Abstract: A silicon or quartz wafer for forming a SAW device is the subject of grinding and lapping operation to form its basic shape. The opposing surfaces, as well as the edges extending therebetween, are the polished to reduce the number and size of defects in the surfaces. Metal is deposited onto one of the opposing surfaces which, in use, will be under compression, to form electronic components thereon, and a multi-metallic coating having an outer layer formed of gold is applied to the other surface to form a solder pad by means of which the wafer may be fastened to a shaft or the like by soldering. Martensitic stainless steel is used as a mount, saddle or housing for the SAW substrate.

Abstract: A monitoring system, particularly suitable for monitoring conditions (e.g. pressure or temperature) of a vehicle tire comprises a passive sensor (102, 104), an antenna (106) associated with said passive sensor, and switching means (108) for controlling the connection between the passive sensor and the antenna such that, in a first state of said switching means, said antenna is prevented from transmitting a signal generated by the passive sensor, and, in a second state of said switching means, said antenna is permitted to transmit a signal generated by the passive sensor. The switching means is operated remotely by means of a control signal. The control signal may be derived from the sum or difference of RF signals (F1 and F2) applied to a filter (112) In alternative embodiments the control signal is the modulating frequency of an AM or FM modulated radio signal or a radio signal carrying a digital code.