On Passive Wireless Sensors Based on Intermodulation Communication

Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto. fi Author Author Name of the doctoral dissertation On Passive Wireless Sensors Based on the Intermodulation Communication Publisher School of Electrical Engineering Unit Department of Radio Science and Engineering Series Aalto University publication series DOCTORAL DISSERTATIONS 122/2015 Field of research Radio Engineering Manuscript submitted 18 June 2015 Date of the defence 9 October 2015 Permission to publish granted (date) 19 August 2015 Language English Monograph Article dissertation (summary + original articles) Abstract Wireless sensors are needed in applications where a wired connection is difficult. Wireless sensors are often equipped with a radio transceiver and a battery or another energy source. These energy sources may limit life-time or operation conditions, and increase the size and cost of wireless sensors. Wireless sensors can also be passive. Due to the limited energy available for these sensors, they typically only support relatively short communication distances and may not provide a means for identifying a certain sensor. This dissertation develops a certain type of passive wireless sensors called the intermodulation communication sensors. This type of passive wireless sensor may potentially have many advantages compared with other passive wireless sensors. Intermodulation communication sensors have been developed in many ways in this dissertation. One challenge was that they were difficult to make compliant with frequency regulations due to the relatively large band needed. This dissertation shows how the bandwidth required can be reduced significantly by using a Quartz crystal or other mechanical resonators. It is also demonstrated that such a resonator enables the utilization of a generic capacitive sensing element in the sensor, making it possible to monitor a broad set of variables. Furthermore, it is shown how intermodulation sensors can be made identifiable. Despite the fact that the studied sensor circuits are fairly simple, many important parameters, such as the read-out distance and measurements resolution strongly depend on the selected circuit components. This dissertation derives design equations for one specific sensor circuitry. The design equations help to choose proper component values in order to achieve the best possible read-out resolution. Passive wireless sensors are often used in large volume applications where low sensor fabrication cost is important. Unit fabrication costs of electronic circuits can typically be lowered by increasing volumes and the integration level. This dissertation studied how the integration of intermodulation communication sensors could be increased by integrating all the passives. The intermodulation communication sensors are interrogated with a specific reader device. This dissertation has contributed to the development and realization of a reader device whose limitations affecting reader performance are studied. The reader device also needs to estimate the sensor state from the measured intermodulation response of the sensor. Furthermore, this dissertation has contributed to the development of an estimation algorithm for the sensor state.Wireless sensors are needed in applications where a wired connection is difficult. Wireless sensors are often equipped with a radio transceiver and a battery or another energy source. These energy sources may limit life-time or operation conditions, and increase the size and cost of wireless sensors. Wireless sensors can also be passive. Due to the limited energy available for these sensors, they typically only support relatively short communication distances and may not provide a means for identifying a certain sensor. This dissertation develops a certain type of passive wireless sensors called the intermodulation communication sensors. This type of passive wireless sensor may potentially have many advantages compared with other passive wireless sensors. Intermodulation communication sensors have been developed in many ways in this dissertation. One challenge was that they were difficult to make compliant with frequency regulations due to the relatively large band needed. This dissertation shows how the bandwidth required can be reduced significantly by using a Quartz crystal or other mechanical resonators. It is also demonstrated that such a resonator enables the utilization of a generic capacitive sensing element in the sensor, making it possible to monitor a broad set of variables. Furthermore, it is shown how intermodulation sensors can be made identifiable. Despite the fact that the studied sensor circuits are fairly simple, many important parameters, such as the read-out distance and measurements resolution strongly depend on the selected circuit components. This dissertation derives design equations for one specific sensor circuitry. The design equations help to choose proper component values in order to achieve the best possible read-out resolution. Passive wireless sensors are often used in large volume applications where low sensor fabrication cost is important. Unit fabrication costs of electronic circuits can typically be lowered by increasing volumes and the integration level. This dissertation studied how the integration of intermodulation communication sensors could be increased by integrating all the passives. The intermodulation communication sensors are interrogated with a specific reader device. This dissertation has contributed to the development and realization of a reader device whose limitations affecting reader performance are studied. The reader device also needs to estimate the sensor state from the measured intermodulation response of the sensor. Furthermore, this dissertation has contributed to the development of an estimation algorithm for the sensor state.