Patent ID: 7817146

Claim:
A sheet comprising: a plurality of wireless measuring units, each of the plurality of wireless measuring units measuring at least one physical property of external environmental conditions surrounding the sheet, in response to receiving a first radio signal, wherein the plurality of wireless measuring units use the first radio signal as an energy source, and a frequency of the first radio signal is one of a plurality of frequencies, with each frequency activating the measurement of only one physical property of external environmental conditions surrounding the sheet, wherein the plurality of wireless measuring units generate and transmit a second radio signal comprising data indicating the at least one measured physical property, the sheet is used alongside an electronic paper, at least one physical property consists of at least one selected from the group consisting of temperature, pressure, light, and acceleration, the at least one physical property is measured by a propagation velocity of a surface acoustic wave, and the at least one physical property is displayed on said electronic paper.