Development Of A Body Surface Neuromuscular Electrical Stimulation Device

Functional injury of nerves and muscles has become a common disease in the international community.The number of patients with these diseases is large and the average age of the patients is high.Body surface neuromuscular electrical stimulation(SNMES)provides a non-invasive and effective treatment for this kind of patients,and its curative effect has been widely confirmed.A safe and effective portable neuromuscular electrical stimulation equipment is urgently needed by such patients.Battery-powered,wireless controled,light and miniaturized,low power consumption are the development trends of portable electrical stimulation equipments,at the same time,a good portable electrical stimulation equipment should provide accurate and wide-range stimulation parameters to adapt to different treatment goals.Noadays most SNMES equipments adopt current source stimulation mode because CSS mode is easy to achieve charge balance,but the circuit structure of CSS mode cannot meet the requirements of low power consumption and small size.In contrast,the circuit structure of voltage source stimulation(VSS)mode has the advantages of small size and low power consumption,but the VSS mode faces big challenges in solving charge balance problem.Based on the above problems,a kind of SNMES equipment is developed by adopting VSS mode in this paper.The main work contents includes:(1)Design of boost module.In order to generate effective electrical stimulation,a boost module based on coupled inductance is proposed to convert the 3.0V-4.2V supply voltage of the power supply battery into a 10V-200 V stimulation voltage.This module adopts a PID/PI feedback loop to adapt to changes of stimulation load,realizing a wide range of rapid adaptive adjustmen of the simulation voltage to load.(2)Design of rectifier module.In this paper,the H-bridge rectifier circuit and bootstrap drive technology are combined to control four high-voltage MOSFET with four independent switch signals,so that the stimulation cycles is divided into several independent stages,a highly adjustable biphasic pulse stimulation waveform is generated with a pulse width of 10-500 us and a stimulation frequency of 2-100 Hz,which provides a basis for charge balance.(3)Design of charge balance module.A charge metering and load model sensing circuit structure is proposed,which includes current sensor,metering capacitors,short circuit switches,and single pole double throw switch.The proposed circuit structure only takes up small size and can monitor the stimulation current in real time,measures the amount of charge flowed through the human body each stimulation,predicts the stimulation load model composed of the human body and electrodes,and further adjust the stimulation pulse width based on the measurement and monitoring results to achieve charge balance.In addition,a short-circuit phase is proposed,which periodically shortcircuits the electrodes and the ground to eliminate the risk of charge accumulation caused by sampling errors.The combination of charge balancing and short-circuit phases keeps charge accumulation below a very low level,that is,the residual voltage after each cycle of stimulation is less than or equal to 36 V.(4)Power consumption optimization.The method of adjusting the switch frequency of the boost module according to the instantaneous output power is proposed to improve the efficiency of the boost module under light load,and greatly reduces the power consumption of the boost module within the switch frequency range allowed by the inductor equipment.In this article,a control SOC integrated with Bluetooth,ADC,OP,etc.is used to integrate the above modules into a complete electrical stimulation system,and finally a prototype has been successfully prototyped with size of 55mm×55mm×15mm,and the prototype is virified by experiments.The developed VSS equipment has been proven having a number of advantages,such as safe and reliable,small in size with a wide range of stimulation parameters,low power consumption(When the stimulation power is 128 m W,the overall power consumption of the system is 579 m W),and having freindly human-computer interaction.