氏名　Deden Dian Sukmana
学位の種類　博士（工学）
学位記番号　博甲第379号
学位授与の日付　平成18年6月30日
学位論文題目　Application of Air-Coupled Ultrasound to Noncontact Surface Roughness Characterization　（非接触表面粗さ評価への空気超音波法の適用）
論文審査委員
　主査　助教授　井原　郁夫
　副査　教授　武藤　睦治
　副査　教授　福澤　康
　副査　教授　柳　和久
　副査　教授　田辺　郁男

• 論文目次
• 論文要旨
• 論文審査の結果の要旨

［平成18（2006）年度博士論文題名一覧］ ［博士論文題名一覧］に戻る．

Abstract　p.i
Acknowledgment　p.ii
Table of Contents　p.iii

Chapter1 Introducation　p.1
　1.1　The importance of surface roughness measurement　p.2
　1.2　Surface roughness measurement techniques　p.4
　1.2.1 Contact technique　p.4
　1.2.2 Noncontact technique　p.5
　1.3　Ultrasonic techniques for surface roughness measurement　p.6
　1.3.1 Coupling media and coupling techniques　p.7
　1.3.2 Surface roughness measurement based on coupling technique　p.10
　1.3.3 Disadvantages of coupling techniques　p.11
　1.4　Scope of the present work　p.13
　References　p.14

　Chapter2 Scattered Ultrasonic Wave from Pough Surface　p.22
　2.1　Introduction　p.23
　2.2　Definitions of the parameters associated with rough surface　p.23
　2.2.1 Root-mean-square height/roughness Rq　p.24
　2.2.2 Surface correlation length λ0　p.25
　2.3　Scattering from rough surface　p.26
　2.3.1 Formulation of scalar Kirchhoff theory　p.28
　2.3.2 Coherent component　p.33
　2.3.3 Incoherent component　p.35
　2.4　Basic theory of air-coupled ultrasonic technique　p.38
　2.4.1 Wave propagation　p.38
　2.4.2 Reflection and transmission at a plane boundary　p.40
　2.4.3 Air-coupled ultrasonic　p.44
　2.5　Air-coupled capacitance transducer BATTM used for characterizing surface roughness　p.46
　2.5.1 Experimental set-up　p.46
　2.5.2 Transducers characteristics　p.46
　2.5.3 Effect of turbulence and temperature on the measurement　p.54
　2.6　Conclusions　p.58
　References　p.58

Chapter3
Relationships between Coherent Component and Surface Roughness　p.63
　3.1　Introduction　p.64
　3.2　Experimental procedures　p.65
　3.2.1 Speciments and their statistical characteristics　p.65
　3.2.2 Experimental set-up　p.72
　3.3　Experimental results　p.73
　3.3.1 Change in reflected waveform with Rq　p.73
　3.3.2 Change in frequency spectra with Rq　p.75
　3.3.3 Frequency dependence of Rq measurement　p.82
　3.3.4 Incident angle dependence of Rq measurement　p.90
　3.4　Conclusions　p.92
　References　p.92

Chapter 4
Relationships between Incoherent Component and Surface Roughness　p.95
　4.1　Introduction　p.96
　4.2　Experimental procedures　p.97
　4.2.1 Speciments and their statistical characteristics　p.97
　4.2.2 Experimental set-up　p.97
　4.3　Experimental results　p.98
　4.3.1 Change in amplitude distribution with scattering angle　p.98
　4.3.2 Change in scattered waveform with surface roughness p.100
　4.3.3 Relationships between the amplitude and both of Rq and λ0　p.108
　4.4　Conclusions　p.113
　References　p.113

Chapter 5
A Quantitative Characterization of Surface Roughness Using Both of Coherent and Incoherent Components　p.115
　5.1　Introduction　p.116
　5.2　Rq estimation from the amplitude of coherent component　p.116
　5.3　λ0 estimation from the amplitude of incoherent component　p.125
　5.4　Effect of predominant of roughness on the measurement　p.129
　5.4.1 Experimental procedures　p.129
　5.4.2 Experimental results　p.130
　5.5　Conclusions　p.136
　References　p.136

Chapter 6 General Conclusions and Future Works　p.138
　6.1　General conclusions　p.139
　6.2　Prospects of the future works　p.141

There are growing demands for noncontact measurements of material surfaces roughness. Although optical method has been known as a conventional noncontact technique for evaluating roughness, its measurable roughness is often limited to less than 1 mm because of the inherent short wavelength of light. Air-coupled ultrasound, owing to its large wavelength and ability to probe the material surface, is considered to be an alternative noncontact technique. In this work,an air-coupled ultrasound technique has been applied to roughness characterization of material surfaces having random and periodic roughness, to examine the feasibility of the ultrasound technique. A pair of broadband air-coupled capacitance transducers having center frequency of 0.5 MHz is used to perform ultrasonic roughness measurement on the several specimens having relatively large scale of the root-mean-square roughness, Rq, from 0.04 mm to 244 mm and surface correlation length, lo, from 29 to 445 mm.

　Chapter 1 reviews the literature study and related works on the surface roughness measurement techniques. The importance of an alternative noncontact technique is mentioned. The scope of the present study is addressed.

　In chapter 2, ultrasonic scattering from a random rough surface is described. A Kirchhoff-based scattering model is used to express the scattering phenomena from random rough surfaces. Based on the model, the relationships between the amplitude of scattered waves and two surface roughness parameters, root-mean-square roughness Rq and surface correlation length lo, are derived for coherent and incoherent components, respectively. Furthermore, the basic theory of air-coupled ultrasound is highlighted. The characteristics of air-coupled capacitance transducers used are presented.

　In chapter 3, surface roughness characterization from coherent component of the scattered waves is presented. The coherent components are measured in the specular reflection configuration for various incident angles of 0o, 30o, 40o, 50o and 60o. The relationships between the amplitude of coherent component and root-mean-square roughness Rq are obtained. It is found that an increase in Rq causes not only reduction in the amplitude but also evanescence of higher frequency components of the reflected waves. It is shown that the amplitude decreases significantly in the range of normalized roughness, Rq?f, less than 100 mm?MHz. The effect of the incident angle on the amplitude measurement is examined. Since the results show that the incident angle has no significant effect on the amplitude measurement, it is considered that selection of incident angles is not a crucial factor for roughness measurement from coherent component in this work. The measured relationships between the amplitude and the Rq agree well with the theoretical ones calculated from the Kirchhoff-based scattering model.

　In chapter 4, surface roughness characterization from incoherent component of the scattered waves is presented. The incoherent components are measured in the nonspecular reflection configuration. The ultrasonic waves are incident at the angle of 60o and the scattered waves are measured at various scattering angles. The change in the amplitude distributions with scattering angles is obtained for specimen surfaces having different roughnesses. It is shown experimentally that the behaviors of incoherent component with surface roughness are quite different from those in coherent component. Rougher surface increases the amplitude of incoherent component, while it decreases the amplitude of coherent component. It is noted that the amplitude of incoherent component depends on not only Rq but also lo. The theoretical and measured relationships between the amplitude of incoherent component and surface roughness parameters, Rq and lo, are obtained. Since the measured relationship between lo and the amplitude agree well with the theoretical ones, it could be possible to estimate lo from the amplitude when the Rq is known.

　In chapter 5, a quantitative determination of surface roughness from both components, coherent and incoherent, is presented. A method has been proposed to determine surface roughness parameters, Rq and lo, from the amplitude of coherent and incoherent components. It is shown that the two parameters determined by the proposed method agree well with the ones determined by a stylus profiling method. In addition, the effect of predominant direction （lay） of the surface texture on the coherent and incoherent components measurements is examined on the specimens having periodic roughness with Rq of 22 mm and different lo from 246 mm to 350 mm. No significant effect is observed on the scattered waves in this experiment.

　General conclusions and future prospects of the research are summarized in chapter 6. It is shown that air-coupled ultrasound can be a useful means to characterize surface topograph with a relatively large roughness Rq, such as greater than 20 mm for which optical techniques cannot be applied.

　本論文は、「Application of Air-Coupled Ultrasound to Noncontact Surface Roughness Characterization（非接触表面粗さ評価への空気超音波法の適用）」と題し、6章より構成されている。

第1章「緒論」では、材料表面の凹凸形状測定や評価技術に関する現状と問題点を概説するとともに、本研究の位置付けと目的を述べている。

第2章「粗い表面からの超音波散乱」では空気超音波を利用した表面粗さ評価に関わる基礎事項について述べている。まず、本研究で扱う二つの工学的粗さパラメータ（二乗平均平方根粗さ Rqと表面相関長lo）について詳細に説明している。次に、静電容量型広帯域空気結合超音波送受信子の基本性能について調べ、これを用いることで中心周波数0.5MHzでの空気超音波パルスエコー計測が可能であることを示している。また、本研究の基礎となるランダムで粗い表面からの弾性波の反射・散乱に関するキルヒホッフモデルを用いた基礎理論について述べている。

第3章「散乱波のコヒーレント成分と表面粗さとの関係」では表面粗さ変化に対する空気超音波散乱波のコヒーレント成分の挙動について実験的・理論的に検討している。まず、本研究で用いる各試験片の表面形態を触針式粗さ計により測定し、それぞれのRqとloを評価している。次に、二つの空気結合超音波送受信子を用いたPitch-Catchモードでのリアルタイムパルスエコー計測装置を製作し、これを用いてランダムな比較的粗い材料表面（Rq=0.04～244mm）の超音波散乱波計測に関する系統的実験を行っている。Rqと散乱波のコヒーレント成分との関係を詳細に調べ、キルヒホッフモデルを用いた理論予測との比較から実験結果の妥当性を検証している。また、Rqに周波数fを乗じた規格化パラメータRq・fを提案し、これを用いることでRqと散乱強度との関係の周波数依存性を規格化できることを明らかにしている。

第4章「散乱波の非コヒーレント成分と表面粗さとの関係」では表面粗さ変化に対する空気超音波散乱波の非コヒーレント成分の挙動について実験的・理論的に検討している。ランダム表面（Rq=0.04～244mm、lo=29～445mm）に対して非鏡面反射状態での散乱波計測に関する系統的実験を行い、非コヒーレント成分の強度がRqだけでなくloにも依存することを実証している。また、キルヒホッフモデルを用いた理論予測との比較から実験結果の妥当性を検証している。

第5章「コヒーレント成分および非コヒーレント成分を用いた表面粗さの定量的評価」では前章の結果に基づいてRqとloの定量的評価法を提案している。散乱波のコヒーレント成分に加えて非コヒーレント成分の強度を指標とすることで、表面形態に関する縦方向情報（Rq）と横方向情報（lo）を定量的に評価できることを実証し、さらに本手法の測定精度と適用限界を明らかにすることで、空気超音波法による表面粗さ計測の実用性を実証している。

第6章では本研究で得られた結果を総括し、今後の展望について述べている。

本論文は工学表面の非接触粗さ計測に対する空気超音波法の適用について検討し、その有用性を実証したものであり、工学上および工業上貢献するところが大きく、博士（工学）の学位論文として十分な価値を有するものと認める。