Skin Thermal Effect by FE Simulation and Experiment of Laser Ultrasonics

Abstract

Abstract. Laser ultrasonics opened possibilities to measure thermal and mechanical property of skin which occupies an essential position and is beneficial in industrial and medical applications. This paper focuses on the thermal effect in the thermal section of the laser ultrasonic technique. A transient thermal analysis is developed and promoted to simulate the interaction between the laser pulse and human skin, using a multilayered finite element model (FEM). Chicken leg had been used and irradiated by KrF laser, the thermal reactions were detected and recorded by a thermal camera. By comparison, the thermal result of experiments and simulation matches. IntroductionThe study and research of the mechanical properties of different materials occupies an essential position in many engineering and industrial applications. Laser ultrasonics uses a short laser pulse as a remote ultrasound input to excite thermal expansion, and then induces ultrasonic waves on surfaces, which contains the information of elastic properties. This technology has been widely used in industry to detect the surface condition of metallic materials and obtain relative mechanical properties of coatings [1][2][3][4][5].Laser ultrasonics has potential to quantify mechanical properties of skin for diagnosis and accurate assessment of skin diseases [6][7]. In skin laser ultrasonics, the study of thermal interaction between a laser pulse and skin becomes a very essential part for the following two reasons:Firstly, it is of great importance to understand the relationships between increased temperature and laser energy along with other parameters (e.g. shape and duration) in terms of the laser safety. Subsequently, the range of safe laser energy and its relative parameters should be defined in order to avoid skin ablation even skin damage.Secondly, the amplitude of laser generated surface waves increases with increasing laser energy. It is important that the laser energy should be kept sufficient to produce ultrasonic waves which are readily detectable by available measurement tools such as interferometers and high frequency ultrasound transducers which allows the generated surface waves to be recorded and analysed .The finite element model provides a clear and detailed process of the thermal effect in skin laser ultrasonics. The previous work shows that the thermal effect of laser-skin interaction is subject to the thermal properties of tested materials and the parameters of laser pulses including the energy,

Algorithm for Analyzing Thermal Images of Laser Irradiated Human Skin

“…[1][2][3] Within this context, using thermal cameras, as the major device to measure that temperature, was favored by some works over using other types of sensors when specific conditions are required. 4,5 However, the output of thermal cameras, i.e. the sequence of thermal digital images, requires an image-processing stage to extract the maximum temperature temporal variations on skin laser's spot.…”

“…As an example, we can track the highest tem- perature temporal change. Then depending on the plot we got we can calculate the active time 5 (active time is the duration of laser pulse in which temperature value is above the damage threshold of skin) or thermal relaxation time (TRT), 4,11 as example. Figure 1 shows the flow chart of the developed algorithm.…”