Wireless Devices For Medical Applications

The deployment of medical electronics in healthcare plays a significant role to overcome many problems in disease treatment and diagnosis. For advanced applications, wireless solutions are preferred. The wireless technologies offer a new dimension of therapy or diagnosis, when wires are often bulky, unsafe, uncomfortable or even impossible to be deployed in some circumstances. The wireless communication devices can be categorized into two groups, active and passive, depending on the power sources operating electronics. The active devices draw powers from a battery, while the others harvest powers from external or internal sources. In this work, two medical applications are studied for pain management and gastroesophageal reflux diagnosis using active and passive wireless approaches, respectively. The pain management systems are based on neurostimulation and neurorecording principles. The system requires batteries in implants for wireless communication. The neurostimulation can significantly improve pain relief when used on carefully selected chronic pain patients. An integrated recording and stimulating system has been designed, developed and used in animal experiments. The system consists of miniature components to record neuronal signals from the spinal cord and to activate the stimulation in the brain wirelessly. The system is equipped with a feedback function and decision making capability to automatically activate the stimulation from the recorded signals. A wearable prototype was tested in anesthetized rats. The results show that, when suitable stimulation parameters are used, the brain stimulation inhibits neural responses which may cause pain. For gastroesophageal reflux diagnosis, a new method of wirelessly detecting reflux in esophagus was proposed. Based on passive telemetry using inductive links, impedance of the refluxates can be determined remotely. The impedance variation can be determined from either amplitude or frequency changes of the detected signals. Planar coils integrated with electrodes on flexible substrates have been fabricated for amplitude detection. A circuitry connected with the sensing electrodes has been built for frequency detection. The devices are characterized in acid and non-acid solutions including the experiments in animals. Both techniques were used in implantable sensors without a battery to distinguish air, water and acid reflux wirelessly with a reader. The design methodology can also be applied to other sensors to monitor physiological conditions in human body.