Latest results at HdM

In the IAD (Innovative Applications of Printing Technologies) research group at the HdM (Hochschule der Medien – Stuttgart Media University), the focus of the project research is on the thin, flexible printed Li-ion foil batteries that will be used to power the BEWELL skin patch. In addition to researching the printability of the electrochemically active materials, a comprehensive benchmarking study of substrates was carried out. The bendability of the battery is an important aspect, while at the same time sufficient barrier properties must be ensured. Ten substrate materials, mono films and composite films, were compared in terms of their mechanical, physical and surface properties. Modulus of elasticity, flexural rigidity, surface free energy, barrier properties (water vapour transmission rate WVTR), processability, dimensional stability and printability were determined. It turned out that a PET/Al/PET film with a total thickness of approx. 31µm had the best properties. Apart from the difficult handling in sheet-to-sheet screen printing presses (curling), the thicker PET films are advantageous there. In a final roll-to-roll process, however, the curling problem of the films does not play a role. The results (see diagrams below for examples) were presented at the IARIGAI (www.iarigai.org ) conference in Athens (at the University of West Attica) in September 2021. The paper was published at http://jpmtr.org/Advances_Vol_472021_online.pdf.

Comparing mechanical properties of different foils
Comparing WVTR of different foils
Prof. Dr. Huebner presenting at the IARIGAI conference

The contacting of the printed foil batteries was investigated and a riveting technique proved to be advantageous, see figures below.

Riveting tool
Film battery with rivets for contacting

Haptics Array

Four thin and conformable haptic elements were attached using an adhesive to an armband made of soft elastic fabric, comfortable to wear. The actuators were driven using a custom made PCB, capable of generating various waveforms and apply voltages between 0 and 95V. The connection between the actuators and the PCB was made using flying cables.

Haptic armband constitutive parts

After testing individual actuators at different locations on the arm, we were able to determine the locations that have the highest detection probability, even using low actuation voltages (<100Vpeak). The most sensible locations are situated around the elbow, especially the inner part of the arm seems to respond well to the haptic excitation. After this initial step, the actuators were placed on the armband on the inner part of the arm as shown in the figure below.

Use of a square pattern of haptic elements to deliver various messages to users.

Then various signals were sent to the tester (5 persons):

  • piezo 1 and 2 alternating rapidly
  • piezo 3 and 4 alternating slowly
  • piezo 2 and 4 simultaneously
  • piezo 1 and 3 simultaneously
  • activation order 1-2-3-4 repeated

The actuation frequency was on 250Hz and the voltage 95Vpeak. The tests were carried out in a lab environment, relatively noisy. The users (5, 3 male, average age 23 years) were not isolated during the tests, they did not wear noise cancelling headphones or any other device that reduced the noise level around them. They were seated or standing, with their arm moving occasionally. They were not forced to keep it from moving or to hold it in a prescribed position. They were asked to imagine that they are walking or running and were asked to act based on the interpretation they gave to each of the 5 signals.

All the users were able to detect the vibration from the actuators, giving an acceptable feedback level. The signals were designed to deliver the following messages to the user: 1 – accelerate, 2 – slow down, 3 – turn right, 4 – turn left, 5 – stop. However, we asked the testers to interpret the meaning of the signals freely. Some of them proved to be rather intuitive (signals 1 and 2), others needed input from the lab staff. The outcome of these tests is thus positive, as the actuators enable to deliver messages to users, and it shows that a learning session should be organized to make the messages clear.

Technology demonstrations

An early technology demonstration was shown in the Prinse 20 seminar end of January at VTT in Oulu Finland. There the Imec Museic evaluation board was connected with printed electrodes in the targeted patch form factor to measure ECG in wrist. The result is shown in Figure 1.

Figure 1: ECG sensing demonstration using printed electrodes and the Imec Museic evaluation board.

The next version of technology demonstrations for skin patches will utilize several functional layers integrated as a vertical stack structure as schematically illustrated in Figure 2.

Figure 2: Skin patch layer structure under development.

Vias on stretchable substrate

Printing multi-layered electronics on stretchable or flexible substrates needs a solution to fabricate electrically conducting vias from one layer to another through the substrates. VTT has developed a reliable via printing process on stretchable TPU substrate. Scientific manuscript is under preparation.

Charging of printed Lithium-Ion-Battery by perovskite solar cell

In order to create fully independent product without need for any external charger and external connectors, the battery is connected with a state-of-the-art perovskite module which has enough output voltage for charging the battery outside and also at indoor light conditions. The perovskite module is built onto flexible PET substrate and has round shape in order to be compatible for integrated with all other elements of the final product. In picture below, the processing steps, top and cross-section views and electrical performance are demonstrated of flexible PSC module created for BEWELL project at IMEC.

Powered by printed Lithium-Ion-Battery LIB

LIB were developed based on the BASMATI layout FP7, Contract No. 646159.

LIB Test cell in BASMASTI format

LIB Test cell in BASMASTI format

The big advantage of the research in BEWELL is a new quasi solid electrolyte, based on the PEO/LiTFSI system. This electrolyte warranties high mechanical stability and good cycle-ability. The EIS diagram of the cell is shown below

EIS diagram of the printed LIB cell

EIS diagram of the printed LIB cell

Also, a good cycle-ability could be shown.

Cycling diagram of the LIB test cell

Cycling diagram of the LIB test cell

This result is very encouraging. In the course of the project the electrolyte will be improved in terms of internal resistance and printability.

Wellbeing Patch by Beiersdorf

Generation 0 was used to measure electrocardiogram (ECG) signal and compared to standard lab equipment. Following a period of rest, the heart rate was raised through exercise on a stationary bike and once again brought to rest.

These are promising results which will be further improved in next generation designs where the electrode spacing is increased and the electrode configuration is optimized.

15.02.2022 update

Skin patch for monitoring emotional stress to control its negative effects on well-being and skin condition.

 

 

Physiological parameters continuously tracked by the skin patch to derive stress and wellbeing:

  • Electro-cardiogram (ECG): Cardiovascular activity, indicator for stress and body exertion
  • Electro-dermal activity (EDA): Sweat-gland activity, main indicator for stress
  • Acceleration sensor: Activity level/sleep
  • Other biosignals: e.g. temperature

Technical features:

  • Printed secondary battery
  • Photovoltaic charging
  • Flexible haptics module
  • Two-part design: Durable and removable part enabled by special adhesives