JP3629481B2 - Ultrasonic vibrator and ultrasonic flow meter using the same - Google Patents

Description

【００８１】
以上の結果より、音響整合層の設置面積（対向面積）は、圧電体が板状部材と接合する接合面積（縮小拡大率１００％以上）あるいは圧電体が板状部材と対向する対向面積より小さい場合、送信感度、受信感度が極端に低下していき、逆に圧電体が板状部材と接合する接合面積（縮小拡大率１００％以上）あるいは圧電体が板状部材と対向する対向面積以上にすることで、送信感度、受信感度の変化はほとんどなく感度変化の差は小さく、伝搬効率の低下を抑制でき、送受信感度の低下を防止することが可能となる。
【００８２】
（実施例３）
次に板状部材と圧電体について検討した。圧電体の大きさは縦・横・高さが７．４ｍｍ×７．４ｍｍ×２．６５ｍｍの直方体とした。３次元解析と同様に圧電体の板状部材との対向面側にスリット構造を設けている。板状部材は円形と正方形とし、板状部材の面積を変化させて超音波振動子を作製した。圧電体を包み込める最小大きさすなわち対角線の長さ（１０．４６ｍｍ）を直径とした円の面積と圧電体の接合面積７．４ｍｍ×７．４ｍｍをそれぞれの基準として、面積を相似的に５０％縮小したものから１５０％まで拡大したものを作製し、それぞれの板状部材の形状で超音波振動子の送受信感度を測定した。表２にその結果を示す。測定条件は実施例２と同様である。
【００８３】
【表２】

【００８４】
表２に示される結果から、円形および正方形の板状部材の両方において、板状部材が圧電体に対して縮小された（天部の面積比が１００％以下）場合、送信感度、受信感度が極端に低下していき、逆に板状部材が圧電体に対して増加する場合は、送信感度、受信感度の変化はほとんどなく感度変化の差は小さい。
【００８５】
このように圧電体が板状部材を介して音響整合層と音響的に結合あるいは物理的に接合される面積が縮小されるため送受信感度は低下する。しかし、圧電体に比べて板状部材の面積が大きくなる場合には、板状部材が大きくなっても音響的に結合する有効面積は殆ど変化しないため、送受信感度へも殆ど影響を与えない。
【００８６】
以上の結果から、板状部材は、板状部材と圧電体との接合面積以上、あるいは板状部材と圧電体が対向する対向面積以上が望ましい。
【００８７】
（実施例４）
次に板状部材と音響整合層について検討した。圧電体の大きさは縦・横・高さが７．４ｍｍ×７．４ｍｍ×２．６５ｍｍの直方体とした。３次元解析と同様に圧電体の板状部材との接合面側にスリット構造を設けている。板状部材は円形と正方形とし、音響整合層の面積を変化させて超音波振動子を作製した。圧電体を包み込める最小大きさ、すなわち対角線の長さ（１０．４６ｍｍ）を直径とした円形および圧電体の接合面積と同面積を基準として、それぞれの面積を相似的に５０％縮小したものから１５０％まで拡大したものを作製し、それぞれの形状で超音波振動子の送受信感度を測定した。表３にその結果を示す。測定条件は実施例２と同様である。
【００８８】
【表３】

【００８９】
以上の結果から音響整合層の面積が板状部材の面積に対して増加する場合には、音響的に結合する面積に変化はないものの、板状部材と接合面積が増加しないために、自由に振動する面積が増加し、主共振、２次共振とは異なるモードが発生する。そのため送受信感度が低下する現象が見られた。また、ノイズレベルも増加した。一方、音響整合層の面積が減少する場合には、板状部材の面積よりも圧電体の面積が大きく影響し、圧電体と音響整合層の関係、すなわち実施例２で検討した結果（表１）と同様の傾向が見られた。従って、板状部材は板状部材と音響整合層の接合面積以上、あるいは音響整合層が板状部材に対向する対向面積以上必要であり、更に音響整合層は圧電体と板状部材の接合面積以上、あるいは圧電体が音響整合層に対向する対向面積以上必要である。
【００９０】
（実施例５）
次に圧電体と、圧電体と板状部材を接合する接着層３１について検討した。圧電体の大きさは縦・横・高さが７．４ｍｍ×７．４ｍｍ×２．６５ｍｍの直方体とした。３次元解析と同様に圧電体の板状部材との接合面側にスリット構造を設けている。音響整合層は圧電体をカバーできる最小面積（直径は１０．４６ｍｍ）とした。また、板状部材は円形とし、接着層３１の面積を変化させて超音波振動子を作製した。圧電体の最大接合面積（７．４ｍｍ×７．４ｍｍ）を基準とし、接着層３１の面積を相似的に５０％縮小したものから１５０％まで拡大したものを作製し、超音波振動子の送受信感度を測定した。さらに、−４０℃〜８０℃のヒートサイクルによる信頼性試験の結果を表４に示す。測定条件は実施例２と同様である。
【００９１】
【表４】

〇：感度変化なし、△：感度低下率１０％以下、×：感度低下率５０％以上
【００９２】
表４の結果から接着層３１の面積が減少すると、送受信感度の低下見られた。また、信頼性試験の結果からも面積比が７０％以下になると感度低下率が５０％以上となり、超音波振動子としての信頼性が低下する。よって、接着層３１の硬化後の面積は圧電体の接合面積以上、あるいは圧電体が接着層３１に対向する対向面積以上必要である。
【００９３】
（実施例６）
次に音響整合層と、音響整合層と板状部材を接合する接着層３０について検討した。圧電体の大きさは縦・横・高さが７．４ｍｍ×７．４ｍｍ×２．６５ｍｍの直方体とした。３次元解析と同様に圧電体の板状部材との接合面側にスリット構造を設けている。音響整合層は圧電体をカバーできる最小面積（直径は１０．４６ｍｍ）とした。また、板状部材は円形、面積は１２８．８４ｍｍ^２として、接着層３０の面積を変化させて超音波振動子を作製した。音響整合層の最大接合面積（８５．８９ｍｍ^２）を基準とし、接着層３０の面積を相似的に５０％縮小したものから１５０％まで拡大したものを作製し、超音波振動子の送受信感度を測定した。さらに、−４０℃〜８０℃のヒートサイクルによる信頼性試験の結果を表５に示す。
【００９４】
【表５】

〇：感度変化なし、△：感度低下率１０％以下、×：感度低下率５０％以上
【００９５】
表５の結果から接着層３０の面積が減少すると、送受信感度の低下見られた。これは板状部材との接合面積が減少し、音響的な結合面積が減少するために伝搬効率が低下する要因と、接合されていない部分が主共振モードとは異なるモードの振動を生じさせる要因から感度が低下する。
【００９６】
また、信頼性試験の結果からも面積比が７０％以下になると感度低下率が５０％以上となり、超音波振動子としての信頼性が低下する。よって、接着層３０の硬化後の面積は音響整合層の接合面積以上、あるいは音響整合層が接着層３０に対向する対向面積以上にする必要がある。
【００９７】
上記各実施例は板状部材との関係にて述べたものであるが、板状部材が図８、図９に示す一体型の有底型のケースであっても同様の効果を示す。但し、実施例３、４に関しては圧電体とケースとの収納関係により、実験結果が異なるために、以下、実施例７、実施例８は図８、図９に示す一体型の有底型のケースに関する第２及び第３実施形態を用いて説明する。
【００９８】
（実施例７）
ケースと圧電体について検討した。圧電体の大きさは縦・横・高さが７．４ｍｍ×７．４ｍｍ×２．６５ｍｍの直方体とした。３次元解析と同様にケースとの圧電体の接合面側にスリット構造を設けている。ケースは有底筒状形状と有底箱形とし、ケース天面の面積を変化させて超音波振動子を作製した。圧電体を包み込める最小大きさすなわち対角線の長さ（１０．４６ｍｍ）を直径とした円形状を基準として、それぞれの面積を相似的に５０％縮小したものから１５０％まで拡大したものを作製し、それぞれの形状で超音波振動子の送受信感度を測定した。表６にその結果を示す。
【００９９】
【表６】

【０１００】
表６示される結果から、有天面筒状および箱形のケース両方とも、ケースが縮小されたとき圧電体がケース内に入らないため超音波振動子ーとして作製することが不可能である。しかし、圧電体に比べてケースが大きい場合には、送受信感度の感度低下は見られない。一方、圧電体と対向するケース面積が大きくなる場合には、ケースが大きくなっても音響的に結合する有効面積は殆ど変化しないため、感度へも殆ど影響を与えない。以上の結果から、ケースはケースと圧電体の接合面積以上、あるいはケースと圧電体が対向する対向面積以上が望ましい。
【０１０１】
（実施例８）
ケースと音響整合層について検討した。圧電体の大きさは縦・横・高さが７．４ｍｍ×７．４ｍｍ×２．６５ｍｍの直方体とした。３次元解析と同様に圧電体はケースとの接合面側にスリット構造を設けている。ケースは有天面筒状形状と有底箱型とし、音響整合層の面積を変化させて超音波振動子を作製した。圧電体を包み込める最小大きさすなわち対角線の長さ（１０．４６ｍｍ）を直径とした円形状を基準として、それぞれの面積を相似的に５０％縮小したものから１５０％まで拡大したものを作製し、それぞれの形状で超音波振動子の超音波送受信感度を測定した。表７にその結果を示す。
【０１０２】
【表７】

【０１０３】
以上の結果から音響整合層の面積がケースの天面の面積に対して増加する場合には、音響的に結合する面積に変化はないものの、ケースと接合面積が増加しないために、自由に振動する面積が増加し、主共振、２次共振とは異なるモードが発生する。そのため、超音波の送受信感度が低下する現象が見られた。また、ノイズレベルも増加した。一方、音響整合層の面積が減少する場合には、ケースの面積よりも圧電体の面積が大きく影響し、圧電体と音響整合層の関係、すなわち実施例２で検討した結果（表１）と同様の傾向が見られた。従って、ケースはケースと音響整合層の接合面積以上、あるいは音響整合層がケースに対向する対向面積以上必要であり、更に、音響整合層は圧電体とケースの接合面積以上、あるいは圧電体が音響整合層に対向する対向面積以上必要である。
【０１０４】
次に、１つの超音波振動子１，１７，１８における、ケース（板状部材）３と音響整合層４との関係について説明する。ここでは、圧電体を基準に、圧電体と音響整合層の面積比を１００％としたときについて説明する。
【０１０５】
ケース（板状部材）３と音響整合層４との面積比率の範囲は、異常共振モードが発生しない範囲として、音響整合層４の面積は、ケース（板状部材）３の面積の１５％〜１５０％が好ましい。ケース（板状部材）３の面積の１５０％とはケース天面と同面積であることを意味する。音響整合層４の面積がケース（板状部材）３の面積の１５０％より大きい場合には、インピーダンスの周波数特性に異常な共振モードが発生するため使用不可能となる。また、音響整合層４の面積が１５％未満になると、音響整合層自身の厚さ方向の形状異方性が強くなり、異なる共振モードが発生するため、使用不可能となる。
【０１０６】
一方、音響整合層４の面積と感度低下率（送信時）のグラフより、感度低下率が２５％以下の範囲とするためには、圧電体６と音響整合層４の形状が同一のときは音響整合層４の面積が圧電体６の面積の３５％〜１５０％、圧電体６と音響整合層４の形状が異なるときは音響整合層４の面積が圧電体６の面積の４５％〜１５０％とすることが好ましい（：図１０、図１１参照）。この理由は、音響整合層４の面積が圧電体６の面積の（３５％〜４５％）未満では、上記流量算出システム上、検出限界に近くなって計測性能（精度）が低下してしまう一方、１５０％を超えると、異常共振が発生してしまうからである。すなわち、図１０によれば、送信時の感度低下率が２５％以下の範囲は、ケース（板状部材）３の面積が１２８．８４ｍｍ^２のとき、正方形の音響整合層４の面積が３０ｍｍ^２以上、円形の音響整合層４の面積が３８ｍｍ^２以上とすればよい。図１１によれば、送受信時の感度低下率が２５％以下の範囲は、ケース（板状部材）３の面積が１２８．８４ｍｍ^２のとき、正方形の音響整合層４の面積が３８ｍｍ^２以上、円形の音響整合層４の面積が４５ｍｍ^２以上とすればよい。感度低下率が２５％を超えると、上記流量算出システム上、検出限界に近くなって計測性能（精度）が低下することから、感度低下率が２５％以下の範囲とすることが好ましい。
【０１０７】
また、超音波振動子の指向性及び感度から考慮すると、音響整合層４の面積は大きいほうがよいので、音響整合層４の面積は、ケース（板状部材）３の面積の１００％〜１５０％の範囲が好ましい。これは、感度低下は２０％までは許されるが、感度低下２５％は限界値であるため上記流量算出システム上の不安定な領域に近く、保証範囲の余裕が無いことから、１００％以上とする一方、１５０％を超えると、異常共振が発生してしまうので、１５０％以下とする。また、１００％〜１５０％の範囲ならば、超音波振動子の指向性を良くすることによって、余計な信号を検出しないため、外乱に強くなる。従って、計測精度を向上させることができる。ただし、音響整合層４が接着層３０より大きい場合には指向性は狭くなり、逆に、音響整合層４が接着層３０より小さい場合には指向性は広くなる。また、圧電体６が接着層３１より大きい場合には感度は高くなり、逆に、圧電体６が接着層３１より小さい場合には感度は低くなる。
【０１０８】
以上から総合的に判断して、音響整合層４の面積は、ケース（板状部材）３の面積の１００〜１５０％が望ましい。ただし、指向性、感度、異常共振を考慮して、超音波振動子を使用する場合にどの特性を重要視するかで、上記１００〜１５０％の範囲内で面積範囲を適宜選択することが望ましい。すなわち、上記１００〜１５０％の範囲内で面積範囲を適宜選択すれば、指向性が良くなり、感度低下率を２５％以下の範囲とすることができ、さらに、異常共振モードの発生を防止することができる。
【０１０９】
（実施例９）
次に、圧電体と音響整合層について検討した。圧電体の大きさは縦・横・高さが７．４ｍｍ×７．４ｍｍ×２．６５ｍｍの直方体とした。３次元解析と同様にケースとの圧電体の接合面側にスリット構造を設けている。ケースは有底筒状形状と有底箱型とし、有底形状のケース天面と同じ形状の音響整合層の面積を変化させて超音波振動子を作製した。有底筒状ケースの天面はφ１１ｍｍ、有底箱形ケースの天面は８ｍｍ×８ｍｍである。圧電体を覆うことが可能な最小の面積を基準として、相対的に５０％縮小したものからケース天面の面積まで拡大したものまで変化させて感度低下率を調べた。その結果を表８に示す。
【０１１０】
【表８】

【０１１１】
以上の結果、音響整合層を圧電体の面積に対して相対的に小さくすると感度が低下し、逆にケース天面の大きさを最大として大きくすると殆ど感度は変化しないことがわかった。よって、音響整合層は圧電体の面積以上、ケースの天面以下必要である。
【０１１２】
次に、超音波振動子の指向性と感度について考察する。
【０１１３】
（Ｉ）送信の場合：
超音波振動子に指向性が生じる理由は、以下の理由からである。すなわち、遠距離であっても超音波の送信方向が超音波振動子の板状部材３の中心軸からずれると、
【０１１４】
【数１】

【０１１５】
の積分において位相差が大きくなって、積分された速度ポテンシャルは超音波振動子の板状部材３の中心軸方向より小さくなる。ここで、図１２（Ａ），（Ｂ）に示すように、超音波振動子の板状部材３が円形ピストンの場合、中心軸からγの方向で中心からの距離がｒ_０である点Ｐ点とを含む平面と、振動面上の（ｘ，ｙ）にあるｄｓからＰ点までの距離は、図１２のように
【０１１６】
【数２】
ｒ＝ｒ_０−ｙｓｉｎγ
であるから、
【０１１７】
【数３】

となる。ただし、分母ではｒ≒ｒ_０として距離を無視しているが、これはΦの絶対値に影響するだけであるから、ｒ≫ａならば差し支えない。この積分の結果は、
【０１１８】
【数４】

となる。ただし、ａは板状部材３の半径である。
また、Ｚは
Ｚ＝ｋ×ａ×ｓｉｎγ＝（πｄ／λ）×ｓｉｎγ＝（πｄｆ／ｃ）×ｓｉｎγ
である。ただし、ａは板状部材３の半径、ｃは超音波の伝搬速度、ｋは超音波の波長定数、ｄは板状部材３の直径、Ｊ_１（Ｚ）はベッセル関数である。
【０１１９】
以上より、超音波振動子において、周波数が一定の場合は、板状部材３の直径が大きいほど指向性が鋭いことになる。板状部材３の直径が一定の場合には、周波数が高いほど指向性が鋭いことになる。
【０１２０】
（ＩＩ）受信の場合：
送音の指向性利得は、同じ音響出力を出しても指向性送音器はその軸方向には無指向性送音器に比べて指向性利得倍の強度を与える。しかし、受波においては指向性利得は全く別の意味を持つ。一つの方向から来る平面波を受けるのに、指向性受音器の軸を向ければ無指向性受音器より感度が良いという傾向があるが、その程度は指向性利得と直接の関係はない。周波数を一定とすれば、指向性受音器の方が受音面積が大きいから感度の良い受音器を作れる。あるいは、両受音器の能率を等しいとすれば、入力パワーが受音面積に比例するから電気出力もそれだけ多くとれる。同じ大きさの受音器を高周波で使えば低周波の場合より指向性利得は大きいが、音圧を一定としたとき高周波の方が指向性利得も比して電気出力が大きくなることはあり得ない。従って、受音の場合は、目的の信号は一つの方向から来る平面波であり、妨害する雑音は全立体角から均等に来ると仮定すると、無指向性受話器を使った場合に比べてＳＮ比が指向性利得だけ改善される。
【０１２１】
以上より判断して、音響整合層４の大きさはできるだけケース（振動板）３の大きさと等しいほうが望ましい。
【０１２２】
一方、超音波流量計として一対の超音波振動子１７，１８を用いた場合の特徴は以下のとおりである。
【０１２３】
まず、一対の超音波振動子１７，１８の相関係数は、インピーダンスの周波数が２００ＫＨｚ〜７５０ＫＨｚ（より好ましくは、３５０ＫＨｚ〜７５０ＫＨｚ）のとき、０．８０以上、好ましくは０．９６０以上とするのが好ましい。ここで、相関係数とは、各超音波振動子１７，１８のインピーダンスの周波数特性（図１３及び図１４）を測定した後、それぞれの周波数に対するインピーダンスがどの程度一致しているかを求めたものである。周波数範囲は使用周波数域の２００ＫＨｚ〜７５０ＫＨｚの各測定点で計算する。
【０１２４】
電流型回路を用いた場合、超音波振動子１７，１８のインピーダンスとしてはできるだけ似ている必要がある。理由としては、図１５及び図１６に示すように理想的な電流型回路の場合には、２次側短絡であれば流路、超音波振動子のインピーダンスに関係なく、出力電流は受信、送信を入れ替えても同じである。しかし、出力電流を測定するためには２次側を完全に短絡状態にすることは不可能で、ある程度の抵抗が必要となる。このとき、理想的な電流型回路にならないため、超音波振動子１７，１８に対してできるだけ似たインピーダンスが要求される。超音波振動子１７，１８の相関係数の値が０．８０以上、好ましくは０．９６０以上であれば、計測回路側でその相関係数を補正することにより、被測定流体の流量を精度良く（例えば、都市ガスでは少なくとも３リットル／ｈ以上の精度で）測定することができる超音波流量計として、それらの超音波振動子１７，１８が使用可能となる。
【０１２５】
また、超音波流量計として使用するときの一対の対向するそれぞれの超音波振動子１７，１８は大略同一形状であり、かつ、それぞれの中心はできるだけ合わせた方がよいとともに、上記一対の対向する超音波振動子１７，１８の対向面（対向する音響整合層の対向面）間の平行度は、できるだけ合わせるほうが望ましい。
【０１２６】
なお、上記様々な実施形態のうちの任意の実施形態を適宜組み合わせることにより、それぞれの有する効果を奏するようにすることができる。
【０１２７】
【発明の効果】
この発明によれば、音響整合層、板状部材、圧電体、接着層の大きさを適正化することで、効率性と信頼性を兼ね備えた超音波振動子および超音波流量計を実現する。
【０１２８】
また、音響整合層の面積を板状部材の面積の１００〜１１０％とする場合には、指向性が良くなり、感度低下率を２５％以下の範囲とすることができ、さらに、異常共振モードの発生を防止することができる。
【０１２９】
さらに、一対の超音波振動子を備える超音波流量計において、上記一対の超音波振動子は大略同一形状であり、インピーダンスの周波数が２００ＫＨｚ〜７５０ＫＨｚのとき、上記一対の超音波振動子の相関係数は０．８０以上であるようにすれば、被測定流体の流量を精度良く（例えば、都市ガスでは少なくとも３リットル／ｈ以上の精度で）測定することができる。
【図面の簡単な説明】
【図１】本発明の第１実施形態における超音波振動子の外観図である。
【図２】上記第１実施形態における超音波振動子の断面図である。
【図３】上記第１実施形態における超音波流量計の断面図である。
【図４】上記第１実施形態における超音波流量計の断面図である。
【図５】（Ａ）上記第１実施形態の超音波振動子におけるインピーダンスの周波数特性の実測値を示す図、（Ｂ）上記第１実施形態の超音波振動子におけるインピーダンスの周波数特性の解析値を示す図である。
【図６】（Ａ）上記第１実施形態における超音波振動子の主共振の解析結果を示す図、（Ｂ）上記第１実施形態における超音波振動子の２次共振の解析結果を示す図である。
【図７】（Ａ）上記第１実施形態における超音波振動子の主共振の解析結果を示す図、（Ｂ）上記第１実施形態における超音波振動子の２次共振の解析結果を示す図である。
【図８】本発明の第２実施形態における超音波振動子の断面図である。
【図９】本発明の第３実施形態における超音波振動子の断面図である。
【図１０】整合層の面積と感度低下率（送信）の関係を示すグラフである。
【図１１】整合層の面積と感度低下率（送受信）の関係を示すグラフである。
【図１２】（Ａ），（Ｂ）は板状部材が円形ピストンの場合の超音波振動子の指向性と感度について説明するための超音波振動子の模式例の正面図及び断面側面図である。
【図１３】超音波振動子のインピーダンスと周波数との関係を示すグラフである。
【図１４】超音波振動子の位相と周波数との関係を示すグラフである。
【図１５】理想的な電流型回路を示す説明図である。
【図１６】理想的な電流型回路を示す説明図である。
【符号の説明】
１…超音波振動子、２…支持体、３…板状部材、４…音響整合層、５…フランジ部、６…圧電体、７…端子板、８ａ，８ｂ…端子、９…絶縁物、１０…導電性ゴム、１１…流量測定部、１２…側壁部、１３…側壁部、１４…シール材、１５…上板部、１６…流路断面、１７…超音波振動子、１８…超音波振動子、１９…振動子取り付け穴、２０…振動子取り付け穴、２１…シール材、２２…シール材、３０…接着層、３１…接着層、３２…有底状ケース、１００…超音波流量計、１００ａ…入口路、１００ｂ…出口路、１０１…計測回路、１０２…流量演算手段。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic transducer and an ultrasonic flowmeter that measure the flow rate and flow velocity of a gas or liquid using ultrasonic waves.
[0002]
[Prior art]
Conventionally, for example, Japanese Patent Application Laid-Open No. 11-325992 is known as an ultrasonic transducer used in this type of ultrasonic flow measuring device, and a piezoelectric body is provided on the inner surface of the top of the case, and an acoustic matching layer is provided on the top. Is provided.
[0003]
[Patent Document 1]
JP-A-11-325992
[0004]
[Problems to be solved by the invention]
However, in the conventional configuration, the acoustic matching layer is simply provided, and no consideration has been given to an appropriate acoustic matching layer, piezoelectric body, and case.
[0005]
In particular, there is nothing that considers an optimal combination of an acoustic matching layer, a piezoelectric body, and a case in terms of transmission / reception sensitivity, and it is not described from the viewpoint of efficiency and reliability.
[0006]
In recent gas flowmeters, the type of gas used and the measurement accuracy (for example, the accuracy required for a flow measurement device for city gas is 0.5 nsec or more, and the ultrasonic transducer has a higher accuracy than this. Improvement of the function of the ultrasonic transducer is desired from the point of (required), and the function improvement of the ultrasonic transducer is also desired from such industrial needs.
[0007]
In particular, an ultrasonic transducer performs its function by receiving an ultrasonic signal transmitted from one ultrasonic transducer with the other ultrasonic transducer. Is a problem. When the sensitivity is improved, the measurement accuracy is improved, and it is economical because it is not necessary to supply more power than necessary to the piezoelectric body.
[0008]
An object of the present invention is to solve the above-described problems, and to improve the sensitivity of an ultrasonic transducer and improve the measurement characteristics of an ultrasonic flowmeter using the ultrasonic transducer, and an ultrasonic flow rate using the ultrasonic transducer Provide a total.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is configured as follows.
[0010]
According to the first aspect of the present invention, the plate-shaped member, the acoustic matching layer installed on one surface of the plate-shaped member via the adhesive layer, and the surface of the plate-shaped member provided with the acoustic matching layer And a piezoelectric body installed on a surface opposite to the piezoelectric layer through a bonding layer, and an installation area of the acoustic matching layer is equal to or larger than a bonding area where the piezoelectric body is bonded to the plate member, or the piezoelectric body is An ultrasonic transducer having an area larger than an area facing the acoustic matching layer via a plate-like member is provided.
[0011]
Moreover, according to the 2nd aspect of this invention, the plate-shaped member, the acoustic matching layer installed in one surface of the said plate-shaped member through the contact bonding layer, and the said acoustic matching layer of the said plate-shaped member are provided. A piezoelectric body disposed on the opposite surface to the surface through a bonding layer, and the opposing area of the plate-like member to the acoustic matching layer is such that the plate-like member and the acoustic matching layer serve as the adhesive layer. There is provided an ultrasonic transducer having a bonding area that is greater than or equal to a bonding area or an area in which the acoustic matching layer is opposed to the plate-like member.
[0012]
Moreover, according to the 3rd aspect of this invention, the plate-shaped member, the acoustic matching layer installed in one surface of the said plate-shaped member through the contact bonding layer, and the said acoustic matching layer of the said plate-shaped member are provided. A piezoelectric body disposed on the opposite surface to the piezoelectric body via a bonding layer, and the area of the plate-like member facing the piezoelectric body is such that the plate-like member and the piezoelectric body are bonded via the adhesive layer. There is provided an ultrasonic transducer having a bonding area equal to or greater than or equal to or greater than an opposing area where the plate member and the piezoelectric body face each other.
[0013]
Moreover, according to the 4th aspect of this invention, the plate-shaped member, the acoustic matching layer installed in one surface of the said plate-shaped member through the contact bonding layer, and the said acoustic matching layer of the said plate-shaped member are provided. And a piezoelectric body disposed on the opposite surface to the surface of the acoustic matching layer via a bonding layer, the opposing area of the acoustic matching layer being greater than or equal to the bonding area of the surface where the piezoelectric body is bonded to the plate member, or the piezoelectric More than the opposing area which a body opposes the said acoustic matching layer via the said plate-shaped member, and the opposing area of the said plate-shaped member is the joining area where the said plate-shaped member and the said acoustic matching layer are joined via the said adhesive layer An ultrasonic transducer in which the acoustic matching layer is greater than or equal to the facing area facing the plate-like member is provided.
[0014]
Moreover, according to the 5th aspect of this invention, the plate-shaped member, the acoustic matching layer installed in one surface of the said plate-shaped member through the contact bonding layer, and the said acoustic matching layer of the said plate-shaped member are provided. And a piezoelectric body disposed on the opposite surface to the surface of the adhesive layer via a bonding layer, and the opposing area of the adhesive layer is greater than or equal to the bonding area of the bonding surface where the piezoelectric body is bonded to the plate-like member, or the piezoelectric Provided is an ultrasonic transducer whose body is not less than the facing area facing the adhesive layer.
[0015]
According to the sixth aspect of the present invention, a plate-shaped member, an acoustic matching layer installed on one surface of the plate-shaped member via an adhesive layer, and the acoustic matching layer of the plate-shaped member are provided. And a piezoelectric body disposed on the opposite surface to the surface of the adhesive layer via a bonding layer, and the opposing area of the adhesive layer is greater than or equal to the bonding area of the acoustic matching layer to be bonded to the plate-like member, or the acoustic matching layer Provides an ultrasonic transducer having an area equal to or greater than the facing area facing the adhesive layer.
[0016]
According to the seventh aspect of the present invention, the area of the acoustic matching layer is 100 to 110% of the area of the plate member. 6 An ultrasonic transducer according to any one of the embodiments is provided.
[0017]
According to the eighth aspect of the present invention, the flow rate measurement unit through which the fluid to be measured flows, and the ultrasonic wave according to any one of the first to seventh aspects, which are provided in the flow rate measurement unit and transmit and receive ultrasonic waves. There is provided an ultrasonic flowmeter comprising an acoustic transducer, a measurement circuit for measuring a propagation time between the ultrasonic transducers, and a flow rate calculation means for calculating a flow rate based on a signal from the measurement circuit.
[0018]
According to the ninth aspect of the present invention, the pair of ultrasonic transducers have substantially the same shape, and the frequency characteristic phase relationship of the impedance of the pair of ultrasonic transducers is within a use range of impedance frequencies of 200 KHz to 750 KHz. The ultrasonic flow meter according to the eighth aspect, wherein the number is 0.80 or more.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments according to the present invention will be described below in detail with reference to the drawings.
[0020]
First, before describing in detail an ultrasonic transducer according to various embodiments of the present invention and an ultrasonic flowmeter using the ultrasonic transducer, various embodiments of the present invention will be described.
[0021]
According to the first embodiment of the present invention, a plate-shaped member, an acoustic matching layer installed on one surface of the plate-shaped member via an adhesive layer, and a surface provided with the acoustic matching layer of the plate-shaped member; A piezoelectric body disposed on the opposite surface via a bonding layer, and the installation area of the acoustic matching layer is greater than or equal to the bonding area where the piezoelectric body is bonded to the plate member, or the piezoelectric body is the plate An ultrasonic transducer having an area larger than the area facing the acoustic matching layer via a member. In terms of transmission / reception sensitivity with this configuration, in the case of an ultrasonic transducer that also performs transmission / reception, when the acoustic matching layer is larger than the piezoelectric body that is a driving source, the ultrasonic signal (or sound pressure) generated from the piezoelectric body is a plate. The ultrasonic signal (or sound pressure) propagated to the acoustic matching layer through the shaped member and hardly propagates.
[0022]
On the other hand, when the opposing area of the acoustic matching layer is smaller than the bonding area between the piezoelectric body and the plate-like member, only part of the ultrasonic signal (or sound pressure) generated by the piezoelectric body can propagate to the acoustic matching layer. Sensitivity decreases. Also, the reception sensitivity is not so much a problem when the acoustic matching layer is larger than the piezoelectric body, but when the acoustic matching layer is smaller than the piezoelectric body, an ultrasonic signal (or sound pressure) that propagates to the piezoelectric body. As a result, the reception density is lowered.
[0023]
Moreover, according to the 2nd form of this invention, the plate-shaped member, the acoustic matching layer installed in one surface of the said plate-shaped member through the contact bonding layer, and the acoustic matching layer of the said plate-shaped member were provided. A piezoelectric body installed on a surface opposite to the surface via a bonding layer, and the area of the plate member facing the acoustic matching layer is such that the plate member and the acoustic matching layer are bonded via an adhesive layer. It is an ultrasonic transducer having a bonding area that is greater than or equal to or greater than the opposing area where the acoustic matching layer is opposed to the plate-like member, and can suppress a decrease in the propagated ultrasonic signal.
[0024]
On the other hand, when the acoustic matching layer is larger than the plate-like member, the region other than the bonding area has insufficient rigidity. Therefore, the mechanical strength is also lowered, so that it is not reliable. Also, from an acoustic point of view, regions other than the junction area cause unnecessary vibration, and a vibration mode different from the main vibration mode propagated in the junction area is likely to be generated. This adversely affects the directivity and sensitivity of the ultrasonic signal.
[0025]
Moreover, according to the 3rd form of this invention, the plate-shaped member, the acoustic matching layer installed through the contact bonding layer on one surface of the said plate-shaped member, and the acoustic matching layer of the said plate-shaped member were provided. A piezoelectric body disposed on a surface opposite to the surface via a bonding layer, and the area of the plate member facing the piezoelectric body is such that the plate member and the piezoelectric body are bonded via the adhesive layer. The ultrasonic transducer has a bonding area of not less than or a facing area where the plate-like member and the piezoelectric body face each other, and can suppress a decrease in the propagated ultrasonic signal.
[0026]
On the other hand, when the plate-like member is smaller than the piezoelectric body, the effect as the plate-like member is obviously lowered or hardly effective.
[0027]
Moreover, according to the 4th form of this invention, the plate-shaped member, the acoustic matching layer installed in one surface of the said plate-shaped member through the contact bonding layer, and the acoustic matching layer of the said plate-shaped member were provided. A piezoelectric body disposed on the opposite surface to the surface through a bonding layer, and the opposing area of the acoustic matching layer is equal to or greater than the bonding area of the surface where the piezoelectric body is bonded to the plate member, or the piezoelectric body is plate-shaped More than the opposing area facing the acoustic matching layer through the member, and the opposing area of the plate-like member is more than the bonding area where the plate-like member and the acoustic matching layer are joined via the adhesive layer, or the acoustic matching layer is the plate-like member This is an ultrasonic transducer having an opposed area that is greater than or equal to the distance between them, and can substantially suppress a decrease in the transmitted ultrasonic signal.
[0028]
According to the fifth aspect of the present invention, the plate-shaped member, the acoustic matching layer installed on one surface of the plate-shaped member via the adhesive layer, and the acoustic matching layer of the plate-shaped member are provided. A piezoelectric body disposed on a surface opposite to the surface via a bonding layer, and an opposing area of the adhesive layer is equal to or greater than a bonding area of a bonding surface where the piezoelectric body is bonded to the plate-like member, or the piezoelectric body Is an ultrasonic transducer having an area larger than the facing area facing the adhesive layer, and can substantially suppress a decrease in the propagated ultrasonic signal.
[0029]
An adhesive layer that acoustically couples and physically joins the acoustic matching layer and the plate-like member will be described. When the adhesive layer is smaller than the bonding area or the opposing area of the plate-like member and the acoustic matching layer, the ultrasonic signal propagated from the piezoelectric body to the plate-like member is propagated to the acoustic matching layer via the adhesive layer. Propagation efficiency decreases and transmission sensitivity decreases. On the other hand, also in the reception sensitivity, the ultrasonic signal propagated to the acoustic matching layer is propagated to the plate member via the adhesive layer. Therefore, when the adhesive layer is smaller than the acoustic matching layer, the ultrasonic signal received by the acoustic matching layer decreases because the area decreases as the area decreases. Here, the facing area refers to an area in which the plate member and the acoustic matching layer are opposed to each other and overlap each other. One index of reliability is the adhesive strength between the acoustic matching layer and the plate-like member. This adhesive strength tends to depend on the area when the thickness of the adhesive layer is constant. Accordingly, by setting the adhesive layer to be equal to or larger than the bonding area between the plate-like member and the acoustic matching layer, the adhesive strength can be increased and the reliability can be improved.
[0030]
According to the sixth aspect of the present invention, the plate-like member, the acoustic matching layer installed on one surface of the plate-like member via the adhesive layer, and the acoustic matching layer of the plate-like member are provided. And a piezoelectric body disposed on the opposite surface to the surface of the adhesive layer via a bonding layer, and the opposing area of the adhesive layer is greater than or equal to the bonding area of the acoustic matching layer to be bonded to the plate-like member, or the acoustic matching layer Is an ultrasonic transducer having an area larger than the facing area facing the adhesive layer, and can substantially suppress a decrease in the propagated ultrasonic signal.
[0031]
On the other hand, an adhesive layer for acoustically coupling and physically joining the piezoelectric body and the plate-like member will be described. When the adhesive layer is smaller than the opposing area or bonding area between the piezoelectric body and the plate-like member, the ultrasonic signal propagated from the piezoelectric body to the plate-like member is propagated to the plate-like member via the adhesive layer, so As the area of the layer decreases, the propagation efficiency decreases and the transmission sensitivity decreases. On the other hand, also in the reception sensitivity, the ultrasonic signal propagated to the acoustic matching layer and propagated to the plate member via the adhesive layer is propagated to the piezoelectric body via the adhesive layer. Therefore, when the adhesive layer is smaller than the piezoelectric body, the ultrasonic signal received by the piezoelectric body is lowered depending on the area reduction.
[0032]
According to the seventh aspect of the present invention, the ultrasonic vibration according to any one of the first to sixth aspects described above, in which the flow rate measurement unit through which the fluid to be measured flows and the ultrasonic wave provided in the flow rate measurement unit is transmitted and received. An ultrasonic flowmeter comprising: a measuring element for measuring a propagation time between the ultrasonic transducer; and a flow rate calculation means for calculating a flow rate based on a signal from the measurement circuit. The flow rate can be measured with high accuracy (for example, at least 3 liters / h or more with city gas).
[0033]
In the specification of the present application, the facing area refers to an area in which the piezoelectric body, the plate-like member, and the acoustic matching layer are directly or indirectly opposed and overlapped.
[0034]
Hereinafter, ultrasonic transducers and ultrasonic flowmeters using the ultrasonic transducers according to various embodiments of the present invention will be described with reference to FIGS.
[0035]
(First embodiment)
FIG. 1 is an external view of an ultrasonic transducer according to the first embodiment of the present invention, FIG. 2 is a cross-sectional view of the ultrasonic transducer, and FIGS. 3 and 4 are cross-sectional views of the ultrasonic flowmeter according to the same embodiment.
[0036]
In FIG. 1, 1 is an ultrasonic transducer, 6 is a piezoelectric body as a driving source, 4 is an acoustic matching layer for transmitting ultrasonic waves to a transmission medium such as gas or liquid, and 3 is one side (outer wall surface). 3a is a plate-like member provided with an acoustic matching layer 4 and an opposite side (inner wall surface) 3b with a piezoelectric body 6. Specifically, the acoustic matching layer 4 is acoustically transmitted through an adhesive layer 30 and an adhesive layer (an example of a bonding layer) 31. A matching layer 4 and a piezoelectric body 6 are provided. The plate-like member 3 is a vibration propagation member that transmits the vibration of the piezoelectric body 6 to the acoustic matching layer 4, and acoustically connects the piezoelectric body 6 and the acoustic matching layer 4.
[0037]
Reference numeral 2 denotes a support for supporting the plate-like member 3. Specifically, the outer peripheral portion of the plate-like member 3 is engaged with and joined to the cylindrical inner peripheral portion. In the first embodiment, the plate-like member 3 and the support 2 constitute a bottomed case 32 having a top part 32a, a side wall part 32b, and an opening part 32c. Reference numeral 5 denotes a flange portion for joining the ultrasonic transducer 1 to a side wall portion that forms a mounting hole for the ultrasonic transducer 1 connected to the flow path of the ultrasonic flowmeter, as will be described later.
[0038]
In FIG. 2, 6 is a piezoelectric body disposed on the inner wall surface of the plate-like member 3, 7 is a terminal plate fixed to the flange portion 5, 8a and 8b are terminals provided on the terminal plate 7, and 9 is a terminal. An insulator for insulating 8a and 8b, and 10 is a conductive rubber for electrically connecting the piezoelectric body 6 and the terminal 8a. The piezoelectric body 6 is closed by a bottomed case 32 and a terminal plate 7 and sealed with an inert gas.
[0039]
FIG. 3 shows a cross-sectional view of an ultrasonic flow meter 100 provided with the ultrasonic transducer 1.
[0040]
A schematic configuration of the ultrasonic flowmeter 100 is shown. A flow rate measurement unit 11 that measures a flow rate of a fluid to be measured that flows in from an inlet passage 100a connected to a supply pipe to which a fluid to be measured such as a gas is supplied; An outlet path 100b that communicates with the unit 11 and guides the fluid to be measured to the outside, and a pair of ultrasonic transducers 17 and 18 that are provided in the flow rate measurement unit 11 to transmit and receive ultrasonic waves (each of which is connected to the ultrasonic transducer 1) And a measurement circuit 101 that measures the propagation time between the ultrasonic transducers 17 and 18, and a flow rate calculation means 102 that calculates a flow rate based on a signal from the measurement circuit 101. Therefore, an ultrasonic wave is transmitted from one ultrasonic transducer 17 to the other ultrasonic transducer 18, and an ultrasonic wave that has passed through a fluid to be measured such as a gas is received by the other ultrasonic transducer 18. Thus, the measurement circuit 101 measures the propagation time between the ultrasonic transducers 17 and 18. Then, conversely, the ultrasonic waves transmitted from the other ultrasonic transducer 17 toward the one ultrasonic transducer 18 and passed through the fluid to be measured such as gas are converted into the one ultrasonic transducer. 18, the measurement circuit 101 measures the propagation time between the ultrasonic transducers 17 and 18. In this way, the ultrasonic propagation time is measured between the pair of ultrasonic transducers 17 and 18 a predetermined number of times, and the flow rate of the fluid under measurement such as gas is calculated by the flow rate calculation means 102 based on the average value. Like to do. Therefore, the ultrasonic transducers 17 and 18 can transmit and receive. Here, the measurement circuit 101 and the flow rate calculation means 102 constitute a flow rate calculation system.
[0041]
As an example, the flow rate measurement unit 11 assumes a household gas meter that measures the flow rate of LP gas or natural gas as a material, and uses aluminum alloy die casting. Then, as shown in FIG. 4, the upper plate portion 15 is screwed to the end faces of the side wall portions 12 and 13 constituting the gas flow path via a sealing material 14 made of, for example, a cork material, so that the flow path cross section 16 is rectangular. Make up things. Further, as shown in FIG. 3, the ultrasonic transducers 17 and 18 are provided obliquely on the side wall portions 12 and 13 so that the transmission / reception surfaces for transmitting and receiving the ultrasonic waves face each other. Specifically, the ultrasonic vibrators 17 and 18 provided in the side walls 12 and 13 are fixed to the mounting holes 19 and 20 via seal materials 21 and 22 made of, for example, O-rings. This is an example, and the present invention is not limited to this.
[0042]
On the other hand, the plate-like member 3 is located between the acoustic matching layer 4 and the piezoelectric body 6, and plays a role of a joint portion or a fixing portion between the acoustic matching layer 4 and the piezoelectric body 6 from a physical viewpoint. From an acoustic point of view, this is a connector for propagating an ultrasonic signal (or sound pressure) from the acoustic matching layer 4 to the piezoelectric body 6 and from the piezoelectric body 6 to the acoustic matching layer 4. Fulfill. Therefore, the physical bonding area of the acoustic matching layer 4, the plate-like member 3, and the piezoelectric body 6 is very important.
[0043]
Next, the operation of the ultrasonic transducer 1 will be described and the propagation efficiency of transmission will be considered.
[0044]
The ultrasonic signal transmitted from the piezoelectric body 6 is propagated to the acoustic matching layer 4 through the adhesive layer 31, the plate-like member (vibration propagation member) 3, and the adhesive layer 30.
[0045]
(Consideration of propagation efficiency of transmission between piezoelectric body and plate member)
When an ultrasonic signal transmitted from the piezoelectric body 6 is propagated to the plate-like member 3, the propagation efficiency from the piezoelectric body 6 to the plate-like member 3 is such that the piezoelectric body 6 as a driving source is acoustically different from the plate-like member 3. Depends on the size of the bonded area to be bonded. This bonding area substantially coincides with the bonding area where the plate member 3, the piezoelectric body 6, and the adhesive layer 31 overlap when the piezoelectric body 6 is bonded to the plate member 3 using the adhesive layer 31. Therefore, in order to efficiently transmit an ultrasonic signal from the piezoelectric body 6 to the plate-like member 3, the plate-like member 3 has a larger area than the bonding area between the plate-like member 3 and the piezoelectric body 6 (the plate-like member 3 and the piezoelectric body). 6 or more) is desirable.
[0046]
Further, the ultrasonic signal propagated to the plate-like member 3 is propagated to the acoustic matching layer 4 via the adhesive layer 30 that joins the plate-like member 3 and the acoustic matching layer 4.
[0047]
(Consideration of propagation efficiency of transmission between plate member and acoustic matching layer)
The acoustic coupling area between the plate-like member 3 and the acoustic matching layer 4 coincides with the area where the plate-like member 3, the acoustic matching layer 4, and the adhesive layer 30 overlap. Therefore, in order to efficiently propagate an ultrasonic signal from the plate-like member 3 to the acoustic matching layer 4, the plate-like member 3 is equal to or larger than the bonding area between the plate-like member 3 and the acoustic matching layer 4 (the acoustic matching layer 4 is Desirably, it is equal to or larger than the facing area facing the plate member 3.
[0048]
From the above, the area where the acoustic coupling areas of the piezoelectric body 6, the plate-like member 3, and the acoustic matching layer 4 overlap is the effective coupling area, and substantially coincides with the bonding area where each is joined. Therefore, the acoustic matching layer 4 needs to be larger than the bonding area of the piezoelectric body 6 and the plate-like member 3 or the facing area where the piezoelectric body 6 faces the acoustic matching layer 4, and the area is smaller than the above condition. Since the ultrasonic signal generated by the piezoelectric body 6 is propagated only at the ratio of the coupling area, the propagation efficiency is lowered and the ultrasonic transmission sensitivity is also lowered. Therefore, the area where the coupling areas of the piezoelectric body 4, the plate-like member 3, and the acoustic matching layer 6 overlap is the acoustic effective coupling area and the physical effective bonding area.
[0049]
Next, consider the case of receiving an ultrasonic signal.
[0050]
In the case of reception, the propagation process is opposite to that in the case of transmission. That is, the ultrasonic signal received from the acoustic matching layer 4 is propagated to the piezoelectric body 6 through the adhesive layer 30, the plate-like member 3, and the adhesive layer 31.
[0051]
(Consideration of propagation efficiency of reception between plate member and acoustic matching layer)
Since the ultrasonic signal received by the acoustic matching layer 4 is propagated to the plate-like member 3 through the adhesive layer 30 that joins the acoustic matching layer 4 and the plate-like member 3, the plate-like member is the same as in the case of transmission. 3 and the acoustic matching layer 4 coincide with the area where the plate-like member 3, the acoustic matching layer 4, and the adhesive layer 30 overlap. Therefore, in order to efficiently transmit an ultrasonic signal from the acoustic matching layer 4 to the plate-like member 3, the plate-like member 3 is equal to or larger than the bonding area of the plate-like member 3 and the acoustic matching layer 4 (the acoustic matching layer 4 is plate-like. It is desirable that the area is equal to or greater than the facing area facing the member 3.
[0052]
Further, the ultrasonic signal propagated to the plate-like member 3 is propagated to the piezoelectric body 6 through an adhesive layer 31 that joins the plate-like member 3 and the piezoelectric body 6.
[0053]
(Consideration of propagation efficiency of reception between plate member and piezoelectric body)
The bonding area between the plate-like member 3 and the piezoelectric body 6 coincides with the area where the plate-like member 3, the piezoelectric body 6 and the adhesive layer 31 overlap. Therefore, in order to efficiently propagate an ultrasonic signal from the plate-like member 3 to the piezoelectric body 6, the plate-like member 3 is larger than the bonding area of the plate-like member 3 and the piezoelectric body 6 (the plate-like member 3 and the piezoelectric body 6. Is more than the facing area facing each other).
[0054]
As described above, the area where the bonding areas of the piezoelectric body 6, the plate-like member 3, and the acoustic matching layer 4 overlap is the acoustic effective coupling area or the physical effective bonding area as in the transmission.
[0055]
Accordingly, at the time of reception, the acoustic matching layer 4 needs to have an area larger than the bonding area between the piezoelectric body 6 and the plate-like member 3 or an opposed area where the piezoelectric body 6 faces the acoustic matching layer 4, as in the transmission. When the condition is smaller than the above condition, since the ultrasonic signal generated by the piezoelectric body 6 is propagated only by the ratio of the bonding area, the propagation efficiency is lowered and the ultrasonic reception sensitivity is also lowered.
[0056]
Next, the adhesive layer 31 will be considered.
[0057]
The adhesive layer 31 that joins the piezoelectric body 6 and the plate-like member 3 has a role of not only physically joining the piezoelectric body 6 and the plate-like member 3 but also acoustically coupling them. The adhesive 31 is, for example, an epoxy-based thermosetting adhesive, and is temporarily bonded to the piezoelectric body 6 and the plate-like member 3 in a viscous state, and cured by heat or the like. Then, after the adhesive layer 31 is cured for bonding, when the opposing area facing the piezoelectric body 6 and the plate-like member 3 is smaller than that of the piezoelectric body 6, an ultrasonic signal generated from the piezoelectric body 6 is applied to the plate-like member 3. When propagating, the bonding area between the piezoelectric body 6 and the plate-like member 3 is reduced, and the propagation efficiency is lowered. For this reason, the transmission sensitivity of ultrasonic waves is reduced.
[0058]
The adhesive for the adhesive layer 31 includes urethane, cyano, and silicone resin adhesives.
[0059]
On the other hand, in the reception in which the ultrasonic signal propagated from the acoustic matching layer 4 is propagated to the plate-like member 3 and propagated to the piezoelectric body 6 through the adhesive layer 31, the opposing area facing the plate-like member 3 is the piezoelectric body. If it is smaller than 6, when the ultrasonic signal propagated to the plate-like member 3 is propagated to the piezoelectric body 6, the bonding area between the piezoelectric body 6 and the plate-like member 3 becomes small, and the propagation efficiency is lowered. , The reception sensitivity of ultrasonic waves decreases.
[0060]
Therefore, the adhesive layer 31 that joins the plate-like member 3 and the piezoelectric body 6 has an area after curing of the adhesive layer 31 that is equal to or larger than the joint area between the piezoelectric body 6 and the plate-like member 3 (the piezoelectric body 6 faces the adhesive layer 31). Or more), a reduction in propagation efficiency can be minimized.
[0061]
In terms of physical bonding, that is, the adhesive strength, the area after the adhesive layer 31 is cured is required to be equal to or larger than the opposing area where the piezoelectric body 6 faces the plate-like member 3. When the area of the adhesive layer 31 after curing is smaller than the area of the piezoelectric body 6 facing the plate-like member 3, the adhesive layer 31 does not wrap around the piezoelectric body 6 so as to be wrapped outside. Since the area is reduced and the anchor effect can hardly be expected, the adhesive strength is lowered. Therefore, the area after curing of the adhesive layer 31 is required to be equal to or larger than the bonding area between the piezoelectric body 6 and the plate-like member 3 or the facing area where the piezoelectric body 6 is opposed to the adhesive layer 31 from physical bonding. Yes, it can improve the adhesive strength and ensure the improvement of reliability.
[0062]
The adhesive layer 30 that joins the acoustic matching layer 4 and the plate-like member 3 is also a thermosetting adhesive, and not only physically joins the acoustic matching layer 4 and the plate-like member 3 but also acoustically. Have the role of combining. Therefore, when the adhesive layer 30 after curing has a smaller facing area facing the acoustic matching layer 4 and the plate-like member 3 after curing, the ultrasonic signal generated from the piezoelectric body 6 is transmitted to the plate-like member. 3. When propagating from the plate-like member 3 to the acoustic matching layer 4, the joint area between the plate-like member 3 and the acoustic matching layer 4 is reduced, the propagation efficiency is lowered, and the ultrasonic transmission sensitivity is lowered.
[0063]
On the other hand, in the case where the ultrasonic signal is received by the acoustic matching layer 4 and then propagated from the acoustic matching layer 4 to the plate-like member 3, in the reception propagated to the plate-like member 3 through the adhesive layer 30, the adhesive layer 30. After curing, when the opposing area facing the plate-like member 3 and the acoustic matching layer 4 is smaller than that of the acoustic matching layer 4, the acoustic signal propagates to the plate-like member 3 when the ultrasonic signal propagated to the acoustic matching layer 4 is propagated. Since the joining area between the matching layer 4 and the plate-like member 3 is reduced and the propagation efficiency is lowered, the ultrasonic reception sensitivity is lowered.
[0064]
Therefore, the area after curing of the adhesive layer 30 that joins the acoustic matching layer 4 and the plate-like member 3 is equal to or larger than the bonding area of the acoustic matching layer 4 or the facing area where the acoustic matching layer 4 faces the adhesive layer 30. Thus, it is possible to minimize the decrease in propagation efficiency. In terms of physical bonding, that is, adhesive strength, the area after the adhesive layer 30 is cured is required to be equal to or greater than the opposing area where the acoustic matching layer 4 faces the plate-like member 3. When the area of the adhesive layer 30 after curing is smaller than the area of the acoustic matching layer 4 facing the plate-like member 3, the adhesive layer 30 does not wrap around the acoustic matching layer 4 so that it substantially does not wrap around. The bonding area is reduced, and the anchoring effect can hardly be expected. Therefore, also from physical bonding, the area after curing of the adhesive layer 30 needs to be equal to or larger than the bonding area of the acoustic matching layer 4 or the facing area where the acoustic matching layer 4 faces the adhesive layer 30. The adhesive strength can be improved and the improvement of reliability can be ensured.
[0065]
The relationship described in the first embodiment is always established regardless of the shape and size of the acoustic matching layer 4, the plate-like member 3, and the piezoelectric body 6.
[0066]
Moreover, as shown in FIG. 8, FIG. 9, the plate-shaped member 3 and the support body 2 are not comprised separately, but the plate-shaped member and the support body were integrally formed as shown in FIG. Similar effects can be obtained in the second embodiment using the bottomed case 33 or the third embodiment in which no adhesive layer exists as shown in FIG.
[0067]
【Example】
In the following, experimental consideration of the first embodiment will be made with specific examples.
[0068]
(Example 1)
In order to confirm the effective area of the acoustic matching layer 4 with respect to the piezoelectric body 6, how the sound pressure generated from the piezoelectric body 6 using the three-dimensional simulation by the finite element method (FEM) is applied to the acoustic matching layer 4. We investigated whether it had an effect.
[0069]
The structure is as shown in FIG. 2 and is piezoelectric body / adhesive / case / adhesive / acoustic matching layer. For the piezoelectric body, the piezoelectric constant d ₃₁ = -185.9 × 10 ^-12 m / V, d ₃₁ = 366.5 × 10 ^-12 m / V, d ₁₅ = 578.5 × 10 ^-12 m / V, elastic constant s ₁₁ = 15.8 × 10 ^-12 m ² / N, s ₃₃ = 17.6 × 10 ^-12 m ² / N, s ₁₂ , S ₁₃ Is calculated from the frequency constant and the electromechanical coupling coefficient (frequency constant n ₁ = 1960 Hz · m, n ₂ = 1430 Hz · m, n ₃ = 1410 Hz · m, n ₄ = 1980 Hz · m, n ₂ = 856Hz · m, electromechanical coupling coefficient k _r = 0.65, k ₃₁ = 0.38, k ₃₃ = 0.71, k _t = 0.50, k ₁₅ = 0.70). Poisson's ratio: 0.3, dielectric constant: ε ₃₃ = 1950 × 0.9, ε = 2130 × 0.9, density: 7.70 g / cm ³ , Machine Q: 70 (attenuation ratio 0.0007114), the plate-like member of the case composed of the support and the plate-like member has a Young's modulus: 0.178 (10 ¹² N / m ² ), Poisson's ratio: 0.29, density 7.93 g / cm ³ The adhesive is Young's modulus: 0.003, Poisson's ratio: 0.3, density 1.4 g / cm ³ , Damping ratio: 0.01, acoustic matching layer Young's modulus: 0.001906 N / m ² Poisson's ratio: 0.3718, transverse elastic modulus: G = 0.0006946 N / m ² The calculation was performed with a transverse wave velocity (2 MHz): 1167 m / s (actual value), a longitudinal wave velocity: 2494 m / s (calculated from the actually measured value of the transverse wave), and a machine Q: 50 (attenuation ratio 0.001).
[0070]
The results are shown in FIGS. FIGS. 5A and 5B are obtained by actually measuring the frequency characteristics of impedance and phase, and by analyzing the simulation. The left is an actual value obtained by measuring the output impedance by supplying an AC voltage to the ultrasonic transducer and changing its frequency, and the right is an analysis value. It can be seen that the measured values and the analyzed values are very well matched. In particular, when the resonance frequencies A to D are compared, respective resonances are observed at substantially the same frequency. When the respective resonance modes are analyzed, A: main resonance (longitudinal wave) f = 475 KHz, B: main resonance (transverse wave) f = 190 KHz, C: secondary resonance 590 KHz, D: split resonance f = 430 KHz, E: Anti-resonance and f = 650 KHz. Among these, the resonance modes that greatly contribute to the generation of the ultrasonic signal are A: main resonance (longitudinal wave) and C: secondary resonance. An ultrasonic signal is generated in these two resonance modes. The mode analysis result in each resonance frequency is illustrated.
[0071]
FIG. 6A is a diagram showing the concentration distribution of each displacement of the piezoelectric body, the plate-like member, and the acoustic matching layer when A: main resonance (longitudinal wave) and f = 475 KHz. As for the displacement, it can be seen that there is a particularly large displacement at the joint surface between the piezoelectric body and the plate-like member or the joint surface of the piezoelectric body with respect to the plate-like member around the central portion of the acoustic matching layer.
[0072]
FIG. 6B is a diagram showing the concentration distribution of the displacement of each of the piezoelectric body, the plate-like member, and the acoustic matching layer when C: secondary resonance is 590 KHz. Displacement is particularly large around the outer periphery of the acoustic matching layer, particularly at the joint surface between the piezoelectric body and the plate-like member, or the joint face of the piezoelectric body with respect to the plate-like member, similar to the main resonance of A. I understand.
[0073]
The main resonance and the secondary resonance affect the vibration of the acoustic matching layer, and the combined component is a combination with FIGS. 6A and 6B. The displacement is particularly large at the joint surface with the plate member or the joint surface of the piezoelectric body with respect to the plate member.
[0074]
FIGS. 7A and 7B are views showing the displacements of FIGS. 6A and 6B from directly above the acoustic matching layer.
[0075]
FIG. 7A shows the concentration distribution of the displacement of each of the piezoelectric body, the plate-like member, and the acoustic matching layer when A: main resonance (longitudinal wave) and f = 475 KHz. FIG. 7B shows concentration distributions of displacements of the piezoelectric body, the plate-like member, and the acoustic matching layer at 590 KHz in C: secondary resonance. In this model, the surface of the piezoelectric element facing the plate member is processed into a slit shape and divided into four. The case is composed of a cylindrical support and a plate-like member (here, it is assumed that the plate-like member and the support are continuously connected with the same material), and the acoustic matching layer is slightly smaller than the plate-like member. The shape was a circle. In the main resonance, a large displacement is mainly seen around the center two divided into four. The displacement area is slightly larger than the bonding area where the piezoelectric body is bonded to the plate member.
[0076]
On the other hand, in the secondary resonance of FIG. 7B, a large displacement is seen near the two outer sides of the piezoelectric body and near the center, and the bonding area or coupling area between the piezoelectric body and the plate-like member is the main driving range. This is the range in which the main displacement can be detected. Since the plate-like member has a circular shape, it was assumed that the boundary with the cylindrical portion of the support was very high in rigidity. Accordingly, a displacement distribution is seen in the shape of the top surface portion (here, the plate-like member) mainly in the vibrating portion.
[0077]
From the above points, it is apparent that the acoustic matching layer needs to be larger than the bonding area between the piezoelectric body and the plate-like member, or more than the facing area where the piezoelectric body faces the acoustic matching layer.
[0078]
(Example 2)
In order to confirm the result of the three-dimensional simulation analysis of Example 1, the following examination was performed. The size of the piezoelectric body was a rectangular parallelepiped having a length, width, and height of 7.4 mm × 7.4 mm × 2.65 mm. Similar to the three-dimensional analysis, a slit structure is provided on the side facing the piezoelectric plate-like member. The acoustic matching layer mainly used two types of shapes. One is a circular shape similar to the three-dimensional analysis, and the other is a square shape that is close to the shape of the piezoelectric body in a plane. The circular shape has a minimum size that can enclose the piezoelectric body, that is, a circular shape having a diagonal length (10.46 mm) as a diameter, and the square shape has the same size (7.4 mm × 7.4 mm) as the piezoelectric body. As a reference, each acoustic matching layer was similarly reduced in area by 50% to 150% and the transmission / reception sensitivity of the ultrasonic transducer was measured for each shape. The results are shown in Table 1.
[0079]
The measurement was performed under the condition that the interval between the ultrasonic transducers was 70 mm, the measurement voltage was 30 V, and the measurement frequency was 500 KHz.
[0080]
[Table 1]

[0081]
From the above results, the installation area (opposite area) of the acoustic matching layer is smaller than the junction area where the piezoelectric body is joined to the plate member (reduction ratio 100% or more) or the opposed area where the piezoelectric body is opposed to the plate member. In this case, the transmission sensitivity and the reception sensitivity are drastically decreased, and conversely, the bonding area where the piezoelectric body is bonded to the plate-like member (a reduction / enlargement ratio of 100% or more) or the opposite area where the piezoelectric body is opposed to the plate-like member is greater than Thus, there is almost no change in transmission sensitivity and reception sensitivity, and the difference in sensitivity change is small, so that a decrease in propagation efficiency can be suppressed, and a decrease in transmission / reception sensitivity can be prevented.
[0082]
(Example 3)
Next, the plate member and the piezoelectric body were examined. The size of the piezoelectric body was a rectangular parallelepiped having a length, width, and height of 7.4 mm × 7.4 mm × 2.65 mm. Similar to the three-dimensional analysis, a slit structure is provided on the side facing the piezoelectric plate-like member. The plate-like member was circular and square, and the area of the plate-like member was changed to produce an ultrasonic transducer. Based on the minimum size that can enclose the piezoelectric body, that is, the area of a circle whose diameter is a diagonal length (10.46 mm) and the bonding area of the piezoelectric body 7.4 mm × 7.4 mm, the area is similar 50%. What reduced and expanded to 150% was produced, and the transmission / reception sensitivity of the ultrasonic transducer | vibrator was measured with the shape of each plate-shaped member. Table 2 shows the results. The measurement conditions are the same as in Example 2.
[0083]
[Table 2]

[0084]
From the results shown in Table 2, in both the circular and square plate-like members, when the plate-like member is reduced with respect to the piezoelectric body (the area ratio of the top is 100% or less), the transmission sensitivity and the reception sensitivity are When the plate-like member increases extremely with respect to the piezoelectric body, the transmission sensitivity and the reception sensitivity hardly change and the difference in sensitivity change is small.
[0085]
As described above, since the area where the piezoelectric body is acoustically coupled or physically joined to the acoustic matching layer via the plate-like member is reduced, the transmission / reception sensitivity is lowered. However, when the area of the plate-like member is larger than that of the piezoelectric body, the effective area for acoustic coupling hardly changes even if the plate-like member is enlarged, so that the transmission / reception sensitivity is hardly affected.
[0086]
From the above results, it is desirable that the plate-like member is equal to or larger than the bonding area between the plate-like member and the piezoelectric body, or larger than the facing area where the plate-like member and the piezoelectric body face each other.
[0087]
(Example 4)
Next, the plate member and the acoustic matching layer were examined. The size of the piezoelectric body was a rectangular parallelepiped having a length, width, and height of 7.4 mm × 7.4 mm × 2.65 mm. Similar to the three-dimensional analysis, a slit structure is provided on the joint surface side with the piezoelectric plate member. The plate-shaped member was formed into a circle and a square, and the area of the acoustic matching layer was changed to produce an ultrasonic transducer. From the minimum size that can enclose the piezoelectric body, that is, a circular shape having a diagonal line length (10.46 mm) as a diameter and the same area as the bonding area of the piezoelectric body, the respective areas are similarly reduced by 50% to 150 %, And the transmission / reception sensitivity of the ultrasonic transducer was measured for each shape. Table 3 shows the results. The measurement conditions are the same as in Example 2.
[0088]
[Table 3]

[0089]
From the above results, when the area of the acoustic matching layer increases with respect to the area of the plate-like member, the area that is acoustically coupled does not change, but the area of bonding with the plate-like member does not increase, so The vibration area increases and a mode different from the main resonance and the secondary resonance is generated. For this reason, a phenomenon in which transmission / reception sensitivity is reduced was observed. The noise level also increased. On the other hand, when the area of the acoustic matching layer decreases, the area of the piezoelectric body has a greater influence than the area of the plate-like member, and the relationship between the piezoelectric body and the acoustic matching layer, that is, the results examined in Example 2 (Table 1). ) And the same tendency was observed. Therefore, the plate-shaped member needs to be larger than the bonding area of the plate-shaped member and the acoustic matching layer, or the acoustic matching layer is larger than the opposing area facing the plate-shaped member, and the acoustic matching layer is further bonded to the piezoelectric body and the plate-shaped member. More than the above, or the area over which the piezoelectric body faces the acoustic matching layer is required.
[0090]
(Example 5)
Next, the piezoelectric body and the adhesive layer 31 for joining the piezoelectric body and the plate-like member were examined. The size of the piezoelectric body was a rectangular parallelepiped having a length, width, and height of 7.4 mm × 7.4 mm × 2.65 mm. Similar to the three-dimensional analysis, a slit structure is provided on the joint surface side with the piezoelectric plate member. The acoustic matching layer has a minimum area (diameter: 10.46 mm) that can cover the piezoelectric body. The plate-like member was circular, and the area of the adhesive layer 31 was changed to produce an ultrasonic vibrator. Based on the maximum bonding area (7.4 mm × 7.4 mm) of the piezoelectric body, the adhesive layer 31 is similarly reduced from 50% to 150%, and the ultrasonic transducer is transmitted and received. Sensitivity was measured. Furthermore, Table 4 shows the result of the reliability test by the heat cycle of −40 ° C. to 80 ° C. The measurement conditions are the same as in Example 2.
[0091]
[Table 4]

○: No change in sensitivity, △: Sensitivity decrease rate of 10% or less, ×: Sensitivity decrease rate of 50% or more
[0092]
From the results in Table 4, when the area of the adhesive layer 31 was decreased, the transmission / reception sensitivity was decreased. Also, from the result of the reliability test, when the area ratio is 70% or less, the sensitivity reduction rate is 50% or more, and the reliability as an ultrasonic transducer is lowered. Therefore, the area after curing of the adhesive layer 31 needs to be greater than or equal to the bonding area of the piezoelectric body, or more than the opposing area where the piezoelectric body faces the adhesive layer 31.
[0093]
(Example 6)
Next, the acoustic matching layer and the adhesive layer 30 that joins the acoustic matching layer and the plate-like member were examined. The size of the piezoelectric body was a rectangular parallelepiped having a length, width, and height of 7.4 mm × 7.4 mm × 2.65 mm. Similar to the three-dimensional analysis, a slit structure is provided on the joint surface side with the piezoelectric plate member. The acoustic matching layer has a minimum area (diameter: 10.46 mm) that can cover the piezoelectric body. The plate-like member is circular and the area is 128.84 mm. ² As described above, an ultrasonic transducer was manufactured by changing the area of the adhesive layer 30. Maximum joint area of acoustic matching layer (85.89mm ² ) Was used as a reference, and the adhesive layer 30 was similarly reduced in area by 50% to 150%, and the transmission / reception sensitivity of the ultrasonic transducer was measured. Furthermore, the result of the reliability test by the heat cycle of -40 degreeC-80 degreeC is shown in Table 5.
[0094]
[Table 5]

○: No change in sensitivity, △: Sensitivity decrease rate of 10% or less, ×: Sensitivity decrease rate of 50% or more
[0095]
From the results in Table 5, when the area of the adhesive layer 30 was reduced, the transmission / reception sensitivity was reduced. This is due to the fact that the bonding area with the plate-like member decreases and the acoustic coupling area decreases, which causes a decrease in propagation efficiency, and the factor where the unbonded part generates vibrations in a mode different from the main resonance mode. Sensitivity decreases.
[0096]
Also, from the result of the reliability test, when the area ratio is 70% or less, the sensitivity reduction rate is 50% or more, and the reliability as an ultrasonic transducer is lowered. Therefore, the area after curing of the adhesive layer 30 needs to be greater than or equal to the bonding area of the acoustic matching layer, or the opposing area where the acoustic matching layer faces the adhesive layer 30.
[0097]
Each of the above embodiments has been described in relation to the plate-like member, but the same effect can be obtained even if the plate-like member is an integrated bottomed case shown in FIGS. However, since the experimental results for Examples 3 and 4 differ depending on the storage relationship between the piezoelectric body and the case, Examples 7 and 8 are the integrated bottomed types shown in FIGS. 8 and 9 below. The second and third embodiments related to the case will be described.
[0098]
(Example 7)
Cases and piezoelectric bodies were studied. The size of the piezoelectric body was a rectangular parallelepiped having a length, width, and height of 7.4 mm × 7.4 mm × 2.65 mm. Similar to the three-dimensional analysis, a slit structure is provided on the bonding surface side of the piezoelectric body with the case. The case has a bottomed cylindrical shape and a bottomed box shape, and an ultrasonic transducer was manufactured by changing the area of the top surface of the case. Based on a circular shape whose diameter is the minimum size that encloses the piezoelectric body, that is, the length of the diagonal line (10.46 mm), the respective areas are similarly reduced from 50% to 150%, The transmission / reception sensitivity of the ultrasonic transducer was measured for each shape. Table 6 shows the results.
[0099]
[Table 6]

[0100]
From the results shown in Table 6, it is impossible to fabricate both the celestial cylindrical case and the box-shaped case as an ultrasonic vibrator because the piezoelectric body does not enter the case when the case is reduced. However, when the case is larger than the piezoelectric body, the sensitivity of the transmission / reception sensitivity is not reduced. On the other hand, when the case area facing the piezoelectric body is increased, the effective area for acoustic coupling hardly changes even when the case is increased, and thus the sensitivity is hardly affected. From the above results, it is desirable that the case be larger than the bonding area between the case and the piezoelectric body, or more than the facing area where the case and the piezoelectric body face each other.
[0101]
(Example 8)
The case and acoustic matching layer were studied. The size of the piezoelectric body was a rectangular parallelepiped having a length, width, and height of 7.4 mm × 7.4 mm × 2.65 mm. Similar to the three-dimensional analysis, the piezoelectric body has a slit structure on the side of the joint surface with the case. The case has a cylindrical shape with a ceiling surface and a bottomed box shape, and an ultrasonic transducer is manufactured by changing the area of the acoustic matching layer. Based on a circular shape whose diameter is the minimum size that encloses the piezoelectric body, that is, the length of the diagonal line (10.46 mm), the respective areas are similarly reduced from 50% to 150%, The ultrasonic transmission / reception sensitivity of the ultrasonic transducer was measured for each shape. Table 7 shows the results.
[0102]
[Table 7]

[0103]
From the above results, when the area of the acoustic matching layer increases with respect to the area of the top surface of the case, the area that is acoustically coupled does not change, but the bonding area with the case does not increase. Area increases, and a mode different from the main resonance and the secondary resonance occurs. For this reason, a phenomenon in which the transmission / reception sensitivity of ultrasonic waves is reduced was observed. The noise level also increased. On the other hand, when the area of the acoustic matching layer decreases, the area of the piezoelectric body has a greater influence than the area of the case, and the relationship between the piezoelectric body and the acoustic matching layer, that is, the results examined in Example 2 (Table 1) A similar trend was seen. Therefore, the case needs to be larger than the bonding area between the case and the acoustic matching layer, or the acoustic matching layer should be larger than the opposing area facing the case. Further, the acoustic matching layer should be larger than the bonding area between the piezoelectric body and the case, or the piezoelectric body is acoustic. More than the facing area facing the matching layer is required.
[0104]
Next, the relationship between the case (plate member) 3 and the acoustic matching layer 4 in one ultrasonic transducer 1, 17, 18 will be described. Here, the case where the area ratio of the piezoelectric body and the acoustic matching layer is 100% will be described with reference to the piezoelectric body.
[0105]
The area ratio range between the case (plate member) 3 and the acoustic matching layer 4 is a range in which an abnormal resonance mode does not occur. The area of the acoustic matching layer 4 is 15% to the area of the case (plate member) 3. 150% is preferred. 150% of the area of the case (plate member) 3 means the same area as the top surface of the case. When the area of the acoustic matching layer 4 is larger than 150% of the area of the case (plate member) 3, an abnormal resonance mode is generated in the frequency characteristic of the impedance, so that the acoustic matching layer 4 cannot be used. Moreover, when the area of the acoustic matching layer 4 is less than 15%, the shape anisotropy in the thickness direction of the acoustic matching layer itself becomes strong, and different resonance modes are generated.
[0106]
On the other hand, from the graph of the area of the acoustic matching layer 4 and the sensitivity reduction rate (during transmission), in order to make the sensitivity reduction rate in the range of 25% or less, when the shape of the piezoelectric body 6 and the acoustic matching layer 4 is the same The area of the acoustic matching layer 4 is 35% to 150% of the area of the piezoelectric body 6, and when the shape of the piezoelectric body 6 and the acoustic matching layer 4 is different, the area of the acoustic matching layer 4 is 45% to 150% of the area of the piezoelectric body 6. % Is preferable (see FIGS. 10 and 11). The reason for this is that if the area of the acoustic matching layer 4 is less than (35% to 45%) of the area of the piezoelectric body 6, the measurement performance (accuracy) deteriorates because it approaches the detection limit in the flow rate calculation system. This is because if it exceeds 150%, abnormal resonance occurs. That is, according to FIG. 10, the area of the case (plate member) 3 is 128.84 mm when the sensitivity decrease rate during transmission is 25% or less. ² The area of the square acoustic matching layer 4 is 30 mm. ² As described above, the area of the circular acoustic matching layer 4 is 38 mm. ² That is all. According to FIG. 11, the area of the case (plate member) 3 is 128.84 mm when the sensitivity decrease rate during transmission / reception is 25% or less. ² The area of the square acoustic matching layer 4 is 38 mm. ² As described above, the area of the circular acoustic matching layer 4 is 45 mm. ² That is all. When the sensitivity reduction rate exceeds 25%, the measurement performance (accuracy) is lowered due to the above flow rate calculation system approaching the detection limit. Therefore, the sensitivity reduction rate is preferably in the range of 25% or less.
[0107]
Considering from the directivity and sensitivity of the ultrasonic transducer, the area of the acoustic matching layer 4 should be large. Therefore, the area of the acoustic matching layer 4 is 100% to 150% of the area of the case (plate member) 3. The range of is preferable. This is because the sensitivity reduction is allowed up to 20%, but the sensitivity reduction 25% is a limit value, so it is close to the unstable region on the flow rate calculation system and there is no margin of the guarantee range. On the other hand, if it exceeds 150%, abnormal resonance occurs, so it is set to 150% or less. In addition, if it is in the range of 100% to 150%, an extra signal is not detected by improving the directivity of the ultrasonic transducer, so that it is resistant to disturbance. Therefore, measurement accuracy can be improved. However, when the acoustic matching layer 4 is larger than the adhesive layer 30, the directivity becomes narrower. Conversely, when the acoustic matching layer 4 is smaller than the adhesive layer 30, the directivity becomes wider. Further, when the piezoelectric body 6 is larger than the adhesive layer 31, the sensitivity is high, and conversely, when the piezoelectric body 6 is smaller than the adhesive layer 31, the sensitivity is low.
[0108]
Judging from the above, the area of the acoustic matching layer 4 is desirably 100 to 150% of the area of the case (plate member) 3. However, in consideration of directivity, sensitivity, and abnormal resonance, it is desirable to appropriately select the area range within the range of 100 to 150% depending on which characteristic is important when using the ultrasonic transducer. . That is, if the area range is appropriately selected within the range of 100 to 150%, the directivity is improved, the sensitivity reduction rate can be made 25% or less, and the occurrence of the abnormal resonance mode is prevented. be able to.
[0109]
Example 9
Next, the piezoelectric body and the acoustic matching layer were examined. The size of the piezoelectric body was a rectangular parallelepiped having a length, width, and height of 7.4 mm × 7.4 mm × 2.65 mm. Similar to the three-dimensional analysis, a slit structure is provided on the bonding surface side of the piezoelectric body with the case. The case has a bottomed cylindrical shape and a bottomed box shape, and an ultrasonic transducer was manufactured by changing the area of the acoustic matching layer having the same shape as the bottom surface of the bottomed case. The top surface of the bottomed cylindrical case is φ11 mm, and the top surface of the bottomed box-shaped case is 8 mm × 8 mm. Using the minimum area that can cover the piezoelectric body as a reference, the sensitivity reduction rate was investigated by changing from a relatively 50% reduction to a case top surface area. The results are shown in Table 8.
[0110]
[Table 8]

[0111]
As a result, it has been found that when the acoustic matching layer is made relatively small with respect to the area of the piezoelectric body, the sensitivity is lowered, and conversely, when the case top surface is maximized, the sensitivity is hardly changed. Therefore, the acoustic matching layer is required to be larger than the area of the piezoelectric body and smaller than the top surface of the case.
[0112]
Next, the directivity and sensitivity of the ultrasonic transducer will be considered.
[0113]
(I) For transmission:
The reason why directivity occurs in the ultrasonic transducer is as follows. That is, when the transmission direction of the ultrasonic wave is deviated from the central axis of the plate-like member 3 of the ultrasonic vibrator even at a long distance,
[0114]
[Expression 1]

[0115]
In this integration, the phase difference becomes large, and the integrated velocity potential becomes smaller than the central axis direction of the plate member 3 of the ultrasonic transducer. Here, as shown in FIGS. 12A and 12B, when the plate member 3 of the ultrasonic transducer is a circular piston, the distance from the center is r in the direction γ from the central axis. ₀ The distance from the plane including the point P that is and the ds to the P point at (x, y) on the vibration surface is as shown in FIG.
[0116]
[Expression 2]
r = r ₀ -Ysinγ
Because
[0117]
[Equation 3]

It becomes. However, r≈r in the denominator ₀ The distance is ignored, but since this only affects the absolute value of Φ, r >> a is acceptable. The result of this integration is
[0118]
[Expression 4]

It becomes. Here, a is the radius of the plate-like member 3.
Z is
Z = k × a × sin γ = (πd / λ) × sin γ = (πdf / c) × sin γ
It is. Where a is the radius of the plate-like member 3, c is the ultrasonic wave propagation velocity, k is the wavelength constant of the ultrasonic wave, d is the diameter of the plate-like member 3, J ₁ (Z) is a Bessel function.
[0119]
As described above, in the ultrasonic vibrator, when the frequency is constant, the directivity becomes sharper as the diameter of the plate-like member 3 is larger. When the diameter of the plate-like member 3 is constant, the directivity becomes sharper as the frequency is higher.
[0120]
(II) When receiving:
As for the directivity gain of sound transmission, even if the same sound output is output, the directivity sound transmitter provides the intensity of the directivity gain double in the axial direction as compared with the non-directional sound transmitter. However, the directivity gain has a completely different meaning in reception. When receiving the plane wave coming from one direction, the direction of the directional receiver tends to be more sensitive than the omnidirectional receiver, but the degree is not directly related to the directional gain. If the frequency is constant, a directional receiver has a larger sound receiving area, so that a sensitive receiver can be made. Alternatively, if the efficiency of both sound receivers is equal, the input power is proportional to the sound receiving area, so that the electrical output can be increased accordingly. If a receiver of the same size is used at a high frequency, the directivity gain is larger than that at a low frequency, but when the sound pressure is constant, the electrical output may be larger at a high frequency than the directivity gain. I don't get it. Therefore, in the case of receiving sound, assuming that the target signal is a plane wave coming from one direction, and the disturbing noise comes uniformly from all solid angles, the signal-to-noise ratio is higher than when using an omnidirectional receiver. Only the directivity gain is improved.
[0121]
Judging from the above, it is desirable that the size of the acoustic matching layer 4 be as large as possible that of the case (diaphragm) 3.
[0122]
On the other hand, the characteristics when a pair of ultrasonic transducers 17 and 18 are used as an ultrasonic flow meter are as follows.
[0123]
First, the correlation coefficient of the pair of ultrasonic transducers 17 and 18 is 0.80 or more, preferably 0.960 or more when the impedance frequency is 200 KHz to 750 KHz (more preferably 350 KHz to 750 KHz). Is preferred. Here, the correlation coefficient is obtained by measuring the frequency characteristics (FIGS. 13 and 14) of the impedances of the ultrasonic transducers 17 and 18 and then determining how much the impedances for the respective frequencies match. It is. The frequency range is calculated at each measurement point of 200 KHz to 750 KHz in the operating frequency range.
[0124]
When the current type circuit is used, the impedances of the ultrasonic transducers 17 and 18 need to be as similar as possible. The reason is that in the case of an ideal current type circuit as shown in FIGS. 15 and 16, if the secondary side is short-circuited, the output current is received and transmitted regardless of the flow path and the impedance of the ultrasonic transducer. It is the same even if they are replaced. However, in order to measure the output current, it is impossible to completely short-circuit the secondary side, and a certain amount of resistance is required. At this time, since it is not an ideal current type circuit, impedances as similar as possible to the ultrasonic transducers 17 and 18 are required. If the value of the correlation coefficient of the ultrasonic transducers 17 and 18 is 0.80 or more, preferably 0.960 or more, the flow rate of the fluid to be measured can be accurately adjusted by correcting the correlation coefficient on the measurement circuit side. The ultrasonic vibrators 17 and 18 can be used as an ultrasonic flowmeter that can be measured well (for example, with city gas with an accuracy of at least 3 liter / h or more).
[0125]
In addition, when used as an ultrasonic flow meter, the pair of opposing ultrasonic transducers 17 and 18 have substantially the same shape, and it is preferable that their centers are aligned as much as possible. The parallelism between the opposing surfaces of the ultrasonic transducers 17 and 18 (the opposing surfaces of the opposing acoustic matching layers) is preferably matched as much as possible.
[0126]
It is to be noted that, by appropriately combining arbitrary embodiments of the various embodiments described above, the effects possessed by them can be produced.
[0127]
【The invention's effect】
According to the present invention, by optimizing the sizes of the acoustic matching layer, the plate-like member, the piezoelectric body, and the adhesive layer, an ultrasonic vibrator and an ultrasonic flowmeter that have both efficiency and reliability are realized.
[0128]
Further, when the area of the acoustic matching layer is 100 to 110% of the area of the plate-like member, the directivity is improved, the sensitivity reduction rate can be in the range of 25% or less, and the abnormal resonance mode Can be prevented.
[0129]
Further, in the ultrasonic flowmeter including a pair of ultrasonic transducers, the pair of ultrasonic transducers have substantially the same shape, and when the impedance frequency is 200 KHz to 750 KHz, the phase relationship between the pair of ultrasonic transducers. If the number is 0.80 or more, the flow rate of the fluid to be measured can be measured with high accuracy (for example, at least 3 liters / h or more with city gas).
[Brief description of the drawings]
FIG. 1 is an external view of an ultrasonic transducer according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view of the ultrasonic transducer in the first embodiment.
FIG. 3 is a cross-sectional view of the ultrasonic flowmeter in the first embodiment.
FIG. 4 is a cross-sectional view of the ultrasonic flowmeter in the first embodiment.
FIGS. 5A and 5B are diagrams showing measured values of impedance frequency characteristics in the ultrasonic transducer of the first embodiment. FIGS. 5B are analysis values of impedance frequency characteristics in the ultrasonic transducer of the first embodiment. FIG.
6A is a diagram showing an analysis result of main resonance of the ultrasonic transducer in the first embodiment, and FIG. 6B is a diagram showing an analysis result of secondary resonance of the ultrasonic transducer in the first embodiment. It is.
7A is a diagram showing an analysis result of main resonance of the ultrasonic transducer in the first embodiment, and FIG. 7B is a diagram showing an analysis result of secondary resonance of the ultrasonic transducer in the first embodiment. It is.
FIG. 8 is a cross-sectional view of an ultrasonic transducer in a second embodiment of the invention.
FIG. 9 is a cross-sectional view of an ultrasonic transducer in a third embodiment of the invention.
FIG. 10 is a graph showing the relationship between the area of the matching layer and the sensitivity reduction rate (transmission).
FIG. 11 is a graph showing the relationship between the area of the matching layer and the sensitivity reduction rate (transmission and reception).
FIGS. 12A and 12B are a front view and a cross-sectional side view of a schematic example of an ultrasonic transducer for explaining the directivity and sensitivity of the ultrasonic transducer when the plate-like member is a circular piston. FIGS. is there.
FIG. 13 is a graph showing a relationship between impedance and frequency of an ultrasonic transducer.
FIG. 14 is a graph showing the relationship between the phase and frequency of an ultrasonic transducer.
FIG. 15 is an explanatory diagram showing an ideal current type circuit;
FIG. 16 is an explanatory diagram showing an ideal current type circuit;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Ultrasonic vibrator, 2 ... Support body, 3 ... Plate-like member, 4 ... Acoustic matching layer, 5 ... Flange part, 6 ... Piezoelectric body, 7 ... Terminal board, 8a, 8b ... Terminal, 9 ... Insulator, DESCRIPTION OF SYMBOLS 10 ... Conductive rubber, 11 ... Flow measurement part, 12 ... Side wall part, 13 ... Side wall part, 14 ... Sealing material, 15 ... Upper plate part, 16 ... Channel cross-section, 17 ... Ultrasonic transducer, 18 ... Ultrasonic wave Vibrator, 19 ... Vibrator mounting hole, 20 ... Vibrator mounting hole, 21 ... Sealing material, 22 ... Sealing material, 30 ... Adhesive layer, 31 ... Adhesive layer, 32 ... Bottomed case, 100 ... Ultrasonic flow meter , 100a ... Inlet passage, 100b ... Outlet passage, 101 ... Measuring circuit, 102 ... Flow rate calculation means.

Claims (9)

A flow rate measurement unit through which the fluid to be measured flows, a pair of ultrasonic transducers provided in the flow rate measurement unit for transmitting and receiving ultrasonic waves, and driving the one ultrasonic transducer in a main resonance mode and a secondary resonance mode An ultrasonic flowmeter comprising means for performing, a measurement circuit for measuring a propagation time between the ultrasonic transducers, and a flow rate calculation means for calculating a flow rate based on a signal from the measurement circuit,
The ultrasonic transducer includes a plate-like member (3), an acoustic matching layer (4) installed on one surface of the plate-like member via an adhesive layer (30), and the acoustic matching of the plate-like member. A piezoelectric body (6) disposed on the surface opposite to the surface on which the layer is provided via a bonding layer (31), and the acoustic matching layer has an installation area in which the piezoelectric body is bonded to the plate-like member. An ultrasonic flowmeter having a bonding area equal to or greater than an area where the piezoelectric body faces the acoustic matching layer via the plate-like member. A flow rate measurement unit through which the fluid to be measured flows, a pair of ultrasonic transducers provided in the flow rate measurement unit for transmitting and receiving ultrasonic waves, and driving the one ultrasonic transducer in a main resonance mode and a secondary resonance mode An ultrasonic flowmeter comprising means for performing, a measurement circuit for measuring a propagation time between the ultrasonic transducers, and a flow rate calculation means for calculating a flow rate based on a signal from the measurement circuit,
The ultrasonic transducer includes a plate-like member (3), an acoustic matching layer (4) installed on one surface of the plate-like member via an adhesive layer (30), and the acoustic matching of the plate-like member. A piezoelectric body (6) disposed on the surface opposite to the surface on which the layer is provided via a bonding layer (31), and the area of the plate member facing the acoustic matching layer is the same as that of the plate member An ultrasonic flowmeter wherein the acoustic matching layer is equal to or larger than a bonding area where the acoustic matching layer is bonded via the adhesive layer, or the acoustic matching layer is equal to or larger than an opposing area facing the plate-like member. A flow rate measurement unit through which the fluid to be measured flows, a pair of ultrasonic transducers provided in the flow rate measurement unit for transmitting and receiving ultrasonic waves, and driving the one ultrasonic transducer in a main resonance mode and a secondary resonance mode An ultrasonic flowmeter comprising means for performing, a measurement circuit for measuring a propagation time between the ultrasonic transducers, and a flow rate calculation means for calculating a flow rate based on a signal from the measurement circuit,
The ultrasonic transducer includes a plate-like member (3), an acoustic matching layer (4) installed on one surface of the plate-like member via an adhesive layer (30), and the acoustic matching of the plate-like member. A piezoelectric body (6) installed on the surface opposite to the surface on which the layer is provided via a bonding layer (31), and the area of the plate member facing the piezoelectric body via the adhesive layer the plate-like member and the piezoelectric body is more junction area Ru are bonded, or the plate-like member and the ultrasonic flow meter is facing area over which the piezoelectric body is opposite. A flow rate measurement unit through which the fluid to be measured flows, a pair of ultrasonic transducers provided in the flow rate measurement unit for transmitting and receiving ultrasonic waves, and driving the one ultrasonic transducer in a main resonance mode and a secondary resonance mode An ultrasonic flowmeter comprising means for performing, a measurement circuit for measuring a propagation time between the ultrasonic transducers, and a flow rate calculation means for calculating a flow rate based on a signal from the measurement circuit,
The ultrasonic transducer includes a plate-like member (3), an acoustic matching layer (4) installed on one surface of the plate-like member via an adhesive layer (30), and the acoustic matching of the plate-like member. And a piezoelectric body (6) disposed on a surface opposite to the surface on which the layer is provided via a bonding layer (31). The opposing area of the acoustic matching layer is such that the piezoelectric body is bonded to the plate-like member. Or more than the opposing area where the piezoelectric body faces the acoustic matching layer via the plate member, and the opposing area of the plate member is such that the plate member and the acoustic matching layer are An ultrasonic flowmeter having a bonding area which is bonded via an adhesive layer, or an area where the acoustic matching layer is opposed to the plate member. A flow rate measurement unit through which the fluid to be measured flows, a pair of ultrasonic transducers provided in the flow rate measurement unit for transmitting and receiving ultrasonic waves, and driving the one ultrasonic transducer in a main resonance mode and a secondary resonance mode An ultrasonic flowmeter comprising means for performing, a measurement circuit for measuring a propagation time between the ultrasonic transducers, and a flow rate calculation means for calculating a flow rate based on a signal from the measurement circuit,
The ultrasonic transducer includes a plate-like member (3), an acoustic matching layer (4) installed on one surface of the plate-like member via an adhesive layer (30), and the acoustic matching of the plate-like member. A piezoelectric body (6) disposed on the surface opposite to the surface on which the layer is provided via a bonding layer (31), and the opposing area of the adhesive layer is such that the piezoelectric body is bonded to the plate-like member. An ultrasonic flowmeter having a bonding area greater than or equal to a bonding area of the bonding surface or an area where the piezoelectric body faces the adhesive layer. A flow rate measurement unit through which the fluid to be measured flows, a pair of ultrasonic transducers provided in the flow rate measurement unit for transmitting and receiving ultrasonic waves, and driving the one ultrasonic transducer in a main resonance mode and a secondary resonance mode An ultrasonic flowmeter comprising means for performing, a measurement circuit for measuring a propagation time between the ultrasonic transducers, and a flow rate calculation means for calculating a flow rate based on a signal from the measurement circuit,
The ultrasonic transducer includes a plate-like member (3), an acoustic matching layer (4) installed on one surface of the plate-like member via an adhesive layer (30), and the acoustic matching of the plate-like member. A piezoelectric body (6) disposed on the surface opposite to the surface on which the layer is provided via a bonding layer (31), and the opposing area of the adhesive layer is such that the acoustic matching layer is bonded to the plate-like member. that junction area than, or ultrasonic flowmeter is facing area over which the acoustic matching layer opposite to the adhesive layer. The area of the acoustic matching layer, an ultrasonic flowmeter according to any one of claims 1 to 6 is 100 to 110% of the area of the plate-like member. The ultrasonic flowmeter according to any one of claims 1 to 7, wherein the pair of ultrasonic transducers (17, 18) have substantially the same shape, and an impedance frequency is in a use range of 200 KHz to 750 KHz. The pair of ultrasonic transducers (17, 18) have substantially the same shape, and the impedance frequency characteristic correlation coefficient of the pair of ultrasonic transducers is 0.80 in the use frequency range of 200 KHz to 750 KHz. It is the above, The ultrasonic flowmeter of Claim 8.

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