Magnetic near-field antennas

Inductive coupling for your application

Magnetic near-field antennas predominantly use inductive coupling via the alternating magnetic field in the intended working area. A current-carrying loop creates a magnetic flux that induces a voltage in a second loop. The coupling depends on geometry, distance and mutual orientation. That's why we define before the design at which positions energy or data should be transmitted and which position deviations are permissible.

Possible project tasks are LF-RFID at 125 or 134.2 kHz as well as HF-RFID and NFC at 13.56 MHz. We will clarify which interface and which standard requirements are relevant based on your product. We also consider customer-specific inductive couplers and defined local field areas. Frequency, power and permissible operating distance are determined project-specifically.

Loop, ferrite and installation environment

We compare circuit board loops, wire windings and, if the task is suitable, ferrite-supported designs. Loop area, number of turns, conductor width, conductor spacing and material influence inductance, losses and parasitic capacitances. The available space alone does not determine the suitable geometry. The counter antenna and desired field distribution are also part of the design.

Metal parts, ground planes, batteries and housings can detune the antenna and change the coupling. We examine their positions in relation to the loop and check whether distance, a changed conductor routing or suitable ferrite material improve integration. We select ferrites to suit the operating frequency and load. Material losses and, if necessary, saturation limit their usefulness and are taken into account in the design.

Design Q factor, bandwidth and matching together

A high quality factor can increase resonant response but narrows the usable bandwidth. For data transmission, modulation and transient response must also suit the system. We therefore select the loaded quality factor for the application and consider the antenna together with its driver, receiver and counterpart device.

We coordinate resonance tuning, impedance matching and, where necessary, intentional damping in the circuit design. We account for component tolerances, connecting leads and PCB parasitics. In tightly coupled systems, we also examine how distance and load conditions affect resonance, current and voltage. This supplements matching at an individual test point with an assessment across the intended operating range.

From simulation and prototype to tested structure

Our development process combines electromagnetic analysis with circuit simulation and practical tuning. We create the antenna layout and matching network, build prototypes and measure the relevant electrical properties. Depending on the task, we examine impedance, resonant frequency, quality factor, transfer response and coupling at representative positions.

Where possible, we evaluate the enclosure, electronics and counterpart device in the intended arrangement. We document measurement conditions, component values and the operating range achieved. This allows targeted assessment of changes to the mechanics, PCB or bill of materials. To begin a project, it helps to have a drawing of the available space, information on nearby materials, the operating frequency and interface, and the required distances and orientations.

Questions about magnetic near-field antennas