Sensor node with wireless energy harvesting and method for operating the sensor node

A sensor node comprising:

• a radio frequency (RF) circuit for wirelessly harvesting energy from, and wirelessly communicating with, an external device to produce a voltage for charging a capacitive element;
• a sensor interface circuit coupled to receive a voltage from the RF circuit and the capacitive element, the sensor interface circuit having a first sensor terminal configured to communicate with an analog sensor and a second sensor interface having a second sensor terminal configured to communicate with a digital sensor;
• a voltage regulator coupled to the capacitive element, wherein energy begins to charge the capacitive element in response to a proximity of the external device to the sensor node, and wherein in response to a voltage level of the voltage regulator reaching a predetermined level, the sensor node providing a notification to the external device;
• and
• a digital control circuit coupled to control sensing operations of one or more sensors coupled to the sensor interface,
• wherein in response to a request from the external device, the sensor node provides a voltage level of the capacitive element to the external device, and wherein the external device uses the voltage level to determine capabilities of the sensor node.

A method for operating a sensor node, the method comprising:

• establishing a wireless communication and wireless energy transfer between the sensor node and an external device;
• using the wireless energy transfer to charge a capacitive element;
• transmitting a notification to the external device in response to a voltage on the capacitive element reaching a first voltage level for supporting minimum functions of the sensor node;
• receiving a request from the external device to measure the voltage on the capacitive element;
• and
• transmitting the voltage on the capacitive element to the external device, wherein the external device determines what functions of the sensor node can be performed based on the voltage on the capacitive element.