## 4 Electroceticals--Intelligent Environments
### Neural Stimulations and Electrode Arrays  
The brain plays a significant role in all functions and activities of life, controlling cell growth, biological and neural activities, physical motions, and many more. Hence, understanding and controlling brain functions have always been an ambitious goal for researchers and industries (Table 1). A bioelectronic device such as the deep brain stimulator has successfully helped patients in treating Parkinson's disease or related neurological disorders, and recently, further technological enhancements such as current directing electrode configurations, neuromorphic electronics, synaptic devices, brain chips, etc., have been pursued for the next generation's stimulation system [68; 69]. [PERSON] et al. successfully developed an implantable device to activate brain neurons. It consists of three parts, a small module of extracranial brain activator, a base station for transmitting power wirelessly, and an intelligent device for monitoring and controlling operations [70]. A small module of a coin size was implanted under the brain's scalp, the base station transfers the power wirelessly to the implanted device to stimulate neurons, and the intelligent device monitors and controls all operations. The pre- and post-stimulation studies revealed noticeable brain activity after injecting stimulative signals. Further, this suggests that brain activity causes a significant improvement in memory and sensory skills [70]. [PERSON] et al. have focused on the operational effectiveness of brain implants for obsessive-compulsive disorder epilepsy and Parkinson's disease [71]. Moreover, the research group extended their attention to other areas such as chronic pain, traumatic brain injury, depression, stroke recovery, etc., [71]. However, developing a low-power wirelessly compatible brain-stimulating device is a significant challenge due to their operational and device compatibility limitation in real-time. [PERSON] et al. have successfully introduced a miniaturized implantable optoelectronic brain stimulator [72]. The device operates with low power and consists of integrating application-specific integrated circuit (ASIC) and triple junction gallium arsenide (GaAs) based photovoltaic (PV) unit fabricated via microfabrication technology to stimulate the cortex, which is shown in Figure 2a,b. The design feasibility was demonstrated on the benchtop and in vivo acute rat model [72]. The developed cortex stimulator and its electronic components assembly representation are illustrated in Figure 2. The utilization of infrared energy as an energy source supplying wirelessly to an implanted device to generate sufficient stimulative responses is mainly because of their larger wavelength nature that can easily and deeply penetrate the human biological material without loss of energy. Furthermore, the infrared wave wavelengths match the organic and inorganic human body material wavelengths, meaning organic and inorganic biological material's resonance frequency is in the range of infrared wave frequency. Therefore, the infrared waves could deeply penetrate the body and supply sufficient energy to a PV cell without creating any abnormal conditions for the biological cells. In this integrated deep brain stimulator system, the gallium arsenide (GaAs) based photovoltaic (PV) device efficiently converts the incoming infrared energy to electricity [72]. The chip of Manchester downlink efficiently delivers the converted incident power to the electrodes to trigger stimuli by remote command (Figure 2c). The developed integrated assembly of the photonic-electronic chip within a small area of 2.9 mm \(\times\) 1.7 mm having wireless capability helps address all relevant issues during stimulation [72]. If the device-defined coding sequence matches the incoming downlink bit sequence among the multiple devices on neurogranin, the device activates the stimulations. The implant delivers the electric charge that is converted photons to electrons to the targeted cortex [72].