PURPOSE: To prevent a spiral conductor for a resonance element from corroding by sealing the resonance element hermetically with a protective covering material, whose ratio of a dielectric constant to the thickness is less than the specified value, and inclusive of gas barrier resin.
CONSTITUTION: In an undergrounding labeled sheet 1 with a resonance element 2 made up of connecting a plane spiral conductor 4 and a condenser 5, this resonance element 2 is hermetically sealed with a protective covering material 8, whose ratio (/T) of a dielectric constant to the thickness Tmm is less than 10, and inclusive of gas barrier resin. This protective covering material 8 is necessary to make the ratio (/T) be small to enable it maintain its detecting capacity even if being buried deep in the ground, and as for the H2S resistant gas barrier resin, polyester, polyamide, ethylene vinyl alcohol copolymer resin, vinylidene chloride resin or the like are usable. With this constitution, the spiral conductor for the resonance element will not corrode for a long period of time.
TSUKADA MASAMITSU
OTA TAIJI
FUJIHIRA RYUTARO
MAEDA MASAHIKO
HEISEI POLYMER KK