Title: MultiSense - Devising and Manufacturing mm-Wave High Data Rate Low Latency On-Skin Technologies
Funder: Engineering and Physical Sciences Research Council

Abstract: This multidisciplinary project will exploit an established UK based team's track record comprising RF & bio-sensing engineers, battery & materials scientists, and CPI, the UK National Catapult for Printed Electronics. Centred around Additive Manufacture and aimed towards scale-up, we will transform nascent wireless skin-based sensing to the high data rate capacity offered by upcoming communications systems using license-free 24 GHz channels. This will enable new streaming of biodata for remote diagnostics, monitoring and care, as well as ultra-low impact wireless EEG for forehead/ear/hair free regions. It will make possible the use of multiple sensing tags on multiple people simultaneously monitoring physiological parameters such as accelerometery (for activity tracking), photoplesmography (for heart rate monitoring), and sweat (for metabolite monitoring). At high data rate, this represents a step change over available technologies. Manufactured on highly flexible, potentially stretchable, substrates the skin tags take the form factor of temporary tattoos and are highly long lasting, discrete for social acceptability, and can follow the micro-contours of the skin to give a large contact surface area and consequently sensing signal-to-noise ratio. To achieve our aims, we will advance wireless mmWave devices, on-skin electronics, low-power bio-sensing, and additive manufacture. Additionally, through CPI, we will develop scale-up processes for these mmWave devices. Through existing investments the applicant team is positioning the UK for the large scale manufacture of on-skin sensor tags. EP/P027075/1 is creating an inkjet printing based manufacturing process for sensors on flexible substrates which avoids cleanrooms, uses graphene based ink formulations for biodegradability, and can be scaled up large run roll-to-roll screen printing. EP/R02331X/1 added the capability to print TiO2/LiFePO4 batteries integrated into the platform, removing a key integration bottleneck. This new proposal 'MultiSense' seeks to build upon the manufacturing base created by these two projects, extending it to overcome the key sensing limitation of current on skin tags: that they can only monitor one parameter from one person at a time, and at a comparatively low data rate. These projects are further limited to producing first principle non-elastic, low capacity integrated batteries and UHF frequency (868 MHz) RF devices which require print resolutions similar to conventional masks for wet etching (typically 200 um). Further, our experience of UHF RFID reveals transmission delays of 6 ms, and a reliable data rate upper limit of only 400 bps (corresponding to a sample rate of just 30 Hz for a modality such as accelerometry). In MultiSense, we propose to overcome these limitations by moving from RFID to 24 GHz ISM (Industrial, Scientific Medical) band transmission, where very substantial uncongested bandwidth is available, offering orders of magnitude higher bit rates than UHF. In addition, the smaller wavelengths will increase antenna miniaturisation on integrated elastic substrate batteries, requiring print resolutions of 50 um. The new batteries will be solid state and polymer based with elastic current collectors. We will also investigate the mmWave signal surface guiding over the skin as a mechanism to allow for inter-patch communications. Sensing robustness will be improved as minor variations/misplacements in the sensor positions could be captured, and potentially corrected for in software. This will impact on diagnostic EEG measurements where currently entire datasets (from cabled electrodes) might be abandoned when individual electrodes disconnect. To enable the measurement of skin-based transmission between patches with new dry electrode designs, we will work with International Research Visitor Professor Koichi Ito of Chiba university, an expert in human phantom design.

Lay abstract: Our overall objective is to create on-skin, temporary tattoo-like sensors which integrate a range of sensing modalities for physiological parameters, with integrated printed batteries, and 24 GHz wireless transmission for extremely high data rate applications. This will significantly enhance the capabilities of ultrathin label-like sensors which can be fabricated at scale by roll-to-roll (R2R) processes. Specifically we will: 1. Design and test sub-mm thick 24 GHz antennas, screen/inkjet printed onto flexible bio-compatible substrates (Deliverable D1). Moving to 24 GHz gives the potential for very high bandwidth, low latency, data communications far beyond that currently possible with on-skin sensor tags, but at present the performance on skin-compatible flexible substrates at 24 GHz mmWave is unknown. To provide the enabling technology for future self-organising networks with self-locating nodes we will create dual radiation mode antennas for 24 GHz off-body and skin-surface transmission (D2). 2. Increase the capacity of printable polymer based layered battery structures to meet the power demands of 24 GHz wireless operation, adding solid state and polymer based with elastic current collectors to increase their suitability for on-skin application (D3). This will leverage the printed battery manufacturing platform which is being created in EP/R02331X/1 and trialled for scale up roll-to-roll processing at the high value manufacturing catapult CPI, but made for inelastic non-skin based applications. 3. Decrease the feature size of the silver/reduced graphene oxide printed manufacturing pipeline created EP/P027075/1, to enable the reduced feature sizes of 50 um needed for dual mode 24 GHz operation with no reduction in conductivity (D4). An additive manufacturing approach will be taken, avoiding cleanrooms, using printing approaches for both scale up, and potentially personalised manufacture. New silver and graphene (for bio-degradability) ink formulations will be explored in Manchester controlling graphene/rGO flake size for dispersion properties, which will then be passed to CPI for sheet fed and R2R processing (D5). 4. Create low power instrumentation for sensing a range of physiological parameters simultaneously, allowing 24 GHz sensing from a single tattoo-like tag, not possible with data-rate limited RFID based approaches (D6). Responding to an unmet clinical need, particular attention will be given to enabling multi-channel electroencephalography (EEG) for hair free regions where 64+ sensors are required on the head to record brain signals of interest in applications such as epilepsy diagnosis and human-computer interaction studies. Creation of a high timing resolution test platform to allow pre-saved signals to be accurately re-played for system characterisation (D7). 5. Devise a wide-band, DC-24 GHz, body phantom where both the bio-acquisition parts and RF parts can be tested simultaneously without requiring a person in-the-loop (D8). This will combine DC phantoms previously reported by CI Casson with visiting researcher Prof. Ito's expertise in RF phantoms. We will develop a complete demonstrator system for the fabricated tags showing their operation with a 24 GHz reader over several metres and including on-skin performance. The system will include a graphical user interface to make clear to stakeholders the potential of the technology (D9).

Research activity codes: 2.6 RESOURCES AND INFRASTRUCTURE (AETIOLOGY);4.5 RESOURCES AND INFRASTRUCTURE (DETECTION)
Health categories: GENERIC HEALTH RELEVANCE