tailieunhanh - composite 2012 Part 6

Tham khảo tài liệu 'composite 2012 part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 5 Open Access Database Three Dimensional Temperature Distribution Analysis of Ultrasound Therapy Equipments Using Thermochromic Liquid Crystal Films Gerardo A. Lopez Munoz and Gerardo. A. Valentino Orozco Department of Bionics Interdisciplinary Professional Unit of Engineering and Advance Technology National Polytechnic Institute Mexico 1. Introduction As a coherent ultrasonic wave propagates through biological tissue it is attenuated due to absorption and scattering. Absorption results from the irreversible conversion of acoustic energy to local heat and it is the primary mode of attenuation in tissue. Ultrasound ability to interact with tissue to produce local heating has been known for a long time and nowadays ultrasound physiotherapy is widely used in health care to treat tissue injuries Haar 1999 . However a large number of therapeutic equipment does not meet international standards. Rigorous quality control to verify whether physiotherapy ultrasound equipment performance is within acceptable range of acoustic intensity output plays a very important role in this context Artho et al. 2002 . Thermographic method of color analysis with thermochromic liquid crystal films is a fast and simple way to evaluate the bidimensional thermal distribution in an acoustic field produced by the ultrasound physiotherapy equipment Jones Carnochan 1986 . Thermochromic liquid crystal films temperature visualization is based on the properties of some cholesteric liquid crystal materials that reflect definite colors at specific temperatures and viewing angles. These properties depend on their molecular organization they are composed of molecular layers where each one has a light rotation respect to the closest adjacent plane around an axis. This propriety generates a helicoidal structure that reflexes the incident white light Ireland Jones 2000 . Correspondence between color and temperature is possible since liquid crystals emit narrow centered bands around one .