A machine that controls motion needs to know where the part it is driving actually is. It might be the angle of a motor shaft, the position of a robot joint or the travel of a slider along a guide. The position sensor provides this information to the control system, which can then compare the real position with the target one and correct the motion. When position is turned into a signal the control electronics can use, we commonly speak of an encoder. An encoder can be rotary or linear; incremental, if it measures changes in position from a reference, or absolute, if it returns the position already at power-on.
The word inductive is often associated with industrial proximity sensors. These devices detect the presence of a metal object and, in the most common version, give an on/off output. There are also linear proximity sensors, which measure the distance to a target. An inductive encoder does something different: it measures angular or linear position continuously, over the whole travel. It uses the same family of electromagnetic phenomena, but combines purpose-designed coils, a shaped metal target and read-out electronics able to reconstruct position with high resolution.
In its most common form, an inductive encoder consists of a fixed part, often built as a PCB, and a passive metal target attached to the moving part. It needs no mechanical contact between the two parts and uses no permanent magnets.
Driven at a frequency in the megahertz range, it generates an alternating magnetic field above the board.
A shaped conductive part that moves relative to the coils. Eddy currents are induced in the metal, locally altering the transmitted field.
Arranged to pick up the perturbation produced by the target and generate signals that vary with position, typically reducible to a sine and a cosine.
An ASIC drives the TX, demodulates the RX signals, computes the position and makes it available to the controller through an analog or digital output.
The shape of the target varies the coupling between transmitter and receivers in a controlled way. As the target moves, the two RX signals change in an approximately sinusoidal way and in quadrature. Position is derived from their ratio, usually through an arctangent function. This ratiometric reading reduces sensitivity to variations that act in the same way on both channels, such as part of the amplitude drift due to supply or temperature. To obtain an absolute encoder over the whole travel, multiple periods, multiple tracks or suitable geometric architectures can be combined.
Describing the principle takes a few lines. Turning it into a sensor that meets an accuracy target in real mechanics is much harder. The shapes of the coils, the target, the airgap, the mounting, the surrounding materials and the limits of the ASIC all interact: changing one parameter to improve one performance can worsen another.
TX, RX and target contain many geometric parameters. Amplitude, linearity, inductance and robustness to misalignment cannot be optimized separately.
The transmitted field is not uniform and the target, at a finite distance, never shields the field perfectly. The signals are distorted from the start.
Eccentricity, airgap variation, tilt and wobble change the reading. A design that is correct at the nominal position may not be in the real assembly.
Shafts, flanges, brackets, housings and conductive shields couple to the field and can change amplitude, offset and linearity.
Vias, height differences between layers, copper etching, registration and target tolerances make the manufactured part different from the ideal geometric model.
Inductance, resistance, resonant frequency and signal amplitude must stay within the window allowed by the chosen front-end.
Fabricating a coil, measuring it and correcting it by hand can work for a first demonstrator, but it quickly becomes slow and expensive once tolerances, mounting conditions and several objectives have to be considered at the same time. The design space is too large to explore with a few prototypes, and the behaviour observed on the bench does not always indicate which part of the geometry should be changed.
Many physical effects cannot be removed: the field will stay non-uniform, the airgap will be finite and the metal parts will keep interacting with the sensor. The design lever is the shape of the coils. By reshaping the RX correctly, the various distortions can be made to compensate one another, so the signals return an accurate position even under the expected real conditions.
IPSMagic is the EMC Gems platform dedicated to designing inductive encoders. Online since 2022, it was the first public SaaS created specifically for this purpose. It lets you define coils and target, simulate the electromagnetic behaviour, automatically optimize the geometry and check performance before building the first prototype.The compute engine does not use a simple geometric approximation: it solves the physics of the coil-and-target set with proprietary methods dedicated to eddy currents. On top of the simulator, a patented optimization algorithm, developed to reduce error while keeping smooth, manufacturable shapes.
Starts from templates for rotary, linear, arc and torque sensors and automatically modifies the receive coils to reach the defined objectives.
Simulates eccentricity, airgap variations, tilt and fixed external conductors, so the design is verified in the mechanics where it will work.
Quickly compares many configurations and focuses physical prototypes on the solutions already selected by simulation.
Checks manufacturing rules, supports through-via conversion when possible and exports structured reports and simulation data.
The electromagnetic design is not tied to a single manufacturer's toolchain, allowing the best front-end to be chosen and supply continuity to be managed better.
IPSMagic comes from years of research by EMC Gems and the University of Udine in computational electromagnetics and inductive sensors. The simulation core derives from integral methods for eddy currents published in scientific journals; the optimization uses proprietary and patented techniques. It is the same technology licensed to international semiconductor and sensor manufacturers.
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