
and their equivalents.