攝護腺癌為台灣男性前五大癌症之一。目前常用治療攝護腺癌的方式為經直腸高強度聚焦超音波(Transrectal HIFU)，其作法是將探頭伸入直腸中，超音波使組織瞬間升溫而使得細胞凋亡。且因具有高度聚焦的特性，可以減少對周圍組織的影響，降低副作用。因此超音波治療成為近年來常用的一種治療方式。目前的商用設備將探頭以機械移動的方式沿著直腸前後移動，以及旋轉來盡量涵蓋治療區域，而這種方式可能會有磨傷直腸壁的風險。因此若能使用單一陣元的探頭來達到改變聚焦長度以及轉向的特性，在探頭就定位之後，以探頭自身的變焦與轉向來涵蓋治療區域，降低直腸壁損傷的風險。
液體鏡頭因其可控制液體形狀的特性，製作成鏡頭後具有使超音波變焦與轉向的潛力，包含薄膜液壓式液體鏡頭、電濕潤式液體鏡頭。然而在現有的研究中，薄膜液壓式液體鏡頭無法達成較快速的變焦及轉向功能，電濕潤式液體鏡頭目前無法同時做到變焦與轉向兩種功能，因此本研究希望開發新式之電濕潤式液體鏡頭，使超音波變焦與轉向，並能以較低電壓來驅動。
本研究設計一顆電濕潤式液體鏡頭搭配自製5.5 MHz、7.2 mm孔徑之平面式單陣元探頭作為發射源。鏡頭內以水與矽油兩種不同聲速的液體形成透鏡，並以給予兩側電壓形成電濕潤現象，來控制兩液體介面的曲率半徑或偏折角。在給予液體鏡頭48 V的低電壓內，可使超音波聚焦長度在26 ~ 32.9 mm變化，在分別給予液體鏡頭兩側0 V與60 V的電壓組合下可達最多5∘的轉向角，並且可以在維持轉向的情況下同時達到變焦的效果，聚焦長度在25 ~ 29 mm中變化，符合本研究設定在單陣元探頭上達成變焦與轉向兩種功能的液體鏡頭。未來將透過改善鍍膜參數來實現更大的變焦範圍及轉向角，並且拓展成二維的轉向功能。

Prostate cancer is one of the most frequently diagnosed cancers in the male population in Taiwan. One of the most common therapies is transrectal high intensity focused ultrasound. A transducer is inserted into rectum to deliver high energy, which rapidly raises the temperature of the prostate and causes necrosis. It also has fewer side effects than other treatments because it is highly focused on a small area. Current commercial devices move the transducer back and forth inside the rectum to cover the whole prostate. However, this approach may cause rectum injury. Thus, if a single element transducer with variable focus and steering is used, it can cover the entire prostate without moving the transducer frequently.
Liquid lens has the potential to change the focal point and steer the ultrasound due to the ability to control the shape of liquid. In current research, membrane liquid lens doesn’t have the ability to change the focal point rapidly or steer ultrasound by membrane liquid lens. Electrowetting liquid lens only have one of the ability to change focus or steer, not both in one device. This research designs a new type of electrowetting liquid lens with variable focus and steering ability with a low applied voltage in one device.
In this research, an electrowetting liquid lens working with a 5.5 MHz, 7.2 mm aperture homemade single element planar transducer was designed. Two materials with different speed of sound, such as water and silicone oil, forms a liquid interface as a lens, and the liquid interface is controlled by electrowetting. The focal length of ultrasound varies from 26 mm to 32.9 mm by applying voltage to liquid lens within 48 V. Also the steering angle of ultrasound can reach a maximum steering angle of 5∘by applying 0 V and 60 V to both sides of the liquid lens. Furthermore, the focal length can be varied from 25 to 29 mm while maintaining the steering angle. These results approve the design of electrowetting liquid lens with variable focus and steering ability. Future work includes improving fabrication parameters to obtain larger focal range and steering angle, and developing two-dimension steering.

[1] 衛福部, “110年國人死因統計結果,” 衛福部, 2021. [線上]. Available: https://www.mohw.gov.tw/dl-78404-173e483e-dcfc-4b50-ab35-54f8b0b568dd.html. [存取日期: 24 11 2022].
[2] P. A. Kupelian, T. R. Willoughby, C. A. Reddy, E. A. Klein, and A. Mahadevan, "Hypofractionated intensity-modulated radiotherapy (70 Gy at 2.5 Gy per fraction) for localized prostate cancer: Cleveland Clinic experience," Int. J. Radiat. Oncol. Biol. Phys, vol. 68, pp. 1424-1430, 2007.
[3] H. Azzouz and J. J. M. C. H. de la Rosette, "HIFU: Local Treatment of Prostate Cancer," EAU-EBU Update Series, vol. 4, no. 2, pp. 62-70, 2006.
[4] G. Haar, "HIFU Tissue Ablation: Concept and Devices," in Therapeutic Ultrasound, New York, Springer, 2016, pp. 3-20.
[5] K. Hynynen, "Fundamental Principles of Therapeutic Ultrasound," in MRI-Guided Focused Ultrasound Surgery, Boca Raton, CRC Press, 2008, p. 20.
[6] I. A. S. Elhelf, H. Albahar, U. Shah, A. Oto, E. Cressman, and M. Almekkawy, "High intensity focused ultrasound: The fundamentals, clinical applications and research trends," Diagnostic and Interventional Imaging, vol. 99, no. 6, pp. 349-359, 2018.
[7] S. Thüroff, and C. G. Chaussy, "Transrectal Prostate Cancer Ablation by Robotic High-Intensity Focused Ultrasound (HIFU) at 3 MHz: 18 Years Clinical Experiences," in Focal Therapy of Prostate Cancer, New York, Springer, 2015, pp. 105-133.
[8] Y. Zhou, "Generation of uniform lesions in high intensity focused ultrasound ablation," Ultrasonics, vol. 53, no. 2, pp. 495-505, 2013.
[9] R. Seip, W. Chen, J. Tavakkoli, L. A. Frizzell, and N. T.Sanghvi, "High-intensity focused ultrasound (HIFU) phased arrays: Recent developments in transrectal transducers and driving electronics design," in Proc. 3rd Int. Symp. Therapeutic Ultrasound, 2003.
[10] 衛福部, “西藥、醫療器材、化粧品許可證查詢:“聲納照護”高強度聚焦超音波消融系統,” 23 02 109. [線上]. Available: https://info.fda.gov.tw/MLMS/ShowFile.aspx?LicId=56032980&Seq=001&Type=9. [存取日期: 24 11 2022].
[11] Y. Hosono, Y. Yamashita, and K. Itsumi, "Effects of Fine Metal Oxide Particle Dopant on the Acoustic Properties of Silicone Rubber Lens for Medical Array Probe," IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol. 54, no. 8, pp. 1589-1595, 2007.
[12] S. J. Patey and J. P. Corcoran, "Physics of ultrasound," Anaesthesia & Intensive Care Medicine, vol. 22, no. 1, pp. 58-63, 2021.
[13] R. Hill, "Principles of Ultrasound," in Transesophageal Echocardiography, Boston, MA, Springer, 1987, pp. 9-27.
[14] V. T. Rathod, "A Review of Acoustic Impedance Matching Techniques for Piezoelectric Sensors and Transducers," sensors, vol. 20, no. 14, p. 4051, 2020.
[15] G. Maimbourg, A. Houdouin, T. Deffieux, M. Tanter, and J.-F. Aubry, "3D-printed adaptive acoustic lens as a disruptive technology for transcranial ultrasound therapy using single-element transducers," Physics in Medicine & Biology, vol. 63, no. 2, p. 025026, 2018.
[16] D. Wang, P. Lin, Z. Chen, C. Fei, Z. Qiu, Q. Chen, X. Sun,Y. Wu and L. Sun, "Evolvable Acoustic Field Generated by a Transducer with 3D-Printed Fresnel Lens," Micromachines, vol. 12, no. 11, p. 1315, 2021.
[17] H. Ren, and S.-T. Wu, Introduction to Adaptive Lenses, New Jersey: John Wiley & Sons, 2012.
[18] K. H. Kang, "How electrostatic fields change contact angle in electrowetting," Langmuir, vol. 18, no. 26, pp. 10318-10322, 2002.
[19] H. Moon, S. K. Cho, R. L. Garrell, and C.-J. “CJ” Kim, "Low voltage electrowetting-on-dielectric," Journal of Applied Physics, vol. 92, no. 7, pp. 4080-4087, 2002.
[20] B. Berge, "Electrocapillarity and wetting of insulator films by water," Seances Acad. Sci., Ser. B, vol. 317, pp. 157-163, 1993.
[21] S. Terrab, A. M. Watson, K. Dease, J. T. Gopinath, and V. M. Bright, "Electrowetting-Based Variable Tuning Prism," in CLEO: 2015, 2015.
[22] S. Terrab, A. M. Watson, C. Roath, J. T. Gopinath, and V. M. Bright, "Adaptive electrowetting lens-prism element," Optics Express, vol. 23, no. 20, p. 25838, 2015.
[23] X. Wei, G. Kawamura, H. Muto, A. Matsuda, "Fabrication on low voltage driven electrowetting liquid lens by dip coating processes," Thin Solid Films, vol. 608, pp. 16-20, 2016.
[24] S. Arscott, "Moving liquids with light: Photoelectrowetting on semiconductors," Scientific Reports, vol. 1, no. 1, 2011.
[25] S. Arscott, "Continuous electrowetting at the low concentration electrolyte-insulator- semiconductor junction," Applied Physics Letters, vol. 105, no. 23, p. 231604, 2014.
[26] M. Dhindsa, S. Kuiper, and J. Heikenfeld, "Reliable and low-voltage electrowetting on thin parylene films," Thin Solid Films, vol. 519, no. 10, pp. 3346-3351, 2011.
[27] A. Schultz, S. Chevalliot, S. Kuiper, and J. Heikenfeld, "Detailed analysis of defect reduction in electrowetting dielectrics through a two-layer 'barrier' approach," Thin Solid Films, vol. 534, pp. 348-355, 2013.
[28] S. Berry, J. Kedzierski, and B. Abedian, "Low voltage electrowetting using thin fluoroploymer films," Journal of Colloid and Interface Science, vol. 303, no. 2, pp. 517-524, 2006.
[29] K. Tom, and T. J. Ashley, "Reverse electrowetting as a new approach to high-power energy harvesting," Nature Communications, vol. 2, no. 1, pp. 447-448, 2011.
[30] M. K. Kilaru, J. Heikenfeld, G. Lin, and J. E. Mark, "Strong charge trapping and bistable electrowetting on nanocomposite fluoropolymer:BaTiO3 dielectrics," Applied Physics Letters, vol. 90, no. 21, p. 212906, 2007.
[31] A. M. Watson, K. Dease, S. Terrab, C. Roath, J. T. Gopinath, and V. M. Bright, "Focus-tunable low-power electrowetting lenses with thin parylene films," Applied Optics, vol. 54, no. 20, pp. 6224-6229, 2015.
[32] L.-Y. Li, R.-Y. Yuan, J.-H. Wang, L. Li, and Q.-H. Wang, "Optofluidic lens based on electrowetting liquid piston," Scientific Reports, vol. 9, no. 1, 2019.
[33] H. Liu, S. Dharmatilleke, D. K. Maurya, and A. A. O. Tay, "Dielectric materials for electrowetting-on-dielectric actuation," Microsystem Technologies, vol. 16, no. 3, pp. 449-460, 2010.
[34] B. Koo and C.-J. Kim, "Evaluation of repeated electrowetting on three different fluoropolymer top coatings," Journal of Micromechanics and Microengineering, vol. 23, no. 6, p. 067002, 7 5 2013.
[35] D. L. Folds, "Focusing Properties of a Cylindrical Liquid‐Filled Compound Acoustic Lens," The Journal of the Acoustical Society of America, vol. 49, no. 5B, pp. 1591-1595, 1970.
[36] Y.J. Yoon, and P.J. Benkeser, "Sound field calculations for an ultrasonic linear phased array with a spherical liquid lens," IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol. 39, no. 2, 1992.
[37] C. Song, L. Xi, and H. Jiang, "Acoustic lens with variable focal length for photoacoustic microscopy," Journal of Applied Physics, vol. 114, no. 19, p. 194703, 2013.
[38] Z. Li, R. Guo, C. Fei, D. Li, D. Chen, C. Zheng, R. Wu, W. Feng, and Y. Yang, "Liquid lens with adjustable focus for ultrasonic imaging," Applied Acoustics, vol. 175, p. 107787, 2021.
[39] S. Deladi, J. F. Suijver, Y. S. Shi, K. Shahzad, B. M. de Boer, A. J. J. Rademakers, C. van der Vleuten, L. Jankovic, E. Bongers, E. Harks, and S. Kuiper, "Miniaturized ultrasound scanner by electrowetting," APPLIED PHYSICS LETTERS, vol. 97, no. 6, p. 064102, 2010.
[40] T. “Leo” Liu and C.-J. “CJ” Kim, "Contact Angle Measurement of Small Capillary Length Liquid in Super-repelled State," Scientific Reports, vol. 7, no. 1, 2017.
[41] R. Bhargava, M. Noga, and L. Lou, "Ultrasound basics," in Atlas of Ultrasound and Nerve Stimulation-Guided Regional Anesthesia, New York, Springer, 2008, pp. 19-33.
[42] H. Ma, Z. Wang, C. Zuo, and Q. Huang, "Three dimensional confocal photoacoustic dermoscopy with an autofocusing sono-opto probe," Journal of Biophotonics, vol. 15, no. 5, 2022.
[43] B. E. Treeby, J. Budisky, E. S. Wise, J. Jaros, and B. T. Cox, "Rapid calculation of acoustic fields from arbitrary continuous-wave sources," The Journal of the Acoustical Society of America, vol. 143, no. 1, pp. 529-537, 2018.
[44] F. A. a. G. M. G. L. D’Ardhuy, "Multi-phase liquid composition and optical electrowetting device that incorporates the same". United States Patent US 2007/0179200 A1, 2 8 2007.
[45] 李榮榤, “介電式液態透鏡之乳化抑制,” 國立清華大學碩士論文, 2009.
[46] A. F. Stalder, T. Melchior, M. Müller, D. Sage, T. Blu, and M. Unser, "Low-Bond Axisymmetric Drop Shape Analysis for Surface Tension and Contact Angle Measurements of Sessile Drops," Colloids and Surfaces A: Physicochemical and Engineering Aspects, vol. 364, no. 1-3, pp. 72-81, 2010.
[47] D. Thomas, M. Audry, R. Thibaut, P. Kleimann, F. Chassagneux, M. Maillard and A. Brioude, "Charge injection in dielectric films during electrowetting actuation under direct current voltage," Thin Solid Films, vol. 590, p. 224–229, 2015.
[48] Y.-J. Li and B. P. Cahill, "Frequency Dependence of Low-Voltage Electrowetting Investigated by Impedance Spectroscopy," Langmuir, vol. 33, no. 45, pp. 13139-13147, 2017.
[49] A. I. Drygiannakis, A. G. Papathanasiou, and A. G. Boudouvis, "On the Connection between Dielectric Breakdown Strength, Trapping of Charge, and Contact Angle Saturation in Electrowetting," Langmuir, vol. 25, no. 1, pp. 147-152, 2009.
[50] C. o. N. Evaluation, "Nondestructive Evaluation : waves," Iowa State University, [Online]. Available: https://www.nde-ed.org/Physics/Waves/reflectiontransmission.xhtml. [Accessed 15 12 2022].
[51] S. K. Hong and H. Lee, "Focused ultrasound and prostate cancer," Ultrasonography, vol. 40, no. 2, pp. 191-196, 2021.