Planar RF Antenna with Duplicate Unit Cells for Cross-Body Communication
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Solution Overview
Problem
The human body's high permittivity and conductivity cause detuning and reduced radiating efficiency of RF signals, making cross-body communications challenging for wearable devices, and conventional antennas like monopole, patch, and dipole designs are impractical due to orientation dependencies.
Innovation Solution
A duplicate-cell antenna with a planar, thin design featuring a ground plane and radiating plane on a dielectric substrate, where unit cells are electrically interconnected and arranged in patterns like 'X' or 'H', with load inductors and conductive patches, allowing for efficient surface wave transmission independent of orientation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If monopole antenna is used for cross-body communication, then surface wave generation is effective, but form factor becomes impracticable for portable devices
Solution Approach 1:
The monopole antenna structure is segmented into multiple planar unit cells arranged in a grid pattern on a substrate. Each unit cell contains conductive elements that collectively generate surface waves, distributing the radiation function across multiple smaller segments rather than requiring a single large orthogonal structure.
Solution Approach 2:
The antenna transitions from a three-dimensional orthogonal monopole structure projecting from a ground plane to a two-dimensional planar configuration embedded in a substrate. This dimensional change allows the antenna to maintain surface wave generation capability while reducing the protruding height and overall form factor suitable for wearable devices.
2Ease of manufacture
If conventional antennas (patch, slot, IFA, dipole) are used for cross-body signaling, then device integration is feasible, but signaling effectiveness becomes orientation dependent
Solution Approach 1:
The antenna employs a symmetric grid pattern of unit cells where each cell contains conductive elements arranged to radiate equally in all directions within the plane. This symmetric design ensures that the antenna maintains consistent signaling effectiveness regardless of its orientation on the user's body, eliminating the orientation dependency of conventional asymmetric antenna designs.
Solution Approach 2:
The planar unit cell structure serves multiple functions simultaneously: it generates surface waves for cross-body communication, maintains orientation independence, integrates into thin wearable substrates, and provides a compact form factor. This multi-functional design eliminates the need to compromise between integration feasibility and adaptability.
3Speed
If RF signals are transmitted through the human body, then direct penetration is attempted, but high permittivity and conductivity cause detuning and shadowing effects
Solution Approach 1:
The antenna uses surface waves traveling along the body surface as an intermediary medium for communication, rather than attempting direct RF penetration through the body. The conductive elements generate electromagnetic surface waves that propagate along the skin, effectively mediating the transmission between devices worn on different parts of the body while avoiding the detuning and shadowing problems of direct penetration.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The antenna achieves effective surface wave transmission and reliable cross-body communication, suitable for body-mountable devices like HMDs and VR controllers, with minimal orientation dependence and suitable for implementation in small, portable devices.
Implementation Method 1
wearable device designers frequently rely on surface waves (also known as creeping waves) to establish cross-body communications between wireless wearable devices
Implementation Method 2
The human body has a high permittivity, which introduces a detuning effect that changes the operational frequency of an antenna in proximity to the body. Moreover, the human body also has a high conductivity, which introduces a high dielectric loss
Data Source
AI summary
An antenna includes a planar dielectric substrate having opposing first and second surfaces, a ground plane disposed at the first surface, the ground plane composed of conductive material, a radiating plane disposed at the second surface and composed of conductive material. The radiating plane implements a plurality of unit cells, with each unit cell having a corresponding section of the conductive material of the radiating plane that is formed in a specified shape, the specified shape including a first portion forming a load inductor and second portion forming a radiating patch electrically coupled to the load inductor. Each unit cell further includes at least one via electrically coupling the load inductor to the ground plane.