JP2004264221A

JP2004264221A - Ultrasonic sensor

Info

Publication number: JP2004264221A
Application number: JP2003056299A
Authority: JP
Inventors: Yoshihiro Sekine; 良浩関根
Original assignee: Ricoh Elemex Corp
Current assignee: Ricoh Elemex Corp
Priority date: 2003-03-03
Filing date: 2003-03-03
Publication date: 2004-09-24

Abstract

<P>PROBLEM TO BE SOLVED: To provide the ultrasonic sensor making it possible to reduce the multiple reflection, to improve the signal to noise ratio and to eliminate excessive acoustic wave absorber and so on. <P>SOLUTION: The ultrasonic sensor is composed of the disc piezoelectric element 22, the sound matching layer 23 arranged in pile in through-thickness center direction and connected to the piezoelectric element 22 according to the same center axis, and the fixed case 24. The sound matching layer 23 is equipped with the first sound matching layer 25 of the cylindrical shape in the center, and the second sound matching layer 26 in the peripheral area. The first sound matching layer 25 and the second sound matching layer 26 are made from the materials different in the acoustic impedance. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、超音波を利用してガス、水道等の流体の流速、流量を計測する超音波センサに関する。
【０００２】
【従来の技術】
一般に、超音波センサでは音圧特性を高める目的で、中心部に音圧を集中して、効率よく空気中へ高周波の音波を放射する狭角指向特性のものが主流である。
【０００３】
【発明が解決しようとする課題】
従来、図１１に示すように、流体の流量を高精度に検出する超音波流量計は、流路１に設けた送信専用センサ２に対向して上流側と下流側に受信専用センサ３ａと３ｂを配置している。この送信専用センサ２として、従来の超音波センサを使用した場合、中央部Ｃ付近の音圧の高いレベルの音波を無駄にしてしまう。加えて、この中央部からの強い音波エネルギーを吸収しないと流路の内部に音波エネルギーが残留したり、多重反射したりして、信号対雑音比（Ｓ／Ｎ比ともいう）を低下させ、検出誤差の要因となる問題がある。そのために、不要音波を減衰させる音波吸収材等を中央部付近に配置する必要があった。
【０００４】
従来の他の例として、図１０において、比較的高精度である限られたエリア内を移動する物体の位置の検出を行う例がある。この例においては、超音波が移動物体にあたった反射波を受け物体の位置が検出される。移動物体までの距離が約２００ｍｍ、幅が５０〜１５０ｍｍの長方体エリア内を移動する物体を検出する際には、従来の超音波センサ、例えば、高周波高感度タイプのセンサでは、その指向特性が狭く半減角度が約３．５度程度であり、この場合、移動物体の移動距離約１０２ｍｍを満遍なく検知するには、各センサの指向性エリアのオーバーラップ幅を５ｍｍとして計算すると、センサ数は最低９個（Ｓ１〜Ｓ９）必要となる。センサとして９個使用ではコスト高となり問題がある。また、移動物体の大きさ、移動速度によっては、例えば、物体の形状等の影響により受信感度が低下し、音波を発射したセンサで必ずしも送受信できるとは限らない場合もありうるため、検出のための信号処理が複雑化し、処理時間が大幅に掛かってしまう問題がある。さらに、高速変化する物体等を正確に検知できなく、十分な計測精度が得られない場合が起こり得る。
【０００５】
本発明は、上記した点を背景になされたもので、多重反射を軽減し、Ｓ／Ｎ比の向上が図れ、余分な音波吸収材等も不要で、十分な計測精度が得られる超音波センサを提供することを課題とする。
【０００６】
【課題を解決するための手段及び作用・効果】
上記課題を解決するために本発明超音波センサは、音響インピーダンスの調整のための音響整合層に、中央穴を有するリング状の圧電素子が振動素子として重なるように接合されたことを特徴とする。
【０００７】
上記構成により、圧電素子の音響整合層との境界部に発生する振動変位が、中心部の変位を少なく、周辺部に現われる変位を大きくさせる分布となり、中心部の音圧を抑え、周辺方向の音圧レベルが高められ、音波の指向特性を広角化ができ、多重反射を軽減し、Ｓ／Ｎ比の向上が図れる。
【０００８】
また、本発明は、音響インピーダンスの調整のための音響整合層に、振動素子としての圧電素子が重なるように接合されるとともに、その音響整合層の中央部と周辺部とが、機械的剛性が異なる材料により形成され、かつ中央部の機械的剛性より周辺部の機械的剛性の方が小さくなるように設定されていることを特徴とする。
【０００９】
上記構成により、中心部の変位を機械的にある程度固定し、周辺部の変位を強調させることが可能で、中心部の音圧を抑え、周辺方向の音圧レベルが高められ、音波の指向特性を広角化ができ、多重反射を軽減し、Ｓ／Ｎ比の向上が図れる。
【００１０】
さらに、本発明は、音響インピーダンスの調整のための音響整合層に、振動素子としての圧電素子が重なるように接合されるとともに、その音響整合層の中央部と周辺部とが、音響インピーダンスが異なる材料により形成され、かつ中央部の音響インピーダンスより周辺部の音響インピーダンスが小さくなるように設定されていることを特徴とする。
【００１１】
上記構成により、中心部の変位を音響的にある程度固定し、周辺部の変位を強調させることが可能で、中心部の音圧を抑え、周辺方向の音圧レベルが高められ、音波の指向特性を広角化ができ、多重反射を軽減し、Ｓ／Ｎ比の向上が図れる。
【００１２】
また、本発明は、音響インピーダンスの調整のための音響整合層に、振動素子としての圧電素子が重なるように接合されるとともに、その音響整合層の中央部より周辺部の方が厚さが薄くなるように形成されていることを特徴とする。
【００１３】
上記構成により、音響整合層が中央部より周辺部の方が厚さが薄くなる形状で、中心部の音圧を抑え、周辺方向の音圧レベルが高められ、音波の指向特性を広角化ができ、多重反射を軽減し、Ｓ／Ｎ比の向上が図れる。
【００１４】
また、具体的には、前記音響接合層は一定の厚みの中央部に対して、前記圧電素子が接合される側とは反対側の面が、周辺部において斜面状に形成されて外縁にいくほど先細りの断面となるようにされることにより、中心部の音圧を抑え、周辺方向の音圧レベルが高めて、音波の指向特性を広角化ができる。
【００１５】
さらに、具体的には、前記音響接合層は一定の厚みの中央部に対して、前記圧電素子が接合される側とは反対側の面が、周辺部において前記圧電素子の接合面とは反対側に凸となる球面状に形成されて外縁にいくほど先細りの断面となるようにされることにより、中心部の音圧を抑え、周辺方向の音圧レベルが高めて、音波の指向特性を広角化ができる。
【００１６】
また、本発明は、音響インピーダンスの調整のための音響整合層に、振動素子としての圧電素子が重なるように接合されるとともに、その圧電素子を内側に収容して該圧電素子の外周を外側から取り囲む周辺ケースが前記音響整合層の周辺部に固定され、
かつ、前記圧電素子と音響整合層の積層方向であるＺ軸方向からみた前記周辺ケースの内壁面の取り囲み形状と前記圧電素子の外形形状とが非相似形をなし、前記積層方向と直交するＸ軸方向における前記周辺ケースの内壁と前記圧電素子の外縁とのケース内壁・圧電素子間距離と、前記積層方向と直交しかつ前記Ｘ軸方向と直交するＹ軸方向における該ケース内壁・圧電素子間距離とが異なるようにされたことを特徴とする。
【００１７】
上記構成により、音響整合層との境界部に発生する振動変位が、Ｘ軸方向（短辺方向）、Ｙ軸方向（長辺方向）の振動変位が異なる変位分布となり、Ｙ軸方向の指向特性が鋭く、これに比べＸ軸方向の指向特性を広角化することができ、多重反射を軽減し、Ｓ／Ｎ比の向上が図れる。
【００１８】
また、具体的には、前記周辺ケースの内壁形状は、前記積層方向であるＺ軸方向からみてＸ軸方向よりＹ軸方向の方が長くなる楕円状又は矩形状をなし、前記圧電素子はこの周辺ケースの内壁形状の中心と同心的な円形状又は正多角形状をなし、そのＹ軸方向における前記ケース内壁・圧電素子間距離は、Ｘ軸方向における該ケース内壁・圧電素子間距離より大きくなるようにされた構成により、Ｙ軸方向の指向特性が鋭く、これに比べＸ軸方向の指向特性を広角化することができる。
【００１９】
さらに、具体的には、前記周辺ケースの内壁形状は、前記積層方向であるＺ軸方向からみて円形状又は正多角形状に形成され、他方、前記圧電素子の外形形状はＸ軸方向よりＹ軸方向の方が長くなる楕円状又は矩形状をなすように形成され、そのＹ軸方向の前記ケース内壁・圧電素子間距離は、Ｘ軸方向の前記ケース内壁・圧電素子間距離より小さくなるようにされた構成により、Ｙ軸方向の指向特性が鋭く、これに比べＸ軸方向の指向特性を広角化することができる。
【００２０】
また、本発明は、前記周辺ケースの内壁面形状の、前記音響整合層への投影領域のおける該音響整合層の厚さが前記圧電素子の振動周波数の１／４波長とされている。
【００２１】
上記構成により、圧電素子の１／４波長整合層との境界部に発生する振動変位が、Ｘ軸方向（短辺方向）、Ｙ軸方向（長辺方向）の振動変位が異なる変位分布となり、Ｘ軸方向の指向特性が鋭く、これに比べＹ軸方向の指向特性を広角化することができ、多重反射を軽減し、Ｓ／Ｎ比の向上が図れる。このような、広角指向特性の超音波センサを流量計に用いることにより、流路の流速の検出に必要となる方向に超音波を効率よく伝播させることができ、１回の境界面反射までの伝播経路長が拡大でき、かつ境界面での多重反射エコーを極力低減し、十分なＳ／Ｎ比を確保でき、比較的少ない反射回数で順逆方向到達時間差（ΔＴ）の計測に十分な値が得られ、計測精度が高められる。また、伝播ロスが少なくでき受信波を増幅する増幅器のゲインを低く抑えられ、駆動電圧も低下でき、低消費電流化が測れる。さらに、不要音波を減衰させる目的の音波吸収材等も不要となる。
【００２２】
【発明の実施の形態】
以下、本発明の実施の形態につき図面に示す実施例を参照して説明する。図１は、本発明の超音波センサの構造を示す説明図であり、超音波センサ１１は、円板状の圧電素子１２と、この圧電素子１２の空気との音響インピーダンスの整合を図るために特殊プラスチックで円板状に形成され、圧電素子１２と厚さ方向に重ねて中心を合わせ接合される音響整合層１３と、この音響整合層１３の周辺を支持し固定する金属製の円筒状の固定ケース１４とを含み構成される。圧電素子１２の中央に円形孔１５を穿設している。圧電素子１２の形状はリング形状を成す。この円形孔１５の穴径（ｄ１とする）と、圧電素子１２の直径（ｄ２とする）との寸法比（ｄ２／ｄ１＝ｒとする）は、ｒ＝３〜５の範囲で形成する。また、圧電素子１２の厚み（ｔ１とする）と、音響整合層１３の厚み（ｔ２とする）との厚み比（ｔ２／ｔ１＝βとする）は、β＝０．５〜４．０の範囲で形成する。使用するセンサ周波数に応じて各寸法を指向特性を３０〜５０°の範囲に広角化できる。例えば、使用周波数が１５０ＫＨｚの場合、寸法は、ｄ２＝１３ｍｍ、ｒ＝３〜４、ｔ１＝１ｍｍ、β＝３〜３．５の範囲で指向特性を広角化できる。
【００２３】
図２は、図１の実施例におけるセンサの指向特性図を示す。この例では、半減角度は１５〜２５°、指向特性は３０〜５０°、９〜１２°の方向に音圧レベルのピーク値がある。このように、圧電素子１２の音響整合層１３との境界部に発生する振動変位が、中心部の変位を少なく、周辺部に現われる変位を大きくさせる分布となり、中心部の音圧を抑え、周辺方向の音圧レベルが高められ、音波の指向特性を広角化ができ、多重反射を軽減し、Ｓ／Ｎ比の向上が図れる。
【００２４】
図３は、本発明の他の実施例を示す説明図である。超音波センサ２１は、円板状の圧電素子２２と、この圧電素子１２と厚さ方向に重ねて中心を合わせ接合される音響整合層２３と、固定ケース２４とを含み構成される。音響整合層２３は、中央の円柱体状の第１音響整合層２５とその周辺部の第２音響整合層２６とを備え、第１音響整合層２５と第２音響整合層２６とは音響インピーダンスの異なる材料から形成される。第１音響整合層２５の音響インピーダンス（Ｚ１とする）と、第２音響整合層２６の音響インピーダンス（Ｚ２とする）との比（Ｚ１／Ｚ２＝Ｂとする）は、Ｚ２＝０．６×１０^６ｋｇ／ｍ^２・ｓとした場合、Ｂ≧３の関係を有する。また、第１音響整合層２５の直径（Ｄ１とする）と、圧電素子２２の直径（Ｄ２とする）との比（Ｄ２／Ｄ１＝ｒとする）は、ｒ＝２〜５の範囲で形成する。さらに、第１音響整合層２５のヤング率（Ｙ１とする）と、第２音響整合層２６のヤング率（Ｙ２とする）との比（Ｙ１／Ｙ２＝ｙとする）は、ｙ≧３．５の範囲の特性を有する２種類の材料から構成することにより、指向特性を広角化できる。
【００２５】
図４は、図３の実施例におけるセンサの指向特性図を示す。この例では、半減角度は１５〜３０°、指向特性は３０〜６０°、１０〜１５°の方向に音圧レベルのピーク値がある。中心部音圧と周辺ピーク値との音圧差は最大１０ｄＢが得られる。このように、中心部の変位を音響的および機械的にある程度固定し、周辺部の変位を強調させることが可能で、中心部の音圧を抑え、周辺方向の音圧レベルが高められ、音波の指向特性を広角化ができ、多重反射を軽減し、Ｓ／Ｎ比の向上が図れる。なお、音響インピーダンスの異なる２種類の材料、また、ヤング率の異なる２種類の材料というように、それぞれ単独の要素で材料の選択をすることも可能である。
【００２６】
図５は、本発明の他の実施例を示す説明図である。超音波センサ３１は、円板状の圧電素子３２と、圧電素子１２と厚さ方向に重ねて中心を合わせ接合される音響整合層３３と、この音響整合層１３の周辺を支持し固定する円筒状の固定ケース２４とを含み構成される。音響整合層３３は、圧電素子３２との接合面に対し他方の端面を円形面とし、軸線を中心として超音波伝播方向に向かうにつれて縮径する外表面の形状を有する。音響整合層３３の形状は円錐台形状を成す。固定ケース３４は、筒の上部の内側に切り欠き部３５を形成し、音響整合層３３の台部の外周部を嵌合し、音響整合層３３の周辺を支持する。音響整合層３３の軸線と直角方向と外表面とのなす傾斜角度（θとする）は、θ＝５〜４５°の範囲とする。また、音響整合層３３の上部の円形面の直径（Ｄ１とする）と、音響整合層３３の外径（Ｄ２とする）との寸法比（Ｄ２／Ｄ１＝ｒとする）は、ｒ＝５〜１０の範囲で調整することで、指向特性を広角化できる。
【００２７】
図６は、図５の実施例におけるセンサの指向特性図を示す。この例では、半減角度は２０〜３５°、指向特性は４０〜７０°、中心部音圧と周辺ピーク値との音圧差は最大１０〜１５ｄＢが得られる。１０〜１５°の方向に音圧レベルのピーク値がある。このように、音響整合層３３の傾斜形状で、中心部の音圧を抑え、周辺方向の音圧レベルが高められ、音波の指向特性を広角化ができ、多重反射を軽減し、Ｓ／Ｎ比の向上が図れる。なお、図９に示すように、音響整合層３３’を半円球状とし、中心部と周辺部との曲率を変え、超音波伝播方向に向かうにつれて縮径する外表面の形状とすることにより、同様に指向特性を広角化できる。
【００２８】
図７は、本発明の他の実施例を示す説明図である。超音波センサ４１は、円板状の圧電素子４２と、圧電素子４２と厚さ方向に重ねて中心を合わせ接合される音響整合層４３と、この音響整合層４３の周辺を支持し固定する筒状の固定ケース４４とを含み構成される。音響整合層４３において、平面でみて、その周辺の固定ケース４４の支持部４５を除いたエリアを１／４波長整合層４６という（１／４λ整合層ともいう）。支持部４５は、一方向のそれぞれの幅４５ａに対し直交する方向のそれぞれの幅４５ｂを狭く、異なる幅に形成する。この１／４波長整合層４６は、その厚みが超音波の波長（λとする）のλ／４で形成される。この１／４波長整合層４６は、平面でみて（厚さ方向でみて）Ｘ軸方向、Ｙ軸方向に対称でかつ寸法比が異なる形状とする。１／４波長整合層は、楕円形状を成す。すなわち、Ｘ軸方向の寸法（Ｌ１とする）と、Ｙ軸方向の寸法（Ｌ２とする）との寸法比（Ｌ２／Ｌ１＝ｒとする）は、ｒ＝１．３５〜１．８５の範囲とする。この１／４波長整合層４６の外形は、圧電素子４２の外形より大きく形成する。これにより、指向特性を広角化できる。
【００２９】
図８は、図７の実施例におけるセンサの指向特性図を示す。この例では、Ｘ軸方向の半減角度は１５〜２３°、Ｘ軸方向の指向特性は３０〜４５°、Ｙ軸方向の半減角度は８〜１５°が得られる。このように、圧電素子４２の１／４波長整合層４６との境界部に発生する振動変位が、Ｘ軸方向（短辺方向）、Ｙ軸方向（長辺方向）の振動変位が異なる変位分布となり、Ｙ軸方向の指向特性が鋭く、これに比べＸ軸方向の指向特性を広角化することができ、多重反射を軽減し、Ｓ／Ｎ比の向上が図れる。なお、図１３に示すように、平面でみて、１／４波長整合層４６’を円形状とし、他方の圧電素子４２’の形状を長方形状とし、そのＸ軸方向（短辺方向）、Ｙ軸方向（長辺方向）の寸法比（ｒ）を前述の範囲で形成することにより、同様にＸ軸方向に指向特性を広角化できる。
【００３０】
上記のような広角指向特性の超音波センサは、超音波流量計の流量計測用センサに好適である。広角指向特性の超音波センサで、流路の流速の検出に必要となる方向に超音波を効率よく伝播させることができ、１回の境界面反射までの伝播経路長が拡大でき、かつ境界面での多重反射エコーを極力低減し、十分なＳ／Ｎ比を確保でき、比較的少ない反射回数で順逆方向到達時間差（ΔＴ）の計測に十分な値が得られ、計測精度が高められる。また、伝播ロスが少なくでき受信波を増幅する増幅器のゲインを低く抑えられ、駆動電圧も低下でき、低消費電流化が測れる。さらに、不要音波を減衰させる目的の音波吸収材等も不要となる。
【００３１】
なお、超音波センサは、送信用、受信用の両方ともに本発明の構造のものを用いた方が好ましいが、そのうち少なくともいずれか一方のみとしても、効果は奏する。また、前述の超音波流量計において、受信用の超音波センサを２個設けた例を示したが、１個の超音波センサとして、送信側と受信側を切替えて、順方向と逆方向の到達時間差を計測する方法としてもよい。さらに、図１２に示すように、送信センサ２側に受信センサ３ａ’と３ｂ’とを設けて、超音波を対向壁で反射させ、これを受信するようにしてもよい。
【００３２】
本発明の超音波センサは、図１０に示す、比較的高精度である限られたエリア内を移動する物体の位置の検出を行う際に適用できる。従来例の超音波の伝播幅を図で実線で示し、本発明の一例を図で破線で示す。前述の本発明の超音波センサを用いて、例えば、指向特性が約３０°の広角度の超音波センサを適用すれば、センサ数を大幅に削減でき、図に示す１個（Ｓ５）で、この移動距離約１０２ｍｍを移動する物体の位置の検出が可能で、しかも、信号処理も簡単化でき、コスト削減も図れる。また、高速変化する物体等の検出も可能となり、計測精度も高められる。
【図面の簡単な説明】
【図１】本発明の超音波センサの構造の一例を示す説明図。
【図２】図１におけるセンサの指向特性図。
【図３】本発明の超音波センサの構造の他の実施例を示す説明図。
【図４】図３におけるセンサの指向特性図。
【図５】本発明の超音波センサの構造の他の実施例を示す説明図。
【図６】図５におけるセンサの指向特性図。
【図７】本発明の超音波センサの構造の他の実施例を示す説明図。
【図８】図７におけるセンサの指向特性図。
【図９】図５の超音波センサの構造の他の実施例を示す説明図。
【図１０】本発明の超音波センサを用いる移動物体の位置検知装置を示す説明図。
【図１１】従来の超音波センサを用いる超音波流量計の要部構成図。
【図１２】本発明の超音波センサを用いる超音波流量計の一例を示す要部構成図。
【図１３】図７の超音波センサの構造の他の実施例を示す説明図。
【符号の説明】
１１，２１，３１，４１超音波センサ
１２，２２，３２，４２，４２’ 圧電素子
１３，２３，３３，３３’，４３音響整合層
１４，２４，３４，４４固定ケース
１５円形孔
２５第１音響整合層
２６第２音響整合層
４６，４６’ １／４波長整合層[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an ultrasonic sensor that measures the flow velocity and flow rate of a fluid such as gas or water using ultrasonic waves.
[0002]
[Prior art]
Generally, in order to enhance the sound pressure characteristic, the ultrasonic sensor mainly has a narrow-angle directivity in which a sound pressure is concentrated at a central portion and a high-frequency sound wave is efficiently emitted into the air.
[0003]
[Problems to be solved by the invention]
Conventionally, as shown in FIG. 11, an ultrasonic flowmeter that detects the flow rate of a fluid with high accuracy is provided with reception-only sensors 3a and 3b on an upstream side and a downstream side opposite to a transmission-only sensor 2 provided in a flow path 1. Is placed. When a conventional ultrasonic sensor is used as the transmission-only sensor 2, a high-level sound wave near the center C is wasted. In addition, if the strong sonic energy from the central portion is not absorbed, the sonic energy remains in the flow path or is multiply reflected, lowering the signal-to-noise ratio (also referred to as the S / N ratio), There is a problem that causes a detection error. Therefore, it is necessary to arrange a sound absorbing material or the like for attenuating unnecessary sound waves near the center.
[0004]
As another example of the related art, there is an example in FIG. 10 in which the position of an object moving in a limited area with relatively high accuracy is detected. In this example, the position of the object is detected by receiving a reflected wave of the ultrasonic wave hitting the moving object. When detecting an object moving in a rectangular area having a distance to a moving object of about 200 mm and a width of 50 to 150 mm, a conventional ultrasonic sensor, for example, a high-frequency high-sensitivity type sensor has a directional characteristic. Is small and the half angle is about 3.5 degrees. In this case, in order to uniformly detect the moving distance of the moving object of about 102 mm, when the overlap width of the directional area of each sensor is calculated as 5 mm, the number of sensors becomes At least nine (S1 to S9) are required. Use of nine sensors increases costs and causes a problem. Also, depending on the size of the moving object, the moving speed, for example, the receiving sensitivity is reduced due to the influence of the shape of the object, etc., and it may not always be possible to transmit and receive with the sensor that emitted the sound wave. However, there is a problem that the signal processing becomes complicated and the processing time is greatly increased. Furthermore, there may be a case where a fast-changing object or the like cannot be accurately detected, and sufficient measurement accuracy cannot be obtained.
[0005]
SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has an ultrasonic sensor capable of reducing multiple reflections, improving an S / N ratio, not requiring an extra sound absorbing material, and obtaining sufficient measurement accuracy. The task is to provide
[0006]
[Means for Solving the Problems and Functions / Effects]
In order to solve the above problem, the ultrasonic sensor according to the present invention is characterized in that a ring-shaped piezoelectric element having a central hole is joined to an acoustic matching layer for adjusting acoustic impedance so as to overlap as a vibration element. .
[0007]
With the above configuration, the vibration displacement occurring at the boundary between the piezoelectric element and the acoustic matching layer has a distribution that reduces the displacement at the center and increases the displacement appearing at the periphery, suppresses the sound pressure at the center, and reduces the sound pressure in the peripheral direction. The sound pressure level is increased, the directional characteristics of the sound wave can be widened, multiple reflections can be reduced, and the S / N ratio can be improved.
[0008]
Further, according to the present invention, a piezoelectric element as a vibration element is joined to an acoustic matching layer for adjusting acoustic impedance so as to overlap, and the central part and the peripheral part of the acoustic matching layer have mechanical rigidity. It is formed of a different material, and is set so that the mechanical rigidity of the peripheral portion is smaller than the mechanical rigidity of the central portion.
[0009]
With the above configuration, it is possible to mechanically fix the displacement of the central part to some extent, to emphasize the displacement of the peripheral part, suppress the sound pressure at the central part, increase the sound pressure level in the peripheral direction, and improve the directional characteristics of sound waves. Can be widened, multiple reflection can be reduced, and the S / N ratio can be improved.
[0010]
Further, according to the present invention, a piezoelectric element as a vibration element is joined to an acoustic matching layer for adjusting acoustic impedance so as to overlap, and a central portion and a peripheral portion of the acoustic matching layer have different acoustic impedances. It is made of a material, and is set so that the acoustic impedance at the peripheral portion is smaller than the acoustic impedance at the central portion.
[0011]
With the above configuration, the displacement of the central part can be acoustically fixed to some extent, the displacement of the peripheral part can be emphasized, the sound pressure of the central part can be suppressed, the sound pressure level in the peripheral direction can be increased, and the directional characteristics of sound waves Can be widened, multiple reflection can be reduced, and the S / N ratio can be improved.
[0012]
According to the present invention, a piezoelectric element as a vibration element is joined to an acoustic matching layer for adjusting acoustic impedance so as to overlap with the acoustic matching layer, and the thickness of the acoustic matching layer is thinner at a peripheral portion than at a central portion. It is characterized by being formed so that it becomes.
[0013]
With the above configuration, the acoustic matching layer has a shape in which the peripheral portion is thinner than the central portion, suppresses the sound pressure in the central portion, increases the sound pressure level in the peripheral direction, and widens the directional characteristics of sound waves. As a result, multiple reflection can be reduced and the S / N ratio can be improved.
[0014]
Further, specifically, the surface of the acoustic bonding layer opposite to the side to which the piezoelectric element is bonded to the center part having a certain thickness is formed in a slope at the peripheral part and goes to the outer edge. By making the cross section gradually tapered, the sound pressure at the center is suppressed, the sound pressure level in the peripheral direction is increased, and the directional characteristics of the sound wave can be widened.
[0015]
Furthermore, specifically, the surface of the acoustic bonding layer opposite to the side to which the piezoelectric element is bonded to the center part having a certain thickness is opposite to the bonding surface of the piezoelectric element in the peripheral part. It is formed in a spherical shape that is convex to the side and has a tapered cross section as it goes to the outer edge, suppressing the sound pressure in the center, increasing the sound pressure level in the peripheral direction, and improving the directional characteristics of sound waves Wide angle can be achieved.
[0016]
Further, according to the present invention, a piezoelectric element as a vibration element is joined to an acoustic matching layer for adjusting acoustic impedance so as to overlap, and the piezoelectric element is accommodated inside and the outer periphery of the piezoelectric element is arranged from outside. A surrounding case is fixed to a periphery of the acoustic matching layer,
Further, the outer shape of the piezoelectric element and the surrounding shape of the inner wall surface of the peripheral case viewed from the Z-axis direction, which is the laminating direction of the piezoelectric element and the acoustic matching layer, have a non-similar shape, and are orthogonal to the laminating direction. The distance between the inner wall of the peripheral case and the outer edge of the piezoelectric element in the axial direction between the inner wall of the case and the piezoelectric element, and the distance between the inner wall of the case and the piezoelectric element in the Y-axis direction orthogonal to the stacking direction and orthogonal to the X-axis direction. It is characterized in that the distance is different.
[0017]
According to the above configuration, the vibration displacement generated at the boundary portion with the acoustic matching layer has a displacement distribution in which the vibration displacement in the X-axis direction (short-side direction) and the vibration displacement in the Y-axis direction (long-side direction) are different, and the directional characteristic in the Y-axis direction However, the directional characteristics in the X-axis direction can be widened, the multiple reflection can be reduced, and the S / N ratio can be improved.
[0018]
Further, specifically, the inner wall shape of the peripheral case has an elliptical shape or a rectangular shape that is longer in the Y-axis direction than in the X-axis direction when viewed from the Z-axis direction, which is the laminating direction. It forms a circular shape or a regular polygonal shape concentric with the center of the inner wall shape of the peripheral case, and the distance between the case inner wall and the piezoelectric element in the Y-axis direction is larger than the distance between the case inner wall and the piezoelectric element in the X-axis direction. With this configuration, the directional characteristics in the Y-axis direction are sharp, and the directional characteristics in the X-axis direction can be made wider in angle.
[0019]
Further, specifically, the inner wall shape of the peripheral case is formed in a circular shape or a regular polygonal shape when viewed from the Z-axis direction which is the laminating direction, while the outer shape of the piezoelectric element is more Y-axis than in the X-axis direction. The direction is longer so as to form an elliptical shape or a rectangular shape, and the distance between the case inner wall and the piezoelectric element in the Y-axis direction is smaller than the distance between the case inner wall and the piezoelectric element in the X-axis direction. With this configuration, the directional characteristics in the Y-axis direction are sharp, and the directional characteristics in the X-axis direction can be made wider in angle.
[0020]
Further, in the present invention, the thickness of the acoustic matching layer in the projection area of the inner wall surface of the peripheral case onto the acoustic matching layer is set to １／ wavelength of the vibration frequency of the piezoelectric element.
[0021]
According to the above configuration, the vibration displacement generated at the boundary between the piezoelectric element and the quarter wavelength matching layer has a displacement distribution in which the vibration displacement in the X-axis direction (short side direction) and the vibration displacement in the Y-axis direction (long side direction) are different. The directional characteristics in the X-axis direction are sharp, and the directional characteristics in the Y-axis direction can be widened, the multiple reflection can be reduced, and the S / N ratio can be improved. By using an ultrasonic sensor having such a wide-angle directivity characteristic for a flow meter, ultrasonic waves can be efficiently propagated in a direction necessary for detecting the flow velocity in the flow path, and it is possible to transmit the ultrasonic waves up to one boundary reflection. The propagation path length can be increased, multiple reflection echoes at the boundary surface can be reduced as much as possible, a sufficient S / N ratio can be secured, and a sufficient value for measuring the forward / backward arrival time difference (ΔT) with a relatively small number of reflections can be obtained. Obtained, and the measurement accuracy is improved. In addition, the propagation loss can be reduced, the gain of the amplifier for amplifying the received wave can be suppressed low, the driving voltage can be reduced, and the reduction in current consumption can be measured. Further, a sound absorbing material for attenuating unnecessary sound waves is not required.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to examples shown in the drawings. FIG. 1 is an explanatory view showing a structure of an ultrasonic sensor according to the present invention. An ultrasonic sensor 11 is used for matching acoustic impedance between a disk-shaped piezoelectric element 12 and air of the piezoelectric element 12. An acoustic matching layer 13 formed of a special plastic in a disc shape and overlapped with the piezoelectric element 12 in the thickness direction and centered and joined, and a metal cylindrical shape supporting and fixing the periphery of the acoustic matching layer 13 And a fixed case 14. A circular hole 15 is formed in the center of the piezoelectric element 12. The shape of the piezoelectric element 12 has a ring shape. The dimensional ratio (d2 / d1 = r) between the hole diameter (d1) of the circular hole 15 and the diameter (d2) of the piezoelectric element 12 is formed in a range of r = 3 to 5. The thickness ratio (t2 / t1 = β) between the thickness of the piezoelectric element 12 (t1) and the thickness of the acoustic matching layer 13 (t2) is β = 0.5 to 4.0. Form in the range. The directional characteristics of each dimension can be widened to a range of 30 to 50 ° depending on the sensor frequency used. For example, when the operating frequency is 150 KHz, the directional characteristics can be widened in dimensions d2 = 13 mm, r = 3 to 4, t1 = 1 mm, and β = 3 to 3.5.
[0023]
FIG. 2 shows a directional characteristic diagram of the sensor in the embodiment of FIG. In this example, the half value angle has a peak value of the sound pressure level in the direction of 15 to 25 °, the directivity characteristic has the direction of 30 to 50 °, and the direction of 9 to 12 °. As described above, the vibration displacement generated at the boundary between the piezoelectric element 12 and the acoustic matching layer 13 has a distribution in which the displacement at the center is small and the displacement appearing at the periphery is large, and the sound pressure at the center is suppressed. The sound pressure level in the direction can be increased, the directional characteristics of sound waves can be widened, multiple reflections can be reduced, and the S / N ratio can be improved.
[0024]
FIG. 3 is an explanatory diagram showing another embodiment of the present invention. The ultrasonic sensor 21 includes a disc-shaped piezoelectric element 22, an acoustic matching layer 23 that is overlapped with the piezoelectric element 12 in the thickness direction and is joined at the center, and a fixed case 24. The acoustic matching layer 23 includes a first acoustic matching layer 25 having a cylindrical shape at the center and a second acoustic matching layer 26 at a peripheral portion of the first acoustic matching layer 25. The first acoustic matching layer 25 and the second acoustic matching layer 26 have an acoustic impedance. From different materials. The ratio (Z1 / Z2 = B) between the acoustic impedance (Z1) of the first acoustic matching layer 25 and the acoustic impedance (Z2) of the second acoustic matching layer 26 is Z2 = 0.6 × In the case of 10 ⁶ kg / m ² · s, there is a relation of B ≧ 3. The ratio (D2 / D1 = r) of the diameter (D1) of the first acoustic matching layer 25 to the diameter (D2) of the piezoelectric element 22 is formed in a range of r = 2 to 5. I do. Further, the ratio (Y1 / Y2 = y) between the Young's modulus (Y1) of the first acoustic matching layer 25 and the Young's modulus (Y2) of the second acoustic matching layer 26 is y ≧ 3. By using two types of materials having the characteristics in the range of 5, the directional characteristics can be widened.
[0025]
FIG. 4 shows a directional characteristic diagram of the sensor in the embodiment of FIG. In this example, the half angle is 15 to 30 °, the directivity characteristic is 30 to 60 °, and the peak value of the sound pressure level is in the direction of 10 to 15 °. The maximum sound pressure difference between the central sound pressure and the peripheral peak value is 10 dB. In this way, the displacement of the central part can be acoustically and mechanically fixed to some extent, the displacement of the peripheral part can be emphasized, the sound pressure in the central part can be suppressed, the sound pressure level in the peripheral direction can be increased, Can be widened, the multiple reflection can be reduced, and the S / N ratio can be improved. In addition, it is also possible to select a material by a single element, such as two types of materials having different acoustic impedances or two types of materials having different Young's moduli.
[0026]
FIG. 5 is an explanatory diagram showing another embodiment of the present invention. The ultrasonic sensor 31 includes a disk-shaped piezoelectric element 32, an acoustic matching layer 33 that is overlapped with the piezoelectric element 12 in the thickness direction and is joined at the center, and a cylinder that supports and fixes the periphery of the acoustic matching layer 13. And a fixed case 24 in the shape of a circle. The acoustic matching layer 33 has a circular surface on the other end surface with respect to the bonding surface with the piezoelectric element 32, and has an outer surface shape whose diameter is reduced with the axis as the center in the ultrasonic wave propagation direction. The shape of the acoustic matching layer 33 has a truncated cone shape. The fixed case 34 forms a cutout 35 inside the upper part of the cylinder, fits the outer periphery of the base of the acoustic matching layer 33, and supports the periphery of the acoustic matching layer 33. The inclination angle (referred to as θ) between the axis perpendicular to the axis of the acoustic matching layer 33 and the outer surface is in the range of θ = 5 to 45 °. The dimensional ratio (D2 / D1 = r) between the diameter (D1) of the upper circular surface of the acoustic matching layer 33 and the outer diameter (D2) of the acoustic matching layer 33 is r = 5. By adjusting in the range of -10 to 10, the directional characteristic can be widened.
[0027]
FIG. 6 shows a directional characteristic diagram of the sensor in the embodiment of FIG. In this example, the half angle is 20 to 35 degrees, the directivity is 40 to 70 degrees, and the maximum sound pressure difference between the central sound pressure and the peripheral peak value is 10 to 15 dB. There is a peak sound pressure level in the direction of 10 to 15 °. As described above, the inclined shape of the acoustic matching layer 33 suppresses the sound pressure in the central portion, increases the sound pressure level in the peripheral direction, widens the directional characteristics of sound waves, reduces multiple reflections, and reduces S / N. The ratio can be improved. As shown in FIG. 9, by making the acoustic matching layer 33 ′ a semi-spherical shape, changing the curvature of the central portion and the peripheral portion, and making the outer surface shape that decreases in diameter in the ultrasonic wave propagation direction, Similarly, the directional characteristics can be widened.
[0028]
FIG. 7 is an explanatory diagram showing another embodiment of the present invention. The ultrasonic sensor 41 includes a disc-shaped piezoelectric element 42, an acoustic matching layer 43 that is overlapped with the piezoelectric element 42 in the thickness direction and is joined at the center, and a cylinder that supports and fixes the periphery of the acoustic matching layer 43. And a fixed case 44 in the shape of a circle. In the acoustic matching layer 43, an area of the acoustic matching layer 43 excluding the supporting portion 45 of the fixed case 44 around the area is referred to as a 波長 wavelength matching layer 46 (also referred to as a λλ matching layer). The support portion 45 is formed to have different widths 45b in a direction orthogonal to each width 45a in one direction, and to have different widths. The quarter wavelength matching layer 46 is formed with a thickness of λ / 4 of the wavelength of the ultrasonic wave (referred to as λ). The quarter wavelength matching layer 46 has a shape that is symmetrical in the X-axis direction and the Y-axis direction when viewed in a plane (when viewed in the thickness direction) and has a different dimensional ratio. The quarter wavelength matching layer has an elliptical shape. That is, the dimension ratio (L2 / L1 = r) of the dimension in the X-axis direction (L1) and the dimension in the Y-axis direction (L2) is in the range of r = 1.35 to 1.85. And The outer shape of the 波長 wavelength matching layer 46 is formed larger than the outer shape of the piezoelectric element 42. Thereby, the directional characteristics can be widened.
[0029]
FIG. 8 shows a directional pattern of the sensor in the embodiment of FIG. In this example, the half angle in the X-axis direction is 15 to 23 °, the directivity in the X-axis direction is 30 to 45 °, and the half-angle in the Y-axis direction is 8 to 15 °. As described above, the vibration displacement generated at the boundary between the piezoelectric element 42 and the 波長 wavelength matching layer 46 is different from the displacement distribution in which the vibration displacement in the X-axis direction (short side direction) and the Y-axis direction (long side direction) are different. Thus, the directional characteristics in the Y-axis direction are sharp. Compared with this, the directional characteristics in the X-axis direction can be widened, multiple reflection can be reduced, and the S / N ratio can be improved. As shown in FIG. 13, the quarter-wavelength matching layer 46 'has a circular shape and the other piezoelectric element 42' has a rectangular shape in plan view, and its X-axis direction (short side direction) and Y-direction. By forming the dimension ratio (r) in the axial direction (long side direction) within the above range, the directional characteristic can be similarly widened in the X-axis direction.
[0030]
The ultrasonic sensor having the wide-angle directivity as described above is suitable for a flow measurement sensor of an ultrasonic flowmeter. An ultrasonic sensor with a wide-angle directional characteristic allows ultrasonic waves to be efficiently propagated in the direction required to detect the flow velocity in the flow path, allows the propagation path length up to one boundary surface reflection to be increased, and allows the boundary surface In this case, a sufficient S / N ratio can be ensured, and a sufficient value for the measurement of the forward / backward arrival time difference (ΔT) can be obtained with a relatively small number of reflections, thereby increasing the measurement accuracy. In addition, the propagation loss can be reduced, the gain of the amplifier for amplifying the received wave can be suppressed low, the driving voltage can be reduced, and the reduction in current consumption can be measured. Further, a sound absorbing material for attenuating unnecessary sound waves is not required.
[0031]
It is preferable to use the ultrasonic sensor having the structure of the present invention for both transmission and reception. However, the effect is exhibited even if at least one of them is used. Also, in the above-described ultrasonic flow meter, an example in which two ultrasonic sensors for reception are provided is shown. However, as one ultrasonic sensor, the transmission side and the reception side are switched, and the forward and reverse directions are switched. A method of measuring the arrival time difference may be used. Further, as shown in FIG. 12, receiving sensors 3a 'and 3b' may be provided on the transmitting sensor 2 side to reflect ultrasonic waves from the opposing wall and receive the reflected ultrasonic waves.
[0032]
The ultrasonic sensor of the present invention can be applied when detecting the position of an object moving in a limited area, which is relatively high in accuracy, as shown in FIG. The propagation width of the conventional ultrasonic wave is shown by a solid line in the figure, and an example of the present invention is shown by a broken line in the figure. If, for example, a wide-angle ultrasonic sensor having a directional characteristic of about 30 ° is applied using the above-described ultrasonic sensor of the present invention, the number of sensors can be greatly reduced, and only one (S5) shown in FIG. It is possible to detect the position of the object moving over the moving distance of about 102 mm, and also simplify the signal processing and reduce the cost. In addition, it is possible to detect an object or the like that changes at a high speed, and the measurement accuracy is improved.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing an example of the structure of an ultrasonic sensor according to the present invention.
FIG. 2 is a directional characteristic diagram of the sensor in FIG. 1;
FIG. 3 is an explanatory view showing another embodiment of the structure of the ultrasonic sensor of the present invention.
FIG. 4 is a directional characteristic diagram of the sensor in FIG. 3;
FIG. 5 is an explanatory view showing another embodiment of the structure of the ultrasonic sensor of the present invention.
6 is a directional characteristic diagram of the sensor in FIG.
FIG. 7 is an explanatory view showing another embodiment of the structure of the ultrasonic sensor of the present invention.
FIG. 8 is a directional characteristic diagram of the sensor in FIG. 7;
FIG. 9 is an explanatory view showing another embodiment of the structure of the ultrasonic sensor of FIG. 5;
FIG. 10 is an explanatory diagram showing a moving object position detecting device using the ultrasonic sensor of the present invention.
FIG. 11 is a main part configuration diagram of an ultrasonic flowmeter using a conventional ultrasonic sensor.
FIG. 12 is a main part configuration diagram showing an example of an ultrasonic flowmeter using the ultrasonic sensor of the present invention.
FIG. 13 is an explanatory view showing another embodiment of the structure of the ultrasonic sensor in FIG. 7;
[Explanation of symbols]
11, 21, 31, 41 Ultrasonic sensors 12, 22, 32, 42, 42 'Piezoelectric elements 13, 23, 33, 33', 43 Acoustic matching layers 14, 24, 34, 44 Fixed case 15 Circular hole 25 First Acoustic matching layer 26 Second acoustic matching layer 46, 46 '1/4 wavelength matching layer

Claims

An ultrasonic sensor wherein a ring-shaped piezoelectric element having a central hole is joined to an acoustic matching layer for adjusting acoustic impedance so as to overlap as a vibration element.

A piezoelectric element as a vibration element is joined to the acoustic matching layer for adjusting the acoustic impedance so as to overlap, and a central portion and a peripheral portion of the acoustic matching layer are formed of materials having different mechanical rigidities, An ultrasonic sensor, wherein the mechanical rigidity of the peripheral portion is set smaller than the mechanical rigidity of the central portion.

A piezoelectric element as a vibration element is joined to the acoustic matching layer for adjusting the acoustic impedance so as to overlap, and a central portion and a peripheral portion of the acoustic matching layer are formed of materials having different acoustic impedances, and An ultrasonic sensor, wherein the acoustic impedance at a peripheral portion is set smaller than the acoustic impedance at a central portion.

A piezoelectric element as a vibration element is joined to an acoustic matching layer for adjusting acoustic impedance so as to overlap, and is formed so that the thickness of the acoustic matching layer is thinner at a peripheral portion than at a central portion. An ultrasonic sensor, comprising:

The surface of the acoustic bonding layer opposite to the side to which the piezoelectric element is bonded to the central portion having a certain thickness is formed in a slope in the peripheral portion, and has a tapered cross section toward the outer edge. The ultrasonic sensor according to claim 4, wherein:

The acoustic bonding layer has a spherical surface in which a surface opposite to a side to which the piezoelectric element is bonded is convex to a side opposite to a bonding surface of the piezoelectric element in a peripheral portion with respect to a central portion having a constant thickness. The ultrasonic sensor according to claim 4, wherein the ultrasonic sensor is formed so as to have a cross section that tapers toward the outer edge.

A piezoelectric element as a vibrating element is joined to an acoustic matching layer for adjusting acoustic impedance so as to overlap with the acoustic matching layer, and a peripheral case that houses the piezoelectric element inside and surrounds the outer periphery of the piezoelectric element from outside is formed by the acoustic case. Fixed to the periphery of the matching layer,
Further, the outer shape of the piezoelectric element and the surrounding shape of the inner wall surface of the peripheral case viewed from the Z-axis direction, which is the laminating direction of the piezoelectric element and the acoustic matching layer, have a non-similar shape, and are orthogonal to the laminating direction. The distance between the inner wall of the peripheral case and the outer edge of the piezoelectric element in the axial direction between the inner wall of the case and the piezoelectric element, and the distance between the inner wall of the case and the piezoelectric element in the Y-axis direction orthogonal to the stacking direction and orthogonal to the X-axis direction. An ultrasonic sensor having a different distance.

The inner wall shape of the peripheral case has an elliptical shape or a rectangular shape that is longer in the Y-axis direction than in the X-axis direction when viewed from the Z-axis direction, which is the lamination direction, and the piezoelectric element is located at the center of the inner wall shape of the peripheral case. 8. A circular shape or a regular polygonal shape concentric with the case, wherein the distance between the case inner wall and the piezoelectric element in the Y-axis direction is larger than the distance between the case inner wall and the piezoelectric element in the X-axis direction. 2. The ultrasonic sensor according to claim 1.

The inner wall shape of the peripheral case is formed in a circular shape or a regular polygonal shape when viewed from the Z-axis direction which is the lamination direction, while the outer shape of the piezoelectric element is an ellipse whose length is longer in the Y-axis direction than in the X-axis direction. 8. The piezoelectric element according to claim 7, wherein the distance between the case inner wall and the piezoelectric element in the Y-axis direction is smaller than the distance between the case inner wall and the piezoelectric element in the X-axis direction. 9. Ultrasonic sensor.

10. The thickness of the acoustic matching layer in a projection region of the inner wall surface of the peripheral case onto the acoustic matching layer is set to be 波長 wavelength of the vibration frequency of the piezoelectric element. 2. The ultrasonic sensor according to claim 1.