Standoff distance variation compensator and equalizer

• US 6,462,561 B1
• Filed: 07/14/2000
• Issued: 10/08/2002
• Est. Priority Date: 07/14/2000
• Status: Expired due to Fees

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Zoughi, Reza, Brown, Lawrence M., Bigelow, Timothy A., Qaddoumi, Nasser Nidal
• Primary Examiner(s): Sherry, Michael
• Assistant Examiner(s): Nguyen, Trung Q.
• Application Number:
  US09/616,971
• Time in Patent Office: 816 Days
• Field of Search: 324/96, 324/639, 324/644, 324/750, 324/753, 324/637, 324/22, 324/333, 324/338, 324/351, 324/346, 324/369, 175/45, 175/48, 175/152, 73/46, 731/52, 340/853, 342/357, 342/451, 701/213
• US Class Current: 324/637
• CPC Class Codes: G01N 22/00 Investigating or analysing materials by the use of microwaves or radio waves, i.e. electromagnetic waves with a wavelength of one millimetre or more G01N3/00 - G01N17/00, G01N24/00 take precedence

Abstract

An inventively enhanced near-field sensor includes circuitry which removes variation in standoff distance (of the sensor from the inspected object) as a factor in the inspection system readings. An original output voltage which varies linearly according to standoff distance is, modified and added to a counterbalancing output voltage which equivalently but oppositely varies linearly according to standoff distance, resulting in a constant output voltage regardless of standoff distance. For calibration purposes, a third output voltage can also be summed along with the modified output voltage and the counterbalancing output voltage. Since the effect of surface variation is nullified, the practitioner can more truly assess the interior physical condition of the inspected object, knowing that the object'"'"'s surface roughess is rendered irrelevant.

Claims

1. For use in association with a sensing device which is capable of transmitting and receiving electromagnetic radiation for inspecting an object, said sensing device including a detector for producing a signal which is indicative of said electromagnetic radiation, apparatus comprising a distance-correction circuit which is adaptable to being in connection with said detector so that said distance-correction circuit adjusts said output voltage signal so as to account for variation in said output voltage signal due to variation in the distance of said sensing device from said object, wherein in the absence of said distance-correction circuit said detector produces a distance-dependent voltage output signal, said distance-dependent voltage output signal being variable in accordance with said distance, and wherein in combination with said distance-correction circuit said detector produces a distance-independent voltage output signal, said distance-independent voltage output signal being invariable in accordance with said distance.

2. Apparatus as recited in claim 1, wherein said distance-dependent voltage output signal varies linearly in accordance with said distance.

3. Apparatus as recited in claim 1, wherein said distance-correction circuit includes:

a proportionality subcircuit, for producing a counteractive voltage output signal which is variable in accordance with said distance so that said distance-dependent voltage output signal and said counteractive voltage output signal vary in accordance with said distance in generally opposite manners;

a compensation subcircuit, for modifying said distance-dependent voltage output signal so as to become a modified voltage output signal so that said modified voltage output signal and said counteractive voltage output signal vary in accordance with said distance in commensurately opposite manners; and

a summation subcircuit, for combining said counteractive voltage output signal and said modified voltage output signal so as to result in said distance-independent voltage output signal.

4. Apparatus as recited in claim 3, wherein said distance-dependent voltage output signal, said counteractive voltage output signal, said modified voltage output signal and said distance-independent voltage output signal each vary linearly in accordance with said distance.

5. Apparatus as recited in claim 4, wherein the absolute value of the slope defined by said modified voltage output signal is equal to the absolute value of the slope defined by said counteractive voltage output signal.

6. Apparatus as recited in claim 3, wherein said proportionality subcircuit includes potentiometer means for being indicative of variation in said distance.

7. Apparatus as recited in claim 3, wherein said proportionality subcircuit includes a spring-loaded piston potentiometer which physically contacts said object so as to be indicative of variation in said distance.

8. Apparatus as recited in claim 3, wherein:

said compensation subcircuit includes a variable resistor having a resistance R_vary;

said distance-dependent voltage output signal has a voltage V_orig;

said modified voltage output signal has a voltage V_mod; and

said voltage V_mod is a function of the product of said voltage V_orig and an expression which includes said resistance R_vary.

9. Apparatus as recited in claim 8, wherein:

said counteractive voltage output signal has a voltage V_counter; and

the absolute value of the slope described by voltage V_counter equals the absolute value of the slope described by V_mod.

10. Apparatus as recited in claim 3, wherein:

said compensation subcircuit includes an operational amplifier, said operational amplifier including a first resistor having a nonvariable resistance R_nonvary1, a second resistor having a nonvariable resistance R_nonvary2 and a third resistor having a variable resistance R_vary;

said distance-dependent voltage output signal has a voltage V_orig;

said modified voltage output signal has a voltage V_mod; and

 

V_mod=V_orig[1+(R_vary+R_nonvary1)/R_nonvary2].

11. Apparatus as recited in claim 10, wherein:

said counteractive voltage output signal has a voltage V_counter; and

the absolute value of the slope defined by voltage V_counter equals the absolute value of the slope defined by V_mod.

12. Apparatus as recited in claim 3, wherein said distance-correction circuit includes:

a proportionality subcircuit, for producing a counteractive voltage output signal which is variable in accordance with said distance so that said distance-dependent voltage output signal and said counteractive voltage output signal vary in accordance with said distance in generally opposite manners;

a compensation subcircuit, for modifying said distance-dependent voltage output signal so as to become a modified voltage output signal so that said modified voltage output signal and said counteractive voltage output signal vary in accordance with said distance in commensurately opposite manners;

an offset subcircuit for producing an offset voltage output signal which is invariable in accordance with said distance; and

a summation subcircuit for combining said counteractive voltage output signal, said modified voltage output signal and said offset voltage output signal so as to result in said distance-independent voltage output signal.

13. Apparatus as recited in claim 12, wherein said distance-dependent voltage output signal, said counteractive voltage output signal, said modified voltage output signal, said offset voltage output signal and said distance-independent voltage output signal each vary linearly in accordance with said distance.

14. Apparatus as recited in claim 12, wherein said offset subcircuit is for producing a said offset voltage output signal having a selected voltage, thereby resulting in a said distance-independent voltage output signal having a selected voltage.

15. Apparatus as recited in claim 12, wherein:

said counteractive voltage output signal has a voltage V_counter;

said modified voltage output signal has a voltage V_mod;

said offset voltage output signal has a voltage V_offset;

said distance-independent voltage output signal has a voltage V; and

V=one of

16. Apparatus as recited in claim 15, wherein said offset subcircuit is for producing a said offset voltage output signal having a selected voltage V_offset, thereby resulting in a said distance-independent voltage output signal having a selected voltage V.

17. Apparatus as recited in claim 16, wherein said offset subcircuit includes a resistor having a variable resistance R_offset, and wherein voltage V_offset is a function of resistance R_offset.

18. Apparatus as recited in claim 15, wherein:

said distance-dependent voltage output signal has a voltage V_orig;

said compensation subcircuit includes a resistor having a resistance R_vary; and

said voltage V_mod is a function of the product of said voltage V_orig and an expression which includes said resistance R_vary.

19. Apparatus as recited in claim 15, wherein:

said distance-dependent voltage output signal has a voltage V_orig;

said compensation subcircuit includes an operational amplifier, said operational amplifier including a first resistor having a nonvariable resistance R_nonvary1, a second resistor having a nonvariable resistance R_nonvary2 and a third resistor having a variable resistance R_vary; and

 

V_mod=V_orig[1+(R_vary+R_nonvary1)/R_nonvary2].

20. Apparatus as recited in claim 19, wherein:

said offset subcircuit is for producing a said offset voltage output signal having a selected voltage V_offset, thereby resulting in a said distance-independent voltage output signal having a selected voltage V;

said offset subcircuit includes a resistor having a variable resistance R_offset; and

said voltage V_offset is a function of said resistance R_offset.

21. Apparatus as recited in claim 1, wherein:

said object has an object surface area which faces said sensing device;

said sensing device has a device opening for permitting said transmitting and said receiving of said electromagnetic radiation; and

said distance is the distance from said device opening to said object surface area.

22. Apparatus as recited in claim 21, wherein:

said surface area is characterized by a degree of surface roughness;

said distance varies in accordance with said surface roughness; and

said distance-independent voltage output signal is invariable in accordance with said surface roughness.

23. Apparatus as recited in claim 1, wherein:

said object has an object surface characterized by a degree of surface roughness;

said sensing device is movable in a direction parallel to said object surface;

said distance-correction circuit includes a piston potentiometer which is coupled with said sensing device and which contactingly traverses said object surface while said sensing device is moving in said direction parallel to said object surface, said piston potentiometer thereby being indicative of variation in said distance which is attributable to said surface roughness; and

said distance-independent voltage output signal is the aggregation of plural component voltage signals, said component voltage signals including a first component voltage signal and a second component voltage signal, said first component voltage signal relating to said piston potentiometer and being variable in accordance with said distance, said second component voltage signal relating to said distance-dependent voltage output signal and being variable in accordance with said distance, wherein said first component voltage signal and said second component voltage signal neutralize each other while said sensing device is moving in said direction parallel to said object surface.

24. Apparatus as recited in claim 23, wherein said component voltage signals include a third component voltage signal which is constant, said third component voltage signal being aggregated along with said first component voltage signal and said second component voltage signal so as to set said distance-independent output signal at a selected value.

25. For effectuation in association with a sensing device which is capable of transmitting and receiving electromagnetic radiation for inspecting an object, said sensing device including a detector for producing an output voltage signal which is indicative of said electromagnetic radiation, a method comprising adjusting said output voltage signal so as to account for variation in said output voltage signal due to variation in the distance of said sensing device from said object, said adjusting including connecting a distance-correction circuit with said detector, wherein:

in the absence of said distance-correction circuit said detector produces a distance-dependent voltage output signal, said distance-dependent voltage output signal being variable in accordance with said distance; and

in combination with said distance-correction circuit said detector produces a distance-independent voltage output signal, said distance-independent voltage output signal being invariable in accordance with said distance.

26. A method as recited in claim 25, wherein said adjusting includes:

producing a counteractive voltage output signal, said counteractive voltage output signal varying in accordance with said distance so that said distance-dependent voltage output signal and said counteractive voltage output signal vary in accordance with said distance in generally opposite manners;

modifying said distance-dependent voltage output signal signal so as to become a modified voltage output signal so that said modified voltage output signal and said counteractive voltage output signal vary in accordance with said distance in commensurately opposite manners; and

combining said counteractive voltage output signal and said modified voltage output signal;

wherein said distance-independent voltage output signal is based on said combining of said counteractive voltage output signal and said modified voltage output signal.

27. A method as recited in claim 26, wherein said distance-dependent voltage output signal, said counteractive voltage output signal, said modified voltage output signal and said distance-independent voltage output signal each vary linearly in accordance with said distance.

28. A method as recited in claim 26, wherein:

said adjusting includes producing an offset voltage output signal;

said combining signals includes combining said counteractive voltage output signal, said modified voltage output signal and said offset voltage output signal; and

said distance-independent voltage output signal is based on said combining of said modified voltage output signal, said counteractive voltage output signal and said offset voltage output signal.

29. A method as recited in claim 28, wherein said distance-dependent voltage output signal, said counteractive voltage output signal, said modified voltage output signal, said offset voltage output signal and said distance-independent voltage output signal each vary linearly in accordance with said distance.

30. A method as recited in claim 29, wherein said producing an offset voltage output signal includes producing a said offset voltage output signal having a selected voltage, thereby resulting in a said distance-independent voltage output signal having a selected voltage.

31. A method as recited in claim 29, wherein:

said producing a counteractive voltage output signal includes using a potentiometer to produce a potentiometer voltage, and includes using a first operational amplifier with respect to said potentiometer voltage, said counteractive voltage output signal being related to said potentiometer voltage;

said modifying said distance-dependent voltage output signal includes using a second operational amplifier with respect to said nonconstant detector signal, said using a second operational amplifier including using a first variable resistor to establish a first resistance, said modified voltage output signal being related to said said first resistance;

said producing an offset voltage output signal includes using a third operational amplifier, said using a third operational amplifier including using a second variable resistor to establish a second resistance, said offset voltage output signal being related to said second resistance; and

said combining said counteractive voltage output signal, said modified voltage output signal and said offset voltage output signal includes performing an additive operation with respect to the voltages corresponding to said counteractive voltage output signal, said modified voltage output aid offset voltage output signal.

32. Apparatus as recited in claim 25, wherein:

said object has an object surface characterized by a degree of surface roughness;

said sensing device is movable in a direction parallel to said object surface;

said adjusting includes coupling a piston potentiometer with said sensing device so as to contactingly traverse said object surface while said sensing device is moving in said direction parallel to said object surface, said piston potentiometer thereby being indicative of variation in said distance which is attributable to said surface roughness; and

said adjusting includes aggregating plural component voltage signals, said component voltage signals including a first component voltage signal and a second component voltage signal, said first component voltage signal relating to said piston potentiometer and being variable in accordance with said distance, said second component voltage signal relating to said distance-dependent voltage output signal and being variable in accordance with said distance, wherein said first component voltage signal and said second component voltage signal neutralize each other while said sensing device is moving in said direction parallel to said object surface.

33. A near-field sensing device of the kind which transmits electromagnetic energy to and receives electromagnetic energy from an entity of interest during nondestructive scanning of an entity, said near-field sensing device being situated at a standoff distance from a surface of said entity and being caused to move parallel to said surface during said scanning, said surface being characterized by surface roughness which affects said standoff distance during said scanning, said near-field sensing device comprising:

a detector which outputs an initial voltage which indicates a condition of said electromagnetic radiation during said scanning, wherein during said scanning said initial voltage is dependent on said standoff distance and hence is dependent on said surface irregularity; and

electronic apparatus which inputs said initial voltage and outputs a final voltage during said scanning, said electronic apparatus including a piston potentiometer which is attached to said near-field sensing device and which contacts said surface during said scanning, wherein during said scanning said piston potentiometer continually measures said standoff distance so as to result in a proportionality voltage which generally represents an additive inverse of said initial voltage, said final voltage being based on the addition of said proportionality voltage and said initial voltage whereby said final voltage is independent of said standoff distance and hence is independent of said surface irregularity.

34. The near-field sensing device according to claim 33, said electronic apparatus comprising:

a first operational amplifier which generates said proportionality voltage, said potentiometer generating a potentiometer voltage, said first operational amplifier adjusting the value of said potentiometer voltage so as to become said proportionality voltage;

a second operational amplifier which generates a compensation voltage, said second operational amplifier adjusting the value of said initial voltage so as to become said compensation voltage, whereby the respective values of said proportionality voltage and said compensation voltage additively counterbalance each other;

a third operational amplifier which generates a constant offset voltage; and

a fourth operational amplifier which generates said final voltage, said fourth operation amplifier being connected to said first operational amplifier, said second operational amplifier and said third operational amplifier, said final voltage being based on the sum of the respective values of said proportionality voltage, said compensation voltage and said offset voltage.

35. The near-field sensing device according to claim 34, wherein said detector includes a crystal diode detector.

36. The near-field sensing device according to claim 34, wherein said second operational amplifier includes a first-variable resistor for performing said adjusting of the value of said initial voltage, and wherein said third operational amplifier includes a second variable resistor for selecting the value of said offset voltage.

37. The near-field device according to claim 34, wherein the value of said offset voltage selectively determines the value of said final voltage.