Transcutaneous Electrical Nerve Stimulation (TENS)

Main Points: Mechanism of pain. Functions and features of TENS unit . Circuit Design. Realizing Design into Hardware. Results. Conclusions .

Mechanism of Pain: Pain is felt as a result of the brain's response to electrical (neural) and chemical (hormonal) changes in the body as a result of damage. Signals from damage or injury are picked up by sensory receptors in nerve endings. The nerves then transmit the signal via the nerves to spinal cord and brain.

Mechanism of Pain:

Pain Relief: Pain can be managed in the short term using analgesics, but long-term use can be detrimental to the patient's health. Side effects of the long use of analgesics may affect on liver, kidney or stomach. In many cases where pain is constant, a medical practitioner or physiotherapist may recommend the use of a TENS unit. Why TENS? Because it is safe, effective and virtually with no side effects.

Functions and Features of TENS: A TENS unit provides electrical stimulation to the painful area using electrodes attached to the skin. Some scientists say: electrical signal v nerve sensation stops natural pain relieving substances (endorphins) no pain massages to brain no pain.

Features: 1- Two different modes: a- Continuous (continuous stream) b- Intermittent (short bursts) Usually the continuous mode is used but for long term treatment intermittent mode is used 2- Adjustable. We can control three variables: a- Output voltage. b- Width of the pulses. c- Pulse rate.

Features: Continuous Mode: Output Voltage: Adjustable from 12V to 80V. Pulse Rate: Adjustable from 4.6Hz to 410Hz. Pulse Width: Adjustable between 70 and 320 µs. Intermittent Mode : Duty cycle: 24% at 1.2Hz

Circuit Design of the Device: 9 volts battery Step up converter: composed of transformer and DC to DC converter. Switching oscillator. Intermittent oscillator.

Circuit Diagram:

Realizing Design into Hardware: Collecting components ‘’flight’’: We call it ‘’flight’’ because we had to bring the components from overseas. Unfortunately the components were collected from Riyadh, Jeddah, Jordan, Japan and China.

Making Project Board: We connected the components in our project board as shown in figure to test the function of the circuit. After that we tested the circuit connections and circuit output we corrected the faults that raised.

Make PCB: We used OrCAD program to make the layout.

After that we printed the layout in PCB by using ultraviolet exposure unit ,then we started mounting components on the PCB.

Results: Continuous mode: The output volt=79v. The frequency=362 Hz.

Results: Intermittent mode: The output volt=82v The frequency=108 Hz.

Discussion: Due to the small size and light weight of the TENS device, we think we can integrate it with other medical devices like therapeutic ultrasound which is used sometimes to reduce joints stiffness.

Discussion: In this device there are only two electrodes, so we think it will be a good idea to double the electrodes to cover more muscles.

Discussion: Placing the electrodes was a little problem for us because the adhesive substance is not effective for long time ,so we had an idea to implant the electrodes inside sock to be worn during the therapy , also make a gloves for hand's muscles.

Discussion: This device might be used to treat the face muscles. (Bell's Palsy disease) , This is often due to the partial facial paralysis that occurs on one side of the face.In this case the face muscle is small compared to other muscles ,so we need small electrodes to capture the effected muscles .

Conclusions: We could reach our goals to make a medical device that relief chronic and acute pains started with studying the electrophysiological parameters, then studying design stages of the circuit which gives these parameters as output. After that we applied the studies from paper to the practical work. During all stages of the project we had to solve some problems which we got by applying the designed circuit onto circuit board, we corrected it to get the expected results. Finally, we tested the output of the circuit by applying the output directly to the muscle.