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A novel wireless sensor and identification system based on passive surface acoustic wave devices is reported. Quasi-orthogonal codes, which allow for multiple access capability, were implemented using a differential delay line scheme on miniaturised passive sensor units. A transceiver interrogation system combining analogue and digital circuitry has been designed and assembled to investigate the wireless devices' performance. Experimental results with 31-chip-long codes verified the expected theoretical response of the prototype wireless device to interrogation with the matching coded sequence. The system, which enables concurrent wireless access to multiple passive devices, creates new possibilities for physical, chemical or biological sensor applications.