JP3608423B2

JP3608423B2 - Electromagnetic ultrasonic measurement method and apparatus

Info

Publication number: JP3608423B2
Application number: JP07550999A
Authority: JP
Inventors: 幸理飯塚; 達也橋本
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 1999-03-19
Filing date: 1999-03-19
Publication date: 2005-01-12
Anticipated expiration: 2019-03-19
Also published as: JP2000266730A

Description

【０００１】
【発明の属する技術分野】
本発明は、電磁超音波を用いて導電性材料の超音波計測を行う技術に関し、特に高い時間分解能で且つ高いＳＮ比を得る計測方法及び装置に関するものである。
【０００２】
【従来の技術】
例えば金属の板や管等の被検体に、非接触で超音波の発生や検出を行う方法の一つとして、電磁超音波法が知られている。
この技術は、導電性の被検体に外部から磁場をかけておき、被検体に近接させたセンサコイルに電流を流すことにより被検体中に渦電流を生じせしめ、その渦電流と磁場とで発生するローレンツ力を用いて被検体中に超音波を発生するものであり、検出についても同様の原理である。
【０００３】
また、被検体が強磁性体の場合は、外部磁場をもってバイアス磁界をかけておき、被検体に近接させたセンサコイルから発生した磁界によりバイアス磁界を変化させ、これにより磁歪を変化させて被検体中に超音波を発生する原理もある。このような電磁超音波法は、外部磁場とセンサコイルとの位置関係次第で様々なモードの超音波が発生・検出でき、かつ非接触であるという大きなメリットがあるものの、現在一般的に用いられている圧電振動子による超音波発生検出法に比較して、電気機械変換効率が非常に低いため感度・ＳＮ比が悪いという問題がある。
【０００４】
このため従来から電磁超音波法の感度を改善する工夫が種々試みられてきた。例えば、被検体中の磁束密度が大きくなるように、非導電性磁性材の保護板（特開昭５６−１３２５５８号公報）や磁性材のセンサコイル（特開昭５７−８４３５０号公報）を使うことによりセンサそのものの感度を改善する方法、センサコイルと被検体間に金属箔を狭んで（特開平２−９６６０７号公報、特開平５−２８８７３３号公報）電気ノイズを低減する方法、２つの受信センサコイルを差動接続で用いて（特開昭５３−１４３３８８号公報、特開昭５７−８４３５２号公報）ノイズを低減する方法などである。
【０００５】
これらの工夫にさらに加えてＳＮ比を高くする方法として、信号処理方法が提案されている。
例えば送信信号を高電圧化する方法として、トリガ式スパークギャップによる方法（特開昭５３−８９４８６号公報）、２方向性サイラトロンによる方法（特開昭５８−１８０９４７号公報）、倍電圧パルサーによる方法（非破壊検査誌Ｖｏｌ．３４，Ｎｏ．１１，ｐｐ．８０８−８１４）など、パルス状の送信信号の振幅を増やす方法がある。
しかしながら、上記の送信信号を高電圧にする方法には次のような問題点がある。すなわち、電圧の尖頭値が１０ｋＶ程度では、センサコイルや接続線の途中でスパーク・ショートしたり、他の機器のノイズ源となってしまう。センサコイルには感度を増すためには巻数が多い方が望ましいが、耐圧を増すためには太くかつ被覆した線を用いる必要があってあまり巻数が増やせない。また、高電圧を発生させるため、送信信号のパルス繰り返し周波数を数１００Ｈｚ程度までしか高くできず、高速に移動する被検体に適用できない。
【０００６】
上記の問題を解決する方法として、被検体中で超音波が共振することを利用した電磁超音波共鳴（非破壊検査誌Ｖｏｌ．４３，Ｎｏ．１２，ｐｐ．７６４−７７０）による方法がある。しかしながらこの方法では、被検体に垂直に入射せしめた超音波の多重反射波の位相が揃って（コヒーレントとなり）共鳴するように、その共鳴周波数でかつパルス幅が長いバースト波を送信信号に用いるため、反射エコーを個別に分離することができず、複数の反射源を持つ被検体や平行面を持たない被検体へ適用することができない。
【０００７】
【発明が解決しようとする課題】
以上のように、電磁超音波法における送信信号の高電圧化はセンサコイルの耐圧の問題があり、一方、パルス幅の長いバースト波によって共鳴させる方法は複数の反射源を持つ被検体や平行面を持たない被検体へ適用することができないという問題があった。
この両者の中間として、あまりパルス幅の長くないバースト波を用いたり、センサコイルを共振回路にする方法が考えられるが、パルス状の送信信号に比較して、受信エコーの時間分解能が大幅に劣化するため、その適用対象は自ずと限られてしまう。このため、現在においても、電磁超音波法の工業現場における実用化は数例に留まっている。
本発明は、このような状況に鑑みて行われたものであり、電磁超音波計測において高い時間分解能でかつ高いＳＮ比を得ることができる計測方法および装置を提供することを目的とする。
【０００８】
【課題を解決するための手段】
本発明の請求項１に係る電磁超音波計測方法は、ローレンツ力または磁歪を用いて被検体に電磁気的に超音波を発生させ、該超音波を検出して被検体の計測を行う電磁超音波計測方法において、送信用センサコイルと該送信用センサコイルに近接した磁極をもつ第１の磁石よりなる送信用電磁超音波探触子および受信用センサコイルと該受信用センサコイルに近接した磁極をもつ第２の磁石よりなる受信用電磁超音波探触子を前記被検体の近傍に配置し、前記送信用センサコイルから前記第１の磁石に発生して前記第１の磁石内で多重反射する電磁超音波が前記第２の磁石の中に入らないように、前記第１の磁石と前記第２の磁石とを構造的に分離し、前記送信用センサコイルを介して所定パルス幅内で周波数、振幅もしくは位相のいずれか、またはこれらの任意の組合せにより変調したバースト信号を送信し、前記受信用センサコイルを介して得た受信信号と、前記送信した信号と同一または類似の波形の参照信号との相関演算を行い、該相関演算後の受信信号を用いて前記被検体の計測を行うものである。
【０００９】
本発明の請求項２に係る電磁超音波計測方法は、前記請求項１に係る電磁超音波計測方法において、前記第１の磁石の磁極と前記第２の磁石の磁極とは異なり、前記送信用センサコイルおよび前記受信用センサコイルは、流れる電流の向きが、揃うようにそれぞれの巻線が巻かれているものである。
本発明の請求項３に係る電磁超音波計測方法は、前記請求項１または２に係る電磁超音波計測方法において、前記送信用電磁超音波探触子および受信用電磁超音波探触子を共に被検体の同一の面側に配置するか、または送信用電磁超音波探触子を被検体の一方の面側に配置し受信用電磁超音波探触子を被検体の他方の面側に配置するものである。
【００１０】
本発明の請求項４に係る電磁超音波計測装置は、ローレンツ力または磁歪を用いて被検体に電磁気的に超音波を発生させ、該超音波を検出して被検体の計測を行う電磁超音波計測装置において、前記被検体の近傍に配置される、送信用センサコイルと該送信用センサコイルに近接した磁極をもつ第１の磁石よりなる送信用電磁超音波探触子および受信用センサコイルと該受信用センサコイルに近接した磁極をもつ第２の磁石よりなる受信用電磁超音波探触子と、所定パルス幅内で周波数、振幅もしくは位相のいずれか、またはこれらの任意の組合せにより変調したバースト信号を数値データとして算出するバースト信号算出手段と、前記バースト信号算出手段の算出したバースト信号を、送信信号、参照信号としてそれぞれ記憶する送信信号記憶手段および参照信号記憶手段と、前記送信信号記憶手段に記憶された送信信号を読出しアナログ信号に変換するＤ／Ａ変換手段と、前記Ｄ／Ａ変換手段の出力するアナログ信号を電力増幅して前記送信用センサコイルに印加する電力増幅手段と、前記受信用センサコイルが得た受信信号を増幅する受信増幅手段と、前記受信増幅手段の増幅した受信信号を数値データに変換するＡ／Ｄ変換手段と、前記Ａ／Ｄ変換手段の出力する数値データと、前記参照信号記憶手段から読出した参照信号との相関演算を行う相関演算手段とを備え、前記送信用センサコイルから前記第１の磁石に発生して前記第１の磁石内で多重反射する電磁超音波が前記第２の磁石の中に入らないように、前記第１の磁石と前記第２の磁石とが構造的に分離されているものである。
【００１１】
本発明の請求項５に係る電磁超音波計測装置は、前記請求項４に係る電磁超音波計測装置において、前記第１の磁石の磁極と前記第２の磁石の磁極とは異なり、前記送信用センサコイルおよび前記受信用センサコイルは、流れる電流の向きが、揃うようにそれぞれの巻線が巻かれているものである。
本発明の請求項６に係る電磁超音波計測装置は、前記請求項４または５に係る電磁超音波計測装置において、前記受信用電磁超音波探触子は、前記被検体の前記送信用電磁超音波探触子の配置された面側またはその対向面側に配置されるものである。
【００１２】
このように構成された発明においては、所定パルス幅を持ち周波数、振幅もしくは位相のいずれか、またはこれらの任意の組合せで変調したバースト信号を送信信号に用いるようにしており、パルス幅が長く平均電力の大きい送信信号を用いることで、あまり高い送信電圧でなくても強い超音波を発生させることができる。
さらに、送信信号と同一又は類似の波形の信号を参照信号とし、受信信号と参照信号との相関演算を行うようにしているので、バースト波のパルス圧縮作用により時間的に長かったエコーのパルス幅が短く圧縮されると共に、送信信号と相関のない電気的ノイズを大幅に低減することができる。このため、電磁超音波共鳴や、センサコイルを共振回路にするような時間分解能が劣化する方法の必要がなくなり、高い時間分解能でかつ高いＳＮ比を得ることができる。
さらに、送信用センサコイルとそれに近接した第１の磁石と、受信用センサコイルとそれに近接した第２の磁石とを分離させて、送信用電磁超音波探触子と受信用電磁超音波探触子とを別ユニットとしているので、送信時に送信用センサコイルに近接した磁石内に発生する超音波エコーを、受信用センサコイルが受信することがなく、エコー性のノイズが少ない極めて優れたＳＮ比を得ることができる。
【００１３】
【発明の実施の形態】
実施形態１
図１は本発明の実施形態１に係る電磁超音波計測装置の構造図である。
図１において、１は被検体、２は送信用センサコイル、３は送信用センサコイル２に近接した磁極（図ではＮ極）をもつ第１の磁石、４は受信用センサコイル、５は受信用センサコイル４に近接した磁極（図ではＳ極）をもつ第２の磁石、１０はバースト信号演算手段、１１は参照信号記憶手段、１２は送信信号記憶手段、１３はＤ／Ａ変換器、１４は電力増幅器、１５は同期信号発生手段、１６は受信用増幅器、１７はＡ／Ｄ変換器、１８は相関器である。
【００１４】
図１においては、被検体１に対して送信用センサコイル２及び受信用センサ４を接近させて、この送信用センサコイル２に磁極（図ではＮ極）を近接させた第１の磁石３を配置し、また受信用センサコイル４に近接させた磁極（図ではＳ極）をもつ第２の磁石５を配置している。
ここで第１の磁石３と第２の磁石５とは、完全に分離された独立する２つの磁石であり、その詳細は図６で後述するが、図４のように断面が“コ”の字型の単一の磁石のＮ極とＳ極ではない。
また、送信用センサコイル２とこれに近接した磁極をもつ第１の磁石３よりなる構成を送信用電磁超音波探触子、受信用センサコイル４とこれに近接した磁極をもつ第２の磁石５よりなる構成を受信用電極超音波探触子という。この送信用と受信用の電極超音波探触子の図１と異なる配置例は図８で後述する。
【００１５】
図１では、送信用センサコイル２に近接させた磁石３の磁極（Ｎ極）と受信用センサコイル４に近接させた磁石５の磁極（Ｓ極）の間に流れる磁束を用いて被検体１に磁場をかけており、この図の場合、各コイル直下では磁束は垂直方向である。この磁束により、送信用センサコイル２から被検体表面に誘起される渦電流にローレンツ力をかけ、電磁超音波を発生するようにしている。一方、受信はこの逆の原理で受信用センサコイル４に信号を得る。
ここで、被検体１は非磁性体であるＳＵＳ３０４、２つのセンサコイル２，４は長径２０ｍｍ、巻数２０ターンとし、２つの磁石３，５には１５×３０×３０ｍｍの永久磁石を用い、図１の示すような配置とした（図６の（ｂ）の斜視分解図を参照）。
【００１６】
図１の動作を説明する。
本発明において、送信のための変調をかけたバースト信号には様々なものが適用できるが、本実施形態ではチャープ（ｃｈｉｒｐ）信号を用いた。このチャープ信号ｓ（ｉ）は、図１のバースト信号演算手段１０によって次の式（１）に基づいて発生される。但しここでｆ_Ｃは中心周波数、Ｂは周波数掃引帯域幅、Ｔはパルス幅、ｆ_Ｓはサンプリング周波数である。またこの例でバースト信号演算手段１０は汎用のコンピュータを用いた。
【００１７】
【数１】

【００１８】
この例におけるチャープ信号は、中心周波数１ＭＨｚ、周波数掃引帯域幅１．６ＭＨｚ、パルス幅２０μｓとし、サンプリング周波数５ＭＨｚで離散化して求めたので、データ点数は１００点である。
バースト信号演算手段１０によって発生された上記のチャープ信号は、シリアル伝送によって、それぞれＲＡＭによって構成される参照信号記憶手段１１と送信信号記憶手段１２に記憶される。
【００１９】
送信信号記憶手段１２に格納されたチャープ信号は、同期信号発生手段１５により発生される同期信号に同期して１００点分の読み出しが開始され、Ｄ／Ａ変換器１３で所定のサンプリング周波数でアナログ信号に変換され、電力増幅器１４で高電圧に増幅される。そして、電力増幅器１４の出力信号は、送信用センサコイル２に印加され、超音波に変換されて被検体１中に発信される。
この例において、同期信号発生手段１５により発生される同期信号は１ＫＨｚの周波数とし、Ｄ／Ａ変換器１３によるチャープ信号のサンプリング周波数は５ＭＨｚとした。また電力増幅器１４は帯域幅０．１〜５ＭＨｚ、５０Ω負荷においてピーク間電圧１０００Ｖｐｐの出力のものを用いた。
【００２０】
受信用センサコイル４が検出した受信信号は、受信用増幅器１６によってＡ／Ｄ変換に必要な電圧まで増幅され、Ａ／Ｄ変換器１７でデジタル信号に変換される。このデジタル信号に離散化された受信信号は、相関器１８にて参照信号記憶手段１１に格納されている参照信号との相関が演算され、この相関演算結果が出力される。
この例において、受信用増幅器１６は帯域幅０．１〜５ＭＨｚ、増幅度７０ｄＢとし、図示されていない増幅度調整器により計測に用いたいエコーが適正なレベルになるように調整した。Ａ／Ｄ変換器１７のサンプリング周波数は、前記の５ＭＨｚとし、同期信号発生手段１５による同期信号に同期してサンプリングを開始するようにした。また、相関器１８には汎用のコンピュータを用い、次の式（２）を用いて相関を計算した。但しここで、ｘ_ｊ（ｉ）は入力信号、ｃ（ｋ）は参照信号、ｙ_ｊ（ｉ）は出力信号、Ｎ_Ｃは参照信号の点数、ｊは探傷信号の繰り返しを表し、ｎは１探傷周期における探傷信号データ点数である。
【００２１】
【数２】

【００２２】
図２はチャープ波を用いた相関演算によるパルス圧縮の動作を説明する波形図である。
図２において、時間τ_１の点は式（２）でｉ＝０の位置に相当する。まず、τ_１の位置で、受信信号と参照信号との相関演算を０〜Ｎ_ｃ−１点のデータ分だけ行う。相関の結果は、図中一番下の相関信号（受信信号と参照信号の類似度を示す信号）として出力される。このτ_１の時点では参照信号と受信信号は類似していないため、出力はほとんど零である。
次に、ｉを一つずつ増やし、図中τ_２，τ_３，…のように順次演算を行っていく。この結果、受信信号中のエコーと参照信号の位相が一致した点（図中の時間軸のほぼ中央）で、最大ピークの相関信号が得られる。この結果、受信エコーのパルス幅は圧縮され、参照信号と相関のない電気的なノイズ信号は大幅に低減される。
【００２３】
次に、本実施形態１による実施例を説明する。図１の構成から相関処理後の受信信号を観察するため、図中には示していないが、相関器１８の後にＤ／Ａ変換器を接続して相関演算出力をアナログ信号に変換し、このアナログ信号をオッシロスコープで観察した。また、従来技術として相関処理を行わない状態での観察の場合は、受信用増幅器１６の直後の信号で観察した。この実験では材料の厚みは１５０ｍｍ、センサのリフトオフ（センサコイルと被検体との間の距離）は１ｍｍとした。
図３は本実施形態１の実験に用いた送信信号を示す図であり、同図の（ａ）は比較のために用いた波数３波の何も変調していないバースト波（トーンバースト波；１ＭＨｚのサイン波）による送信信号を示し、（ｂ）は図１の送信信号記憶手段１２でのチャープ波による送信信号を示している。
【００２４】
図４は、本発明者らが先に出願した特願平９−３１１８５９号（平成９年１１月１３日出願で未公開）の発明における電磁超音波探触子の構成を示す図であり、同図の（ａ）は断面図を、（ｂ）は（ａ）の斜視分解図を示している。
上記先出願の発明における電磁超音波探触子は、図４のように断面が“コ”の字型の単一の磁石３（又は５）と、送受信共用の単一のセンサコイル２（又は４）により構成される。そして、“コ”の字型の磁石の各磁極の下のセンサコイルに流れる電流の向きがそれぞれ揃うように、センサコイルの巻線は巻かれる。図４の例では、磁石の左側の磁極（Ｎ極）の下のセンサコイルには紙面の表から裏に向う電流が流れ、磁石の右側の磁極（Ｓ極）の下のセンサコイルには紙面の裏から表に向う電流が流れるように構成される。
【００２５】
図５は図４の電極超音波探触子を用いた実験結果を示す図であり、同図の（ａ）はトーンバースト波を送信に用いてかつ相関処理を行わない時の受信波形を、（ｂ）はチャープ波を送信に用いてかつ相関処理を行なった時の受信波形を示している。なお、図５の（ｂ）で、相関処理を行うための参照信号は、図３の（ｂ）と同一波形の信号を用いている。
図５の（ａ）では、波数が多い時間分解能の悪いエコー波形であり、かつ電気性ノイズの混入によりＳＮ比も低い。一方、図５の（ｂ）では、エコーの波数は約１．５波と非常に高い時間分解能が得られ、かつ送信信号の電圧が１０００Ｖ程度でも電気性ノイズはほとんど抑えられている。
【００２６】
しかしながら、図５の（ｂ）には、以下の理由によるノイズがまだ残っている。すなわち、磁石も導電体であるため、送信信号がセンサコイルに印加されると、センサコイルに近接した磁極には渦電流が流れてローレンツ力が発生し、磁石内に電磁超音波が発せられる。この磁石内の超音波は多重反射を繰り返す。この超音波エコーは振動であるため、センサコイルに面した磁極面にはローレンツ力の逆の作用で渦電流が発生し、その渦電流はセンサコイルにて受信される。
このように、“コ”の字型の単一の磁石と送受信共用の単一のセンサコイルよりなる図４の構成の電磁超音波探触子では、送信信号により磁石内に発生する電磁超音波に基づく渦電流をセンサコイルが受信するため、この受信信号がエコー性のノイズとして観察される。特に変調されたバースト波を用いて相関処理を行うと、電気性ノイズに対するＳＮ比が向上するため、図５の（ｂ）に示されるように磁石内の超音波反射が明瞭に受信される。
【００２７】
図６は本発明の実験で用いた電磁超音波探触子の構成を示す図であり、同図の（ａ）は断面図を、（ｂ）は斜視分解図を示している。
図６の電磁超音波探触子は、送信用センサコイル２とこの送信用センサコイル２に近接した磁極をもつ第１の磁石３によりなる送信用電磁超音波探触子と、受信用センサコイル４とこの受信用センサコイル４に近接した磁極を持ちかつ前記第１の磁石３とは分離された第２の磁石５によりなる受信用電磁超音波探触子とで構成されている。
そして、第１，第２の磁石３，５の各磁極の下のセンサコイルに流れる電流の向きが、それぞれ揃うようにセンサコイル２，４の巻線は巻かれる。図６の例では、磁石３のＮ極の下のセンサコイル２の右半分には紙面の表から裏に向う電流が流れ、磁石５のＳ極の下のセンサコイル４の左半分には紙面の裏から表に向う電流が流れるように構成される。
【００２８】
図７は図６の電磁超音波探触子を用いた実験結果を示す図である。
図７では、エコーの波数は約１．５波と非常に高い時間分解能であり、ノイズもほとんどない非常に優れたＳＮ比を得ることができた。
これは、図６の構成の電磁超音波探触子によって、送信用センサコイル２に近接した磁極Ｎをもつ磁石３と、受信用センサコイル４に近接した磁極Ｓをもつ磁石５とが物理的に分離されているため、送信用センサコイル２から磁石３に発生して磁石３内で多重反射する電磁超音波は、受信用センサコイル４に近接した磁極をもつ磁石５の中に入らないからである。この結果図７では、エコー性のノイズは極めて少くなっている。
【００２９】
上記説明のように、本実施形態１によれば、所定パルス幅を持ち周波数変調したチャープ波を送信信号に用いており、このパルス幅が十分長いので送信信号の電圧をあまり高くしなくても大きな平均電力を送信できることになり、その結果、強い超音波を発生させ計測感度を向上させることができる。
さらに、送信信号と同一波形のチャープ信号を参照信号とし、受信信号と参照信号との相関演算を行っているので、受信チャープ波のパルス圧縮作用により時間的に長かったエコーのパルス幅が圧縮される。
加えて、送信用センサコイルに近接した磁極を持つ磁石と受信用センサコイルに近接した磁極を持つ磁石とを構造的に分離しているため、送信用センサコイル２から磁石３に超音波が発せられ、磁石３内で多重反射を起こしても、この振動状の超音波は受信用センサコイル４に近接した磁極を持つ磁石５の中に入らない。この結果、エコー性のノイズも少ない極めてＳＮ比の良い計測信号を得ることができる。
【００３０】
電磁超音波法では、一般の圧電振動子による超音波計測法と異なり、振動子の機械的な共振がないため、元々広帯域性を有するものであるが、従来は感度が低かったため、電磁超音波共鳴や、センサコイルの共振回路化など、時間分解能を大幅に劣化せざるを得ず、広帯域パルスの発生は困難であった。
本実施形態１で示した発明は、この電磁超音波が本来持っている広帯域性に着目し、パルス圧縮の信号処理と組み合わせることにより、単に計測感度を高めるのみならず、電磁超音波本来の広帯域性を引き出すようにして、また電気的なノイズも抑圧されるので、次に問題となる磁石内反射に対しての対策を施した点に特徴を有するものである。
【００３１】
実施形態２
図８は本発明の実施形態２に係る電磁超音波計測装置の構成図である。
前記図１の実施形態１では、送信用センサコイル２に近接させた磁極（図ではＮ極）と受信用センサコイル４に近接させた磁極（図ではＳ極）の間を流れる磁束を用いて被検体表面に磁場をかけると共に、送信用センサコイル２と受信用センサコイル４を被検体１に対して同じ面に配置した反射法としていたが、実施形態２では透過法とし、図８に示すように、送信用センサコイル２と第１の磁石３によりなる送信用電磁超音波探触子は被検体１の一方の面に配置し、また受信用センサコイル４と第２の磁石５によりなる受信用電極超音波探触子は被検体１の他方の面に配置した。
このため、第１の磁石３は“コ”の字型として磁極を２つとし、その一方の磁極から他方の磁極に磁束を流し、被検体１に磁場をかけるようにした。そして、送信用センサコイル２はその２つの磁極に近接させた。また、被検体１の対面側の対称位置に受信用センサコイル４と第２の磁石５を同様に配置した。
【００３２】
図９は図８の電磁超音波計測装置の計測例を示す図である。図９では、１５０ｍｍの厚みの被検体を透過させた波形を示しており、ＳＮ比が良くかつ時間分解能の高い計測信号が得られた。このように本発明は、反射法だけでなく透過法においても適用可能である。
【００３３】
なお、上記実施形態１，２では、送信用センサコイルに供給する送信信号として、所定パルス幅を持ち周波数変調したチャープ波（方形窓の波形）を用いる例を示したが、本発明はこれに限定されるものでなく、例えば、所定パルス幅内で周波数及び振幅を変調した波（例えばハミング窓やフォンハン窓の波等）を用いても、さらに所定パルス幅内で周波数，振幅，もしくは位相のいずれか、またはこれらの任意の組合せにより変調した送信信号を用いてもよい。
【００３４】
また、上記実施形態１，２では、相関演算を行うためにの参照信号として送信信号と同一波形の信号を用いる例を示したが、本発明はこれに限定されるものではなく、送信信号と類似波形の信号を用いるようにしてもよい。
即ち、相関処理後の波形が、ＳＮ比が良く且つ高い時間分解能となるように、送信信号及び参照信号を適宜選択して使用すればよい。
【００３５】
また上記実施形態１，２では、被検体に垂直磁場をかけてローレンツ力による横波を発生・検出する方法で説明したが、磁歪による電磁超音波でも同様であり、またセンサコイルと磁石の配置を変化させることで縦波や表面波など超音波の形式を種々変えて、本発明を実施することが可能である。
【００３６】
【発明の効果】
以上のように本発明によれば、ローレンツ力または磁歪を用いて被検体に電磁気的に超音波を発生させ、該超音波を検出して被検体の計測を行う電磁超音波計測方法および装置において、送信用センサコイルと該送信用センサコイルに近接した磁極をもつ第１の磁石よりなる送信用電磁超音波探触子および受信用センサコイルと該受信用センサコイルに近接した磁極をもつ第２の磁石よりなる受信用電磁超音波探触子を前記被検体の近傍に配置し、前記送信用センサコイルから前記第１の磁石に発生して前記第１の磁石内で多重反射する電磁超音波が前記第２の磁石の中に入らないように、前記第１の磁石と前記第２の磁石とを構造的に分離し、前記送信用センサコイルを介して所定パルス幅内で周波数、振幅もしくは位相のいずれか、またはこれらの任意の組合せにより変調したバースト信号を送信し、前記受信用センサコイルを介して得た受信信号と、前記送信した信号と同一または類似の波形の参照信号との相関演算を行い、該相関演算後の受信信号を用いて前記被検体の計測を行うようにしたので、比較的低い送信電圧でも高い時間分解能でかつ高いＳＮ比の計測信号が得られ、センサの耐圧の問題がなくなり、また他の機器に対するノイズ源にならず、かつ高いパルス繰り返し周波数が得られ、複数の反射源を持つ被検体や平行面を持たない被検体にも本発明の適用が可能となる。この結果、電磁超音波を様々な計測用途で適用できるようになる。
【００３７】
また本発明によれば、前記送信用電磁超音波探触子および受信用電磁超音波探触子を共に被検体の同一の面側に配置して反射法で計測を行うことも、また送信用電磁超音波探触子を被検体の一方の面側に配置し受信用電磁超音波探触子を被検体の対向面側に配置して透過法で計測を行うことも可能であるので、被検体の大きさや形状に応じて適合するいずれかの計測法を採用することができる。
【図面の簡単な説明】
【図１】本発明の実施形態１に係る電磁超音波計測装置の構成図である。
【図２】図１の相関器の相関演算を説明する波形図である。
【図３】本実施形態１の実験に用いた送信信号を示す図である。
【図４】先出願の発明における電磁超音波探触子の構成を示す図である。
【図５】図４の電磁超音波探触子を用いた実験結果を示す図である。
【図６】本発明の実験で用いた電磁超音波探触子の構成を示す図である。
【図７】図６の電磁超音波探触子を用いた実験結果を示す図である。
【図８】本発明の実施形態２に係る電磁超音波計測装置の構成図である。
【図９】図８の電磁超音波計測装置の計測例を示す図である。
【符号の説明】
１．被検体
２．送信用センサコイル
３．送信用センサコイルに近接した磁極を持つ第１の磁石
４．受信用センサコイル
５．受信用センサコイルに近接した磁極を持つ第２の磁石
１０．バースト信号演算手段
１１．参照信号記憶手段
１２．送信信号記憶手段
１３．Ｄ／Ａ変換器
１４．電力増幅器
１５．同期信号発生手段
１６．受信用増幅器
１７．Ａ／Ｄ変換器
１８．相関器[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for performing ultrasonic measurement of a conductive material using electromagnetic ultrasonic waves, and particularly relates to a measurement method and apparatus for obtaining a high SN ratio with high time resolution.
[0002]
[Prior art]
For example, an electromagnetic ultrasonic method is known as one of methods for generating and detecting ultrasonic waves in a non-contact manner on an object such as a metal plate or tube.
This technology generates an eddy current in a subject by applying a magnetic field from the outside to a conductive subject and passing a current through a sensor coil close to the subject. The ultrasonic wave is generated in the subject by using the Lorentz force, and the detection is based on the same principle.
[0003]
If the subject is a ferromagnetic material, a bias magnetic field is applied with an external magnetic field, and the bias magnetic field is changed by the magnetic field generated from the sensor coil close to the subject, thereby changing the magnetostriction to change the subject. There is also a principle of generating ultrasonic waves inside. Although such an electromagnetic ultrasonic method has a great merit that it can generate and detect ultrasonic waves in various modes depending on the positional relationship between the external magnetic field and the sensor coil and is non-contact, it is generally used at present. There is a problem that the sensitivity and SN ratio is poor because the electromechanical conversion efficiency is very low as compared with the ultrasonic wave generation detection method using the piezoelectric vibrator.
[0004]
For this reason, various attempts have been made to improve the sensitivity of the electromagnetic ultrasonic method. For example, a non-conductive magnetic material protective plate (Japanese Patent Laid-Open No. 56-132558) and a magnetic material sensor coil (Japanese Patent Laid-Open No. 57-84350) are used so that the magnetic flux density in the subject increases. A method of improving the sensitivity of the sensor itself, a method of reducing electrical noise by narrowing a metal foil between a sensor coil and a subject (Japanese Patent Laid-Open Nos. 2-96607 and 5-288733), and two receptions There is a method of reducing noise by using a sensor coil in a differential connection (Japanese Patent Laid-Open Nos. 53-143388 and 57-84352).
[0005]
In addition to these devices, a signal processing method has been proposed as a method for increasing the SN ratio.
For example, as a method for increasing the voltage of a transmission signal, a method using a trigger type spark gap (Japanese Patent Laid-Open No. 53-89486), a method using a two-way thyratron (Japanese Patent Laid-Open No. 58-180947), a method using a voltage doubler pulser (Non-destructive inspection magazine Vol. 34, No. 11, pp. 808-814), etc., there is a method for increasing the amplitude of a pulsed transmission signal.
However, the above method for increasing the transmission signal has the following problems. That is, when the peak value of the voltage is about 10 kV, a spark or short circuit occurs in the middle of the sensor coil or the connection line, or it becomes a noise source for other devices. In order to increase sensitivity, it is desirable that the sensor coil has a large number of turns. However, in order to increase the withstand voltage, it is necessary to use a thick and coated wire, and the number of turns cannot be increased. In addition, since a high voltage is generated, the pulse repetition frequency of the transmission signal can only be increased to about several hundred Hz, and cannot be applied to a subject moving at high speed.
[0006]
As a method for solving the above-described problem, there is a method based on electromagnetic ultrasonic resonance (non-destructive inspection journal Vol. 43, No. 12, pp. 765-770) utilizing the fact that ultrasonic waves resonate in a subject. However, in this method, a burst wave having a long resonance pulse and a long pulse width is used as a transmission signal so that the phases of the multiple reflected waves of the ultrasonic wave perpendicularly incident on the subject are aligned (recognize) and resonate. The reflected echoes cannot be separated individually and cannot be applied to a subject having a plurality of reflection sources or a subject having no parallel plane.
[0007]
[Problems to be solved by the invention]
As described above, the increase in the voltage of the transmission signal in the electromagnetic ultrasonic method has a problem of the withstand voltage of the sensor coil. There was a problem that it could not be applied to a subject having no.
As an intermediate between these two methods, it is possible to use burst waves with a pulse width that is not so long, or to use a sensor coil as a resonance circuit, but the time resolution of the received echo is significantly degraded compared to a pulsed transmission signal. Therefore, the application target is naturally limited. For this reason, there are only a few examples of practical application of the electromagnetic ultrasonic method in the industrial field.
The present invention has been made in view of such a situation, and an object of the present invention is to provide a measurement method and apparatus capable of obtaining a high SN ratio with high time resolution in electromagnetic ultrasonic measurement.
[0008]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided an electromagnetic ultrasonic measurement method in which an ultrasonic wave is electromagnetically generated in a subject using Lorentz force or magnetostriction, and the ultrasonic wave is detected to measure the subject. In the measurement method, a transmission electromagnetic ultrasonic probe including a transmission sensor coil and a first magnet having a magnetic pole close to the transmission sensor coil, a reception sensor coil, and a magnetic pole close to the reception sensor coil A receiving electromagnetic ultrasonic probe comprising a second magnet is disposed in the vicinity of the subject, is generated from the transmitting sensor coil to the first magnet, and is multiple-reflected within the first magnet. The first magnet and the second magnet are structurally separated so that electromagnetic ultrasonic waves do not enter the second magnet, and the frequency is within a predetermined pulse width via the transmission sensor coil. , Either amplitude or phase Alternatively, a burst signal modulated by any combination of these is transmitted, and a correlation operation is performed between the received signal obtained through the receiving sensor coil and a reference signal having the same or similar waveform as the transmitted signal, The subject is measured using the received signal after the correlation calculation.
[0009]
The electromagnetic ultrasonic measurement method according to claim 2 of the present invention is the electromagnetic ultrasonic measurement method according to claim 1, wherein the magnetic pole of the first magnet and the magnetic pole of the second magnet are different from each other. The sensor coil and the receiving sensor coil are wound with respective windings so that the directions of the flowing currents are aligned.
An electromagnetic ultrasonic measurement method according to a third aspect of the present invention is the electromagnetic ultrasonic measurement method according to the first or second aspect, wherein both the transmission electromagnetic ultrasonic probe and the reception electromagnetic ultrasonic probe are combined. Place the subject on the same side of the subject, or place the transmitting electromagnetic ultrasonic probe on one side of the subject and place the receiving electromagnetic ultrasonic probe on the other side of the subject To do.
[0010]
According to a fourth aspect of the present invention, there is provided an electromagnetic ultrasonic measurement apparatus that electromagnetically generates ultrasonic waves on a subject using Lorentz force or magnetostriction, and detects the ultrasonic waves to measure the subject. In the measurement apparatus, a transmission electromagnetic ultrasonic probe and a reception sensor coil, which are arranged in the vicinity of the subject, and include a transmission sensor coil and a first magnet having a magnetic pole close to the transmission sensor coil, A receiving electromagnetic ultrasonic probe composed of a second magnet having a magnetic pole close to the receiving sensor coil, and modulated by any one of frequency, amplitude, phase, or any combination within a predetermined pulse width Burst signal calculation means for calculating a burst signal as numerical data, and a transmission signal for storing the burst signal calculated by the burst signal calculation means as a transmission signal and a reference signal, respectively Memory means and reference signal storage means; D / A conversion means for reading out and converting the transmission signal stored in the transmission signal storage means; and analog amplification output from the D / A conversion means for power amplification. A power amplifying means applied to the transmitting sensor coil, a receiving amplifying means for amplifying the received signal obtained by the receiving sensor coil, and an A / D conversion for converting the received signal amplified by the receiving amplifying means into numerical data Means for calculating a correlation between the numerical data output from the A / D conversion means and the reference signal read from the reference signal storage means, and the first magnet from the sensor coil for transmission. The first magnet and the second magnet are structurally separated from each other so that electromagnetic ultrasonic waves generated in the first magnet and multiple-reflected in the first magnet do not enter the second magnet. Have Than it is.
[0011]
An electromagnetic ultrasonic measurement apparatus according to a fifth aspect of the present invention is the electromagnetic ultrasonic measurement apparatus according to the fourth aspect, wherein the magnetic pole of the first magnet and the magnetic pole of the second magnet are different from each other for the transmission. The sensor coil and the receiving sensor coil are wound with respective windings so that the directions of the flowing currents are aligned.
The electromagnetic ultrasonic measurement apparatus according to a sixth aspect of the present invention is the electromagnetic ultrasonic measurement apparatus according to the fourth or fifth aspect, wherein the reception electromagnetic ultrasonic probe is the transmission electromagnetic ultrasonic wave of the subject. It is arranged on the surface side where the acoustic probe is arranged or on the opposite surface side.
[0012]
In the invention configured as described above, a burst signal having a predetermined pulse width and modulated by any one of frequency, amplitude or phase, or any combination thereof is used as a transmission signal, and the pulse width is long and average. By using a transmission signal with high power, strong ultrasonic waves can be generated even if the transmission voltage is not very high.
Furthermore, since the correlation calculation between the received signal and the reference signal is performed using a signal having the same or similar waveform as the transmission signal, the pulse width of the echo that was long in time due to the pulse compression effect of the burst wave Can be shortened and electrical noise having no correlation with the transmission signal can be greatly reduced. For this reason, there is no need for electromagnetic ultrasonic resonance or a method for degrading time resolution such as making a sensor coil a resonance circuit, and high SN ratio can be obtained with high time resolution.
Further, the transmission sensor coil and the first magnet adjacent thereto, and the reception sensor coil and the second magnet adjacent thereto are separated, so that the transmission electromagnetic ultrasonic probe and the reception electromagnetic ultrasonic probe are separated. Since the child is a separate unit, the ultrasonic echo generated in the magnet close to the transmission sensor coil at the time of transmission is not received by the reception sensor coil, and an extremely excellent SN ratio with little echo noise Can be obtained.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1
FIG. 1 is a structural diagram of an electromagnetic ultrasonic measurement apparatus according to Embodiment 1 of the present invention.
In FIG. 1, 1 is a subject, 2 is a sensor coil for transmission, 3 is a first magnet having a magnetic pole (N pole in the figure) close to the sensor coil 2 for transmission, 4 is a sensor coil for reception, and 5 is reception. A second magnet having a magnetic pole (S pole in the figure) close to the

sensor coil

4, 10 is a burst signal calculation means, 11 is a reference signal storage means, 12 is a transmission signal storage means, 13 is a D / A converter, 14 is a power amplifier, 15 is a synchronizing signal generating means, 16 is a receiving amplifier, 17 is an A / D converter, and 18 is a correlator.
[0014]
In FIG. 1, a transmission magnet coil 2 and a reception sensor 4 are brought close to a subject 1, and a first magnet 3 having a magnetic pole (N pole in the figure) in proximity to the transmission sensor coil 2 is shown. A second magnet 5 having a magnetic pole (in the figure, S pole) close to the receiving sensor coil 4 is arranged.
Here, the first magnet 3 and the second magnet 5 are two completely separated independent magnets, the details of which will be described later with reference to FIG. It is not the north and south poles of a single-shaped magnet.
Further, the configuration of the transmission sensor coil 2 and the first magnet 3 having a magnetic pole close to the transmission sensor coil 2 is a transmission electromagnetic ultrasonic probe, the reception sensor coil 4 and the second magnet having a magnetic pole close to the transmission magnet coil. The structure consisting of 5 is called a receiving electrode ultrasonic probe. A disposition example of the transmitting and receiving electrode ultrasonic probes different from FIG. 1 will be described later with reference to FIG.
[0015]
In FIG. 1, the subject 1 uses magnetic flux flowing between the magnetic pole (N pole) of the magnet 3 close to the transmitting sensor coil 2 and the magnetic pole (S pole) of the magnet 5 close to the receiving sensor coil 4. In this figure, the magnetic flux is perpendicular to each coil. By this magnetic flux, Lorentz force is applied to the eddy current induced from the transmitting sensor coil 2 on the surface of the subject to generate electromagnetic ultrasonic waves. On the other hand, reception receives a signal from the receiving sensor coil 4 based on the reverse principle.
Here, the subject 1 is SUS304, which is a non-magnetic material, the two

sensor coils

2 and 4 have a major axis of 20 mm, the number of turns is 20 turns, and the two

magnets

3 and 5 are 15 × 30 × 30 mm permanent magnets. 1 (see the perspective exploded view of FIG. 6B).
[0016]
The operation of FIG. 1 will be described.
In the present invention, various types of burst signals that are modulated for transmission can be applied. In the present embodiment, a chirp signal is used. The chirp signal s (i) is generated based on the following equation (1) by the burst signal calculation means 10 of FIG. Where f _C Is the center frequency, B is the frequency sweep bandwidth, T is the pulse width, f _S Is the sampling frequency. In this example, the burst signal calculation means 10 is a general-purpose computer.
[0017]
[Expression 1]

[0018]
The chirp signal in this example has a center frequency of 1 MHz, a frequency sweep bandwidth of 1.6 MHz, a pulse width of 20 μs, and is obtained by discretization at a sampling frequency of 5 MHz, so the number of data points is 100.
The chirp signal generated by the burst signal calculation means 10 is stored in the reference signal storage means 11 and the transmission signal storage means 12 each constituted by a RAM by serial transmission.
[0019]
The chirp signal stored in the transmission signal storage means 12 is read out for 100 points in synchronism with the synchronization signal generated by the synchronization signal generation means 15, and is analogized at a predetermined sampling frequency by the D / A converter 13. It is converted into a signal and amplified to a high voltage by the power amplifier 14. The output signal of the power amplifier 14 is applied to the transmission sensor coil 2, converted into an ultrasonic wave, and transmitted into the subject 1.
In this example, the synchronization signal generated by the synchronization signal generating means 15 has a frequency of 1 KHz, and the sampling frequency of the chirp signal by the D / A converter 13 is 5 MHz. The power amplifier 14 used was a band width of 0.1 to 5 MHz, a 50Ω load and an output with a peak-to-peak voltage of 1000 Vpp.
[0020]
The reception signal detected by the reception sensor coil 4 is amplified to a voltage necessary for A / D conversion by the reception amplifier 16 and converted into a digital signal by the A / D converter 17. The received signal that has been discretized into this digital signal is subjected to correlation with the reference signal stored in the reference signal storage means 11 by the correlator 18 and the correlation calculation result is output.
In this example, the receiving amplifier 16 has a bandwidth of 0.1 to 5 MHz and an amplification degree of 70 dB, and is adjusted by an amplification degree regulator (not shown) so that an echo to be used for measurement is at an appropriate level. The sampling frequency of the A / D converter 17 is set to 5 MHz, and sampling is started in synchronization with the synchronization signal from the synchronization signal generating means 15. The correlator 18 was a general-purpose computer, and the correlation was calculated using the following equation (2). Where x _j (I) is an input signal, c (k) is a reference signal, y _j (I) is the output signal, N _C Represents the number of reference signals, j represents repetition of the flaw detection signal, and n represents the number of flaw detection signal data in one flaw detection cycle.
[0021]
[Expression 2]

[0022]
FIG. 2 is a waveform diagram for explaining the operation of pulse compression by correlation calculation using a chirp wave.
In FIG. 2, time τ ₁ This point corresponds to the position of i = 0 in the equation (2). First, τ ₁ The correlation calculation between the received signal and the reference signal at 0 to N _c -1 point is performed for data. The correlation result is output as the lowest correlation signal (a signal indicating the similarity between the received signal and the reference signal) in the figure. This τ ₁ At this point, the reference signal and the received signal are not similar, so the output is almost zero.
Next, i is incremented by one and τ in the figure ₂ , Τ ₃ , ... are performed sequentially. As a result, the correlation signal having the maximum peak is obtained at the point where the phase of the echo in the received signal matches the phase of the reference signal (approximately the center of the time axis in the figure). As a result, the pulse width of the received echo is compressed, and the electrical noise signal uncorrelated with the reference signal is greatly reduced.
[0023]
Next, examples according to the first embodiment will be described. In order to observe the received signal after the correlation processing from the configuration of FIG. 1, a D / A converter is connected after the correlator 18 to convert the correlation calculation output into an analog signal. The analog signal was observed with an oscilloscope. Further, in the case of observation in a state where correlation processing is not performed as a conventional technique, the observation is performed with a signal immediately after the receiving amplifier 16. In this experiment, the material thickness was 150 mm, and the sensor lift-off (distance between the sensor coil and the subject) was 1 mm.
FIG. 3 is a diagram showing a transmission signal used in the experiment of the first embodiment. FIG. 3A shows a burst wave (tone burst wave; none of the three wave numbers used for comparison; 1B shows a transmission signal by a chirp wave in the transmission signal storage means 12 of FIG.
[0024]
FIG. 4 is a diagram showing a configuration of an electromagnetic ultrasonic probe in the invention of Japanese Patent Application No. 9-311859 filed earlier by the present inventors (unpublished on November 13, 1997), (A) of the same figure is sectional drawing, (b) has shown the perspective exploded view of (a).
As shown in FIG. 4, the electromagnetic ultrasonic probe in the invention of the above-mentioned prior application includes a single magnet 3 (or 5) having a U-shaped cross section as shown in FIG. 4). Then, the windings of the sensor coil are wound so that the directions of the currents flowing through the sensor coils under the magnetic poles of the “U” -shaped magnet are aligned. In the example of FIG. 4, a current flowing from the front to the back of the paper flows through the sensor coil under the left magnetic pole (N pole) of the magnet, and the sensor coil under the right magnetic pole (S pole) of the magnet flows through the paper. It is configured such that current flows from the back to the front.
[0025]
FIG. 5 is a diagram showing experimental results using the electrode ultrasonic probe of FIG. 4, and (a) in FIG. 5 shows a received waveform when a tone burst wave is used for transmission and no correlation processing is performed. (B) shows a received waveform when a chirp wave is used for transmission and correlation processing is performed. In FIG. 5B, the reference signal for performing the correlation process uses a signal having the same waveform as that in FIG.
In FIG. 5A, the echo waveform has a large wave number and a poor time resolution, and the SN ratio is also low due to the mixing of electrical noise. On the other hand, in FIG. 5B, the echo wave number is about 1.5 waves and a very high time resolution is obtained, and electrical noise is almost suppressed even when the voltage of the transmission signal is about 1000V.
[0026]
However, in FIG. 5B, noise still remains for the following reason. That is, since the magnet is also a conductor, when a transmission signal is applied to the sensor coil, an eddy current flows through the magnetic pole close to the sensor coil, a Lorentz force is generated, and an electromagnetic ultrasonic wave is generated in the magnet. The ultrasonic waves in the magnet repeat multiple reflections. Since this ultrasonic echo is a vibration, an eddy current is generated on the magnetic pole surface facing the sensor coil by the reverse action of the Lorentz force, and the eddy current is received by the sensor coil.
As described above, in the electromagnetic ultrasonic probe having the configuration shown in FIG. 4 composed of a single “U” -shaped magnet and a single sensor coil used for both transmission and reception, an electromagnetic ultrasonic wave generated in the magnet by a transmission signal. Since the sensor coil receives the eddy current based on this, this received signal is observed as echo noise. In particular, when correlation processing is performed using a modulated burst wave, the S / N ratio with respect to electrical noise is improved, so that ultrasonic reflection in the magnet is clearly received as shown in FIG.
[0027]
6A and 6B are diagrams showing the configuration of the electromagnetic ultrasonic probe used in the experiment of the present invention. FIG. 6A is a sectional view, and FIG. 6B is an exploded perspective view.
The electromagnetic ultrasonic probe shown in FIG. 6 includes a transmission electromagnetic coil composed of a transmission sensor coil 2 and a first magnet 3 having a magnetic pole close to the transmission sensor coil 2, and a reception sensor coil. 4 and a receiving electromagnetic ultrasonic probe comprising a second magnet 5 having a magnetic pole close to the receiving sensor coil 4 and separated from the first magnet 3.
The windings of the sensor coils 2 and 4 are wound so that the directions of currents flowing through the sensor coils under the magnetic poles of the first and

second magnets

3 and 5 are aligned. In the example of FIG. 6, a current flowing from the front to the back of the paper flows in the right half of the sensor coil 2 below the N pole of the magnet 3, and the left half of the sensor coil 4 below the S pole of the magnet 5 It is configured such that current flows from the back to the front.
[0028]
FIG. 7 is a diagram showing experimental results using the electromagnetic ultrasonic probe of FIG.
In FIG. 7, the wave number of the echo has a very high time resolution of about 1.5 waves, and an excellent signal-to-noise ratio with almost no noise was obtained.
This is because the magnet 3 having the magnetic pole N close to the transmitting sensor coil 2 and the magnet 5 having the magnetic pole S close to the receiving sensor coil 4 are physically separated by the electromagnetic ultrasonic probe having the configuration shown in FIG. Therefore, the electromagnetic ultrasonic wave generated from the transmission sensor coil 2 to the magnet 3 and multiple-reflected in the magnet 3 does not enter the magnet 5 having the magnetic pole close to the reception sensor coil 4. It is. As a result, in FIG. 7, the echo noise is extremely small.
[0029]
As described above, according to the first embodiment, a chirp wave having a predetermined pulse width and frequency-modulated is used for a transmission signal, and since this pulse width is sufficiently long, the voltage of the transmission signal does not need to be increased too much. Large average power can be transmitted. As a result, strong ultrasonic waves can be generated to improve measurement sensitivity.
Furthermore, since the chirp signal having the same waveform as the transmission signal is used as the reference signal and the correlation calculation between the received signal and the reference signal is performed, the pulse width of the echo that was long in time is compressed by the pulse compression action of the received chirp wave. The
In addition, since the magnet having the magnetic pole close to the transmitting sensor coil and the magnet having the magnetic pole close to the receiving sensor coil are structurally separated, ultrasonic waves are emitted from the transmitting sensor coil 2 to the magnet 3. Even if multiple reflection occurs in the magnet 3, the vibrational ultrasonic wave does not enter the magnet 5 having the magnetic pole close to the receiving sensor coil 4. As a result, it is possible to obtain a measurement signal having a very good S / N ratio with little echo noise.
[0030]
Unlike the ultrasonic measurement method using a general piezoelectric vibrator, the electromagnetic ultrasonic method originally has a broadband characteristic because there is no mechanical resonance of the vibrator. The time resolution such as resonance and the resonance circuit of the sensor coil must be greatly deteriorated, and the generation of the broadband pulse is difficult.
The invention shown in the first embodiment pays attention to the wide band nature inherent to the electromagnetic ultrasonic wave, and not only improves the measurement sensitivity by combining with the signal processing of pulse compression, but also the original wide band of the electromagnetic ultrasonic wave. In addition, since electrical noise is also suppressed, it has a feature in that a countermeasure is taken against reflection in the magnet, which is the next problem.
[0031]
Embodiment 2
FIG. 8 is a configuration diagram of an electromagnetic ultrasonic measurement apparatus according to Embodiment 2 of the present invention.
In the first embodiment shown in FIG. 1, the magnetic flux flowing between the magnetic pole (N pole in the figure) close to the transmitting sensor coil 2 and the magnetic pole (S pole in the figure) close to the receiving sensor coil 4 is used. While a reflection method is used in which a magnetic field is applied to the subject surface and the transmission sensor coil 2 and the reception sensor coil 4 are arranged on the same surface with respect to the subject 1, the transmission method is used in the second embodiment, which is shown in FIG. As described above, the transmission electromagnetic ultrasonic probe including the transmission sensor coil 2 and the first magnet 3 is disposed on one surface of the subject 1, and includes the reception sensor coil 4 and the second magnet 5. The receiving electrode ultrasonic probe was disposed on the other surface of the subject 1.
Therefore, the first magnet 3 has a “U” shape and has two magnetic poles. A magnetic flux is passed from one of the magnetic poles to the other magnetic pole to apply a magnetic field to the subject 1. Then, the transmission sensor coil 2 was brought close to the two magnetic poles. Further, the receiving sensor coil 4 and the second magnet 5 are similarly arranged at the symmetrical position on the facing side of the subject 1.
[0032]
FIG. 9 is a diagram showing a measurement example of the electromagnetic ultrasonic measurement apparatus of FIG. FIG. 9 shows a waveform transmitted through an object having a thickness of 150 mm, and a measurement signal with a good SN ratio and high time resolution was obtained. Thus, the present invention can be applied not only in the reflection method but also in the transmission method.
[0033]
In the first and second embodiments, an example is shown in which a chirp wave (waveform of a rectangular window) having a predetermined pulse width and frequency-modulated is used as a transmission signal to be supplied to a transmission sensor coil. For example, even if a wave whose frequency and amplitude are modulated within a predetermined pulse width (for example, a wave of a Hamming window or a von Hann window) is used, the frequency, amplitude, or phase is further within the predetermined pulse width. A transmission signal modulated by any one or any combination thereof may be used.
[0034]
In the first and second embodiments, the example in which the signal having the same waveform as the transmission signal is used as the reference signal for performing the correlation calculation is shown, but the present invention is not limited to this, and the transmission signal and You may make it use the signal of a similar waveform.
That is, the transmission signal and the reference signal may be appropriately selected and used so that the waveform after correlation processing has a good SN ratio and high time resolution.
[0035]
In the first and second embodiments, the method of generating and detecting a transverse wave by Lorentz force by applying a vertical magnetic field to the subject has been described. However, the same applies to electromagnetic ultrasonic waves by magnetostriction, and the arrangement of sensor coils and magnets is the same. It is possible to implement the present invention by changing various types of ultrasonic waves such as longitudinal waves and surface waves by changing them.
[0036]
【The invention's effect】
As described above, according to the present invention, in an electromagnetic ultrasonic measurement method and apparatus for measuring a subject by electromagnetically generating an ultrasonic wave on a subject using Lorentz force or magnetostriction and detecting the ultrasonic wave , A transmitting electromagnetic ultrasonic probe comprising a transmitting sensor coil and a first magnet having a magnetic pole close to the transmitting sensor coil, and a receiving sensor coil and a second having a magnetic pole adjacent to the receiving sensor coil A receiving electromagnetic ultrasonic probe made up of a plurality of magnets is disposed in the vicinity of the subject, and the electromagnetic ultrasonic waves generated from the transmitting sensor coil to the first magnet and subjected to multiple reflections in the first magnet So that the first magnet and the second magnet are structurally separated so as not to enter the second magnet, and the frequency, amplitude, or within a predetermined pulse width via the transmission sensor coil One of the phases, or A burst signal modulated by any combination of these is transmitted, a correlation operation is performed between the received signal obtained via the receiving sensor coil and a reference signal having the same or similar waveform as the transmitted signal, and the correlation Since the measurement of the subject is performed using the received signal after the calculation, a measurement signal with a high time resolution and a high SN ratio can be obtained even with a relatively low transmission voltage, and there is no problem with the withstand voltage of the sensor. The present invention can be applied to a subject that does not become a noise source for other devices and that has a high pulse repetition frequency and that has a plurality of reflection sources and does not have a parallel surface. As a result, electromagnetic ultrasonic waves can be applied in various measurement applications.
[0037]
According to the present invention, it is also possible to perform the measurement by the reflection method by arranging both the transmitting electromagnetic ultrasonic probe and the receiving electromagnetic ultrasonic probe on the same surface side of the subject. An electromagnetic ultrasonic probe can be placed on one side of the subject and a receiving electromagnetic ultrasonic probe can be placed on the opposite side of the subject to perform measurement using the transmission method. Any measurement method suitable for the size and shape of the specimen can be employed.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an electromagnetic ultrasonic measurement apparatus according to a first embodiment of the present invention.
FIG. 2 is a waveform diagram for explaining a correlation calculation of the correlator of FIG. 1;
FIG. 3 is a diagram showing a transmission signal used in the experiment of the first embodiment.
FIG. 4 is a diagram showing a configuration of an electromagnetic ultrasonic probe in the invention of the prior application.
FIG. 5 is a diagram showing a result of an experiment using the electromagnetic ultrasonic probe of FIG.
FIG. 6 is a diagram showing a configuration of an electromagnetic ultrasonic probe used in an experiment of the present invention.
7 is a diagram showing experimental results using the electromagnetic ultrasonic probe shown in FIG. 6; FIG.
FIG. 8 is a configuration diagram of an electromagnetic ultrasonic measurement apparatus according to Embodiment 2 of the present invention.
9 is a diagram showing a measurement example of the electromagnetic ultrasonic measurement device of FIG.
[Explanation of symbols]
1. Subject
2. Sensor coil for transmission
3. A first magnet having a magnetic pole close to the sensor coil for transmission
4). Sensor coil for reception
5. A second magnet having a magnetic pole close to the sensor coil for reception
10. Burst signal calculation means
11. Reference signal storage means
12 Transmission signal storage means
13. D / A converter
14 Power amplifier
15. Synchronous signal generation means
16. Receiver amplifier
17. A / D converter
18. Correlator

Claims

In an electromagnetic ultrasonic measurement method for generating an ultrasonic wave electromagnetically in a subject using Lorentz force or magnetostriction, and measuring the subject by detecting the ultrasonic wave,
A transmission electromagnetic ultrasonic probe comprising a transmission sensor coil and a first magnet having a magnetic pole close to the transmission sensor coil, and a second sensor coil having a magnetic pole adjacent to the reception sensor coil and the reception sensor coil. A receiving electromagnetic ultrasonic probe made of a magnet is arranged in the vicinity of the subject,
The first magnet and the first magnet are arranged so that electromagnetic waves generated from the transmitting sensor coil on the first magnet and multiple-reflected in the first magnet do not enter the second magnet. Structurally separating the two magnets,
A burst signal modulated by any one of frequency, amplitude or phase within a predetermined pulse width, or any combination thereof within a predetermined pulse width is transmitted through the transmission sensor coil, and the received signal obtained through the reception sensor coil An electromagnetic ultrasonic measurement method comprising: performing a correlation calculation with a reference signal having the same or similar waveform as the transmitted signal, and measuring the subject using the received signal after the correlation calculation.

Unlike the magnetic pole of the first magnet and the magnetic pole of the second magnet, the transmitting sensor coil and the receiving sensor coil are wound with respective windings so that the directions of the flowing currents are aligned. The electromagnetic ultrasonic measurement method according to claim 1.

The transmitting electromagnetic ultrasonic probe and the receiving electromagnetic ultrasonic probe are both disposed on the same surface side of the subject, or the transmitting electromagnetic ultrasonic probe is disposed on one surface side of the subject. electromagnetic ultrasonic measuring method according to claim 1 or 2, wherein the arrangement is arranged to receive electromagnetic ultrasonic probe on the other side of the subject.

In an electromagnetic ultrasonic measurement apparatus that generates an ultrasonic wave electromagnetically in a subject using Lorentz force or magnetostriction and detects the ultrasonic wave to measure the subject,
A transmitting electromagnetic ultrasonic probe, a receiving sensor coil, and a receiving sensor, which are arranged in the vicinity of the subject and are composed of a transmitting sensor coil and a first magnet having a magnetic pole close to the transmitting sensor coil. A receiving electromagnetic ultrasonic probe comprising a second magnet having a magnetic pole close to the coil;
Burst signal calculation means for calculating a burst signal modulated by any one of frequency, amplitude or phase within a predetermined pulse width, or any combination thereof as numerical data;
Transmission signal storage means and reference signal storage means for storing the burst signal calculated by the burst signal calculation means as a transmission signal and a reference signal, respectively;
D / A conversion means for reading and converting the transmission signal stored in the transmission signal storage means into an analog signal;
Power amplifying means for amplifying the analog signal output from the D / A converting means and applying it to the transmitting sensor coil;
Receiving amplification means for amplifying the received signal obtained by the receiving sensor coil;
A / D conversion means for converting the reception signal amplified by the reception amplification means into numerical data;
Correlation calculation means for performing a correlation calculation between the numerical data output from the A / D conversion means and the reference signal read from the reference signal storage means ,
The first magnet and the first magnet are arranged so that electromagnetic waves generated from the transmission sensor coil on the first magnet and multiply reflected in the first magnet do not enter the second magnet. An electromagnetic ultrasonic measurement apparatus, wherein the two magnets are structurally separated .

Unlike the magnetic pole of the first magnet and the magnetic pole of the second magnet, the transmitting sensor coil and the receiving sensor coil are wound with respective windings so that the directions of the flowing currents are aligned. The electromagnetic ultrasonic measurement apparatus according to claim 4.

The receiving electromagnetic ultrasonic probe according to claim 4 or 5, wherein said is disposed arranged side or the opposing side of the transmission electromagnetic ultrasonic transducer of the subject Electromagnetic ultrasonic measuring device.