GB2222256A - Detector of body tissue dimensional change - Google Patents

Abstract

A device for detecting the change in dimension of a sample of human or animal body tissue, comprises a body of semiconductor material (1) (e.g. Hall effect device) and a magnet means (2), one of these being rotatable about the other. An arm (5), to which the sample can be connected, is attached to the rotatable element. When a current is passed through the semiconductor material and a magnetic field is applied at right-angles to the current, a voltage VH (effect voltage) can be measured between the sides of the semiconductor. <IMAGE>

Description

DETECTOR The present invention relates to a device for detecting the change in dimension of a sample of human or animal body tissue, for example the contraction or extension of a length of stomach muscle.

Known devices for this purpose include the following: 1. A graduated optical density vane that moves between an infrared source and a sensor. This is simple in concept bu the optical density vane requires specialised equipment and knowhow to manufacture it.

2. A moveable capacitor plate attached to a rotating shaft moving between fixed plates and forming a differential capacitor. This can be very sensitive but the capacitor vanes are difficult to manufacture. Sophisticated circuitry is required to drive the transducer, such as a stable oscillator and phase-sensitive detector. The apparatus is therefore expensive.

3. A magnetically coupled transducer which is a differential system similar to the plate capacitor transducer. This again requires sophisticated circuitry to drive it. It is stable in output voltages; its output charge is better than 1% for f15" and its output sensitivity is around 100mV/degree. However, this type of unit tends to be very expensive and has an angular deflection limited to +159.

An aim of the present invention is to provide a detecting device which is relatively simple and inexpensive.

Accordingly, the invention provides a device for detecting the change in dimension of a sample of human or animal body tissue, comprising a body of semiconductor material and magnet means, one of these being rotatable about the other, and wherein an arm, to which the sample can be connected, is attached to the rotatable means or body.

When a current is passed through the semiconductor material and a magnetic field is applied at right-angles to the current, a voltage VH (Hall effect voltage) can be measured between the sides of the semiconductor.

The relationship between the magnetic field and the current is: VH = RH B I d RH = Hall effect coefficient of the semiconductor material - for example Germanium semiconductor material produces the largest VH (Hall effect voltage) B = Magnetic Field (Gauss say) I = Current Amperes d = Thickness of material in cm say.

From this basic formula it can be seen that with RH, I and d constant, VH, the voltage across the semiconductor material, is directly proportional to B the magentic field.

A constant current and voltage amplification has to be provided which is cheaply and conveniently provided on the Honeywell manufacturers Hall effect device chip LOHET II (LINEAR OUTPUT HALL EFFECT TRANSDUCER).

In addition to being relatively simple and inexpensive, the invention has the advantage that the polarity of the output voltage from the transducer changes simply about the null point, so that complex circuitry to polarise the voltage about the null point is not required.

Preferably, the magnet means is rotatable about the transducer and may comprise a pair of magnets mounted in the wall of a hollow cylinder, inside of which the transducer can lie.

A preferred embodiment of the invention is described below, by example only, with reference to the accompanying drawings, wherein: Fig. 1 is a sectional view of a detecting device according to the invention; Fig. 2 is a front view of the device of Fig. 1; Fig. 3 is a diagram indicating the output from the transducer; and Fig. 4 is a diagram indicating, schematically, the movement of the arm and the accuracy of the detection.

As shown in Figs. 1 and 2, the detecting device comprises, a Hall Effect transducer 1 and magnet means 2.

The magnet means comprises a pair of magnets 3 mounted in a cylinder 4 surrounding the transducer 1. An arm 5 is attached to the cylinder 4 and a sample of body tissue can be connected to this arm.

The basic idea of the Hall Effect isotonic transducer is simple in concept. If a current is passed through a piece of semiconductor material a voltage can be measured across opposite faces, at right angles to the current flow, depending on the strength of the magnetic field that is applied across the material.

The Hall Effect isotonic (displacement) transducer can be built around the Honeywell SS9 series linear output Hall Effect transducer (LOHET II). The SS9 utilizes a new Hall Effect integrated chip which provides increased temperature stability and performance.

The cylinder 4 is attached to the arm or lever 5 via a spindle 6 and is freely rotatable about the tranducer 1 by means of a bearing 7. The cylinder, transducer and bearing are mounted within housing 8 having a rear end cap 9 through which the transducer connections can pass.

As seen in Fig. 2, the rotational movement of the arm (and thus the cylinder and magnets) about the horizontal is limited to approximately 30 each way, for reasons to be explained below.

A low moment of inertia has been achieved by using low mass materials for the lever and rotating parts of the transducer. The two magnets used to produce the Hall Effect are light plastic polymer bonded rare earth magnets. To reduce the mass of the magnets further they are bonded into a perspex cylinder and then machined down to a small diameter hollow cylinder to fit snuggly over the Hall Effect I.C.

This has left the mass low and concentrated towards the centre of rotation thus keeping the moment of inertia low.

The transducer drive unit circuitry is housed in a R/S metal case of dimensions 204 x 152 x 76 mm. The drive unit can drive one isotonic transducer or any number up to 4.

The power supply provides +4v DC mains derived and mains filtered. The +4v lines are also suppressed against voltage transients. Also inside the transducer drive unit there are four low voltage drift operational amplifiers (OP 07's) which are used to isolate the outputs of the LOHET II's built into the isotonic transducers. The OP 07's also provide filtering and gain. That is, the gain can be altered to adjust the sensitivity (mV/degree). The gain or sensitivity cna be increased quite considerably or fixed at some precise value. The gains of the operational amplifiers in the present unit are set to 2.

In use, the detector is clamped in position above the preparation, so that the lever moves in a vertical plane and is horizontal when at the midpoint of its travel.

The organ bath and tissue is prepared and tied on to the lever of the isotonic transducer. The whole of the assembly is tensioned so that the lever of the transducer appears horizontal to the eye ready for the experiment.

Power is applied to the isotonic transducer and its output is monitored with a DVM (digital volt meter) switched to the DC voltage range. If the output potential reading on the DVM is not zero, the body of the isotonic transducer is unclamped and gently rotated until the reading on the DVM is zero.

The transducer is then reclamped and is ready to connect to the pen recorder. Any small offset from the output of the transducer can usually be offset by the pen recorder.

The basic idea of the Isotonic Hall Effect transducer is simple in concept. As the lever rotates about the central axis, the magnetic housing and magnets move with it since the housing is integral with the lever. The output voltage from the Hall Effect device, which is fixed at the centre of rotation, is proportional to the vertical component of the magnetic field between the magnets.

Although the output voltage VH varies directly as the sine of the angle, the transducer output is restricted to the near linear portion between the points A and B on the side curve - See Fig. 4.

Since the sine and tangent of small angles are equal sin 20 = .36, tan 20e = .34) the relationship between VH in mV and 0 in degrees is linear up to +20 to better than 6%. Actually, the error is less than this owing to the selfcompensating nature of the isotonic measurement. Because of the normal method of attachment of the cord and muscle (or ileum) to the lever of the isotonic transducer the contraction or extension of the muscle is closely proportional to the output voltage VH. See Fig. 4 and the following proof.

VH = IBksinO Sin O = A'D b (b = length of lever and is constant) VH = C(A'D) where C = IBk b where: AE is the uncontracted length of muscle and cord. After contraction of the muscle the muscle and cord length is DE.

If the angle at E is small or AE is long compared to the length of the lever then the displacement AB = A'D which is proportional to VH.

Advantages of the above described detector include the following: With most rotational transducers there must be some measure of identifying the polarity of the output voltage about the null point. As it has already been explained, the current types of isotonic transducers using capacitive or magnetic principles requires complex circuitry to polarise the voltage about the nul point.

Because of the physics of the Hall Effect, the polarity of the voltage changes simply, about the null point, if the component of the magnetic field changes. The reversal of the magnetic field is changed by simply rotating the magnet about the Hall Effect device.

The Hall Effect isotonic transducer basically requires only a power supply, an amplifier and two light plastic magnets. Up to the present time we have been using Honeywell devices with the Hall Effect chip and amplifier mounted on a chip. These devices are cheap and readily available. And with the use of light plastic polymer rare earth magnets a cheap, sensitive and reliable unit can be made.

The isotonic detector is cylindrical in section, 25mm in diameter, 90mm long and weighs 80 gms.

The materials used in the construction of the isotonic transducer are perspex, duralamin and stainless steel.

Linearity to +25 or 3% worse case.

Sensitivity 50mV/degree minimum (adjustable) Moment of inertia of transducer without lever 0.75 gm cm2 Moment of inertia of lever 4.1 gm cm2 Total amount of inertia 4.85 gm cm2 Breakaway torque less than 0.05 gm cm Output impedance 470 can be near zero if required.

Output drift with time is less than 2mV.

Sensitivity - 1 minute of arc. That is, a voltage change can be observed when the lever is moved through 1 minute of arc.

Claims (5)

1. A device for detecting the change in dimension of a sample of human or animal body tissue, comprising a body of semiconductor material and magnet means, one of these being rotatable about the other, and wherein an arm, to which the sample can be connected, is attached to the rotatable means or body.

2. A device according to claim 1, wherein the magnet means are rotatable.

3. A device according to claim 2, wherein the magnet means comprise a pair of magnets mounted in the wall of a cylinder which surrounds the semiconductor material.

4. A device according to any preceding claim, wherein the body of semiconductor material is a Hall Effect tranducer.

5. A device for detecting the change in dimension of a sample of human or animal body tissue, substantially as herein described and as illustrated in the drawings.