Semi-passive RFID tags are a type of RFID tag that can enable data collection but not necessarily enable data read-out or transmission. With the maturity of RFID technology, we can often see a variety of RFID labels in our lives. Can you tell which are active, passive, and semi-passive RFID tags in these labels? How much do you know about semi-passive RFID tags? Next, let’s take a deeper look at semi-passive RFID tags.

What is Semi Passive RFID Tag?

Semi-passive RFID tags with power supply
Semi-passive RFID tags with power supply

A semi passive RFID tag is also called a battery-assisted tag (BAT). It contains a small onboard battery inside, but this battery usually powers the sensor and IC. Like a passive RFID tag, it does not actively transmit signals to the reader. It primarily uses backscatter to communicate with the reader. It does not have a signal transmitter inside, so it does not generate radio noise either.

It is more popular than passive RFID tags. It has a relatively extended read range, and the body accommodates onboard environmental sensors. For the item to which the tag is attached, the semi-passive tag is more helpful in recording its ecological experience. It provides excellent convenience to laboratory staff.

A test result shows that if the tag is placed at 4 meters from the reader and reads the output rate of 21, it can achieve more than 50% of the reading rate decibel.

Why do Semi Passive RFID Tags Contain Batteries?

Semi Passive RFID Tags with a small on-board battery inside
Semi Passive RFID Tags with a small on-board battery inside

Semi-passive RFID tags contain batteries for two reasons. One is that the battery is needed to power the IC. The forward link typically provides power to the tag and also provides tag communication capabilities. Its range is generally much shorter than the return link. The return link refers to the round trip from the reader to the tag and back to the reader. So it has a more extended range than the forward link. It shows that the limiting factor of the passive tag reading range is power supply rather than distance. The tag is not how far away from the antenna it can decode the signal, but where in the antenna it is powered. Thus the battery inside the tag can continuously power the IC and has a more extended read range than a passive tag.

The second is that the environmental sensor is located on the tag. The ecological sensor requires a constant source of power to guarantee operation. It also requires a higher power level than the IC inside the tag. Passive tags do not have internal batteries, so they cannot provide a reliable power source for environmental sensors. It can only passively receive the energy supplied by the reader, which is also still very limited.

If a battery is added to the passive RFID tag, it can bring reliable power to power the sensor and tag IC. Of course, even with a battery, it is cheaper than active RFID.

The sensor inside a semi-passive tag can continuously collect data. It can also transmit that data with a unique ID when the reader interrogates the tag. The semi-passive tag has a great deal of promise. For example, it can automatically collect the object’s temperature experience as it moves around. It is well suited for applications such as temperature-sensitive drugs or food. The semi passive tag can effectively record when the object exceeds a specific temperature limit while in transit. The recording of the time allows a rough calculation of the expiration date or efficacy of the medicine. Of course, sensors with the ability to collect temperature, pressure, vibration, etc., can be placed on the tag.

How do Semi Passive RFID Tags Work?

Readers read range of Semi Passive RFID Tags gain energy
Readers read range of Semi Passive RFID Tags gain energy

In most cases, a semi-passive RFID tag is dormant. The power supply inside it provides power only to the part that holds the data and does not do anything with the rest. Due to the relatively low power consumption, it can last for a long time.

Electromagnetic induction is generated when the tag enters the recognition range of the reader. The RFID reader will first activate the label with a low-frequency signal so that the tag enters the working state. Then the microwave signal and tag data transmission. First, low-frequency signal precision positioning activation, then work with the high-frequency signal. That is, multiple low-frequency readers are placed at different locations within the coverage of the HF signal.

These readers are based on activating semi-active RFID tags. These readers mainly activate semi-active RFID tags. Working in this way allows for product positioning, information collection, and delivery functions. It dramatically satisfies the strict environmental requirements of some products.

Advantages of Semi Passive RFID

  • Long-Range Detection

You can read semi-passive RFID tags over longer distances than passive tags as they have an active energy source to broadcast their information back. They can be read up to 30m, depending on the environment and type of tag used. This makes them ideal for tracking assets over long distances in warehouses or manufacturing facilities

  • Longer Read Range

The presence of a battery in a semi-passive RFID tag allows for a longer read range compared to a passive RFID tag. This is because the tag can transmit data over longer distances. It makes it possible to read tags from greater distances. This is particularly useful in applications where tags need to be read from a distance. Some of the more common ones are supply chain management and inventory tracking.

  • Improved Accuracy

The energy provided by the battery in a semi-passive RFID tag also makes it possible to read the tag with improved accuracy. Such tags with batteries can emit stronger signals. It makes it easier for the reader to receive the data and reduces the chance of errors.

  • Lower Cost

The cost of a semi-passive RFID tag is typically lower than that of an active RFID tag because it does not require additional batteries, which you must replace periodically, as well as other components, including sensors. This makes them a cost-effective option for large-scale tracking applications.

  • Increased Data Capacity

Due to their internal memory and battery, semi-passive RFID tags can store more data than passive tags. This allows for more accurate tracking of assets and the ability to store more complex information, such as product serial numbers and asset location data.

  • Increased Privac

Semi-passive RFID tags are often more secure than passive RFID tags as they require users to authenticate themselves and then send an activation signal to read the tag data. This can reduce the chances of someone maliciously reading the tag and gaining access to confidential data.

  • Durable and Low Maintenance

Semi-passive RFID tags are sealed in plastic with no external components, which makes them highly durable and resistant to wear and tear. They also require very little maintenance as they do not require frequent battery replacements.

  • Flexibility

You can use semi-passive RFID tags in various applications since they are smaller and do not require additional energy sources. Due to their small size, you can use them in harsh industrial and retail settings.

  • Ease of Use

Semi-passive RFID tags are easy to set up and manage as all that is required is to activate them with an activation signal and then read the data stored in the chip. This makes them a popular choice for asset-tracking applications.

Active vs Passive vs Semi Passive RFID Tag

Active RFID Tags

It contains a battery, and a transmitter inside that actively emits a signal to the reader. When the tag comes within range of the reader, the two generate a magnetic field coupling. The tag will actively transmit data to the reader. Because the active RFID tag is small, it is usually embedded in the smartphone’s protective case through rivets, screws, etc.

It is typically used in large-scale applications where labels are read over long distances. The most common applications are construction, petroleum, and other industrial and logistics applications. It can generally transmit data at high frequencies and over long distances. More common is the electronic toll. It is more significant than passive and semi-passive but also has a larger capacity. It houses environmental sensors that collect temperature, humidity, and other data. Thus it can be used as an application to protect high-value and sensitive assets.

It also has obvious limiting attributes. It requires a higher cost, limited battery life, and larger size. It still has a very impressive ROI for tracking and protecting high-value assets.

Passive RFID Tags

It is a passive factor that relies on a reader to deliver energy. Because of this, the reader can generally only read the tag at a very close distance. Usually, some smaller-scale applications and RFID inventory systems use passive RFID tags.

It also has its undeniable advantages. Its cost per tag is lower than the other two. It has a longer life and can be embedded in almost any product. It’s primarily used in item-level tracking applications, badge access control, etc.

Semi Passive RFID Tags

It is an intermediate product between active and passive. Semi-passive RFID tags are similar to passive RFID tags in size and manufacturing. It is compact and takes less time to produce. But it also contains a power source like active RFID tags.

It brings together many of the advantages of both. These advantages include a lower production price than active tags and longer read distance than passive tags. And support for partial sensors and memory functions. Of course, it also has a fatal disadvantage: limited battery life. It is usually used for: access control entry, item location, area location management, security alarms, etc.

Also Read: RFID Inventory System: What are Its Pros and Cons?

So When do You Use Them?

Semi Passive RFID Tags for item location
Semi Passive RFID Tags for item location

Active RFID tags can operate at high frequencies between 433MHz – 960MHz. It gives it a much longer range to transmit data. Readers can read the data stored on the tag at a distance of over 100 meters. It is the most suitable choice for tracking real-time location, inventory, and asset management. In addition to this, it can operate on a variety of other frequencies. Especially at lower frequencies, it can even be used on materials such as water and metal.

Passive RFID tags come in quite a few variants. The most common are inlays and hard tags. The inlays are usually attached to the physical asset by an adhesive, which is the cheapest option. Hard passive tags are made of materials such as plastic and metal, which are rugged and durable. It is ideal for products that must stay in harsh environments for long periods.

Semi-passive RFID tags are a hybrid of the previous two types of tags. It is more cost-effective as compared to active and passive. It is the ideal and inexpensive option for environmental and condition monitoring of items.

Operators need to choose the correct label according to their needs and according to the characteristics of the product. Choose between active and semi-passive in particular. If your product is unique, you need to consider the surrounding environment. Depending on the particularity and cost-effectiveness of the product, semi-passive RFID tags may be the best fit for you. Assuming you want to track and manage your warehouse inventory, passive RFID tags may be your ideal choice.

Semi-passive RFID tags may not be as widely known as active RFID tags and passive RFID tags. But in terms of practical production applications, it is cheaper and has a broader range of use. It is suitable for use in products with stringent environmental requirements during transportation.

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