Abstract: An electrostatic transducer (100) comprises an electrically conductive backplane member (102) having an array of through apertures (112); a spacer member (104) disposed over the backplane member (102), the spacer member (104) having an array of holes (114) therethrough, the holes (114) each having a maximum lateral dimension less than twice a minimum lateral dimension; and a flexible electrically conductive membrane (106) disposed over the spacer member (104). The transducer (100) is arranged in use to apply an electrical potential which gives rise to an attractive electrostatic force between the backplane member (102) and the membrane (106) thereby moving portions of the membrane (106) spanning said holes in the spacer member (104) towards said backplane member (102).

Abstract: An electrostatic transducer (100) comprises an electrically conductive first member (102) having an array of through apertures (112) and one or more further members (104, 106). The one or more further members (104, 106) include a flexible electrically conductive second member (106) arranged in use to be displaced from an equilibrium position towards the first member (102) by an electrostatic force in response to an electrical potential applied to one or both of the first member (102) and the second member (106). At least one (104) of the one or more further members is resiliently deformable and is arranged in use to exert a resilient biasing force biasing said second member (106) back towards said equilibrium position when displaced therefrom by said electrical potential.

Abstract: A class D audio amplifier provides both an audio output signal and a DC bias voltage to an electrostatic transducer (9). In the amplifier, a modulated sequence of pulses is generated by an input module (1) in response to an input audio signal. The sequence of pulses is amplified by an output module (3) using high speed switching output transistors (4, 5). An output signal is generated by applying a low pass filter (8) to the amplified pulses, and the output signal is provided to the transducer to produce audible output. The amplified sequence of pulses is also used to drive a voltage multiplier module (10) to provide bias voltage for the electrostatic transducer (9). In other embodiments, the bias voltage is provided by a bias voltage module which reverses the bias voltage at intervals, and a phase reverser (13) reverses the phase of the signals fed to the output module (3) simultaneously with reversal of the bias voltage.

Abstract: An electrostatic transducer (100) comprises an electrically conductive backplane member (102) having an array of through apertures (112); a spacer member (104) disposed over the backplane member (102), the spacer member (104) having an array of holes (114) therethrough, the holes (114) each having a maximum lateral dimension less than twice a minimum lateral dimension; and a flexible electrically conductive membrane (106) disposed over the spacer member (104). The transducer (100) is arranged in use to apply an electrical potential which gives rise to an attractive electrostatic force between the backplane member (102) and the membrane (106) thereby moving portions of the membrane (106) spanning said holes in the spacer member (104) towards said backplane member (102).

Abstract: An electrostatic transducer (100) comprises an electrically conductive first member (102) having an array of through apertures (112) and one or more further members (104, 106). The one or more further members (104, 106) include a flexible electrically conductive second member (106) arranged in use to be displaced from an equilibrium position towards the first member (102) by an electrostatic force in response to an electrical potential applied to one or both of the first member (102) and the second member (106). At least one (104) of the one or more further members is resiliently deformable and is arranged in use to exert a resilient biasing force biasing said second member (106) back towards said equilibrium position when displaced therefrom by said electrical potential.

Abstract: An electrostatic transducer comprises an electrically conductive first layer (1), a flexible insulating second layer (25) disposed over the first layer, and a flexible electrically conductive third layer (26) disposed over the second layer. Between the first and the second layers are provided spacers (24) and between the second and the third layers are provided spacers (27). The spacers may be provided by strips of adhesive or by bonding the layers together by welding, for example. The first layer (1) is provided with an array of through apertures (5) each having an inlet (6) facing the second layer (2) and an outlet (7). In response to signals applied to the first and third layers, the second and third layers have portions which are displaced towards the outlets of the apertures by electrostatic forces. The apertures (5) may have conducting walls and the walls may converge.

Abstract: An electrostatic transducer comprises an electrically conductive first layer (1), a flexible insulating second layer (25) disposed over the first layer, and a flexible electrically conductive third layer (26) disposed over the second layer. Between the first and the second layers are provided spacers (24) and between the second and the third layers are provided spacers (27). The spacers may be provided by strips of adhesive or by bonding the layers together by welding, for example. The first layer (1) is provided with an array of through apertures (5) each having an inlet (6) facing the second layer (2) and an outlet (7). In response to signals applied to the first and third layers, the second and third layers have portions which are displaced towards the outlets of the apertures by electrostatic forces. The apertures (5) may have conducting walls and the walls may converge.

Abstract: A class D audio amplifier which provides both an alternating signal and a DC bias voltage to an electrostatic transducer (9). The amplifier comprises an input module (1) for generating a modulated sequence of pulses in response to an input audio signal, and an output module (3) for amplifying the sequence of pulses, which includes high speed switching output transistors (4, 5). A power supply (6) provides a supply voltage to the switching output transistors (4,5). A low pass filter (8) receives the amplified sequence of pulses and generates an output signal for the transducer. The amplified sequence of pulses from the output module (3) is fed to a voltage multiplier module (10) which provides a constant bias voltage for the electrostatic transducer.

Abstract: The present invention provides a liquid viscosity sensor comprising an ultrasonic source, a sampling body and an ultrasonic receiver. The sampling body includes a sampling face contactable by a sample of liquid, in use. The source is operable to generate a longitudinal ultrasonic wave which follows a path through the body to the sampling face and onwards to the receiver. The body is configured such that the longitudinal wave emanating from the source is transformed into a horizontally polarised shear wave prior to reaching the sampling face, and the horizontally polarised shear wave is re-transformed into a longitudinal wave before reaching the receiver. There is provided a sensor adapted to utilise the interaction of a horizontally polarised shear wave at a liquid solid interface to measure viscosity, while eliminating the need to provide both a source and receiver configured to generate and receive horizontally polarised shear waves.

Abstract: A system to perform measurements on liquids, meat, viscous sugar or starch-based materials, and other foodstuffs using air-coupled ultrasound is provided. The technique uses ultrasonic transducers (advantageously capacitive transducers with polymer membranes), to generate ultrasonic signals in air, and to receive these signals after they have passed through the material under test. An ultrasonic pulse-compression process is then applied to increase the sensitivity of signals transmitted through the materials.