L. Niño de Rivera

Adaptive multi-channel portable stimulator based on PWM: A tool for micro-stimulation using multi-array electrodes

Electrical Stimulators are widely used in various medical specialties. Depending on the tissue that is going to be stimulated, physicians may adjust the characteristics of the stimulus signals such as frequency, amplitude, length and waveform. Commercial stimulators usually are just capable to generate preloaded waveforms and they cannot be adjusted freely. Moreover, the number of available channels is usually very low. However, not all medical treatments require the same stimulus. Actually, many medical conditions where the electrical stimulation is needed demand specific waveforms with different characteristics. Stimulus can vary in frequency, amplitude, time of application and form. This study describes a portable multichannel and adaptive electrical stimulator. The portable 16-channels stimulator presented in this paper consist of five sections; 1) an interface where the user is able to design the stimulation signal, 2) the transmission modules, one connected to a Personal Computer and the other one to the stimulation device, 3) microcontroller (MCU) that is going to organize the information received from the PC in order to generate the Pulse Width Modulation (PWM) signals (These PWM signals are injected into a set of low pass filters to transform these digital signals into analog waveforms) and 4) an attenuator to regulate the amplitude signal and restricts the current to avoid tissue damage. The presented system permits to design the stimulation signals according to the physician desires. The system was tested with real tissue under different stimulation patterns showing low current consumption and high input to output voltages relationship.

Wireless trans-corneal stimulus for the optical nerve based on adaptive modeling using continuous neural networks

Retinal prosthesis design has become a hot field of researching around the world. Restoring partial vision to the blind patients that suffer from degenerative disease has become an important medical and scientific task. However, there are some doubts on how to propose the stimulation signals. The same question arises when the stimulation may be done by trans-corneal or transdermic pathways. One method that could be used is to apply a no-parametric algorithm to obtain a nonlinear model representing the relationship between the optical nerve response signal and the stimulus inputs. Then, it can be applied an inverse model methodology to identify the unknown inputs required to obtain the desired optical nerve response. In this study, we proposed an adaptive modeling based in continuous neural networks (CNN) to obtain an artificial model of the relationship between the optical nerve response and the selective stimulation. This model tries to determine the adequate stimulation signals that will be applied on the trans-corneal or transepidermic part of the eye. Indeed, the input signal effectiveness will be measured as the degree of accuracy obtaining the desired response in the optical nerve. A set of CNN working as a parallel identifier provides the adaptive model of the aforementioned relation. An artificial optical nerve response was developed as well as the electrical stimulator for the trans-corneal area. These both designs were applied into the CNN identifier to test the methodology suggested in this paper. The numerical results demonstrate the accuracy achieved by the modeling algorithm.

Design of Embedded Image Based Electrical Trans-Corneal Stimulator

Once the human optical system stops working by different causes, it is usual to look for a possible cure based on optometric methodology. Visual prosthesis may be an option, especially when the optical nerve has not been damaged. One alternative to develop such prosthesis is to use an electrical transcorneal stimulator. Some recent papers have applied the cerebral plastic concept to justify why a repeated electrical stimulation can help blind (by an optical defect) patients to give a new reinterpretation of the reality. This paper reports the development of a particular electrical stimulator for the transcorneal area. Indeed, this device has embedded software used to treat the image captured by a CMOS camera, to produce the image segmentation throughout a set of polygons and to regulate the signal amplitude. The waveform was selected from the signals forms obtained in a regular retinographic study. The system has been tested off-line showing a good correspondence with the theoretical proposal. Ex-vivo tests also have been developed to analyze the tissue response using the signals produced by the stimulator.

Acquisition and processing of ERG signals

This paper proposes a low cost acquisition and processing system for electrical biopotentials that can be obtained of the cornea (electroretinography, ERG), of the brain (electroencephalography, EEG) and of the heart (electrocardiography, ECG) to mention ones. This system is built with discrete circuits and has a minimum level of amplification of 60 dB and a maximum of 100 dB alike has a pass band Butterworth filter of 4th grade with a bandwidth of 0.16 to 300 Hz. For the signals acquisition we used the sound card of the PC and through one program developed in MatLab, several techniques of filtered are applied in order to improve the signal and finally show it in a graph. This work shows biological signals acquired from the retina of a 24 years old man.

Optical vibrational states of diamond nanocrsytals

The phonon band structure and Raman response of diamond nanowires are calculated by means of the Born potential, including central and non-central interatomic forces, and a supercell model. The Raman scattering is studied by means of the local bond-polarization model based on the displacement-displacement Greens function within the linear response theory. Free standing, infinitely long and homogeneous quantum wires cross sections with the wire axis along the [001] direction are considered. The results show an important shift of the main Raman peak (highest optical mode) towards lower energies, in comparison with the bulk crystalline diamond case.