Reading UHF wireless tags with a distance of 10m that can be attached to metal

Mitsubishi Electric has successfully developed a wireless tag (RFID tag) using the UHF (950MHz) band, which can be used on metal surfaces with a reading distance of up to 10m (Fig. 1). Previously, in terms of passive UHF radio tags that do not use batteries, there has been a product that claims to be affixed to a non-metallic surface and has a reading distance of 8 meters. This time it has exceeded this distance. For such labels that can be used on metal surfaces, "Using a product with a reading distance of about 1m has been used in an empirical test by the Japan Ministry of Economics and Industry" (Mitsubishi Electric). If the UHF wireless tag is used to achieve a read distance of 10 meters, it will also be convenient to use in areas such as distribution management of metal containers.

The reason why this time can be used on a metal surface is that the wireless tag antenna uses a micro-strip antenna (also known as a patch antenna, Patch Antenna). The label is divided into three layers: a sponge-like lining is placed on an aluminum alloy plate, and a base plate on which an antenna element and a wireless IC chip are placed is mounted thereon ( FIG. 1 ). The aluminum alloy plate and the antenna element are separated by a distance of about 3 mm from the lining. If this type of antenna is used, the metal body with the aluminum alloy plate and the wireless tag itself can serve as a part of the antenna base. Ordinary wireless tags use dipole antennas or antennas that use electromagnetic induction. Therefore, it is difficult to fully function on a metal surface.

Mitsubishi Electric said: “The price of a wireless tag is expected to be around several hundred yen. It is supposed to be read by forklift trucks on containers in factories and warehouses, or used in management of entry and exit rooms. We do not produce low costs. "The mini-labels." Said that will never participate in cost competition at a price of about 10 yen or so, like ordinary labels. In the future, the company will adopt corresponding solutions to the miniaturization and high-speed movement of readers, which will be practical in the middle of 2006.

Ordinary wireless tag reading distance can reach 7m

According to the introduction of Mitsubishi Electric, there are two major factors that can increase the reading distance of the wireless tag to 10m. One is that the wireless tag increases the antenna gain by increasing the antenna. As a result, the external dimensions of the wireless tag have reached 100mm x 200mm x 5mm, which is much larger and thicker than other passive wireless tags.

The other is to greatly reduce the adverse effects on the reader's transmit and receive circuits. Specifically, (1) separate the transmitter and receiver by setting the transmitting antenna and the receiving antenna separately; (2) reducing interference between channels by reducing unwanted radiation of the transmitting circuit; (3) transmitting circuit and receiving Electromagnetic shielding is inserted between the circuits.

The radio wave power of the reader is about 1W. When the wireless tag distance is about 7m, the received power is only 1nW, which is a difference of 1 billion times. In the passive wireless tag system, how to achieve high sensitivity while achieving high sensitivity is a subject that has long been a problem to be solved. In November 2004, Mitsubishi Electric used its own wireless tag technology to achieve a reading distance of 7m. Utilizing the solution to this reader problem, the reading distance of ordinary UHF wireless tags can also reach 7m.