Systems and methods for synchronous detection of signals

• US 7,126,323 B1
• Filed: 07/26/2004
• Issued: 10/24/2006
• Est. Priority Date: 07/25/2003
• Status: Expired due to Fees

• Current Assignee: Admiralty Corporation One Securities Center, Admiralty Corporation (Admiralty Holding Co.)
• Original Assignee: Admiralty Corporation (Admiralty Holding Co.)
• Inventors: Larsen, James Wagner
• Primary Examiner(s): LEDYNH, BOT L
• Application Number:
  US10/899,391
• Time in Patent Office: 820 Days
• Field of Search: 324/76.77, 324/91, 324/118
• US Class Current: 324/76.77
• CPC Class Codes: G01S 7/2886 using I/Q processing
• CPC Class Codes: G01S 7/35 Details of non-pulse systems
• CPC Class Codes: G01S 7/411 Identification of targets based on measurements of radar reflectivity G01S7/415 takes precedence

Abstract

Systems and processes for synchronous demodulation of signals in detection contexts in order to improve frequency, magnitude and/or phase response over pulsed signal methods. According to a preferred embodiment, a return signal is demodulated for the time corresponding to when its corresponding transmitting signal has been discontinued or has fallen below a certain level. Multiple transmission frequencies, transmitters, and or sensors, among other things, may be used.

Claims

1. A method for synchronous detection of a pulsed signal in a transmit-receive detection system comprising:

transmitting at least one transmitted signal, said signal having a frequency, continuously for a period of time;

receiving a return signal on at least one sensor, said return signal corresponding to said transmitted signal;

synchronously demodulating said return signal to calculate the relative magnitudes and phases between said at least one return signal and said at least one transmitted signal;

ceasing to transmit said transmitted signal;

after ceasing to transmit said transmitted signal, continuing to demodulate said return signal whereby a timing relationship with said at least one transmitted signal is maintained.

2. The method of claim 1 wherein a plurality of transmitted signals are transmitted.

3. The method of claim 2 wherein each of said transmitted signals features a different frequency.

4. The method of claim 1 wherein said transmitting and said receiving are performed using a plurality of transmitters and sensors.

5. The method of claim 1 wherein said transmitting is performed using different transmitters to transmit different frequencies or sets of frequencies.

6. The method of claim 5 wherein at least two of said different frequencies are of a different physical nature.

7. The method of claim 6 wherein one of said different frequencies is sound, and another of said frequencies is an electric field.

8. The method of claim 1 wherein said receiving is performed using different sensors to receive different frequencies or sets of frequencies.

9. The method of claim 8 wherein at least two of said different frequencies are of a different physical nature.

10. The method of claim 9 wherein one of said different frequencies is sound, and another of said frequencies is an electric field.

11. The method of claim 1 wherein the synchronous demodulation ceases and is restarted maintaining the timing relationship with said at least one transmitted signal for at least one period during transmission of the continuous signal and for a time after the transmitter signal has stopped.

12. The method of claim 1 wherein said synchronous demodulation is performed using an analog phase detector.

13. The method of claim 1 wherein said synchronous demodulation is performed using an analog phase detector.

14. The method of claim 1 wherein said synchronous demodulation is performed by a computer using software.

15. The method of claim 1 wherein said at least one transmitted signal comprises a pulse stream and at least one of said pulses includes changed frequency content in order to enhance detectability under specific conditions.

16. The method of claim 15 wherein frequency content of pulses in the pulse stream is changed in real-time for the purpose of enhancing penetration in changing background materials.

17. The method of claim 15 wherein frequency content of pulses in the pulse stream is changed in real-time for the purpose of enhancing penetration in changing material type or composition in eddy current material analysis.

18. The method of claim 15 wherein frequency content of pulses in the pulse stream are changed in real-time for the purpose of enhancing detectability of certain objects based on the return signal.

19. The method of claim 18 wherein if the return signal indicates presence of a nonmagnetic but highly resistive material, changing the frequency content of said transmitted signal to determine thickness of the material based on skin depth estimations.

20. The method of claim 19 wherein said changing is performed in order to differentiate between thick resistive materials and thin conductive materials such as foils, that would otherwise exhibit similar frequency responses over certain frequencies.

21. A method of synchronous detection of a pulsed signal in a transmit-receive detection system comprising:

transmitting, continuously for a period of time, a plurality of transmitted signals, at least some of said signals including a frequency different from a frequency in other of said signals;

receiving a plurality of return signals on at least one sensor, said return signals corresponding to said transmitted signals;

synchronously demodulating said return signals to calculate the relative magnitudes and phases between said return signals and said transmitted signals;

ceasing to transmit at least some of said transmitted signals;

after ceasing to transmit said at least some of said transmitted signals, continuing to demodulate said return signals whereby a timing relationship with said transmitted signals is maintained.

22. A method of synchronous detection of a pulsed signal in a transmit-receive detection system comprising:

transmitting, continuously for a period of time, a plurality of transmitted signals, at least some of said signals including a frequency different from a frequency in other of said signals, said transmitting performed using a plurality of transmitters;

receiving a plurality of return signals on a plurality of sensors, said return signals corresponding to said transmitted signals;

synchronously demodulating said return signals to calculate the relative magnitudes and phases between said return signals and said transmitted signals;

ceasing to transmit at least some of said transmitted signals;

after ceasing to transmit said at least some of said transmitted signals, continuing to demodulate said return signals whereby a timing relationship with said transmitted signals is maintained.