Implantable pressure sensor device 100 comprises first pressure-dependent transducer 102a and second, reference transducer 102b, which each respond at different alternating e.g. RF electrical signals, separated for example by 1-2MHz. Antenna coupling 104a, 104b may be arranged in parallel with the transducers. Support on deflectable membrane 101 may render one transducer more pressure responsive than the other, for instance because one transducer lies over a cavity 112 containing gas at reference pressure. The different amounts of deflection may also arise due to different substrate thicknesses, which may e.g. be less than 200μm or more than 5µm. Interdigitated transducers (IDTs) may be used, having interlocking comb-shaped conductive fingers on a surface of piezoelectric substrate, possibly arranged to provide surface acoustic wave (SAW) devices, in which the frequency response is determined by the fingers spatial arrangement. Bulk acoustic wave (BAW) resonators may be used. Details of such an IDT are also disclosed.
