Low power and agile sensor data retrieval using dual interface passive RF tag

Consider a situation where one desires to retrieve sensor data from an arbitrary environment via a moving interrogator. Maintenance of street lights and electric apparatus in conduits for example. The fundamental problems with this system have been 1)the trade-off relation between power consumption by sensor and the data retrieval rate for the interrogator, and 2)the data retrieval agility for the moving interrogator. A higher duty ratio incurs more power consumption in sensors whereas a lower duty ratio leads to a less reliable retrieval rate. Even though there have been such efforts as" adaptive sleep period control "which was derived from the packet arrival rate, they didn't systemically solve the problem, particularly for moving-interrogator environment. This paper presents a solution of separating the timing of sensor-sampling and the timing of sensor-data retrieval. The asynchronous data retrieval mechanism is facilitated by a dual interfaced UHF passive RF tag known as a "recorder tag" which the authors have been developing. This paper examines the power consumption composition of a prototype recorder tag. The power consumption efficiency of the proposed data-retrieval method is discussed in comparison with that of the existing method in terms of "Sensor Sampling Interval vs. Battery Life Expectancy." The authors also evaluated the viability of retrieving sensor data through a moving-interrogator. We specifically inspected the relationship of "Interrogator's Moving Speed vs Successful Data Retrieval Rate." The tests showed that with a commercial 1.2V rechargeable battery, the recorder tag lasts for 21 days forluminance and temperature sensing using a 30 minute samplinginterval, extending the traditional battery lifespan ten times longer, yet still preserving 100% time availability for sensor data retrieval. The power consumption is expected to be eight times as efficient when using optimized circuitry. Experiments in an emulated fading environment reveal that the data retrieval rate is observed to be the highest when the maximum relative speed between the moving-interrogator and the recorder tag is less than 3km/h, with an optimized distance of separation being 10cm for a 27dBm EIRP interrogator. The moving speed, 3km/h, can be improved by optimizing the anti-collision procedure and by enhancing the sensitivity of the recorder tag.