## 1 Introduction
### Skin-Mimicking Phantoms  
To overcome the difficulties and ethical problems of conducting studies on living organisms, tissue-like phantoms are used. Traditionally, experiments are conducted on animals, humans, cadavers, and ex-plants to study tissue interactions [17]. Experiments on human and animal skin are difficult to perform because of the wide variability in skin composition. Because of the ethical problems and variability in composition, research on tissue-like phantoms is increasing. One of the main advantages of using skin tissue phantoms is that they provide a controlled and reproducible environment for experimentation, which is difficult to achieve with human subjects. Over the years, an extensive amount of literature has been published on tissue phantoms for various applications [18; 19; 20; 21; 22; 23]. Commercially available cultured in vitro skin tissue cells are a possibility for use in research or for clinical purposes. However, there are significant difficulties in preparation, handling, storage, and standardization [19]. The use of in vitro tissue models for thermographic studies under realistic physical conditions is very difficult. The physical properties of such in vitro models are too different from those of real skin and are characterized by large variations [17]. Physical skin models are stable over the long term, are easy to fabricate, store and manipulate, and also have better control over their physical properties. The high repeatability and reliability of physical model parameters can be achieved without having to worry about ethical issues [17]. However, skin tissue phantoms have some limitations like the lack of blood flow and cellular response and the difficulty in mimicking the complex structure and composition of human skin. Additionally, skin tissue phantoms are typically much simpler than actual human skin: they are customized to mimic specific skin conditions, which can limit their ability to accurately replicate the behavior of human skin. The structure of human skin is divided into three layers: the epidermis, dermis (papillary and reticular), and hypodermis [24]. The epidermis is the thin uppermost layer mainly composed of migrating keratinocytes that eventually form the outermost layer, which is known as the stratum corneum [25]. The dermis, which is divided into the papillary dermis and the reticular dermis, provides structural strength to the skin. The hypodermis, located beneath the dermis, acts as a fatty layer that protects the body from mechanical impact, heat, and cold [26]. When constructing a tissue-mimicking phantom for thermal analysis, two crucial parameters to consider are the specific heat capacity \(c\) in (\(\mathrm{J}\cdot\mathrm{kg}^{-1}\cdot\mathrm{K}^{-1}\)) and the thermal conductivity \(k\) in (\(\mathrm{W}\cdot\mathrm{m}^{-1}\cdot\mathrm{K}^{-1}\)). The properties of human skin tissue vary depending on the individual and the location of the body. For instance, the thickness of the epidermis (uppermost layer) can range from 0.45 to 2 mm [27]. [PERSON] and [PERSON] [24] reported ranges of thermophysical properties used in their research on a tissue-simulating phantom and a finite element heat transfer model of the skin. In addition to specific heat capacity \(c\) and thermal conductivity \(k\), other parameters like the blood perfusion rate \(\omega_{b}\) in the skin layers, metabolic heat generation (\(Q\)) of different skin layers, and layer thickness \(h\) also influence the surface temperature response [24]. Human skin consists of several highly inhomogeneous and anisotropic materials. The skin is one of the largest organs of the human body and actively exchanges mass and heat with the human body and environment, which makes this a very big and complex active open system [17; 28; 29]. Physical skin models are strong simplifications which try to imitate certain parameters or a combination of parameters of the skin. Depending on the area of research, a physical skin model can consist of different combinations of materials, structures and morphologies.