GB1575273A

GB1575273A - Acoustic microscopes

Info

Publication number: GB1575273A
Application number: GB1972578A
Authority: GB
Original assignee: Marconi Co Ltd
Current assignee: BAE Systems Electronics Ltd
Priority date: 1978-05-16
Filing date: 1978-05-16
Publication date: 1980-09-17

Description

(54) IMPROVEMENTS IN OR RELATING TO ACOUSTIC MICROSCOPES (71) We, THE MARCONI COMPANY LIMITED, a British Company, of Marconi House, New Street, Chelmsford, Essex.

CMl 1PL, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to acoustic microscopes.

As is known focused sound waves may be used for high magnification microscopy. As is also well known, the shorter the wavelength of operation, the higher the resolution tends to be, but at the same time transmission losses tend to increase at the higher frequencies with such microscopes as at present known.

One object of the present invention is to provide an improved acoustic microscope, which is capable of operating at relatively high frequencies with satisfactorily low transmission loss.

According to this invention, an acoustic microscope comprises a carrier for an object microscopically to be examined and an acoustic transmitter having a transducer adjacent said object carrier consisting of a curved sheet of electrically polarised plastics material having on either surface thereof a surface electrode and means for energising said two surface electrodes whereby acoustic energy generated by said transducer is concentrated in a region occupied in operation by an object carried by said carrier.

Preferably said curved sheet of electrically polarised plastics material is hemispherical.

Preferably again said transducer is mounted in one end of a cylindrical support member at the other end of which is provided an acoustic attenuator. Where said curved sheet of electrically polarised plastics material is hemispherical, normally this will be mounted in a hemispherical depression in said one end of said support member.

Preferably means are provided for driving said object carrier in two orthogonal directions whereby an object carried by said object carrier may be scanned.

Said acoustic microscope may be provided as a transmission acoustic microscope, in which case an acoustic receiver will be provided with a transducer adjacent said object carrier, but on the side thereof remote from the transducer of said acoustic transmitter.

Preferably said acoustic transmitter and said acoustic receiver are similar.

Said acoustic microscope may also be provided as a reflection microscope, in which case said acoustic transmitter is provided to act additionally as an acoustic receiver.

Normally acoustic frequency generating means, preferably capable of generating signals in the gigahertz region, will be connected to energise the two surface electrodes of the transducer of said acoustic transmitter and an amplifier will be connected to receive signals from the two surface electrodes of the transducer operating as a receiving transducer. Where said last mentioned two transducers are constituted by the one transducer, said generator and said amplifier will normally be connected to said two surface electrodes of that one transducer via a transmit/receive switch, whereby to be operative alternately.

Preferably the output of said amplifier is connected to a cathode ray display unit having a line and frame scan signal generator which is also connected to control orthogonal microdrive units arranged to move said object carrier in two orthogonal directions, whereby an object carried by said object carrier may be scanned.

Normally said transducer or transducers and said object carrier are enclosed within a chamber which may be evacuated or into which gas or liquid may be introduced.

The invention is further described with reference to the accompanying drawings in which, Figures 1 and 2 schematically illustrate a transmission acoustic microscope in accordance with the present invention, and Figure 3 illustrates a reflection acoustic microscope in accordance with the present invention.

Referring to Figure 1, the acoustic microscope consists of an object carrier 1, which is arranged to be moved vertically (as viewed) by a vertical microdrive unit 2 and horizontally (i.e. in a direction perpendicular to the plane of the drawing) by a horizontal microdrive unit 3. The object carrier 1 is provided to carry a slide or like object, which is required to be viewed with high magnification.

On one side of the object carrier 1 is an acoustic wave transmitter 4, whilst on the other side of the object carrier 1 is an acoustic wave receiver 5. Transmitter 4 and receiver 5 are essentially similar.

The acoustic wave transmitter 4 consists of a cylindrical support member 6 of brass, the end of which adjacent object carrier 1 is formed with a hemispherical depression represented at 7, which has a focus at a finite point 8 in the object plane of the object carrier 1. The opposite end of the member 6 is formed as an acoustic attenuator 9. Fitted within the hemispherical depression 7 is a transducer which as best seen from Figure 1 consists of a hemispherical shaped sheet of electrically polarised piezo electric plastic sheet 10, specifically polyvinylidene fluoride polarised in a high field as knownperse. The inner surface of hemispherical sheet 10 is provided with a hemispherically shaped surface electrode 11, whilst the other surface of sheet 10 is provided with a hemispherically shaped surface electrode 12.Attached to inner surface electrode 11 is a lead 13, whilst attached to outer surface electrode 12 is a lead 14.

Correspondingly, acoustic wave receiver 5 consists of a cylindrical support member 15 having at an end adjacent the object carrier 1 a hemispherical depression represented at 16 and at the other end an acoustic attenuator 17. Within hemispherical depression 16 is a receiving transducer, which is essentially similar to that illustrated in Figure 2, but in this case the leads corresponding to leads 13 and 14 are referenced 18 and 19.

The leads 13 and 14 attached to the two surface electrodes of the transmitting transducer of transmitting member 4 are connected to an acoustic generator 20 capable of generating frequencies in the gigahertz region.

The leads 18 and 19 of the receiving transducer of receiving member 5 are connected via an amplifier 21, which provides input video signals for a display unit 22. Line and frame scan control signals for the display unit 22 are derived from a line and frame scan generator 23, which also provides suitable control signals to the vertical microdrive unit 2 and the horizontal microdrive unit 3, so that the horizontal microdrive unit 3 moves the object carrier 1 in one step per frame, whilst the vertical microdrive unit 2 moves the object carrier 1 in order to provide verti cal scanning during that frame.

The transmission and reception members 4 and 5 together with their transducers and the object carrier 1 are enclosed as represented by the dashed line 24 within a chamber in which a suitable liquid or gas medium is introduced.

Referring to Figure 3, in essence the microscope is similar to that already described with reference to Figure 1 except that in this case, the receiving member 5 is omitted together with its transducer and the transducer of the transmitting member 4 is utilised in addition for reception by reflection. The video generator 20 and the amplifier 21 are connected to the leads 13 and 14 of the transducer via a gate 25 in the form of a transmit/receive switch which is controlled as represented by the lead 26, alternately to connect the generator 20 and the amplifier 21 to the leads 13 and 14. Thus the transducer of the member 4 operates alternately in a transmissive and a receptive mode so that signals transmitted by the transducer in a transmissive period are received back from the object carried by the object carrier 1 during a non transmissive receptive period.

WHAT WE CLAIM IS: 1. An acoustic microscope comprising a carrier for an object microscopically to be examined and an acoustic transmitter having a transducer adjacent said object carrier consisting of a curved sheet of electrically polarised plastics material having on either surface thereof a surface electrode and means for energising said two surface electrodes whereby acoustic energy generated by said transducer is concentrated in a region occupied in operation by an object carried by said carrier.

2. A microscope as claimed in claim 1 and wherein said curved sheet of electrically polarised plastics material is hemispherical.

3. A microscope as claimed in claim 1 or 2 and wherein said transducer is mounted in one end of a cylindrical support member at the other end of which is provided an acoustic attenuator.

4. A microscope as claimed in any of the above claims wherein said curved sheet of electrically polarised plastics material is hemispherical and is mounted in a hemispherical depression in said one end of said support member.

5. A microscope as claimed in any of the above claims and wherein means are provided for driving said object carrier in two orthogonal directions whereby an object car

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. which, Figures 1 and 2 schematically illustrate a transmission acoustic microscope in accordance with the present invention, and Figure 3 illustrates a reflection acoustic microscope in accordance with the present invention. Referring to Figure 1, the acoustic microscope consists of an object carrier 1, which is arranged to be moved vertically (as viewed) by a vertical microdrive unit 2 and horizontally (i.e. in a direction perpendicular to the plane of the drawing) by a horizontal microdrive unit 3. The object carrier 1 is provided to carry a slide or like object, which is required to be viewed with high magnification. On one side of the object carrier 1 is an acoustic wave transmitter 4, whilst on the other side of the object carrier 1 is an acoustic wave receiver 5. Transmitter 4 and receiver 5 are essentially similar. The acoustic wave transmitter 4 consists of a cylindrical support member 6 of brass, the end of which adjacent object carrier 1 is formed with a hemispherical depression represented at 7, which has a focus at a finite point 8 in the object plane of the object carrier 1. The opposite end of the member 6 is formed as an acoustic attenuator 9. Fitted within the hemispherical depression 7 is a transducer which as best seen from Figure 1 consists of a hemispherical shaped sheet of electrically polarised piezo electric plastic sheet 10, specifically polyvinylidene fluoride polarised in a high field as knownperse. The inner surface of hemispherical sheet 10 is provided with a hemispherically shaped surface electrode 11, whilst the other surface of sheet 10 is provided with a hemispherically shaped surface electrode 12.Attached to inner surface electrode 11 is a lead 13, whilst attached to outer surface electrode 12 is a lead 14. Correspondingly, acoustic wave receiver 5 consists of a cylindrical support member 15 having at an end adjacent the object carrier 1 a hemispherical depression represented at 16 and at the other end an acoustic attenuator 17. Within hemispherical depression 16 is a receiving transducer, which is essentially similar to that illustrated in Figure 2, but in this case the leads corresponding to leads 13 and 14 are referenced 18 and 19. The leads 13 and 14 attached to the two surface electrodes of the transmitting transducer of transmitting member 4 are connected to an acoustic generator 20 capable of generating frequencies in the gigahertz region. The leads 18 and 19 of the receiving transducer of receiving member 5 are connected via an amplifier 21, which provides input video signals for a display unit 22. Line and frame scan control signals for the display unit 22 are derived from a line and frame scan generator 23, which also provides suitable control signals to the vertical microdrive unit 2 and the horizontal microdrive unit 3, so that the horizontal microdrive unit 3 moves the object carrier 1 in one step per frame, whilst the vertical microdrive unit 2 moves the object carrier 1 in order to provide verti cal scanning during that frame. The transmission and reception members 4 and 5 together with their transducers and the object carrier 1 are enclosed as represented by the dashed line 24 within a chamber in which a suitable liquid or gas medium is introduced. Referring to Figure 3, in essence the microscope is similar to that already described with reference to Figure 1 except that in this case, the receiving member 5 is omitted together with its transducer and the transducer of the transmitting member 4 is utilised in addition for reception by reflection. The video generator 20 and the amplifier 21 are connected to the leads 13 and 14 of the transducer via a gate 25 in the form of a transmit/receive switch which is controlled as represented by the lead 26, alternately to connect the generator 20 and the amplifier 21 to the leads 13 and 14. Thus the transducer of the member 4 operates alternately in a transmissive and a receptive mode so that signals transmitted by the transducer in a transmissive period are received back from the object carried by the object carrier 1 during a non transmissive receptive period. WHAT WE CLAIM IS:

1. An acoustic microscope comprising a carrier for an object microscopically to be examined and an acoustic transmitter having a transducer adjacent said object carrier consisting of a curved sheet of electrically polarised plastics material having on either surface thereof a surface electrode and means for energising said two surface electrodes whereby acoustic energy generated by said transducer is concentrated in a region occupied in operation by an object carried by said carrier.

ried by said object carrier may be scanned.

6. A microscope as claimed in any of the above claims and provided as a transmission acoustic microscope an acoustic receiver being provided with a transducer adjacent said object carrier, but on the side thereof remote from the transducer of said acoustic transmitter.

7. A microscope as claimed in any of the above claims and wherein said acoustic transmitter and said acoustic receiver are similar.

8. A microscope as claimed in any of claims 1 to 5 and provided as a reflection microscope said acoustic transmitter being provided to act additionally as an acoustic receiver.

9. A microscope as claimed in any of the above claims and wherein acoustic frequency generating means are connected to energise the two surface electrodes of the transducer of said acoustic transmitter and an amplifier is connected to receive signals from the two surface electrodes of the transducer operating as a receiving transducer.

10. A microscope as claimed in claim 9 and wherein said acoustic frequency generating means is capable of generating signals in the gigahertz region.

11. A microscope as claimed in claim 9 or 10 wherein said last mentioned two transducers are constituted by the one transducer, said generator and said amplifier being connected to said two surface electrodes of that one transducer via a transmit/receive switch, whereby to be operative alternately.

12. A microscope as claimed in any of claims 9 to 11 and wherein the output of said amplifier is connected to a cathode ray display unit having a line and frame scan signal generator which is also connected to control orthogonal microdrive units arranged to move said object carrier in two orthogonal directions, whereby an object carried by said object carrier may be scanned.

13. A microscope as claimed in any of the above claims and wherein said transducer or transducers and said object carrier are enclosed within a chamber which may be evacuated or into which gas or liquid may be introduced.

14. An acoustic microscope substantially as herein described with reference to Figures 1 and 2 of the accompanying drawings.

15. An acoustic microscope substantially as herein described with reference to Figure 3 of the accompanying drawings.