fig1 illustrates schematically an rfid 3 , together with its associated antenna 6 . the rfid 3 generally takes the form of an integrated circuit , packaged within a protective housing . many rfids transmit and receive using frequencies on the order of 900 mega - hertz , mhz . in general , many types of antenna are equal in length to a fraction of the wavelength used , such as ¼ , ½ , and so on , and the radiation pattern of the antenna will change , as the wavelength changes . similarly , the radiation pattern of the antenna will also change , if the length of the antenna changes , but the wavelength remains the same . this principle also applies to rfids : the radiation pattern will change if the antenna length changes , but the wavelength remains constant . one form of the invention utilizes this principle , by changing the length of the antenna of an rfid . this change alters the radiation pattern , in a manner which drastically reduces the reception and transmission range of the rfid . fig2 provides an example . initially , the rfid 9 utilizes antenna 12 at the left side of the figure . then , the antenna 12 is shortened , as on the right side of the figure . several approaches can be taken to changing the antenna length . fig3 illustrates one approach , wherein an electrical connection is added , which alters the antenna circuit , to shorten or lengthen the antenna . alternately , the added connection can change the antenna from one type to another . in any case , the change alters the radiation pattern in the desired manner . the electrical connection can be added in numerous different ways . for example , as in fig4 , the rfid can be equipped with two external contact pads 21 and 24 , as shown on the left side of the figure . these contact pads 21 and 24 are ordinarily coated with a protective substance 27 , such as the coating used to obscure options on lottery tickets . to de - activate the rfid , the user takes a two - step approach . one , if the coating 27 is present , the user removes it , as by abrading it using the edge of a coin , as done with lottery tickets . two , the user connects the two contact pads 21 and 24 together electrically . the connection can be made by soldering a jumper wire w wire between the two contact pads 21 and 24 , as shown at the upper right part of the figure . alternately , a conductive paint ( not shown ) can be applied between the two pads 21 and 24 . as another alternate , a metallic foil 25 can be overlaid onto the contact pads 21 and 24 . the foil can be attached by a conductive adhesive . the foil can be treated as a label , and can bear printed matter , such as the legend “ inactivated ,” as indicated in the figure . the added connection can change the length of the antenna , as fig4 indicates , thereby changing the radiation pattern , by effectively changing the length of the antenna , in terms of number of wavelengths of the radiation used . for example , the length can be changed from ¼ to 1 / 10 wavelength . the added connection can also change the type of the antenna , as fig5 indicates , thereby changing the radiation pattern . for example , as fig6 indicates at the left , the antenna 9 was initially a linear antenna , using a feed f . phantom conductors 9 a are not initially used . adding the jumper w , on the right of the figure , connection changes the antenna to a loop antenna , which has different properties than does a linear antenna . the loop antenna is fed by two feeds f . in another approach , the added connection changes the antenna length to zero , as in fig7 . the added jumpers w short - circuit the two ends of the antenna 9 together , through conductor 9 a . in another approach , an electrical connection is broken , thereby changing the length of the antenna , or the type of the antenna . in a sense , this approach is the converse of the addition of an electrical connection . for example , the rfid 3 on the left side of fig8 is equipped with external contacts 33 and 36 . these contacts 33 and 36 are connected together by a fine wire or thin metallic foil 39 . the wire / foil 39 can be protected by an optional protective layer 42 , again resembling the protective coating used on lottery tickets . to break the connection , the user abrades away the coating 42 and the wire / foil 39 , using a knife or the edge of a coin , producing the structure on the right side of fig8 , wherein the wire / foil 39 is now broken . this approach can change the length or type of antenna , by reversing the procedures described in connection with fig3 - 7 . for example , if the initial structure is that shown at the right side of fig6 , then breaking the jumper w as described in connection with fig8 can produce the structure at the left side of fig6 . in fig8 , the connection which is broken is external to , or on the surface of , the rfid 3 . in another approach to breaking a connection , the connection in question is located internal to the rfid . the connection can take the form of a fusible material such as that used in programmable read only memories , proms . fig9 illustrates a basic principle of a prom , and shows one programmable bit . initially , when the prom is manufactured , as on the left side of the figure , the fusible link 45 is intact . the output 48 is logical one , as indicated , because the output 48 is connected directly to five volts . to re - program the prom , a voltage is applied to points a and b . this voltage melts the fusible link 45 , breaking the connection between points c and d , and changing the output to a logical zero , as shown on the right side of the figure . to apply this principle , an rfid is equipped with a fusible link 51 , as that shown in fig1 . to change the radiation pattern of the antenna , a voltage is applied to points e and f , which melts fusible link 51 . this breaks a connection , which can change antenna length , or type , as discussed above . in one embodiment , points e and f are contact points , external to the rfid . two probes ( not shown ) are applied to points e and f , and the probes are connected to a battery or power supply , which supplies the voltage needed to melt the fusible link 51 . principles used by other types of memory can be used , to make and break electrical connections within the rfid . one example is the eprom , electrically programmable read only memory , which is programmed by application of voltages , and then erased by application of light , such as ultra - violet light . another example is the eeprom , electrically erasable programmable read only memory , which is similar to the eprom , except that voltage is used to erase the memory , instead of light . several of the preceding approaches utilized external contact points on the rfid , to cause a change in the topography of the antenna . that is , ( 1 ) an external jumper w was added , as in fig6 , ( 2 ) an external jumper w was broken , as in fig8 , or ( 3 ) an voltage was applied , as described in connection with fig1 . in another approach , no external contact points are involved . instead , a command to change the topography is issued by an interrogating device , and the rfid responds by closing one or more transistors . the closure applies a voltage to a fusible link , such as the fusible element 51 in fig1 . for example , fig1 illustrates an rfid 3 . a receiver 53 contains an output data line dl which carries data received from an interrogating device ( not shown ). an eavesdropping circuit 54 listens to that data , through tap 57 . the eavesdropping circuit 54 does not affect the normal operation of the rfid , except in one instance , namely , when a specific sequence of data is received . that specific sequence , in effect , is a code word that orders the eavesdropping circuit 54 into action . when that code word is received , the eavesdropping circuit 54 melts the fusible link 51 , as indicated by the dashed arrow pointing to the link 51 . the connection previously made by the fusible link 51 is now broken . this connection can correspond to that between points 33 and 36 in fig6 , for example . when it is broken , the antenna topography is altered . alternately , as shown in fig1 , the antenna 9 can be directly disconnected from the receiver 53 , or other components needed to transmit and receive data . detection of the code word is known in the art . a common apparatus for detecting a specific sequence of bits is the “ state machine ”. state machines are described in fundamentals of logic design , by charles h . roth , jr ., ( west pub . co ., 1985 , isbn 0 - 314 - 85292 - 1 ). if a power supply is not available to apply a voltage to the fusible link 51 in fig1 , other alternatives are available . for example , in fig1 , an internal inductor 66 , which includes a coil 67 and an iron core 68 , is connected across the fusible link 51 . the inductor 66 acts as one - half of a transformer . to melt the fusible link 51 , the user brings an external inductor 70 into registry with internal inductor 66 , thereby creating a transformer . when an alternating current 71 is applied to the external inductor 70 , a time - changing magnetic flux ( not shown ) is generated , which generates a voltage in the internal inductor 66 . this voltage melts the fusible link . in one embodiment , the external inductor 70 is mounted in a base , which is placed on a table . to inactivate an rfid , the user slides the rfid across the base , to thereby energize the internal inductor 66 . alternately , the rfid may be equipped with a solar cell ( not shown ), in place of internal inductor 66 . the solar cell may be covered by an opaque label , which prevents light from reaching it . to de - activate the rfid , the label is removed , thereby applying a voltage to the fusible link 51 . alternately , the solar cell can be designed so that ordinary sunlight is insufficient to fuse the link 51 , but a more intense light is required . 1 . in one form of the invention , an rfid responds to two types of incoming data . one type is an ordinary command , which requests the rfid to transmit the contents of its memory . another type is a command to reconfigure antenna topography . this latter type of command can take the form of ( 1 ) adding electrical connections , or ( 2 ) breaking electrical connections . the latter type of command can take the form of ( 1 ) mechanical action which makes or breaks the connection , or ( 2 ) a signal which induces other apparatus to perform the making or breaking . 2 . a distinction should be made between a superficially similar apparatus and the present invention . apparatus exist which allow payment of a fee , by passing the apparatus near a sensor . for example , a toll can be paid to a toll gate on a toll highway by waving an appropriate card past a toll sensor . the amount of the toll is deducted from the card . such cards accomplish a function which could be viewed as similar to a function accomplished by the invention , namely , inactivation of the card upon occurrence of a specified event . the specified event is depletion of the amount of money stored in the card , whereupon the card is thought to become inactive . however , at least two distinctions are present between such cards and the rfids of the invention . one is that it is believed that the cards do not actually become inactive . instead , they merely fail to transmit the code required to satisfy the toll gate . and they may actually transmit a code indicating that their stored balance is insufficient to cover a toll . that is not true inactivity . a second distinction is that such cards can be re - loaded with data indicating a replenished balance , and be re - used . 3 . in another approach , the rfid antenna is disabled by attaching a metallic foil sheet 25 , as in fig4 . the sheet reflects rf energy , and prevents it from escaping . 4 . many types of rfids are available . in general , one type is smaller than an ordinary mag - stripe credit card . an ansii standard exists which defines dimensions of such cards . 5 . it is recognized that not all the approaches described above will de - activate an rfid with complete certainty . for example , the rfid contains internal wiring . it is well known that this wiring can act as an antenna . thus , if a sufficiently strong signal is transmitted by an interrogation device , which is sufficiently close to the rfid , the rfid can pick up that signal , even if the rfid &# 39 ; s antenna is completely removed . however , the rfid , in lacking the antenna , now transmits an extremely weak signal to the interrogation device . therefore , the invention contemplates reduction of the rfid &# 39 ; s transmitted signal intensity by any and all of the following amounts : 50 , 55 , 60 , 65 , 70 , 75 , 80 , 85 , 90 , 95 , and 99 percent . signal intensity refers to electric field strength , one foot from the rfid . from another perspective , the invention contemplates reduction of the rfid &# 39 ; s transmitted signal intensity , at one foot , by any and all of the following amounts : 20 , 25 , 30 , 35 , 40 , 45 , 50 , 55 , 60 , 65 , 70 , 75 , 80 , 85 , 90 , 95 , and 100 decibels , db . numerous substitutions and modifications can be undertaken without departing from the true spirit and scope of the invention . what is desired to be secured by letters patent is the invention as defined in the following claims .