Orthogonal frequency coding for SAW tagging and sensors

Surface acoustic wave (SAW)-based sensors can offer wireless, passive operation in numerous environments, and various device embodiments are used for retrieval of the sensed data information. Single sensor systems typically can use a single carrier frequency and a simple device embodiment because tagging is riot required. In a multisensor environment, it is necessary to both identify the sensor and retrieve the sensed information. This paper presents the concept of orthogonal frequency coding (OFC) for implications to SAW sensor technology. The OFC offers all advantages inherent to spread spectrum communications, including enhanced processing gain and lower interrogation power spectral density (PSD). It is shown that the time ambiguity in the OFC compressed pulse is significantly reduced as compared with a single frequency tag having the same code length, and additional coding can be added using a pseudo-noise (PN) sequence. The OFC approach is general and should be applicable to many differing SAW sensors for temperature, pressure, liquid, gases, etc. Device embodiments are shown, and a potential transceiver is described. Measured device results are presented and compared with coupling of modes (COM) model predictions to demonstrate performance. Devices then are used in computer simulations of the proposed transceiver design, and the results of an OFC sensor system are discussed.

[1]  Lie-Liang Yang,et al.  Overlapping-ary Frequency Shift Keying Spread-Spectrum Multiple-Access Systems Using Random Signature Sequences , 1999 .

[2]  Leonhard Reindl,et al.  Monitoring the tire pressure at cars using passive SAW sensors , 1997, 1997 IEEE Ultrasonics Symposium Proceedings. An International Symposium (Cat. No.97CH36118).

[3]  D.C. Malocha,et al.  Orthogonal frequency coding for SAW device applications , 2004, IEEE Ultrasonics Symposium, 2004.

[4]  R. Chang.  Synthesis of band-limited orthogonal signals for multichannel data transmission , 1966 .

[5]  D.C. Malocha,et al.  SAW sensors using orthogonal frequency coding , 2004, Proceedings of the 2004 IEEE International Frequency Control Symposium and Exposition, 2004..

[6]  Leonhard Reindl,et al.  Wavelet transform with a SAW convolver for sensor application , 1995, 1995 IEEE Ultrasonics Symposium. Proceedings. An International Symposium.

[7]  J. W. Tukey,et al.  The Measurement of Power Spectra from the Point of View of Communications Engineering , 1958 .

[8]  C. Hartmann,et al.  A global SAW ID tag with large data capacity , 2002, 2002 IEEE Ultrasonics Symposium, 2002. Proceedings..

[9]  A. Pohl,et al.  Comparison between BAW and SAW sensor principles , 1997, Proceedings of International Frequency Control Symposium.

[10]  S.E. Carter,et al.  SAW device implementation of a weighted stepped chirp code signal for direct sequence spread spectrum communications systems , 2000, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[11]  Wolf-Eckhart Bulst,et al.  Mechanical sensors based on surface acoustic waves , 1994 .

[12]  Leonhard Reindl,et al.  CDMA for wireless SAW sensor applications , 1996, Proceedings of ISSSTA'95 International Symposium on Spread Spectrum Techniques and Applications.

[13]  C. D. Bishop,et al.  The Classical Truncated Cosine Series Functions with Applications to SAW Filters , 1987, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[14]  F. Schmidt,et al.  Wireless interrogator system for SAW-identification-marks and SAW-sensor components , 1996, Proceedings of 1996 IEEE International Frequency Control Symposium.

[15]  Lie-Liang Yang,et al.  Overlapping M-ary frequency shift keying spread-spectrum multiple-access systems using random signal sequences , 1999 .

[16]  Leonhard Reindl,et al.  Spread spectrum techniques for wirelessly interrogable passive SAW sensors , 1996, Proceedings of ISSSTA'95 International Symposium on Spread Spectrum Techniques and Applications.