建構超音波擴散聲場提升微藻生長之研究

Construct Ultrasonic Diffusion Field to Enhance Microalgae Biomass Productivity

楊旭光(Shiuh-Kuang Yang) ； 黃怡澄(Yi-Cheng Huang) ； 林鍵騰(Chien-Teng Lin)

《應用聲學與振動學刊》 10卷1&2期 (2018/12) Pp. 29-38

https://doi.org/10.6282/JASV.201812_10(2).0004

摘要

本研究的目的在於設計製造出一種超音波擴散聲場，以改善建設性生物超音波照射不均的問題，在實務應用上就能夠提高照射效率，並降低樣本因照射聲場不均所造成的差異。本研究所設計的改良式擴散聲場，將其壁面調整為互不平行，並加入凸透鏡形狀之聲透鏡構造，並與同樣調整過壁面而不含凸透鏡構造的傳統擴散聲場，運用有限元素法分析並比較改良式與傳統擴散聲場間差異，最後將兩種聲場應用於淡水小球藻，以誘發超音波生物效應。一般產生超音波聲源的超音波探頭在激發時，其聲能量集中於換能器前端，具明顯指向性且呈現高斯分布情形。本研究為了改善聲場均勻性，於超音波探頭前端選用壓克力製成之凸透鏡用來發散超音波，並且將四周壁面微調使之不互相平行。研究結果顯示經多重反射後達穩態時，加裝凸透鏡的對照組與不含此構造之聲場相比，在能量的分布上更加均勻，且照射死角之陰影區能有效降低。運用水中麥克風實際量測製作的模型可知，傳統擴散聲場聲強標準差為1.46 dB，而改良式擴散聲場為0.76 dB。本研究接著運用傳統擴散聲場及改良式擴散聲場，並配合Rayleigh-Plesset的空孔振動理論以淡水小球藻的自然頻率進行照射，經過超音波照射的微藻具有生長速率提升的效果，並且能更快達到該培養環境下的生長靜止期，使用改良型擴散聲場約能提早兩天，而傳統擴散聲場則約能提早一天到達靜止期。

關鍵字

擴散聲場 ； 超音波生物效應 ； 聲透鏡 ； 微藻 ； 指向性 ； 均勻性

並列摘要

The objective of this study is to develop an ultrasonic diffusion field and improve the uniformity of distributed sound energy while inducing constructive ultrasonic bio-effect. The irradiation efficiency can be increased by such ultrasound irradiation field as described in practical application which reduces individual differences caused by the uneven sound energy distribution. In this study, optimized diffusion field boundaries are adjusted to be non-paralleled to each one and equipped with convex acoustic lens. The traditional diffusion field design is also boundary-adjusted but without the convex lens. The finite element method is utilized to analyze the differences between optimized and traditional diffusion field design, and the solution of Chlorella vulgaris is placed in these diffusion fields in comparison and observe the actual ultrasonic bio-effect of this application. While exciting an ultrasound transducer, the sound energy distribution concentrates in front of the transducer which has strong directivity and forms Gaussian distribution pattern. In this study, a convex acoustic lens made of acrylic is placed in front of the ultrasound transducer which is used to diverge sound energy. The results show that ultrasound reflects for multiple times between non-parallel walls, the sound energy distributes more uniformly and less shadow zone in the optimized diffusion field compared with traditional diffusion field. The sound intensity level deviation of traditional and optimized diffusion field model is 1.46 and 0.76 dB respectively, which is measured by hydrophone. The traditional and optimized ultrasonic diffusion field is utilized to irradiate the algae solution with ultrasound at its resonance frequency which is calculated by Rayleigh-Plesset cavitation theory. The growth rate of C. vulgaris has increased while the microalgae growth stationary phase can be reached about two days in advance for the case with optimized diffusion field and about one day for the case with traditional diffusion field.

並列關鍵字

Diffusion Field ； Ultrasonic Bio-Effect ； Acoustic Lens ； Microalgae ； Directivity ； Uniformity