GB2277268A - Transcutaneous electrical nerve stimulator without skin contact - Google Patents

Abstract

A TeNS device which transmits electrical signals on to an area of the body to relieve pain without the use of electrical contact to the skin has pulse signals transmitted by antennae built within a self-contained unit. Means are provided whereby the frequency of the signals can be pre-set or automatically cycle within two set frequencies. The frequency is determined by a variable resistor R1 which may be coupled to an automatic timing circuit. <IMAGE>

Description

Improvements Relating to Tanscutaneous Electrical Nerve Stimu lators These are often known as TeNS and are referred to as TeNS devices in the following text.

TeNS devices have been used in hospitals for many years for the relief of pain. These devices consist of a control box and electrodes connected to the control box by electrical wires. The control box which is usually operated by the mains electrical supply, produces electrical pulses which are carried by the electrical wires to the electrodes which are, during treatment for pain, placed at or around the area to be treated.

The control box generally has a number of adjustable controls one of which is to adjust the voltage appearing at the electrodes. The other controls may give control of the waveform of the pulses. frequency of the pulses and automatic change of frequency of pulses between two frequencies.

The TeNS devices are of a transportable nature designed to be used in hospitals by trained personnel.

Treatment at the hospitals involves the patient connected to the TeNS device and usually the patient is required to be lying down. The electrodes are attached to the skin at or around the area to be treated. Often special creams are used on to the skin to ensure that good electrical contact is made. Several arrangements are known to be used for attaching the electrodes such as use of tapes or bandages and suction cups. Each electrode is connected to the TeNS device by wires to carry the electrical signals. The controls are adjusted to a desired waveform and to a fixed or automatically varying frequency. The TeNS device is then switched on and is normally arranged such that the voltage of the pulses is virtually zero. The voltage is then slowly increased until the patient feels a comfortable level of electrical sensation. After a few minutes, the sensitivity of the skin changes and the sensations reduce and the signal voltage is further increased to a comfortable level.

The treatments may be given for any length of time but usually for up to about thirty minutes and is determined by the hospital staff knowledgeable with the use of TeNS devices.

Battery operated portable TeNS devices are now available which can be used in a similar manner but allow the user to move about whilst connected to the TeNS device.

These portable devices generally have two or four electrodes which have to be suitably placed on the skin near the painful area.

These portable devices have controls that generally provide a control for the output voltage of the pulses and frequency of pulses. A further control may also be provided for controlling the waveform of the pulses within a limited range. The electrode provided with these devices are usually of the self-adhesive type or of a type which require to be taped on to the skin.

These portable devices allow the user to move about whilst wearing the device. However, the movement of the user can cause the electrode to dislodge and to give poor contact to the skin. The poor contact then gives an uncomfortable burning sensation requiring immediate attention.

In all, the present TeNS devices, there is a necessity for the use of electrodes with each one connected by wires to the control box.

As can be appreciated, these devices are cumbersorne to use and have several disadvantages. There is the problem of correctly holding the electrodes on the skin which can become loose or detached causing a burning sensation.

Clothing worn by the user may need to be removed to gain access for the application of the electrodes. The connecting wires have to be suitably positioned about the body so that they are not likely to be pulled and the controls have to be set to the desired settings which are initially unknown and are usually found by trial and error. These machines are inhibitive when in use and socially undesirable. The battery power is often very short in the order of tens of hours. 4 The present invention discloses a means by which all these disadvantages are overcome.

In accordance with the invention, there is provided an electrically insulating control box wherein arrangments are provided to include all the necessary components to give pain relief without the use of electrodes or wire.

Contained within this box is the battery, an electronic assembly which controls the frequency of pulses and provides high voltage pulses and an antennae arrangement which are used to transmit the output pulses. Using the battery as the source of electrical supply, the pulses are produced electronically and include means by which changes of frequency of the pulses can be automatically varied or adjusted to a fixed frequency. When used with the automatic arrangement, the frequency can be set to change gradually or in steps between two frequency limits.

The pulses produced are of a low voltage as determined by the battery used which may be any of the type generally available and be suitable for the size of the control box used.

As the pulses are of a low voltage, a step-up transformer is used to increase the pulse voltage to several hundred volts and may be increased to several thousand volts depending on the desired output power required.

The output wires of the transformer in themselves, would be too small to effectively transmit the high voltage energy pulses. Therefore, provisions are made within the control box to increase the transmission area by use of antennae.

The antennae are designed so that two or more electrically conductive areas are formed, preferably adjacent to each other and connected to the output winding of the transformer. Depending on the number of 'antennae used and their shape, more than one high voltage winding may be used.

In use, the control box is held in close proximity to the painful area of the body so that the transmitted voltage can be received.

As these signals travel through the air, there is no need for direct contact to the skin and as these signals are able to penetrate through normal clothing, the control box may be held in position more easily than presently known TeNS devices.

The size of the antennae arrangement requires to be large enough to give adequate coverage of the area to be treated and hence have a good transmission area and equally be small enough to be effective. Experience has shown that this TeNS device can give satisfactory results when made to a size of a typical bank card but of course, can be smaller or larger.

Further advantages of this TeNS device are that as no electrical contact is necessary to the skin, then the sensitivity of the skin does not alter as no sensations are felt at all. For the same reasons, the shape of the wave form used is of no consequence. Due to the latter reason, the pulse width can be kept very small and therefore, the battery drain is reduced,considerably extending the useful battery life.

The present invention will now be further described showing one arrangement, by way of example, embodying the present invention with reference to the accompanying drawings.

Figure 1 illustrates one preferred antennae arrangement based upon the use of copper clad printed circuit board PCB which has been etched to leave two areas of copper shown shaded and marked antenna 1 and antenna 2. The two copper areas are shown connected to each of the secondary winding T3 of transformer T. Transformer T also has two primary windings T1 and T2 where one end of each winding is connected together and connected to a light emitting diode LED. The other side of the LED is connected to the battery BT via a switch S. The other pole of the battery is connected to the emittor E of the transistor TR1 with capacitor C2 connected across the battery BT after the switch S. The collector C of transistor TR1 is connected to the free end of the winding TI.

The free end of winding T2 is connected to the base B of transistor TR1 via resistor R1 and capacitor C1 which are connected in parallel.

The operation of the circuit described is now explained.

When switch S is closed, capacitor C2 will charge to the battery voltage and maintain a steady voltage. Current will flow through the LED, winding T2 and resistor R1 into the base B of the transistor TRI. As the capacitor C1 would be in a discharged state, it would increase the voltage appearing at the base of transistor TR 1 9ivill conduct and current will rise in winding T1. As T1 and T2 are inductively connected, the rising current is induced into winding T2 and charges capacitor C1.When the rising current in T1 reaches its maximum as determined by the resistive components of T1 and TR1, the current stabilises and hence no further current is induced into winding T2.

However, as capacitor C1 has now been charged and with reference to the positive side of the supply, C1 causes the base voltage of TR1 to go negative and thereby switching off the transistor TR1. Capacitor C1 then is discharged by resistor R1 until the voltage at the base of transistor TR1 is sufficient to cause it to start to conduct and cause current to flow through T1 and inductively in T2.

Regenerative action takes place, causing transistor TR1 to rapidly saturate and maximum current again flows to repeat the cycle described above. Each conduction of the transistor TR1 produces a pulse which is induced into winding T3.

Transformer T consists of windings T1 and T2 which consist of a few turns, e.g. twenty per winding Whereas T3 has a relatively higher number of turns e.g. 1000. The construction of the transformer may be of any of the presently known arrangements. The ampiification of the pulses appearing at Ti being determined by the ratio of the windings T1 and T3. Winding T2 provides a feed-back signal to switch the transistor TRi.

As the pulses produced are of a very short duration and the time between pulses is relatively much greater, the battery power consumption is minimal. Furthermore, as the time between each pulse is determined by the discharge time of capacitor C1 in conjunction with resistor R1. the change in battery voltage has negligible effect on the frequency of the pulses.

To give a larger transmission of these so produced high voltage pulses from T3, the ends of the winding are connected to electrically conductive areas of a suitable size.

These electrically conductive areas shown as antenna 1 and antenna 2 are conveniently formed by use of a printed circuit board as described earlier.

The light emitting diode LED is included as a visual indication to show the circuit is switched on and operating and may be omitted if desired.

With switch S closed, capacitor 2 is charged to the battery BT voltage and provides stabilisation of the battery voltage during pulses when transistor TR1 conducts. However, this capacitor may be omitted if the choice of battery used is capable of providing the power required when during the conduction period of transistor TR1 a pulse is produced.

Resistor R1 is a variable resistor the resistance of which can be set to provide the desired frequency of pulses.

Referring now to figure 2, the circuit shows additional features of the invention so far explained with reference to figure 1.

As previously explained, the resistor R1 controls the discharge time of the capacitor C1. Figure 2 shows one means by which the discharge rate of capacitor C1 can be automatically altered to give a gradually changing frequency of pulses from one set frequency to another set frequency and gradually change back to the first said frequency.

Figure 2 shows an integrated circuit it555, which is one of a range of integrated circuits designed for fiming and pulse generating applications. in this application, the integrated circuit it555 is connected in an astable mode producing a square wave output when switch S is closed.

The pin connection for the integrated circuit It 565 and the additional components is as follows.

Pin 1 is connected to the negative (-) side of the battery BT and pins 4 and 8 are connected to the positive4 (+) side of the same battery via the light emitting diode LED and the switch S. Pins 2 and 6 are connected together and also to resistors R4 and R5 and capacitor C3. The other end of R5 is connected to pin 3 of 1C555 and the other end of C3 is connected to the positive side of the battery BT as pins 4 and 8 described above. One end of the resistor R3 and the emitter E of the transistor TR2 is also connected to the same connection as just described. The free ends of resistors R3 and R4 and the base B of transistor TR2 are connected together. The collector C of the transistor TR2 is connected to the base B of transistor TR1 via resistor R2.

The integrated circuit 1C555 is preferably of a low power consumption type. The pin designation are predermined by the manufacturer and when connected as described above, pin 3 gives a square wave output. The frequency of the output square wave can be set to the required frequency by the value of the resistor R5 and the value of the capacitor C3.

If, for example, R5 and C3 values are chosen to give one cycle per ten seconds, then the output voltage at pin 3 of lC555 will give approximately a five second voltage which is near to one polarity of the battery and then for approximately five seconds a voltage which is near to the other polarity of the battery and continue to repeat the cycle.

To provide this continuous square wave output, when the voltage at pin 3 is lC555 is near the negative side of the battery polarity, capacitor C3 is charged at a rate determined by R5. When this voltage, predetermined by the integrated circuit lC555 and sensed by pihs 2 and 6 the 1C555 triggers and causes the pin 3 voltage to be near to the positive side of the battery, Capacitor C3 is then discharged at a similar rate as above by resistor R5 until a second trigger voltage is reached whereby the voltage at pin 3 again changes to the negative side of the battery.

In this way, a continuous square wave output at pin 3 of 1C555 can be generated as long as the battery supply is made available by closing switch S.

From the operation of the circuit just given, it will be understood that whilst the voltage at pin 3 of 1C555 is changing from one said voltage to the other said voltage determined by resistor R5 and capacitor C3, the voltage across the capacitor C3 is gradually changing in sympathy with the voltage at pin 3 at a time constant determined by the value of the capacitor C3 and resistor R5.

If,for example, the time cycle already referred to is ten seconds, then the voltage across the capacitor C3 will gradually increase for five seconds and decreases over the next five seconds and continues to repeat the cycle every ten seconds. This gradually changing voltage is used to change the conductance of transistor TR2 via resistor R4 and R3, the values of which determine the operating point of TR2. The values of R3 and R4 are chosen such that when capacitor C3 is in a discharged state, the voltage at the base B of transistor TR2 is low and the transistor TR2 is in a non- conductive state. Equally, when the capacitor C3 is charging the voltage at base B of Transistor TR2 is also increasing thereby the conductivity of the transistor is increased in sympathy.

As already explained with reference to figure 1, resistor R1 determines the frequency of pulses generated in conjunction with capacitor Ci.

When transistor TR2 is in a non-conductive state, then effectively, resistor R1 gives one frequency due to its value and effects the discharge time of capacitor C1.

When the transistor TR2 is in a conductive state, then the discharge time of capacitor C1 is determined by the combination of the transistor conductivity and resistor R2 which are connected across resistor R1. The combined effect is to change the discharge rate of capacity C1 and hence give another frequency of pulses. a As the conductivity of transistor TR2 is continually changing as determined by capacitor C3 and resistor R5 in conjunction with the integrated circuit IC555, then the pulses appearing at the antenna 1 and 2 will gradually change between two pre-set frequency limits pre-determined in the manner explained.

Figure 3 shows a general lay-out of the components shown in figure 2 whereby they are soldered to a printed circuit board PCB which has the appropriate conducting tracks left to connect the components to form the circuit.

Figure 4 shows a double-sided printed circuit board whereby the antennae are formed on one side and the tracks on the other side. The components are then surface mounted and thereby allowing the assembly to be constructed on one PCB.

In conventional printed circuit boards, the components are on the plain side of the board with the component wires fed through holes and soldered on to the conductive tracks on the other side.

Claims (9)

1. A Transcutaneous Electrical Nerve Stimulator (TeNS) that transmits electrical energy to relieve pain without the necessity of making any physical or electrical contact to the skin.

2. A TeNS device as Claimed in Claim 1 wherein transmission of electrical pulses isvby means of electrically conductive areas to provide effective transmission.

3. A TeNS device as Claimed in Claim 2 wherein the electrically conductive areas are enclosed within an electrically insulating box which also contains the pulse generating components and the battery supply.

4. A TeNS device as Claimed in Claim 2 and Claim 3 wherein the pulses are generated electronically.

5. A TeNS device as Claimed in Claim 4 wherein controls are provided to adjust the frequency of pulses.

6. A TeNS device as Claimed in Claim 5 wherein the frequency of pulses automatically changes within pre-determined frequencies.

7. A constructional arrangement wherein the transmitting conductive areas as Claimed in Claim 2 are formed on one side of a double sided printed circuit board and the other side of the board is arranged to mount the necessary components to produce and control the pulses as Claimed Claims 3 to 6.

8. A self-contained TeNS device capable of providing pain relief as Claimed in any of the preceeding Claims.

9. A self contained TeNS device as claimed in any of the preceeding claims that provides relief or cure for any physiological or psychological conditions.