Recently, a contactless reader and/or writer (hereinafter sometimes referred to simply as reader/writer) for reading from and writing into a contactless smart card or contactless IC card, and an RF ID tag, has been used widely more and more. A contactless smart card is used, for example, for supervision of entry into and exit from a room, personal identification, traffic ticketing and electronic money. An RF ID tag is used, for example, in commodity management, room entry and exit supervision, and physical distribution management. Also, PAN (Personal Area Network) communications using contactless smart cards and RF ID tags have been proposed. It is expected that such a reader/writer will be incorporated into small-sized information processing apparatuses, such as personal computers, PDAs and cellular phones. It is also expected that contactless smart card and RF ID tag functions will be incorporated into mobile apparatuses, such as PDAs and cellular phones.
FIG. 19 illustrates transmitting and receiving RF signals between a contactless reader/writer (R/W) 90 and a contactless smart card or an RF ID tag 20 incorporated in an information processing apparatus 10 via respective coil antennas ANT, through magnetic coupling or transformer coupling. The reader/writer 90 transmits a carrier modulated with a command signal to the contactless smart card 20. The smart card 20 rectifies the modulated carrier signal to obtain driving power. When the intensity of modulated magnetic field from the reader/writer 90 is sufficiently large, the power supply of the contactless smart card 20 is ON, and communications are initiated in response to a command provided by the reader/writer 90. The contactless smart card 20 does not provide a carrier signal, but modulates the modulated carrier signal magnetic field generated by the reader/writer 90 to send a command response or the like to the reader/writer 90. Such modulated carrier signal transmission and reception is usually done through magnetic coupling or transformer coupling via their planar coil antennas having large areas.
For communications between the contactless smart card 20 and the reader/writer 90, the magnetic environments of the coil antennas of both of them must be good. A small-sized apparatus, such as a notebook personal computer, a PDA or a cellular phone, is provided with electrical metal shields over its case and substrates, or over the components built in it in order to prevent undesired RF signals from radiating from the built-in components. Thus, when a card or a reader/writer is incorporated into such an apparatus, the formation of magnetic field by the coil antennas is interfered and desirable communications cannot be achieved.
Saito disclosed, in Japanese Patent Application Publication JP 2001-284935-A published on Oct. 12, 2001, a small-sized antenna device for electromagnetic wireless communications which can be built in a portable wireless apparatus. A small-sized antenna is formed of a grounded conductor, and a loop antenna is formed of straight or non-straight parallel portions and non-straight first and second rising portions, which loop antenna, together with the grounded conductor, forms the antenna device.
In Japanese Patent Application Publication JP HEI 11-213116-A published on Aug. 6, 1999, Yamamoto et al. disclosed a contactless smart card which is resistant to bending, easy to produce and free of electric field disturbance. An intermediate sheet of the card includes an insulating sheet having a set of two adjacent linear holes facing each other, an antenna coil formed by a conductor pattern formed on the opposing and side surfaces to wrap around the portion of the insulating sheet located between the linear holes, and an IC chip connected to the end terminals of the antenna coil. The intermediate sheet has its opposing surfaces covered with card-shaped resin or paper layers.
In order for the coil antenna ANT of the reader/writer 90 of FIG. 19 to produce a satisfactory magnetic field, influence of the electrical shields on the coil antennas of both of the contactless smart card 20 and the reader/writer 90 need be eliminated. As one solution, an area of the electric shield of the case corresponding to the size of the coil antennas may be removed, which, however, causes insufficient prevention of an undesired RF signal generated in the apparatus from being radiated. Another solution may be to provide a large distance between the electric shield of the case and the coil antenna, which, however, forms an undesirable space between the coil antennas and the electric shield. This is disadvantageous in designing cases for apparatuses, in particular, cases for, e.g. PDAs and cellular phones, which are desired to be minimized in size. A further solution may be to mount a coil antenna outside the case. This, however, causes an undesired protrusion to be formed on the case, which is disadvantageous in designing apparatus cases. A still further solution may be to dispose a sheet having high magnetic permeability between the case and the coil antenna so that a satisfactory magnetic field can be formed in the vicinity of the electric shield. However, high magnetic permeability sheets are expensive.
The inventors have recognized that there is need for a coil antenna which is inexpensive, affects little the designing of a case of an apparatus, and can be built in the apparatus.
An object of the invention is to provide a small coil antenna which can be housed in a small internal space of an apparatus.
Another object of the invention is to provide an information processing apparatus with a coil antenna housed in a small internal space of the apparatus.
A further object of the invention is to realize an information processing apparatus with a simple, inexpensive coil antenna.