Wake-up wireless sensor nodes

Abstract

A wireless sensor node is described. The wireless sensor node may include a wake-up circuitry configured to awaken the sensor when a request is received. The sensor may be placed in a sleep mode, thus saving battery usage until a wake-up signal requesting use of the sensor is received. Powering of the wake-up circuitry may be supplied through energy captured using an energy harvester. In one example, the energy for powering the wake-up circuitry is extracted from the same signal used for awakening the sensor. The wireless sensor mode may operate in a passive mode, in which the energy for powering the wake-up circuitry is harvested, or in a power supply-assisted mode, in which some of the power is provided by a power supply. High quality factors filters may be used to increase the signal-to-noise ratio of the wake-up signals, thus improving the node's ability to recognize activation requests.

What is claimed is: 
     
         1 . An apparatus comprising:
 wake-up circuitry connected to an antenna and configured to activate a sensor unit from a sleep mode upon receipt of a wake-up signal received by the antenna;   an energy harvester connected to the antenna and configured to capture electromagnetic energy received from the antenna; and   a switch connected to the wake-up circuitry, the energy harvester and a power supply, the switch being configured to select the power supply or the energy harvester as a source of power for the wake-up circuitry.   
     
     
         2 . The apparatus of  claim 1 , wherein the energy harvester is configured to capture the electromagnetic energy by extracting power from the wake-up signal received by the antenna. 
     
     
         3 . The apparatus of  claim 1 , wherein the antenna is connected to the sensor unit and is configured to transfer data indicative of information sensed by the sensor unit outside the apparatus. 
     
     
         4 . The apparatus of  claim 1 , further comprising a bandpass filter disposed between the antenna and the wake-up circuitry, the bandpass filter having a quality factor (Q) that is between 1000 and 10000. 
     
     
         5 . The apparatus of  claim 1 , further comprising a memory unit configured to store therein a wake-up code, wherein the wake-up circuitry is configured to compare a packet of the wake-up signal to the wake-up code and to activate the sensor unit from the sleep mode if it determines that the packet substantially matches the wake-up code. 
     
     
         6 . The apparatus of  claim 1 , wherein the energy harvester comprises a Dickson multiplier or a diode-capacitor circuit. 
     
     
         7 . A method for operating an apparatus, the method comprising:
 receiving a wake-up signal through an antenna;   with wake-up circuitry, activating a sensor unit from a sleep mode upon receiving the wake-up signal;   with an energy harvester, harvesting electromagnetic energy from the wake-up signal; and   powering the wake-up circuitry in one of a passive mode or a power supply-assisted mode, wherein:
 in the power supply-assisted mode, the wake-up circuitry is configured to be powered at least partially by a power supply; and 
 the passive mode, the wake-up circuitry is configured to be powered at least partially using the electromagnetic energy harvested from the wake-up signal. 
   
     
     
         8 . The method of  claim 7 , further comprising receiving input selecting one power mode between the passive mode and the power supply-assisted mode. 
     
     
         9 . The method of  claim 7 , further comprising transmitting data indicative of information sensed by the sensor unit through the antenna. 
     
     
         10 . The method of  claim 7 , wherein:
 in the passive mode, the wake-up circuitry is configured to be powered using electromagnetic energy extracted from the wake-up signal with the energy harvester.   
     
     
         11 . The method of  claim 7 , further comprising filtering the received wake-up signal with a bandpass filter disposed between the antenna and the wake-up circuitry, the bandpass filter having a quality factor (Q) that is between 1000 and 10000. 
     
     
         12 . The method of  claim 7 , further comprising extracting electromagnetic energy from the wake-up signal and storing the extracted electromagnetic energy in an energy storing device, wherein:
 in the passive mode, the wake-up circuitry is configured to be powered using the stored electromagnetic energy.   
     
     
         13 . An apparatus comprising:
 wake-up circuitry connected to an antenna and configured to activate a sensor unit from a sleep mode upon receipt of a wake-up signal having a packet that substantially matches a known wake-up code, the wake-up signal being received by the antenna; and   an energy harvester connected to the antenna and configured to capture electromagnetic energy received from the antenna; wherein the apparatus is configured to power the wake-up circuitry at least partially with the electromagnetic energy harvested from the wake-up signal by the energy harvester.   
     
     
         14 . The apparatus of  claim 13 , wherein the energy harvester is configured to capture the electromagnetic energy by extracting power from the wake-up signal received by the antenna. 
     
     
         15 . The apparatus of  claim 13 , wherein the antenna is connected to the sensor unit and is configured to transfer data indicative of information sensed by the sensor unit outside the apparatus. 
     
     
         16 . The apparatus of  claim 13 , further comprising a bandpass filter disposed between the antenna and the wake-up circuitry, the bandpass filter having a quality factor (Q) that is between 1000 and 10000. 
     
     
         17 . The apparatus of  claim 16 , wherein the bandpass filter and the wake-up circuitry are disposed on separate integrated circuits. 
     
     
         18 . The apparatus of  claim 16 , wherein the bandpass filter comprises a surface acoustic wave (SAW) filter. 
     
     
         19 . The apparatus of  claim 16 , wherein the bandpass filter comprises a quartz crystal filter. 
     
     
         20 . The apparatus of  claim 13 , wherein the energy harvester comprises a Dickson multiplier or a diode-capacitor circuit.