RADIATION DEVICE OR SIGNAL

• US 20100155609A1
• Filed: 09/11/2007
• Published: 06/24/2010
• Est. Priority Date: 09/11/2006
• Status: Abandoned Application

• Current Assignee: Cook Incorporated (Cook Group Incorporated), Medway N H S Trust
• Original Assignee: Medway N H S Trust
• Inventors: Silva, Ronald Laksham
• Application Number:
  US12/440,774
• Publication Number:
  US 20100155609A1
• Time in Patent Office: Days
• US Class Current: 250/363.60
• CPC Class Codes: G01S 7/00 Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
• CPC Class Codes: G01T 1/295 using coded aperture devices, e.g. Fresnel zone plates handling of radiation of particles, e.g. using diaphragms, collimators, diffraction G21K1/00
• CPC Class Codes: G02B 3/08 with discontinuous faces, e.g. Fresnel lens diffractive Fresnel lenses G02B5/1876
• CPC Class Codes: G02B 5/1876 Diffractive Fresnel lenses; Zone plates; Kinoforms G02B5/1842, G02B5/1847 take precedence; optical systems having diffractive correction means G02B27/0037; Fresnel lenses operating by refraction G02B3/08
• CPC Class Codes: G10K 11/26 Sound-focusing or directing, e.g. scanning

Abstract

A zoned radiation device for converging radiation of a wavelength λ to a focus at distance b, the device comprising a first set of zones and a second set of zones, wherein the first set of zones have a different characteristic to the second set and wherein the area of the zones decrease as their distance from a predetermined point increases, and one or more zone distances at which a zone of the first set with a first characteristic switches to a second zone with a second characteristic are configured such that the device can focus the radiation with wavelength λ at a distance b with an autocorrelation/point spread function that is sharper than the autocorrelation/point spread function produced by zones configured to a Fresnel zone construction.

Claims

1. A zoned radiation device for converging radiation of a wavelength λ

to a focus at distance b, the device comprising a first set of zones and a second set of zones, wherein the first set of zones have a different characteristic to the second set and wherein the area of the zones decrease as their distance from a predetermined point increases, and one or more zone distances at which a zone of the first set with a first characteristic switches to a second zone with a second characteristic are configured such that the device can focus the radiation with wavelength λ

at a distance b with an autocorrelation/point spread function that is sharper than the autocorrelation/point spread function produced by zones configured to a Fresnel zone construction.

2. A zoned radiation device according to claim 1 wherein the zone distances are radii.

3. A zoned radiation device according to claim 2 wherein the radii are radii from the predetermined point.

4. A zoned radiation device according to any preceding claim wherein the predetermined distance is the centre of the device and/or zones.

5. A zoned radiation device according to any preceding claim wherein the first and/or second set of zones comprises one or more zones and preferably a plurality of zones.

6. A zoned radiation device according to any preceding claim wherein the areas of the zones decrease from the point as a function of n where n is an integer that increases by one for each zone.

7. A zoned radiation device according to claim 6 wherein the areas of the zones vary approximately in proportion to {log_e(n)−

log_e(n−

1)}.

8. A zoned radiation device according to any preceding claim wherein the one or more zone distances are substantially close to fitting the equation {bλ

log_e(n)}^1/2 or {b λ

log_e(n)+(λ

/2 log_e(n))²}^1/2 measured from the centre of the zones such that the device can focus the radiation with wavelength λ

at b with an auto correlation function that is significantly sharper than the autocorrelation function produced by radii configured to the Fresnel construction of (nbλ

)^1/2 or (nbλ

+(n²λ

²)/4)^1/2.

9. A zoned radiation device according to any preceding claim wherein the zones are configured to produce a built in obliquity compensation factor which is preferably approximately proportional to {log_e (n)−

log_e(n−

1)}.

10. A zoned radiation device according to any preceding claim wherein the first characteristic comprises a degree of transparency that is high relative to the second set of zones and the second characteristic comprises a degree of transparency that is low relative to the first set of zones, preferably wherein the second set of zones are opaque to the radiation of wavelength λ

.

11. A zoned radiation device according to any preceding claim wherein the second set of zones comprises a refractive material which imposes a phase shift on radiation which passes through it and preferably is significantly transparent to the radiation.

12. A zoned radiation device according to claim 11 wherein the phase shift imposed on radiation of wavelength λ

is ±

π

{log_e(n)−

log_e(n−

1)} preferably with the sign positive throughout, negative throughout or with alternating between + and −

with n.

13. A zoned radiation device according to claim 11 wherein at least some of the second set of zones comprises refractive material configured so that radiation of wavelength λ

is operably converged by it to arrive at the focus with the correct phase.

14. A zoned radiation device according to claim 13 wherein the device comprises a material having a refractive index η

and a thickness of about τ

where τ

=(λ

/2η

){log_e(n)−

log_e(n−

1)}.

15. A zoned radiation device according to any preceding claim for converging, thermal neutrons, acoustic radiation, seismic waves, or electromagnetic radiation such as gamma or x-rays.

16. A zoned radiation device according to any preceding claim wherein the zones are configured so that the image aberration is less than the image aberration produced by zones configured to the Fresnel construction.

17. A zoned radiation device according to any preceding claim wherein the configuration of zones is derivable from a solution to a wave equation that includes phase and a non-constant amplitude.

18. A collimator or ophthalmic lens comprising the device of any preceding claim for collimating or focusing radiation.

19. A monochromatizer comprising a device of any of claims 1 to 15 and an further aperture spaced from the device at a distance of about b that operably removes unwanted wavelengths of radiation.

20. A teleconverter lenses for a compact digital cameras comprising a radiation device according to claim 16 preferably when dependent on claim 13 or 14.

21. A two-dimensional array of apertures or lenses, preferably for use in acoustic ink printing, comprising one or a plurality of devices according to any of claims 1 to 17.

22. A coded aperture comprising the device of any preceding claim for casting shadows in a plane from, and preferably not significantly diffracting, radiation of a wavelength smaller than λ

.

23. A coded aperture imaging apparatus, for imaging an object, comprising an aperture according to claim 22 and one or more of external radiation source, a detector which can be sensitive to colour and/or polarization, a data processor and an image display for displaying a reconstructed image.

24. A coded aperture imaging apparatus according to claim 23 when dependent on claim 15 wherein the image may encode information based on amplitude.

25. A coded aperture imaging apparatus according to claim 23 or 24 wherein the processor is programmed to reconstruct an image of the object by using a decoding function which is preferably designed to reduce the side-lobes of the autocorrelation/point-spread-function of the coded aperture.

26. A coded aperture imaging apparatus according to claim 25 wherein the decoding function is scaled so that it operably obtains a reconstructed image of a two-dimensional slice of a three-dimensional object.

27. Apparatus according to any of claims 23 to 26 where in the detector is a flat panel detector configured to convert radiation, directly to a coded image

28. Apparatus according to any of claims 23 to 26 where in the detector is a flat panel detector configured to convert radiation, indirectly preferably by a fluorescent material in conjunction with a photo diode, to form the coded image.

29. Apparatus according to any of claims 23 to 28 configured to sequentially capture views of an object and/or that comprises a plurality of coded apertures according to claim 20 a to capture different views of the object.

30. Apparatus according to any of claims 23 to 29 wherein the processor is programmed to replace the coded image by a replacement image preferably by multiplying the values of the coded image by −

1 in a digital version of the coded image or by making a contact print of the coded image, such as in use with photographic methods for recording the coded image.

31. A coded aperture system comprising apparatus according to any of claims 23 to 30 and an object wherein the detector is positioned relative to the object to receive radiation from the object within a cone of illumination, the base of the cone given approximately by

$d_{\max }\le$

0.5 * S ci 

( a ca b ca )

and the height of this cone given by a₂, where

$+\mathrm{¿<br><br>}<br><br><br><br>a_2=\mathrm{¿<br><br>}<br><br><br><br>a_{\mathrm{ca}}$ $a_1<br><br>\mathrm{¿<br><br>}$ $\mathrm{¿<br><br>}$

the total distance from the object to the coded aperture, d_max is the maximum diameter of the object, S_ci diameter of the coded image at the detector.

32. The use of a zoned device or imaging system according to any of claims 1 to 31 in astronomy, nuclear medicine, molecular imaging, contraband detection, land mine detection, small animal imaging, detecting improvised explosive devices and imaging of inertial confinement fusion targets and/or with an object that is anatomical and/or radioactive.

33. The use of a device according to any preceding claim for wireless applications, acoustic microscopy, and/or in concert halls for analysing and applying the acoustic response of a concert hall to music recorded in a studio.

34. A method of determining the presence of tumours comprising the step of evaluating a reconstructed image produced by using an aperture or apparatus according to any of claims 22 to 31.

35. A method of three-dimensional imaging from single projections of a coded image using a coded aperture or apparatus according to any of claims 22 to 31.

36. A method of determining the existence of contraband articles comprising the step of evaluating a reconstructed image produced by using an aperture or apparatus according to any of claims 22 to 31.

37. An off axis zoned radiation device comprising a device according to any of claims 1 to 31 wherein the zones are off axis, the centre of the device being separate form the predetermined point.

38. A zoned radiation device according to any of claims 1 to 31 wherein the zones are annular or circular

39. A 1-dimensional or linear zoned radiation device comprising a device according to any of claims 1 to 31 wherein the zone distances from a line through the predetermined point are substantially constant along each zone.

45. A signal comprising a cycle according to claim 44 and a second cycle of chirp pulses according to any of claims 30 to 33 wherein the pulses have a different initial phase φ

(0) from the pulses of the first cycle.

47. A method of coded aperture imaging of an object using the coded aperture or apparatus of any of claims 22 to 31

48. A method of coded aperture imaging of an object according to claim 38 comprising the step of changing the position of the object relative to the coded aperture mask and the detector to obtain an image of a cross-sectional slice of a three-dimensional object.

50. A 1-dimensional or linear zoned radiation device comprising a device according to any of claims 1 to 31 wherein the zone distances comprise arcs of a circle.

40. A non-linear chirp signal for carrying, collecting or determining data, the chirp having a frequency that increases or decreases with time, wherein the rate of increase or decrease of frequency of the chirp is configured such that the signal has an autocorrelation/impulse response function that is sharper than the autocorrelation/impulse response function produced by a linear chirp signal.

41. A non-linear chirp signal according to claim 40 wherein the configuration of the rate of increase of frequency is derivable from a solution to a wave equation that includes phase and a non-constant amplitude.

42. A non-linear chirp signal according to claim 40 or 41 wherein the image may carry or collect or determine information based on/including encoded amplitude terms.

43. A non-linear chirp signal according to any of claims 40 to 42 of a form substantially close to

$x$

( t ) = cos 

{ 2 

π



( a ch b ch 

exp 

( b ch 

t ) ) 

t + ϕ



( 0 ) }

where a_ch is an amplitude term and b_ch is the chirp rate and φ

(0) is the phase at time zero, to produce a sharp autocorrelation function with small side lobes.

44. A cycle of chirp pulses according to any of claims 40 to 43 wherein the pulses have a different initial phase φ

(0) from each other.

46. A signal comprising a supercycle of the cycle of claim 44 and the second cycle of claim 45 to produce pulses, such as to invert the longitudinal magnetisation in the sample in NMR applications, and/or for detecting the signals emitted by the sample in response to inversion of the longitudinal magnetisation.

49. A method of producing a chirp signal or cycle comprising producing a signal or cycle according to any of claims 40 to 46 and/or the steps of constructing circles with radii approximately equal to {bλ

log_e(n)}^1/2 or {bλ

log_e(n)+(λ

/2 log_e(n))²}^1/2;

evaluating the distance between adjacent radii Δ

R_n=(R_n−

R_n-1) where n=2, 3, 4, 5;

plotting the reciprocal of Δ

R_n against radius R_n;

fitting a curve to this spatial frequency vs radius variation as this functional form f(r) defines the instantaneous spatial frequency variation as a function of distance;

determining the amplitude term a and the chirp rate b from curve fitting;

using the relationship between the phase of the quantum chirp signal φ

(r) and the instantaneous spatial frequency variation given by

$f<br><br>\left(r\right)=\frac{1}{2<br><br>\mathrm{\pi <br><br>}}<br><br>\frac{<br><br>\mathrm{\varphi <br><br>}<br><br>\left(r\right)}{<br><br>r}$

to construct a spatial signal approximately of the form x(r)=cos(φ

(r)) and finally constructing a temporal chirp signal by replacing the distance variable with time and the spatial frequency with temporal frequency;

preferably producing a temporal chirp of the form

$x<br><br>\left(t\right)=\cos <br><br>\left\{2<br><br>\mathrm{\pi <br><br>}<br><br>\left(\frac{a_{\mathrm{ch}}}{b_{\mathrm{ch}}}<br><br>\exp <br><br>\left(b_{\mathrm{ch}}<br><br>t\right)\right)<br><br>t+\mathrm{\varphi <br><br>}<br><br>\left(0\right)\right\}$

where a_ch is an amplitude term and b_ch is the chirp rate and φ

(0) is the phase at time zero.