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Thermoreflectance techniques, particularly frequency-domain thermoreflectance (FDTR), play a crucial role in measuring the thermal properties of bulk and thin-film materials. These methods precisely measure thermal conductivity, specific heat capacity, and interfacial thermal conductance by analyzing the temperature-dependent reflectivity changes in materials. However, the complex interplay among parameters presents challenges in data analysis, where single-variable analysis often fails to accurately capture intra-layer and inter-layer interactions. In this work, the FDTR is used as a case study and the relationships between sensitivity coefficients of various parameters are systematically explored through singular value decomposition (SVD). Specifically, the SVD of sensitivity matrix S of the system's parameters is performed to identify smaller singular values and their corresponding right singular vectors, which are the basis vectors of the null space of matrix S . These vectors reveal the relationships among parameter sensitivities, and by contrast, these relationships reveal the most fundamental combination parameters that determine the thermoreflectance signal. This method not only clarifies the dependency relationship between variables but also determines the maximum number of parameters that can be experimentally extracted, and the parameters that must be known beforehand. To demonstrate the practical value of these combination parameters, this work conducts a detailed analysis of FDTR signals from an aluminum/sapphire sample. Unlike traditional FDTR experiments, which typically fit only thermal conductivity and interfacial thermal conductance of substrate, our sensitivity analysis reveals that it is possible to simultaneously determine the thermal conductivity of the metal film, substrate’s thermal conductivity, substrate’s specific heat capacity, and interfacial thermal conductance. The fitting results are consistent with reference values from the literature and measurements from other thermoreflectance techniques, thus validating the effectiveness and reliability of our method. This comprehensive analysis not only deepens the understanding of thermoreflectance phenomena but also provides strong support for the future development of thermal characterization technology and material research, showing the significant potential application of SVD in complex multi-parameter systems.
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Keywords:
- thermoreflectance /
- singular value decomposition (SVD) /
- thermal property measurement /
- inverse problems
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图 1 频域热反射法实验系统示意图
Figure 1. Schematic diagram of the frequency domain thermoreflectance experimental setup.
图 2 铝/蓝宝石样品的频域热反射分析 (a1), (a2) 1 kHz—70 MHz频率范围内的相位信号和归一化幅值信号; (b1), (b2) 单个参数敏感性随频率的变化; (c1), (c2)组合参数敏感性随频率的变化
Figure 2. FDTR analysis of aluminum/sapphire samples: (a1), (a2) Phase and normalized amplitude signals across frequencies from 1 kHz to 70 MHz; (b1), (b2) how the sensitivity of individual parameters varies with frequency; (c1), (c2) changes in the sensitivity of combined parameters across the frequency spectrum.
图 3 (a) ${k_{z1}}$, ${k_{r1}}$, ${C_1}$, ${h_1}$的敏感性曲线, 横坐标为频率; (b) 各个${v_j}$与敏感性矩阵${{\boldsymbol{S}}_1}$相乘得到的结果
Figure 3. (a) Sensitivity curves for ${k_{z1}}$, ${k_{r1}}$, ${C_1}$, and ${h_1}$, with frequency as the horizontal axis; (b) the results of multiplying each ${v_j}$ by the sensitivity matrix ${{\boldsymbol{S}}_1}$.
表 1 三明治结构模拟样品的系统参数
Table 1. System parameters of a sandwich structure simulated sample.
${k_z}$/${\text{(W}} {\cdot }{{\text{m}}^{{{ - 1}}}} \cdot {{\text{K}}^{{{ - 1}}}})$ ${k_r}$/${\text{(W}}{ \cdot }{{\text{m}}^{{{ - 1}}}} \cdot {{\text{K}}^{{{ - 1}}}})$ $C$/${\text{(MJ}} {\cdot} {{\text{m}}^{ - 3}}{{\cdot}}{{\text{K}}^{{{ - 1}}}}{)}$ $h$/${\text{nm}}$ ${r_0}$/$ {\text{μm}}$ G1/${\text{(MW}}{ \cdot} {{\text{m}}^{ - 2}}{{\cdot}}{{\text{K}}^{ - 1}})$ G2/${\text{(MW}} {\cdot }{{\text{m}}^{ - 2}}{{\cdot}}{{\text{K}}^{ - 1}})$ 1(Al) $150$ $150$ $2.44$ $100$ $8$ 10 10 2 $10$ $100$ $2$ $2000$ 3(Sub) $100$ $10$ $1.5$ $\infty $ 
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表 2 面内各向同性多层结构中的组合参数
Table 2. Combined parameters in isotropic multilayer structures in-plane.
层序号 组合参数 1 $\dfrac{{\sqrt {{k_{z1}}{C_1}} }}{{{h_1}{C_1}}}, \;\dfrac{{{k_{r1}}}}{{{C_1}r_0^2}}$ 1/2 $\dfrac{{{G_1}}}{{{h_1}{C_1}}}$ $\vdots $ $\vdots $ n $\dfrac{{\sqrt {{k_{zn}}{C_n}} }}{{{h_n}{C_n}}}, \;\dfrac{{\sqrt {{k_{zn}}{C_n}} }}{{{h_{n - 1}}{C_{n - 1}}}}, \;\dfrac{{{k_{rn}}}}{{{C_n}r_0^2}}$ n/(n+1) $\dfrac{{{G_n}}}{{{h_n}{C_n}}}$ $\vdots $ $\vdots $ N $\dfrac{{\sqrt {{k_{zN}}{C_N}} }}{{{h_{N - 1}}{C_{N - 1}}}},\; \dfrac{{{k_{rN}}}}{{{C_N}r_0^2}}$
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