Method and apparatus for measuring radio-frequency energy

• US 9,618,552 B2
• Filed: 03/08/2012
• Issued: 04/11/2017
• Est. Priority Date: 03/08/2012
• Status: Active Grant

• Current Assignee: Duke University, Ricoh Company Limited
• Original Assignee: Duke University, Ricoh Company Limited
• Inventors: Gudan, Ken, Chemishkian, Sergey, Reynolds, Matthew S.
• Primary Examiner(s): Beyen, Zewdu A
• Application Number:
  US13/415,555
• Publication Number:
  US 20130238265A1
• Time in Patent Office: 1,860 Days
• Field of Search: 370252
• CPC Class Codes: G01R 29/0871 Complete apparatus or systems; circuits, e.g. receivers or amplifiers G01R29/0878, G01R29/0892 take precedence; dosimeters, warning devices G01R29/0857
• CPC Class Codes: H04B 17/23 Indication means, e.g. displays, alarms, audible means
• CPC Class Codes: H04B 17/318 Received signal strength

Abstract

A method and apparatus is disclosed herein for measuring radio-frequency energy. In one embodiment, the apparatus comprises one or more antennas, a wideband radio frequency detector (e.g., a logarithmic amplifier (LogAmp)) coupled to the one or more antennas to measure ambient RF energy, wherein the wideband radio frequency detector has an analog output indicative of RF input power received by the one or more antennas, and an analog-to-digital converter coupled to the wideband radio frequency detector to convert the analog output to a digital value, the digital value being applied to a calibration function, to provide a number representing RF energy.

Claims

1. An ambient radio-frequency (RF) energy measurement apparatus for measuring energy available for RF harvesting at a particular location, the apparatus comprising:

a plurality of antennas;

at least one wideband radio frequency detector coupled to the plurality of antennas to measure ambient RF energy, wherein each wideband radio frequency detector has an analog output indicative of RF input power received by the plurality of antennas;

at least one analog-to-digital converter coupled to each wideband radio frequency detector to convert the analog output to a digital value;

a spectrum analyzer coupled to the plurality of antennas through an RF multiplexer to perform an RF frequency measurement;

a Wi-Fi sniffer to confirm presence of Wi-Fi traffic within data measured by the spectrum analyzer and the at least one wideband radio frequency detector; and

a controller coupled to the spectrum analyzer and the at least one wideband radio frequency detector to generate an output indicative of ambient RF energy available for RF harvesting based on data from the spectrum analyzer and the at least one wideband radio frequency detector,

wherein each digital value is applied to a calibration function to provide a number representing RF energy available at a particular location.

2. The measurement apparatus defined in claim 1 wherein the at least one wideband radio frequency detector and the spectrum analyzer simultaneously measure the total energy across a band, and further wherein the controller integrates measurements across the band to determine the RF power available.

3. The measurement apparatus defined in claim 1 wherein the controller correlates wideband radio frequency detector energy measurement data with measurement data from the spectrum analyzer.

4. The measurement apparatus defined in claim 1 wherein the controller is operable to:

compute average power based on the spectrum analyzer data;

compute a correction factor based on the data from the at least one wideband radio frequency detector;

compute an insertion loss between the antennas and the measurement equipment for each RF path through the apparatus;

apply the correction factor and insertion loss to the spectrum analyzer average power to adjust to average power, the adjusted average power representing the RF energy available for harvesting.

5. The measurement apparatus defined in claim 4 wherein the controller computes the correction factor by:

converting wideband radio frequency detector power data; and

correlating wideband radio frequency detector power data to the data from the spectrum analyzer.

6. The measurement apparatus defined in claim 1 wherein the spectrum analyzer measures power in a plurality of frequencies spread across the Wi-Fi spectrum range, and further wherein the controller reads power measured by the spectrum analyzer through frequencies associated with the plurality of frequencies and averages multiple readings to determine average power.

7. The measurement apparatus defined in claim 1 further comprising:

a multiplexer having a plurality of inputs and an output, each of the plurality of outputs coupled to one antenna in the plurality of antennas; and

an RF splitter coupled to the output of the multiplexer, and having a first output coupled to an input of the spectrum analyzer and a second output coupled to an input of the at least one wideband radio frequency detector.

8. The measurement apparatus defined in claim 7 wherein the multiplexer comprises a plurality of RF switches operable together to perform a n:

1 RF multiplexer, and a switch controller coupled to the plurality of n switches to control the output of the switch matrix so that only one switch produces an output at a time.

9. The measurement apparatus defined in claim 1 wherein the plurality of antennas comprises a plurality of linearly polarized antennas, wherein antennas of a first group of the plurality of antennas are horizontally polarized and antennas of a second group are vertically polarized.

10. The measurement apparatus defined in claim 1 wherein the plurality of antennas, the at least one wideband radio frequency detector and the analog-to-digital converter are contained in a hand-held portable device.

11. The measurement apparatus defined in claim 1 wherein the RF energy comprises Wi-Fi energy.

12. A method for processing radio-frequency (RF) energy to determine RF energy available for RF harvesting, the method comprising:

confirming, by a Wi-Fi sniffer, presence of Wi-Fi traffic within data measured by a spectrum analyzer and at least one wideband radio frequency detector, the spectrum analyzer to make RF frequency measurements;

measuring RF energy using the at least one wideband radio frequency detector coupled to a plurality of antennas;

generating an analog output indicative of RF input power received by the plurality of antennas;

converting the analog output to a digital value; and

applying the digital value to a calibration function to obtain a number representing RF energy.

13. The method apparatus defined in claim 12 further comprising:

obtaining an RF frequency measurement from the spectrum analyzer; and

generating an output indicative of ambient RF energy available for RF harvesting based on the digital value from the at least one wideband radio frequency detector and data from the spectrum analyzer.

14. The method defined in claim 13 further comprising:

computing average power based on RF frequency measurements from the spectrum analyzer;

computing a correction factor based on digital values generated based on the data from the at least one wideband radio frequency detector;

measuring the insertion loss between the antennas and the measurement equipment for each RF path through the apparatus;

applying the correction factor and insertion loss to the average power to adjust to average power, the adjusted average power representing the RF energy available for harvesting.

15. The method defined in claim 14 wherein computing the correction factor comprises:

converting wideband radio frequency detector power data; and

correlating wideband radio frequency detector power data to data from the spectrum analyzer.

16. The method defined in claim 12 wherein the RF energy comprises Wi-Fi energy.