Flexible Fan-Out Wafer-Level Packaging Based Wireless Multichannel Surface Electromyography (sEMG) System for Muscle Monitoring

Surface Electromyography (sEMG) wearable devices are a non-invasive solution for muscle monitoring both for therapeutics as well as in spinal cord and neurosurgery. Conventional sEMG devices are typically rigid, bulky, wired, expensive, and need specialized medical personnel to operate them whereas flexible sEMG systems are compact, lightweight, flexible, wireless, and inexpensive. The “rigid PCB” approach is a popular way to make wearable sEMG systems, and there are commercially available products such as BioStampRC from MC10, Delsys TrignoTM Avanti. Most of these devices have electronics circuitry integrated on rigid PCBs which limit the overall flexibility of the device, as well as making them uncomfortable to wear.

Here, we demonstrate an sEMG system on our flexible platform called “FlexTrateTM” that allows solderless heterogeneous integration using die-first flexible Fan-Out Wafer-Level Packaging (FOWLP) technique. FlexTrateTM allows heterogeneous integration of bare dielets at 20-40 µm pad pitches not achievable using flexible PCB technology. Moreover, integrating smaller inorganic dielets in place of bulky packaged chips on a flexible organic platform allows for lower form factor and flexibility. The state-of-the-art flexible and wearable sEMG systems are simple and typically support just one sEMG channel. In this work, we have demonstrated up to 12-bipolar configuration sEMG channels on FlexTrateTM. We call this system “FlexsEMG”.

Increasing the number of channels helps to provide increased spatial resolution and improves analysis of the muscles by evaluation of muscle fiber conduction velocity (MFCV) which is a biomarker for many physiological and muscular conditions. Overall, the FlexsEMG system is 75 mm x 45 mm x 1 mm in size and integrates a Bluetooth low energy (BLE) 5.0 version chip, an efficient front-end data processing dielet that supports 12-bipolar sEMG channels, passives, multiple gold capped copper vertically corrugated dry electrodes. The device is powered by a rechargeable battery and a removable adhesive is used to secure the device on the skin. The FlexsEMG system is mechanically robust, light weight (~ 5 g), and is completely foldable without any performance degradation. The completely biocompatible system can be used as a long-term wearable device to wirelessly monitor muscular activity and abnormalities in real time. We use our device to record the sEMG signals of the biceps brachii muscles. The recorded signals have a high signal to noise ratio (SNR) of > 20 dB as the subject’s biceps brachii muscles are contracted from lifting a 4.5 kg weight. We also evaluated mean frequency and MFCV of the bicep muscle using this device. The ability to acquire the signals in a mobile setting enables the study of many muscular physiological phenomena and disorders especially in a clinical setting during surgery and rehabilitation.

A. Alam1, Randall Irwin1, Pragathi Venkatesh1, M. Molter1, A. Kapoor1, B. Gaonkar2, S , M. S. Joseph3, L. Macyszyn2, and S. S. Iyer1 1ECE Department, Henry Samueli School of Engineering, 2Department of Neurosurgery, David Geffen School of Medicine, Center for Heterogeneous Integration and Performance Scaling, UCLA, 3CSULA, CA, USA, email: arsalanalam89@ucla.edu