U.S. Philips Corporation

Domino Printing Sciences Plc

Richard F Mitchell

Richard Stevens

Martin Redwood

Philip D White

Frederick Warren Smith

Christopher K Davis

Eileen Read

Jerzy Marcin Zaba

Paul A Moore

David W Parker

Robert J Murray

William Anthony Denne

John S Palfreeman

Bernard David Rapson

A liquid collection apparatus comprises a liquid collecting device and liquid conduit for transferring liquid from the liquid collection device. Porous liquid absorption device is positioned between the liquid collection device and the liquid conduit. Pump device pumps liquid from the liquid conduit, the pump device generating a pressure in the conduit that is sufficient to draw liquid through the liquid collection device but is insufficient to draw a gas/liquid surface through the liquid absorption device.

Liquid collection

In order to obtain greater flexibility in the design of a linear-phase electrical filter comprising an acoustic surface wave device including a pair of apodized transducers intercoupled by means of a multi-strip coupler, for example to obtain more equal contributions by the two transducers to the gain versus frequency characteristic of the filter, the transducers are apodized differently but have mutually complementary non-linear phase characteristics. First a transfer characteristic corresponding to the collective contribution to the desired overall gain versus frequency characteristic of the filter, is derived in terms of the z-transform and the roots or the reciprocals of the roots of the resulting polynomial in z.sup.-1 are found. These roots or reciprocals are then divided into two groups so that at least one pair of non-identical roots or reciprocals which have equal ratios between their real and imaginary parts and the product of the moduli of which is equal to unity are included one in each group. Two further polynomials are then found which have as their roots or the reciprocals of their roots those of the first group and those of the second group. The two transducers include successive active electrode pairs which have relative weights proportional to the coefficients of the successively increasing powers of the variable in one further polynomial and the variable in the other further polynomial. The active electrode pairs are connected with polarities in accordance with the signs of the corresponding coefficients.

Acoustic surface wave filter device with asymmetric transducers and

A surface acoustic wave bandpass filter consists of input and output interdigital transducers (IP, OP) with an interposed track changing multistrip array (MSA). A conventional broadband array (MSA) is divided into two groups of strips with respect to a center of symmetry (C) separated by different distances along the input track (T1) and the output track (T2) such that the array (MSA) suppresses a predetermined frequency. If the input and output transducers (IP, OP) both have a double electrode configuration, electrode separation .lambda.o/4, providing a fundamental passband at a corresponding frequency f.sub.o and an equal amplitude passband at the third harmonic 3f.sub.o, then a separation difference of .lambda.o/6 between the groups of the array (MSA) in the two tracks (T1, T2) can suppress the third harmonic passband in the filter output. The two groups of the multistrip array may be further sub-divided to suppress more than one frequency (FIG. 5). Also a multistrip array arranged in groups to provide a shaped bandpass response may have each group divided to suppress a selected harmonic passband of the array (FIG. 6).

Acoustic wave devices

In order to make optimum use of the available transmission channels in an information transmission system, such as a trunked mobile ratio transmission system, where a number of uncoordinated users may wish to signal to a central control point in addition to using the channels for another purpose, the central control point monitors the channels and, when a channel is or becomes free, sends a command signal on that channel. When a user who is waiting to signal receives the command signal he chooses one of a predetermined number of immediately following time slots in an effectively random manner and sends his request in that slot in digital message form. The central control point sends an acknowledgement in the next time slot if and only if it receives the request in an error-free manner. If a user does not receive such an acknowledgement in response to the transmission of such a request he tries again when he receives the next command. The channel is used for other purposes, if necessary, at times other than those occupied by a command signal plus the subsequent predetermined number of time slots. If requests from more than one user should clash in the same time slot they will not be received by the control point in an error-free manner, this being determined by means of error check bits provided in the request message.

Information transmission system

In order to form a first-come first-served queue in an information transmission system employing a common transmission channel when several transmitters of the system try to gain access to the channel when it is already occupied, without employing a further transmission channel to a point at which an account is kept of the order in which the various transmitters request access, each transmitter which tries to gain access in these circumstances is caused to delay after the channel subsequently free before it actually accesses the channel, this delay being inversely proportional to the time the corresponding transmitter has waited. Thus the transmitter which has waited the longest gains the channel first and causes the other waiting transmitters to continue to wait.

Transmitter apparatus for an information transmission system

In an acoustic wave device having a pair of spaced apart reflectors forming a resonant cavity, each reflector consists of an array of parallel reflective elements. At least one of the reflectors is weighted not by simple withdrawal of reflecting elements from a nominal uniform array but instead by substituting reflective elements of the uniform array with elements providing both net-zero reflection at required positions and also at least partial compensation for the velocity perturbation which would be produced by such simple withdrawal. Such weighting may be used to suppress the side lobes of the reflector response and hence improve the stopband performance of the acoustic wave device and, for example, a coupled resonator filter in which that device is incorporated.

An acoustic wave resonator device comprises a substrate carrying a pair of spaced apart reflectors forming a resonant cavity that supports only three adjacent distinct resonant mode frequencies. An interdigital transducer is disposed on the substrate between the reflectors and includes an array of electrodes symmetrically arranged relative to a central point of the cavity to form a plurality of electrode pairs with the electrodes of each pair equally spaced on opposite sides of the central point. The central point of the cavity coincides with a node or an anti-node of the standing wave. If the two electrodes of each electrode pair are connected to the same terminal then the transducer has zero net coupling with one set of alternate modes of the cavity, whereas if said two electrodes are connected to opposite terminals then the transducer has zero net coupling with the other set of alternate modes.

An acoustic wave resonator device includes two pairs of coupled spaced apart reflectors which define two resonant cavities. The two cavities are each provided with two interdigital transducers which provide intercavity coupling. Additional reactance coupling between the transducers in one cavity combines with the equivalent cavity reactance to provide series or parallel resonance at a selected pole frequency.

An acoustic surface wave device employs a substrate structurally orientated to enhance the propagation of acoustic surface skimming bulk waves. Multiple reflections from opposed end faces of the substrate establish an acoustic surface skimming bulk standing wave at a predetermined frequency. An interdigital transducer couples to the standing wave. A plurality of devices may be intercoupled to provide a bandpass filter.

The input and output transducers associated with an acoustic surface wave resonator, or with respective acoustically coupled cavities, are split into staggered pairs. Furthermore they are located with respect to the standing wave pattern(s) and connected to input and output terminals in such manner as to suppress the response of the output transducer to travelling waves received directly from the input transducer and reduce the stopband level of the device associated with that response.

Acoustic surgave wave resonator devices

An electrode structure within the cavity of an acoustic surface wave resonator, e.g. an interdigital transducer or a multistrip coupler, has two sections separated by an odd integral multiple of a quarter wavelength of the standing wave in the cavity and located with respect to the center of the cavity so that all the electrodes are midway between a node and an adjacent antinode of the standing wave. Distortion of the resonator response due to reflection by the electrodes of the transducer or coupler is suppressed by this arrangement.

Acoustic surface wave devices

A surface acoustic wave band-pass filter comprising a piezoelectric substrate having on one surface first and second SAW resonators tuned to the same frequency and coupled together. An input transducer is coupled to the first resonator and an output transducer is coupled to the second resonator. Each resonator is preferably formed by two spaced apart aligned grating reflectors and the two resonators are preferably coupled by an array of discrete parallel metallic strips extending between the two cavity resonators.

Electrical filters including coupled resonators

An acoustic surface wave device comprising a monocrystalline body of piezoelectric material having a launching and receiving transducer applied to a planar ASW propagation surface. The piezoelectric material and the orientation of the propagation surface and the axial propagation direction relative to the crystal axes are selected to provide zero piezoelectric coupling between the transducers and a longitudinal axial bulk wave and that one of the two shear axial bulk waves that has substantially no component of particle motion perpendicular to said propagation surface. A method of manufacturing the aforesaid ASW device is also disclosed.

A surface wave TV I.F. filter has a transducer with two passbands. Each is unsymmetrical with respect to itself and a mirror image of the other. A second transducer suppresses one of the passbands.

Acoustic surface-wave devices

An acoustic surface wave filter comprising a monocrystalline wafer of bismuth silicon oxide having a special orientation of the ASW propagation surface and the interdigital transducers relative to the crystal plane whereby pick-up of undesired bulk waves is reduced.

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Merstham, United Kingdom

Richard F Mitchell