JP3709439B2 - Apparatus and method for displaying image of object by terahertz electromagnetic wave - Google Patents

Description

【００３９】
αは１、１．５等の任意に定める定数である。Ｑは物体の厚さｄに依存しない量である。
【００４０】
（１）と（３）を基に、
Ｐ² ＝βω_c Δｔln（Ａ₀ ／Ａ）＝Δk Δn(ω_c ／ｃ) ² ｄ²
であるＰを導入する。βは１、１．５等の任意に定める定数である。このＰ² は、厚さに強く依存し、材質による依存の程度は小さい量である。本発明は測定データ（Ａ₀ 、Ａ、ω_c 、Δｔ）をもとにこのパラメータＱとＰ² の値を求め、そのパラメータをもとに物体の画像表示をするようにした。
【００４１】
図４は、小麦粉中の３つのプラスチックのサンプルをテラヘルツ電磁波による測定結果をもとに、従来の振幅モード、時間遅延モード、およびパラメータＱ、Ｐ² をもとに画像表示した例を示す。
【００４２】
左上、右上および下側に一つずつのプラスチックの小片がある。下側と右上の物体はポリオキシメチレン（ＰＯＭ）の小さい板である。上左の小片はアクリルニトリル−ブタジエン−スチロール コポリマ−（ＡＳＢ）の小さい板である。下側のＰＯＭ板の厚さは２．８ｍｍであり、上部の二つの板の厚さは１．０ｍｍである。
【００４３】
図４（ａ）は振幅モードであり、図４（ｂ）は時間遅延モードでの画像表示である。厚いＰＯＭ板は（ａ）と（ｂ）ともにコントラストがはっきりしているが、二枚の薄い板のコントラストは厚い板ほどはっきりしていない。図４（ｃ）において、Ｐ² は明度で表現している。板が厚い程Ｐ² の値は大きくなり、明るく（白く）表している。また、Ｑは赤から緑までの彩度で表している。緑側は大きいＱを表し、赤側が小さいＱを表している。図４（ｃ）ではＡＢＳは赤で表され、ＰＯＭは緑で表されている。図４（ｃ）から明らかなように、本発明によれば物体の厚さに関係なく物体の材質による違いがわかるように画像表示することが可能になる。
【００４４】
図５は、本発明のＱモードにより物体を画像表示した別の例を示す（但し、物体は粉体中に含まれていない）。ＰＯＭ棒の画像が画面の上部にあり、野球のホームベースの形状の二枚のＰＰ（ポリプロピレン）板（図６（ｂ）参照）の画像が画面の下側の左右にある。ＰＯＭの棒は厚さが左側から右側に向かって、１．５ｍｍから３．０ｍｍまで連続的に変化するものである（図６（ａ）参照）。二枚のＰＰ板は厚さがそれぞれ１．８ｍｍと２．８ｍｍであり、左側は薄い方であり、右側は厚い方である。
【００４５】
図５（ａ）は振幅モードで表示したものである。図５（ｂ）は時間遅延モードで表した画像である。右側に向かって厚さが厚くなり、明度が高くなる（白くなる）ように表している。ＰＯＭの画像では厚さの変化が画像で明度変化として表れている。ＰＰの画像では厚さの厚い方は白く表示されているが、厚さの薄い方は黒く表され、厚さの違いが表されている。図５（ｃ）はＱで表した画像である。ＰＯＭはピンクで表され、ＰＰは青く表され、材料の違いが明瞭に表示されている。
【００４６】
図６は、図５の画像化の対象になったＰＯＭ棒とＰＰ板の形状を示す。図６（ａ）はＰＯＭ棒であり、厚さが左側から右側に向かって、１．５ｍｍから３．０ｍｍまで連続的に変化している。図６（ｂ）は、ＰＰ板であり、厚さが１．８ｍｍと２．８ｍｍについて、画像化された。
【００４７】
図７は本発明の画像処理部のフローチャ−トを示す。
【００４８】
測定データを入力し保持する（Ｓ１）。さらに、Ａ₀ 、Ａ、Δｔ、ω_c を求め、保持する（Ｓ２）。Ａ₀ 、Ａ、Δｔ、ω_c によりＱを計算し、保持する（Ｓ３）。次に、Ａ₀ 、Ａ、Δｔ、ω_c によりをＰ² を計算し、保持する（Ｓ４）。Ｑに基づいて画像表示するか判定する（Ｓ５）。Ｓ５において、Ｑに基づく画像表示をするのであれば、Ｓ６において、Ｑの値に基づいて画像表示するための処理をする（Ｓ６）。Ｓ５において、Ｑに基づく画像表示をするのでなければ、Ｓ７において、Ｐ² に基づいて画像表示するか判断する（Ｓ７）。Ｓ７において、Ｐ² に基づいて画像表示するのであれば、Ｓ８においてＰ² の値に基づいて画像表示するための処理をする。Ｓ９で画像表示をする。Ｓ６のＱの値に基づいて画像表示する方法は、例えば、Ｑの値に応じて画像表示する彩度を定めるものである。また。Ｓ８におけるＰ² の値に基づいた画像表示は、例えば、Ｐ² の値に応じて画像表示の明度（輝度）を定めるものである。
【００４９】
図８は、本発明の画像処理部の構成であり、ＣＰＵとメモリにより構成されるものである。図８において、６２は画像処理部である。８０は測定データ入力部であって、ロック・インアンプから送られてくる測定データを入力するものである。８１は測定データ保持部であって、測定データを保持するものである。測定データは、テラヘルツ電磁波の周波数９１、試料の位置と測定時間（時刻）に対応したテラヘルツ電磁波の信号値９２である。８２は演算部であり、最大振幅演算、時間遅延演算、Ｑ演算、Ｐ² 演算を行うものである。８３は演算データ保持部であって、最大振幅、時間遅延、Ｑ、Ｐ² を保持するものである。８４は表示処理部であって、演算データをもとに画像表示データを作成するものである。８５は表示装置である。
【００５０】
測定データ保持部８１において、周波数９１は測定されたテラヘルツ電磁波の周波数をあらわす。位置−時間−信号値９２は測定されたテラヘルツ電磁波の試料における位置、測定時間（時刻）、信号値を表す。
【００５１】
演算部８２において、９３は最大振幅演算であって、試料を透過するテラヘルツ電磁波の振幅の最高値と最低値の差を求めるものである。９４は時間遅延演算部であって、物体を通過したテラヘルツ電磁波と物体を通過しなかったテラヘルツ電磁波のパルス最大値の時間差を求めるものである。９５はＱ演算部であって、Ｑを物体を通過しなかったテラヘルツ電磁波の最大振幅、物体を通過したテラヘルツ電磁波の最大振幅、伝搬遅延時間（時間遅延）、ω_c に基づいてＱを演算するものである。９６はＰ² 演算部であって、物体を通過しなかったテラヘルツ電磁波の最大振幅、物体を通過したテラヘルツ電磁波の最大振幅、時間遅延、ω_c に基づいてＰ² を演算するものである。
【００５２】
演算データ保持部８３において、最大振幅９７、時間遅延９８、Ｑ９９、Ｐ² １００は、それぞれ最大振幅演算部９３、時間遅延演算部９４、Ｑ演算部９５、Ｐ² 演算部９６で演算されたデータを表す。表示処理部８４において、彩度付与１０１は画像表示するデータに彩度を付与する処理を表す。例えば、Ｑの値に応じてあらかじめ決められている彩度を付与する処理である。明度付与１０２は画像表示するデータに明度を付与する処理を表す。例えば、Ｐ² の値に応じてあらかじめ決められている明度を付与する処理である。
【００５３】
図８の構成の動作を説明する。測定されたテラヘルツ電磁波の周波数、試料の位置、観測時間（時刻）に対応した信号値が入力され測定データ保持部に保持される。最大振幅演算部９３は、測定データをもとに試料を透過するテラヘルツ電磁波の振幅の最高値と最低値の差を求める時間遅延演算部９４は、測定データをもとに物体を通過したテラヘルツ電磁波と物体を通過しなかったテラヘルツ電磁波のパルス最大値の時間差を求める。Ｑ演算部９５は、物体を通過しなかったテラヘルツ電磁波の最大振幅、物体を通過したテラヘルツ電磁波の最大振幅、時間遅延、ω_c に基づいてＱを演算する。Ｐ² 演算部９６は、物体を通過しなかったテラヘルツ電磁波の最大振幅、物体を通過したテラヘルツ電磁波の最大振幅、時間遅延、ω_c に基づいてＰ² を演算するものである。
【００５４】
各演算部で測定されたデータは演算データ保持部８３に保持する。表示処理部８４は演算データ保持部８３に保持されている演算データをもとに表示装置８５に座像表示するデータを作成する。例えば、Ｑの値に応じてあらかじめ決められている彩度を付与する。また、Ｐ² の値に応じてあらかじめ決められている明度を付与する。表示装置８５は表示処理部８４で作成された表示データを画像表示する。
【００５５】
【発明の効果】
本発明によれば、テラヘルツ電磁波を利用して、物体の厚さに関わりなく物体の材質の相違が明確になるように画像表示できる、あるいは物体の厚さの相違が明確になるように画像表示することができる。特に、本発明は粉体中に埋もれている複数の物体をその材料の相違がわかるように表示することができる。あるいは、粉体中に埋もれている厚さの異なる複数の物体を厚さの違いがわかるように画像表示することができる。
【図面の簡単な説明】
【図１】本発明の実施の形態を示す図である。
【図２】本発明の試料の走査のフローチャートを示す図である。
【図３】テラヘルツ電磁波の各周波数における各種粉体の透過率を示す図である。
【図４】本発明で測定した物体の画像の例である。
【図５】本発明で測定した物体の画像の例である。
【図６】図５における物体の形状を表す図である。
【図７】本発明の画像処理部のフローチャートである。
【図８】本発明の画像処理部の構成である。
【図９】テラヘルツ電磁波による従来の表示モードの画像である。
【図１０】テラヘルツ電磁波による従来の表示モードの画像である。
【図１１】テラヘルツ電磁波による従来の表示モードの画像である。
【図１２】テラヘルツ電磁波分光により試料を画像化するための原理的説明図である。
【符号の説明】
１：気密容器
２：励起光源
３：レーザ光源
４、５、６、７、８、９、１０、１１、１２: 反射鏡
１５：チョッパー
２１：テラヘルツ電磁波発生器
２２：テラヘルツ電磁波受信器
３１：凹面反射鏡１
３２：凹面反射鏡２
３３：凹面反射鏡３
３４：凹面反射鏡４
４０: 試料
４１: 載置台
４３：物体
５１：電気的駆動部
５２：チョッパー駆動器
５３：時間遅延部
６１：ロックイン・アンプ
６２：画像処理部
６３：表示装置[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image display apparatus and method for an object using terahertz electromagnetic waves. In particular, terahertz electromagnetic waves are used to display an image so that the difference in the material of the object is clear regardless of the thickness of the object, or an image is displayed so that the difference in the thickness of the object is clear. The present invention relates to an image display apparatus and method.
[0002]
[Prior art]
By using terahertz electromagnetic waves, it is possible to detect an object such as plastic that is impossible with X-rays. Therefore, it can be used as an alternative to X-rays in airport safety checks and the like (see, for example, Patent Document 1).
[0003]
FIG. 12 shows in principle the method of imaging a sample by terahertz electromagnetic wave spectroscopy. In FIG. 12, 5, 6, 7, and 8 are reflecting mirrors (5 is a semi-transparent mirror). Reference numeral 21 denotes a terahertz electromagnetic wave generator in which a GaAs epitaxial film is formed on a semi-insulating GaAs substrate by low-temperature growth, and a dipole antenna 23 and a coplanar transmission path (AuGe / Ni / Au) 24 are disposed thereon. It is. Reference numeral 26 denotes an incident beam, which is a light pulse by a laser. Reference numeral 27 denotes pulsed light A that has passed through the semi-transparent mirror. 28 is pulsed light B reflected by a semi-transparent mirror and delayed by time τ. Reference numeral 29 denotes a terahertz electromagnetic wave generated by a terahertz electromagnetic wave generator. Reference numeral 40 denotes a sample to be measured. A time delay unit 53 delays the pulsed light reflected by the half mirror 5 by a time τ. Reference numeral 61 denotes a lock-in amplifier that processes an electric signal output from the terahertz electromagnetic wave receiver 22. Reference numeral 62 denotes an image processing unit which performs processing for imaging based on a signal output from the lock-in amplifier 61.
[0004]
The operation of the configuration of FIG. 12 will be described. The dipole antenna of the terahertz electromagnetic wave generator 21 is DC biased. When the pulsed light A is applied to the gap between the dipole antennas 23 of the terahertz electromagnetic wave generator 21, terahertz electromagnetic waves are generated from the dipole antenna 23, and the terahertz electromagnetic waves 29 reflected by the reflecting mirror 6 are incident on the sample 40. When the terahertz electromagnetic wave 29 passes through the sample 40, the electric field strength and the propagation phase change according to the material of the sample. The terahertz electromagnetic wave that has passed through the sample 40 is received by the dipole antenna of the terahertz electromagnetic wave receiver 22. On the other hand, the pulsed light B delayed by the time τ irradiates the gap portion of the dipole antenna of the terahertz electromagnetic wave receiver 22. The electric signal output from the terahertz electromagnetic wave receiver 22 is a signal having a magnitude corresponding to the electric field intensity of the terahertz electromagnetic wave 29 at time τ because the electric field intensity of the terahertz electromagnetic wave 29 is sampled by the pulsed light B. . By scanning the sample 40 in the xy direction and changing the delay time τ at each point on the xy plane of the sample 40, an image on the xy plane in the z coordinate corresponding to τ of the sample 40 is obtained. Obtainable. The inventor of the present invention has developed an inspection apparatus for observing foreign matters in powder (see Patent Document 2).
[0005]
Conventionally, when an object is observed with a terahertz imaging apparatus, the display mode is a waveform in a time domain, for example, an amplitude mode, an arrival time, or a main peak width (referred to as a pulse width mode). Was.
[0006]
9, FIG. 10 and FIG. 11 show examples in which an object in powder is observed with a terahertz electromagnetic wave of about 0.5 THz by the conventional observation method using the system of FIG.
[0007]
FIG. 9 shows two objects in powdered sugar in various display modes. There is an eggshell on the left, and plastic pieces on the right. The upper left image (a) is observed in a fixed time mode (image display based on single screen data at a fixed time). There are inherent problems with this display mode when imaging objects in powder. The powder tends to have a higher density in the lower part than in the upper part. Therefore, there is a difference in the arrival time of the pulse and the object cannot be clearly displayed as an image. In the lower half (a), the image of the object is mostly white. The top of the image is black. There is a difference of approximately 0.5 THz electromagnetic wave half cycle, that is, about 1 ps, between the upper and lower images. This means that pulsed THz electromagnetic waves can be an effective means of studying the vertical density distribution and local variations of the powder, but make imaging of objects in the powder difficult.
[0008]
FIG. 9B shows an amplitude mode based on the same measurement values as in FIG. 9A, and maps the peak of the pulse amplitude at each sample position. The presence of two objects is clearly imaged as compared to the case of FIG. Eggshell fragments appear darker than plastic fragments and surrounding powder. This is because transmitted light is reduced due to strong absorption of terahertz electromagnetic waves.
[0009]
FIG. 9C in the lower left shows a time delay mode and a display mode at the arrival time of the maximum pulse value. In order to compensate for the vertical change in the powder density, an offset surface obtained based on the time difference between the upper part and the lower part was used. The eggshell was much thinner than the plastic debris (approximately 0.4 mm and 1.5 mm, respectively), but the two objects produced the same degree of pulse delay. This reflects that the refractive index of the eggshell is greater than that of the plastic (approximately 2.7 and 1.6, respectively).
[0010]
FIG. 9D shows image display in the display mode based on the width of the maximum pulse value. Both objects are darker than the background, indicating a decrease in pulse width. The reason for this is considered to be that the high-frequency component of the terahertz electromagnetic wave does not easily pass through the powder (see FIG. 3).
[0011]
FIGS. 10A and 10B are photographs of a small piece of plastic and a small piece of glass taken by terahertz electromagnetic waves. There is a plastic piece at the top and a glass piece at the bottom. FIG. 10A shows the amplitude mode, and FIG. 10B shows the time delay mode.
[0012]
FIG. 11 shows an image of a cable clamp in flour. FIG. 11A is a sketch of a cable clamp. FIGS. 11B, 11C, and 11D are images in an amplitude mode, a time delay mode, and a pulse width mode using a terahertz electromagnetic wave, respectively. The contrast of the object background in FIGS. 11B and 11C is high, which indicates that the amount of the plastic material part through which the terahertz electromagnetic wave beam passes is large. This is particularly evident on the hook (right side) of the clamp made of a hard plastic material. The body of the clamp (left side) has a cavity, which creates a strong contrast between the side and bottom walls. The top of the cavity is open. The hole at the bottom of the main body has a diameter of 1.5 mm, which is smaller than the optical resolution of the terahertz electromagnetic wave passing through the powder, but is clearly shown in the image. The bottom of the clamp is displayed thicker than it actually is. The reason is considered that the sample was shaken so that the powder was uniformly filled in the box, and the clamp was rotated around the horizontal axis of the paper surface from the sketch state of FIG. The top and middle dark parts of the clamp body in the time delay mode of FIG. 11 (c) indicate that the hollow part of the body is probably filled with a thin density of wheat. This can be confirmed in the pulse width mode (d), where the pulse width is reduced in the same way as the surrounding flour.
[Patent Document 1]
JP 2000-514549
[Patent Document 2]
JP 2001-66375 A
[0013]
[Problems to be solved by the invention]
A conventional image display apparatus displays an image in an amplitude mode, a time delay mode, a pulse width mode, or the like in the time domain based on an amplitude change or a propagation phase change amount of a terahertz electromagnetic wave that has passed through an object. In such a mode, the difference between a plurality of objects having different thicknesses and materials cannot be displayed only by the difference in materials regardless of the thickness. Alternatively, it was not possible to display an image so that the difference in thickness of the object can be clearly seen.
[0014]
The present invention uses terahertz electromagnetic waves to display an image so that the difference in the material of the object becomes clear regardless of the thickness of the object, or to display an image so that the difference in the thickness of the object becomes clear. An object of the present invention is to provide an image display apparatus and method.
[0015]
[Means for Solving the Problems]
An image display device for an object using a terahertz electromagnetic wave according to the present invention includes an irradiating means for irradiating the object with a terahertz electromagnetic wave, a receiving means for receiving the terahertz electromagnetic wave that has passed through the object and converting it into an electrical signal, and an output of the receiving means. Means for acquiring the amplitude of the terahertz electromagnetic wave that has passed through the object and the amplitude of the terahertz electromagnetic wave that has not passed, means for acquiring the time difference of the propagation time, and the thickness of the object through which the terahertz electromagnetic wave passes based on the amplitude and time difference At least one of means for obtaining a parameter that does not depend on the object, means for obtaining a parameter having a large dependence on the thickness of the object and a small dependence on the material, and an image display means for displaying an image based on the parameter Prepare.
[0016]
The object image display method using the terahertz electromagnetic wave according to the present invention is also directed to irradiating the object with the terahertz electromagnetic wave, receiving the terahertz electromagnetic wave that has passed through the object, and the amplitude of the terahertz electromagnetic wave having passed through the object based on the output of the receiving means. And the time difference between the amplitude and propagation time of the terahertz electromagnetic wave that does not pass through the object, the parameter that does not depend on the thickness of the object through which the terahertz electromagnetic wave passes based on the amplitude and time difference, and the dependence on the thickness of the object is large In addition, at least one of the parameters with small dependence on the material is obtained, and an image is displayed based on the parameter.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 (a) shows an embodiment for observing the physical state of powder using terahertz electromagnetic waves. In FIG. 1, reference numeral 1 denotes an airtight container that houses a terahertz electromagnetic wave generator 21, a terahertz electromagnetic wave receiver 22, a concave reflecting mirror 1, a concave reflecting mirror 2, a concave reflecting mirror 3, a concave reflecting mirror 4, and a sample 40. It is what. Terahertz electromagnetic waves are attenuated due to absorption by water vapor, so that the measurement results are obtained with as little attenuation as possible. If necessary, evacuate with a vacuum pump.
[0018]
An excitation light source 2 is a semiconductor laser or the like. Reference numeral 3 denotes a laser light source, which is driven by the excitation light from the excitation light source 2 to generate pulsed laser light, such as a Ti: Sapphire laser. The laser light source 3 outputs pulsed light having a wavelength of 780 to 800 nm and a pulse width of 10 to 150 fs. Driven by the electric drive unit 51, the pulsed light is generated at a repetition frequency of, for example, 1 kHz.
[0019]
Reference numerals 4, 5, 6, 7, 8, 9, 10, 11, and 12 reflect mirrors that reflect the laser light generated by the laser light source 3 (5 is a semi-transparent mirror). Reference numerals 31, 32, 33, and 34 denote a concave reflecting mirror 1, a concave reflecting mirror 2, a concave reflecting mirror 3, and a concave reflecting mirror 4, respectively, which are off-axis parabolic mirrors. The concave reflecting mirror 1 is focused on the terahertz electromagnetic wave generator 21. The concave reflecting mirror 2 and the concave reflecting mirror 3 are focused on the sample 40. The concave reflecting mirror 4 is focused on the terahertz electromagnetic wave receiver 22.
[0020]
Reference numeral 21 denotes a terahertz electromagnetic wave generator (terahertz electromagnetic wave generating means) which receives pulsed laser light and generates terahertz electromagnetic waves. Reference numeral 22 denotes a terahertz electromagnetic wave receiver (terahertz electromagnetic wave receiving means) which generates an electric signal corresponding to the incident electric field strength when irradiated with the terahertz electromagnetic wave. Reference numeral 15 denotes a chopper (frequency dividing means) which chops an optical pulse output from the laser light source 3 and converts, for example, a pulse laser beam having a repetition frequency of 1 kHz into a pulsed light A having a frequency of 500 Hz. is there. Instead of a chopper, a modulation means for modulating the optical path length of an optical pulse with a low-frequency vibration frequency may be used.
[0021]
Reference numeral 40 denotes a sample in which an object to be measured is buried in powder, and is stored in a container. The material of the container of the sample 40 may be any material as long as it absorbs less terahertz electromagnetic waves. For example, a plastic container that does not absorb terahertz electromagnetic waves may be used. Reference numeral 51 denotes an electrical drive unit that electrically drives the laser light source 3 and the chopper drive unit 52. For example, driving is performed so that femtosecond light pulses output from the laser light source 3 are output at a cycle of 1 kHz. A chopper driving unit 52 drives the chopper 15. The chopper driving unit 52 operates so as to be synchronized with the output of the laser light source 3, and for example, when the electric driving unit 51 drives the laser light source 3 so as to output light pulses at a 1 kHz period, The chopper 15 is driven so as to chop the pulsed light A at 500 Hz. A time delay unit 53 changes the optical path length of the pulsed light B. Reference numeral 61 denotes a lock-in amplifier that processes an electrical signal output from the terahertz electromagnetic wave receiver 22 by using a chop period signal of the chopper driving unit 52 as a reference signal.
[0022]
FIG. 1B shows a cross section of the sample 40 along the yz plane. FIG. 1C is a cross-sectional view of the sample 40 along the xy plane. The sample 40 is placed on the mounting table 41, can move in the xy plane, and the irradiation of the terahertz electromagnetic wave scans the xy plane of the sample.
[0023]
The operation of the configuration shown in FIG. The laser light source 3 is electrically driven by the electric drive unit 51 and is optically excited by the output light of the excitation light source 2, and outputs laser pulse light having a wavelength of 780 to 800 nm and a pulse width of 130 fs at a repetition period of 1 kHz. To do. The pulsed light output from the laser light source 3 is reflected by the concave reflecting mirror 4, and a part of the reflected light is reflected by the semi-transparent mirror 5 and chopped by the chopper 15 to become pulsed light A having a repetition frequency of 500 Hz. Reflected by the mirror 7, the gap of the antenna of the terahertz electromagnetic wave generator 21 is irradiated. On the other hand, a part of the pulsed light output from the laser light source 3 and reflected by the concave reflecting mirror 4 is transmitted through the semi-transparent mirror 5, reflected by the reflecting mirror 8, and further reflected by the reflecting mirror 9, and the time delay unit 53. Are reflected by the reflecting mirrors 10 and 11 and the reflecting mirror 12 and are applied to the antenna gap of the terahertz electromagnetic wave receiver 22.
[0024]
The terahertz electromagnetic wave generator 21 is irradiated with the pulsed light A and generates a terahertz electromagnetic wave. Since the gap of the antenna of the terahertz electromagnetic wave generator 21 irradiated with the pulsed light A is at the focal point of the concave reflecting mirror 1, it is reflected by the concave reflecting mirror 1 and becomes a light beam parallel to the optical axis of the concave reflecting mirror 1. , Is incident on the concave reflecting mirror 2. The terahertz electromagnetic wave reflected by the concave reflecting mirror 2 enters the sample 40, propagates through the sample, and enters the concave reflecting mirror 3. The focal points of the concave reflecting mirror 2 and the concave reflecting mirror 3 are both in the xy plane of the sample 40, and the terahertz electromagnetic wave that has passed through the sample is reflected by the concave reflecting mirror 3 and travels in parallel to the optical axis, thereby reflecting the concave surface. Incident on the mirror 4. Since the gap of the antenna of the terahertz electromagnetic wave receiver 22 is at the focal point of the concave reflecting mirror 4, the terahertz electromagnetic wave reflected by the concave reflecting mirror 4 irradiates the antenna of the terahertz electromagnetic wave receiver 22.
[0025]
On the other hand, the pulsed light output from the laser light source 3 and passed through the semi-transparent mirror 5 is delayed by a distance corresponding to the time τ in the optical path by the time delay unit 53 to become pulsed light B, reflected by the reflecting mirror 12, and reflected by terahertz As the probe light of the electromagnetic wave receiver 22, the antenna gap of the terahertz electromagnetic wave receiver 22 is irradiated. Since the probe light (pulsed light B) irradiates the antenna gap of the terahertz electromagnetic wave receiver 22 with a delay of time τ from the pulse A, the terahertz electromagnetic wave receiver 22 generates an electric signal corresponding to the electric field strength of the terahertz electromagnetic wave at the time τ. Is output. By continuously changing the time τ, the electric field intensity at each time τ of the terahertz electromagnetic wave passing through the xy plane can be measured, and the time change of the electric field intensity and the propagation phase can be measured.
[0026]
The lock-in amplifier 61 processes an electrical signal output from the terahertz electromagnetic wave receiver 22 using the chopper period signal as a reference signal, and the image processing unit 62 determines τ for the intensity of the terahertz electromagnetic wave output from the lock-in amplifier 61. The electric field strength of each xy plane for each z coordinate obtained by changing is stored in the memory as image data. Furthermore, the image processing unit performs processing for obtaining a difference in propagation time (phase) based on a difference in electric field strength between coordinates or a difference in maximum electric field strength in the z-axis direction according to the measurement purpose, Hold the result in memory. Further, the display device displays and outputs the image data subjected to image processing.
[0027]
FIG. 2 is a flowchart of scanning in the xy plane and time delay scanning of the pulsed light B (corresponding to scanning in the z-axis direction). (A) is a flowchart of scanning of the x, y, and z axes. (B) is a detailed flowchart of time delay scanning (z-axis scanning).
[0028]
In FIG. 2A, an initial value in the xy plane is set in S1. In S2, the coordinate is moved. In S3, time delay scanning is performed (refer to FIG. 2B for details of time delay). In S4, it is determined whether x = m (m is the maximum value of the x-coordinate). If x = m is not satisfied, the value of x is incremented by 1, and the processing after S2 is repeated. If x = m in S4, it is determined in S5 whether y = n (the maximum value of the y coordinate). If y = n is not satisfied, the process from S2 is repeated by setting x = 1 and y = y + 1 in S6. If y = n in S5, it moves to the initial position (the center of the xy plane) in S8, and the scanning is finished.
[0029]
FIG. 2B is a detailed flowchart of time delay scanning (the flowchart of S3 in FIG. 2A). Time delay scanning, there are two ways of standard mode and high speed mode, previously determined to be accomplished by treatment with either advance. In S30, the standard mode or the high speed mode is selected. If it is the standard mode, measurement is performed by the method after S31.
[0030]
The standard mode will be described. If it is the standard mode in S30, z = 1 is set in S31. Moves in the z direction at S32 (time delay). Next, it measures by S33. In S34, it is determined whether z = k (maximum value of z-axis (maximum delay time)). If z = k is not satisfied, z = z + 1 is set in S36, and the processes after S32 are repeated. If z = k in S34, x and y coordinate scanning processing (processing after S4 in FIG. 2A) is performed in S35.
[0031]
Next, high-speed mode processing will be described. In S41, z = 1 is set. In S42, the time axis is continuously delayed. Measure in S43. In S44, it is determined whether z = k. If z = k is not satisfied, z = z + 1 is set in S47, and the processing after S43 is repeated. If S = 44 and z = k, the process waits for the time delay unit to return to the initial position in S45. In step S46, the x and y coordinates are scanned.
[0032]
FIG. 3 shows the measured transmittance of terahertz electromagnetic waves for powdered sugar, flour and baby powder. It is shown that sugar penetrates from 0.1 THz to 0.3 THz and wheat flour penetrates from 0.1 THz to 0.5 THz. Baby powder is shown to transmit in the range of 0.1 THz to 1.2 THz. From FIG. 3, a terahertz electromagnetic wave of 0.1 THz to 0.3 THz can be used for measurement of physical properties for sugar, and a terahertz electromagnetic wave of 0.1 THz to 0.5 THz can be used for wheat flour. Moreover, about baby powder, the terahertz electromagnetic wave of the range of 0.1 THz-1.2 THz can be used.
[0033]
Changes in the arrival time and amplitude of the terahertz electromagnetic wave generated by the object in the powder depend on the refractive index and extinction coefficient of the object, respectively. If the thickness of the object is known, the refractive index and extinction coefficient can be easily determined from the measured data. However, this is not possible if the thickness of the object is unknown. In view of this, the present inventor determined an amount (parameter) that does not depend on the thickness of the object in the powder, and displayed an image based on this amount.
[0034]
The time difference Δt between the propagation time of the terahertz electromagnetic wave that has passed through the object and the pulse of the terahertz electromagnetic wave that has not passed through the object is as follows.
[0035]
Δt = t−t₀= Δn d / c (1)
Where Δn = difference in refractive index between the object and the powder, d is the thickness of the object, c is the speed of light in vacuum, subscript 0 represents a pulse that does not pass through the object, and subscript Variables without are for pulses that pass through the object. The amplitude is
A / A₀= Exp (−Δk ω_cd / c) (2)
It is. Where Δk is the difference between the extinction coefficient of the object and the powder,_cIs the central angular frequency of the terahertz electromagnetic wave and is used here only as a scaling constant. In equation (2), the loss due to reflection on the object surface is ignored. However, this loss is (n−n₀)²/ (N + n₀)²Usually, it is a small value (the difference in refractive index due to the substance is small). For example, n = 1.6 for plastic and n = 1.3 to 1.4 for flour, sugar and powdered sugar (however, depending on the density of the flour) The amplitude error is 1% or less.
[0036]
Equation (2) is expressed as follows.
[0037]
ln (A₀/ A) = Δk ω_cd / c (3)
In order to obtain two linear equations of d, the following parameter Q is introduced.
[0038]
[Equation 3]

[0039]
α is an arbitrarily determined constant such as 1, 1.5. Q is an amount that does not depend on the thickness d of the object.
[0040]
Based on (1) and (3)
P²= Βω_cΔtln (A₀/ A) = Δk Δn (ω_c/ C)²d²
Is introduced. β is an arbitrarily determined constant such as 1, 1.5. This P²Depends strongly on the thickness, and the degree of dependence on the material is a small amount. The present invention provides measurement data (A₀, A, ω_c, Δt), this parameter Q and P²The image of the object was displayed based on the parameter.
[0041]
FIG. 4 shows a conventional amplitude mode, time delay mode, and parameters Q and P based on the measurement results of three plastic samples in wheat flour using terahertz electromagnetic waves.²An example of image display based on
[0042]
There is a small piece of plastic on the top left, top right and bottom. The lower and upper right objects are small plates of polyoxymethylene (POM). The upper left piece is a small plate of acrylonitrile-butadiene-styrene copolymer (ASB). The thickness of the lower POM plate is 2.8 mm, and the thickness of the upper two plates is 1.0 mm.
[0043]
FIG. 4A shows the amplitude mode, and FIG. 4B shows the image display in the time delay mode. The thick POM plate has a clear contrast in both (a) and (b), but the contrast of the two thin plates is not as clear as the thick plate. In FIG. 4C, P²Is expressed by brightness. The thicker the plate, the more P²The value of becomes larger and brighter (white). Q is represented by saturation from red to green. The green side represents a large Q and the red side represents a small Q. In FIG. 4C, ABS is represented in red and POM is represented in green. As is apparent from FIG. 4C, according to the present invention, it is possible to display an image so that the difference depending on the material of the object can be understood regardless of the thickness of the object.
[0044]
FIG. 5 shows another example in which an object is displayed as an image in the Q mode of the present invention (however, the object is not included in the powder). An image of the POM stick is at the top of the screen, and images of two PP (polypropylene) plates (see FIG. 6B) in the shape of a baseball home base are on the left and right of the lower side of the screen. The thickness of the POM rod continuously changes from 1.5 mm to 3.0 mm from the left side to the right side (see FIG. 6A). The two PP plates are 1.8 mm and 2.8 mm in thickness, respectively, the left side is the thinner one, and the right side is the thicker one.
[0045]
FIG. 5A is displayed in the amplitude mode. FIG. 5B is an image represented in the time delay mode. The thickness increases toward the right side, and the brightness increases (whitens). In the POM image, a change in thickness appears as a change in brightness in the image. In the PP image, the thicker one is displayed in white, but the thinner one is shown in black, indicating the difference in thickness. FIG. 5C is an image represented by Q. POM is expressed in pink, PP is expressed in blue, and the difference in material is clearly displayed.
[0046]
FIG. 6 shows the shapes of the POM bar and PP plate that are the objects of imaging in FIG. FIG. 6A shows a POM rod, and the thickness continuously changes from 1.5 mm to 3.0 mm from the left side to the right side. FIG.6 (b) is PP board, and it imaged about thickness 1.8mm and 2.8mm.
[0047]
FIG. 7 shows a flowchart of the image processing unit of the present invention.
[0048]
Measurement data is input and held (S1). In addition, A₀, A, Δt, ω_cIs obtained and held (S2). A₀, A, Δt, ω_cQ is calculated and held (S3). Next, A₀, A, Δt, ω_cBy P²Is calculated and held (S4). It is determined whether to display an image based on Q (S5). If an image display based on Q is performed in S5, a process for displaying an image based on the value of Q is performed in S6 (S6). If the image display based on Q is not performed in S5, P²Whether to display an image is determined based on (S7). In S7, P²If the image is displayed based on the²A process for displaying an image is performed based on the value of. In S9, an image is displayed. The method of displaying an image based on the value of Q in S6, for example, determines the saturation for image display according to the value of Q. Also. P in S8²An image display based on the value of²The brightness (luminance) of image display is determined according to the value of.
[0049]
FIG. 8 shows the configuration of the image processing unit of the present invention, which includes a CPU and a memory. In FIG. 8, reference numeral 62 denotes an image processing unit. Reference numeral 80 denotes a measurement data input unit for inputting measurement data sent from the lock-in amplifier. A measurement data holding unit 81 holds measurement data. The measurement data includes a terahertz electromagnetic wave frequency 91 and a terahertz electromagnetic wave signal value 92 corresponding to the position of the sample and the measurement time (time). Reference numeral 82 denotes a calculation unit which performs maximum amplitude calculation, time delay calculation, Q calculation, P²Performs computation. Reference numeral 83 denotes a calculation data holding unit, which is the maximum amplitude, time delay, Q, P²Is to hold. A display processing unit 84 creates image display data based on the calculation data. Reference numeral 85 denotes a display device.
[0050]
In the measurement data holding unit 81, the frequency 91 represents the frequency of the measured terahertz electromagnetic wave. The position-time-signal value 92 represents the measured position of the terahertz electromagnetic wave in the sample, the measurement time (time), and the signal value.
[0051]
In the calculation unit 82, reference numeral 93 denotes a maximum amplitude calculation for obtaining a difference between the maximum value and the minimum value of the amplitude of the terahertz electromagnetic wave transmitted through the sample. Reference numeral 94 denotes a time delay calculation unit that obtains a time difference between the maximum pulse values of the terahertz electromagnetic wave that has passed through the object and the terahertz electromagnetic wave that has not passed through the object. Reference numeral 95 denotes a Q calculation unit, which is the maximum amplitude of the terahertz electromagnetic wave that has not passed through the object through Q, the maximum amplitude of the terahertz electromagnetic wave that has passed through the object, propagation delay time (time delay), ω_cQ is calculated based on the above. 96 is P²Calculation unit, maximum amplitude of terahertz electromagnetic wave that did not pass through object, maximum amplitude of terahertz electromagnetic wave that passed through object, time delay, ω_cP based on²Is calculated.
[0052]
In the calculation data holding unit 83, the maximum amplitude 97, time delay 98, Q99, P²100 denotes a maximum amplitude calculator 93, a time delay calculator 94, a Q calculator 95, and a P²The data calculated by the calculation unit 96 is represented. In the display processing unit 84, the saturation addition 101 represents a process of adding saturation to the data to be displayed on the image. For example, it is a process of giving a saturation determined in advance according to the value of Q. Lightness assignment 102 represents processing for assigning lightness to data to be displayed. For example, P²This is a process of giving a predetermined brightness according to the value of.
[0053]
The operation of the configuration of FIG. 8 will be described. Signal values corresponding to the measured frequency of the terahertz electromagnetic wave, the position of the sample, and the observation time (time) are input and held in the measurement data holding unit. The maximum amplitude calculation unit 93 obtains the difference between the maximum value and the minimum value of the terahertz electromagnetic wave that passes through the sample based on the measurement data. The time delay calculation unit 94 calculates the terahertz electromagnetic wave that has passed through the object based on the measurement data. And the time difference between the pulse maximum values of the terahertz electromagnetic waves that did not pass through the object. The Q calculation unit 95 calculates the maximum amplitude of the terahertz electromagnetic wave that has not passed through the object, the maximum amplitude of the terahertz electromagnetic wave that has passed through the object, time delay, ω_cQ is calculated based on P²The calculation unit 96 calculates the maximum amplitude of the terahertz electromagnetic wave that has not passed through the object, the maximum amplitude of the terahertz electromagnetic wave that has passed through the object, a time delay, ω_cP based on²Is calculated.
[0054]
Data measured by each calculation unit is held in the calculation data holding unit 83. The display processing unit 84 creates data for sitting on the display device 85 based on the calculation data held in the calculation data holding unit 83. For example, a predetermined saturation is given according to the value of Q. P²A predetermined brightness is assigned according to the value of. The display device 85 displays the display data created by the display processing unit 84 as an image.
[0055]
【The invention's effect】
According to the present invention, terahertz electromagnetic waves can be used to display an image so that the difference in material of the object is clear regardless of the thickness of the object, or to display a difference in thickness of the object. can do. In particular, the present invention can display a plurality of objects buried in powder so that the difference in the materials can be seen. Alternatively, a plurality of objects having different thicknesses buried in the powder can be displayed as images so that the difference in thickness can be seen.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of the present invention.
FIG. 2 is a view showing a flowchart of scanning of a sample according to the present invention.
FIG. 3 is a diagram showing the transmittance of various powders at each frequency of a terahertz electromagnetic wave.
FIG. 4 is an example of an image of an object measured by the present invention.
FIG. 5 is an example of an image of an object measured by the present invention.
6 is a diagram illustrating the shape of the object in FIG. 5. FIG.
FIG. 7 is a flowchart of an image processing unit according to the present invention.
FIG. 8 is a configuration of an image processing unit of the present invention.
FIG. 9 is an image in a conventional display mode using terahertz electromagnetic waves.
FIG. 10 is an image in a conventional display mode using terahertz electromagnetic waves.
FIG. 11 is an image of a conventional display mode using terahertz electromagnetic waves.
FIG. 12 is a principle explanatory diagram for imaging a sample by terahertz electromagnetic wave spectroscopy.
[Explanation of symbols]
1: Airtight container
2: Excitation light source
3: Laser light source
4, 5, 6, 7, 8, 9, 10, 11, 12: Reflector
15: Chopper
21: Terahertz electromagnetic wave generator
22: Terahertz electromagnetic wave receiver
31: Concave reflector 1
32: Concave reflector 2
33: Concave reflector 3
34: Concave reflector 4
40: Sample
41: Mounting table
43: Object
51: Electrical drive unit
52: Chopper driver
53: Time delay part
61: Lock-in amplifier
62: Image processing unit
63: Display device

Claims (2)

An irradiation means for irradiating an object in powder contained in a container with terahertz electromagnetic waves;
Receiving means for receiving terahertz electromagnetic waves passing through the object and converting them into electrical signals;
Means for obtaining the amplitude of the terahertz electromagnetic wave that has passed through the object based on the output of the receiving means and the amplitude of the terahertz electromagnetic wave that has not passed through the object; means for obtaining a time difference in propagation time;
Depending on the material of the object through which the terahertz electromagnetic wave passes based on the amplitude and the time difference, when the parameter not depending on the thickness of the object is Q, the amplitude of the terahertz electromagnetic wave when not passing through the object is A ₀ , A is the amplitude when passing through, Δt is the time difference of the propagation time, ω _c is the central angular frequency of the transmitted terahertz electromagnetic wave of the powder, Δk is the difference in refractive index between the object and the powder, and Δn is the object and powder. The difference in extinction coefficient of the body, α is an arbitrary constant,
Q = α (ln (A ₀ / A)) / (ω _c Δt) = αΔk / Δn
Means to find
When P ² is a parameter having a large dependence on the thickness of the object and a small dependence on the material, c is the speed of light in vacuum, d is the thickness of the object, β is an arbitrary constant,
P ² = βω _c Δtln (A ₀ / A) = ΔkΔn (ω _c / c) ² d ²
Means to find
An image display device for an object using terahertz electromagnetic waves, comprising: an image processing unit that performs image processing based on the parameters obtained by the means for obtaining each parameter; and a display device that displays the image processed image . Irradiate an object in powder contained in a container with terahertz electromagnetic waves,
Receives terahertz electromagnetic waves that have passed through the object,
Obtaining the amplitude of the terahertz electromagnetic wave passing through the object and the amplitude of the terahertz electromagnetic wave not passing through the object based on the output of the receiving means, and obtaining a time difference in propagation time;
Depending on the material of the object through which the terahertz electromagnetic wave passes based on the amplitude and the time difference, when the parameter independent of the thickness of the object is Q, the amplitude of the terahertz electromagnetic wave when not passing through the object is A ₀ , The amplitude when passing through the object is A, the time difference of the propagation time is Δt, the central angular frequency of the transmitted terahertz electromagnetic wave of the powder is ω _c , Δk is the difference in refractive index between the object and the powder, Δn is the difference in the extinction coefficient between the object and the powder, α is an arbitrary constant,
Q = α ( ln (A ₀ / A)) / (ω _c Δt) = αΔk / Δn
Seeking
P is a parameter that has a large dependence on the thickness of the object and a small dependence on the material. ² Where c is the speed of light in vacuum, d is the thickness of the object, β is an arbitrary constant,
P ² = Βω _c Δt ln (A ₀ / A) = ΔkΔn (ω _c / C) ² d ²
Seeking
An object image display method using terahertz electromagnetic waves, wherein image display is performed by performing image processing based on each parameter.

Images