近年，直接描画でパターン形成することにより材料使用量を大幅に削減できるインクジェット（以下， IJと記す）技術への注目が高まっており，Flat Panel Display（以下，FPDと記す）や電子デバイス製造 等の産業分野へ応用範囲を広げている1）．しかし，産業用のUには民生用のIJプリンタに比べ，より厳 しい吐出安定性が要求されるため，FPD分野での数例を除いて製造ラインへの本格導入が進んでいないの が現状である．吐出安定性を阻害する要因としては，アクチュエータの不良ドライブ回路の故障，ダス トによるノズル詰まり，IJヘッド内への気泡の混入2）など幾つか考えられるが，最も対策に苦慮するの が気泡の問題である．%The stability of jetting is a major requirement for industrial inkjet heads. Air bubbles entrapped in a piezo-driven inkjet head can occasionally cause jetting failures. The piezo actuators can be used as sensors to detect the acoustic influence caused by air bubbles. As in our previous paper, we developed a controllable bubble generation method by focused THG Nd:YVO_4 laser with the secondary Bjerknes forces and could intentionally generate bubbles from about 5 micron to 150 micron in radius at the designated point near the nozzle inside the inkjet heads.rnIn this paper, experimental results on the relationship between the electric signal from the piezo actuators and bubbles are presented. We find the existence of a kind of a dead zone where the emitted sound pressure from a bubble is insensitive to the bubble size. Our numerical study shows this phenomenon is attributed to the increase of the radiation impedance with an increasing bubble size in reverberant sound fields as in the inkjet heads. We also present CFD simulation results using models with a bubble inside an inkjet head in order to make an estimate of the bubble size and position to cause jetting failures.
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