Measuring energy-charging rate of an energy harvester

1. A wireless Internet of things (IoT) tag, comprising:

at least one antenna configured to harvest an ambient energy;

an energy harvester coupled to the at least one antenna;

an energy storage coupled to the energy harvester and configured to store harvested energy;

a power management unit (PMU), wherein the PMU is configured to at least provide an indication on an energy level at the energy storage; and

a system of chip (SoC), wherein the SoC is powered by the harvested energy as stored in the energy storage; and

an energy detector configured to the energy storage, wherein the energy detector is configured to measure an energy-charging rate of the energy harvester, wherein the energy detector comprises a time counter configured to measure a time elapsed from a discharge level to a reference level, wherein the reference level is a predetermined voltage level and measured by the PMU.

2. The wireless IoT tag of claim 1 , wherein the energy detector is configured to:

receive the indication that the energy level at the energy storage is at the reference level;

receive a discharge state signal after a predefined time interval elapsed from a discharge operation;

start the time counter, upon receiving the discharge state signal;

measure a charge time of the energy storage until the energy level at the energy storage reaches the reference level;

read a time counter value as the charge time; and

determine the energy-charging rate between the discharge level and the reference level within the measured charge time.

3. The wireless IoT tag of claim 2 , wherein the energy-charging rate is indicative on how the at least one antenna is tuned to a frequency of a source of the ambient energy.

4. The wireless IoT tag of claim 2 , wherein when the energy-charging rate is below a predefined threshold, an antenna tuner is triggered to tune the at least one antenna to a frequency of a source of the ambient energy.

5. The wireless IoT tag of claim 2 , wherein the energy-charging rate is utilized to determine at least one of: an input power level at the at least one antenna and an energy conversion efficiency of the energy harvester.

6. The wireless IoT tag of claim 1 , wherein the at least one antenna operates at a frequency band including any one of: a Bluetooth low energy (BLE) frequency band, an Industrial, Scientific, and Medical (ISM) frequency band, a frequency modulation (FM) band, and a cellular frequency band.

7. A method for measuring energy-charging rate of an energy harvester, comprising:

receiving an indication that an energy level at an energy storage is a reference level, wherein the energy storage is configured to store harvested energy, wherein the reference level is a predetermined voltage level and measured by a PMU;

receiving a discharge state signal after a predefined time interval elapsed from a discharge operation;

starting a time counter, upon receiving the discharge state signal, wherein the time counter is configured to measure a time elapse from a discharge level to the reference level;

measuring a charge time of the energy storage until the energy level at the energy storage reaches the reference level;

reading a time counter value as the charge time; and

determining the energy-charging rate between the discharge level and the reference level within the measured charge time.

8. The method of claim 7 , wherein the energy-charging rate is indicative on how at least one antenna is tuned to a frequency of a source of an ambient energy.

9. The method of claim 7 , wherein when the energy-charging rate is below a predefined threshold, an antenna tuner is triggered to tune at least one antenna to a frequency of a source of an ambient energy.

10. The method of claim 7 , wherein the energy-charging rate is utilized to determine at least one of: an input power level at at least one antenna and an energy conversion efficiency of the energy harvester.