In recent years, wearable computing devices have attracted a great deal of attention for its convenience. Wearable computing devices give users convenience using wearable terminals, networks and cloud computing systems. Accordingly, there is a demand for providing small sized wearable devices and networks which can be used at anytime and anywhere by the user.
An active wireless tag system which uses batteries for supplying power to the wireless tag system which has advantages in read-range performances and communication stabilities. However, active wireless tag systems have drawbacks, such as, complicated system configurations and necessities to change batteries because batteries are required to operate the wireless tag systems. Further, size of the active wireless tag system becomes bigger. Accordingly, the active wireless tag system is not suitable for wearable terminals.
On the other hand, passive wireless tag systems are convenient for wearable terminals due to their simple system configurations and no-battery operations. However, the passive wireless tag system needs power conversion systems therein to supply power for semiconductor devices having communication and data processing functions. This power conversion is performed by receiving radio wave frequency of UHF band, and micro wave band from a reader/writer for the wireless tag system as a power source.
As a result, under a certain usage environment, when power conversion is not adequately performed, read-range and communication performances of the wireless tag become unstable due to insufficient power conversion caused by and radio wave absorption. Particularly, when the wireless tag system is used as a wearable terminal attached with the human body, UHF band radio wave is absorbed by the human body, because water occupies 60% of the human body. As a result, the power conversion is not fully performed to supply necessary power to the semiconductors inside the wireless tag. Under this environment, the read-range characteristics and communication capabilities of the wireless tag attached to human body become unstable. There are necessities to solve these problems of instability in read-range characteristics and communication capabilities associated with wearable devices caused by insufficient power conversion due to the radio wave absorption.
In the case of an arm-wearable terminal, such as an arm-wristband, the size of the arm wearable terminal needs to be miniaturized. Further, an antenna system installed in the arm wearable terminal needs to efficiently receive radio waves in UHF and Micro-wave bands with high sensitivity. Also the antenna system needs to be less expensive. Further, the wide directivity wearable terminal is needed to effectively receive the radio wave from one direction of a reader/writer.
Japanese Patent Application Publication No. 2010-231582 discloses a wireless tag having good high-frequency transfer characteristics and transfer characteristics under the environment where temperature changes. In FIG. 1 of Japanese Patent Application Publication No. 2010-231582 discloses a wireless tag which is structured by a dielectric layer P, on both side of which, prepreg layers are disposed, wherein a conductive material layer is provided on one side of the laminated body and a metal foil layer on the other side of the laminated body.
Japanese Patent Application Publication Number 2000-33523 discloses a wireless tag configured by an antenna, a ground conductive body, a half-wave length resonator configured by a micro-strip line having a dielectric body disposed between the antenna and the ground conductive body, one or a plurality of line-shaped conductor bodies being connected with a center point of the antenna and an IC (Integrated Circuit) disposed between the antenna and the ground conductive body.
The wireless tag disclosed in Japanese Patent Application Publication Numbers 2010-231582 and 2000-33523 can be used under environment including conductive materials. However, the wireless tag has some issues, such as poor performances in read-range characteristics (low sensitivity due to the high density configuration) and poor performances in antenna directivity performances required by the small sized wearable terminals. Further, the wireless tag has some other issues on antenna system to efficiently receive radio waves in UHF band and micro wave band to satisfy required performances when the wireless tag needs to be minimized