The patent's inventor is Single,
This patent was filed on
From the background information supplied by the inventors, news correspondents obtained the following quote: "This invention relates to an implanted auditory prosthesis. The invention relates particularly, but not necessarily exclusively, to a method of, and a control system for, charging of a battery of a totally implantable auditory prosthesis such as a cochlear implant or an implanted hearing aid.
"Hearing loss, which may be due to many different causes, is generally of two types, conductive and sensorineural. In some cases, a person may have hearing loss of both types. Conductive hearing loss occurs when the normal mechanical pathways for sound to reach the hair cells in the cochlea are impeded, for example, by damage to the ossicles. Conductive hearing loss is often helped by use of conventional hearing aids which amplify sound so that acoustic information reaches the cochlea and the hair cells.
"In many people who are profoundly deaf, however, the reason for their deafness is sensorineural hearing loss. This type of hearing loss is due to the absence of, or destruction of, the hair cells in the cochlea, which convert acoustic signals into nerve impulses. These people are thus unable to derive suitable benefit from conventional hearing aid systems, no matter how loud the acoustic stimulus is made, because there is damage to, or absence of, the mechanism for nerve impulses to be generated from sound in the normal manner.
"It is for this purpose that cochlear implant systems have been developed. Such systems bypass the hair cells in the cochlea and directly deliver electrical stimulation to the auditory nerve fibres, thereby allowing the brain to perceive a hearing sensation resembling the natural hearing sensation normally delivered to the auditory nerve.
"Typically, cochlear implant systems consist essentially of two components, an external component, commonly referred to as a processor unit and an internal, implanted component, commonly referred to as a stimulator/receiver unit, the latter receiving signals from the processor unit to provide the sound sensation to a user.
"The external component includes a microphone for detecting sounds, such as speech and environmental sounds, a speech processor that converts speech into a coded signal, a power source, for example a battery, and an external transmitter antenna coil.
"The coded signal output by the sound processor is transmitted transcutaneously to the implanted stimulator/receiver unit situated within a recess of the temporal bone of the user. This transcutaneous transmission occurs via the external transmitter antenna coil which is positioned to communicate with an implanted receiver antenna coil of the stimulator/receiver unit. Therefore, the communication serves two essential purposes; firstly to transmit, transcutaneously, the coded signal and, secondly, to provide power to the implanted stimulator/receiver unit. The transcutaneous link is, normally, in the form of an RF link, but other links have been proposed and implemented with varying degrees of success.
"The implanted stimulator/receiver unit includes, in addition to the receiver antenna coil that receives the coded signal and possibly power from the external processor component, a stimulator that processes the coded signal and outputs a stimulation signal to an intracochlear electrode assembly which applies the electrical stimulation via the basilar membrane to the auditory nerve producing a hearing sensation corresponding to the originally detected sound.
"Recently, the Applicant has developed a totally implantable cochlear implant where all the components, including the microphone, are implanted subcutaneously. This results in a more versatile system providing the recipient with greater freedom and ability to use the implant in what would previously have been regarded as adverse environments, eg. wet environments. The Applicant's implant is described in greater detail in PCT/AU01/00769 which is incorporated herein by reference. The implant is powered by an implantable rechargeable battery which receives charging signals, when required, transcutaneously via an external charging device and an implanted receiver antenna coil. Because the battery is part of an implanted system, there is a need to make the battery life as long as possible to reduce the frequency of explantation and/or re-implantation of the implant for the purposes of battery replacement.
"Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application."
Supplementing the background information on this patent, VerticalNews reporters also obtained the inventor's summary information for this patent: "Throughout this specification the word 'comprise', or variations such as 'comprises' or 'comprising', will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
"According to a first aspect of the invention, there is provided a method of controlling charging of a battery of a totally implantable auditory prosthesis, the method comprising:
"determining a first charge related battery characteristic;
"determining a second charge related battery characteristic;
"detecting when a charge cycle of the battery commences; and
"monitoring where the charge level of the battery is in relation to the first charge related battery characteristic when the charge cycle commences and adjusting the second charge related battery characteristic depending on the relationship between the charge level and the first charge related battery characteristic at the commencement of the charge cycle.
"For ease of explanation, the first charge related battery characteristic is sometimes referred to in this specification as a 'safety margin' of the battery. This safety margin may be a predetermined minimum amount of charge contained in the battery.
"In one embodiment of the invention, the second charge related battery characteristic may be a preset charge level of the battery. The preset charge level may be determined such that it is lower than a maximum possible state-of-charge of the battery. The battery may be charged to this preset charge level and, in so doing, due to the fact that the battery is not consistently being charged to its maximum battery charge, the life of the battery may be extended, because side reactions are thereby minimised.
"When a charge cycle commences, the method may include monitoring the charge level of the battery relative to the safety margin. If the charge level at which charging commences is higher than the safety margin, the method may include lowering the preset charge level. This may occur each time that, when a charge cycle commences, the charge level of the battery is greater than the safety margin. If, however, upon commencement of a charge cycle the charge level of the battery is lower than the safety margin, the method may include, initially, increasing the preset charge level.
"Typically, the method may include setting the safety margin to be a voltage corresponding to a charge required for use of the implant for a predetermined period of time. The period of time may, for example, be a complete day, i.e. a 24 hour period.
"In a second embodiment of the invention, the second charge related battery characteristic may be a charge rate of the battery. As in the case of the first embodiment of the invention, the first charge related battery characteristic, in this embodiment, may be the safety margin.
"In this second embodiment of the invention, the method may include adjusting the rate of charge of the battery, rather than the degree of charge, depending on the charge level of the battery relative to the safety margin. Thus, if the charge level is lower than the safety margin, the method may include increasing the charge rate. Conversely, if the charge level is above the safety margin, the method may include decreasing the charge rate.
"In respect of both embodiments, the method may include controlling the amount of charge normally stored in the battery. The amount of charge normally stored in the battery may be controlled using feedback control. For example, on a daily basis, the preset charge level (in the case of the first embodiment of the invention) or the charge rate (in the case of the second embodiment of the invention) may be adjusted. The size of the adjustment may be related to the safety margin. Typically, an adjustment step size may be approximately 1%-10% of the safety margin, more particularly, about 3%-7% of the safety margin and, optimally, about 5% of the safety margin.
"Still further, the method may include adjusting the safety margin to take into account ageing of the battery. The safety margin may be automatically adjusted by characterising the battery as it ages. The method may therefore include creating a look-up table in an electronic memory of the implant that provides the safety margin point for each preset charge level or charge rate, as the case may be, so that, when the preset charge level or charge rate is updated, so is the safety margin. The table may be constructed so that the safety margin is equal to a fixed period of time.
"The time represented by the safety margin may also need to be adjusted depending on the recipient's needs. The recipient or a third party may indicate the time that they require the safety margin to be set at and, by knowing the characteristics of the battery and the current drawn by the specific recipient's data map, a voltage corresponding to the safety margin desired by the recipient may be included in the electronic memory of the implant. The safety margin may be downloaded along with the recipient's map into the memory of the implant.
"According to a second aspect of the invention, there is provided a control system for controlling charging of a battery of a totally implantable auditory prosthesis, the control system comprising:
"a controller for controlling charging of the battery, the controller being a programmable controller having data relating to a first charge related battery characteristic and a second charge related battery characteristic and for adjusting the second charge related battery characteristic dependent upon where a charge level of the battery is relative to the first charge related battery characteristic when a charging cycle commences; and
"a switching arrangement for switching a charging source into charging communication with the battery when charging of the battery is required.
"As in the case of the first aspect of the invention, the second charge related battery characteristic may, in accordance with one embodiment of the invention, be a preset charge level of the battery and may, in accordance with a second embodiment of the invention, be a charge rate of the battery. The first charge related battery characteristic may be the safety margin, as defined, of the battery.
"In the case of the first embodiment of this aspect of the invention, the switching arrangement may be a switch controlled by the controller. The charging source may include a radio frequency (RF) link which provides charge to the battery when required and/or power to the implant. The switch may be connected between the RF link and the battery and may be closed under the action of the controller when the battery of the implant requires charging.
"The control system may include an analog-to-digital converter for converting a battery voltage to a number to be fed to the controller.
"The controller may store numbers corresponding to voltages that, in turn, correspond to the preset charge level, a minimum battery charge and the safety margin. The relationship between charge level and voltage is not linear but is stable so that it can be measured for the battery. A simple look-up table may be stored in a memory of the controller to be used for voltage-to-charge conversion.
"The controller may detect when charging of the battery has commenced, i.e. when the switch has closed, so that the controller can determine if the preset charge level needs to be adjusted. This may be done by monitoring the RF link power periodically, for example, once per minute.
"In the case of the second embodiment of the invention, the switching arrangement may comprise a switching circuit. The switching circuit may comprise a voltage-to-current converter feeding to a current amplifier and mirror. The converter may include an operational amplifier, an output of which is connected to a switch means in the form of a field effect transistor (FET). The operational amplifier may have a first, 'current control' input which causes the output of the amplifier to turn the FET on. The FET may be connected between a pair of resistors. When the FET is turned on, current flows through a first resistor connected to a source of the FET. All the current also flows through the second resistor connected to a drain of the FET. Current may flow through the first resistor until the voltages at inputs of the current amplifier are equal.
"Current flow through the second resistor may induce a voltage at an input of the current amplifier. A second switch means may be connected to an output of the current amplifier with the battery to be charged being connected to the second switch means. The second switch means may also be a FET.
"The components of the switching arrangement may be selected so that only a small voltage differential exists between the voltage from the RF link and the battery voltage.
"The charge current may be adjusted by changing the 'current control' voltage. This may be done using an analog voltage or may be controlled by a digital number if a digital-to-analog converter is to be used.
"In the case of the second embodiment of the invention, the switching arrangement may replace the switch of the first embodiment of the invention."
For the URL and additional information on this patent, see: Single,
Keywords for this news article include: Audiology, Prosthetics, Ear Diseases, Hearing Loss, Otolaryngology, Medical Devices, Hearing Disorders, Sensation Disorders, Nervous System Diseases, Neurologic Manifestations.
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