Flexible Ultrasonic Sensors Based on Printed Electronics: Principles, Architecture and Perspectives

Flexible ultrasonic sensors based on printed electronics

Printed electronics now makes it possible to imagine a new generation of sensing devices: lighter, thinner, more flexible and easier to integrate into complex systems.

Among these emerging technologies, flexible ultrasonic sensors represent a highly promising approach for applications such as non-destructive testing, structural health monitoring, embedded measurement systems, and material diagnostics.

At NeoTronis, we are exploring the development of these innovative architectures by combining flexible substrates, printable functional materials, and electronic designs adapted to mechanical and acoustic constraints.

1. Principle of an Ultrasonic Sensor

An ultrasonic sensor operates by generating and/or detecting mechanical waves with frequencies above the audible range, typically higher than 20 kHz.

Ultrasound frequency spectrum: from audible sound to high frequencies

In a conventional architecture, an active element converts:

• an electrical signal into a mechanical wave in emission mode;

• or a mechanical wave into an electrical signal in reception mode.

This conversion is usually based on a piezoelectric material, which can deform when exposed to an electric field and, conversely, generate an electrical charge when subjected to mechanical stress.

Ultrasonic sensors are commonly used for:

• distance or position measurement;

• interface or defect detection;

• material characterization;

• structural health monitoring;

• detection of cracks, delamination or inclusions;

• medical or wearable instrumentation.

  
  

2. Why Make Ultrasonic Sensors Flexible?

Conventional ultrasonic transducers are generally based on rigid structures, which can be bulky and difficult to integrate onto non-flat surfaces.

However, many modern applications require mechanical conformability, such as:

• bonding onto curved surfaces;

• integration into lightweight or flexible parts;

• use on moving structures;

• reduction of weight and thickness;

• discreet integration into an existing product.

A flexible ultrasonic sensor makes it possible to place the transducer closer to the target surface while minimizing its mechanical impact on the monitored system.

This approach is particularly relevant for:

• composite materials;

• curved metallic structures;

• technical films;

• wearable or embedded systems;

• applications with strong integration constraints.

  
  

3. Contribution of Printed Electronics

Printed electronics consists of depositing functional materials onto a substrate using processes such as:

• screen printing;

• inkjet printing;

• dispensing;

• slot-die coating;

• or other functional printing techniques.

For flexible ultrasonic sensors, this approach can be used to print all or part of the following elements:

• conductive tracks;

• electrodes;

• dielectric layers;

• functional active layers;

• connection interfaces;

• specific patterns designed to optimize signal propagation or reception.

The main advantages are:

• Design freedom

  • Printing enables the creation of specific geometries adapted to the targeted function: patches, sensor arrays, segmented electrodes, matrix structures, and more.

• Compatibility with flexible substrates

  The sensor architecture can be deposited on flexible supports such as:

  • PET;

  • PEN;

  • polyimide;

  • TPU;

  • other technical films.

• Reduced thickness and weight

  • The overall structure can be significantly thinner and lighter than a conventional ultrasonic sensor.

• Industrial potential

  • Printed processes are compatible with semi-industrial or industrial production approaches, including roll-to-roll or panel-based manufacturing.

4. Typical Architecture of a Printed Flexible Ultrasonic Sensor

A flexible ultrasonic sensor based on printed electronics generally relies on a multilayer architecture. As an example, it may include:

• Flexible substrate

  • The main mechanical support, ensuring the geometric stability of the structure.

• Printed conductive electrodes

  • These can be produced using silver, carbon, copper or other conductive inks compatible with the chosen process.

• Piezoelectric or electromechanically sensitive active layer

  • This layer performs the electromechanical transduction.

    Depending on the architecture, it can be printed, laminated or integrated as a functional film.

• Encapsulation or protection layer

  • This layer protects the system against humidity, abrasion, environmental stress or chemical exposure.

• Connection area

  • This allows the sensor to be connected to the excitation, readout or signal processing electronics.

Multilayer architecture of a printed flexible ultrasonic sensor

Depending on the application, the sensor can be designed as:

• emission-only;

• reception-only;

• or both emission and reception.

Sensor arrays can also be developed for scanning, multipoint monitoring or localization applications.

5. Technical Design Challenges

Developing a flexible ultrasonic sensor does not simply mean making a conventional transducer flexible. Several physical and technological constraints must be considered.

• Electromechanical coupling

  The conversion efficiency between electrical energy and acoustic energy strongly depends on:

  • the active material;

  • layer thickness;

  • interface quality;

  • adhesion between layers;

  • electrode geometry.

• Resonance frequency

  • The operating frequency is a key parameter.

    It depends on several factors, including:

    • the nature of the piezoelectric material;

    • its thickness;

    • the overall mechanical structure;

    • mounting conditions;

    • the propagation medium.

    In a flexible sensor, this frequency can also be affected by the curvature or deformation of the substrate.

• Acoustic attenuation

  • Polymer materials used as substrates or encapsulation layers may introduce higher acoustic losses than traditional rigid structures.

    The choice of materials and layer stack must therefore be optimized to preserve signal quality.

• Stability under bending

  The device must maintain its performance under:

  • bending;

  • cyclic mechanical stress;

  • variations in bending radius;

  • thermal and humidity cycles.

• Electrical connection

  • The interconnection area is often a critical point.

    It must ensure:

    • electrical robustness;

    • mechanical reliability;

    • compatibility with assembly processes;

    • good repeatability.

      
      

6. Sensor Interface Electronics

A flexible ultrasonic sensor is not limited to its printed structure. Its performance also strongly depends on the associated interface electronics.

A typical system may include:

• an excitation circuit to generate electrical pulses;

• a low-noise receiving stage;

• analog signal conditioning;

• filtering and amplification;

• an analog-to-digital converter;

• a digital processing chain.

Depending on the application, the system may require:

• time-of-flight measurement;

• echo detection;

• amplitude analysis;

• frequency-domain processing;

• correlation algorithms;

• drift compensation;

• diagnostic algorithms.

At NeoTronis, this system-level approach is essential: an efficient sensor also requires robust and well-adapted readout electronics, consistent with the physics of the transducer.

7. Use Cases and Application Areas

Printed flexible ultrasonic sensors can be relevant for many sectors.

• Non-Destructive Testing

  • Inspection of parts or structures without damaging them, including detection of cracks, delamination, voids or internal defects.

• Structural Health Monitoring

  • Continuous monitoring of structures such as composites, panels, tanks, technical parts or bonded assemblies.

• Industry and Instrumentation

  • Measurement of presence, thickness, interfaces or material condition in compact systems.

• Mobility and Aerospace

  • Integration onto curved surfaces, lightweight structures or advanced materials.

• Medical and Wearable Devices

  • Thin and conformable sensors adapted to complex contact geometries.

• Soft Robotics

  • Integration into deformable systems requiring mechanically compatible sensors.

8. Technological Challenges Still to Be Addressed

Although this technology is highly promising, several challenges remain before moving from concept to industrial product:

• control of printed layer repeatability;

• long-term performance stability;

• environmental resistance;

• optimization of acoustic efficiency;

• reliability of interconnections;

• sensor calibration;

• validation in real application conditions;

• compatibility with customer assembly processes.

Developing a high-performance flexible sensor therefore requires a global approach combining:

• materials science;

• printing processes;

• mechanical design;

• analog and digital electronics;

• testing and characterization protocols.

  
  

9. The NeoTronis Approach

At NeoTronis, we develop innovative electronic solutions by combining:

• printed electronics;

• flexible sensors;

• embedded systems;

• signal conditioning electronics;

• functional prototyping;

• experimental validation.

Our goal is to support industrial companies and project owners in the design of custom devices, from:

• feasibility study;

• material and architecture selection;

• sensor design;

• associated electronics development;

• through to demonstrator or functional prototype.

Flexible ultrasonic sensors are a concrete example of this approach: combining functional performance, integration flexibility and process innovation.

Conclusion

Flexible ultrasonic sensors based on printed electronics open the way to a new generation of measurement and monitoring systems, capable of being integrated onto complex surfaces while maintaining a thin and lightweight architecture.

Beyond mechanical flexibility, the real value of this approach lies in the ability to co-design the sensor, its substrate, its electronics and its final use case as a complete system.