Subcutaneous Transmitter (A3048)

Contents

Description

[06-JUN-25] The Subcutaneous Transmitter (A3048) is an implantable telemetry sensor for small animals. It provides amplification and filtering of a single biopotential input. When equipped with a CR1216 battery its mass is only 1.5 g. All versions of the A3048 operate within our Telemetry System. All versions turn on and off with a magnet.

Figure: Subcutaneous Transmitter A3048S. The A3048S is equipped with a CR1225 battery. The battery is mounted beside the circuit.

The A3048 amplifier can provide gain of ×100 for frequencies up to 160 Hz, or it can provide gain of ×25 for frequencies up to 640 Hz. The A3048 logic may be programmed to sample at 64, 128, 256, 512, 1024, or 2048 SPS. The low-pass filter may be configured for a corner frequency of 20, 40, 80, 160, 320, or 640 Hz. The high-pass filter can be configured to for a corner frequency of 0.2 Hz or 2 Hz, or it can be removed entirely to allow the amplifier to provide gain all the way down to 0.0 Hz (DC). All versions of the A3048 are equipped with flexible red and blue leads and a loop antenna. The length of the leads, the size of the battery, the operating life, the termination of the leads, the sample rate, the gain of the amplifier, and the passband of the amplifier vary from one version to the next.

All A3048 SCTs transmit on a single telemetry channel. Each transmitter has a label under its silicone coating. Thius label specifies the batch number, B, and the telemetry channel number, N. All versions of the A3048 are covered by a one-year warranty against corrosion and manufacturing defect.

Ordering

[06-JUN-25] There are many possible configurations of the A3048 SCT. Each configuration becomes an established "version" when we manufacture it for a customer. We list the available A3048 versions in the section below. You will find our latest prices in our Price List. To determine which SCT is best for your application, feel free to consult the OSI Chatbot. To obtain a quotation for manufacture and delivery, or to ask us questions directly, please email us at info@opensouresintruments.com.

Versions

[07-JUN-25] The Subcutaneous Transmitter (A3048) can be equipped with several sizes of battery and leads up to 130 mm long. It can be configured with a variety of passbands, dynamic ranges, and sample rates. You specify the version you want with a full SCT part number. The part number begins with "A2048" and is followed by the primary version letter. The primary version letter specifies the battery we load on the circuit. Following the primary version letter, we have a sample rate code number. We use the numbers 1-5 to indicate 128, 256, 512, 1014, and 2048 SPS respectively. We add the letter "Z" to indicate that the passband of the amplifier extends down to 0.0 Hz, making a "DC transmitter". If we omit the "Z", the passband begins at 0.2 Hz, making an "AC transmitter". Now comes a dash followed by letters indicating the terminations of the leads. After another dash comes a letter and a number specifying the type and length of the leads. After a final dash we have a letter specifying the antenna.

Figure: A2048 Part Numbering Scheme. Click on the large boxes to jump to tables listing letter codes and options.

See our Electrode Catalog for a list of available lead terminations, and also for a presentation of the various depth electrodes to which these terminations can be attached. See our Leads Table for a description of our several types of insulated, helical steel leads. See our Antennas table for a description of the various types of antenna we can deploy on our implants. The following versions are defined already, but we are happy to define new ones to suit your needs. The operating life is the minimum time for which a newly-made transmitter will operate continuously. The shelf life is the time the transmitter can remain turned off in storage and still retain 90% of its operating life.

For the analog input we specify the passband, sample rate, input dynamic range, and channel number offset. The passband is the range of frequencies to which the amplifier responds. The passband has a low and high end, both of which we specify in the tbale. The bandwidth of an input is the difference between the high and low ends of its passband. For all A3048 SCTs, bandwidth is approximately equal to the high end of the passband.

The dynamic range of the input is always 0-65535 when expressed in terms of the sample value we obtain from the A3048's sixteen-bit ADC. The zero-value of an input is the sample value we obtain when we short the two inputs together. The zero-value depends upon the battery voltage, VB, according to zero-value = 1.8 V × 65535 ÷ VB. The dynamic range is the battery voltage divided by the gain of the amplifier. When we specify dynamic range, we assume VB = 3.0 V, which is true for almost the entire life of the lithium batteries we use with the A3048 SCTs. When the amplifier gain is 100, the dynamic range is 30 mV and spans −18 mV to +12 mV.

Figure: Subcutaneous Transmitter A3048R. The R-versions are equipped with the CR1216 battery. This particular example is equipped with 36 mm × 0.7 mm leads. There is a D-Pin termination on the red lead, and a bare wire A-Coil termination on the blue lead.

See the Battery Life chapter of our telemetry manual for an explanation of how operating life varies with SCT mass and sample rate. In almost all cases, we set the sample rate of an input equal to 3.2×B, where B is the bandwidth in Hz. This sample rate makes it possible for the low-pass filter to provide 20 dB attenuation at one half the sample rate, which is 1.6×B. Frequencies above one half the sample rate will be distorted by sampling, but the 20-dB attenuition ensures that such signals do not corrupt the signal we record from the SCT's passband.

Analog Inputs

[07-FEB-25] When configured for AC recording, the A3048 input consists of a in series with a resistor. These together form a high-pass filter with corner frequency 0.16 Hz and input impedance 10 MΩ The most common versions of the A3048 provide a gain of ×100, another high-pass filter, and a three-pole low-pass filter. When we remove the high-pass filter, the passband of the amplifier will extend all the way down to 0.0 Hz, thus configuring the SCT for DC recording. We can configure the low-pass filter with any of the corner frequencies 20, 40, 80, 160, 320, and 620 Hz. These frequencies are matched with sampling rates 64, 128, 256, 512, 1024, and 2048 SPS respectively.

The figure below shows the frequency response of a batch of twenty-two A3048R2 transmitters recorded during Quality Control Two (QC2). You will find a database of such plots here. We send one such plot along with each batch of transmitters we ship. What is the frequency response of an A3048 SCT?

Figure: Frequency Response of a Batch of A3048R2s. These devices provide a passband of 0.3-80 Hz at sample rate 256 SPS. We apply a sinusoid through a 10-MΩ resistor.

In the response shown above, we see both the high-pass filter corner frequency and the low-pass corner frequency. If we define "corner frequency" as the frequency at which the gain drops to 70% of the gain in the passband of the amplifier, the corner frequencies for this batch of transmitters are 0.2 Hz and 90 Hz. The actual bandwidth is slightly greater than the nominal 80 Hz specified for the A3048R2. The most important function of the low-pass filter is to reduce the amplifier voltage gain by at least a factor of ten at a frequency that is one half the sample rate. We see that this is indeed the case for our batch of A3048R2s. They sample at 256 SPS and their gain at 128 Hz is less than 10% of their gain at 10 Hz.

The amplifier is powered by the battery voltage, VB, which is typically 3.0 V at 37°C, but will be 3.1 V for the first 5% of the battery's life and drop below 2.6 V in the final 5%. The amplifier saturates within 20 mV of 0V and VB. The following saturating sweep response shows how well the amplifiers handle large inputs. For a comparison of the A3048S2 saturation behavior and that of its predecessor the A3028S2, see here.

Figure: Saturation of the A3048S2 Input. Show me what the A3048 SCT output signal looks like when its input is saturating.

We measure the electrical noise on the A3048 input by placing the entire transmitter in water and letting it settle for a few minutes. Typical noise for an A3048S2 with 80-Hz bandwidth is 5 μV rms. The figure below shows the spectrum of electrical noise for a batch of A3048S2s.

Figure: Spectrum of Electrical Noise on Inputs of a Batch of A3048S2s. Vertical: 0.4 μV/div. Horizontal: 10 Hz/div.

The A3048P-series transmitters are equipped with a CR927 coin cell. The CR927 is 9-mm in diameter and 2.7 mm thick. When loaded with the CR927, some transmitters will exhibit switching noise of amplitude up to 2 μV rms. This noise is caused by an interaction between transmitter's magnetic switch, which turns on and off at around 5 Hz, and the source impedance of the battery, which is larger for smaller batteries. Here is the electrical noise spectrum of a batch of A3048P2s.

Figure: Spectrum of Electrical Noise on Inputs of a Batch of A3048P2s. Vertical: 0.4 μV/div. Horizontal: 10 Hz/div. What are the sources of noise in an A3048 SCT? What is switching noise in the context of SCT inputs?

The switching noise we see in the A3048P transmitters consists of 10-ms pulses at roughly 5 Hz. The height of these pulses decreases with temperature. At 37°C, they will be no more than 10 μVpp, but at room temperature they can be as large as 30 μVpp. A typical EEG signal from a bare wire electrode in a mouse is 40 μV rms, 160 μVpp. Switching noise pulses of 10-μV are hard to see.

Figure: Distortion of Sinusoid by the A3048S2 SCT versus Frequency. Blue: 10 mVpp. Orange: 1 mVpp. Non-sinusoidal power as a fraction of sinusoidal power in parts per million. Sine wave generated by BK Precision 4053B, specified total harmonic distortion <1 ppm.

The distortion of a signal by an SCT is the extent to which the SCT changes the shape of the signal's sinusoidal components. We apply a 10 mVpp sinusoid to the input of an A3048S2, which provides 0.2-80 Hz passband and 30-mV dynamic range. We increase the frequency from 0.125 Hz to 100 Hz. For each frequency, we obtain the spectrum of the signal and measure the power outside the sinusoidal frequency as a fraction of the sinusoidal power using this script. We express the result in parts per million. The distortion of the recorded signal is dominated by random electronic noise. There are no significant peaks in the spectrum outside the fundamental.

Figure: Spectrum of 50-Hz, 10-mVpp Sinusoid Recorded by A3048S2 SCT. Horizonal: 10 Hz/div. Vertical: 0.4 μV/div. The peak is 4000 μV.

We note that the distortion generated by the A3048 family of SCTs is hundreds of time less powerful than that of the discontinued A3028 family of SCTs. The A3048 samples the signal uniformly, thus eliminating the scatter noise present in the A3028 signal.

Battery Voltage

[08-JUN-25] We refer you to the Battery Voltage chapter of our Telemetry Manual for a discussion of how we can measure an A3048-family SCT's battery voltage during operation.

Battery Life

[06-JUN-25] All A3048 SCTs are equipped with non-rechargeable lithium coin cells. Their operating life is how long they can amplify and detect their single input voltage when their battery is fresh. Their shelf life is how long they can wait on the shelf in their sleep state before they have used 10% of their battery capacity. We list operating and shelf life in the A3048 Version Table. We provide a detailed discussion of SCT operating life in the Battery Life chapter of our Telemetry Manual. Here we will present some tables and measurements specific to the A3048 family.

The above table of operating life shows how sample rate and battery capacity dictate operating life. The table gives the minimum operating life of a newly-made transmitter. The average operating life is roughly 5% higher, and in some cases even higher. We recently saw an A3048S2 with minimum operating life 41 days run for a full 50 days before expiring.

Figure: Measured Current Consumption versus Sample Rate. For A3048AV1, slope 0.106 μA/SPS, intercept 16.1 μA.

The current consumption of the A3048 SCTs increases linearly with sample rate, but starts at around 18 μA for sample rate zero.

Implantation

[08-JUN-25] We refer you to the Implantation chapter of our Telemetry Manual for a discussion and presentation of the various protocols for implanting the A3049 SCT in a small animal.

Synchronization

[19-DEC-22] When we want to mark in our SCT recordings the time at which some event took place, such as the start of a video recording, the moment that a light was flashed, or when an noise commenced, we can use an auxiliary SCT to record a synchronizing signal along with the signals received from implanted SCTs. See the Synchronization section of the A3028 manual for details.

Encapsulation

[29-NOV-23] All versions of the A3048 are encapsulated in black epoxy and coated with silicone. The silicone is "unrestricted medical grade" MED-6607, meaning it is approved for implants of unlimited duration in any animal, humans included. The A3048's leads and antenna are encapsulated with dyed silicone, then coated with the same unrestricted medical grade silicone. The only materials the transmitter and its leads present to the subject animal's body are either unrestricted medical grade silicone or stainless steel.

Design and Development

[09-JUN-25] For design files and development logbook, see the A3048 design and development page at D3048.