Patent ID: 8305291

Claim:
A tire-state detection device, comprising: a sensor configured to detect a predetermined physical state of a tire; an antenna having a predetermined resonance frequency, the antenna circling around a predetermined axis circumference at a predetermined diameter and having a coiled shape extending in an axial direction; a detection circuit configured to transmit information regarding a result of a detection made by the sensor from the antenna as radio waves; a case configured to house the sensor, the antenna and the detection circuit, and configured to allow radio waves to pass therethrough, the case being further configured to fit on a rim in the tire when the tire-state detection device is to be used, a printed wiring board being provided inside the case, the printed wiring board being secured to the case and the antenna being securely provided to one surface of the printed wiring board; a planar conductor configured as being electrically insulated from the antenna at a position set a predetermined distance away from the antenna so as to form an interface between the antenna and the rim when the case is fitted to the rim, the planar conductor being set to a potential that is equivalent to a reference potential of the detection circuit, and the planar conductor being secured to the printed wiring board by a plurality of holders so that another surface of the printed wiring board and one surface of the planar conductor are parallel at a predetermined distance, and so that a predetermined space is formed between another surface of the printed wiring board and one surface of the planar conductor.