## 3 Fabrication Methods
### DW Methods
Various 3D-printed multilayer-phased array antenna systems have been designed for WBAN applications [173]. In [174], a common freeze-casting technique was used to fabricate liquid-based 3D antennas. Researchers tested micro components of the liquid metal alloy for 3 DP (at 30 \({}^{\circ}\)C). Additionally, liquid metal has emerged as a viable option for creating injectable 3D bio-electrodes used in ECG and EEG measurements. Advanced, high-resolution, 3D-reconfigurable liquid-metal structures with stretchable properties have been designed to integrate seamlessly into the human body, as depicted in Figure 10a [175]. This design enables the creation of reconfigurable antennas that can be tuned by altering their structures, as well as reversible, movable interconnections that function as mechanical switches. In the realm of 3D printing, the intricate housing structure of the antenna, which may include components like a microfluidic channel, can be fabricated directly onto the substrate using primarily the FDM technique, as illustrated in Figure 10b. Furthermore, researchers have developed a heat sink composed of silicon micro pin fins to efficiently cool a Stratix 10 GX-based field-programmable gate array (FPGA) that consists of multiple heterogeneous dice [176]. To enhance the thermal performance of a design, a piece of 3D-printed plastic with an embedded silicon micro pin-fin heat sink was used to seal the tops of the pin fins and connect the heat sink to the inlet and outlet tubing. Various 3D-printing methods of liquid metal are available to design antenna and electronic devices, such as liquid-metal melt deposition printing, liquid-phase printing, suspension printing, microcontact printing, and in vivo 3D-printed moulding methods [177]. An ultra-compact implanted antenna that is integrated with a Nanostim leadless cardiac pacemakers (LCP) system is presented for use in biotelemetry [178]. A compact antenna that can work in the 2.4 GHz ISM band is created for integration with an LCP. Wearable antennas that are primarily functioning in _ultra-high frequency_ (UHF) and microwave bands have been developed using AM [179]. In [180], it is reported that 3D polymer-conductive hybrid materials were designed using the 3D-FDM method that can be used in wearable applications; an example is shown in Figure 10c. RFID antennas may be designed utilising a 3D-DW method on a textile material, for example, see the design reported in [181]. In recent developments, the integration of FDM for the substrate and syringe dispensing for metallic layers has enabled the creation of a 5G antenna embedded within a medallion [182]. It is suggested to employ removable fingernail-mounted 3D mm-wave and microwave antennas for on-body communications [183]. For this purpose, EGaIn was utilised as the conductive part of the radiator, while Visijet M3 crystal resin was employed as a dielectric for 3D-printed planar and helical antennas [184]. A groundbreaking approach involves the utilisation of 3D printing to create new and innovative gradient refractive index (GRIN) lenses for an H-plane horn antenna [185]. These lenses are constructed using high-permittivity ceramic ZrO\({}_{2}\), resulting in enhanced performance and functionality. As reported in [186], a 3D-printed wire electrostatic discharge (WESD) structure comprising six upper capacitors was designed, enabling verification of the curved surface. This demonstrates the capability of 3D-printing technology to seamlessly integrate WESDs into various wearable devices, including sensors, energy harvesting systems, and light emitting diodes (LEDs), as shown in Figure 10d. Utilising the DIW method and the PEDOT: PSS solution, researchers have successfully developed a high-resolution 3D-conducting polymer. This conducting polymer, along with its composites, has been extensively employed to construct flexible electrodes in diverse applications. The DIW method, in combination with the PEDOT: PSS solution, offers a versatile approach for fabricating flexible electrodes with exceptional precision.