Product News - Automotive RFID

Reduce Emitter Antennae Length by 50% for Automotive Electronics

RFID Automotive Car Access - Video

Premo New Technology reduces Emitter Antennae Length by 50% for Automotive Electronics.

The Diabolo™ Core Patented Technology for emitter antennae in Car Keyless Entry Systems developed by Premo spares space and allows shorter and nmore robust devices.

Automotive Passive Keyless Systems ( Fig 1) are growing in global market penetration. By 2025 more than 25% of newly assembled light vehicles is forecasted to have a Keyless Entry system. A global production that is more than 30M systems per year. Market demand for better performance in terms of longer reading range, less energy consumption, smaller size and component count and costs is leading to systems with less antennae ( 3 instead of 5) but necessarily, the antennas must be longer to generate larger fields equivalent to radiation pattern of 5 antennae. Premo has developed 2 alternatives:

  • Longer flexible antennas based on Alma ™ Technology for Mid-Range and Long Range
  • The new Diabolo ™ technology that generates the same magnetic field that long brittle conventional single core ferrite antennas with 50% shorter length and improving mechanical resistance and reliability.


Fig.1 .

Passive Keyless Entry system is a generic term for an automotive technology which allows a driver to lock and unlock a vehicle without using the corresponding key fob buttons. Once a driver enters a vehicle with an equipped PKE or Keyless Go keyfob (or cardkey), they have the ability to start and stop the engine, without inserting the Smart Key. A transponder antenna built within the key fob allows the vehicle to identify a driver. The SMD components located in the smart key are required high levels of sensitivity, good temperature stability and robustness against mechanical shocks and drops.

The system works ( Fid 2) by having a series of LF (low frequency 125 kHz) transmitting antennas both inside and outside the vehicle. The external antennas are located in the door handles, mirrors, or trunk position.

The system works ( Fid 2) by having a series of LF (low frequency 125 kHz) transmitting antennas both inside and outside the vehicle. The external antennas are located in the door handles, mirrors, or trunk position.

There are two clear areas, the Car side and the Keyfob side. Current technology trends push the car side to reduce the component count so that less antennas are needed and to improve the performance to move from 4-5 short range antennas to 3 Mid-range antennas and ultimately to 2-1 Long Range Antennas

Fig.2 .

PKE/KGO/KES Systems work by having a series of LF (low frequency, 20kHz, 125kHz & 134kHz) transmitter antennas, depending on chip-set used, both inside and outside the vehicle. External antennas are located in the door handler, mirrors or trunk position. When vehicle is triggered either, close to vehicle, pulling the handle or touching it an LF signal is transmitted from the antennas to the Key. Key is activated and transmitted its ID back to the vehicle using RF channel, if Key code is correct the electronic module unlocks the vehicle.

The antennas typically have to meet the AEC-Q200 (specific automotive quality standard) and waterproof specs from IP54 to IP69K standards due to their specific packaging (rugged plastic box filled with polyurethane foam, PA LPM protection, Epoxi coatings or over-molding or HPM in PBT GF30 for IP69K).

According to the introduction, Mid-range antennas are longer than Short-Range antennas and Long-range antennas are even longer than Mid-range antennae ( Fig3 ).

Fig.3 .

Longer devices have obvious advantages:

– Longer range

– Lower component count thus:

– Higher System reliability

– Lower total system cost.

Nevertheless, because of the intrinsic brittleness of ferrites, longer antennae need longer cores that have several drawbacks:

– Very brittle.

– Very poor thermal stability

– Reduced Mechanical performance:

– Very poor bending resistance

– Very Poor torsion resistance

Because of this, there are costs and manufacturability challenges:

– Long ferrite cores production become critical because of a “banana effect” during the shrinkage in sintering process.

– Small contraction and dilatation of a high L/D ratio makes a high impact in effective magnetic permeability thus producing a lack of stability of L and SRF parameters over temperature range.

– Mechanical protection of the core with plastic housings and or resins become costly and critical as combined thermal coefficients are critical.

– Manufacturing costs soar as the tools and molds are much bigger and complex (higher Capex) while throughput is lower than in smaller parts because of the brittleness and lower mechanical resistance.

Cost of materials, and process is then much higher thus reducing the advantage of a lower component count per vehicles.

The logic of a lower total system costs by using less antennas is spoiled if those antennas cost is much higher than their short-range equivalents.

Therefore, the technical challenge is achieving all the advantage of Mid-range and Long-range antennas without the above-mentioned drawbacks of brittleness, costly materials, processes and investments and critical temperature and mechanical performance.

I a short sentence Diabolo ™ Antennas stand for: All the good features of Mid-Range antennas while preserving and keeping all the good features of the short-range antennas (cost effective, mechanically robust and thermally stable).

Premo innovation consist of using a Core with a Variable Cross-Sectional area that is maximum at both extremes of the antenna and minimum at the center of the antenna where the winding is located.

For a constant H field, the induction B is proportional to the density of magnetic field lines and the effective magnetic permeability of the material. For the same magnetic material and the same number of turns (identical winding N = constant) , the induction B in a portion of the core with half the cross sectional area is double. Thus, a decreasing section core would concentrate magnetic field to maximize induction B at the point where cross sectional areas is minimum.

Fig.4 .


Fig.5 .

A simple approach is a single core that has a constant reduction of section up to 50% and a winding of N turns in the center at the point with the lowest Cross Sectional area like in Fig 5

For an external magnetic field H and given the same effective magnetic permeability of the core, the Magnetic Flux φ through the core is constant and the induction at every point is B= φ/S being S the cross sectional area perpendicular to the flux.

In shape of figure 5 and Fig 6 in following shapes the induction B at the narrowest point is double than the one at the widest.

Fig.6 .

A larger cross sectional area can be presented to the external H field, then increasing the Magnetic Flux φ through the core when a radius R is given like in FIG 6 in order to guide the maximum number of field lines though our low Reluctance Path that is the core.

The invention of cross sectional area reduction in emitter antennas, have a significant advantage in Mid-Range antennas as a similar range, induction, sensitivity, size and cost can be achieved when compared to the prior art mid-range antennas.

A logic evolution from a constant height core is a 3D core that can present a constant reduction of cross sectional area including a reduction of height like in Fig 7

A graphic representation of the effect of concentration of field lines when the Magnetic Flux φ is constant along the core can be seen in FIG 4.

The effect of magnetic amplification has been described as the improvement of effective permeability (µr) of apparent permeability (µapp) considered as the ratio between the internal flux density in the core (Bn) and the external flux density (Bext)

Being µr the relative permeability of the core and Nz the demagnetizing field factor.

As knowing this Nz factor is difficult, for a given shape there are empirical formulas charts and abacus. In the case of a rod (a pure cylindric shape) we introduced already the L/D empirical chart (courtesy of Ferroxcube):

A simplified equation for the demagnetizing factor in direction z (longitudinal) is:

The graphic representation for a rod is the already mentioned graph.

Magnetic concentration of a Diabolo ™ shape core with D the larger diameter, d the smaller diameter and µr the relative magnetic permeability of the core, the apparent permeability µapp will be:

In summary, the greater the ratio L/D and the larger the ratio d/D the better.

An optimized embodiment of core that presents a progressive cross section reduction and a maximum surface on both sides of the core is as per Figure 8.

Fig.8 .

Fig 9 shape simulation shows the much higher induction ( red ) in the minimum section area:

Fig.9 .

Long Flexible antennas Like Premo Alma ™ Technology AF series described in patent EP3333 860A1 can be made with this invention also, including echelons / links as per following figure 10 :

Fig.10 .


Image.1 .

Image 1 shows a real off tool Diabolo ™ Antenna that is 60mm or 50% shorter than Premo Conventional KGA mid-range conventional antenna ( Image 2):

Image.2 .


Table 1 shows H magnetic fields generated at 3m by identical excitation currents.

The invention solves the technical challenges in the following way.All the good features of Mid-Range antennas while preserving and keeping all the good features of the short-range antennas (cost effective, mechanically robust and thermally stable)

Good features of Mid-Range Antennas

  • Long range
  • The invention generates the same magnetic field than a Mid and long-range antenna in a smaller size.
  • Lower component count
  • Same number of devices can be installed per vehicles.
  • Lower Assembly cost
  • A lower number of devices to be installed means lower assembly time and assembly costs.

Good Features of Short- Range antennas

  • Cost Effective: the invention has a lower cost (target accomplished) than a Mid Range antenna:
  • Less Ferrite
  • Less Copper wire due to lower N value to achieve same inductance L
  • Smaller plastic housing and less potting/ coating / encapsulating materials to secure waterproof


Mechanically Robust

  • A shorter device with a lower L/D ratio withstands bending, torsion and flexion better.

Thermally stable

  • A shorter core produces smaller absolute changes in dimension with temperature. Contractions and dilatations affect less to the change of shape. The effect is minimized when the L/D ration is lower as the changes in effective permeability due to changes in L/D with temperature expansions are lower.

An embodiment with progressive reduction of core Width and Height.

Comparison results of a 124x 6.5x 3 Mid-Range core vs an 80x8x 29/6 Diabolo ™ core of identical MnZn Material.

Measuring H Field at 1meters and 3meters the 40% shorter Diabolo ™ core presents similar values and a much higher Q factor due to its higher effective permeability and lower number of turns thus lower DC Resistance.


PREMO is a Spain-based company engaged in the development, manufacture, and sale of electronic components with special focus on the key enabling technologies of the 4th Industrial Revolution: IoT, M2M, VR, Connected and Electric Vehicles. Our product portfolio includes RFID antennas (worldwide leader), AR/ VR Motion Tracking Sensors, power transformers, inductors & chokes, current sensors, EMC filters, and PLC components. In addition to our broad range of standard components (off-the-shelf products), PREMO also designs custom solutions to fit customer requirements, based on the latest technologies to help your systems be more efficient.

Over 1200 employees at 5 design centers and 3 production locations (Morocco, China & Vietnam), and an extensive sales network, let PREMO have a global presence in more than 36 countries to meet our customers specific needs.

We’ve been a preferred supplier for more than 56 years thanks to our strong commitment to business excellence, engineering support, reliable delivery and the quality of our products.



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