Giant Sensitivity through Fully-Passive and Chip-Less Parametric Temperature Sensors

In this work, we present a new passive and batteryless temperature (T ) sensor, leveraging the unique dynamics of a varactor-based parametric frequency divider (PFD) to boost, by orders of magnitude, the temperature sensitivity attained by commercial and low-cost temperature sensitive components. We show that by including a ceramic thermistor in a PFD circuit made of off-the-shelf low-cost lumped components, the minimum PFD input power (P
_th
) triggering a sub-harmonic oscillation starts to depend on T . Such unexplored feature makes the generated PFD output power, at half of the driving frequency, exhibit a record-high sensitivity with respect to T that largely surpasses the maximum one attainable by operating the same thermistor in conventional read-out circuits. In order to demonstrate this unreported special operational feature, we built a PFD prototype on a Printed-Circuit-Board (PCB), operating at an input frequency of 886MHz (i.e. an output frequency of 443MHz) and strategically including a commercial thermistor in its network. Despite the fact that no supplied DC power was used, the output power of the built system showed a record-high sensitivity (up to 2.5dB/°C), thus offering exciting opportunities to attain low-cost chip-less temperature sensors for a variety of applications, ranging from smart manufacturing to environmental and agriculture monitoring.