Telemetric surface acoustic wave chemical sensors

The present paper deals with surface acoustic wave (SAW) chemical sensors that operate without power supply and can be read wirelessly by electromagnetic interrogation signals. These novel chemical sensors are based on the well-known SAW identification (ID) tag principle with a sensitive coating applied to the device surface. It is shown that a gas detection limit of a few ppm to some hundred ppm requires a reflector time distance of several microseconds, corresponding to a spatial distance of typically 10 mm. This relatively large device geometry places an upper limit on the additional insertion attenuation caused by the sensitive layer and restricts the possible coating materials. As a practical demonstration, we have designed and investigated a humidity sensor at 433.92 MHz a frequency band allotted to industrial, scientific, and medical apparatus in Germany. The measured return loss without sensitive layer was between 20 and 25 dB. A coating of cross-linked polyvinyl alcohol served as sensitive layer, the thickness of which was kept at 3 to 10 nm. With these devices, relative humidity changes of a few percent are detected quite easily. This illustrates the fact that telemetric SAW chemical sensors ran actually be realized.

[1]  K. Yamanouchi,et al.  Sensitivity of an anadically oxidized aluminium film on a surface acoustic wave sensor to humidity , 1994 .

[2]  SAW humidity sensor using dielectric hygroscopic polymer film , 1994, 1994 Proceedings of IEEE Ultrasonics Symposium.

[3]  S. Furukawa,et al.  Humidity sensor using surface acoustic waves propagating along layered structures , 1994, 1994 IEEE MTT-S International Microwave Symposium Digest (Cat. No.94CH3389-4).

[4]  S. Furukawa,et al.  New SAW humidity sensor using double-coated hygroscopic film , 1995, 1995 IEEE Ultrasonics Symposium. Proceedings. An International Symposium.

[5]  Supriyo Datta,et al.  Surface Acoustic Wave Devices , 1986 .

[6]  Leonhard Reindl,et al.  Remote sensing of physical parameters by means of passive surface acoustic wave devices (“ID-TAG”) , 1994, 1994 Proceedings of IEEE Ultrasonics Symposium.

[7]  David S. Ballantine,et al.  Acoustic wave sensors : theory, design, and physico-chemical applications , 1997 .

[8]  Leonhard Reindl,et al.  Wireless passive SAW sensor systems for industrial and domestic applications , 1998, Proceedings of the 1998 IEEE International Frequency Control Symposium (Cat. No.98CH36165).

[9]  M. Hoummady,et al.  Surface acoustic wave (SAW) dew point sensor: application to dew point hygrometry , 1995 .

[10]  Cinzia Caliendo,et al.  A new surface acoustic wave humidity sensor based on a polyethynylfluorenol membrane , 1994 .

[11]  Li Haiguo,et al.  SAW temperature and humidity sensor with high resolution , 1993 .

[12]  Humidity Sensor Using Surface Acoustic Wave Delay Line with Hygroscopic Dielectric Film , 1993 .

[13]  Cinzia Caliendo,et al.  Surface acoustic wave humidity sensor , 1993 .

[14]  Xiaoqi Bao,et al.  SAW Temperature Sensor and Remote Reading System , 1987, IEEE 1987 Ultrasonics Symposium.

[15]  K. Yamanouchi,et al.  2.5 GHz-range SAW propagation and reflection characteristics and application to passive electronic tag and matched filter , 1993 .

[16]  S. Joshi,et al.  Measurement of Humidity Using Surface Acoustic Waves , 1985, IEEE 1985 Ultrasonics Symposium.