A Wideband Slot Antenna in a Box for Wearable Sensor Nodes

A wideband slot antenna was designed to be embedded in the interior walls of a wireless sensor node to avoid the undesirable effects of the human body on the performance of the sensor. A box ( 59 ×36 ×14 mm³) made from ABS plastic was used as a platform for the antenna. Silver ink was painted on internal walls of the box to make the slot. The 10-dB bandwidth of the antenna is 39% (2.1-3.1 GHz). The antenna features a full ground plane underneath to reduce the interaction between body and the antenna, which affects the radiation efficiency. The simulated total efficiency of antenna is more than 90% in free space and reduces to 55% at 2.45 GHz and 62% at 3 GHz determined by adding the voxel body model in the simulation process. The simulated peak gain of the antenna is 4.1 dBi in free space at 2.5 GHz, which reduces to 3 dBi after adding the body model. The measured peak gain of antenna in xy-plane is 2.8 dBi at 2.5 GHz.