JP4004845B2 - Array type ultrasonic transducer - Google Patents

Description

【００１３】
【数２】
ＱmR＞ＱmT （２）
ここで、ｄ33：圧電定数、Ｓ：開口、Ｑm：共振尖鋭度、Ｖr：縦波音速、ｎ：高調波の次数、ｆr：:基本波周波数、Ｆ：音場パラメータ、添え字Ｔ：送信用トランスデューサ、添え字Ｒ：受信用トランスデューサである。
【００１４】
このように超音波の共振尖鋭度Ｑを大きく設計することは感度向上や、受信信号の内の基本波成分の抑圧に効果的だが、一方で超音波の尾曳きを長くし、深さ方向分解能を劣化させることにつながる場合がある。
【００１５】
従って、本発明による送受信分離型超音波トランスデューサにおいて、付随的に発生する技術課題に受信感度を大きく保ちながら、超音波の尾曳きを長くさせないという技術課題がある。
【００１６】
上記課題を解決するために本発明においては次の様な手段を用いている。すなわち、基本波を送信し、高調波を受信するアレイ型超音波トランスデューサにおいて、アレイを構成する各圧電振動子エレメントが送信用圧電振動子と受信用圧電振動子からなり、これらがほぼ同一面上に、送信用振動子による音場の中心軸と、受信用振動子による音場の中心軸が一致するように分割配置され、なおかつ、複数対の送信用圧電振動子が対称性よく１以上の記数個の受信用圧電振動子を挟むように配置させる。
【００１７】
この配置の最小単位は一対の送信用圧電振動子に１個の受信用圧電振動子が挟まれた構造であるが、それぞれの中心軸が一致する配置であれば、複数対と１以上の記数個の組み合わせでも良い。
【００１８】
さらに前記圧電振動子の背面に形成するダンピング層の構造、材質は、それぞれの圧電振動子ごとに差異を設け、超音波送受面側に配置させる音響整合層の厚さも変化させ、音響レンズは凹面状とし、音速が生体の音速より大きい音速を有した材質を用いる。
【００１９】
前記したような本発明に付随的に発生する技術課題、すなわち、深さ方向分解能低下の解決手段として、アレイを構成する各振動子エレメントの受信用圧電振動子エレメントに接続する同軸ケーブルの端部で、同軸ケーブルの静電容量Ｃsと受信用圧電振動子の制動容量Ｃoとの合成容量Ｃxとその端部で付加する付加コンデンサＣaや付加インダクタＬaとで共振回路を構成する。
【００２０】
受信用圧電振動子を挟むように配置した一対の圧電振動子から基本波超音波を送信し、一対の送信用圧電振動子に挟まれた受信用圧電振動子で高調波信号を受信する。本発明によるアレイ型超音波トランスデューサはアレイを構成する各エレメントが基本波送信用圧電振動子と高調波受信用圧電振動子が同一面内で分割配置されているので、それぞれの圧電振動子の背面には異なる特性のダンピング層、前面には適した厚みの音響整合層を別々に形成することが可能である。
【００２１】
送受信分離型超音波トランスデューサの受信感度が式（１）に基づいて感度Ｓensが大きくなるように圧電振動子材料の組み合わせが最適化される。
【００２２】
また基本波成分と高調波成分が混在する受信信その内、基本波成分を出来るだけ抑圧するために、式（２）の条件も満たしている。従って大きな受信感度と効率的な基本波成分の抑圧が可能である。
【００２３】
さらに、音響整合層も送信基本波超音波の周波数ｆ0に対する最適整合層厚みはＶ／４ ｆ 0で、高調波、例えば第２高調波２ｆ0に対する最適整合層厚みＶ／８ ｆ 0となる。音響整合層は１／４λの厚さで最適の音響整合状態、１／２λの厚さで最悪の音響整合状態となる。すなわち、均一な厚みの音響整合層では基本波送信用振動子に適合させると、高調波受信用振動子に不適合、高調波受信用振動子に適合させると、基本波送信用振動子に不適合となってしまう。
【００２４】
本発明による超音波トランスデューサでは片面凹面状で音速が生体の音速より大きい材質を用いるので音響整合層は平行平板ではないが、基本波送信用振動子前面と高調波受信用振動子前面のそれぞれの音響レンズの平均厚みを１／４λの厚みに適合させることができる。
【００２５】
一方、式（１）に基づいて共振尖鋭度Ｑを大きくすると、感度は高くなるものの、超音波信号の尾曳きが長くなり、深さ方向分解能が悪化する問題があった。
【００２６】
この技術課題に対し、本発明による超音波トランスデューサは、ほぼ同一面内の異なる位置に送信用圧電振動子と受信用圧電振動子を配置しているので、それぞれの背面に式（２）を満たすダンピング層を形成することが出来、前面には異なる厚さの音響整合層を配置出来る様になり送受信分離型構造の特徴を十分に発揮させることが出来るようになる。
【００２７】
本発明では音響レンズとして生体より音速の速い材質の凹面レンズを利用しているので、中心位置に配置した共振周波数ｎｆ0受信用圧電振動子前面の音響レンズの平均厚さを１／４λに設定でき、その両側に配置した共振周波数ｆ0の送信用圧電振動子前面の音響レンズの平均厚さをも１／４λに設定できる。
【００２８】
なお、この考えに立てば、凸レンズを用い中心に配置した圧電振動子で送信、その両側に配置した圧電振動子で受信という構成が考えられるが、この場合、前者の場合に比較して音圧の変動が大きく、好ましい音場が得られなくなる。
【００２９】
【課題を解決するための手段】
本発明のアレイ型超音波トランスデューサは、基本波を送信する送信用圧電振動子と、当該基本波に基づく高調波を受信する受信用圧電振動子とを有する圧電振動子エレメントを備えるアレイ型超音波トランスデューサにおいて、前記圧電振動子エレメントは、前記送信用圧電振動子及び前記受信用圧電振動子とがほぼ同一面上に分割配置され、前記送信用圧電振動子によって形成される音場の中心軸と、前記受信用圧電振動子によって形成される音場の中心軸が一致するように配置され、さらに、前記受信用圧電振動子から出力される高調波パルス信号の中心周波数を第１の周波数とした際に、当該第１の周波数に対して僅かに異なる第２の周波数を中心周波数とする並列共振回路を備えたことを特徴とする。
【００３０】
【発明の実施の形態】
以下、図面を参照しながら本発明の実施の形態について述べる。
【００３１】
第１の実施の形態：
図１ないし図５は本発明の第１の実施の形態に係わり、図１はアレイ型超音波トランスデューサの外観を示す外観図、図２は図１の圧電素子と電極配置の様子を示す図、図３は図１のアレイ型超音波トランスデューサをアレイ方向から見た断面図、図４は図１のアレイ型超音波トランスデューサをエレベーション方向から見た断面図、図５は図１のアレイ型超音波トランスデューサを構成する各エレメントの制御装置側の同軸ケーブル端子へ接続する接続回路の構成を示す図である。
【００３２】
（構成）
本発明によるアレイ型超音波トランスデューサの外観は図１に示すように、圧電振動子、ダンピング層、音響整合層、内部配線、等を内容するハウジング５０、音響レンズ４、同軸ケーブル束１２、同軸ケーブル束１２をハウジングに固定する為の同軸ケーブル固定樹脂からなる。
【００３３】
また、ハウジング５０に内容された内部構造は図３に示すように、１対の基本波の周波数にほぼ等しい共振周波数を持った例えばＰＺＴからなり、両面に電極１４ａ、１４ｂが形成された圧電素子１３（図２参照）からなる基本波送信用圧電振動子１ａ、１ｂと、１対の配線用基板７ａ，７ｂを隔てて、他の圧電材質、例えばチタン酸鉛、ニオブ酸カリウム、あるいはニオブ酸リチウム等の圧電材料からなり、両面に電極が形成され、高調波の周波数にほぼ等しい共振周波数を持った高調波受信用圧電振動子２と、基本波送信用圧電振動子１ａ、１ｂの背面（超音波を送受信しない側）に、例えば柔軟性を持つエポキシ樹脂に酸化タングステンや酸化アルミウムを適量混合した材料からなり、その形成により送信振動子の共振尖鋭度Ｑrが好ましくは２〜４になる送信振動子用ダンピング層５と、高調波受信用圧電振動子２の背面に例えば柔軟性を持つエポキシ樹脂に酸化タングステンや酸化アルミウムを送信振動子用とは異なる適量混合した材料からなり、その形成により受信振動子の共振尖鋭度ＱEが好ましくは４〜８になる送信振動子用ダンピング層６と、基本波送信用圧電振動子１ａ、１ｂ、高調波受信用圧電振動子２の前面に基本波送信用圧電振動子１ａ、１ｂ、高調波受信用圧電振動子２の各電極を同電位とする機能を兼ね備えた音響整合層３と、さらにその前面にシリコーンゴム等からなる音響レンズ４とが配設されている。
【００３４】
基本波送信用圧電振動子１ａ、１ｂと高調波受信用圧電振動子２を隔離する機能を兼持しだ衝立て状プリント基板７ａ，７ｂにはアレイを構成するエレメントの数のストライプ電極８ａ，８ｂ，８ｃが形成され、圧電振動子の各電極から微小配線１１ａ，１１ｂ，１１ｃで電気的に接続されている。
【００３５】
なお、本実施の形態では前記音響整合層３は素材そのものが導電性を有するものを用いているが、さらに導電性を確実に低下させるために、その基本波送信用圧電振動子１ａ、１ｂ、高調波受信用圧電振動子２の電極に接する側の面を金等の金属膜を形成する構造も有効である。
【００３６】
そして前記ストライプ電極８ａ，８ｂ，８ｃは、各エレメント８０（１）〜８０（ｎ）毎（図４参照）に細径同軸ケーブル２５（１）〜２５（ｎ）（図４参照）を接続し、細径同軸ケーブル２５（１）〜２５（ｎ）は束ねられ、同軸ケーブル束１２として図１に示すように衝立て状配線プリント基板７ａ，７ｂの周囲に絶縁性樹脂で固定され、さらに密閉封止用樹脂１０で完全に固定される。
【００３７】
ハウジング側板９ａ，９ｂはこれらの部材を側面から固定すると同時に、外側面に配置した金等の金属からなる導電膜を接地電位として接地用配線１６ａ，１６ｂを経て微細同軸ケーブルの図示していないシールド線へ接続されている。
【００３８】
アレイを構成する各エレメントはエレベーション方向から見ると図４のように構成されている。すなわち、一対の基本波送信用圧電振動子１ａ、１ｂと、それらに挟まれるともにその音響中心軸が一致するように配置された高調波受信用圧電振動子２からなる振動子エレメント２１（１）〜２１（ｎ）がダイシング溝２０（１）〜２０（ｎ−１）を挟んで配置している。ダイシング溝２０（１）〜２０（ｎ−１）は、音響整合層全厚と高調波受信用圧電振動子の途中までが切り込まれ、ダイシングされない残部２３を有している。
【００３９】
一方、高調波受信用圧電振動子２は、基本波送信用圧電振動子１ａ、１ｂの１／２〜１／３の厚さであり、全厚にわたりダイシングされている。高調波受信用圧電振動子２は音響整合層３及び衝立て状配線用プリント基板７ａ，７ｂに図示されていない接着剤で固定されている。
【００４０】
送信駆動用同軸ケーブル３４（図５参照）の信号線の一方の端子は基本波送信用圧電振動子２７（図５参照）の電極２９に配線用プリント基板７ａ，７ｂを中推して接続され、他方の端子３８は制御装置のパルサー部に接続される。一方、受信用同軸ケーブル３５（図５参照）の信号線の一方の端子は高調波受信用圧電振動子２８（図５参照）の電極30に配線用プリント基板７ｂを中推して接続され、他方の端子はコンデンサ３６、コイル３７からなる接続回路４０を経て制御装置のレシーバ部に接続される。コンデンサ３６は信号線３４に直列に、コイル３７は同軸ケーブルの信号線とグランド３１１の間に接続する。唇超音波トランスデューサの共通接地電極３１、同軸ケーブルのシールド線部は接地３１１に接続される。
【００４１】
（作用）
パルサーから基本波送信用圧電振動子１ａ、１ｂに、基本波送信超音波パルスの中心周波数をその中心周波数とするスペクトルを持つ駆動パルス信号が印加されると一対の基本波送信用圧電振動子１ａ、１ｂから基本波超音波が送信され合成され音響レンズ４で集束された送信超音波音場が形成される。
【００４２】
この合成超音波音場内に存在する生体組織の音響インピーダンス界面で超音波は反射される。この反射超音波は、送信超音波が生体組織を伝播する内に生体組織の持つ非線形性や、音響インピーダンス界面が体内に注入された造影剤バブルだとすると、造影剤バブルの送信超音波による共振や破裂によって発生する高調波成分を基本波成分と共に含んだ信号となる。
【００４３】
この内の高調波成分の中心周波数とほぼ等しい共振周波数を持つ高調波受信用圧電振動子２で受信すると、基本波成分は抑圧され、基本波成分に比べ、高い信号レベルの高調波成分を有する受信信号が得られる。この時の受信感度Ｓensは式（１）及び（２）で表される。
【００４４】
式（１）から分かるように大きな感度を得るには、式（１）にしたがって、基本波送信用圧電振動子１ａ、１ｂに関しては、圧電定数ｄ33の大きな圧電材料、受信用にはｇ33Ｖlの大きな圧電材料、例えばチタン酸鉛、ニオブ酸カリウム、ニオブ酸リチウムを用いいることが好ましい。
【００４５】
また共振尖鋭度Ｑも送信用、受信用とも大きいほど受信感度が大きくなるが、大きすぎると超音波振動の尾曳きが長くなる深さ方向分解能を悪化させる原因となる。また式（２）に示したように送信用、受信用のＱに差異を設けると、より基本波成分を抑圧し易くなる。そこで、送信用ＱをＱT＝２〜４、受信用ＱをＱR＝４〜８になるように、それぞれの背面に形成するダンピング層の材質設計を行う。
【００４６】
本実施の形態では導電性を全く持たせないようにするため、柔軟性エポキシ樹脂に酸化タングステンを分散する組成を用い、酸化タングステンの混合率に差異を設けて混合し、送信用ＱをＱT＝２〜４、受信用ＱをＱR＝４〜８になるように調整している。
【００４７】
このような構造でも基本波成分は残っている場合がある。高調波成分は焦点より近い領域での音圧はトランスデューサとの距離が小さくなればなるほど急激に音圧レベルが小さくなる。このことは近距離において発生しがちな多重反射が現れないという好ましい作用があるが、高調波成分のみの超音波像はトランスデューサ近傍で何も写らないことになり、診断機能がなくなることを意味する。
【００４８】
そこで、基本波成分の残存を或程度残す使い方があり、その場合は高調波受信用圧電振動子２からの出力信号に基本波成分が或程度混在するほうを好ましいとするので、そのまま制御装置のレシーバ回路に入力すれば良い。
【００４９】
しかし、基本波混在は超音波画像の分解能を劣化させるのｆで出来るだけ抑圧するというのが、一般的な考え方であり、これに従うと図５に示すようにコンデンサ３６とコイル３７からなる接続回路４０を通すことが必要になる。コンデンサ３６とコイル３７をこの位置で付加することにより新たに高調波受信用圧電振動子２の制動容量Ｃ0、同軸ケーブルの静電容量Ｃs、付加コンデンサ３６、及び付加コイル３７とからなる並列共振回路を形成し、この並列共振回路の共振周波数が高調波信号の中心周波数の近傍になるようにＣa、Ｌaを調整する。殆ど一致するように調整すると、高調波受信用圧電振動子２からの出力信号は感度は向上するが、信号のＱが大きくなり、尾曳きが大きくなることにより深さ方向分解能が低下する。そこで、両周波数を少しずらし、Ｑの増加分を高調波信号の高帯域化を図る調整を行う。
【００５０】
このようにして得られる殆ど高調波成分だけからなる各エレメントからの信号をリニア的に電子走査したり、セクタ的に電子走査し、これらの信号をスキャンコンバータ等で信号処理及び画像処理して最終的にモニタに画像表示したり、記憶媒体に保存する。
【００５１】
（効果）
以上のように、アレイを構成する各エレメントを分割型構造とし、一対の基本波送信用圧電振動子と、それらに挟まれるように配置する高調波受信用圧電振動子を双方の振動子が形成する超音波音場の中心軸が合致するように配置し、かつ各圧電振動子やダンピング層の特性を、式（１）及び（２）に従うように寸法、材質設計をし、かつ以上説明したような衝立て状配線用プリント基板で、両圧電振動子を隔離固定し、更に受信電圧信号を付加コンデンサや付加コイルで処理することにより、一つのエレメントからは高調波信号成分が強調された信号が得られ、リニア走査或いはセクタ走査して各エレメントからの信号を画像処理することにより、高調波信号を用いた特徴的な診断画像、即ち、空間分解能やコントラスト分解能に優れた超音波診断画像が得られることになる。
【００５２】
第２の実施の形態：
図６は本発明の第２の実施の形態に係るアレイ型超音波トランスデューサの外観を示す外観図である。
【００５３】
第２の実施の形態は、第１の実施の形態とほとんど同じであるので、異なる点のみ説明し、同一の構成には同じ符号をつけ説明は省略する。
【００５４】
（構成）
図６に示すように、本実施の形態の第１の実施の形態と異なる部分は音響レンズ４の形状、材質が異なることである。この音響レンズ材料は導電率が高く、快削性に富むグラファイトコンパウンド゛材料で超音波出射側の面が曲率半径Ｒ（４１）でシリンドリカルに研削加工されている。
【００５５】
圧電振動子の電極側に接する面は圧電振動子の電極を共通接地電位に、より効果的にするために、図示していない電極が形成されることもある。
【００５６】
なお、このように導電性が良く、熱伝導性が良い材料を配置させると放熱が超音波送受信側のみで良くなる。このため圧電振動子内の温度分布に傾斜がつき、それにより、基本波送信超音波に最初から圧電高次振動成分が含まれることになる。そこで、基本波送信用圧電振動子１ａ，１ｂ、高調波受信用圧電振動子２の双方に固着させている配線用プリント基板の材料に誘電率、誘電ロスが小さく且つ熱伝導率が大きく放熱性が良いチッ化アルミニウムセラミックスを用いる。
【００５７】
（作用・効果）
このように音響レンズを凹面にすることによって、基本波送信用圧電振動子前面の平均厚みをその基本波周波数での１／４λ程度に厚く、高調波受信用圧電振動子前面の平均厚みをその周波数での１／４λ程度に薄くすることが可能となる。
【００５８】
すなわち、音響レンズの効果と、音響整合層の効果、特に位相条件を満たす効果を兼ねさせることが可能となり、送信超音波音圧を高調波がより発生しやすい音圧に増加させることができるようになる。
【００５９】
また、配線用プリント基板７ａ，７ｂを上記のような材質構造にすることによって、圧電振動子内の温度分布の傾斜を抑圧し、基本波送信超音波に最初から圧電高次振動成分が含まれ、高調波検出の効率を低下することを抑えることが可能になる。
【００６０】
以上、本実施の形態により高感度で高調波イメージングが出来るようになる。なお、本実施の形態でば凹面加工する音響レンズ材料として導電性の良好なグラファイト系素材を用いるとしたが、必ずしもこのような素材に限定されるものではなく、例えばエポキシ製樹脂の片面を凹面加工し、圧電振動子電極に接する側に面に金等の導電性膜を形成した構造でも良い。この場合は熱放散はおこりにくくなり、圧電振動子内に温度傾斜は殆ど起こらなくなる。アレイ型超音波トランスデューサの用途が発熱し易いセクタ電子スキャンでなければこのような構造、材質で構わない。
【００６１】
第３の実施の形態：
図７及び図８は本発明の第３の実施の形態に係るアレイ型超音波トランスデューサの外観を示す外観図、図８は図７の音響整合層の構成を示す断面図である。
【００６２】
第３の実施の形態は、第１及び第２の実施の形態とほとんど同じであるので、異なる点のみ説明し、同一の構成には同じ符号をつけ説明は省略する。
【００６３】
（構成・作用）
図７に示すように、本実施の形態の第１及び第２の実施の形態と異なる部分は音響レンズ４と基本波送信用圧電振動子１ａ、１ｂ、高調波受信用圧電振動子２の間に音響整合層３を設け、かつ、圧電振動子前面の音響整合層の厚みが基本波、高調波それぞれの周波数に対して１／４λの厚さになるように、図８に示すように、音響整合層３の圧電振動子に接する側の面に窪地１８を形成し、この窪地１８に高調波受信用圧電振動子２と一対の衝立て状配線用プリント基板７ａ，７ｂを固着配置させていることである。
【００６４】
該窪地１８を有した音響整合層３がエポキシ樹脂又はエポキシ樹脂に無機微粉末を混合した材質のように節煙性材料の場合はＣＶＤ等の方法で段切れの無い電極膜１９を形成する必要がある。音響整合層３が導電性を有する場合は、特に電極膜１９を形成する必要はないが、この場合でも電極膜１９を形成しても構わない。
【００６５】
なお、本実施の形態における音響レンズ４の材質は純粋なエポキシ樹脂やポリスチレン樹脂のように音響整合層３と生体や水のそれぞれの音響インピーダンスの中間的な音響インピーダンスを持つ材料が好ましい。
【００６６】
（効果）
本実施の形態によれば、音響整合層３の厚みは基本波送信用圧電振動子１ａ、１ｂ前面では基本渡周渡散での１／４λに、また高調波受信用圧電振動子２前面では高調波周波数に対し、１／４λの厚さに平行平板として設定されるので音響整合効果を最大に引き出すことが可能で、大きな送信超音波音圧が得られ、高調波成分が発生し易くなる。
【００６７】
また、音響レンズ４の材質として音響整合層３の音響インピーダンスと生体の音響インピーダンスの中間的な値の音響インピーダンスを有する材質を用いているので、この音響レンズは第２の音響整合層の役割を果たすことが可能で、さらに高調波成分が発生し易くなる。
【００６８】
さらに、本実施の形態によれば、音響整合層３に窪地１８が形成されていて、一対の衝立て状配線用プリント基板７ａ，７ｂも窪地１８に勘合するように固定配置させるので、一対の基本波送信用圧電振動子１ａ，１ｂが形成する送信音場の中心軸と、高調波受信用圧電振動子２が形成する受信音場の中心軸を正確に合致させ易くなり、きれいな送受信音場が形成できるようになる。
【００６９】
これにより音響整合層３の効果で良好な高調波受信感度が得られるだけでなく、中心軸まわりの音場の対称性が改善され、空間分解能、コントラスト分解能に優れた超音波像が得られるようになる。また組み立て精度が向上し、歩留まりが良くなることによるコストダウンも可能となる。
【００７０】
第４の実施の形態：
図９は本発明の第４の実施の形態に係るアレイ型超音波トランスデューサの外観を示す外観図である。
【００７１】
第２の実施の形態は、第３の実施の形態とほとんど同じであるので、異なる点のみ説明し、同一の構成には同じ符号をつけ説明は省略する。
【００７２】
本実施の形態が第３の実施の形態と異なる点は、図８に示すように、音響整合層３に平行平板構造の第２の層３０１を設け、その前面に音響レンズ４を配置したということである。これによってさらに送受信感度は大きくなり、Ｓ／Ｎ改善につながることになる。
【００７３】
以上述べた実施の形態によるハーモニックイメージング用アレイ型電子スキャン用超音波トランスデューサを用いることによって、空間分解能、コントラスト分解能、時間分解能、及び感度に優れた超音波診断画像を構築できるようになる。
【００７４】
なお、本実施の形態で説明したアレイ型超音波トランスデューサは、リニア型、セクタ型に限定されるものではなく、中央部分を凸状に膨らませて表示範囲が略扇状になるようにしたコンベックス型や、細長棒状の軸の周囲に配置して軸に垂直方向の断面情報を表示するようにした、いわゆる電子ラジアル型（表示範囲：１８０°〜３６０°）に適用できるのはもちろんである。
【００７５】
さらに凹面状の音響レンズを付けたタイプにおいて、体表から走査するときには、生体との間の空気層を除去する手段として、粘度の高いゲル状または半固形状の超音波伝達媒体を間に入れるのがよい。
【００７６】
また体腔内から走査する超音波内視鏡や可撓性細長の超音波プローブに本発明のアレイ型超音波トランスデューサを組み込んで、消化管壁等の病変の診断ができるようにすることももちろん可能であり、このときの超音波伝達媒体としては、脱気水あるいは脱気水を内部に注入したバルーンを周囲に付けるのがよい。
【００７７】
［付記］
（付記項１） 前記音響整合層の前記受信用振動子上の位置において、前記音響整合層の超音波受波面側が前記圧電振動子エレメントの長手方向に凹面加工されている
ことを特徴とした請求項３に記載のアレイ型超音波トランスデューサ。
【００７８】
（付記項２） 前記音響整合層が２層で、第１の音響整合層が導電性材料からなり、第２の音響整合層が樹脂材料からなる
ことを特徴とした請求項１に記載のアレイ型超音波トランスデューサ。
【００７９】
（付記項３） 前記送信用振動子と前記受信用振動子の分割溝にエレメントピッチに相当する数の微細配線がプリントされたプリント基板を衝立て状に配置させ、衡立て状プリント基板は送信振動子用ダンピング材と受信振動子用ダンピング材によって固定された構造を有している
ことを特徴とした請求項１に記載のアレイ型超音波トランスデューサ。
【００８０】
（付記項４） 前記衡立て状プリント基板の基材が低誘電率材料からなる
ことを特徴とした付記項３に記載のアレイ型超音波トランスデューサ。
【００８１】
（付記項５） 前記衝立て状プリント基板の基材が高熱伝導率材料からなる
ことを特徴とした付記項３に記載のアレイ型超音波トランスデューサ。
【００８２】
（付記項６） 前記衡立て状プリント基板の基材が窒化アルミニウムからなる
ことを特徴とした付記項３に記載のアレイ型超音波トランスデューサ。
【００８３】
（付記項７） 前記音響レンズが凹面である
ことを特徴とした請求項３に記載のアレイ型超音波トランスデューサ。
【００８４】
（付記項８） 前記受信用圧電振動子から出力される高調波パルス信号の中心周波数ｎｆ0を僅かに異なる周波数を中心周波数とする並列共振回路を備えている
ことを特徴とした請求項１に記載のアレイ型超音波トランスデューサ。
【００８５】
（付記項９）請求項１ないし３に記載のアレイ型超音波トランスデューサを挿入部先端付近に配置した
ことを特徴とする体腔内検査用超音波プローブあるいは超音波内視鏡。
【００８６】
本発明は、上述した実施の形態に限定されるものではなく、本発明の要旨を変えない範囲において、種々の変更、改変等が可能である。
【００８７】
【発明の効果】
以上説明したように本発明によれば、基本波送信周波数ｆ0、高調波受信周波数ｎｆ0（ｎは２以上の整数）のそれぞれの周波数に対応したダンピング層等の付加部材を構成し、高感度、高空間分解能、高コントラスト分解能のハーモニックイメージングを行うことができるという効果がある。
【図面の簡単な説明】
【図１】本発明の第１の実施の形態に係るアレイ型超音波トランスデューサの外観を示す外観図
【図２】図１の圧電素子と電極配置の様子を示す図
【図３】図１のアレイ型超音波トランスデューサをアレイ方向から見た断面図
【図４】図１のアレイ型超音波トランスデューサをエレベーション方向から見た断面図
【図５】図１のアレイ型超音波トランスデューサを構成する各エレメントの制御装置側の同軸ケーブル端子へ接続する接続回路の構成を示す図
【図６】本発明の第２の実施の形態に係るアレイ型超音波トランスデューサの外観を示す外観図
【図７】本発明の第３の実施の形態に係るアレイ型超音波トランスデューサの外観を示す外観図
【図８】図７の音響整合層の構成を示す断面図
【図９】本発明の第４の実施の形態に係るアレイ型超音波トランスデューサの外観を示す外観図
【図１０】従来の送受信分離型トランスデューサを示す図
【符号の説明】
１ａ、１ｂ…基本波送信用圧電振動子
２…高調波受信用圧電振動子
３…音響整合層
４…音響レンズ
５，６…送信振動子用ダンピング層
７ａ，７ｂ…配線用基板
８ａ，８ｂ，８ｃ…ストライプ電極
９ａ，９ｂ…ハウジング側板
１０…密閉封止用樹脂
１１ａ，１１ｂ，１１ｃ…微小配線
１２…同軸ケーブル束
１３…圧電素子
１４ａ、１４ｂ…電極
１６ａ，１６ｂ…接地用配線
２０（１）〜２０（ｎ−１）…ダイシング溝
２１（１）〜２１（ｎ）…振動子エレメント
２５（１）〜２５（ｎ）…細径同軸ケーブル[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an array-type ultrasonic transducer used for harmonic imaging ultrasonic diagnosis.
[0002]
[Prior art]
In recent years, it has been found that harmonic imaging diagnosis using harmonic signals can provide a clear diagnostic image that cannot be obtained by conventional B-mode diagnosis, and is becoming a standard diagnostic modality.
[0003]
In comparison with the fundamental wave, harmonic imaging
(1) Since the side lobe level is small, the S / N is good and the contrast resolution is good.
(2) The higher the frequency, the narrower the beam width and the better the lateral resolution.
(3) Since the sound pressure is small at a short distance and the fluctuation of the sound pressure is small, multiple reflections do not occur.
(4) Attenuation beyond the focal point is similar to that of the fundamental wave, and the deep velocity can be increased compared to the ultrasonic wave having the harmonic frequency as the fundamental wave.
It has many advantages.
[0004]
As a specific structure of the array type ultrasonic transducer for harmonic imaging, a piezoelectric vibrator in which each transducer element constituting the array is a broadband integrated type is used.
[0005]
A method of transmitting fundamental waves in the frequency region on the low frequency side of the broadband characteristics and receiving harmonics in the frequency region on the high frequency side is generally used. In this case, narrowband ultrasonic waves are used so that the spectrum of the fundamental wave transmission ultrasonic wave and the spectrum of the harmonic wave reception ultrasonic wave do not overlap as much as possible. Since narrow-band ultrasound is generally an ultrasound pulse signal with a long tail, it has an adverse effect on depth resolution.
[0006]
As a specific structure of an array type ultrasonic transducer for other harmonic imaging, for example, a transmitting piezoelectric vibrator and a receiving piezoelectric vibrator are separately described in Japanese Patent Laid-Open Nos. 8-187245 and 11-276478. A separate transmission / reception transducer has been proposed.
[0007]
For example, in Japanese Patent Application Laid-Open No. 11-276478, as shown in FIG. 10, an ultrasonic probe and an ultrasonic diagnostic apparatus suitable for transmitting a fundamental wave and receiving an ultrasonic wave including a harmonic are provided. A first piezoelectric layer 212 composed of a plurality of arranged first piezoelectric vibrators 2121 having a first acoustic impedance Z1 and responsible for transmission / reception of ultrasonic waves having a center frequency f1, and a second acoustic impedance. The second piezoelectric layer 2 is composed of a plurality of second piezoelectric elements 2131 arranged with Z2 (Z2 <Z1), is superposed on the first piezoelectric layer 212, and is responsible for receiving ultrasonic waves with a center frequency f2 = 2f1. 1 to 3 are provided.
[0008]
[Problems to be solved by the invention]
As described above, array-type ultrasonic transducers in which a fundamental-wave transmitting piezoelectric transducer and a harmonic-receiving piezoelectric transducer are stacked have been proposed. However, the problem with these structures is the fundamental wave. This is the influence of the piezoelectric noise generated when the transmission ultrasonic wave passes through the reception piezoelectric vibrator during transmission and the piezoelectric noise caused by the transmission piezoelectric vibrator arranged on the back surface of the reception piezoelectric vibrator during reception. These noises adversely affect the high contrast resolution characteristic of harmonic imaging, and impair the groundwork of harmonic imaging.
[0009]
In addition, the structure and dimensional design corresponding to the processing frequency are also performed in the damping layer, the acoustic matching layer, and the additional material of the acoustic lens that are usually provided. However, in the conventional structure arranged in a layered structure, it is impossible to design individual structures and materials for transmission and reception.
[0010]
The present invention has been made in view of the above circumstances, and constitutes an additional member such as a damping layer corresponding to each of the fundamental transmission frequency f0 and the harmonic reception frequency nf0 (n is an integer of 2 or more). An object of the present invention is to provide an array-type ultrasonic transducer capable of performing harmonic imaging with high sensitivity, high spatial resolution, and high contrast resolution.
[0011]
As another accompanying technical problem, there is a technical problem when using an integrated ultrasonic transducer exhibiting wideband characteristics as described above, that is, degradation in depth resolution due to transmission / reception of narrowband ultrasonic waves. Also in the ultrasonic transducer according to the invention, in order to increase the reception sensitivity and suppress the fundamental wave component mixed in the received ultrasonic wave, the damping layer design based on the following equations (1) and (2) is performed. .
[0012]
[Expression 1]

[0013]
[Expression 2]
QmR> QmT (2)
Where d33: piezoelectric constant, S: aperture, Qm: resonance sharpness, Vr: longitudinal wave speed, n: harmonic order, fr :: fundamental frequency, F: sound field parameters, subscript T: for transmission Transducer, subscript R: a receiving transducer.
[0014]
Designing a large resonance sharpness Q of ultrasonic waves in this way is effective for improving sensitivity and suppressing the fundamental wave component of the received signal, but on the other hand, lengthening the ultrasonic tail and increasing the depth resolution May lead to deterioration.
[0015]
Therefore, in the transmission / reception separation type ultrasonic transducer according to the present invention, there is a technical problem that an incidental technical problem is that the reception of the ultrasonic wave is not prolonged while the reception sensitivity is kept high.
[0016]
In order to solve the above problems, the following means are used in the present invention. That is, in an array-type ultrasonic transducer that transmits fundamental waves and receives harmonics, each piezoelectric vibrator element that constitutes the array is composed of a transmitting piezoelectric vibrator and a receiving piezoelectric vibrator, which are substantially on the same plane. Furthermore, the central axis of the sound field by the transmitting vibrator and the central axis of the sound field by the receiving vibrator are arranged so as to coincide with each other, and more than one pair of transmitting piezoelectric vibrators have one or more symmetry. The several receiving piezoelectric vibrators are arranged so as to be sandwiched therebetween.
[0017]
The minimum unit of this arrangement is a structure in which one receiving piezoelectric vibrator is sandwiched between a pair of transmitting piezoelectric vibrators. Several combinations may be used.
[0018]
Further, the structure and material of the damping layer formed on the back surface of the piezoelectric vibrator are different for each piezoelectric vibrator, the thickness of the acoustic matching layer disposed on the ultrasonic transmitting / receiving surface side is also changed, and the acoustic lens is concave. A material having a sound speed higher than that of a living body is used.
[0019]
As described above, the technical problem that accompanies the present invention, that is, as a means for reducing the resolution in the depth direction, the end of the coaxial cable connected to the receiving piezoelectric transducer element of each transducer element constituting the array Thus, a resonance circuit is constituted by the combined capacitance Cx of the electrostatic capacitance Cs of the coaxial cable and the braking capacitance Co of the receiving piezoelectric vibrator and the additional capacitor Ca and the additional inductor La added at the end thereof.
[0020]
A fundamental ultrasonic wave is transmitted from a pair of piezoelectric vibrators arranged so as to sandwich the receiving piezoelectric vibrator, and a harmonic signal is received by the receiving piezoelectric vibrator sandwiched between the pair of transmitting piezoelectric vibrators. In the array type ultrasonic transducer according to the present invention, the fundamental wave transmitting piezoelectric vibrator and the harmonic receiving piezoelectric vibrator are divided and arranged in the same plane in each element constituting the array. It is possible to separately form a damping layer having different characteristics and an acoustic matching layer having a suitable thickness on the front surface.
[0021]
The combination of the piezoelectric vibrator materials is optimized so that the sensitivity of the transmission / reception separation type ultrasonic transducer is increased based on the formula (1).
[0022]
Further, in order to suppress the fundamental wave component as much as possible in the received signal in which the fundamental wave component and the harmonic wave component are mixed, the condition of Expression (2) is also satisfied. Therefore, large reception sensitivity and efficient suppression of the fundamental wave component are possible.
[0023]
Furthermore, the acoustic matching layer also has an optimum matching layer thickness V / 4 f 0 with respect to the frequency f 0 of the transmission fundamental wave ultrasonic wave, and an optimum matching layer thickness V / 8 f 0 with respect to the harmonic, for example, the second harmonic 2 f 0. The acoustic matching layer has an optimum acoustic matching state at a thickness of 1 / 4λ and a worst acoustic matching state at a thickness of 1 / 2λ. In other words, if an acoustic matching layer with a uniform thickness is adapted to a fundamental wave transmission transducer, it is not suitable for a harmonic reception transducer, and if adapted to a harmonic reception transducer, it is not suitable for a fundamental transmission transducer. turn into.
[0024]
In the ultrasonic transducer according to the present invention, the acoustic matching layer is not a parallel plate because it is concave on one side and the speed of sound is higher than the speed of sound of a living body, but each of the front face of the fundamental wave transmitting vibrator and the front face of the harmonic wave receiving vibrator is used. The average thickness of the acoustic lens can be adapted to a thickness of 1 / 4λ.
[0025]
On the other hand, when the resonance sharpness Q is increased based on the equation (1), the sensitivity is increased, but the tailing of the ultrasonic signal becomes long and the depth resolution is deteriorated.
[0026]
In response to this technical problem, the ultrasonic transducer according to the present invention has the transmitting piezoelectric vibrator and the receiving piezoelectric vibrator arranged at different positions in substantially the same plane. A damping layer can be formed, and an acoustic matching layer with a different thickness can be disposed on the front surface, so that the characteristics of the transmission / reception separation type structure can be fully exhibited.
[0027]
In the present invention, a concave lens made of a material having a higher sound speed than that of a living body is used as the acoustic lens. Therefore, the average thickness of the acoustic lens in front of the resonance frequency nf0 receiving piezoelectric vibrator arranged at the center position can be set to 1 / 4λ. The average thickness of the acoustic lens on the front surface of the transmitting piezoelectric vibrator having the resonance frequency f0 arranged on both sides can be set to 1 / 4λ.
[0028]
Based on this idea, a configuration may be considered in which transmission is performed by a piezoelectric vibrator arranged at the center using a convex lens, and reception is performed by piezoelectric vibrators arranged on both sides thereof. In this case, the sound pressure is compared with the former case. The fluctuation of the noise is large and a preferable sound field cannot be obtained.
[0029]
[Means for Solving the Problems]
  The array-type ultrasonic transducer of the present invention includes a transmitting piezoelectric vibrator that transmits a fundamental wave,Based on the fundamental waveReceiving piezoelectric vibrator for receiving harmonics andHavePiezoelectric vibrator elementPrepareIn the array type ultrasonic transducer, the piezoelectric vibrator elementIsThe transmitting piezoelectric vibrator and the receiving piezoelectric vibrator;ButDivided and arranged on substantially the same plane, for the transmissionPiezoelectricThe central axis of the sound field formed by the vibrator and the receivingPiezoelectricArranged so that the central axes of the sound field formed by the transducers coincide.Furthermore, when the center frequency of the harmonic pulse signal output from the receiving piezoelectric vibrator is the first frequency, the second frequency slightly different from the first frequency is set as the center frequency. A parallel resonant circuit is provided.
[0030]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0031]
First embodiment:
1 to 5 relate to a first embodiment of the present invention, FIG. 1 is an external view showing an external appearance of an array type ultrasonic transducer, FIG. 2 is a view showing a state of arrangement of piezoelectric elements and electrodes in FIG. 3 is a cross-sectional view of the array-type ultrasonic transducer of FIG. 1 viewed from the array direction, FIG. 4 is a cross-sectional view of the array-type ultrasonic transducer of FIG. 1 viewed from the elevation direction, and FIG. It is a figure which shows the structure of the connection circuit connected to the coaxial cable terminal by the side of the control apparatus of each element which comprises a sound wave transducer.
[0032]
(Constitution)
As shown in FIG. 1, the external appearance of the array type ultrasonic transducer according to the present invention includes a housing 50, an acoustic lens 4, a coaxial cable bundle 12, a coaxial cable containing a piezoelectric vibrator, a damping layer, an acoustic matching layer, an internal wiring, and the like. It consists of a coaxial cable fixing resin for fixing the bundle 12 to the housing.
[0033]
Further, as shown in FIG. 3, the internal structure contained in the housing 50 is composed of, for example, PZT having a resonance frequency substantially equal to the frequency of a pair of fundamental waves, and a piezoelectric element having electrodes 14a and 14b formed on both surfaces. 13 (see FIG. 2), the piezoelectric transducers 1a and 1b for fundamental wave transmission and a pair of wiring substrates 7a and 7b are separated from each other, for example, lead titanate, potassium niobate, or niobic acid. It is made of a piezoelectric material such as lithium, electrodes are formed on both surfaces, and the back side of the harmonic wave receiving piezoelectric vibrator 2 having a resonance frequency substantially equal to the harmonic frequency and the fundamental wave transmitting piezoelectric vibrators 1a and 1b ( It is made of a material in which an appropriate amount of tungsten oxide or aluminum oxide is mixed with a flexible epoxy resin on the side where ultrasonic waves are not transmitted / received, and the resonance sharpness Qr of the transmitting vibrator is preferred due to its formation. For example, an appropriate amount of tungsten oxide or aluminum oxide is mixed with epoxy resin having flexibility on the back surface of the transmission vibrator damping layer 5 and the harmonic reception piezoelectric vibrator 2 which are 2 to 4 different from those for the transmission vibrator. The transmitting vibrator damping layer 6 having the resonance sharpness QE of the receiving vibrator preferably 4 to 8 by the formation thereof, the fundamental wave transmitting piezoelectric vibrators 1a and 1b, and the harmonic receiving piezoelectric vibration. The acoustic matching layer 3 having a function of bringing the electrodes of the fundamental wave transmitting piezoelectric vibrators 1a and 1b and the harmonic wave receiving piezoelectric vibrator 2 to the same potential on the front surface of the child 2 and further, silicone rubber or the like on the front surface thereof. An acoustic lens 4 is provided.
[0034]
The screen-like printed circuit boards 7a and 7b having the function of isolating the fundamental wave transmitting piezoelectric vibrators 1a and 1b and the harmonic wave receiving piezoelectric vibrator 2 have stripe electrodes 8a and 8b corresponding to the number of elements constituting the array. 8b and 8c are formed, and are electrically connected to each electrode of the piezoelectric vibrator by the micro wirings 11a, 11b, and 11c.
[0035]
In this embodiment, the acoustic matching layer 3 is made of a material that is conductive. However, in order to further reduce the conductivity, the fundamental wave transmitting piezoelectric vibrators 1a, 1b, A structure in which a metal film such as gold is formed on the surface in contact with the electrodes of the harmonic wave receiving piezoelectric vibrator 2 is also effective.
[0036]
The stripe electrodes 8a, 8b, and 8c connect the thin coaxial cables 25 (1) to 25 (n) (see FIG. 4) to the elements 80 (1) to 80 (n) (see FIG. 4). The small-diameter coaxial cables 25 (1) to 25 (n) are bundled and fixed as a coaxial cable bundle 12 with insulating resin around the screen printed wiring boards 7a and 7b as shown in FIG. It is completely fixed with the sealing resin 10.
[0037]
The housing side plates 9a and 9b fix these members from the side, and at the same time, a conductive film made of metal such as gold disposed on the outer side is grounded to ground potentials 16a and 16b, and a shield (not shown) of the fine coaxial cable. Connected to the line.
[0038]
Each element constituting the array is configured as shown in FIG. 4 when viewed from the elevation direction. That is, a transducer element 21 (1) including a pair of fundamental wave transmitting piezoelectric vibrators 1a and 1b and a harmonic wave receiving piezoelectric vibrator 2 sandwiched between them and arranged so that their acoustic central axes coincide with each other. To 21 (n) are arranged across the dicing grooves 20 (1) to 20 (n-1). The dicing grooves 20 (1) to 20 (n-1) have a remaining portion 23 that is cut into the acoustic matching layer full thickness and part of the harmonic receiving piezoelectric vibrator and is not diced.
[0039]
On the other hand, the harmonic wave receiving piezoelectric vibrator 2 is 1/2 to 1/3 the thickness of the fundamental wave transmitting piezoelectric vibrators 1a and 1b, and is diced over the entire thickness. The harmonic wave receiving piezoelectric vibrator 2 is fixed to the acoustic matching layer 3 and the printed wiring boards 7a and 7b for screen-like wiring with an adhesive (not shown).
[0040]
One terminal of the signal line of the transmission driving coaxial cable 34 (see FIG. 5) is connected to the electrode 29 of the fundamental wave transmitting piezoelectric vibrator 27 (see FIG. 5) through the wiring printed boards 7a and 7b. The other terminal 38 is connected to the pulsar section of the control device. On the other hand, one terminal of the signal line of the receiving coaxial cable 35 (see FIG. 5) is connected to the electrode 30 of the harmonic receiving piezoelectric vibrator 28 (see FIG. 5) through the wiring printed board 7b, and the other terminal. These terminals are connected to a receiver section of the control device through a connection circuit 40 including a capacitor 36 and a coil 37. The capacitor 36 is connected in series with the signal line 34, and the coil 37 is connected between the signal line of the coaxial cable and the ground 311. The common ground electrode 31 of the lip ultrasonic transducer and the shield line portion of the coaxial cable are connected to the ground 311.
[0041]
(Function)
When a drive pulse signal having a spectrum having the center frequency of the fundamental wave transmission ultrasonic pulse as its center frequency is applied from the pulser to the fundamental wave transmission piezoelectric vibrators 1a and 1b, a pair of fundamental wave transmission piezoelectric vibrators 1a. 1b, the fundamental ultrasonic wave is transmitted and synthesized, and a transmission ultrasonic sound field focused by the acoustic lens 4 is formed.
[0042]
The ultrasonic waves are reflected at the acoustic impedance interface of the living tissue existing in the synthetic ultrasonic field. If the reflected ultrasound is a contrast medium bubble in which the transmitted ultrasound propagates through the living tissue and the nonlinearity of the living tissue, or the acoustic impedance interface is injected into the body, resonance or rupture due to the transmitted ultrasound of the contrast medium bubble. Is a signal that includes the harmonic component generated by, together with the fundamental component.
[0043]
When the harmonic wave receiving piezoelectric vibrator 2 having a resonance frequency substantially equal to the center frequency of the harmonic component is received, the fundamental wave component is suppressed, and has a higher harmonic component having a higher signal level than the fundamental wave component. A received signal is obtained. The reception sensitivity Sens at this time is expressed by equations (1) and (2).
[0044]
In order to obtain a large sensitivity as can be seen from the equation (1), according to the equation (1), for the fundamental wave transmitting piezoelectric vibrators 1a and 1b, a piezoelectric material having a large piezoelectric constant d33, and a large g33Vl for receiving. A piezoelectric material such as lead titanate, potassium niobate or lithium niobate is preferably used.
[0045]
Further, the larger the resonance sharpness Q is for both transmission and reception, the higher the reception sensitivity is. However, if the resonance sharpness Q is too large, the depth resolution in the depth direction in which the tailing of the ultrasonic vibration becomes longer is deteriorated. Further, as shown in the equation (2), if a difference is provided between the transmission Q and the reception Q, it becomes easier to suppress the fundamental wave component. Therefore, the material design of the damping layer formed on each back surface is performed so that the transmission Q is QT = 2 to 4 and the reception Q is QR = 4 to 8.
[0046]
In this embodiment, in order not to have conductivity at all, a composition in which tungsten oxide is dispersed in a flexible epoxy resin is used, mixing is performed with a difference in the mixing ratio of tungsten oxide, and transmission Q is set to QT = 2 to 4 and the reception Q is adjusted to be QR = 4 to 8.
[0047]
Even in such a structure, the fundamental wave component may remain. As for the harmonic pressure, the sound pressure level in the region closer to the focal point decreases rapidly as the distance from the transducer decreases. This has a favorable effect that multiple reflections that tend to occur at short distances do not appear, but an ultrasonic image of only the harmonic component is not captured in the vicinity of the transducer, meaning that the diagnostic function is lost. .
[0048]
Therefore, there is a usage in which the fundamental wave component remains to some extent. In that case, it is preferable that the fundamental wave component is mixed to some extent in the output signal from the harmonic wave receiving piezoelectric vibrator 2. What is necessary is just to input into a receiver circuit.
[0049]
However, it is a general idea that mixing of fundamental waves is suppressed as much as possible by f, which degrades the resolution of the ultrasonic image, and according to this, a connection circuit comprising a capacitor 36 and a coil 37 as shown in FIG. 40 is required. By adding a capacitor 36 and a coil 37 at this position, a new parallel resonance circuit including a braking capacitance C0 of the harmonic wave receiving piezoelectric vibrator 2, a capacitance Cs of the coaxial cable, an additional capacitor 36, and an additional coil 37 is provided. And adjust Ca and La so that the resonance frequency of the parallel resonance circuit is close to the center frequency of the harmonic signal. When the adjustment is made so that they are almost the same, the sensitivity of the output signal from the harmonic receiving piezoelectric vibrator 2 is improved, but the Q of the signal increases and the tailing increases, so that the resolution in the depth direction decreases. Therefore, both frequencies are shifted slightly, and an adjustment for increasing the bandwidth of the harmonic signal is performed by increasing Q.
[0050]
The signal from each element consisting of almost only the harmonic component obtained in this way is linearly electronically scanned or sectorally electronically scanned, and these signals are subjected to signal processing and image processing by a scan converter or the like to be finally processed. The image is displayed on a monitor or stored in a storage medium.
[0051]
(effect)
As described above, each element constituting the array has a split structure, and both vibrators form a pair of fundamental wave transmitting piezoelectric vibrators and a harmonic receiving piezoelectric vibrator arranged so as to be sandwiched between them. And the characteristics of each piezoelectric vibrator and damping layer are sized and designed according to the formulas (1) and (2) and explained above. A signal in which harmonic signal components are emphasized from one element by isolating and fixing both piezoelectric vibrators on such a printed wiring board, and processing the received voltage signal with an additional capacitor or additional coil. A characteristic diagnostic image using a harmonic signal, that is, a super image with excellent spatial resolution and contrast resolution, is obtained by performing linear scanning or sector scanning and image processing from each element. So that the wave diagnostic image is obtained.
[0052]
Second embodiment:
FIG. 6 is an external view showing the external appearance of an array type ultrasonic transducer according to the second embodiment of the present invention.
[0053]
Since the second embodiment is almost the same as the first embodiment, only different points will be described, and the same components are denoted by the same reference numerals and description thereof will be omitted.
[0054]
(Constitution)
As shown in FIG. 6, the part of the present embodiment different from the first embodiment is that the shape and material of the acoustic lens 4 are different. This acoustic lens material is a graphite compound material having high conductivity and high free-cutting properties, and the surface on the ultrasonic wave emitting side is cylindrically ground with a radius of curvature R (41).
[0055]
An electrode (not shown) may be formed on the surface in contact with the electrode side of the piezoelectric vibrator to make the electrode of the piezoelectric vibrator more effective at a common ground potential.
[0056]
In addition, if a material having good conductivity and good heat conductivity is arranged in this way, heat radiation is improved only on the ultrasonic wave transmitting / receiving side. For this reason, the temperature distribution in the piezoelectric vibrator is inclined, and as a result, a piezoelectric higher-order vibration component is included in the fundamental wave transmission ultrasonic wave from the beginning. Therefore, the material of the printed circuit board for wiring fixed to both the fundamental wave transmitting piezoelectric vibrators 1a and 1b and the harmonic wave receiving piezoelectric vibrator 2 has a small dielectric constant, dielectric loss, large thermal conductivity, and heat dissipation. Use good aluminum nitride ceramics.
[0057]
(Action / Effect)
By making the acoustic lens concave in this manner, the average thickness of the front surface of the fundamental wave transmitting piezoelectric vibrator is increased to about ¼λ at the fundamental wave frequency, and the average thickness of the front surface of the harmonic wave receiving piezoelectric vibrator is reduced to that thickness. It is possible to reduce the thickness to about 1 / 4λ in frequency.
[0058]
That is, it is possible to combine the effect of the acoustic lens and the effect of the acoustic matching layer, particularly the effect of satisfying the phase condition, so that the transmitted ultrasonic sound pressure can be increased to a sound pressure at which harmonics are more likely to occur. become.
[0059]
Further, by making the printed circuit boards 7a and 7b for wiring as described above, the inclination of the temperature distribution in the piezoelectric vibrator is suppressed, and the fundamental wave transmission ultrasonic wave includes a piezoelectric high-order vibration component from the beginning. Thus, it is possible to suppress a reduction in the efficiency of harmonic detection.
[0060]
As described above, the present embodiment makes it possible to perform harmonic imaging with high sensitivity. In this embodiment, a graphite material having good conductivity is used as an acoustic lens material to be processed into a concave surface. However, the material is not necessarily limited to such a material. For example, one surface of an epoxy resin is concave. A structure in which a conductive film such as gold is formed on the surface on the side in contact with the piezoelectric vibrator electrode may be used. In this case, heat dissipation is difficult to occur, and temperature gradient hardly occurs in the piezoelectric vibrator. Such a structure and material may be used as long as the array type ultrasonic transducer is not used for sector electronic scanning that easily generates heat.
[0061]
Third embodiment:
7 and 8 are external views showing the appearance of an array-type ultrasonic transducer according to the third embodiment of the present invention, and FIG. 8 is a cross-sectional view showing the configuration of the acoustic matching layer of FIG.
[0062]
Since the third embodiment is almost the same as the first and second embodiments, only different points will be described, and the same components are denoted by the same reference numerals and description thereof will be omitted.
[0063]
(Configuration and action)
As shown in FIG. 7, the part of the present embodiment different from the first and second embodiments is between the acoustic lens 4, the fundamental wave transmitting piezoelectric vibrators 1a and 1b, and the harmonic wave receiving piezoelectric vibrator 2. 8 and the thickness of the acoustic matching layer on the front surface of the piezoelectric vibrator is 1 / 4λ with respect to the frequencies of the fundamental wave and the harmonic wave, as shown in FIG. A recess 18 is formed on the surface of the acoustic matching layer 3 on the side in contact with the piezoelectric vibrator, and the harmonic receiving piezoelectric vibrator 2 and a pair of screen printed wiring boards 7a and 7b are fixedly disposed in the recess 18. It is that you are.
[0064]
In the case where the acoustic matching layer 3 having the depressions 18 is a smoke-saving material such as an epoxy resin or a material obtained by mixing inorganic fine powder in an epoxy resin, it is necessary to form an electrode film 19 having no step by a method such as CVD. is there. When the acoustic matching layer 3 has conductivity, it is not necessary to form the electrode film 19 in particular, but the electrode film 19 may be formed even in this case.
[0065]
The material of the acoustic lens 4 in the present embodiment is preferably a material having an intermediate acoustic impedance between the acoustic matching layer 3 and the biological impedance of water or water, such as pure epoxy resin or polystyrene resin.
[0066]
(effect)
According to the present embodiment, the thickness of the acoustic matching layer 3 is ¼ λ of the fundamental wave transmission on the front surface of the fundamental wave transmitting piezoelectric vibrators 1a and 1b, and on the front surface of the harmonic wave receiving piezoelectric vibrator 2. Since it is set as a parallel plate with a thickness of 1 / 4λ with respect to the harmonic frequency, it is possible to maximize the acoustic matching effect, obtain a large transmitted ultrasonic sound pressure, and easily generate harmonic components. .
[0067]
Moreover, since the material which has the acoustic impedance of the intermediate value of the acoustic impedance of the acoustic matching layer 3 and the living body's acoustic impedance is used as the material of the acoustic lens 4, this acoustic lens plays the role of the second acoustic matching layer. It is possible to achieve this, and harmonic components are more likely to be generated.
[0068]
Furthermore, according to the present embodiment, the depression 18 is formed in the acoustic matching layer 3, and the pair of screen printed wiring boards 7a, 7b are fixedly arranged so as to fit into the depression 18, so that a pair of It is easy to accurately match the central axis of the transmission sound field formed by the fundamental wave transmitting piezoelectric vibrators 1a and 1b with the central axis of the reception sound field formed by the harmonic wave reception piezoelectric vibrator 2, and a clean transmission / reception sound field Can be formed.
[0069]
As a result, not only good harmonic reception sensitivity can be obtained by the effect of the acoustic matching layer 3, but also the symmetry of the sound field around the central axis is improved, and an ultrasonic image with excellent spatial resolution and contrast resolution can be obtained. become. Further, the assembly accuracy is improved, and the cost can be reduced by improving the yield.
[0070]
Fourth embodiment:
FIG. 9 is an external view showing the external appearance of an array type ultrasonic transducer according to the fourth embodiment of the present invention.
[0071]
Since the second embodiment is almost the same as the third embodiment, only different points will be described, and the same components are denoted by the same reference numerals and description thereof will be omitted.
[0072]
This embodiment differs from the third embodiment in that a second layer 301 having a parallel plate structure is provided on the acoustic matching layer 3 and the acoustic lens 4 is disposed on the front surface thereof as shown in FIG. That is. This further increases the transmission / reception sensitivity, leading to S / N improvement.
[0073]
By using the array type electronic scanning ultrasonic transducer for harmonic imaging according to the embodiment described above, an ultrasonic diagnostic image having excellent spatial resolution, contrast resolution, time resolution, and sensitivity can be constructed.
[0074]
The array-type ultrasonic transducer described in the present embodiment is not limited to the linear type and the sector type, but is a convex type in which the central portion is bulged so that the display range is substantially fan-shaped. Needless to say, the present invention can be applied to a so-called electronic radial type (display range: 180 ° to 360 °) arranged around a long rod-like shaft so as to display cross-sectional information perpendicular to the shaft.
[0075]
Furthermore, in a type with a concave acoustic lens, when scanning from the body surface, a gel-like or semi-solid ultrasonic transmission medium with high viscosity is inserted as a means for removing the air layer between the living body and the body. It is good.
[0076]
It is also possible to diagnose lesions such as the digestive tract wall by incorporating the array type ultrasonic transducer of the present invention into an ultrasonic endoscope that scans from inside the body cavity or a flexible elongated ultrasonic probe. As an ultrasonic transmission medium at this time, it is preferable to attach deaerated water or a balloon filled with deaerated water to the periphery.
[0077]
[Appendix]
(Additional Item 1) At the position on the receiving transducer of the acoustic matching layer, the ultrasonic wave receiving surface side of the acoustic matching layer is concaved in the longitudinal direction of the piezoelectric transducer element.
The array type ultrasonic transducer according to claim 3, wherein:
[0078]
(Additional Item 2) The acoustic matching layer is composed of two layers, the first acoustic matching layer is made of a conductive material, and the second acoustic matching layer is made of a resin material.
The array type ultrasonic transducer according to claim 1, wherein:
[0079]
(Additional Item 3) A printed circuit board on which fine wirings corresponding to the element pitch are printed in the dividing grooves of the transmitting vibrator and the receiving vibrator is arranged in a partition shape, and the strut-shaped printed circuit board transmits. It has a structure fixed by a damping material for a vibrator and a damping material for a receiving vibrator.
The array type ultrasonic transducer according to claim 1, wherein:
[0080]
(Additional Item 4) A base material of the stretched printed board is made of a low dielectric constant material.
The array-type ultrasonic transducer according to Additional Item 3, wherein
[0081]
(Additional Item 5) A base material of the screen-like printed circuit board is made of a high thermal conductivity material.
The array-type ultrasonic transducer according to Additional Item 3, wherein
[0082]
(Additional Item 6) A base material of the stretched printed board is made of aluminum nitride.
The array-type ultrasonic transducer according to Additional Item 3, wherein
[0083]
(Additional Item 7) The acoustic lens is concave.
The array type ultrasonic transducer according to claim 3, wherein:
[0084]
(Additional Item 8) A parallel resonant circuit having a center frequency nf0 of a harmonic pulse signal output from the receiving piezoelectric vibrator having a slightly different center frequency is provided.
The array type ultrasonic transducer according to claim 1, wherein:
[0085]
(Additional Item 9) The array type ultrasonic transducer according to any one of claims 1 to 3 is disposed near the distal end of the insertion portion.
An ultrasonic probe for in-vivo examination or an ultrasonic endoscope.
[0086]
The present invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the scope of the present invention.
[0087]
【The invention's effect】
As described above, according to the present invention, an additional member such as a damping layer corresponding to each frequency of the fundamental wave transmission frequency f0 and the harmonic reception frequency nf0 (n is an integer of 2 or more) is formed, and high sensitivity, There is an effect that harmonic imaging with high spatial resolution and high contrast resolution can be performed.
[Brief description of the drawings]
FIG. 1 is an external view showing an external appearance of an array type ultrasonic transducer according to a first embodiment of the invention.
FIG. 2 is a diagram showing a state of the piezoelectric element and electrode arrangement of FIG.
3 is a cross-sectional view of the array-type ultrasonic transducer of FIG. 1 as viewed from the array direction.
4 is a cross-sectional view of the array-type ultrasonic transducer of FIG. 1 as viewed from the elevation direction.
5 is a diagram showing a configuration of a connection circuit for connecting to a coaxial cable terminal on the control device side of each element constituting the array-type ultrasonic transducer of FIG. 1;
FIG. 6 is an external view showing an external appearance of an array type ultrasonic transducer according to a second embodiment of the present invention.
FIG. 7 is an external view showing the external appearance of an array type ultrasonic transducer according to a third embodiment of the invention.
8 is a cross-sectional view showing the configuration of the acoustic matching layer in FIG.
FIG. 9 is an external view showing the external appearance of an array type ultrasonic transducer according to a fourth embodiment of the invention.
FIG. 10 is a diagram showing a conventional transmission / reception separation type transducer;
[Explanation of symbols]
1a, 1b ... fundamental wave transmitting piezoelectric vibrator
2 ... Harmonic receiving piezoelectric vibrator
3 ... Acoustic matching layer
4 ... Acoustic lens
5, 6 ... Damping layer for transmitting vibrator
7a, 7b ... Substrate for wiring
8a, 8b, 8c ... stripe electrodes
9a, 9b ... Housing side plate
10 ... Sealing and sealing resin
11a, 11b, 11c ... micro wiring
12 ... Coaxial cable bundle
13: Piezoelectric element
14a, 14b ... electrodes
16a, 16b ... Grounding wiring
20 (1) to 20 (n-1) ... dicing groove
21 (1) to 21 (n) ... vibrator element
25 (1) to 25 (n) ... thin coaxial cable

Claims (4)

A transmitting piezoelectric vibrator for transmitting the fundamental wave, the array type ultrasonic transducer comprising a piezoelectric transducer element and a receiving piezoelectric vibrator for receiving the harmonics based on the fundamental wave,
The piezoelectric transducer element, the transmission piezoelectric vibrator and the receiving piezoelectric vibrator is divided arranged on substantially the same plane, with the center axis of the sound field formed by the transmitting piezoelectric transducer, the receiving Arranged so that the central axis of the sound field formed by the piezoelectric vibrator for use coincides ,
Further, when the center frequency of the harmonic pulse signal output from the reception piezoelectric vibrator is the first frequency, the parallel frequency having the second frequency slightly different from the first frequency as the center frequency. An array-type ultrasonic transducer comprising a resonance circuit .   2. The second frequency according to claim 1, wherein the second frequency is a frequency that is different from the first frequency so as to broaden a harmonic pulse signal output from the reception piezoelectric vibrator. Array type ultrasonic transducer.   The piezoelectric vibrator elements arranged so that the central axes of the sound fields coincide with each other are composed of an even number of 2 or more in the transmitting piezoelectric vibrator and an odd number of 1 or more in the receiving piezoelectric vibrator.
  The array-type ultrasonic transducer according to claim 1 or 2, wherein   The means for bringing the electrodes on the ultrasonic transmission / reception side of the transmitting piezoelectric vibrator and the receiving piezoelectric vibrator to the same potential also serves as an acoustic matching layer or an acoustic lens.
  The array type ultrasonic transducer according to any one of claims 1 to 3, wherein

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